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Saft, Conergy and Tenesol Launch Li-ion Residential PV Energy Storage Project

Saft, Conergy and Tenesol have launched SOLION, a Franco-German project to develop an integrated energy storage system able to be produced on an industrial scale for decentralized on-grid, residential PV systems. This project will introduce large lithium-ion batteries into PV systems on the largest scale yet tested in Europe.

Example of residential PV system with energy storage. Click to enlarge.

Saft is responsible for the design and the manufacturing of the storage system. The storage function (battery) design will be based on Li-ion battery modules which will be connected in series to obtain the energy and voltage required by the application.

Each module will include an electronic board for data acquisition (voltage, temperature, ..) and cell balancing in order to optimize the battery life time and to allow charge/discharge control, state of charge measurement, etc.

This electronic board will be connected to the system management which will pilot the battery. The interfaces will be developed both with Tenesol and Conergy. Saft will deliver the batteries both to Conergy and to Tenesol, who will produce the other components and will assembly the SOLION product (battery + inverter + system management).

The role of energy storage in an on-grid application—such as that of a residence with solar panels connected to the grid—is to store excess PV energy until it is needed. Effectively, energy storage will ‘time-shift’ PV energy produced during the day, peaking at noon, to make it available on demand. This will both maximize local consumption and enhance the efficiency of the PV system. Surplus energy can also be fed back into the grid, for which the owner of the PV system would be remunerated at a higher tariff.

Energy storage will also increase security of supply while making individual consumers less dependant on the grid and help to boost the development of energy self-sufficient houses and buildings and contribute to the continuous growth of PV as part of the global energy mix, according to the partners.

The main benefit of on-grid energy storage for utilities is that it will reduce the peak load on their grid while at the same time making PV a source of predictable, dispatchable power that they can call on when needed. Reduced grid losses ie the energy lost by transporting power from a centralized generator to the point of use will result in some energy savings. Savings due to reduced consumption in PV powered households are anticipated to be 10 to 20%.

Seventy-five systems will be deployed—25 in Germany and 50 in France. These trials will validate the performance of the system, its economic viability, the added value of energy storage in an on-grid PV system and the benefits for stakeholders.

Conergy AG is a leading solar enterprise in Europe and with over 70,000 solar systems installed also a global market leader in the field of solar system integration. Tenesol, created in 1983 is one of the first PV system manufacturer and integrator in France. The company, today a joint-venture (50/50) of EDF and Total, is addressing markets worldwide mainly in grid connected applications but also for off-grid in developing countries regarding professional applications and rural electrification.

SOLION has been recognized by the Eureka/Eurogia and Tenerrdis programs, and is supported by the French Ministry of Economy Finance and Employment (DGE) and the German Ministry of Environment (BMU). A German utility (E-ON), three German research institutes (ISEA, ISET & ZSW) and one French research institute (INES-CEA) are associated with this project.


tom deplume

I have wondered for some time that someone living in an area with time of day variations in electricity prices could buy cheap energy overnight and sell it back to the utility for a profit at peak prices. A sort of house2grid form of V2G.


If you have PV system, you can do one of 3 things:

a: have so little that you just cover your base load, thus wasting nothing,
b: Sell the excess back to the utility (at what price ?)
c: Use a battery to keep it to yourself and smooth out the energy across the day.

a: is a half hearted solution,

b: is only viable if the grid pay you the retail rate for electricity (which they would be insane to do).

c: Is a more sensible approach - store it until U need it, with the option of selling excess back to the grid at peak times.

The trick is to stay on grid, but use your batteries to avoid wasting any power in normal day to day use. use the grid to handle your peaks or cloudy days/weeks, but unless you are trying to make a point, stay on grid.

I am not sure that you need Li batteries for that, you just have to look at charge/discharge efficiency and cycles vs cost.

This isn't an EV battery, it is a stationary one, and does not need to be light, it mainly needs to be cheap and high capacity.


This is a study program and makes NO sense.
If you have PV system in the US (e.g. Phoenix, AZ), you can do one of 3 things:

a: have so little PV that you cover only your minimum daytime base load, thus wasting nothing,
b: Have more PV capacity and sell the excess back to the utility at mid day –
c: Use a large PV array and large batteries to keep it to yourself and smooth out the energy across the day.

a: is a poor solution as cost of PV array to provide about 2kW (to carry ~ 20% of peak summer load) and waste almost none, costs about $25k of which you can scam ~ $12k rebate from the government.

b: is eminently viable because the grid must pay you the same hourly retail rate you pay. In PHX, pay $57k, get $25k rebate and pay back is not too bad - like 8 years as your electric bill will drop from about $500/m to $200/m. You sell the excess daytime energy to the grid at 4x the rate that you pay at night to buy it back.

c: Is non-starter, unless there is no grid (to provide a free battery) where you are.

If there were any kind of stationary battery that was remotely affordable and moderately durable for this application, (an application that needs HUGE HUGE capacity), they would probably be quite useful in a car. A little extra size and weight but costing only pennies per kWh would be a winner in a car
PV home power IS becoming affordable.
Batteries are very expensive for night power when a grid is near and is only doable if the house uses very, very little power BUT then, if that's the case, forget PV, just go on the grid and pay your $30 bucks a month.

Henry Gibson

It is unfortunate that the production of ZEBRA batteries is now in Switzerland instead of Germany. This is an ideal use for them; and they are far easier to build and use than LiIon batteries.

It is also unfortunate that Sodium Sulphur batteries are made in Japan. This is also their ideal use.

It would be a good use for American Firefly batteries as well.

EFFPOWER might want to make a higher capacity lower power design of its lead battery.

VRB builds a flow battery that is a lot easier to maintain and expand its capacity with larger tanks underneath the house or garden. Somebody in Japan also builds vanadium batteries. Perhaps a German company is still around.

If the cost of batteries is divided by the number of cycles and the energy delivered in each cycle, you will get a value that is the cost of the use of the battery. LiIon and other batteries multiply the power cost

The power companies can just forget the solar cells and use the batteries to store and retrieve power at will.

There is a large flow battery unit from VRB in the state of Utah in the US near the end of a transmission line.

Eventually, methane will be made at Nuclear reactors from collected CO2 and water to fill the empty gas pipes. Ethanol will also be made there for cars. France will ship ethanol and methane to Germany in pipes from its nuclear reactors.

A much better use of the batteries would be to pair them with cogeneration units. Honda, Enatec, Whispergen, LION and others make such units. If you have a natural gas pipe and a large battery you have no need for the grid except to sell power at subsidized rates. The use of the grid helps to hide the highly subsidized solar cell industry.

Cogeneration has much greater ability to reduce carbon fuel use and CO2 release than does solar. Every dwelling can now have a cogeneration unit and they should be required for every business and large dwelling or set of appartments.

A Honda unit can be used anywhere that there is a gas pipe. It is not too large for any building. Capstone turbines can be used for larger buildings. It may be cheaper to have multiple small units than much of a storage battery. A large low technology flywheel can provide power whilst the engine generators or turbines are turned on and off. Gas energy is cheaply stored by leaving it in the pipe or ground. The grid is only useful for hydro, nuclear or coal energy.

Except for subsidies, Solar cells are too expensive still for grid connected power systems. ..HG..


If ZEBRA batteries had a very long cycle life, then every house in the country would have one.

Buy electricity at night, or when the wind blows for 5 cents per kWh, then sell during the day for 10 cents per kWh.

The modest heat loss from the ZEBRA cells would also contribute to keeping the house warm.


It might be nice to have a battery system as a sort of surge smoother and UPS. When the power goes out, the net metered system has to "island" as a requirement. They do not want linemen fried. You could still power your house as if nothing happened with a well deigned system and switch back when the power came on again.

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