PG&E Approved to Buy Power from SolarReserve CSP Project with Molten Salt Storage

Andrew Herndon, Bloomberg
January 29, 2013 | 13 Comments

PG&E Corp., the owner of California's largest utility, received approval from regulators to buy power from a 150-megawatt solar-thermal project in the state's Sonoran Desert, the first commercial-scale system in the state to include energy-storage capabilities.

Closely held developer SolarReserve LLC will sell the output from its Rice project in Riverside County to PG&E’s Pacific Gas & Electric utility for 25 years beginning June 1, 2016, according to a filing with the California Public Utilities Commission, which approved the contract at a meeting today in San Francisco. Terms weren’t disclosed.

The project will use thousands of mirrors to focus sunlight onto a central tower containing molten salt, which is funneled through a steam generator to produce electricity. The salt retains heat and can produce power at night, an advantage over photovoltaic panels that cost less and only work when the sun is shining, according to Commissioner Mike Florio.

“This is expensive, there’s no getting around it, but I think this technology is something that’s worth investing in,” Florio said at the meeting.

The molten salt system includes as much as 10 hours of energy-storage capability. It will cost about $600 million and construction may begin early next year, according to Kevin Smith, chief executive officer of Santa Monica, California-based SolarReserve.

Rice will be “the first large scale solar project in California with energy storage,” Smith said today by e-mail. The power-purchase agreement will help PG&E meet a state law requiring utilities to get 25 percent of their electricity from renewable sources by the end of 2016 and 33 percent by 2020.

Different Approach

SolarReserve’s system differs from solar-thermal plants planned by BrightSource Energy Inc. in California that also feature molten-salt storage and use water as a heat-transfer fluid.

The SolarReserve system “is hopefully a more efficient technology,” Florio said. “I don’t think we want to put all of our eggs in one basket in exploring these new and innovative technologies.”

SolarReserve expects to begin operating this year its similar 110-megawatt Crescent Dunes project near Tonopah, Nevada, that will provide power for NV Energy Inc. and be “the first commercial scale molten salt power tower in the world,” Smith said.

Lead image: Approved via Shutterstock

13 Comments

Gary Richardson
February 27, 2013

The state also needs to look into encouraging vertical integration of factories on site if the thermal output is the desired product. Reason being is that a company can benefit from lower costs of manufacturing if they don't have to pay to have the heat turned into electricity and then back into heat. If higher temperatures are needed, at least the thermal output can lower the costs of reaching the desired temperature. Petrochemical refining is one example, melting steel is another, also autoclave processing of composites and ceramics. If the refining is onsite, any captured CO2 can be used instead of water for some manufacturing process to make money while meeting clean energy standards. When a population grows around it, district heating and cooling is also cheaper than converting the energy two times as well.

F SC
February 19, 2013

It is only a matter of time until solar supplies about half our electricity. (Hopefully it will not be too late for our planet). When that happens, storage will become imperative for load balancing. As of today, thermal is the only available technology which can scale storage. Batteries have nasty chemicals and short life spans. Flywheels are a bit on the far side. Pumped hydro needs massive infrastructure.
Today, photovoltaic is benefiting from fantastic price reductions, but solar thermal unique advantage in storage will keep it relevant despite higher prices. I am happy that full scale demonstration projects are being built. It will be interesting.

Gary Richardson
February 5, 2013

The question is affordability to do so.

Lorin Vant-Hull
February 5, 2013

Gary,
It is important to remember that levelized cost of energy is the relevant parameter, so complexity which will surely carry significant cost increases must be avoided. Also, collecting low quality heat over a large field is not a productive enterprize.

Gary Richardson
February 5, 2013

Perhaps even thermo-electric quantum-wells may be worth exploring.

Gary Richardson
February 5, 2013

It would also be interesting to see if electric fields generated by thermo-electrics can be positioned/oriented to optimize band-gap transfer (PV), photon doubling(PV), or light bending(Lens).

Gary Richardson
February 5, 2013

Not necessarily so, the bisected angle may be avoided by creating a hybrid smart mirror/lens to separate wavelengths to solar thermal/PV sources respectively. Capitalizion of negative refraction directs desired wavelengths toward PV while reflecting undesired wavelengths toward a thermal receiver. This may offer an improvement on PV panels if heat is reduced because some PV panels have higher efficiencies at lower temperatures.
The picture to the right on the address below shows the direction of negative refraction but doesn't show selective negative refraction.

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

Nano-fluidic channels or gaps with media small enough to fit between wavelengths (Hydrogen/Helium) may be able to capture unwanted heat at the lens without affecting resolution to create a third co-generation source. The need to capture heat at the lens may depend on the heat conduction levels at the lens. Alternatively, materials with thermo-electric properties may be suitable for use in these superlens for a benefit that pays for itself over other meta-material ingredients. A fourth co-generation source may be thermal-electrics integrated into the solar cell layers.

Lorin Vant-Hull
February 4, 2013

Garyrich: The cosine loss I am referring to is simply the loss of effective area of the solar panel due to the need to bisect the angle between the receiver and the sun. No material can affect this.

Your second point is well taken. I was a bit careless in my statement. The absorbing surface on the receiver will reflect some of the light of all wavelengths, but current absorbers capture about 95% of all incident light, the rest is reflected so the receiver appears to be VERY bright due to the high concentration of 500-2000 times. Due to the high temperature required to drive an efficient steam turbine 500-600 degC (or a Brayton or Stirling cycle engine at more like 1000 degC) radiation losses are quite high--20-50kW/square meter, which is why the high concentration is employed

Gary Richardson
February 4, 2013

@lorin
I disagree, not all heat and light is converted at the receiver.
The reason for not receiving 100% of the solar spectrum is the material's limits in conducting heat and absorbing different spectrums. However, some spectrums may work better on solar heat and others in solar electric. All materials have limits on the permittivity levels allowed for each wavelength.

Gary Richardson
February 2, 2013

@lorin
I haven't heard much use of meta materials to create high performing mirrors that may address the cosines losses you mention.

Lorin Vant-Hull
February 1, 2013

garyrich repeats a frequent suggestion for using all the solar energy availabe. BUT, solar thermal systems already do so: the IR, visible, and UV light is ALL converted to heat at the receiver. Also, tracking the sun onto a receiver means the tracked PV panel is not perpendicular to the sunlight but would experience a cosine loss of 10 to 30% depending on the location of the heliostat and the time of day. Then too, the thermal receiver would only receive about half as much energy reducing its cost effectiveness. Losses in refecting the energy unused in the solar cell would further reduce the energy at the thermal reciever. Those are the top-of-the-head reasons that idea is not used, although it may well have been tried by someone. Of course, the main advantage concentrating solar thermal systems have relative to PV (or wind) is the availability of thermal storage, which allows them to match loads better, or shift energy to times when it is more valuable, like afternoon peaks, etc. The heated salt is simply stored in a hot tank. When electricity is requested, some of it is pumped through a heat exchanger to make steam, and returned to a 'cold tank' (at ~250 C) where it is stored until sunlight is available when it is pumped back through the heated receiver and then to the hot tank.

Sfinkx Corporation
February 1, 2013

Speaking of molten-salt storage, Donald Sadoway's energy storage battery technology uses that and liquid metal and shows great potential to revolutionize efficient, grid-scale energy storage. His company, AMBRI, could provide a more efficient solution to our Battery Energy Storage Systems (http://sfinkx.com/shop/battery-energy-storage-systems) down the road.

Gary Richardson
January 30, 2013

It would be interesting to see a PV Heliostat that converts the portion of light that can't generate heat and reflect the rest toward the thermal receivers.