Arizona solar plant achieves six hours after sun goes down

In parts of AZ there are serious brown outs and rolling blackouts in the summers as A/C kicks in everywhere, which is probably the biggest draw.

I'm opposed to coal altogether for pollution reasons alone. It's bad enough between the cars and airport traffic, don't need more.

This is a matter of tradition and convenience. It is quite possible to use a just-in-time steam generator.

In fact many steam power systems are vapor phase only (non-condensing) to avoid corrosion and droplet impact damage. Steam is used because it is cheap and nontoxic.

Nuclear reactors are easy to turn on and off once a day. Naval reactors do it as a matter of course. There's just no point. If you build a grid scale reactor, you might as well leave it running all the time, at which point you optimize away the rapid start capability.

There might be one reason they let this spin up and down.

We mostly power the grid through a bunch of constantly humming systems, but our usage has all kinds of peaks (diurnal, seasonal... the British grid has a massive peak right around the time Eastenders ends and everyone puts on a kettle[1]).

If you are adding some power to the baseline, that's helpful. If you're promising the grid you can add some power during one of the daily or seasonal peaks, that's almost as valuable as adding a new source of always-on power. By providing energy for even just six hours a day, you might save the grid from requiring a new always-on plant. So in terms of opportunity costs, even by being twice as expensive moment to moment, you're still cutting costs in half (unless everyone followed your strategy).

So there's probably some number of hours of shutdown where it's worth the coal, some number where it's not, all contingent on what plants are nearby, and how close your customers typically are.

Related but tangential, one of the unintended benefits of electric cars would be adding a bunch of consumption at night, smoothing the diurnal cycle, letting us pursue more lower-cost always-on generation. (This is before you even consider distributed storage proposals that let the grid draw from parked cars in emergencies.)

Predictability is almost as good as a natural resource.

[1] http://www.bbc.co.uk/britainfromabove/stories/people/teatime...

Note that's when running at "maximum power". You don't have to extract the heat that fast. Given a hypothetical and utterly irresponsible grid supplied solely by this design, you'd overbuild to the point that you'd have enough stored heat to last all night.

It would; just look at the amount of farmland currently used to produce plants used for the production of biofuels. It's a big impact on the food production capacity of the world, and it's mainly used to mix with regular oil-based fuels so that the oil/gas companies adhere to government standards, tax reductions and customer goodwill, whilst the biofuel producers get government grants and fundings and more tax deductions.

Of course, that's (iirc) first-generation biofuel, second/third generation (or grade) biofuel uses biowaste (shells, green stuff, animal waste, stuff that would otherwise be processed into compost or fertilizer).

source: my memory

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3 square miles is 7.77 square km. Just over 1 kW of sunlight falls per square meter, so I will round up and say that there are 8 GW falling on the plant total. 280 MW over 8 GW = 0.035.

So 280 MW of production is 3.5% efficient of peak irradiance.

BUT average irradiance is smaller than peak:

http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_p...

It looks like 5 kWh per m2 per day for Arizona, so that's 5 kWh per m2 times 7,700,000 sq m = 38.85 GWh per day irradiance on 7.77 sq km. Assuming the plant can put out its maximum capacity for the 18 hours it runs each day, that's 280 MW times 18 hrs = 5 GWh per day. 5 GWh over 38.85 GWh = 0.1287.

So it's operating at almost 13% efficiency of average irradiance.

That is very good, considering that they are able to store heat much more cheaply and environmentally friendly than storing electricity in batteries.

The most important thing of all is that it doesn't have to wait for innovations in photovoltaics. Anyone can buy land, set up parabolic mirrors, and tinker with forgotten heat engines like Stirling cycle engines or Tesla turbine engines that easily achieve 30, 40, 50% efficiency and approach the Carnot limit. Conversion of rotational motion from a turbine to electricity with a generator is a solved problem at 95% efficiency.

Oh and these plants can be supplemented by biomass, say biodiesel from algae or fuel pellets made of hemp. If that's too granola for the fossil fuel industry, they can also use natural gas.

In fact if you study this long enough, you find that there are only two real hurdles: energy storage and connection to the grid (made difficult because of resistance from established utilities). Generation turns out to be relatively inexpensive because there's a sea of free energy all around us. To put it in perspective, Grand Coulee dam puts out less power than the irradiance falling on the solar plant. It's just more efficient at converting the motion of falling water to electricity:

http://en.wikipedia.org/wiki/List_of_largest_hydroelectric_p...

It puts out 6.8 GW times 24 hrs = 163 GWh/day. That's 33 of these solar plants. So every 100 sq miles (260 sq km) of desert is equal to the 324 sq km of area flooded by Grand Coulee.

Solar thermal is the hydroelectric of the future and uses less land, which will only improve going forward. IMHO this will someday dwarf wind and nearly eliminate intermittency issues.

There's nothing to be baffled about, it's a fair question. You even provided the answer: "It will heat depending on how quickly you can get energy to it, and it will cool depending on how quickly you can remove energy from it."

On the other hand, there's no "electric heater" here to use to heat up the liquid used to absorb solar heat (not to mention ice or freezers...); it's the sun or nothing. Given that the sun doesn't give us peak solar flux until the midday it's entirely possible that solar energy production in the first few hours of the day would only keep up with instantaneous energy needs instead of having enough of an excess to reheat the heat storage fluid for energy production later that night.

Whether this is actually an issue or not depends on the numbers, but it's not a baffling question at all and there's no reason to be so condescending about it.