Monday, November 18, 2013

Enormous solar power stations

Three spectacularly large solar power stations have recently been in the news: Ivanpah, located in California, but within spitting distance of Las Vegas, is a concentrating solar power station in which 300,000 flat mirrors focus sunshine onto three power-towers. Solana, located in Gila Bend, Arizona, has a collecting field of about 3200 parabolic-trough mirrors, each about 25 feet wide, 500 feet long and 10 feet high, and it can generate electricity at night thanks to its ability to store high-temperature heat in vast molten salt stores. Kagoshima, near the Southern tip of Japan, has 290,000 solar photovoltaic panels.
All three are enormous, and must be amazing to visit: Ivanpah occupies about 14 km2; Solana, 12.6 km2, and Kagoshima, 1 km2.

Now, I'm always interested in powers per unit area of energy-generating and energy-converting facilities, so I worked out the average power per unit area of all three of these, using the estimated outputs available on the internet. Interestingly, all three power stations are expected to generate about 8.7 W/m2, on average. This is at the low end of the range of powers per unit area of concentrating solar power stations that I discussed in Chapter 25 of Sustainable Energy - without the hot air; Andasol, the older cousin of Solana in Spain, is expected to produce about 10 W/m2, for example.

I published a paper on Solar energy in the context of energy use, energy transportation, and energy storage in the Phil Trans R Soc A Journal earlier this year, and these three new data points lie firmly in the middle of the other data that I showed in that paper's figure 8 (original figures are available here). .

These data should be useful to people who like to say "to power all of (some region) all we need is a solar farm the size of (so many football fields, or Greater Londons, or Waleses), if they want to get their facts right. For example, Softbank Corporation President Masayoshi Son recently alleged that "turning just 20% of Japan’s unused rice paddies into solar farms would replace all 50 million kilowatts of energy generated by the Tokyo Electric Power Company". Unfortunately, this is wishful thinking, as it is wrong by a factor about 5. The area of unused rice paddies is, according to Softbank, 1.3 million acres (a little more than 1% of the land area of Japan). If 20% of that unused-rice-paddies area were to deliver 8.7 W/m2 on average, the average output would be about 9 GW. To genuinely replace TEPCO, one would need to generate roughly five times as much electricity, and one would have to deliver it when the consumers want it.

Maybe a better way to put it (rather than in terms of TEPCO) is in national terms or in personal terms: to deliver Japan's total average electricity consumption (about 1000 TWh/y) would require 13,000 km2 of solar power stations (3.4% of Japan's land area), and systems to match solar production to customer demand; to deliver a Japanese person's average electricity consumption of 21 kWh per day, each person would need a 100 m2 share of a solar farm (that's the land area, not the panel area or mirror area). And, as always, don't forget that electricity is only about one third or one fifth of all energy consumption (depending how you do the accounting). So if you want to get a country like Japan or the UK off fossil fuels, you need to not only do something about the current electricity demand but also deal with transport, heating, and other industrial energy use.

Sources: NREL;; NREL;; and google planimeter.


Sb said...


Could you show the maths behind the calculations below the pictures.

Ivanpar is approx 12 times larger than Kagoshima yet for the same power density of 8.7/8.6 only produces approx 5 times the power?

Is Kagoshima twice as efficient as Ivanpar and if so why would you want to build an Ivanpar?

Sb said...


Could you show the maths behind the figures under the pictures.

Ivanpar is 12 times the size of Kagoshima but only seems to make 5 times the power? but they have approx the same power density? I cant see how the figures were derived


D said... and related sites.
Latitude 57N, roughly similar to Aberdeen. More solar energy is available in London or Cambridge.

Ignored by DECC; I wonder why.

Wardski said...

Very nice to see occasional follow-ups on your SEWTHA book (like for the hydrogen)! Thanks for all your past (and current) hard work on this topic

Unknown said...

Thank you for putting these figures out in the open!

There's nowhere near enough numbers in the discussions of energy supply, but your book is always a great starting point.

jmdesp said...

Of note is the fact that Kagoshima is the southern most location of the 4 main Japanese islands. So productivity anywhere else in main Japan would be significantly lower.

Most of the solar is instead currently installed on the Hokkaido island which is at a latitude about 1300 km north of Kagoshima, since this is where land is cheapest.

David MacKay FRS said...

In reply to Sb [November 18, 2013]: Ivanpar does not "produce 5 times the power" - you are comparing the "capacity" - which is 5 times as big; but capacity is not the average power production. The average power production is the capacity times the load factor. If you put Ivanpar in Japan it would have a lower load factor, like Kagoshima. If you put Kagoshima within spitting distance of Las Vegas it would have a higher load factor.

Unknown said...

Agua Caliente solar farm is installed with more than five million PV panels. This $1.8bn solar project was originally initiated by NextLight Renewable Power, which was acquired by First Solar and now NRG Energy acquired the project from First Solar.

Unknown said...

How well would a solar power station work in the north west of England in an area of few sunny days?

Unknown said...

They've been able to improve the efficiency of the solar panels quite a bit in the last little while. I've seen tons of people installing solar panels on their houses. I've even seen a couple that engineered road solar panels to give energy to entire cities with the cities' own roads. It's pretty cool.