Distributed Generation - A Learning Laboratory

Jared Wennermark, P.E United Cooperative Services

2601 S. 1-35 West Burleson, TX 76097

j ared @ united-cs. com

Cameron Smallwood, P.E. Senior Member, IEEE

United Cooperative Services 2601 S. 1-35 West

Burleson, TX 76097 cameron @ united-cs .com

Jameson Parker, Graduate Electrical Engineer

United Cooperative Services 2601 S. 1-35 West

Burleson, TX 76097 jameson@united-cs.com

Abstract -- Distributed Generation (DG) is now marketed to residential electric consumers across the United States. Utilities have developed interconnection standards and procedures to safely connect these systems to the grid. By streamlining the DG interconnection process as part of an Energy Innovation campaign at United Cooperative Services (United), there are now over 60 member installations of wind and solar systems across its system. Further, United has installed 13 different distributed generation technologies at its offices in an effort to create a Learning Laboratory for its members and the public. In addition to providing public access to observe these systems in operation, detailed cost and true production data are available on United's website for Cooperative members to use in making their own decisions about the value of DG. Establishing this Learning Laboratory has allowed United to gain valuable experience with current DG technologies, their energy production values, investment payback periods, and maintenance realities.

Index Terms—distributed power generation, energy resources, IEEE standards, photovoltaic systems, power system interconnection, solar energy, solar power generation, wind energy, wind power generation.

I. INTRODUCTION

Innovation campaign is a United effort supported though policy, communication and programs designed to promote a four-pronged approach to controlling energy costs on the demand side, rather than simply building new and ever more expensive power generation plants. The four elements of United's Energy Innovation program are:

1 ) Energy Conservation-energy use

-changing behavior to reduce

The advancement of residentially-applied technologies, rising energy costs, desire for grid independence, and concern for the environment are all factors that have resulted in more interest in Distributed Generation (DG) across the country. Historically, many utilities discouraged interconnection of DG to the grid for various reasons, some technical and some economic. But ultimately, new interconnection standards, regulatory incentives, and public pressure have led to a warmer reception of DG at many utilities and installed capacity has been growing ever since. However, a knowledge gap still exists in the general public between what is known and expected and what can actually be achieved with the installation of DG. This report will detail how United Cooperative Services (United) has facilitated interconnection of DG for its members, and what United has done to educate and inform the public about its value and potential.

A. Energy Innovation To address the rapidly rising cost of energy at the time,

United embarked on a campaign in 2008 to help its members become more engaged in their use of electricity. The Energy

2) Energy Efficiency—reducing energy use through technology upgrade and improvement

3) Demand Response—shifting energy use to different times to shave peak demand

4) Distributed Generation (DG) — small-scale generation on the distribution system close to the point of end use

While United has worked diligently in each of these areas, the focus of this paper will be to explain how United has been proactive in supporting the DG component of Energy Innovation.

B. DG at United: Past to Present

Historically, DG systems in Texas were generally considered either novelties or experimental in nature. Interconnection standards were not fully developed, and concerns about safety and the hesitancy to change processes at the utility to accommodate competing sources of energy were all stumbling blocks to acceptance. Further, with electricity prices relatively low and stable and technologies in their developmental stages, the economics dictated that the case for DG was not compelling and utility consumers shouldn't be encouraged to pursue its utilization. However, with continued development of wind and photovoltaic (solar) technologies, and a steady rise in natural gas prices starting in about the year 2000 that led to higher electricity costs, energy consumers started taking a closer look at DG (see Fig. 1). Prior to the year 2000 there were no DG systems interconnected at United, but at that time photovoltaic costs began a steady downward trend that has continued through today (see Fig. 2). Residential wind costs actually increased from 2002 to 2008 for several economic and technical reasons, but have also steadily declined since then [1]. Industry awareness of the potential of DG gradually

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Year

Fig. 1. Natural Gas Prices for Electricity in Texas [2]

Year

Fig. 2. Average Installed Cost for Photovoltaics in the U.S. [3]

increased, culminating in the adoption of the DG interconnection standard IEEE 1547 (Standard for Interconnecting Distributed Resources with Electric Power Systems) in 2003. With a universally accepted standard in place, and with concerns about energy cost and availability on the rise, United responded in that same year by adding a DG section to its tariff with associated fees to account for the cost of this type of service to the cooperative membership. When natural gas spiked in 2005, along with passage of the Energy Policy Act of 2005 that gave tax credits of up to 30% towards solar installation costs, United experienced a growing influx of serious inquiries about DG interconnection from members. Passage of The Energy Improvement Act of 2008, which pushed the expiration date of the previous solar credits to

2016 and extended them to wind power, added impetus to the growing trend. With the introduction of the Energy Innovation campaign in 2008, United made clear that its goal was not only to remove obstacles to DG, but to provide ways to facilitate it for those members interested in controlling their power costs.

C. Current DG Program at United In 2010, in the spirit of United's Energy Innovation

campaign, the Board of Directors did two things that paved the way for an uptick in small residential DG interconnections. First, they voted to suspend indefinitely the monthly charge in the tariff for DG systems smaller than 50 kW. This class of DG systems is the fastest growing and most relevant to the membership of United. Along with the removal of the monthly fees, United introduced the EnergySmarts DG Grant program which awards up to $500 for each wind or $1000 for each solar DG installation that qualifies. The difference in the award level is to account for the fact that solar arrays are more beneficial to United's demand profile than wind turbines at the summer peak time. At the same time, United's technical staff finalized its version of the DG Procedures & Guidelines Manual for Members, based on a document produced by Texas Electric Cooperatives. This information packet includes all of the program documentation, requirements, and agreements necessary for a member to interconnect their DG systems to the grid. Specifically, the program differentiates residential sized DG (<50 kW) from larger scale systems and allows for net metering, a great cost advantage for members since power is essentially purchased from them at the retail rate instead of the avoided cost to the cooperative of purchasing the same power. Notably, United also removed the liability insurance requirement for residential DG as it was found generally to be cost prohibitive to the members, as well as in conflict with rules initiated by the Public Utility Commission of Texas (applicable to investor-owned utilities only) that waived this requirement for retail consumers. United's web site was updated with a DG section that has all of the program information as well as helpful links on financial analysis, available grants, and vendors in the area; thus a media campaign was begun to communicate United's commitment in this area.

Once a member has made the decision to go forward with a DG project, the plan must be approved by United's engineers before agreements are executed. For most applications, the proposed equipment is already UL 1741 listed, which means it has been tested by a certified laboratory and found in compliance with the aforementioned IEEE 1547 standard. The standard specifies electrical characteristics like voltage, frequency, and harmonic content of the inverter output. In a few cases there has been no UL listing, so the engineer must review equipment specifications in detail to be satisfied that it meets the IEEE 1547 standard. This has occurred with several members who have designed and developed their own systems or who have purchased small plug-in-type units. On-site inspection is a straightforward review of the physical

7. DG Interconnection

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electrical interconnection and a few electrical measures toverify proper operation. Key to the physical interconnectionis the requirement that the system has an externally visiblesafety disconnect that allows United's personnel tocompletely isolate the DG from the distribution system ifnecessary. United goes the extra step of requiring appropriatesignage indicating an alternate power source both at thetransformer and the next upstream sectionalizing device. Thissignage also indicates the location of the actual unit therebyallowing field crews to be aware of the existence of the unit(see Fig. 3).

Fig. 3. Typical Sign Posted at DG Location

The engineer in the field verifies proper operation of the DGsystem by measuring voltage, frequency, power factor, andharmonic content both before and after interconnection. Gridpower is then removed to verify that the system is not allowedto support an islanded load, and if everything has passedinspection a net meter is installed in order to meter theinstallation properly. The net meter United uses is a Landis &Gyr Focus AL model equipped with a TS2 AMR module thathas registers for received, delivered, and net kWh. United'sstandard meter is configured in "additive" mode so that itregisters kWh in only one direction even if the meter isplugged in upside down as a security measure, which wouldnot work for DG.

With a number of member systems now interconnected atUnited, there have been some lessons learned in the process.First, United now requires a lever style disconnect switch onthe AC side of inverters to meet the visible disconnectrequirement of the NEC and United's guidelines. Thisprovides a simple means of simulating loss of power to theinverter (to test for islanding) without having to cut power tothe entire home like it would be for a disconnect on the DCside. It is more difficult to access voltage test points on thebreaker style disconnects because there are essentially twocovers that have to be removed. Second, during a poweroutage, wind turbine blades stop turning on some models andon other models do not. So wind turbines are not a reliablemeans of visually determining what sections of line are out ofpower when field personnel are troubleshooting in the area.

Third, it is wise to schedule site visits to inspect wind andsolar units at a time when weather is cooperating, since mostinverters turn off without receiving input from the turbine orsolar panels, rendering testing difficult or impossible. Fourth,the utility should become familiar with the DG equipment thatis being installed and its expected output, because at somepoint in the future there may be questions about propercrediting of generation by the consumer. Beingknowledgeable about the DG technology, the metering, andthe billing process goes a long way in resolving these issuesthat are often due to DG systems that are not producing aspromised by the vendor. Finally, there may come a timewhen a DG installation does not pass a power qualityinspection, most likely when examining some of thehomemade systems whose designs are available on theinternet. The utility should be prepared for this scenario anddecide what specific course of action will be taken beforemaking an exception that could set a precedent that is hard toreverse.

D. Growth ofDGThe actual growth of member installed DG at United

reflects the internal and external factors that are in playasdiscussed in this work. United started tracking seriousinquiries about DG in 2007, defined as those calls that areforwarded by member service representatives to engineers forin depth discussion about interconnection. This trend shows amarked increase in interest in 2008 and 2009 that coincideswith the rise in natural gas prices, expansion of Federal taxcredits, and United's Energy Innovation campaign (see Fig.4). Even when natural gas prices dropped, the falling pricesof wind and solar technologies, the modifications to United'sDG tariff, and availability of grant funds stimulated continuedinterest from members and resulted in a number of inquiriesthat led to installations, albeit at lower levels than before.

Fig. 4. Cumulative DG Installations and Inquiries at United

II. THE LEARNING LABORATORYAs part of the effort to accommodate the growing interest

in DG and in response to feedback from members with DGinterconnections, United created the concept of a "learninglaboratory" in 2010. The idea was to install various types of

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photovoltaic and wind generation technologies at United's offices throughout the service territory. The decision to invest in this project was bolstered by the availability in 2010 of grant funds from the USD A's Renewable Energy Systems and Energy Efficiency Improvements Program, which provides up to 25% of the cost of renewable energy projects to small businesses in rural areas.

A. Goals The purposes for creating the learning laboratory were as

follows:

1) To provide United employees with direct knowledge and experience with solar array and wind turbine installation, operation, and maintenance in order to better serve the cooperative membership.

2) To provide cooperative members and the general public with access to different solar and wind technologies for educational purposes.

3) To allow United to collect and share energy production data with members and the public from different technologies and manufacturers to assist them in determining the value of residential DG.

4) To demonstrate United's commitment to addressing the concern of rising electricity costs through alternative sources of energy.

B. Preparation and Training Before embarking on the project, some of United's

employees were sent to specialized training in photovoltaic system installation. This weeklong course provided detailed instruction on what would be required for United to perform turnkey procurement, siting, and installation of the solar arrays for the Learning Laboratory project. Two United employees attended a North American Board of Certified Energy Practitioners (NAB CEP) PV Entry Level Course to receive the training and take the entry level exam. Both employees were awarded certification for entry level PV installation.

No formal training for the wind turbine installations was deemed necessary due to similarities between wind turbine construction and electric power distribution construction. United reviewed the installation documentation from the various manufacturers and discussed any questions with them directly, as well as clarifying details with other installers. In some instances, additional notes, wiring diagrams, etc. were created by United to provide more guidance during the installation process than was included in the factory documentation.

The initial scope and the specific plans for the Learning Laboratory installations were driven by the USDA grant application process, which required a highly detailed level of description of the project. United learned a tremendous amount about current photovoltaic technology and costs from distributors at the training course that was attended. From

this information United selected a variety of systems that would accomplish the goals previously mentioned. For wind turbine selection, United talked with several manufacturers directly, reviewed on-line small wind community reviews, and gleaned information from cooperative members that had installed wind turbines. While some of what was proposed in the grant application was actually installed, there were alterations and modifications to United's plans that were necessary due to product availability and newer technology on the market at the time of procurement.

In spite of the fact that United's service territory is mainly in rural areas, all of its office locations where the DG systems were to be installed are within city limits. In addition to the typical building and electrical permits required by municipalities for new construction, United had to gain approval specifically for these renewable energy installations. United discovered that most municipalities were not prepared for the request to install and operate DG, and their policies were either non-existent or prohibitive. The typical objection was the wind turbine height, but even solar array location was a problem in some instances. Depending on the specific city and its zoning ordinances, construction approval involved special use permits, rezoning, and variance requests that in some instances required United to present a case demonstrating hardship if the permit was denied. Fortunately, United was able to gain most of the approvals that were sought, and in some cases was instrumental in helping cities craft their DG policies.

C. Systems Installed As the name implies, there were many lessons learned

during the installation of each of the systems procured for the Learning Laboratory. A summary description of each of the systems is shown in Table I, followed by a discussion of the issues encountered at each office site where they were installed. In each case, a separate single phase transformer and service were installed at each office building, including a digital meter capable of net metering, to more closely resemble the experience of a residential installation. The meter was equipped with a Metrum cellular modem so that 15 minute interval data could be retrieved and accessed via United's website. The electrical connections from the systems to each service were made per the NEC and manufacturers recommendations using an in-house licensed electrician. Each installation was required to follow United's guidelines for DG interconnection as well as to comply with local ordinances.

Stephenville Solar 1 folarWorld panels/Kaco L g 1 Inverter Stephenville Solar 2 Sanyo panels/Fronius Inverter 9/30/10 1.7 GranburyWind Skystream 3.7 w/integral 2 J

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Granbury Solar Canadian Solar panels/PV Powered Inv. 8/09/11 1.1

Cleburne Solar 1 Westinghouse Solar Array 7/26/12 1.5

Cleburne Solar 2 SunPower panels/Enphase Inverters 9/21/11 1.4

Cleburne Solar 3 SunPower panels/Enphase Inverters and Zomeworks tracking

9/21/11 1.4

Cleburne Wind 1 Sonkyo Windspot 3.5/Aurora Inverter 7/24/12 3.5

Cleburne Wind 2 Xzeres 110HV/SMA Windy Boy Inverter 7/24/12 2.5

Meridian Solar Schott panels/Enphase Inverters 6/15/12 1.4

Possum Kingdom Solar

Kyocera panels/PV Powered Inverter 8/09/12 1.3

Burleson Solar Schuco panels/SMA Inverter 3/30/12 2.3

Burleson Wind Bergey Excel 10/Bergey PowerSync II Inverter 3/27/12 10.0

1 ) Stephenville Office Two solar arrays were ground mounted on concrete piers

at our Stephenville office (see Fig. 5). These solar arrays would normally be roof mounted, but for the purpose of allowing public view and access, they were installed in this way. The panels are designed to mount to aluminum rails that attach to the roof, but instead the rails were fastened to concrete piers that were engineered to handle the wind loading of the arrays, which is the critical load in this case. In both cases, the concrete piers were not aligned correctly by the contractor hired to do the work, so some adjustments had to be made for successful racking of the panels. Additionally, the pier height allowed less than 0.3 m (1 foot) of ground clearance from the panels once installed, so a bark mulch barrier was later created around the arrays to reduce the possibility of damage during lawn maintenance.

Fig. 5. Solar Arrays in Stephenville

The first system installed was a 1.8 kW array consisting of eight SolarWorld solar modules and a Kaco inverter. There were no problems with the physical installation of the panels;

however there was a manufacturer defect in the Kaco inverter. There were a certain number of inverters manufactured that were known to disconnect from the grid under the status code "Underfrequency" even when no such condition existed. This known problem required this inverter to be replaced, which was covered under the manufacturer's warranty, and the problem was resolved. There have been no other operational problems since installation as of this writing.

The second system installed in Stephenville was a 1.72 kW array consisting of eight Sanyo solar modules and a Fronius inverter. During the first installation attempt it was discovered that the panel mounting clamps sent by the distributor were not the correct size. These had to be exchanged for the proper clamps before the installation could be completed. There have been no operational problems since installation as of this writing.

2) Granbury Office A wind turbine and solar array were installed at United's

Granbury office (see Fig. 6). The wind turbine is a Skystream 3.7 from Southwest Windpower that was mounted on a 17 m (55 ft.) monopole steel tower. The height of the tower was chosen to obtain the recommended 9 m (30 ft.) of clearance from structures in the vicinity that can cause turbulence in the wind flow. During the tower foundation installation, the contractor did not place the mounting bolt template back into the foundation form after finishing the surface of the concrete. As a result, the anchor bolts were slightly misaligned when the concrete cured and there were questions as to whether or not the tower could be installed without modifying the foundation. United verified that the foundation bolts would

Fig. 6. Solar Array and Wind Turbine in Granbury

accommodate the tower base by lowering the bottom section onto the foundation with the help of a digger truck. After verifying that no modifications to the foundation would be necessary, the bottom section was removed and the complete

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tower was assembled on the ground per the manufacturer's instructions. The complete tower was raised with the digger truck and the turbine attached with a bucket truck equipped with a 17 m (55 ft.) boom without incident.

After approximately 6 months of successful operation, the turbine failed. In order get the unit operational again in a timely manner without voiding the warranty, United obtained approval from the manufacturer to troubleshoot the problem. Because of the lack of helpful documentation included with the unit, United worked with the manufacturer to develop a troubleshooting guide. Using this guide, United determined the cause of the failure to be a damaged brush assembly in the turbine. Specifically, the brush contact block for one of the 120V power supply legs had been severed, creating an open circuit. The turbine is designed to shut down without both legs of the 240 V supply present, so the turbine functioned as expected for this failure mode.

A new brush assembly was provided by the manufacturer under warranty, and since its replacement, the Skystream has operated without further incident as of the time of this report. Unfortunately, the time it took to troubleshoot the problem, get the replacement parts, and make the repair caused the unit to be out of operation for about three months. This loss in production is reflected in the results presented later in this writing, and definitely has a negative impact on the financial analysis for this unit. One positive that came out of this equipment failure was the brush assembly replacement required a thorough disassembly of the nacelle (or turbine generator enclosure), so United gained valuable experience that could prove useful if problems occur in the future.

During the troubleshooting process, a hairline crack was discovered in one of the turbine blades. Since turbine blades have to be properly balanced as a set, all the blades must be replaced instead of the single damaged blade. The first set of somewhat fragile replacement blades was damaged during shipping, so a second set was shipped under warranty.

The solar array installed at the Granbury office is a 1.1 kW array consisting of five Canadian Solar panels and a PV Powered inverter installed on the ground, though it would typically be roof mounted. At this site, United chose to install foundation piers that extended approximately one meter (three feet) above ground level in order to better protect the solar arrays from incidental contact during lawn maintenance as previously mentioned regarding the Stephenville location. The racking of the solar panels was straightforward and without incident, other than a modification that was made due to one of the piers sinking about five inches after curing. The electrical connections to the service were made as designed, per the NEC and manufacturers recommendations using an in-house licensed electrician as before. There have been no operational issues with this installation as of this writing.

3) Cleburne Office United installed three solar arrays and two wind turbines at

its Cleburne office (see Fig. 7). Two of the solar installations

are 1.38 kW arrays consisting of six Sunpower panels each and employing an Enphase microinverter on each panel. The difference between these two installations is that one is equipped with a single-axis Zomeworks tracking mechanism and the other is a fixed array. United opted to have a third party install these arrays since they would be mounted on monopole structures that utilize a unique racking method. There were no complications during the installation and there have been no operational problems since their installation as of this writing.

Fig. 7. Solar Arrays and Wind Turbines in Cleburne

The third solar array installed was a 1.48 kW array consisting of eight Westinghouse panels also employing an Enphase microinverter on each module. For illustrative purposes, United constructed a mock shingle roof near ground level to install the racks and panels on. There were multiple problems in receiving complete, correct, and timely material shipment from the distributor for this installation. But since the system has been installed, there have been no operational issues as of this writing.

The first wind turbine installed in Cleburne is a 3.5 kW Sonkyo Windspot mounted on an 18 m (60 ft.) monopole tower. The height of the tower was chosen to obtain the recommended 9 m (30 ft.) of clearance from structures in the vicinity. This turbine was installed by a third party company and there were no issues during the installation. Additionally, the system has been operating without any problems as of this writing.

The other wind turbine installed in Cleburne is a 2.5 kW Xzeres wind turbine mounted on an 18 m (60 ft.) monopole tower. The height of this tower was also chosen to obtain the recommended 9 m (30 ft.) of clearance from structures in the vicinity. There were a couple of issues that were discovered during the installation, mainly due to the out-of-date installation manual provided with the unit. According to the manual there was supposed to be a factory installed surge arrestor in the yaw head. This wasn't the standard practice

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from the manufacturer anymore and it is required to be installed by the purchaser. Additionally, there were extra leads coming from the alternator that were not mentioned in the manual. Another item that didn't match the pictures and description in the manual was the lack of a back plate for the alternator. While the manufacturer reassured United that this was an approved design feature that had been tested, there was still concern that the taped alternator windings would be exposed to the elements.

Since the Xzeres wind turbine has been in operation, the SM A Windy Boy inverter has malfunctioned on several occasions. The inverter is designed to send turbine output to a dump load instead of to the grid under certain overvoltage conditions, but it started locking itself in this state for no apparent reason. The temporary solution was to restart or reprogram the unit, but that is obviously inconvenient and inefficient, and resulted in wasted energy. This loss in production is reflected in the results presented later in this writing, and definitely has a negative impact on financial analysis for this unit. After purchasing the appropriate communications cable and troubleshooting the problem with the manufacturer, the only permanent solution was to replace the inverter and make some additional programming changes. There have been no other operational problems with the turbine itself or the turbine controller in the Xzeres installation as of this writing.

4) Meridian Office At the Meridian office, a 1.44 kW solar array consisting of

six Schott panels was installed, with each panel employing an Enphase microinverter (see Fig. 8). United opted to have a third party install this array since it is mounted on a monopole structure that utilizes a unique racking method, and it also incorporates a single-axis Zomeworks tracking system.

Fig. 8. Solar Array in Meridian

During the installation there was a delay of a few days because the "whip" cable that connects all the Enphase

inverters together was designed for 208 V service instead of the 240 V service that is available at that location. There have been no operational issues with the Meridian solar array as of this writing.

5) Possum Kingdom Lake Office At the Possum Kingdom Lake office, a 1.26 kW solar

array consisting of six Kyocera panels and a PV Powered inverter was installed (see Fig. 9). During the site evaluation, the shading on the property dictated that that the best location for optimal sun exposure happened to be in the middle of a septic line field. To avoid disturbing this field, a location susceptible to some shading during the early morning and late

evening hours was selected. While this would not seem to significantly affect the production of the installation since solar radiation is limited at that time of day, it is apparent when production is compared to other solar installations at United that are not obstructed. There have not been any operational issues since the completion of this installation as of this writing.

6) Burleson Office A wind turbine and solar array was installed at the

Burleson office (see Fig. 10 and Fig. 11). The wind turbine is a 10 kW peak rated capacity Bergey Excel on a 27.5 m (90 ft.) monopole tower. The height of the tower was not only chosen to obtain the recommended clearance from structures in the vicinity, but also to maximize the production of this unit by accessing higher wind levels. In this case, local ordinances allowed installation of a structure of this height. There were complications when unpacking the tower due to its immense size, and United had a third party company install the turbine with no issues. Since installation, thunderstorms with frequent lightning strikes have caused the turbine's inverter to lose grid power temporarily on several occasions due to normal recloser operation. By design, because the

Fig. 9. Solar Array in Possum Kingdom Lake

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inverter lost power three times within an hour on oneoccasion, it disconnected itself from the grid permanently andhad to be manually reset. While inconvenient, significantproduction was not lost as it was able to be reset withintwelve hours since United monitors output at least daily.There have been no operational issues with this turbine as ofthis writing.

Fig. 10. Wind Turbine in Burleson

Fig. 11. Solar Array in Burleson

The solar array is a 2.3 kW array consisting of ten Schucopanels and a SMA Sunny Boy inverter, which was installedon the ground although it would typically be roof mounted.The installation initially called for eleven panels, but an errorin the concrete pier design made that impractical. Unitedchose to only install ten panels and use the spare as ademonstration unit for public events. While the inverterswere accessible at all DG locations, at Burleson the inverters

were installed and prominently displayed in the front officearea where they could be more visible to the public (see Fig.12) There have been no operational issues with thisinstallation as of this writing.

Fig. 12. Inverters in Burleson

III. RESULTSOnce the Learning Laboratory had been in operation for

some time, United was able to analyze the results to date andperform a financial analysis using actual cost and energyproduction data. Production interval data for all of United'sDG systems was collected and made available on the web byOlameter, a third party vendor that provides these types ofservices. Olameter's web-based tool allows for easy analysisand comparison of the DG data both internally at United andfor its members. For example, Fig. 13 shows a comparison ofproduction on a particular day from Cleburne Solar 2 (thefixed solar array) and Cleburne solar 3 (the tracking solararray). This simple graphic illustrates the increased capacity

Fig. 13. Fixed vs. Tracking Solar Production displayed in Olameter Tool

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factor for a tracking array due to increased production during the shoulder hours of the day. Fig. 14 shows the same tracking solar array (Cleburne 3) versus the other tracking solar array at Meridian on a particular day. Notice the effect

Fig. 14. Cleburne vs. Meridian Tracking Solar Production displayed in Olameter Tool

of the partial shading in the early morning hours at Meridian. Fig. 15 and Fig. 16 depict typical days for Burleson solar and Burleson wind, respectively, versus the peak day for each. These graphs demonstrate the effect of passing cloud cover on solar production and the volatility of wind output. These examples demonstrate some of the capability to graph and analyze production data with the Olameter tool, which proved to be useful in understanding the behavior of each of the systems in the Learning Laboratory.

Fig. 15. Burleson Solar Typical Day vs. Peak Day Production

Fig. 16. Burleson Wind Typical Day vs. Peak Day Production

For those installations that had not been in place for a full year, the production data was extrapolated to allow for an accurate comparison over that time frame. United was pleased to see that actual overall output was over 5% higher than what was projected using expected capacity factors and unit ratings. This was in spite of some of the system failures mentioned previously in this report. The cost of construction for the DG systems fell within the range of published costs (see Table II). Of note is the fact that the tracking solar systems (Cleburne 3 and Meridian) have a significantly higher capacity factor. Also, the higher tower height for the wind turbine at Burleson resulted in a slightly higher capacity factor when compared to the others.

TABLEN LEARNING LABORATORY SYSTEM PRODUCTION AND COST

Stephenville Solar 1 L8 19.4 7.82 4.92 Stephenville Solar 2 1.7 19.4 8.84 5.61 Granbury Wind 2A 6.6 12.52 8.52 Granbury Solar U 18.3 7.44 4.30 Cleburne Solar 1 L5 18.8 7.18 4.35 Cleburne Solar 2 1.4 20.8 12.81 8.24 Cleburne Solar 3 1.4 25.1 13.39 8.65 Cleburne Wind 1 3,5 7.0 6.58 4.46 Cleburne Wind 2 Z5 7.0 14.42 9.89 Meridian Solar 1.4 22.5 13.12 8.49 Possum Kingdom Solar L3 17.1 10.74 6.72 Burleson Solar 2.3 20.8 5.98 3.75 Burleson Wind 10.0 9.4 8.85 6.15

As for the financial analysis, there are numerous ways of determining the value of an investment option, but payback period seems like the simplest metric to use when discussing the value of DG with members and the public. United also felt that a simple payback analysis (dividing installed costs by annual energy production savings) was inadequate because of the many other factors that should be considered. For a more accurate and comprehensive analysis, several assumptions were made from the perspective of the average member that might invest in DG. First, it was assumed that the

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aforementioned Federal tax credit and United's DG creditswere available to offset the installation costs. Second, theanalysis assumed that money would be borrowed to fund theinstallation at 6% interest on a 30 year term, based on currentrates for home improvement loans. Third, the DG equipmentwas assumed to have a useful life of 30 years based onmanufacturer's estimates of 25 to 30 years. Fourth, inflationwas estimated at 2.5% per year based on historical averagesand current projections. Finally, maintenance was estimatedat 1% of installed cost per year. While some solarmanufacturers claim zero maintenance cost (other thanroutine washing of the panels), and wind turbinemanufacturers claim as high as 5% per year, United felt thiswas a reasonable amount that allows for the cost of a newpanel and inverter, or a single turbine or controller repairduring the life of the installation. With these fixedassumptions, the only economic variable was the future costof electricity throughout the investment period (United'scurrent electric rates were used for the baseline). Sensitivityanalysis showed that by far, future cost of electricity had thegreatest impact on payback period.

A. Solar Payback AnalysisFor the solar payback analysis, adjustments were made to theactual installation costs to reflect that the arrays mounted onconcrete piers would normally be roof mounted. Fig. 17compares the payback period for the various systems installedin the Learning Laboratory. Clearly, most of the systems do

residential consumer would need to install them. Clearly,these investments would not pay for themselves within theirexpected life unless the growth in electricity costs far exceeds8% per year (see Fig. 18). This is due first to the higher cost

Fig. 18. Payback Period for United Wind Installations

per watt of wind technology as compared to solar, andsecond, the lower capacity factors due to average windavailability in the area of installation at United. Wind speedinformation from local airports measured at 9 m (30 ft.)indicates that average wind speed in the Fort Worth area forthe past year was 3.9 mps (8.7 mph) [4]. Using the samefinancial analysis parameters, wind speed would need toaverage approximately 5.8 mps (13 mph) based onmanufacturer's literature for the Burleson wind turbine tohave a capacity factor sufficient to produce a payback of lessthan 30 years, even with 8% energy cost growth.

C. Cost ofLearning Laboratory Generation to UnitedAside from evaluating the costs and payback periods of

these systems for potential consumers, it is interesting toconsider what the equivalent cost of energy to United resultedfrom this project. For United's accounting purposes, thesesystems are depreciated over 16 years with 5% O&M peryear, with the resulting costs/kWh as shown in Table III. Thiscompares to the average cost of traditional energy in 2012 toUnited of $0.55/kWh.

TABLE illLEARNING LABORATORY COST OF GENERATION TO UNITED

Fig. 17. Payback Period for United Solar Installations

not pay for themselves within their expected life unless theoutlook for energy costs is a rise of at least 6% or more peryear. As would be expected, the roof mounted solar arrayshave a shorter payback period than the more expensivemonopole mounted arrays, even with the added trackingsystem.

B. Wind Payback AnalysisPayback analysis for the wind installations was

straightforward since they were installed the same way a

System Name

Stephenville Solar 1Stephenville Solar 2Granbury WindGranbury SolarCleburne Solar 1Cleburne Solar 2Cleburne Solar 3Cleburne Wind 1Cleburne Wind 2

Cost Cost w/USDA Grant($IkWh) ($IkWh)

0.69 0.590.75 0.652.51 2.170.93 0.800.92 0.790.90 0.770.77 0.671.09 0.942.18 1.88

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Meridian Solar 0.93 0.80 Possum Kingdom Solar 0.95 0.82 Burleson Solar 0.58 0.50 Burleson Wind 1.07 0.92 TOTAL Solar 0.79 0.69 TOTAL Wind 1.58 1.36 TOTAL 1.06 0.92

IV. CONCLUSIONS The Learning Laboratory has been a success based on the

initial goals of the project. United employees have gained invaluable experience with wind and solar technology, and are using that knowledge to assist cooperative members with their DG efforts. United's DG facilities have stimulated conversations with members and the public when they visit and witness firsthand what residential renewable energy looks like up close. The production and cost data that is being collected is shared on United's website, including a versatile tool that can graph the production data of all of the systems. And finally, through this project and United's other programs and initiatives, United has demonstrated its commitment to Energy Innovation.

Energy costs are rising. The latest projection for this region from ACES power marketers indicates that future market prices for energy will rise an average of about 9% per year through 2040 (based on forward pricing as of 12/3/2012). If this prediction holds true, and production costs of wind and solar technologies continue to decline, residential DG could be a worthwhile investment and a significant piece of the energy puzzle in the future.

REFERENCES

[1] M. Bolinger and R.Wiser, Understanding Trends in Wind Turbine Prices Over the Past Decade, Lawrence Berkeley National Laboratory, Berkeley, CA. Available: http://eetd.lbl.gov/ea/ems/reports/lbnl-5119e.pdf

[2] U.S. Energy Information Administration, Available: http://www.eia.gov/dnav/ng/hist/n3045tx3a.htmE.

[3] G. Barbóse, N. Darghouth, R... Wiser, and J. Seel, Tracking the Sun IV: An Historical Summary of the Installed Cost of Photovoltaics in the United States from 1998 to 2010, Lawrence Berkeley National Laboratory, Berkeley, CA. Available: http://eetd.lbl.gov/ea/emp/reports/lbnl-5047e.pdf

[4] National Weather Service Forecast Office, Available: http ://w w w. n ws. noaa.gov/climate/index.php ?wfo=fwd.

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