September Solar Usage

Here’s how my solar panels and battery system have been performing this month. I might do this more frequently, it’s hard going back in the historical data in my monitoring software and these posts are easy to find.

This appears to be an average consumption graph for when we’re at home but not really doing much. You can see I have run the kettle three times today.

Here’s today’s battery capacity graph. It starts off at 100% from 4:30am. The panels didn’t make much power today, the weather is that generic grey and overcast sky which must block a lot of the sun’s energy.

There was a period during the day where the consumption matched generation which is good to see.

Solar generation was all over the place though. You’d think a flat grey sky would give a fairly even curve, but it seems not.

I did create a Home Assistant automation / sensor that attempts to predict how long the batteries will last. I don’t know how accurate it is, but it claims the batteries will run out just before 10PM.

I suppose something to figure out is how I can record every instance of the battery running out, and then how much power was bought from the grid during that time.

Something I was considering was replacing the two lead acid batteries in my shed with a LiFePO4 12V battery and turning that system back on. During winter more battery capacity would be helpful I think, but I’d need to gather some data to see if it was cost effective.

I at least know that from Easter (maybe sooner, I got my panels installed during Easter, I have no data on how well they perform earlier in the year) until about now the house can pretty much run off grid for 20 hours a day. In fact I have too much electricity during that time.

Also because the batteries get charged to 100% overnight, more battery capacity would help in winter, but would be wasted in summer. Having a separate set of batteries in my shed would let me use those as a place to put excess solar energy in summer, and in winter I could charge them over night too.

If you didn’t know, my servers are in my shed and draw about 100-130W constantly, so if I had another 2kWh of battery storage my servers wouldn’t be drawing from the house battery.

But I need to work out some maths to see if it’s even worth doing. It might just be cheaper to pay the electricity bill. Talking of electricity bills, my energy provider sent me an email saying I was now going to get paid 8p per kWh for energy I export, and my night rate was becoming 0.5p per kWh cheaper and going down to 9p per kWh. I wonder if my export rate will magically go down again in Summer when I’m actually exporting power…