Storehouses for Solar Energy Can Step In When the Sun Goes Down

[jpak]

http://www.nytimes.com/2012/01/03/business/energy-environment/building-storehouses-for-the-suns-energy-for-use-after-dark.html

If solar energy is eventually going to matter— that is, generate a significant portion of the nation’s electricity — the industry must overcome a major stumbling block, experts say: finding a way to store it for use when the sun isn’t shining.

That challenge seems to be creating an opening for a different form of power, solar thermal, which makes electricity by using the sun’s heat to boil water. The water can be used to heat salt that stores the energy until later, when the sun dips and households power up their appliances and air-conditioning at peak demand hours in the summer.

Two California companies are planning to deploy the storage technology: SolarReserve, which is building a plant in the Nevada desert scheduled to start up next year, and BrightSource, which plans three plants in California that would begin operating in 2016 and 2017. Together, the four projects will be capable of powering tens of thousand of households throughout a summer evening.

Whether the technology will be widely adopted remains to be seen, but companies like Google, Chevron and Good Energies are investing in it, and the utilities NV Energy and Southern California Edison have signed long-term contracts to buy power from these radically different new power plants.

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[Ghost Dog]

1. Molten salt storage

... A variety of fluids have been tested to transport the sun's heat, including water, air, oil, and sodium, but molten salt was selected[who?] as best.[69] Molten salt is used in solar power tower systems because it is liquid at atmosphere pressure, it provides an efficient, low-cost medium in which to store thermal energy, its operating temperatures are compatible with today's high-pressure and high-temperature steam turbines, and it is non-flammable and nontoxic. In addition, molten salt is used in the chemical and metals industries as a heat-transport fluid, so experience with molten-salt systems exists in non-solar settings...

... The Andasol power plant in Spain is the first commercial solar thermal power plant to utilize molten salt for heat storage and nighttime generation. It came online March 2009.[70] On July 4, 2011, a company in Spain celebrated an historic moment for the solar industry: Torresol’s 19.9 MW concentrating solar power plant became the first ever to generate uninterrupted electricity for 24 hours straight. It achieved this using a molten salt heat storage design.[71]

/... http://en.wikipedia.org/wiki/Solar_thermal_energy#Molten_salt_storage



http://inhabitat.com/video-gemasolar-plant-in-spain-is-the-worlds-first-24hr-solar-plant/

This is also what Desertec is building across the Maghreb.

... The benefits of Concentrated Solar Power (CSP) technology are found in its dispatchability. CSP plants can basically be operated in a similar way to gas power stations. Using CSP technology, power can be generated from solar energy for up to 24 hours a day by means of thermal storage... This technology, which is easy to install and operate, has due to price developments become economically attractive in recent years...

/... http://www.dii-eumena.com/work-areas/power-generation.html

[FBaggins]

2. This really varies from situation to situation.

There are plenty of parts of the country where solar not only provides more 'bang for the buck", but where peak demand needs coincide well with peak solar production. If you're in Phoeniz, you use much more electricity during the hottest part of the day than you do at night... so the community could easily have a (comparatively) high solar PV penetration with no more storage than just what is necessary for leveling and short-term demand shifting. No need for hours and hours of storage.

There are other parts of the country where storage needs would be much pricier and solar can't reach anywhere near as significant a penetration.

[kristopher]

3. For a more technical appaisal...

This NREL study by Denholm & Mehos looks at the shifting value of CSP. IMO it is best viewed a statement on the worth of storage more broadly as it is actually an analysis of the way increasing levels of penetration for renewables leads to shifting use of generating resources and a rising level of excess production from those that are variable. The increased value of the CSP systems is directly tied to the way storage brings efficiency to the excess production.

US Gov press release - no copyright concerns. Link to study follows.

Thermal Energy Storage in CSP Plants Could Boost Penetration of Solar, Wind Power
December 6, 2011

Concentrating solar power (CSP)plants with thermal energy storage (TES) can dispatch power even during periods of high demand or reduced solar output. A new report published by the National Renewable Energy Laboratory says this flexibility could boost the use of other types of renewable energy, such as solar photovoltaic (PV)or wind power, that are generated intermittently.

The report, "Enabling Greater Penetration of Solar Power via the Use of CSP with Thermal Energy Storage" was published last week. Authors Paul Denholm and Mark Mehos describe how CSP systems with TES address the challenges anticipated as greater levels of variable resources, such as PV and wind, are integrated into the Western Interconnect?the major power grid that extends from western Canada, south to Baja California in Mexico, and eastward over the Rocky Mountains to the Great Plains.

There are two major challenges to economically integrating such variable and uncertain resources into the grid. One is the mismatch between when the sun shines, or the wind blows, and when there is a demand for energy. To address this obstacle, CSP with TES can shift energy production to periods of high demand or reduced solar or wind output.

A second challenge is the limited flexibility of conventional generators, such as fossil-fueled power plants, to accommodate variable generation resources, like PV and wind. In this case, CSP with TES can provide substantial grid flexibility by rapidly changing output, via higher ramp rates, in response to the highly variable net load created by high penetration of solar and wind generation.

The report describes how NREL examined the degree to which CSP may complement PV by performing a set of simulations in the U.S. Southwest. The results indicate the general potential of CSP with TES to enable greater use of solar generation, including additional PV.

The authors state that the preliminary analysis performed in their work will require more advanced grid simulations to verify the actual ability of CSP to act as an enabling technology for other variable generation sources. An important next step will include complete production simulations, using utility-grade software, which consider three things: the realistic performance of the generation fleet, transmission constraints, and actual CSP operation.

For more information, see Enabling Greater Penetration of Solar Power via the Use of CSP with Thermal Energy Storage.
http://www.nrel.gov/docs/fy12osti/52978.pdf

http://www.nrel.gov/pv/news/2011/1657.html