We’ve now had our solar and battery system for about half a year.
Getting the system commissioned in mid-January means you get to see your solar output grow each week. In early days the panels generated 3 kwH per day at best and leaving the battery empty. We started exporting excess electrons around the spring equinox time, and the output reached over 30 kwH towards the end of May. In June, despite the weather around the summer solstice being rather disappointing, we exported about 2/3 of the solar panels’ output. Although Britain stopped its feed-in tariff scheme a few years ago, our energy supplier’s export tariff is quite generous, making a good dent in the monthly bill.
One thing I discovered soon after the system started operating was how engrossing the phone app that came with it was. It receives data from a data logger dongle plugged into the inverter at 5-minute intervals and turns it into a nice little diagram showing how electricity is flowing through the system and how much charge the battery has.
It also gives you a colour-coded chart: green for solar output, turquoise for load consumption, brown for import from the grid, blue for power supply from the battery and mauve for export. You obsessively check the app everyday, excited by every little growth in the generation output and the shrinkage of imported watts. You learn much power each appliance uses. And you can see how much of the usage is met by the panels, the battery and the grid because each one of these measurements can be turned on and off. This feature has turned out to be very useful.
The chart on the left above shows all the measurements at once. You immediately notice a big spike around 10:30 in the morning and smaller spikes around 9:30 and 12:30, plus smaller increase in power usage around mid-day and again in early evening around half past five to six. You can also see that we exported most of the green electrons we generated between nine in the morning and nine at night.
The chart on the right shows everything except imports turned off so that you can see how much electricity we drew from the grid, i.e., the power we had to pay for. The solar panels and battery kept the house going fine at lunch time and during the early-evening peak demand hours, but the two spikes in the morning, particularly the 10:30 one, were clearly too big to cover with solar panels and battery.
These two spikes come from the 10 kw electric shower, used at medium power setting at 9:30 and full power at 10:30. Until I got this app, I hadn’t realised how power-hungry the shower unit was. I suppose it’s better than using the gas combi boiler to heat the water to shower since the grid in Scotland is generally green already, but it’s obviously not as good as home-produced, free green electricity. I’m now looking into ways to heat water using solar power.