We’ve now had the solar PV system working since August. We were lucky to get it installed early on in the building process, so could therefore start producing energy as soon as was possible. And because we weren’t living in the house, most of the energy we were producing at that time was being sold. As a result, our first energy bill after installation, was not a bill but a rebate – for ¥19,500 (about $190).
The best conditions are of course bright, cloudless days, but also the cooler days of autumn and spring, due to the fact that solar PV efficiency is reduced by high temperatures. On a good day the system will make on average about 25kwh.
In the example pictured above the total made so far that day was 19.93kwh, we had used a total of 5.15kwh but as most of this was needed at night most of the energy we were billed for that day (4.42kwh) was not home produced energy. As a result, most of the energy made we were able to sell at the premium rate which is about double the regular electricity rate.
With this in mind, in order to mazimise the amount we get back (energy sold), we reduce our energy use during the day when the system is producing energy. Except the wood stove, the whole house runs on electricity and the hot water system, washing machine etc are all set to work at night. This also means rather than paying ¥22 per kWh, we are being charged at an off-peak rate of ¥11. This minimised any charges and therefore gives us a greater net rebate.
So in addition to having a carbon positive househould in terms of the energy we use/produce, the solar system also helps us track our energy use more carefully (currently around 7kwh per day). According to Strinkthatfootprint.com the avarage household electricity use in Japan (so excluding gas energy use) is around 15kwh.