We've now paid off the two-year loan for the solar panels. That means that we own the roof over our heads. This is a great thing. We still don't own the walls or the land beneath us, as those are long-term low-interest loans, but at least we own the roof.
Perhaps we should have put the panels in with the builder's contract, but it seemed to make the financing easier to pay some of this up front and get a separate loan for the rest of it. The rate was higher, but since we paid it back in two years rather than thirty-five, the total cost of the loan was a lot less. The first thing the bank advised us when we put the loan application in was to cut the costs by taking some of the panels off the roof. This is strange because it was about the same time they published this report in Japanese which seems positive towards domestic solar.
Over the year and a half of generation, we've earned 47,000 yen per month on average, and paid 7,500 yen for our electricity bill. We sold 89% of what we generated, so without our panels we would have paid another couple of thousand yen on the electricity bills.
At this rate we'll pay back the investment on the panels in around eight and a half years. I'm not sure who else the bank is lending to, but a return on investments in under nine years seems fairly healthy, and I really don't know why they aren't insisting that all houses they finance put panels on the roof, even offering to fund them in return for the electricity companies paying directly to the bank to repay them.
In terms of kWh we've generated an average 36 kWh per day, which is a little over twice the 16 kWH we use. In terms of the amount of electricity we are getting for each kilowatt of solar panel we have installed, that's 1450 kWh/kW per year or 4 kWh/kW per day.
I'm not exactly sure how much of the cost we can attribute to the roof and how much to the panels. I have a back-of-the-envelope estimate from the architect, printed out on an undated piece of A4 with some of the figures to the nearest yen, and some to the nearest 10,000, which compares the option we took with a conventional roof and solar panels installed on top. It compares an older quote from Rooftech for an integrated roof system of 4.44 kW (actually written as kWh) which was around 3 million yen plus an estimate of 1.35 million for the roof work needed underneath their roof, which ends up as 4.35 million; 4.04 million after getting the grant. The other quote was 2.4 million for 4.81 kW of panels, with a roof estimated at 1.81 million coming to 4.21 million; 3.87 million after the grant.
In other words, the integrated roof and panel system was more expensive than installing panels on a conventional roof, but only about 3 or 4 percent. It should be added that this was for around half the roof area covered with solar panels, and it's not clear what kind of roof the alternative was. Anyway, we chose to go for the integrated roof because it seemed well worth the potentially slightly extra cost for the simpler design elegance.
