February 24, 2009
Large Solar Thermal Electric Plant In Spain

The largest solar thermal plant in the world is now operational in Spain. (thanks "Fat Man" for the heads-up)

The salts—a mixture of sodium and potassium nitrate, otherwise used as fertilizers—allow enough of the sun's heat to be stored that the power plant can pump out electricity for nearly eight hours after the sun starts to set. "It's enough for 7.5 hours to produce energy with full capacity of 50 megawatts," says Sven Moormann, a spokesman for Solar Millennium, AG, the German solar company that developed the Andasol plant. "The hours of production are nearly double [those of a solar-thermal] power plant without storage and we have the possibility to plan our electricity production."

7.5 hours is long enough to provide peak electric power during the peak late afternoon and evening hours of a very hot summer day. The article says this is the first heat storage facility for a concentrated solar facility on this scale. So we need to wait and see how well it works in practice. The $380 million cost for a 50 MW facility sounds pretty pricey to me, especially since this isn't 50 MW of 24x7 power.

Maybe someone else can make better sense of this SciAm article than I can. They quote only a doubling in electricity cost for electricity from this method as compared to coal. How can solar thermal (i.e. concentrated solar) cost twice as much as coal regardless of whether molten salt storage is used?

All told, that means thermal energy storage at Andasol 1 or power plants like it costs roughly $50 per kilowatt-hour to install, according to NREL's Glatzmaier. But it doesn't add much to the cost of the resulting electricity because it allows the turbines to be generating for longer periods and those costs can be spread out over more hours of electricity production. Electricity from a solar-thermal power plant costs roughly 13 cents a kilowatt-hour, according to Glatzmaier, both with and without molten salt storage systems.

Coal electric with no conventional pollutant emissions would cost more. Add in the cost of carbon capture and then nuclear power becomes cheaper than coal. Concentrating solar isn't going to compete with coal all that much. Nuclear, geothermal, and (with limits) wind are the real competitors to coal because coal is a base load source of electric power. Solar isn't for base load.

That price is still nearly twice as much as electricity from a coal-fired power plant—the current cheapest generation option if environmental costs are not taken into account. But Arizona's APS and others can then use solar energy to meet the maximum electricity demand later in the day. "Our peak demand [for electricity] is later in the evening, once solar production is trailing off," Lockwood says. That's "the reason we went that direction and are so interested in storage technology."

This is the big reason why concentrating solar might have a big future regardless of what happens with photovoltaic prices. The heat generated by concentrating the light is a lot easier to store than electricity. Concentrating solar with salt storage can stretch across the peak demand hours - at least in the US where summer is peak demand time. In Britain peak electric demand is in winter when not a lot of sun shines. So solar power does not work well in Britain.

The costs for this project seem high when total kwh per year are considered.

The 50MWe AndaSol plant is located in the community of Aldeire in the Marquesado valley in the Province of Granada, Southern Spain. Thanks to the high altitude (1,100 m) and the desert climate, the Marquesado Valley offers exceptionally high annual direct insolation of 2,200 kWh/m˛yr. The 549’360m˛ parabolic trough solar field is built-up by 1,008 EUROTrough collectors, arranged in 168 parallel loops. It will occupy app. 200 hectares of land. It will generate live steam of 100 bar/371°C to the reheat steam turbine with a cycle efficiency of 38%, gross. With an annual direct normal radiation of 2,200 kWh/m˛ per year, the AndaSol plant will generate almost 182 million kWh per year of clean solar electricity in 100% solar operation. The plant will be built, owned and operated by the specific project company, Partner 1. Partner 1 will sell as renewable independent power producer the generated solar electricity to the utility under the standard renewable power purchase terms regulated by the Spanish Royal Decree 2818/98. Using solar beam radiation as it’s primary energy, the solar plant will avoid approximately 172,000 tons of CO2 annually in Southern Spain otherwise being emitted by coal and heavy fuel oil operated power plants in the region.

In a market that 182 million kwh might sell for, say, 10 cents per kwh. It would probably sell for less in the US where the average retail cost of electricity is about 11 cents per kwh. But let us assume a higher price in Europe. Okay, that would still only amount to $18.2 million per year. Seems like a small return on a few hundred million dollar investment plus operating costs and maintenance costs. But if this electricity is sold during peak hours maybe it sells for more than 10 cents per kwh? Does a political deal assure a higher price? If so, how much higher?

Let us consider the avoided CO2 emissions. If the 172,000 tons of avoided emissions were taxed at $30 per ton (which is one figure I've heard proposed for how much carbon emissions should be taxed) then the amount of avoided carbon taxes would be only $5.2 million per year. That doesn't improve profitability very much.

I am curious to know more about the real costs for concentrated solar plus molten salt storage. Anyone have better sources of information on this topic?

Share |      Randall Parker, 2009 February 24 10:38 PM  Energy Solar

Mike E said at February 26, 2009 10:13 AM:

The cost oddity may be because a solar thermal plant with heat storage will need smaller/fewer turbines than one without (you're getting the same total power, more or less, but the turbines are running 16 hours a day instead of 8). Apparently the cost of the storage is roughtly cancelled out by the reduced turbine cost... this suggests hybrid plants, with no storage but a non-solar heat source (natural gas?) for non-sunny hours might also be a good intermediate-term option in some places.

Randall Parker said at February 26, 2009 7:59 PM:

Mike E,

Thanks, very interesting point. If you spin your turbines more hours you can amortize the capital costs over more hours of operations and you don't have as many turbines that way. Makes sense.

So the cost of turbines needs comparison to the cost of storage when doing concentrating solar. Note that PV doesn't have this advantage of cancelling costs. I hadn't thought of that before.

Some Guy said at March 5, 2009 2:01 PM:

what I don't understand is why they didn't just increase the salt volume to give them a couple of days worth of storage capacity. The incremental cost of the salt and the storage tanks wouldn't be much higher, and they'd turn it into a full-time power plant.

Randall Parker said at March 5, 2009 6:14 PM:

Some Guy,

Solar makes more economic sense to sell its (more expensive) electricity during the peak demand period. Saving more heat to sell electricity at 2 AM (when wholesale electricity prices are much lower) does not make economic sense.

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