Gemasolar has 15 hours of storage and supplies electricity to 25,000 homes in the Andaluc

By Alison Ebbage 

In a recent study the US National Renewable Energy Laboratory (NREL), simulated the value of CSP in the energy grid in California in a scenario where 33% of the energy mix was sourced from renewables. It looked at the value of CSP with thermal energy storage (TES) to plants without storage. The incremental value of CSP with TES was $30/MWh to $51/MWh compared to a baseload resource, or $32/MWh to $40/MWh compared to PV.
Because the storage capacity of CSP allows for timed release of power into the grid, CSP’s value to the overall energy mix is high. The California report follows a similar study conducted in Colorado last year and drew similar conclusions. The figures were arrived at using a combination of avoided fuel (and associated emissions) as well as reduced operations and maintenance (O&M) and power plant start costs. In addition to operational value, generators add capacity value to the system that can be estimated by examining generator operation during periods of high net demand.

Paul Denholm, one of the authors of the NREL reports comments: “The reports simulated the value of CSP in the energy grid. There are very few utility companies that include CSP in their overall production cost model planning tool and we wanted to see what would happen. We found that CSP with storage had enough value to displace higher cost fuels. This is not just a monetary value it is based on its value to the grid in terms of overall power provision.”

Another report, by the CSP Alliance, also looked at the worth of CSP with storage. It summarised a broad cross-section of analysis conducted by the national energy labs and academic institutions and again found that the worth in terms of both monetary value and value to the grid as a whole of CSP with storage is high.

Timing

Effectively the worth of CSP with storage lies in the fact that a six-hour storage capacity can lower peak net loads when the sun isn’t shining. The net load is the normal load minus variable renewables such as photovoltaic and wind. CSP can also continue to flatten the peak load in the evenings when PV isn’t contributing to the mix because the sun has set.

In practice this allows utility companies the flexibility they need to meet varying peak demand times and to react instantly to an upsurge in demand. For example in California peak demand is mid afternoon when people want to use air conditioning but in other areas peak demand is early morning or early evening. And in MENA peak demand is for heating and lighting at night so there especially CSP with storage has inherent worth.

Complimentary
The added value of CSP with storage increases in line with the uptake in renewables as a whole. The Californian aim is to reach a renewable contribution of one third by 2020 and the latest report simulated this renewables percentage. Far from competing with PV, the two are actually working in harmony and to each others’ strengths. The value of the storage works both to replace PV’s day time contribution and crucially to avoid replacing PV with fossil fuels.

Frank Wilkins, executive director at the CSP Alliance comments: “Once PV reaches above five or six percent of the grid then there is an issue with peak demand and daylight.”

And the value of storage has been reflected in two recent US plants that have been approved; both contain significant amounts of storage. Firstly, the BrightSource Sonoran West project. It is the first from the company to include storage and received approval from the California Utilities Commission, (CPUC) in Oct 2012. CPUC President Michael Peevey said: “The operational flexibility provided by storage significantly improves the value this [Sonoran West] facility brings to the grid compared to most other sources of renewable energy.”

Added to this is Solar Reserve’s Rice project which received CPUC approval in Jan 2013. It has a 150 MW tower with 8-10 hrs storage.

Denholm says: “The perception of CSP will certainly improve. Although PV is lower cost it is not as flexible and CSP with storage can add so much value to the overall mix. Although CSP is not currently in the analytical model used by the big utility companies they almost certainly now will need to reevaluate and include it.”

Wilkins adds: “In the long term both the utility companies and grid operators know that they need the flexibility that CSP can provide and thus will be more favourably inclined towards CSP. Although its starting base is lower its growth rate is reassuringly high.”