Sunday, March 18, 2012

Keeping the Lights On: Why Concentrating Solar Power is Vital to Tomorrow’s Energy Mix

Picture a solar power station. You think of a bunch of solar panels, right? Photovoltaic (PV) solar power, which uses cells to turn the sun’s rays directly into electricity, accounts for, by far, the majority of solar power installed worldwide. FIGURE?

But it’s another kind of solar power, concentrating solar power (CSP), which might prove even more important. Look at a CSP power station and you’ll see not solar panels, but acres and acres of mirrors, all focusing the sun’s rays onto a single central tower, in which fluid is heated to very high temperatures by the focused sunlight. The super-heated fluid can then be used to generate power much like a steam engine.

CSP is a fairly recent development, but it’s growing fast. Over 7 GW of CSP are expected to be installed in the US in the next few years. But many people don’t understand the advantages CSP offers. Now, GreentechMedia has published a great new guide to why CSP has to be a vital part of our future energy supply.

Flexible beats baseload

You often hear advocates of fossil fuels talking about ‘baseload power.’ Coal and gas stations can supply a constant flow of power which, it’s argued, is needed to keep the lights on at night when PV doesn’t operate, and during times when there’s little wind so turbines don’t spin.

As a sun-powered technology, CSP can’t provide baseload power (which comes with its own problems). But it can provide something better — flexible power. Because CSP produces thermal energy (the heated fluid), its energy can be easily stored using simple thermal energy storage technology. As GreentechMedia‘s piece puts it, “PV doesn’t entirely answer the needs of the transmission system, while CSP with thermal energy storage (TES) can.”

This energy can then be converted into electricity as and when it’s required. “Dispatchable CSP can discharge from storage to serve high-price peak loads that occur outside the daylight hours, including the late afternoon and early evening,” Dr Udi Helman, a director at BrightSource Energy, told GreentechMedia.

This flexibility makes CSP every bit as useful as coal or gas power in terms of keeping the lights on and people’s kettles boiling — if not moreso.

PV cannot be dialed up or down, whereas by channeling more or less CSP output to storage, it can be ramped. Once in storage, it can also be released in varying amounts. This is the kind of flexibility conventional generators have which allows utilities, by altering the level of their output, to accommodate the forecast uncertainty and variability of non-dispatchable renewable generation. This provides grid operators with ramping reserves and regulation services.

It’s not a zero-sum game

By providing a highly flexible source of power that can make up for shortfalls in supply from other sources, CSP could actually enable the use of more PV and wind power.

CSP plants with TES have the flexibility of conventional thermal plants, according to Helman, and “offer higher ramp rates and ranges than large thermal plants.” This could not only replace some conventional generation but could “provide a more flexible generation mix” that would “result in greater use of non-dispatchable solar PV and wind.”

In short, CSP is just as important to a renewable future as PV or wind power. And it makes it possible to foresee a future energy supply which meets our needs without fossil fuels or nuclear.

Of course, in some countries, hydropower — which, like coal and gas, is relatively constant — can fill the role of providing baseload power without emissions or hazard. But in the US, CSP deserves to be a central part of the mix. And if the Desertec project gets its way, CSP installations in the Sahara will also be central to Europe’s energy supply in future.

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