By Jason Deign in Barcelona

Mike Keller remembers the time he presented his hybrid power concept at a green energy conference in Des Moines, USA. “I was not sure how we would be received,” he says. “But I was quite surprised. Nobody threw any tomatoes at us.” 

His unease was understandable. While the renewable energy community is well used to odd partnerships, from CSP with gas to concentrated PV with wind, Keller’s proposal involves a tie-up with one fuel source many green power pundits regard as anathema: nuclear.

Specifically, Keller’s company, Hybrid Power Technologies, aims to create high-efficiency, low emissions plants using a small modular reactor (SMR) to compress air going into a combined-cycle power block.

CSP-nuclear synergies

While primarily designed to improve coal or natural gas power generation, the concept could also improve the efficiency of CSP when configured as a hybrid nuclear integrated solar combined cycle (ISCC) plant, Keller says.

Keller calculates such a configuration would have a much greater yield than a traditional ISCC, with a steam turbine output of 228 MWe (compared to 132 MWe for an ISCC), station net output of 785 MWe (versus 228 MWe) and station generation of 1,693 GWh (against 627 GWh).

And this is along with significant emissions reductions compared to a traditional ISCC: 0.25 tons per MWh, against 0.41. In Des Moines, says Keller, “Folks were very interested because the hybrid concept is able to move renewable energy into a much more competitive environment.”

Keller is not the only one who sees synergies between CSP and nuclear power. Mark Lewis, an elected official of the State of Arizona, has got legislative support for a concept called ‘energy parks’ where SMRs would sit alongside solar thermal plants.

In his view, solar field deployments could be able to give investors a positive cash flow within three to four years and help fund longer-term nuclear developments that would ultimately provide the bulk of base load power, with all the parks’ output being emissions-free.

Lewis’s view is that without nuclear the US will see a proliferation of single and combined-cycle gas plants to provide base line and backup power as more renewable energy is fed into the grid—and that will not help with emissions.

“Hooking CSP to a natural gas-fired peaker is pretty much standard procedure for the next 20 years,” he says. “Corporate financiers are happy to finance single-cycle or combined-cycle gas because they show a profit in a short amount of time.”

Taking aim at gas plants is all well and good, but CSP purists may rightly question whether solar thermal really needs nuclear, particularly if advances in heat storage can overcome intermittency issues.

Fuel consumption

“I think there are a couple of issues,” says GTM Research senior analyst Brett Prior. “Why you would do this is that you do not want to burn that much of the fuel, so by using solar you are reducing fuel consumption.

“But it’s not like you are going to turn down the nuclear plant because it’s sunny. And it doesn’t clearly satisfy the goals of renewable portfolio standards or feed-in tariffs.”

Finding suitable sites could also be an issue for hybrid plants, he says; nuclear power tends to need water while CSP is best suited to deserts. But the bigger question is probably whether the economics make sense. Right now, neither CSP nor nuclear are cheap.

According to figures from the US National Renewable Energy Laboratory, the investment needed for a 100MW CSP plant with six hours of storage would result in a cost of energy of around USD$0.14/kWh.

The figures for nuclear are more debatable, partly because of a dearth of recent projects on which to base up-to-date estimates. Prior cites studies that point to around $0.11/kWh, beating CSP.

But other estimates, which may still be conservative according to US congressional budget reports, translate to a cost of energy for nuclear of around $0.17 to $0.22, making CSP quicker, cleaner and cheaper to deploy.

Admittedly, the SMRs proposed for hybrid deployments supposedly cost around a tenth of a traditional nuclear power plant.

However, they are a technology that has yet to prove itself in practice; World Nuclear Association deputy director general Steve Kidd says none have been licensed even though the concept has been around for years.

And some of the figures being juggled by hybrid plant promoters seem slightly optimistic on the nuclear side. Mark Lewis says: “Nuclear is on a par with PV solar. CSP economies are a little better but you still have to replace all the plumbing every few years.”

Even with a renewal cycle well under the proven two-to-three decade lifespan of current CSP plants, it is reasonable to ask whether the decommissioning costs for solar thermal could ever approach those for nuclear. There may be a case for hybrids, but it remains to be proved.

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Jason Deign: jdeign@csptoday.com

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