Residential Energy Storage

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Residential

Energy

Storage

in FranceEnergeia Internship Research

Quentin Perrier



Introduction

After a short stagnation in 2009 due to the economic crisis, global investment in renewable energies

took off again, jumping by 32% in 2010, to a record $211 billion.1 And this momentum is very likely to

increase. The first reason is the necessity to deal with climate change: according to the AIE,

renewable energies are expected to be the second greatest contribution for CO2 emissions reductionby 2035, energy efficiency being the first.2

The second reason is the increasing profitability of renewable technologies. Costs are quickly

reducing thanks to current research3, whereas fossil fuel reserves depletion drives prices on a long-

term upward trend. Therefore, it is only a matter of time before wind and solar energies become

economically competitive all over the world – it is already the case for solar power in a number of

sunny countries.

One challenge is particularly well-known to renewable energy proponents: the intermittence of this

resource. Much of the potential for generated power does not coincide with demand. Therefore,

finding new solutions to store energy becomes essential. By storing the power produced from

renewable sources off-peak and releasing it during on-peak periods, energy storage can transformthis low-value, unscheduled power into schedulable, high-value products.

With a share of 38% in final energy consumption in France4, and a prevailing role in the daily and

seasonal peak periods, residential consumption will be the focus for technological innovations and

political decisions.

What are the main technologies for residential energy storage? What are the markets and policies

outlooks? These are the questions this paper will address.

Residential energy storage is not a new idea: hot water has been stored in water tanks for a longtime now, using either conventional electricity during off-peak low-price periods or solar thermal

energy.

However, the deployment of renewables at the individual level, mainly through photovoltaic, will

highly depend on the efficiency of electrical batteries. Only those batteries will make photovoltaic

power affordable. We will first focus on this crucial technology and see the original path that has

been taken in France.

Another technology whose development is ramping up is hydrogen power. Its potential applications

are well-known for cars, but residential storage is also an important market for this technology, as

we will see.

Although less famous, other innovations are also emerging. As heat and cooling is the main source of

residential consumption, R&D has focused on different ways to reduce it, and has come up withinteresting technologies. One of the most mature of them is based on phase-change materials, which

we will examine in the third and final part.

1United Nations Environment Program, Global Trends in renewable energy investment 2011

2AIE, World Energy Outlook 2010

3

According to Bloomberg New Energy Finance estimates, the price of PV modules per MW has fallen by 60%since the summer of 2008, and Wind turbine prices have fallen by 18% per MW in the last two years 4

French Ministry of sustainable development statistics



Contents

Introduction ............................................................................................................................................. 1

Batteries .................................................................................................................................................. 3

French Market for batteries ................................................................................................................ 3

Review of the different technologies .................................................................................................. 4

General presentation of a battery ................................................................................................... 4

Key technologies.............................................................................................................................. 5

Market trend in France........................................................................................................................ 5

The Sol-ion Project .......................................................................................................................... 6

Autolib’ ............................................................................................................................................ 6

Hydrogen ................................................................................................................................................. 7

Presentation of the technology ........................................................................................................... 7

Market developments ......................................................................................................................... 8

Phase-change materials .......................................................................................................................... 9

Introduction ......................................................................................................................................... 9

Review of the different technologies .................................................................................................. 9

Current applications .......................................................................................................................... 10

Passive MCPs systems ................................................................................................................... 10

Active MCPs systems ..................................................................................................................... 10

Conclusion ............................................................................................................................................. 11



Batteries

Following the protocol of Kyoto and the European Commission Energy and Climate package, the

French government has decided to take a further step toward renewable power, setting targets of

1100 MW of PV installed by 2012 and 5400 MW by 2020. A fixed feed-in tariff of 58c€ per kW is

guaranteed for a period of 20 years to encourage long-term investments in the residential sector.

Although solar PV fits demand better than wind energy, energy storage remains a crucial stake for its

competitiveness. The advantages for French users to store PV power would be threefold. First, the

power generated in excess of demand during the day can be stored instead of being lost. Then, this

electricity can be used whenever needed by the consumer, for free. Finally, it can be sold to the

network during peak hours. This last option is the perfect illustration of a win-win situation: the

consumer can earn money selling its power at high price, and the manager of the grid is saving

expensive and polluting fast-responding extra capacity.

A raging competition has started in France and all over the world. Each firm is trying to impose its

technology and win the market by being the first to deliver batteries that are safe, affordable,efficient, and with short energy payback times.

French Market for batteries

The market for batteries is closely related to the market for PV. As more information is available for

the latter, we will base our market study on it.

More than 10,000 households are using PV power in France. 7 000 of them do not have access to the

grid and rely exclusively on this source. The 3,000 remainders are connected to the grid and able to

sell their production to EDF.

Historically, the French market for PV was designed for off the grid sites. Thus, those sites still

represent a high share of PV in France, but the expansion of grid connected sites is ten times higher

in terms of financial investments and, in 2005, they overtook isolated sites in terms of capacity for

the first time. 5

Figure 4: Photovoltaic capacity installed in France by type of application

5Source: ADEME



Source: ADEME

On-grid PV is quickly taking off in France, but the increase is still very low in terms of capacity

compared to other European countries. In 2008, the 44,5MWp installed in Spain were 60 times

higher than in France.6

Half of the capacity financed till now has been installed in DOM-TOM. This was due to the strong tax

exemption incentives and a feed-in tariff twice as high as in France.

Because of different climates between the North of France, the South and the DOM-TOM, PV solar

energy will need to fulfill different applications. Those different uses of PV energy segment the

markets for PV solar panels and therefore batteries. Solar radiations vary from 6kWh/m²/day in the

overseas territories to 5kWh/m²/day in the South to 3kWh/m²/day in the North.7

Since studies show that 1kW of residential PV power require 1 to 2 kWh of battery8, the market for

batteries in France will be segmented between products of capacity in the range of 3Wh to 10kWh.

(Depending on whether the site is on-grid or off the grid, the capacity of the battery might have to be

adjusted).

The outlook of the French government is a quick increase in on-grid application, facilitated by a dropin production prices and feed-in tariffs. The objective of a 5,4GW installed capacity in 2020 is creating

a strong demand, for which several technologies coexist.

Let’s now examine what are the technologies available to supply this growing demand for batteries.

Review of the different technologies

General presentation of a battery

The basic block of a PV system is called the cell. It is a semiconductor device that uses the energy of

solar photons to put electrons in movement, therefore converting solar energy in direct current (DC).

Cells are grouped together to form modules, whose power typically vary from 50 to 200 W. Those

modules can then be combined to match the need. Modules can be connected in series to raise the

total voltage (see figure 2) and/or in parallel to yield a higher current (see figure 3) .

Figure 1 : Modules in serie

Based on those general principles, various technologies currently coexist, though at different levels

of maturity. Let us now now compare them in details.

6In 2008, Spain installed 2,671MWp and Germany 1,505MWp, whereas France only installed 44,5MWp.

Source: Europe’s Energy Portal 7Source: European Atlas of solar radiations

8Michael Lippert, conference at the German ambassy, 04/14/2011

Figure 3 : Modules in parallel



Key technologies

The main technologies are lead-acid, lithium ion and flow batteries.

Battery technology Advantages DrawbacksLead-acid Low cost

High currents

Low energy-to-weight and power-

to-weight ratios

Flow batteries Flexible layout

Long cycle life

Complicated to produce

Low energy density

Lithium-ion High energy density

No memory effect

Slow discharge when not used

Risk of explosion – protection

system needed

Lithium ion polymer Can take various shape

Low weight

Safer than Li-ion

Lower energy density than Li-ion

More expensive than Li-ion

Risk of inflammation

Less life cyclesLithium metal polymer No memory effect

Entirely solid, no explosion risk

Low self-discharge

No major pollutant

Need a high temperature to work

(85°C)

Lead-acid batteries are the oldest type of rechargeable batteries. They are able to supply high

currents and a low cost. Therefore, they are widely used in motor vehicles to provide the current

required by starter motors. Theirs drawbacks are low energy-to-weight and energy-to-volume ratios

compared to the newer technologies.

Flow batteries have the advantage of a flexible layout, long cycle life and no harmful emissions. Some

types also offer easy maintenance and tolerance to overcharge/discharge. Nevertheless, their

production is rather complicated as they require pumps, sensors and controls units. In addition, their

energy density is rather low compared to lithium-ion batteries.

Lithium-ion batteries (LIB) use the most recent technology. They have one of the best energy

densities, no memory effect (loss of capacity after several discharges at the same level), and a slow

loss of charge when not in use. Therefore, they are perfectly designed for portable electronics. They

are also used in military vehicles and aerospace. LIBs are among the strongest candidates for electric

vehicles batteries.

There are numerous types of Lithium batteries, but the two mains types are lithium polymere

batteries and lithium ion batteries. In France, a great stress has been put on Lithium Metal Polymere

(LMP) and Lithium-ion, as we will see with the Autolib’ project.

Market trend in France

As it is only a matter of time before technologies for residential batteries become mature and

competitive, a race has started to be the first to deliver it.



In France, two main fields of experiments have been undertaken: the Sol-ion project by Saft and the

launch of Autolib’ by the group Bolloré.

The Sol-ion Project

Saft, the world specialist in the design and manufacture of batteries for industry, has engaged with

Voltwerk, Tenesol and others in an EU-backed project called Sol-ion. This project aims at assessingthe performance and the economic viability of the PV technology, including solar panels, batteries

and grid management.

The development phase has already been carried out with the creation of an integrated energy

conversion and storage kit. The project is now into its field phase, with 75 Sol-ion energy kits

deployed in France and Germany. This is the largest scale ever tested in Europe for a PV system.

The battery technology used by Saft is Li-ion. The Sol-ion kit has a battery rated from 5 to 15 kWh, a

nominal voltage of 170v to 350v, and an energy production of 5kWp. The battery life expectancy is

20 years.

The battery is designed to cover 60% to 70% of a household needs. The project aims at proving that

PV can achieve a 50% bill reduction, while reducing the average cost of the kWh of 10%.

Autolib’

The 2 of December 2011, the group Bolloré launched Autolib’, a car sharing program in Paris. The

scheme is the same as Velib’, a cycle sharing system launched in 2007 in Paris. The eponym PDF, Mr

Bolloré, plans to make around 3,000 small electric cars available for use by the general public, based

around 1,120 citywide parking and charging stations by late 2012.

This system is a wide field test for the battery chosen by the Bolloré group. The chosen car, calledBluecar, is produced by the company Batscap, a branch of the Bolloré group. The group has heavily

invested in this project: 1.5 billion for designing the car and the battery, plus a hundred millions per

year to run the project. This service is not expected to be profitable before 8 years.

Such an investment was made because what is at stake is much more important than just Autolib’.

Autolib’ is used as a field test and a demonstration to prove the efficiency the Bolloré batteries,

which could afterward in both electrical vehicles and residential houses. The Bolloré group has

already indicated that its factory is producing batteries for both.

Assessing than the Lithium-ion technology chose by all its rivals was warming to fast, Bolloré alone

opted for the Lithium Metal Polymer (LMP) batteries. Autolib’ is the necessary test to prove the

accuracy of his bet.

This project was highly estimated by Paris town council, which considered it as “the most promising

option” compared to the offers made by Veolia and SNCF-RATP. However, the project is too recent to

allow a sound and comprehensive feed-back. But the verdict will come very soon.



Hydrogen

Another technology that is ramping up thanks to the car industry is hydrogen. A recent report from

the Pike Research institute reveals that commercialization of fuel cell vehicles will accelerate in 2015

and grow to reach $16.9 billion in annual revenue by 2020.9

Although it is less famous, the application of hydrogen for residential storage is also going through

fast developments. And the possibilities and business project for this use lay be equally as important

as cars’ if the combination of solar and wind power-hydrogen generation and storage –fuel cell

systems proves successful.10

Presentation of the technology

Hydrogen can be used as a fuel to produce power if used in special cells. The most common way to

produce hydrogen is to use natural gas, and to a growing but lesser extend biogas.

Another way to produce it is to electrolyze water. Electrolyze uses the simple reaction:

2 H2O → 2H2 + O2

And the opposite reaction is used to produce electricity. As we can see, this method relies on a cheap

and available raw material: water. However, it has two main drawbacks.

The first is the amount of power need for the reaction. Electrolyze requires a lot of power, hence

being more costly than the others ways of H2 production. However, using electrolyze may prove

competitive if combined with intermittent renewable sources, by storing off-peak low-value power

and releasing during peak periods. This technology also has the advantage of being totally carbon

free. In addition to the environmental benefits, it could become more and more competitive has CO2

taxation might be adopted in Europe.

The second difficulty comes from the fact that H2 cannot be found in nature. It is not stable in normal

pressure and temperature conditions. Therefore, H2 is generally stored in high pressure or extremely

low temperatures, which raises the question of energy security in individual homes.

Hopefully, new solutions are developed. For example, McPhy Energy has found a way to store

hydrogen in its solid form, building a storing system which is estimated as “safe” and with “a high

yield”.11

Currently, most hydrogen storage applications are used for a group of houses rather than individualhouses. However, applications for individual homes are expected to emerge. Storing hydrogen is an

excellent complement for residential electrical batteries. Batteries could be used for daily use,

whereas hydrogen could be store in winter, when solar radiations are lower.

Additionally, producing hydrogen at home could be used in the future to refuel private hydrogen fuel

cell cars.

9Pike Research, Fuel Cell Vehicle Market to Reach $16.9 Billion by 2020, October 7, 2011

10

Cleantechnica, Hydrogen Storage-Fuel Cell System to Smooth Out Intermittent Wind Power in Germany

11Enerzine, De l'Hydrogène solide pour stocker l'énergie renouvelable



Market developments

In Europe, the leader country for hydrogen is Germany. Not only has Germany the highest

deployment of intermittent renewables in Europe, but they also suddenly decided, on May 30, 2011,

as a consequence of Fukushima, to ditch nuclear power by 2022 – although the nuclear share total

domestic power generation was 23.5%.12

Therefore, developing new technologies to store energy is

even more vital for their power security.

The technology is starting to be already be deployed in the German city of Herten. Ontario’s

Hydrogenics has won the contract on the 12 of October 2011. If this field test proves satisfactory,

many others cities might adopt it.

In France, storing hydrogen is still in development phase. The 26 of January 2011, a program has

been launch by the National Agency for Research, called “Renewable production and Power

management” (PROGELEC), to ramp up French research on the integration of renewable energies

and a better power management.

12CIA World Factbook



Phase-change materials

Introduction

60% of existing buildings were built before 1974, date of the first regulatory rules. Their average

energy consumption is 350kWh/m²/year. The new regulatory rules, published the 26 of October

2010, aim at curbing new buildings consumption to an average maximum of 50kWh/m²/year by

January 1, 2013. Those policies have created strong incentives for R&D in order to improve buildings

thermal isolation. And one of the most promising fields is based on phase-change materials.

Phase-change materials (PCM) interest is based on the physical ability of certain bodies to absorb a

large amount of heat during a change of phase, without a change of temperature. Phase-change

materials are already used in several fields: cooling of fragile products, permanent memory systems

in computing, textile industry. And their use is now taking off in building construction.

Using PCM for buildings is not a new idea, but technical difficulties, like the inflammability of the

products, have delayed their application till now. A new technology using micro-encapsulation hasovercome the obstacles and let to a renewed interest for a residential use of PCM since the

beginning of the century.13

Review of the different technologies

PCMs can broadly be arranged into three categories: eutectics, salt hydrates, and organic materials.

PCMs technologies Advantages Drawbacks

Eutectics Fixed phase change

temperature

High volumetric latent heat

Small quantity of data on

physical properties

Organic PCMs Wide range of fusion

temperatures

Highly compatible

Flammable

Smaller conductivity

Smaller latent heat

Inorganics PCMs Available

Affordable

Corrosive

Eutectics are solutions of mixed salts. They have two advantages: they have a fixed phase change

temperature and volumetric latent heat slightly above organic compounds. Drawbacks are the small

quantity of data available concerning their physical properties and they are not widely used in the

industry.

Organic PCMs fusion temperature ranges from 0°C to 150°C. They include paraffins, waxes, oils, fatty

acids and polyglycols. Their disadvantages are a smaller conductivity, a small latent heat, and their

high inflammability. However, they are available on a wide range of temperatures and are

compatible with conventional construction materials.

Inorganic PCMs like water, salt solutions, have the advantage of being available, affordable and

flammable. Nevertheless, they tend to damage conventional construction material, therefore

needing special technologies to be used, like nucleation.

13Rieder and Catarina, 2007



Current applications

MCPs are used for their ability three application: keeping heat, keeping cold, and storing heat. For

residential houses, they can improve isolation, passive cooling or heat storage.14 PCMs can be used

either in a passive or active way.

Passive MCPs systems

Passive PCMs systems simply store energy when temperature is above their melting point

temperature, and release it when temperature.

The first residential application for passive MCPs is building isolation. During summer, MCPs

encapsulated in walls can absorb heat during the day and release it during the night. The advantage

is twofold. During the day, PCMs have a cooling effect of 3 to 5°C – reducing cooling power bill up to

30%. During the night, they release the heat, providing a constant temperature. As MCPs can be

installed in new and renovated buildings, the market is sizeable.

With 26 million individual homes, 8.2 group housing, and an average 417,000 buildings renovatedeach year15, the market for buildings material PCMs is sizable.

The second application is heat storage. MCPs can be used in water tanks to improve their efficiency.

As water tanks have an average life cycle of 10 years, the market can be evaluated to 3.4 million

water tanks each year.

In France, a few products are already available on the market: Micronal (paraffine in polymer

microcapsules), BASF, or Energain from the company DuPont. But those are only a small part of all

the applications under study. Many more applications should appear in the coming years. The

development of PCMs is expected to be very fast, as they are not only ecological, but also

economical.

Active MCPs systems

In active MCPs systems, a fluid circulates thanks to a mechanical system. This controlled system

enables to store and release heat on demand rather than in a passive way.

For cooling purpose during hot days, the “hot” air of the house is pumped. It is put in contact with

PCMs which absorb the heat. Then the cool air is re-injected in the house. During the night, the pump

is activated to bring the outside fresh air in the system to release the heat accumulated in PCMs.

For heating during cold nights, the idea is quite similar: during the day, heat (from a heating systemlike solar thermal) is accumulated in PCMs. During the night, the fresh air of the house circulates

through the system, absorbs its heat, and is then released in the building.

As we can see, those are active on-grid system. In cooling system, PCMs enables to uses affordable

off-peak electricity (to activate the pump during the night to reset PCMs) for heating purpose during

peak periods. In heating system, they enable to store the unscheduled heat produced and use it on

demand. Those systems are still at field experiment stage. But, like passive PCMs systems, they have

a promising market ahead of them (see passive PCMs systems).

14Europe Network Company, Matériaux à changements de phase, September 2008

15Source : INSEE



Conclusion

The well-known renewable intermittence is not an overwhelming challenge any more, with the

development of smart grid and energy intelligent houses. For the latter, electrical batteries and

phase-change materials are mature technologies that will be deployed in the coming years, and the

hydrogen technology should quickly follow.

In concrete terms, two main changes drive the development of residential energy storage in France.

The first is the adoption of new regulatory rules by the French government , called “Grenelle de

l’environnement”, which set ambitious goals for lowering houses consumption. The second is the

coming apparition environment friendly cars, with either electrical batteries or hydrogen fuel cells.

Although not at the cutting edge in renewable energies, France is lucky enough to have a leader

amongst its neighbor countries: Germany. With a common project called Sol-ion, France made one

step further towards catching up and becoming of the leader in photovoltaic energy and electrical

storage.

France is also trying to develop a unique technology for electrical batteries, thanks to the will of the

Bolloré group PDG. Autolib’ is a large field experiment for his LMP batteries, and its success could

accelerate the growth of the markets for both electrical cars and residential batteries.

Another promising technology, hydrogen storage, is not yet mature in France. No large field

experiment has been run yet, whereas in Germany a city has already signed for it. Thus, the market

in France might ramp up with German technology. As this technology might be a great complement

for electrical batteries and hydrogen cars, it is also expected to expand very fast as soon as the

technology is ready.

The last mature technology is phase change materials. Not only can they improve isolation, thus

reducing power consumption and the electrical bill; but they can also be used on-grid for cooling or

heating on demand, which gives more flexibility to grid operators.

Obviously, this paper has not examined in details all the technologies available for residential energy

storage, but tried to focus on the newest and most promising solutions.

Some others technologies exist, although they are still at an early stage. Experiments are made to

mechanically store energy in rotational energy, using flywheels with rotors suspended by magneticbearings. Other researchers try to find innovative solution to store energy by pressuring air. Maybe

those technologies will emerge in the future, but they will stay extremely marginal in the short and

mid-term.

Others storage techniques have long existed, mostly hot water storage in water tanks, and biofuels

storage, like wood, for heating purpose. Storing residential energy is not a new idea, but it is an idea

whose concrete applications must urgently improve to improve energy security and curb global

temperature rise.

Residential Energy Storage

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