Solar PV Inverter_National Renewable Energy

8/7/2019 Solar PV Inverter_National Renewable Energy

1/100

National Renewable Energy LaboratoryInnovation for Our Energy Future

A national laboratory of the U.S. Department of EOffice of Energy Efficiency & Renewable E

NREL is operated by Midwest Research Institute Battelle Contract No. DE-AC36-99-GO10337

A Review of PV Inverter

Technology Cost andPerformance Projections

Navigant Consulting Inc.Burlington, Massachusetts

Subcontract Report

NREL/SR-620-38771

January 2006


2/100

A Review of PV Inverter

Technology Cost andPerformance Projections

Navigant Consulting Inc.Burlington, Massachusetts

NREL Technical Monitor: R. MargolisPrepared under Subcontract No. KACX-4-44451-01

Subcontract Report

NREL/SR-620-38771

January 2006

National Renewable Energy Laboratory1617 Cole Boulevard, Golden, Colorado 80401-3393

303-275-3000 www.nrel.gov

Operated for the U.S. Department of EnergyOffice of Energy Efficiency and Renewable Energy

by Midwest Research Institute Battelle

Contract No. DE-AC36-99-GO10337


3/100

NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government.Neither the United States government nor any agency thereof, nor any of their employees, makes anywarranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, orusefulness of any information, apparatus, product, or process disclosed, or represents that its use would notinfringe privately owned rights. Reference herein to any specific commercial product, process, or service bytrade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement,recommendation, or favoring by the United States government or any agency thereof. The views andopinions of authors expressed herein do not necessarily state or reflect those of the United Statesgovernment or any agency thereof.

Available electronically at http://www.osti.gov/bridge

Available for a processing fee to U.S. Department of Energyand its contractors, in paper, from:

U.S. Department of EnergyOffice of Scientific and Technical InformationP.O. Box 62Oak Ridge, TN 37831-0062phone: 865.576.8401fax: 865.576.5728email: mailto:[email protected]

Available for sale to the public, in paper, from:U.S. Department of CommerceNational Technical Information Service5285 Port Royal RoadSpringfield, VA 22161

phone: 800.553.6847fax: 703.605.6900email: [email protected] ordering: http://www.ntis.gov/ordering.htm

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste
http://www.osti.gov/bridgemailto:[email protected]:[email protected]://www.ntis.gov/ordering.htmhttp://www.ntis.gov/ordering.htmmailto:[email protected]:[email protected]://www.osti.gov/bridge


4/100

A Review of PV InverTechnology Cost andPerformance ProjectioFinal Presentation Report to

National Renewable Energy Laboratory

This work was supported by the U.S. Department of Energys(U.S. DOE) Office of Energy Efficiency and Renewable Energy(EERE) under National Renewable Energy Laboratory (NREL)Contract No. KACX-4-44451-04

January 2006


5/100

1

Table of Contents

1 Executive Summary

2 Introduction

3 Historical Perspective

4 Future Performance and Cost Estimat

5 Challenges for Achieving Future Tar

6 Addressing the Challenges

7 Suggested Role for Government


6/100

2

Table of Contents

1 Executive Summary

2 Introduction







7/100

3

Executive Summary Study Objective

Navigant Consulting Inc. (NCI) evaluated PV invertecost improvements required to meet U.S. DOE goals f

The National Renewable Energy Laboratory (NREL) has a maimplementation of the U.S. Department of Energys (DOEs) SProgram. Sandia National Laboratories (SNL) has a major roldevelopment, characterization, standards, certifications, and

The Solar Energy Technologies Program recently published awhich establishes a goal of reducing the Levelized Energy Co(PV) systems to $0.06/kWh by 2020.

The Multiyear Technical Plan estimates that, in order to meetinverter prices will need to decline to $0.25-0.30 Wp by 2020.

DOE determined the need to conduct a rigorous review of theand economic targets, including the target set for PV inverter

NREL requested that NCI conduct a review of historical and performance improvements for PV inverters, including identiidentified and the approaches government might use to addr


8/100

4

Executive Summary Key Issues Addressed

NRELs questions regarding PV inverter cost and perrole they should play, were broken down into three k

What are the critical cost and performance imprneeds for PV inverters that government should s

promote PV market growth?

Do PV inverters facechallenges in meeting theU.S. DOEs Solar EnergyTechnologies Program

targets?*

Is there a clearunderstanding and

consensus for addressingkey PV inverter

challenges?

* This includes the question: Will inverters reach the cost goal set by the Solar Energy T


9/100

5

Executive Summary Key Issues Addressed

Many potential roles for government were identifiedimprove the chances that DOE program targets are ac



Do PV inverters facechallenges in meeting DOEs

Solar Energy TechnologiesProgram targets?*

Is there a clear understandingand consensus for addressingkey PV inverter challenges?

Whp

ch

Sales-volume increases andlearning-curve improvementsalone appear unlikely to achievethe targeted inverter selling priceof $0.25-0.30/W by 2020.

Inverter lifetimes greater than 15years appear difficult to achieve.

Improvements in manufacturing,design, and technology are

needed to achieve the price andperformance targets.

Reducing regulatory complexityand long-term, consistent policywill also be required.

Manufacturers and industryexperts do not agree on needs toaddress key inverter challenges.

Support is needed in severalareas:

Manufacturing and testingimprovements: processimprovement, training, qualitymanagement, HALT/HASS

assistance, and documenting fieldperformance data.

Design: alternative topologies,thermal management, modeling,and DER inverters.

Technology: advanced switching,capacitors, and components.

Amrmqua

Sp

tm

I

Es

Ea


10/100

6

Executive Summary Future Performance

Achieving the targeted improvements of lower cost areliability for inverters is not a foregone conclusion f

Based on learning-curve forecasts, the targeted cost reductions foachieved with current market growth and learning-rate levels.

Significant uncertainty exists around the potential for future mexceed current levels for an extended period of time.

Additional cost reductions will require an acceleration of learn

Inverter prices have been dropping by about 10% with ever

cumulative production, compared to 20% for PV modules. Reliability and life issues for inverters have the potential to dama

the industry and long-term adoption of PV.

Because of market demands, manufacturers today are focusedover improving reliability.

Reliability and life improvements may not be achieved with coindustry.

In order to increase the probability of achieving the goals of indunecessary for the PV market to become sustainable over the longgovernment support for inverter R&D is likely to be necessary.


11/100

7

Executive Summary Overcoming Key Challenges

NCIs assessment is that there is an important role foto support PV inverter improvements for the next sev

In general, larger companies in the PV inverter business view the role of govassistance (via programs to reduce cost and increase reliability) as being lessand the long-term future of the industry.

Most larger companies that NCI spoke to believe that increasing sales vfactor that will lead to lower cost and higher reliability for PV inverters

Despite the views of larger companies, introducing a new inverter product hventure for some large companies. For example:

Xantrex experienced significant problems with their early PV inverters market share to new European market entrants.

Philips entered the PV inverter market in Europe, only to exit a few yeasignificant technical problems with their first product.

The PV market will be in a critical growth phase during the next 5-10 years,significant policy and market support to achieve the overall cost and performsustainable market.

If small manufacturers have more difficulty meeting the reliability requiremcannot afford to provide adequate after-sales service, it could hurt the PV in(inadequately performing inverters will hurt the industry).

While some consolidation in the inverter business should be expected, the binnovation provided by the smaller companies are likely to be important to early stage of development.


12/100

8

Executive Summary Suggested Role for Government

Long-term cost reduction and performance improvemgreatly from the ongoing support of additional gover

Inverter testing at Sandia National Labs is extremely valuable to the insupport of development of testing protocols is important to the indust

Documentation of failure analysis in the industry is not conducted unfor government would be in collecting and documenting inverter failuindustry.

Modeling tools would be helpful to manufacturers, but developing ac

challenging. An assessment of issues and needs related to modeling wbefore embarking on new modeling efforts.

The High Reliability Inverter Initiative (HRII) program is generally cosuccessful. Follow-on public-private R&D partnerships such as this shgovernment support.

Cost and efficiency benefits of tranformerless inverters are understoodand cons of tranformerless inverters as a means of educating inspector

be beneficial to encourage adoption of regulations and codes that allow

Analysis of the interaction of the various federal, state, and municipalbe increasingly important to future industry growth needed for long-t


13/100

9

Executive Summary Suggested Role for Government

Several issues identified are common to all DER invebe addressed as part of crosscutting research program

Comprehensive information on inverter components (capacitors, power semiconductors, etc.) and options would assist manufacturbest products.

Innovative inverter topologies have been suggested to provide mfor government may be in support of experimental topologies as a

the industry. Manufacturers would benefit from understanding the costs and b

Accelerated Life Testing (HALT) and Highly Accelerated Stress Stesting programs. Government could assist by providing general experience from other industries.

Several other areas identified for PV inverters may also have broa

inverters, such as modeling and specific HALT and HASS testingprograms targeted specifically for PV are likely to be required.


14/100

10

Table of Contents

1 Executive Summary

2 Introduction







15/100

11

Introduction Objective

Navigant Consulting Inc. (NCI) evaluated the PV invand cost improvements required to meet U.S. DOE go

The National Renewable Energy Laboratory (NREL) has a maimplementation of the U.S. Department of Energys (DOEs) SProgram. Sandia National Laboratories (SNL) has a major roldevelopment, characterization, standards, certifications, and

The Solar Energy Technologies Program recently published awhich establishes a goal of reducing the Levelized Energy Co(PV) systems to $0.06/kWh by 2020.

The Multiyear Technical Plan estimates that, in order to meetinverter prices will need to decline to $0.25-0.30 Wp by 2020.

DOE determined the need to conduct a rigorous review of theand economic targets, including the target set for PV inverter

NREL requested that NCI conduct a review of historical and performance improvements for PV inverters, including identiidentified and the approaches government might use to addr


16/100

12

Introduction Issues Analysis

NRELs key questions regarding PV inverter cost andthe role they should play, can be broken down into th



Do PV inverters facechallenges in meeting theU.S. DOEs Solar EnergyTechnologies Program

targets?*

Is there a clearunderstanding and

consensus for addressingkey PV inverter

challenges?

* This includes the question: Will inverters reach cost goal set by the Solar Energy Tech


17/100

13

Introduction Approach

NCIs five-step project approach provided the basis fNRELs questions.

HistoricalPerspective

1

FuturePerformanceand CostEstimates

2

ChallengesforAchievingTargets

3

AddressingChallengesforAchieving

Targets

4

GovernmRole inAddressChalleng

5

Do PV inverters face challenges inmeeting the U.S. DOEs Solar

Energy Technologies Programstargets?

What role shouplay in addr

challenges that

Is there a clear understanding andconsensus for addressing key PV

inverter challenges?


18/100

14

Introduction Step 1 Historical Perspective

NCI first collected data on inverter trends for the pas

Historical Perspective

1

Objective

Provide

performance andcost informationon typicalinverters used forU.S. residentialand commercialbuildings, andcentral

power/utilityapplications.

Tasks

Pricing information and key

performance information forinverters during the past 3-5 years.

Key information about productattributes, such as weight, voltagerange, and sizes of commercial andresidential units.

Advantages and limitations of past

products.

Obtai

from Call t

Xantrperfo

IntervmoduEurop

Barceas weother


19/100

15

Introduction Step 2 Future Performance and Cost Estimates

NCI conducted interviews with inverter players in EuStates to identify likely cost and performance trends

Future Performance andCost Estimates

2

Objective

Provideinformation oninverter cost andperformancetrends that areexpected duringthe next 10-20years.

Tasks

Show how inverter prices are likely tochange during the next 10-20 years.

(Include assumptions about marketsize driving economies of scale andlearning)

Discuss likely customer inverter needsfor residential, commercial, and centralinverter applications.

Show likely changes in inverterperformance during the next 10-20years.

Ub

CSMdan

Inm

EBvred


20/100

16

Introduction Step 3 Challenges for Achieving Targets

The interviews provided information on some of the achieving the cost and performance targets.

Challenges for AchievingTargets

3

Objective

Identifychallenges forachieving the costand performancetargets.

Tasks

Discuss potential barriers for cost andperformance targets for residential,commercial, and central stationapplications.

Discuss technical, manufacturing,regulatory, policy, and marketchallenges.

RIn

mmd

InoSt

EF


21/100

17

Introduction Step 4 Addressing Challenges

NCI then identified possible ways to address the chaachieving the cost and performance targets.

Addressing Challengesfor Achieving Targets

4

Objective

Identify possibleways to overcomekey cost andperformancechallenges.

Tasks

Identify possible ways to addressinverter challenges during the next 10years that can help industry achieve itscost and performance targets.

Cwstm

Sufi


22/100


23/100

19

Table of Contents

1 Executive Summary

2 Introduction







24/100

20

Historical Perspective U.S. PV Market Size and Growth

The U.S. grid-connected market has been strongest inbuy-down programs make systems more economicall

There has not been a national subsidy program for PV, only atax credit on commercial applications and a 5-year acceleratesupport has been dependent largely on state programs.

The recently passed Energy Bill includes $400 million worth oand solar thermal), including a 30% investment tax credit for

homeowners and commercial building owners for the next 2 credit is capped at $2,000 per credit.

NCI estimates the U.S. grid-connected market to be 51 MW inlargest market with 37 MW installed in 2004, resulting in a cuabout 93 MW for grid-connected systems at the end of 2004.

The most common installation size for residential systems in Installations of greater than 10 kW are becoming more commEnergy Commission (CEC) is considering a feed-in tariff (util

In the United States, where grid reliability has been a problemdemand for grid-connected inverters that can also provide babatteries is higher than in Europe.

U.S. Market


25/100

21

Historical Perspective U.S. PV Market Installation Sizes

CEC data shows the proportion of installations of 3 kdeclining, while 10-30 kW installations are on the rise

Installation Size Distribution in CEC Program (kW

Residential and Small Commercial (


26/100

22

Historical Perspective U.S. PV Market Installation Sizes

Compared to CEC, data for New Jersey residential aninstallations shows an even stronger trend toward lar

Installation Size Distribution in NJ (kW instal

Residential and Small Commercial (


27/100

23

Historical Perspective U.S. PV Market Inverter Sizes

CEC data shows that inverters in the 2-3 kW range domarket (SMA SB 2500). Sharps Sunvista 3500 accoun

growth in the 3-5 kW range.Inverter Size Distribution in CEC Progra

Installed PV System CapacitySize ofinverter(s)used (kW) 2001 2002 2003

0 - < 2.0 183.9 5.5% 429.8 5.3% 5

7

1

3

5

5

2

10

67.8%

4.2%

6.3%

6.5%

2.4%

7.4%

100.0%

37.5%

0.6%

0.3%

2.2%

0.0%

53.9%

100.0%

658.8

2.0 - < 3.0 1,243.7 5,466.2 9,905.0

3.0 - < 5.0 20.0 339.8 173.0

5.0 - < 10.0 8.8 509.4 430.2

10.0 - < 30.0 73.6 520.9 668.5

30.0 + 0.0 192.8 760.5

Inverter sizenot reported

1,790.0 599.7 282.0

TOTAL 3,319.9 8,058.6 12,878.0

Source: CData shown are for systems installed within CEC program only.


28/100

24

Historical Perspective Inverter Features Evolution 1990-2000

Despite modest production volumes, inverters have esignificantly since the 1980s through manufacturer in

technology improvements.

1991 The early 1990s saw the first large-scale seriesproduction of PV inverters (SMA PV-WR).

1980s Inverters were bulky, heavy, difficult to install,unreliable, and their efficiency was in the 85-90%range. They were strictly devices for converting DCto AC.

1995 First PV string inverter (SMA SB 700). Allowsconnection of modules in series, modular systems,higher system efficiency, and reliability. Stringinverter becomes most common on the market.

Late1990s

Basic data-acquisition system, plug-and-play instal

Transformerless and high frequency (HF) designs rea

Reliability improves. Warranties (2-5 years) offered.


29/100

25

Historical Perspective Inverter Features Recent Developments

Along with a trend toward increasing sizes, invertersincreasingly sophisticated, with added capabilities.

Inverter manufacturers have been increasing the size of modelsand small commercial applications. New models are generally a

Many manufacturers report that the typical residential installatikW range, and that 10 kW installations are also becoming more

Larger Size (> 2 kW)

The latest inverters feature data logging and communication camanufacturers provide the software required to process the dat

Allows quick diagnostic when the system is not operatingallows the user to adjust system parameters for optimal op

Data logging, communications, and diagno

A master inverter controls the operation of one or two slavethe slaves are brought online only when the power produced bysufficient. In this way, inverters always operate at an optimizedhigher system efficiency.

Master-Slave Configuration for Improved Efficiency


30/100

26


Multi-string inverters allow a single inverter to convefrom several module strings, reducing inverter costs f

In many installations, strings of PV modules operate under drequires a separate inverter for each string. Multi-string techn(usually two or three) strings to be connected to a single inveinverters feature a separate Maximum Power Point Tracker (Mensuring maximum energy yield.

Examples of differences that can be accommodated with a sinare:

Orientation

Shading

Number of modules

Module type or cell type

This feature appears to be an increasingly important one, as sthere is a need to accommodate modules in different orientat

Many popular residential inverter models being used in the Unot have this feature.

Multi-string Capability


31/100

27


Transformerless designs popular in Germany and Jinverter size, cost, and weight, while improving effic

The transformer in conventional inverter designs is responsible for losefficiency and accounts for the larger part of the inverters weight. Destransformer are cheaper, more efficient, and lighter.

However, transformers also provide automatic protection against DC grid in case of system malfunction. Transformerless designs featurecontrol components to provide DC injection protection.

High frequency (HF) transformers are a compromise between the convtransformers and transformerless designs. HF transformers are small, electrical isolation.

Even though manufacturers claim that transformerless inverters can bthey cannot be installed in some countries1:

Issues related to galvanic protection are the most important hur

of their use. Manufacturers expect changes in regulations or in utility requir

inverters with transformers will continue to be needed to serve

Transformerless / HF Design

1. Transformerless inverters are not currently allowed in Spain and Italy. In the United States, the NEallows ungrounded PV arrays, but resistance from the utilities prevents the use of transformerless in


32/100

28

Historical Perspective Inverter Prices Cost vs. Price

Data on production cost are not available for inverterdata must be used as a proxy.

In the long run, price trends reflect cost trends; but, in the shorother dynamics at play that are not related to actual production

Price trends over periods of 10 years or less may not reflect cosand should be analyzed with care and in context.

time

$

Cost ofproduction

Price

Stability

period

Shakeoutperiod

During stabilgrow and newmarket the the decrease

During shakby fierce combankruptciesprices can de

costs.

Source: References 12 and 13


33/100

29

Historical Perspective Inverter Prices Determining Factors

An average price per kW is difficult to ascertain for

The rated power of the inverter is not the only factor that de

The technology varies considerably from manufacturer tto differences in efficiency, size, weight, reliability, etc. Tthe cost of producing inverters and the price that consum

Additional features, such as a visual display, data monitcommunication capabilities, can lead to substantial price

inverters of comparable rated power. Analysis of inverter price trends over time must take into ac

inverter features.

In the past 5-10 years, inverters have evolved significantlinstallation, user friendliness, efficiency, size and weightsignificantly. As a result, a simple analysis of $/kW pricethe real improvement in inverters.

Inverter size has an important impact on cost. For instance, a50% cheaper than a 1 kW unit on a $/kW basis. So, even withsize range, a single average $/kW figure inevitably hides larg


34/100

30

Historical Perspective Inverter Prices TEAM-UP residential insta

Inverter prices reported by SEPA for the TEAM-UP inthe $1.50/kW to $2.00/kW range for residential applica

From 1996 to 2000, 644 residential installations were put in plaprice data was not reported for all installations.

$0.00

$0.50

$1.00

$1.50

$2.00

$2.50

1996 1997 1

Year Number ofinstallations

kW Average size(kW)

1996 91 350.93 3.86

1997 83 309.08 3.72

1998 65 83.05 1.28

1999 201 296.3 1.47

2000 199 183.14 0.92

Source: Reference 14

Inverter Prices for TEInstalla

1. From to 2001, the Solar Electric Power Association (SEPA) managed TEAM-UP, a cost-sharing progrid-tied PV installations.

2. Inverter prices reported for 1997 by SEPA for the TEAM-UP initiative were later determined not towas also not available for the entire sample size. Because of limitations in sizes of available invertereported on $/kW basis may not accurately reflect the true selling prices being used at the time.

2

2


35/100

31

Historical Perspective Inverter Prices TEAM-UP large installatio

Inverter prices for larger installations (> 70 kW) for Tgenerally in the $0.40/kW to $0.80/kW price range.

From 1996 to 2000, 23 systems ranging from 70 kW to 400 kW

$0.00

$0.20

$0.40

$0.60

$0.80

$1.00

1996 1997 1

Inverter Prices for TEInstalla

Year Number ofinstallations

kW Average size(kW)

1996 2 317.2 158.60

1997 4 478.4 119.60

1998 7 648.1 92.59

1999 4 393.6 98.40

2000 6 1029.4 171.57



36/100

32

Historical Perspective Inverter Prices NCI Survey of U.S. Prices

In 2004, prices for small inverters (


37/100

33

Historical Perspective Inverter Prices Solarbuzz Data

Solarbuzz tracks average inverter prices in Europe an

During the past 2 years, prices have fallen by about 13% in

Contrary to NCI data, Solarbuzz reports stable prices in the

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

Jul-03

Sep-03

Nov-03

Jan-04

Mar-04

May-04

Jul-04

Sep-04

Nov-04

Jan-05

Mar-05

May-05

$/W


38/100

34

Historical Perspective Inverter Prices IEA PVPS Data

The IEA PVPS program conducted surveys of PV invand 2002 for U.S., European, and Japanese manufactu

Inverter Prices


39/100

35

Historical Perspective Inverter Dimensions IEA PVPS Data

IEA PVPS data shows that smaller inverters (~1kW) habout 15L/kW, whereas larger ones (~5kW) are aroun

Inverter Volumes (2002 data)

N

ormalizedInverterSystem

Volume(liter/k

W)



40/100

36

Historical Perspective Inverter Weight IEA PVPS Data

IEA PVPS data shows that the weight of transformerlinverters (~5kg/kW) is 50-75% less than that of LF uni

Inverter Weights (2002 data)



41/100

37

Historical Perspective Inverter Reliability

Inverter reliability has an impact on life-cycle cost. Efinverter cost reductions should consider reliability im

0 510

PV Project Sim

Assumes expenses on other parts of t

The inverter accounts for 10-20% of theinitial system cost.

Inverters generally need to be replacedevery 5-10 years, whereas modules andother system components have a life of 25years or more.

Investment in a new inverter is required3-5 times over the life of a PV system.

Inverter r

Present v

1)Discoun

2)Inverter

CashFlow($)


42/100


43/100


44/100

40

Historical Perspective Inverter Reliability Recent Developments

Reliability of inverters is still inadequate, but improvmade.

Inverter mean time between failure (MTBF) is repof 5 to 10 years.1* This short MTBF has a significancompetitiveness of PV systems and will inhibit ex

1. Reference 8. *Note: MTBF is indicative of inverter economic life. It is a calculated number based on statnumbers assigned to each component used in a design, and depends on the stress and thermal environm

2. Reference 2

Recent improvements in reliability:

In recent years, almost every manufacturer of PV inverters has imexpected lifetime substantially.2

A 5-year warranty has become the norm in the industry, whereamost common just a few years ago.

These longer warranties are somewhat controversial. The manufclaim that they have gained a better understanding of the causescollecting and studying field data, that they have reduced part cquality components, and modified product design to lessen comvulnerabilities were identified. Other manufacturers and industrthese warranties are mere marketing tools.

Manufacturers currently are evaluating offering extended warraavailable for an additional cost. This has become common for othand is a way for consumers to reduce risk associated with near-t


45/100

41

Historical Perspective Inverter Reliability Recent Developments

In the past year, North American manufacturers haveinnovative products and set new standards for invert

PV Powered (PVP) of Oregon and Sustainable Energy Techn(SET) of Canada offer a 10-year warranty, the best available iindustry.

PVP and SET inverters have a lower part count than other prod

market today,* which increases reliability because:1.Fewer parts mean fewer failures.

2.Higher-quality parts can be used while still meeting inverte

Both manufacturers use Digital Signal Processing (DSP).

A DSP chip translates the waveform into digital format, whprocessed, evaluated, and modified in very short time perio

inverter can respond quickly to a wide range of situations, wreliability and efficiency.

* Note: Other manufacturers point out that different methods of counting parts may b


46/100

42

Table of Contents

1 Executive Summary

2 Introduction




6 Addressing Challenges



47/100

43

Future Performance Experience Curve Basic Concept

Experience curves model the relationship between coand production volume, which indicates the level of

Basic Assumption: Cost of production declines by a constant percentage the total number of units produced. This cost-reduction rate is called theranges from 0% to 35% across various technologies.

0

20

40

60

80

100

0 100 200 300 400 500 600 700 800 900 1000

LR=0.1

LR=0.2

LR=0.3

1

10

100

1 10

Cumulative Production Cumulative Pr

ProductionCost

ProductionCost(logscale)


48/100


49/100

45

Future Performance Experience Curve Results for PV

Data used to estimate the learning ratio for inverters inverter retail prices in the Netherlands and in Germ

Experience curve for inverter list prices (19

Learning Rate: 7%

Learn

Note: The Progress Ratio (PR) is related to the Learning Ratio (LR): PR =

Source: References 12 and 13


50/100

46

Future Performance Experience Curve Discussion of Inverter Da

Until recently, the markets for inverters in each counseparate, but this situation is changing, particularly in

Market boundaries: For PV inverters, differences in regulationhindered the emergence of a global market. During the period manufacturers served only one country.

The extent of the Learning System for inverters was natiolearning rate was obtained on the basis of installed capacity

Note: Germany and the Netherlands were selected, because for other countries was insufficient.

Today, the market for inverters can be broadly segmented amoGermany), and the United States. It has internationalized someseveral manufacturers serving more than one of the above segmbe noted that manufacturers serving multiple markets typically

each market.

Going forward, the learning system for inverters will become especially across European countries. This trend will be less mbecause of the level of state control of regulations.


51/100

47

Future Performance Experience Curve Discussion of Inverter Da

Production volumes can be measured in units or megmegawatts is a more practical alternative.

Production volumes: The Photex study measured production in MW rather than in numhistorical data and projections of PV installed capacity are generally available in MW is this methodology.

Because average inverter sizes have generally been increasing (from < 2 kW to > 3-5 kW)if it was based on number of units rather than MW. This is because the growth rate as mbeen lower than the growth rate in MW, but the observed prices are obviously not affectmeasured.

LRunits > LRMW

If the analysis is done based on units, then LRunits would have to be applied to projectionrequire making an assumption concerning future trends in inverter sizes.

If the past trend of increasing inverter sizes is assumed to continue, then the price pwhether the learning curve analysis is based on units or MW.

If inverter sizes are assumed to stabilize, then the learning-curve analysis based on uThis is because LRunits > LRMW, while the growth rate in units would be the same as

Future trends in inverter sizes cannot be determined with a great degregreat number of factors that influence inverter prices and the high uncelearning-curve analysis, adding this extra step to the analysis is not like

*NOTE: Inverter prices have been decreasing partly because size has been increasing. Hence, if inverter sizethe learning rate inferred from past prices will be too high when applied to future production. This is true wMW, i.e. LRunits or LRMW would both be too high. But the fact remains that LRunits>LRMW (they do not changdata and are therefore independent of our assumptions about future size trends), so a learning-curve analysprices than an analysis based on MW. But both analyses would overstate the price reductions, if inverter siz


52/100


53/100


54/100

50

Future Performance Experience Curve Discussion of Projections

Based on NCI analysis of learning-curve rates, we bereasonable estimate for both the U.S. and internation

Our central estimate for the learning rate is 10%, which is slighfigure obtained by the PHOTEX study. We believe the learninthe future for the following reasons:

1.Consolidation: As the inverter market matures, smaller marooted out and a limited number of manufacturers will takshares. As these manufacturers benefit from increasing vollikely to accelerate.

2.Globalization: As manufacturers expand into new marketsuppliers, they will benefit from larger sales volumes. In adin several markets will limit their exposure to unpredictablshould promote investment. The eventual harmonization oinstallations, interconnection, and inverters will help to acc

The high degree of similarity between U.S. and world projectiworld and U.S. PV markets are both growing at a similar rate:2005 represents about 40% of installed capacity for the Unitedonly slightly higher for the world, at 44%. Should the market gthe future, inverter price trends may differ more significantly world markets.


55/100

51

Future Performance Experience Curve Discussion of Projections

Our central estimate based on learning-curve projectiprices going down by about 42% by 2020.

This assumes a 20% per annum market growth and a 10% learnin

However, additional features and other technology improvemenover time, such as data logging capabilities, communications andAdditional features are likely to be added in the future. Thereforcompare inverter prices over time, as the products are not unifor

Therefore, while the DOE goal may appear difficult to achieve onlearning-curve improvements, it is likely that future products wicustomer benefits.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

DOE G

InvThe DOE target for inverter prices is $0.25-0.30/W by 2020.

If the basis for current inverter prices is taken as~$1.00/W, which is representative of inverters in the 1-3kW size range, then the price forecast for 2020 is $0.58/W,or about twice the DOE target.

If the basis for current inverter prices is taken as~$0.65/W, which is representative of inverters in the 3-6kW size range (Xantrex GT 3.0, SMA SB 6000), then theprice forecast for 2020 is $0.38/W, still about 30% higherthan the DOE goal.


56/100

52

Future Performance Future Prices Manufacturer Expectations

Inverter manufacturers have diverging cost expectatioprojections made in the past have generally been ina

SMA stated in mid-2004 that it wanted to reduce inverter prices b2006.1 The observed evolution in inverter prices since then suggesunlikely that this objective will be obtained. However, it is interestfurther stated that:

Cost reductions to less than 250/kW did not seem possible witBreak-through technologies that may enable further cost reducmodule-integrated inverters, high-frequency converters, and h

More recently, SMA has stated that their goal for inverter costs waspecific price ($/kW) by 50% every five years.2

Photon International reports that inverter prices have gone down2005 and that most manufacturers expect costs to decrease by 15-2years3. However, expectations vary across manufacturers:

Exendis expects reductions of more than 30% during the next 5

Sun Power foresees only slight reductions in cost in the near fuinverter prices to stabilize, at least for the next few years.

1. References 12 and 13

2. Reference 16

3. Reference 2


57/100

53

Future Performance Reliability Manufacturer Expectations

Inverter manufacturers do not think that lifetime on tyears is achievable in the near term

Xantrex, Managing Director: Why make inverters with a longer life when replacing the inverter every 10 years or so anyway? The inverters available products with higher efficiency.

SMA America, President: Why focus on higher reliability? Our customerscost. In any case, its more cost-effective to just replace the inverter in 10 yea

Sustainable Energy Technologies, Director of Operations: A 20-year lifetleast 10 years away.

Mitsubishi: A 20-plus-year life for inverters is impossible. Some parts of thbe replaced over such an extended period.

SMA, Head of Solar: A 20-year lifetime is not possible.

Fronius, Head of Sales (Germany): Inverter MTBF may reach 12 years by cant be achieved.

GE Energy indicated that 20-year life would not be practical without a sign15-year life is more reasonable, and that should be reviewed based on life-cy

Contrary to statements made in a recent Photon International article (April other industry experts we spoke to do not believe that capacitor improvemeinverters that can keep going for more than 20 years.

and most interviewed by NCI do not see this as


58/100

54

Future Performance Next-Generation Inverters Needed Improve

Next-generation inverters will enhance the competitithrough lower cost, higher reliability, and better perf

Next-Generation Inverter

Feature Description

HigherEfficiency

Currently, maximum efficiencies are on the order of 95% fortransformerless designs and innovative topologies are yieldione model claiming 98%.1

Lower Cost A price target of around $0.2-0.3/W by 2020 has been set for a reduction of 50-75% from current levels. This is most likelyincreased production volumes and learning-curve improvem

Better Reliability Inverter MTBF is now in the 5- to 10-year range. Ideally, invother PV system components (i.e. 25 years), but many questiimprovements will ever be achievable at a reasonable cost. Inan MTBF of >10 years is likely to be achievable through imprheat dissipation, and reducing complexity.

Advanced

CommunicationCapabilities

Today, inverters can record and relay information using man

protocols. Next-generation units should use a universal comrelay more comprehensive system information, enabling advand communication with the utility to support grid stability

DG Inverter An inverter that can convert DC input from various DG souwind) will benefit from economies of scale, and new technolcheaper, more reliable products for many DG applications.

1. SMA Sunny Mini Central 8000TL


59/100

55

Future Performance Summary

Achieving the targeted improvements of lower cost areliability for inverters is not a foregone conclusion f

Based on learning-curve forecasts, the targeted cost reductions foachieved with current market growth and learning-rate levels.

Significant uncertainty exists around the potential for future mexceed current levels for an extended period of time.

Additional cost reductions will require an acceleration of learn

Inverter prices have been dropping by about 10% with ever

cumulative production, compared to 20% for PV modules. Reliability and life issues for inverters have the potential to dama

the industry and long-term adoption of PV.

Because of market demands, manufacturers today are focusedover improving reliability.

Reliability and life improvements may not be achieved with coindustry.

In order to increase the probability of achieving the goals of indunecessary for the PV market to become sustainable over the longgovernment support for inverter R&D is likely to be necessary.


60/100

56

Table of Contents

1 Executive Summary

2 Introduction







61/100

57

Challenges Overview

The PV inverter industry faces some significant challits longer-term targets for cost and performance impr

Research shows that inverters have a slower learning curve than the PV moimplies that cost and performance improvements for inverters will lag behi

Historical data shows that inverter costs have been falling approximately 5

We anticipate this cost reduction curve to continue into the future, assumas forecast.

Manufacturers generally feel that designing inverters for longer than 15 yegeneral, is not necessary. Most manufacturers say that the more important

lower first-cost. A 20-year MTBF is viewed as not possible and may not be an appropriat

Inconsistent national and state regulatory standards have hurt PV inverter grow in the past, limiting many to focus on regional markets.

This issue is gradually improving; but, in the United States, differences will likely continue to impede cost benefits associated with larger markethe next few years.

On the other hand, given their small size and relatively low level of sophismanufacturers may benefit tremendously from small improvements to des(e.g. low-hanging fruit for cost and performance improvements).

Improvement in components (such as capacitors), the trend to high-freqtransformerless designs are examples of opportunities that will contribuperformance improvements.


62/100

58

Challenges Overview

Many of the challenges for PV inverters are a result omanufacturing and an inconsistent regulatory enviro

Manufacturing 1. Inadequate product-improvement processes2. Lack of training

3. Products rushed to market too quickly

4. Lack of good quality-control processes

5. Lack of investment in sophisticated testing and manufa

6. Components purchased in small quantities

Design/Technology 7. Advanced semiconductor devices for switching needed8. Need to improve efficiency

9. Limited experimentation with alternative inverter topol

10. Capacitors available on the market are not well-suited t

11. Lack of sophistication in inverter designs (e.g. leveragin

Regulatory 12. Regulations differ across PV markets13. Regulatory complexity generally increases cost

14. U.S. grid-interconnection regulations are a heavy burde

15. U.S. requirements for PV installation increase costs subs16. Utility resistance to ungrounded systems

Policy 17. Few states have adequate incentives to promote PV mar18. Changing policies hamper long-term investment decisio


63/100


64/100

60

Challenges Manufacturing Issues Small Production Volumes

Low production volumes make it impossible for manadvantage of mass-production technologies and volu

5. Lack ofinvestment insophisticatedtesting andmanufacturingequipment

Most inverter manufacturers are small companies

They cannot afford expensive testing equipment bavolume.

Low production volumes cannot justify the investmautomated production line, and they do not have th

Inverter manufacturers cannot make investments that wproduct quality, because their sales volumes dont currmethods to detect design flaws such as Highly Accelenot used.

6. Componentspurchased insmall quantities

Most inverter manufacturers purchase components in smodest sales volume:

They cannot benefit from discounts offered on largechain management

With each new order for a given component, invert

purchase from different suppliers, depending on wprice. This results in wide component variations anproduct.

Inverter manufacturers typically do not audit their

Purchasing components in small quantities leads to higand impacts reliability.


65/100

61

Challenges Design/Technical Issues Component Limitations

Components available on the market today do not adtechnical requirements of the inverters.

7. Advancedsemiconductordevices neededfor switching. (e.g.SiC devices)

The various switching devices used in inverters to care another weak point for inverter reliability.

There are technologies (e.g. SiC switches and integrpromise for better performance, but inverter manufin influencing the direction of R&D and most have capabilities in this area.

Switch reliability is currently inadequate for PV invheat generation. New developments (such as SiC) aelectronics/semiconductor industry issue, and inverhave little influence in directing research in this ind


66/100

62

Challenges Design/Technical Issues Design and Testing Standard

Lack of resources and design experience hampers invdesign and development improvements.

Converting DC to AC current can be doneusing a variety of approaches. The variousdesigns that inverter manufacturersincorporate in their inverters to accomplishthis task are known as topologies.

Various topologies yield different inverterperformances in terms of reliability, efficiency,and cost. While there is generally a trade-offbetween these three objectives, sometopologies are simply better than others andcan improve inverters in every respect.

Inverter manufacturers do not have the resources to exextensively, so potential inverter improvements may be

9. Limitedexperimentationwith invertertopologies

CostCost

Maximum efficiencies are typically near 95% for U.S. indo not have consistent methods for rating inverters andthe load curve for quoting the rating.

Consumers do not have an easy way to compare invert

Certification processes could provide standard test metDesign improvements and elimination of transformers 2% or more.

8. Need to improveefficiency and thestandards forratings1

1. The CEC recently adopted and is using a major portion of Sandia's Test Protocol for Certification of InverteCalifornia's published numbers. Still, more needs to be done for features such as MPPT.


67/100


68/100

64

Challenges Regulatory Issues Inconsistent Requirements and Comple

Lack of an international standard creates regional maIn the U.S., regulations are particularly burdensome f

12. Regulationsdiffer across PVmarkets

Regulations for grid-connected PV inverters vary acrequirements across some countries (e.g. Germany,Switzerland) vary only slightly, and manufacturersinverter models to reach these markets.

Requirements are most stringent in the United Statemanufacturers who want to serve this market need

specifically for the United States in order to meet re This lack of uniformity creates regional markets, m

for manufacturers to create a global product (as witstandardization across markets, potential economie

13. Regulatorycomplexityincreases cost

Regulatory differences between states or countries modifications and specialization, which increases co

Different safety requirements, interconnection, or te

increase the cost for manufacturers for selling their markets.

Product lines vary by market, and some companiesstates and not others. These issues lead to higher pr


69/100

65

Challenges Regulatory Issues Requirements for Grid Connection

Requirements for grid connection vary significantly iIEEE standards that are expensive for manufacturers

14. U.S. grid-connectionregulations are aheavy burden oninvertermanufacturers

U.S. manufacturers face confusing regulations.

In 2005, UL 1741 and IEEE 1547 have apparently way that should help resolve some of the confusiwith these two standards. Ongoing changes to thstandards is likely to continue to create challenge

Acquiring the UL 1741 standard costs nearly $10

for small players; and modifications typically reqwhich is a barrier to making improvements.

Utilities can also adopt their own standards, add

UL standards are a damper on innovation, because prequire new testing for modest changes to designs. Ugovernment can also require their own standards, w


70/100

66

Challenges Regulatory Issues System Configuration and Grounding

Inverter and installation costs are significantly higheby complex requirements and local codes that still re

15. U.S.requirements forPV installationsincrease costssubstantially

Manufacturers who sell PV inverters in European maStates report that installation costs are substantially

The installed cost of a 5 kW system is about 4.2 opposed to $6.50 9.00/W in the United States (HSolar Electronics Division, Fronius, January 2005)

The cost of installation of a 5 kW system is about

Germany, as opposed to $1,400/kW in the U.S. One of the areas of higher cost in the United States is

for externally accessible AC disconnects and conduit

Roughly speaking, installation costs for PV in the Unthat of Germany.

16. Utility and localresistance to

ungroundedsystems

Ungrounded PV array installations are allowed by thCode, which means that transformerless inverters co

However, it is expected that these systems may be diand regulators to accept without substantial additionstandards.

Resistance to transformerless designs impacts opporinverter improvements: higher efficiency, lower weig


71/100

67

Challenges Policy Issues Fragmentation and Inconsistency

PV market growth is restricted to a handful of states, for inverter manufacturers and hampering investmen

17. Few states haveadequateincentives topromote PVmarket growth

Several states have very good incentives for PV (e.g. states in areas such the Southeast have no buy-downincentives to stimulate installations of PV.

Where incentives are inadequate, the PV market wiland potential economies of scale in the United Stateswill remain untapped.

18. Changingpolicies hamperinvestment

Major investment on the part of inverter manufacturof confidence in future income streams.

Uncertain or changing incentives for PV create the wmanufacturers, who respond by putting their producas possible, without investing in lengthy product devassembly and testing equipment.

Without stable PV support policies, inverter manufamake substantial investments to improve their produ


72/100


73/100


74/100

70

Challenges Conclusion

NCIs assessment is that there is an important role fothe support of PV inverter improvements for the next

In general, larger companies in the PV inverter business view the role of govassistance (via programs to reduce cost and increase reliability) as being lessand the long-term future of the industry.

Most larger companies NCI spoke to believe that increasing sales volumfactor that will lead to lower cost and higher reliability for PV inverters

Despite the views of larger companies, introducing a new inverter product hventure for some large companies. For example:

Xantrex experienced significant problems with their early PV inverters market share to new European market entrants.

Philips entered the PV inverter market in Europe, only to exit a few yeasignificant technical problems with their first product.

The PV market will be in a critical growth phase during the next 5-10 years,significant policy and market support to achieve the overall cost and performsustainable market.

If small manufacturers have more difficulty meeting the reliability requiremcannot afford to provide adequate after-sales service, it could hurt the PV in(inadequately performing inverters will hurt the industry).

While some consolidation in the inverter business should be expected, the binnovation provided by the smaller companies are likely to be important to early stage of development.


75/100


76/100

72

Addressing the Challenges Overview

Apart from influencing standards and increasing margains will come from addressing design/manufacturi

Challenge Addressing th

Manufacturing/Testing

1. Inadequate product improvement processes

2. Lack of training

3. Products rushed to market too quickly

4. Lack of good quality-control processes

5. Lack of investment in sophisticated testing andmanufacturing equipment

6. Components purchased in small quantities

Assistance for inverterprocess improvement

Better understanding o

Training and support i

Standard testing metho

Assistance with HALTlowering risk associate

Consistent information

Technology/Design

7. Advanced semiconductor devices for switching needed(e.g. SiC diodes)

8. Need to improve efficiency

9. Limited experimentation with alternative invertertopologies

10. Capacitors available on the market are not well-suited toPV inverter applications

11. Lack of sophistication in inverter designs

12. Regulations differ across PV markets

13. Regulatory complexity generally increases cost

14. U.S. grid-interconnection regulations are a heavy burdenon inverter manufacturers

15. U.S. requirements for PV installation increase costssubstantially

16. Utility resistance to ungrounded systems

Regulatory

17. Few states have adequate incentives to promote PVmarket growth

18. Changing policies hamper investment

Development of advancomponent technologi

Modeling tools for expthermal management t

Support design of alterreduce cost of inverter

Modular designs that wcomponents for multip

Development of appro

Harmonization of regu

Simplification and stanrequirements

Studies and assessmensafety issues, and a bro

Policy Long-term programs f

Policy that supports thsupport the inverter in


77/100

73

Addressing the Challenges Assistance for Inverter Manufacturers

Some manufacturers can benefit from assistance in pthe tasks they cannot do, due to their small size and l

Inverter Manufacturing and Testing

ProcessImprovementTechniques andTraining

General support in understanding process-impother industries (semiconductors, electronics, etmanufacturing cost.

Training and support in quality-control techniqvolume manufacturing industries (semiconduc

FailureDocumentation

Development of a database to document inverteAnalysis of this database would allow inverter failure modes and correct their designs to impr

Testing Support Performance, HALTand HASS

Assist manufacturers by providing support for imaging for thermal management testing, highlidentify weaknesses, HALT and HASS, etc.

Assistance in developing methods and protocolspecifying inverter efficiency.

Component Testingand Documentation

Test components (e.g. capacitors) to measure ththeir performance and document the results. Tvariation between components available on thedocumentation would allow inverter manufactuavailable components to incorporate into their p


78/100

74

Addressing the Challenges Assistance with Technology and Desig

Many potential inverter technology and design improbeen identified.

New Inverter Technology and Design (1 of 3

DER inverters1 Inverters used for a variety of DER applications couquantities, allowing manufacturers to benefit from

The challenge for PV inverter manufacturers is to urequirements of other DER applications and designother applications.

Note: Sustainable Energy Technologies has already that relies on essentially the same design as its fuel

Modeling Develop and provide modeling tools to enable manvarious inverter designs.

Develop models for environmental conditions and to help inverter designers understand operational r

Innovative

Topologies

Innovative topologies can reduce capacitor requiremthermal management problems that lead to prematcomponents but developing new topologies takes

Installation andConnection Features

Connectors have been a reliability issue for inverterneeded to simplify, standardize, and improve inver

1. Inverters that can be used for multiple distributed generation energy sources are referred to as distributedgeneration (DG) or distributed energy resource (DER) inverters.


79/100


80/100

76

Addressing the Challenges Advanced Inverter Components

Inverter manufacturers need cheaper, more reliable cmake less expensive, more reliable inverters.

New Inverter Technology and Design (3 of 3) - Advanced

Capacitors Inverter manufacturers frequently state that the care inadequate. Specifically, manufacturers need cost of todays capacitors.

R&D is needed to develop improved capacitors, bindustry does not have the resources to carry outthe capacitor industry, due to the relatively low vother electronics applications.

Switches Switches based on SiC hold the promise of better tolerate higher temperatures, can handle very higlow resistance, and can operate at high frequencyinverter improvements in weight, size, cost, reliab

Commercial applications of SiC are currently lim

immaturity and high cost.

Transient SurgeDevices

Research in TSDs is currently minimal, but improboth DC and AC circuits.


81/100

77

Addressing the Challenges Assistance with Regulatory Standards

Manufacturers need regulatory standards that are cleacross markets and not constantly changing.

Regulatory Assistance

Harmonization Push for harmonization of the various standardsconnection of PV inverters and other DER.

Reduce Burden onManufacturers

Increase participation of manufacturers in develosubsidizing cost of attending meetings.

Subsidize cost of acquiring standards.

Acceptance ofUngrounded Arrays

Address utility misgivings regarding safety concarrays and transformerless inverters. Experienceneeds to be transferred to the United States.

CommunicationsStandard

A standard for communicating DG system inform

1. Remote monitoring and system diagnostics osoftware platform.

2. Efficient communication between DG inverteminimize DG interruptions and improve grid

Note: Efforts underway at IEEE and IEC will addre

Standard Metrics forInverterPerformance

There are no established methods for rating inveconsumers and installers can use to compare invbe reported in any number of ways). This wouldthe market and favor better inverters while rooti

1. The CEC recently adopted and is using a major portion of Sandia's Test Protocol for Certification of Inver


82/100

78

Addressing the Challenges Assistance with PV Policy

One of the most important challenges facing the indulong-term, consistent policy to support market develo

national basis.

Policy Assistance

Long-Term,Consistent PVPolicy Support

The U.S. policies for support of PV are currently dstate, and local programs. While some programs are multiyear programs to meet PV installation g

Long-term support to programs to build the mark

without stops and starts, will help the industry mvolumes in a way that will allow continual cost rereliability and performance improvement. Becausmost important driver in achieving goals of the inof the most critical to the industry. These policieswhole, not just for inverters.


83/100

79

Table of Contents

1 Executive Summary

2 Introduction




6 Addressing Challenges



84/100

80

Suggested Role for Government Overview

Long-term cost reduction and performance improvemgreatly from the ongoing support of additional gover

Inverter testing at Sandia National Labs is extremely valuable to the insupport of development of testing protocols is important to the indust

Documentation of failure analysis in the industry is not conducted unfor government would be in collecting and documenting inverter failuindustry.

Modeling tools would be helpful to manufacturers, but developing ac

challenging. An assessment of issues and needs related to modeling wbefore embarking on new modeling efforts.

The HRII program is generally considered to have been successful. FoR&D partnerships such as this should receive government support.

Cost and efficiency benefits of tranformerless inverters are understoodand cons of tranformerless inverters as a means of educating inspectorbe beneficial.

Analysis of the interaction of the various federal, state, and municipalbe increasingly important to future industry growth needed for long-t


85/100


86/100


87/100

83

Suggested Role for Government Inverter Testing

Inverter testing at Sandia National Laboratories helpexperiment with innovative designs and improve the

Inverter Testing

Benchmarking tests to evaluate inverters against manufacturer specificatgenerally agree that a comprehensive program of inverter testing and perbe very valuable to the industry.

Development testing protocols to assist manufacturers in testing new inv

Utility compatibility and islanding tests. This type of testing provides m

information on their inverters ability to meet UL 1741 requirements. Varisystem-specific tests to be performed to understand the effect of PV inverexists regarding the value of this, but it will remain a requirement.

Temperature evaluations. These tests allow manufacturers to study tempvarious strategies for thermal management, which are critical for product

Verification, validation, and characterization is extremely valuable who often do not have extensive in-house testing capabilities. Sandthe resources necessary to support development of inverters for the


88/100

84

Suggested Role for Government Failure Documentation

Government can assist manufacturers in improving pby studying and documenting failure of inverters in t

Documentation of Inverter Failures

Data of failure of inverters in the field is lacking. Most inverter manufactunumber of shipped units that were returned by customers, and little morelook into what caused the inverter to fail.

Larger companies are apparently capturing and documenting informationbut information is considered confidential.

A comprehensive database of inverter failures would enable manufactureweakness in designs and take corrective measures.

A possible role for government would be to conduct an extensive stdocument inverter failures and provide the results to manufacturer


89/100

85

Suggested Role for Government Component Documentation

Documentation of information on key inverter compoassist manufacturers with design choices.

Component documentation

Inverter manufacturers have commented there are substantial differencescomponents (e.g. capacitors) available from different suppliers.

Inconsistent specification, data sheets, and testing results exist on some ofinverters (e.g. capacitors, fans, electrical connectors, power semiconductofor manufacturers to make proper comparisons of options.

A comprehensive study of inverter components would help manufavailable products.

However, because components used in inverters are also used in m

likely this type of work should be conducted as crosscutting researcand power electronics.


90/100


91/100


92/100

88

Suggested Role for Government Public-Private R&D Partnership

The success of HRII indicates that government shoulfunding another similar initiative.

Public-Private R&D Partnership

The High Reliability Inverter Initiative (HRII), launched in 2002, will comcontractors selected (GE, Satcon, Xantrex) are developing prototypes of aone manufacturer has commented that their involvement in HRII has sigdevelopment, by allowing them to explore options that would otherwise

It should be noted that Sandia received many responses to their RFQ, six

excellent. But only three manufacturers could be selected due to funding Programs such as this may be appropriate for development of advanced

switches, capacitors, and connectors that would benefit the broader DER

A formal review of the HRII program should be completed and shallow others to understand some of the key findings.

At this point, the results of HRII appear promising. Pending an evappraisal of HRII success, another similar initiative may be a good

Use of similar approaches for DER inverter components should be


93/100

89

Suggested Role for Government Alternative Inverter Topologies

Innovative inverter topologies could be a source for areduction and reliability and performance improvem

for government may be to fund studies to understand

Alternative Inverter Topologies

Innovative control and inverter design topologies have the potential to beimproved thermal management, and improved reliability. Several manufthere could be many advantages to the exploration of alternative topologi

Alternative topologies could be used to standardize sub components thproduct lines or in power electronics for other DER products.

Government could consider funding studies on the potential benefitopologies. Many benefits have been suggested, but there does not direct evidence of the specific gains that might be achieved.

Research could focus on experimental topologies, with the objectiv


94/100


95/100

91

Suggested Role for Government Standards

Standards are a major complaint of manufacturers, bufor DOE in this area may be limited.

Standards

Grid connection: Manufacturers repeatedly ask for standards to be harmonizeand transformerless inverters to be accepted, and for relaxation of installation r

Communication: Standards for communicating PV system information are neefor utility interaction. Without a single, universal standard, manufacturers willstandards that will lead to fragmentation and hamper growth of this technolog

Performance metrics: Sandia and Endecon Engineering (now BEW) are curren

Performance Test Procedure. Manufacturers have been asking for this type of sactivity should continue.

Grid connection and installation: These standards are the domain of orIEEE (IEEE 1547), and NFPA (NEC 2005). However, DOE may be able toor provide leadership to help bring about the changes that inverter manaddition, the following specific recommendations have been made relati

1. Subsidize the cost of acquiring the UL 1741 standard.

2. Subsidize the cost of attending UL 1741 meetings to encourage indu

Communication: EPRI is leading the effort to develop a communicationshould support this initiative.

Performance metrics: Sandia and Endecon Engineering are currently dePerformance Test Protocol. Manufacturers have been asking for this typthis activity should continue.


96/100

92

Suggested Role for Government Policy Assessment

Understanding the role of incentive programs and pobe critical to the long-term growth necessary to meet

performance, and reliability goals.

The Impact of Alternative Policies and Incentives for PV

Increasing market volume is one of the major drivers in achieving cost aninverters. Market volume in the United States is growing, but not to the Japan.

There is significant fragmentation in policies to promote the adoption of and New York lead the country with programs to buy-down the price ofpolicy provides investment tax incentives. European feed-in tariffs have rapidly growing market and are driving most of the investment in the in

An assessment of impact of alternative policies would benefit the indust

Government could fund a study of the impact of PV policy progra

understanding the relationship of program design to market growmaking U.S. policies more effective. Understanding the interactionmunicipal programs will be increasingly important to further indu


97/100

93

References

1. Photon International, Invasion of the inverters, April 2004.

2. Photon International, Market Survey of Inverters, April 2005.

3. Renewable Energy World, Choosing the right inverter, March-April 2004.

4. Photovoltaics, Looking to Spain, September-October 2004.

5. R.West et al., Status and Needs of Power Electronics for Photovoltaic Inverters: SummSAND2002-1085, May 2002.

6. Dan Ton, Ward Bower, Summary Report on the DOE High-tech Inverter Workshop, J

7. Dan Ton, Ward Bower, Summary Report on the DOE Workshop On a Systems-drivenDevelopment, September 2003.

8. Gonzalez et al., PV Inverter Testing, Modeling, and New Initiatives, NCPV and SolaNREL/CD-520-33586.

9. Bonn, Russell H., Developing a Next Generation PV Inverter, IEEE 2002.

10. Sarjeant et al., Capacitive Components for Power Electronics, IEEE 2001.

11. IEA, Grid-connected photovoltaic power systems: Survey of inverter and related protectReport IEA-PVPS T5-05: 2002, December 2002.

12. Jan Schaeffer et al, Learning from the Sun, Final report of the Photex project, Augu

13. Jan Schaeffer et al, Photovoltaic Experiences, Synthesis report of the Photex-projec

14. Solar Electric Power Association, Residential PV Systems Cost Report, December 2

15. Solar Electric Power Association, Large Systems Cost Report 2001 Update, Septem

16. Photon International, PV industry in high spirits at Intersolar, August 2005


98/100

94

References

Conference Interviews June 6-9, Barcelona, Spain

1. Mitsubishi

2. SMA

3. Fronius

4. Outback

5. GE

6. Xantrex

7. Sustainable Energy Technologies8. Heliotronics

9. SunPower

10. Siemens

11. PowerLight

12. SolarMax


99/100


100/100

REPORT DOCUMENTATION PAGEForm Approved

OMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of thiscollection of information, including suggestions for reducing the burden, to Department of Defense, Executive Services and Communications Directorate (0704-0188). Respondentsshould be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display acurrently valid OMB control number.

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.1. REPORT DATE (DD-MM-YYYY)

January 20062. REPORT TYPE

Subcontractor Report3. DATES COVERED (From - To)

5a. CONTRACT NUMBER

DE-AC36-99-GO10337

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

A Review of PV Inverter Technology Cost and PerformanceProjections

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBERNREL/SR-620-38771

5e. TASK NUMBERPVC6.1501

6. AUTHOR(S)Navigant Consulting Inc.

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)Navigant Consulting Inc.

77 South Bedford St.Burlington, MA 01803

8. PERFORMING ORGANIZATIONREPORT NUMBERKACX-4-44451-04

10. SPONSOR/MONITOR'S ACRONYM(S)NREL

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)National Renewable Energy Laboratory1617 Cole Blvd.Golden, CO 80401-3393

11. SPONSORING/MONITORINGAGENCY REPORT NUMBERNREL/SR-620-38771

12. DISTRIBUTION AVAILABILITY STATEMENTNational Technical Information ServiceU.S. Department of Commerce5285 Port Royal RoadSpringfield, VA 22161

13. SUPPLEMENTARY NOTESNREL Technical Monitor: Robert Margolis

14. ABSTRACT (Maximum 200 Words)The National Renewable Energy Laboratory (NREL) has a major responsibility in the implementation of the U.S.Department of Energys (DOEs) Solar Energy Technologies Program. Sandia National Laboratories (SNL) has amajor role in supporting inverter development, characterization, standards, certifications, and verifications. The SolarE T h l i P tl bli h d M lti T h i l Pl hi h t bli h l f d i

Solar PV Inverter_National Renewable Energy

Documents

Transcript of Solar PV Inverter_National Renewable Energy