Solar panels

[RetireJapan]

I've been looking further into solar panels and am now drafting my second blog post. Before that I could do with your help!

So a few things have cleared up. You can use the power from commercial installations (over 10kw) yourself and are not forced to sell all the electricity.

Given that, would it be better to get a 9.8kw installation and get paid higher prices for ten years, with no guarantee of being able to sell the electricity after that, or 10kw+ (our builder says 15kw is about as large as we should consider, given the size of the roof and the possible need to pay to upgrade the local grid if we go much over that) and lock in lower feed-in tariffs for twenty years.

We've been quoted 2.8 million for just under 10kw and 4 million for 15kw.

The twenty years of lower tariffs seems like a better option at the moment.

What do you think?

[Tony]

I think these days, locking in for 20 years of selling all the power you produce is probably not as good a deal as it used to be. I would say go for the 20 years of selling what you don't use. I can't imagine you'd need 15kw though, seems a bit overkill, maybe just go for 10kw. It's also probably a good idea to have them install a battery inverter, that way, once your 20 years is up, you can plug a battery, like a tesla powerwall 2, straight in, and just be outright self-sufficient.

[RetireJapan]

Yeah, definitely planning to get a battery at some point. I'm expecting prices to come down a lot over the next 10-20 years

The gamble is that currently feed-in tariff for <10kw is 30 yen for 10 years, then unknown after that (current market feed-in tariff is 11 yen). Feed-in tariff for >10kw is 23 yen for twenty years, then unknown. Which is better? We'd have to know the future price of electricity (both to buy and sell) and the cost of batteries to be sure

[markshinshu]

I think you're right, but you may be better looking at it from a design perspective. How many panels can fit on your roof, or roofs if you have a car port as well? The panels will produce optimum power if they are due south and between 30 and 35 degrees to the horizontal. Within 15 degrees doesn't make much difference to the annual output but further from that will significantly reduce the output. (More details here: http://hatsudenkakaku.info/entry22.html). If sunlight is obstructed anywhere on the solar array (for example by a tree or a lamp post) it can affect the power output of the whole array. The way panels are connected to each other and to the power conditioners makes a difference: http://minuszeroeco.blogspot.jp/2014/06 ... -more.html

Away from the predictable world of physics into economics, it's difficult to know what will happen to electricity prices in the future. Right now it makes sense to sell electricity you generate and buy electricity you use, because of feed in tariffs, so you don't want to use your own electricity. This is very unlikely to be true in ten or twenty years. By then there will be a lot of installed solar that has been paid for but is still producing electricity (ie zero cost), and solar panel prices will likely have halved a few more times. There is a slim chance that the renewable energy revolution will deliver cheaper power, but I don't think the sums completely add up, and you can probably expect them to pay 11 yen for any excess you generate. You probably don't need to be self sufficient, unless there is a natural disaster or if they do decide to stop paying little people for electricity. In that case 10kW should cover your own energy needs, probably including any electric vehicles. You can buy a battery later (and in fact if you buy an electric car, they will throw one in for you!) The prices of batteries will come down, but there will probably not be the same exponential drop in prices that we get with computers, LEDs or solar panels. With more renewables there is a need for more capacitance in the system, so it's possible there will be some kind of subsidies for getting batteries, which will again change the economics.

[RetireJapan]

Hi markshinshu

Thanks! As I understand it, power costs 30-odd yen in the daytime and the feed-in tariffs are only 30 yen (domestic) and 23 yen (commercial) so it makes sense to use your own power in the daytime and sell the excess then buy at night.

Our new house faces due south and the roof will be at 3.5 inches??? Apparently that is what we can get away with in terms of planning permission.

Not sure how they hook up the panels, will need to ask about that. We do have some tall trees nearby.

[Tony]

I have to say, I like the idea of Tesla's solar rooves, and even though they are apparently still sturdier than regular roof tiles, it still seems a bit expensive.

[gogakuhei]

I have to say, I like the idea of Tesla's solar rooves, and even though they are apparently still sturdier than regular roof tiles, it still seems a bit expensive.

I just wish these were available already, since we are looking at building and it would be nice to just install it from the beginning.

I have no idea what the pricing on a Tesla Roof would look like, but the Powerwall seems to be much cheaper than a Japanese battery with equivalent capacity.