ᐅ Which energy storage system is best suited for use with a solar power system?

Hello!
What recommendations and arguments do you have for which storage system to use in combination with a solar power system?
We have been offered:
- Solarwatt MyReserve with 2, 3, or 4 battery modules (equivalent to 4.8, 7.2, or 9.6 kWh)
- BYD-Box HV 5.1, 7.7, or 10.2 from the brand Kostal.

The solar system is designed for 9.9 kWp. We are often at home during the day, almost always in the afternoons, so I think we may not need the largest battery. But comments on this are also welcome!

Thank you for your feedback.

What kind of funding are you receiving/applying for the storage system?

I have learned by now that every system (whether photovoltaic or battery storage) is too small when you need it and too big when you don’t. Of course, this applies only to self-consumption.

We have a system with 8.68 kWp and a 6.4 kWh (BYD HV) battery. After 4.5 months, the household consumption is as follows: 65% from photovoltaics, 30% from the battery, and 5% from the grid. These are the very favorable months without heating. But the above statement also holds true for the less favorable months.

If you manage household consumption with care and don’t let your partner bake whenever she feels like it, you start the next charging cycle with a battery state of charge of 20-30%. Just to put things into perspective.

Example: On a Sunday, the battery is full at around 9:30 AM because of sufficient sunlight. From then on, excess energy is fed into the grid. At 3:30 PM, my wife wants to cook and bake. Two ovens, one stove, and the washing machine are running, consuming 7.3 kWh. Since it is cloudy by then, only 1.3 kWh comes from the photovoltaic system. This emptied the battery in just under an hour. At 4:30 PM, it’s still cloudy, and only 2 kWh is coming from photovoltaics. Base loads continue consuming 600 watts, and the battery does not recharge until the evening. With evening TV and base loads, energy is drawn from the grid starting at 2 AM.

And this is midsummer. In winter, when photovoltaics stop producing around 3 PM due to dusk, even the largest system with battery storage is ineffective—especially if the heat pump starts with a 7 kW draw.

So, size your battery only big enough to get you through the night for the next 10 years, from daylight saving time change to daylight saving time change (i.e., spring to autumn). Modular systems like BYD don’t help much either, because you can only add capacity within one year due to cell drift.

Storage is just burning money

Zaba12 schrieb:

I have learned by now that any system (photovoltaic or battery storage) is too small when you need it and too big when you don’t—at least when it comes to self-consumption.

We have an 8.68kWp (kilowatt-peak) system with a 6.4kWh (kilowatt-hour) battery storage (BYD HV). After 4.5 months, the household consumption looks like this: 65% from solar, 30% from the battery, and 5% from the grid. These are the very good months without heating. But the above statement also holds true for the bad months, of course.

If you manage household consumption sensibly and your wife doesn’t bake whenever she feels like it, you start the next charging cycle with a battery level of 20-30%. Just for context.

Example: On Sunday around 9:30 a.m., the battery is full because there is enough sunlight. From then on, excess power is fed into the grid. At 3:30 p.m., my wife wants to cook and bake. Two ovens, one stove, and the washing machine are running. That consumes 7.3kWh (kilowatt-hours). Since it’s cloudy by then, only 1.3kWh comes from the solar panels. As a result, the battery is empty after just under an hour. At 4:30 p.m., it’s still cloudy. The solar system produces only 2kWh (kilowatt-hours). Base loads continue to run at 600 watts, and the battery is not fully charged until the evening. With evening TV and base loads, electricity is drawn from the grid starting at 2 a.m.

And this is during midsummer. In winter, when the solar system generates nothing from 3 p.m. on because it’s getting dark, even the largest system with storage won’t help—as long as the heat pump is kicking in with 7kWh (kilowatt-hours).

So size the battery only large enough to get through the night for the next 10 years—from one time change to the next (spring to autumn). Modular systems like BYD’s aren’t helpful either, because you can only add capacity within one year due to cell drift.

Thanks for the report. Have you ever calculated when the whole system pays off? This is a genuine question, not provocative, since our solar installer also offered us a BYD battery.

What exactly is cell drift?

OWLer schrieb:

when it pays off

Never. This is serious and not meant to provoke. These things are simply still too expensive. And self-consumption is also not free. You cover that cost through your profit and loss statement.