Some Skepticism On Solar Thermal Power’s Storage Potential

Editor’s Note: EarthTechling, always looking to bring you interesting cleantech articles, is proud to repost this column from partner Institute For Local Self Reliance. Author credit goes to John Farrell.

Earlier this week New York Times reporter Matt Wald had a piece on the role of energy storage in supporting the expansion of renewable energy.  However, his specific focus on solar thermal power generation overlooks the potentially high costs of relying on solar thermal power as well as the potential for distributed “storehousing” of renewable energy.

Solar thermal power is generally understood as centralized electricity generation by concentrating solar energy to heat water, make stream and power a turbine to generate electricity.  Solar thermal supports heat storage (for an additional cost) that allows the power plant to shift electricity production to other times of day.  It’s a technology at the early stages of commercialization, and is generally pursued because the cost of solar thermal storage is low compared to the total capital cost (although the cost of solar electricity is much higher than for other solar technology).

Rice Solar Energy Project

image via SolarReserve

For example, the article highlights the SolarReserve solar thermal project, a 110-megawatt power plant that received a federal loan guarantee worth $737 million.  If the SolarReserve project is built at the same cost as its loan guarantee (unlikely, as it seems the guarantees are usually for about 80% of the project cost), then its cost is around $6.70 per peak Watt.  In contrast, the Solar Energy Industries Association reported that utility scale solar PV in the second quarter of 2011 was installing at an average cost of $3.75 per Watt.

The comparison isn’t precisely apples-to-apples, of course.  The SolarReserve project will operate at a higher capacity factor than a PV project of comparable size.  The bigger question is whether the $3 per Watt difference justifies the amount of storage provided.  Battery storage for PV cost about $0.50 per Watt for each hour.  So a PV project at the average 2011 price could add 6 hours of battery storage and be built for the same cost as the SolarReserve.  It may explain why a fair number of solar developers have switched from concentrating solar thermal power technology to PV in the past year.

The other consideration is how much storage makes economic sense.  In general, battery storage doesn’t have to last all night, but merely fill the gaps between production and consumption of electricity.  Storage for solar thermal is relatively cheap, so the SolarReserve project has 10 hours or more of energy storage and only adds about 5% to the cost of the project.  But does solar PV need 10 hours of storage to compete?  Unlikely.

With solar, the goal is to generate power during the time of peak demand for electricity (hot, sunny afternoons). The NREL researcher quoted in Wald’s article suggests that widespread adoption of PV (a phrase not explained, unfortunately) would quell demand for electricity during the afternoon and make the early evening – when PV no longer produces – the key timeframe for electricity generation, implying a big advantage for solar thermal.  But solar PV projects don’t need to match solar thermal’s storage capacity to win the economic argument.  If a PV project has just 2-3 hours of storage, enough to shift its output into the evening peak hours, it will largely fulfill peak demand and still cost less than solar thermal.

The NREL researcher suggested that energy storage could be worth as much as 4 cents per kWh (largely from the avoided cost of building new natural gas plants).   But if solar PV can meet the peak electricity demand with shorter storage and at lower cost, it’s unlikely that the solar thermal power plants will be able to compete.  Shifting production into early evening to serve peak electricity demand can be very profitable, but trying to sell noontime sunshine at 10 PM when wind power is increasing is something else entirely.

Storage doesn’t have to be a power plant add-on, either.  Other sources of storage like electric vehicles may be able to have an increasing impact.  Researchers at the University of California, Berkeley, project that the U.S. will have 10 million electric vehicles on the road by 2020, offering a combined storage capacity – if they are similar to the Nissan Leaf – of 240 million kWh (enough to power over 7 million homes for an hour).   PNNL did a study late last year and found that 2.1 million EVs in the Pacific Northwest could support enough storage to add an additional 10 GW of wind power in the region.

I’m also skeptical of the ability of solar thermal to have anything more than a marginal impact, simply because of the development timeframe.  According to Greentech Media, the total concentrating solar thermal power capacity under construction or with a permit and PPA in hand is just over 1.1 GW.  That probably won’t be fully deployed until 2017.  In the meantime, there was over 1 GW of solar PV deployed in the U.S. in 2011 alone.  With no growth at all, solar PV would install 5 times the capacity of solar thermal power by 2017.   And by 2017, the cost of solar PV (if continuing to fall at current rates of ~7% per year) would be $2.45 per Watt.  Solar thermal electricity generation doesn’t seem to be benefiting from the same learning curve nor installing at a pace that will allow it to catch up. And the ongoing cost differential allows for many other options for storing solar power other than combining storage and solar power generation in costly, centralized solar thermal power plants.

I don’t have the answer to the storage question, but I’m skeptical that costly, centralized solar thermal power plants are the best answer to matching renewable energy supply with electricity demand.

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    • Well the real question is how much dispatchable power you need and at what time.n

    • Energy Insight

      When comparing the cost of installing PV and installing Solar thermal with storage, the capital cost per MW isn’t a good comparison.u00a0 It’s really how many kw-hours are generated.u00a0 Public releases from SolarReserve identified that their 110 MW facility will generate 500,000 megawatt-hours per year.u00a0 That’s about 2 to 3 times more thanu00a0the kilowatt-hours generated by the same size PV project.u00a0nnIn addition, the requirements of NV Energy (the Nevada utility)u00a0are such that their peak requirements are really from 12 noon until 10 or 11PM at night (Las Vegas is the load center).u00a0 PV operates in the morning and starts to run down after 3 or 4 PM.u00a0 So 2 or 3 hours of storage won’t cut it.u00a0 More like a minimum of 7 or 8 hours.u00a0 That’s football field after football field of batteries and lots of costs.nnUnquestionably,u00a0a lot of PV will get built, especially as prices continue to fall from overseas PV manufacturers, but the role of solar thermal with high efficiency storage will play a role in our energy solutions in the US.u00a0u00a0International markets may be a good market for this US designedu00a0technology as well, asu00a0less robust transmission systems need the stability of solar thermal with storage rather than the minute-to-minute swings of PV and wind.

      • You raise some good points — especially about the necessity for extended storage. Thanks for commenting.

    • Solar Guy

      The author seems to be ill informed about the subjects he is discussing. Does he know the difference between a kWe and a kWh? It is clear from his article that he doesn’t. He is comparing a plant that will probably generate 2.5 times as much electricity as a PV plant of the same electric capacity. Does he realize that a lot of people want to come home after work and turn their lights and TV on (I do). nAccording to his own numbers it would cost $50,000,000 for every nhour of battery storage for a 100 MWe PV plant.That is a lot of lead acid batteries that have nto be replaced and recycled every 5 years or so. The author is also comparing the cost of a mature technology like PV to a first of a kind plant. We would never build any new technology if the first unit had to compete with existing commercial technology. This is the whole reason this project was eligible for the federal loan guarantee program.u00a0

    • Tex Wilkins

      nnnnnnnnnnnnnnnnnnJohn:nnnu00a0nnnYou are notnalone in trying to better understand the potential of solar thermal poweru2019snstorage. As intermittent renewable resources (wind and solar) provide annincreasing percentage of the electric grid, many others are also pondering whatnrole solar thermal with storage can play in cost-effectively maintaining anstable and reliable grid. These include the Department of Energy, CalifornianEnergy Commission, and the Electric Power Research Institute (EPRI), each ofnwhich is studying the impact of storage on the electric grid. People requirenpower when the sun doesnu2019t shine and the wind doesnu2019t blow. This poses problems,nhowever, for those responsible for operating the grid.nnnu00a0nnnSeveral recent studiesnhave broached the subject and initial findings suggest that solar thermal withnstorage has a critical role to play in meeting our clean energy goals whilenmaintaining a stable grid. A study by the Lawrence Berkeley National Lab pointsnout that solar thermal with storage is roughly $10/MWh more valuable than solarnwithout storage based on time of day energy value and capacity value.[1]nNavigant, along with Sandia National Laboratory and the Pacific NorthwestnNational Laboratory completed a study for NV Energy that indicated thatnintegration of PV into the Nevada grid will result in both higher operatingnreserves and fuel costs because of the complexity of managing the fluctuationsnof PV power.[2]nThe National Renewable Energy Laboratory (NREL) released a report indicatingnthat the inclusion of solar thermal plants with storage provides flexibilitynthat mitigates those fluctuations and will enable more PV systems to benintegrated into the grid.[3]nu00a0These studies are just the beginning.nMuch more will be learned of the potential of thermal storage when studies bynNREL, EPRI, and various system operators are completed in 2012.nnnu00a0nnnThere were ancouple of points in your article that I would like to clarify. You accuratelynmentioned that the comparison of the SolarReserve project to a similarly sizednPV plant u201cisnu2019t precisely apples-to-apples.u201d Thatu2019s correct. u00a0SolarReserveu2019s solar thermal project, with 10nhours of storage already integrated into the system, would generate almostntwice as much energy as the PV plant each year. You also mention that 6 hoursnof battery storage could be added to bring the cost of PV to the same level as solarnthermal. This would be very expensive. Using your estimate of 50 cents/W fornbattery storage, the cost of 6 hours of storage for a 110 MW plant would ben$330 M and those batteries would have to be replaced every 5 years whereas thenthermal storage is expected to have a lifetime of well over 20 years. Hopefully,nresearch on battery technology will increase their life expectance and lowerntheir cost. Similarly, however, the cost of solar thermal technology isnexpected to decrease. nnnu00a0nnnThe costncomparison of solar thermal to PV is also not an apples-to-apples comparison.nPV is a much more mature technology than solar thermal. Due to government actionsnin the U.S., Japan, Germany, and China, the cost of PV has dropped dramaticallynin the last ten years. Recent actions by Spain and the U.S. are just startingnto drive down the cost of solar thermal. This has led to over 1 GW of solarnthermal projects now being constructed in the U.S. This is three times as muchnas has been built in the U.S. to date. It is expected that these projects willnbring about lower costs. Whether or not the decrease follows the steep downwardncost trajectory of PV or wind remains to be seen. nnnu00a0nnnThenfinal point I would like to make is that this is not a race to see if onenrenewable technology is better than the others. There are issues and benefitsnwith each. The NREL study shows that PV and solar thermal are complementary. Solarnthermal technology with storage provides the flexibility that may result innmore PV being integrated safely into a grid that was not designed fornintermittent renewable energy. It will take the studies now underway tondetermine the potential of solar thermal poweru2019s storage to provide cleannenergy while helping maintain a stable grid.nnnu00a0nnnFrank (Tex)nWilkinsnnnConsultant andnuntil August 2011 the CSP Team Leader at DOEnnnnnnnnnnn[1] Mills, Phadke, and Wiser, Exploration ofnResource and Transmission Expansion Decisions in the Western Renewable EnergynZone Initiative, Environmental Energy Technologies Division, Lawrence BerkeleynNational Laboratory, LBNL-3077E, February 2010,, et al, Large-Scale PVnIntegration Study Preparednfor NV Energy, July 30, 2011,, Mehos, Enabling Greater Penetration of Solar Power via the Use of CSPnwith Thermal Energy Storage, NREL/TP-6A20-52978, November 2011.u00a0nnnnnnnn

    • logeshs

      Solar is one of the most safest and quickest way to store and generate energy when in need. The life time of solar is always higher than all other techniques and it reduces electricity bill of our routine needs.