So, how much solar power is SoftBank producing?

Following on from last night’s post, I checked the data in this story.

The first of two phases of the overall project sees 8,680 Kyocera modules equaling approximately 2.1MW of solar power installed in the southern part of Kyoto City, Japan. This will generate roughly 2.1GWh of electricity annually, which is enough to supply power for approximately 580 households.

A quick Google tells me that the 2.1MW should be written as 2.1MWp, with the ‘p’ for ‘peak’, and a calculation tells me that 2.1GWh/y from 2.1MW works out at an effective 2.7 hours a day, or a perhaps easier to understand form is to state the output as 5.8MWh/day. Phase two will double the size, so provide the power for 1,160 households, or almost 0.2% of the households in Kyoto City. At that size it feels more like a PR exercise and a technology demonstration than a serious attempt to supply renewable power.

On the other hand, SB Energy Corp will see an income of 42 yen * 5,800 kWh * 2 or just under half a million yen per day, or just over 175 million yen per year. Google suggests a US retail price of around $400 per panel, so even at retail prices, this park might cost around 550 million yen to kit out, thus even allowing for all the other costs and variables, I would hazard a guess that it will be significantly less than 10 years to pay back the investment.

Note that according to the feed-in tariff law, this rate is guaranteed (or can it be renegotiated?) to last 20 years for large-scale 10kW+ plants, but only 10 years for smaller domestic-scale production. Furthermore, large plants get paid even for electricity they use to run the installation; domestic owners only get paid for the excess they send back to the grid. Now I think about it, I wonder if SoftBank might plonk a data centre or a mobile transmitter on site and get paid to run it?

You can also monitor TEPCO’s larger scale megasolar plants at Komekurayama, Ukishima and Ougishima online.

Looking at Komekurayama on the rather sunny 29th of June, it has a peak rating of 13MW judging by the left-hand legend, and generated 65.890MWh that day, which works out at a respectable effective 5 hours per day of output. However, the rather wet 1st of July managed just 11.280MWh, or the equivalent of a mere 52 minutes of peak output.

PS: I wonder how the reaction will be if/when one of these projects uses Chinese panels?

PPS: I’ll have to do a post to clarify my stance, but I reckon it’s similar to many people here; nukes are needed for now at least, financially-viable renewables are good, as is separating generation and transmission, and last but not least a Sir John Harvey-Jones or Gordon Ramsay needs to rampage through KEPCO, TEPCO and the rest with a very sharp axe!

  1. It’s tough to find an objective source that isn’t geared toward engineers (no offence), but I found this (non-objective) paper interesting:

    One point is that as well as separating generation and transmission, one needs to think about storage too, as most renewable energy sources do not provide consistent output (good luck lighting your house with Solar at night-time, otherwise).

  2. Until some magic cheap, high-capacity, fast-charging, long-lasting, non-toxic, no-loss battery system is invented, we’ll always need some stable baseline of power generation. Many of these renewables are not available 24/7. Solar isn’t even 1/3 of that. And solar takes space. Maybe at best peak you can get 200W from 1 sq.meter. So you need a field 50m x 100m to get 1MW. Or a solar field 5km x 1km to get 1GW (about 1 big nuke plant) but only on sunny days at noon. With magic batteries, maybe 5 times that will get you 1GW 24/7. So 5km x 5km. And I’m not even counting gaps between the panels.

    That’s a lot of trees to cut down and cute animals to displace.

    Still, if you’ve got roof space, and you stay connected to a reliable electric supply on the grid, and someone helps you pay off the startup costs (that someone being your neighbors’ tax money), solar can make some sense.

    Ever notice how green subsidies tend to end up in the hands of those who already have money anyway? Be it buying back power at 3 or 4 times the normal rate from those who can afford to install a solar panel system, or giving people cash credits if they can not only afford a new car – but a hybrid, or giving buckets of cash to corporations who do green projects.

    Politically, that’s kind of ironic considering where the push is coming from, isn’t it? Though maybe it just helps get those evil guys on the other side of the aisle to play along. :roll: :wink:

    I’m along for the renewable energy push because I’m old school. I just don’t like air pollution.

    Besdies, it’s bad for the children. Won’t somebody please think of the children! :wink:

  3. As for who gets green subsidies, I’ve always held that the best thing for the environment is for environmentalism to be profitable.

  4. @Level3:

    200W/m^2 is probably a good place to start, but we need to be very explicit in what we are talking about. Remember all the kids confusing µ and m after 3/11/2011? :facepalm:

    Anyway, your estimate of 25 square kilometers is pretty good I think. Let’s go there a bit more quantitatively and give others the chance to step in with better knowledge of PV efficiency and atmospheric absorption. In the end, we might have conclusions based on (gasp) data. :wink:

    Assuming a solar constant of 1365W/m^2 and an axial tilt of 23.5˚, the maximum amount of energy received at the top of the atmosphere at 35˚N (the latitude of Kyoto), averaged over the entire year, is readily calculated to be 350W/m^2. (Think of this as an average daily average. Summer and winter solstices are 500W and 180W, respectively.)

    Here, I’ll assume for Kyoto that half reaches the surface (175W/m^2). What’s the efficiency of PVs? 10%, 15%, 20%, 25%?

    Twenty percent efficiency would result in 35W/m^2 being converted to electricity, requiring an approximate 29 km^2 area of wall-to-wall panels to produce 1GW on average throughout the year. Assuming 25% efficiency results in 23 km^2.

    So an assumption of 5km x 5km might not be so bad. How are the panels spaced?

  5. I’m not so good at the sciencey stuff, but it may be worthwhile keeping a lookout for Son’s investments in gas. Renewables and gas tend to go together, in the absence of proper storage.

    It’s depressing that the most effective form of energy storage we have appears to be pushing water up a hill.

  6. @The Dude:

    The annual average net sunlight in Kyoto is about 12MJ/m^2 per day, as is Tokyo, or 3.6kWh/m^2 per day. A typical noontime peak in June on a clear day is 850W/m^2 on a horizontal surface. I guess the air permeability is a bit under 0.7 there, but Kyoto does seem a bit more hazy than Osaka.

    I can assure you that I am basing things on data and academic (but almost no practical) expertise. Otherwise my lecture on optimizing solar panel angles for sunlight is fucked. As you know, it’s basically just trigonometry, a few simple equations, (and a few more complicated equations if you’re calculating the orbital path from scratch) and making sure you get the plus or minus sign right by using common sense.

    My first post was just based on memory of the highest insolation values in summer and assuming 20% efficiency to yield a best case scenario, which still sucks in terms of area needed per GW.

  7. @Level3:

    My apologies if I left the impression that I was being critical of you. I wasn’t. The comment on drawing conclusions with no data was also directed towards people who frequent other places.

  8. @The Dude:

    No prob. If there’s no history of asshattery, I always try to assume that something that could be taken as personally critical or snide, written in print with no tone and no smileys, is not personal. I’m not always successful. But I just try to recognize that the paranoid urge – to assume even the slightest challenge is some kind of hatred – should be ignored.

    Wish those other people could figure this out.

    I mean, it’s probably the prime reason why I find them so offensive and am so motivated to denounce them. Because I recognize all the urges these paranoid hateful sad people have. I have them, too, probably even worse then a lot of them. (Though not all. There’s one or two I think are a complete psychopaths… No, they’re not Japanese.) I know what they’re thinking and what they want to do, what they would do if they thought they could get away with it.

    But we know those evil urges should not be indulged. They seem not to have figured that out fully. And that scares me, because I think the only thing that holds them back from the more extreme urges is just the worry of being arrested, rather than self-restraint or letting morality trump their id.

    Then there are the ones who don’t even seem to care about being in trouble with the law. They worry me. And that’s why people choose to be anonymous…

    Well, that was dark… :lol:

    Plus, it’s just part of science. If I’m wrong, then you SHOULD point it out. It’s worse to let me keep making the same error. Like not telling me I have a giant blob of curry on my chin before my big presentation.

    (Again, I wish the other people would learn this. But they seem not to care about presenting Swiss cheese arguments that are so easy to prove wrong. Their intolerance of criticism is their loss.)

    Even if you just think I’m wrong, you should still ask the question, because it never hurts to double check things. And it’s not really ME that’s wrong, it’s the data, or the math, or the bad interpretation of the data. Everyone makes mistakes.
    When a prof points out ways to make my paper better, I don’t think he or she is attacking me.

    I say “Thank you”.

    Thanks, Dude.


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