The storage capacity of concentrating solar power (CSP) can add significant value to a utility company’s optimal mix of energy sources, a new report by the US National Renewable Energy Laboratory (NREL) suggests.
The report is said to have found that CSP with a six-hour storage capacity can lower peak net loads (the normal load minus variable renewables) when the sun is not shining — enough to add $35.80 (£22.33) per megawatt-hour to the capacity and operational value of the utility compared with photovoltaic (PV) solar power alone, and even higher extra value when compared with CSP without storage.
According to a statement, the additional value comes because thermal storage allows CSP to displace more expensive gas-fired generation during peak loads, rather than displacing lower-priced coal, and because it can continue to flatten the peak load in the evenings when PV is not contributing to the mix as the sun has set.
The report, ‘Simulating the value of concentrating solar power with thermal energy storage in a production cost model’, by NREL’s Paul Denholm and Marissa Hummon, noted that the $35.80-per-megawatt extra value would come in a scenario in which there is relatively high penetration of renewables into the utility’s mix — about 34 per cent. If the penetration was lower, the extra value would be lessened.
The authors simulated grid operations in two balancing areas primarily in Colorado.
The Colorado study marks one of the first times that the operational and capacity value of CSP with thermal storage has been evaluated using a production cost model.
The NREL authors employed Energy Exemplar’s PLEXOS simulation model, which allowed them to isolate the relative value of thermal energy storage (TES) with and without storage.
CSP with TES, with an ability to store thermal energy in, say, molten salt, can use its heat energy to drive turbines at power plants over much longer stretches of the day.
‘We’ve known for a long time that CSP with storage adds significant value; however, we are now able to quantify this value in the language utilities understand,’ said Mark Mehos, manager of NREL’s Concentrating Solar Power programme.
Compared with other renewable options, at high penetration levels CSP with TES can be despatched to displace natural gas rather than coal — an important consideration as electricity produced from natural-gas-fired generators is typically more expensive than that produced from coal.
‘With CSP with thermal storage, you aren’t diving as deep into the generation stack, displacing cheaper and cheaper fuel,’ Denholm said. ‘You’re always displacing the highest-cost fuel.’
Also, CSP with TES can lower peak net loads in the evenings when electricity use can still be high but PV is not available, thereby helping utilities offset the need to build new gas-fired generators in order to meet the electricity demand when the sun goes down.
‘CSP with thermal storage can continually reduce that peak demand as the peak moves into the evening,’ Hummon said. ‘It continually maintains a high operational value and high capacity value.’