ᐅ 9.2 kW system – what size battery storage is recommended?

Mahri23 schrieb:

I have a 13 kWp system and a 7.5 kWh battery. It works great for me. From March onward, I will be almost completely self-sufficient. Choose the battery size based on your nightly consumption. The battery should cover your household’s night-time usage even in the summer months. Nothing more. It’s better to increase the solar array size so your system pays off faster. Having a larger battery doesn’t help you much in summer 😉 and then it becomes too expensive in proportion.

Thanks for the assessment. That sounds reasonable. The problem is that I currently have no idea what range my night-time consumption will settle into 🙂. But I’ll try to estimate it.

Edit: I would say or estimate we’re probably around 7.65 kWh at night (6:00 pm - 6:00 am). Then a 6 kWh battery would probably be more suitable.

In my opinion, reaching 200 cycles with a heat pump and an electric car is very optimistic. Of course, if you charge the electric car from the storage battery (which makes absolutely no sense), it is achievable.

Your calculation also misses the feed-in tariff you lose, 3-4 cents in taxes, and then an additional 20% storage losses on everything.

But if you are aware that it’s not cost-effective and doesn’t really benefit the environment, I have no objection to you buying a storage battery. I would like to have one too... ;-)

Regarding the size: To achieve many cycles, two things need to come together. A consumption pattern that, as @Mahri23 already mentioned, empties the storage in summer AND a reasonable ratio of system size to storage capacity to fill it as often as possible during the year. The recommended minimum ratio is 2:1. Better is 3:1.

So, if you do not plan to increase your generator capacity, which I highly recommend based on your profile, a storage size of around 5 kW would be reasonable. With some effort and a bit of luck, you can break even over the lifetime.

Backup power is a completely different topic with many variables.

DASI90 schrieb:

as well as the wall box for the electric car.

You don’t need a battery for that – an 80 kWh car battery and a home battery under 10 kW don’t really match. Let the photovoltaic system charge the car fully on sunny days, that makes sense.

DASI90 schrieb:

Edit: I would estimate that we probably use around 7.65 kWh overnight (6:00 PM – 6:00 AM). Then a 6 kWh battery would probably be more suitable.

Wow, what do you need that much electricity for? And how do you recharge the battery in winter?

Benutzer200 schrieb:

You don’t need a storage system for that – an 80 kWh car battery and a home battery under 10 kW don’t match. Let the photovoltaic system fully charge the car on sunny days; that makes sense.

Wow, what do you need that much electricity for? And how do you recharge the storage in winter?

The latter was a quick estimate based on the annual consumption and the information from the grid stating that about 43% is needed during that time. Yes, exactly—the winter and the large battery were my initial concerns as well.

In winter (Nov-Dec-Jan), the small battery is usually empty. The heat pump runs continuously, you want to use hot water and wash dishes or clothes during the day, and if you add the electric car, there’s often nothing left.
I have almost 30 kWp on the roof, and only very rarely is there any surplus for the car. (On average, over those three months, I was able to charge the electric car with 3 out of 27 kWh generated per day. And it was almost daily connected to electricity from 2 p.m.)
From February onward, the situation improves again. Then the yield is usually enough to cover the demand of about 20 km/day.

In short: nothing beats large, fully utilized roofs. I’m currently planning to equip the south-facing facade and the garage with 20-25 kWp.

Deliverer schrieb:

...I have just under 30 kWp on the roof, and there is really only rarely any surplus left for the car. (On average over three months, I was able to charge the EV with 3 out of 27 kWh generated per day. And it was almost daily connected to power from 2 pm onwards)
From February, this will improve again. The output will then fully cover the demand of about 20 km/day.
In short: nothing beats large, fully utilized roofs. I am currently planning to equip the south facade and the garage with 20-25 kWp.

Correct, no matter what others say. Currently, it is safe to install up to around 35 kWp on the roof if possible. If desired, a small battery of about 6 kWh can be added for nighttime electricity needs. This may, with some luck, just break even financially (assuming the battery was not purchased at the currently excessively high prices). All of this should be connected to a large hybrid inverter and limited to 29.99 kWp due to the 70% rule.

I would give anything for a roof like that that would make this possible 😳