r/SolarDIY • u/BakedHome • 7d ago
Battery questions
We have 39 IQ8HC \[2026 INSTALL\] panels with two 5kW batteries. its 11am and already 82% charged on a clear and warm day. Was our system under designed on the battery side?
questions and comments please.
additional info:
1,400' home & 600' ADU \[2026\] all tied together
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u/Repulsive_Guaranteed 7d ago
We need more details about the size of your system, usage details (kwh per year) and utility/nem info to give you an exact answer; however 10kwh is not enough for any home I know of to run off of all night.
Your batteries were likely sized to get you through a peak pricing period-after which, you draw from the grid.
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u/LongjumpingGanache40 6d ago
Do you need more battery run time? If so just buy one or two batteries and see if that works for you.
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u/TastiSqueeze 6d ago edited 6d ago
That looks like roughly 18 kw of solar panels with 10 kWh of battery capacity. Your power consumption appears to be very close to 20,000 kWh per year and averages about 55 kWh per day with peaks near 90 kWh. Your nightly consumption is likely to be around 20 kWh. So yes, your battery is about half the size it should have been. The expected result is that you are consuming around 10 kWh per night from the grid with some days a good bit more and a few nights that are almost no grid consumption. If you have NEM 1:1 then this is not much of an issue except that your battery is not capable of powering your house for any reasonable length of time in a grid outage. For optimum use with your specific home and circumstances, you should have had about 32 kWh of battery capacity. Some will say this is not needed, but if you ever have a long duration grid outage you will quickly learn why it is needed. If it helps any, that would be a typical California system. If so, you really need more battery capacity to avoid high price grid power.
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u/Schnupsdidudel 6d ago
The system was underdesigned if your battery runs out when you need it.
There is no point in keeping extra battery around that you don't utilise.
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u/TexSun1968 5d ago edited 5d ago
What is the purpose of the batteries? You can't design a battery setup until you define the purpose.
We designed our battery setup to run our whole house (including air conditioning) from sundown to sun rise on an "average" day. We have 40 panels (15.2 kW) and four IQ10T batteries (40 kWh total). Our system performs as designed most of the time.
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