Help with photovoltaic decision

Bidirectional charging has become quite user-friendly by now. There are plenty of wall boxes that can do it, and with all common e-cars. The problem is more with the warranty. Who pays if the battery is dead after 4 years, its cycles are actually used up, but the time period hasn't yet expired? This whole thing needs to be negotiated with the car manufacturers. Otherwise, you have great solutions, but no one wants to use them before the warranty expires, and actually not after either, because then the battery and thus the car lose value faster.

For my part, I would rather rely on "Saisonspeicher". Some companies already offer this, but it is still too expensive. Effectively, these are decommissioned car batteries that you can attach to the house wall and then fill nicely up until autumn and then draw from them over the winter. This requires a very good battery management. It must recognize that good weather is coming in the next few days, so the heat pump is allowed to draw power in the evenings. Otherwise, it hangs on the grid and the battery is spared for standby operation, etc., so that it lasts as long as possible over the winter and is only really finally empty shortly before the end.

Hi,

does anyone seriously plan or rather believe something like that?

Effectively, these are decommissioned car batteries that you can stick to the house wall and then fill nicely until autumn and then draw on them over the winter.

To really implement it like that "fill nicely until autumn and then draw on it over the winter," we are certainly talking about 1000-2000 kWh that such a battery would have to store. So roughly 20-40 car batteries weighing 300-500 kg each. Together with the necessary control and energy management systems, that would probably be several 20-foot containers. You really need a big house wall to "stick them on."
And all that magic for exactly one charging cycle per winter? ;-) Sorry, but that would be completely crazy!

Used car batteries as decentralized large-scale storage in the grid, yes! But for private users?!?

You can't fool physics, complete self-sufficiency doesn't work in this latitude, no matter what some fantasist pins on their PowerPoint slides.

Seriously:

The idea of using old car batteries as stationary storage has been around forever. Are such systems even available for private users? Somehow I can't imagine a use case for that.
Such storage would have to come from an old car – I definitely don't want a LiOn battery from a crashed car. So you imagine 6-10 year old cells, whose cell chemistry is only designed for 10-15 years. That means I will have to deal with failures almost from the start. And if you "refurbish" the cells first (however that is supposed to work), I might as well just take new ones.

Fun fact – Tesla also relies on lithium iron phosphate battery cells (LiFePO4) for the new generation of its Powerwall, not the previously used cells like in their cars. Even though I wouldn’t touch products from this company with a ten-foot pole anymore – they are technically competent on this topic and know what they are doing – so there must be good reasons why they themselves are moving away from this idea.

Best regards,

Andreas

Hi, is anyone seriously planning or better yet believing something like this? To actually implement it like that "nice and full until autumn and then throughout the winter" we are certainly talking about 1000-2000 kWh that such a battery would have to store. So roughly 20-40 car batteries each weighing 300-500 kg. Together with the necessary control and energy management systems, that would be several 20-foot containers. You really need a large wall to "stick them on." And all that magic for exactly one charging cycle per winter? ;-) Sorry, but that would be completely crazy! Combined car batteries as decentralized large storage in the grid, yes! But for private users?!? You can't fool physics, completely self-sufficient is not possible in these latitudes, no matter what some fantasist pins on their PowerPoint slides. Seriously: The idea of using old car batteries as stationary storage has been around forever. Are there already such systems for private users to buy? Somehow I can't imagine a use case. Such a storage would have to come from an old car - I certainly don't want a LiOn battery from an accident car. So you end up with 6-10-year-old cells which are designed by cell chemistry for only 10-15 years. That means you'll have to deal with failures from almost the start. And if you "refurbish" the cells (however that should work) you might as well just take new ones. Fun fact - Tesla also uses lithium iron phosphate battery cells (LiFePO4) for the new generation of its Powerwall and no longer the previously used cells like in their cars. Even if I wouldn’t touch products from this company with a pair of pliers anymore - they are technically competent on this topic and know what they are doing - so there will be good reasons why they themselves turn away from this idea. Best regards, Andreas

Yes, in fact there are already some companies. In Norway, this seems to be quite well used. Friends of ours have a holiday home there and report that they increasingly see a large battery on the walls. That is roughly, according to the rule of thumb, 100 kWh on the wall. Good cells from various batteries are then cobbled together. Hence probably the proud price. There is a lot of manual labor involved. You also won't get through the winter with one charge. The goal is rather to cover the basic demand of the house (without major consumers like heat pump or electric car or stove) as far as possible during the winter. If plenty of sun is forecast in the next days, the systems calculate how much power can be expected and then supply it to the major consumers. How reliably that works, I can’t say. I only know the vision and can very well imagine it.

The question is whether these are actually old car batteries or whether they are off-grid systems from remote houses that get through the winter with a lot of photovoltaics, large batteries, and fireplaces. Alternatively, they have had flexible prices like Tibber for some time and then charge when wind power floods the European market and thus drives prices down.

That's roughly about 100kWh at the wall.

You can also buy large storage units from us. 100kWh for small businesses (also usable privately) costs around +/- €10,000. The models specifically designed for private users, ranging from 40-50 kWh, start at about €7,000. Issues, of course, include space, weight, and cooling.

I only know the vision and can easily imagine it.

You are mixing up buffer storage and seasonal storage. Batteries are unsuitable for the latter. The fact that the legend "You get your own electricity in winter" is used from a marketing perspective is a different matter. This very simple idea is just too simplistic.