By Jason Deign

An increasing appreciation of the potential for combining CSP with PV is leading to the question: what about wind? Wind power and CSP rarely get considered together. But a close scrutiny of the cost of storing wind power reveals there could be a case for hybrid plants.

“It’s not quite as complementary [as PV],” said Kevin Smith, chief executive officer at SolarReserve, and there are “higher intermittency issues,” but wind power has the advantage of being even cheaper than PV. “It really is about cents per kilowatt an hour.”

As with PV, the main reason for adding CSP to a wind farm is to take advantage of the potential for low-cost energy storage using molten salts. Wind power is, if anything, even more intermittent than PV. Grid operators currently deal with this intermittency in a variety of ways.

At low levels of penetration, it is usually enough to rely on day-ahead forecasting to assess output and ramp other forms of generation up or down as needed to compensate for the variable power coming off wind farms.

And over large enough regions, ups and downs in production in one place tend to be balanced out by ups and downs elsewhere. As wind power penetration grows, however, there is an increasing need to curtail excess production so as not to overload the grid.

In places with favourable geography, an alternative to curtailment is to use pumped hydro storage to store excess output for use later on. This has been highly successful in markets such as Spain, where wind power accounted for a fifth of all energy generation in 2014.

But pumped hydro is unlikely to be an option in many desert environments where CSP, conversely, might be well suited. Furthermore, the other option for storage, batteries, is still far from being cost effective.

As an example, Southern California Edison’s Tehachapi Energy Storage Project, where batteries store wind energy, delivers 32 megawatt-hours of storage and cost a reported USD$49.9 million, which translates to more than $1,500 per kilowatt-hour.

Present-day costs

The SolarReserve Crescent Dunes project, in comparison, has 35 times as much storage, includes energy generation and cost less than $150 million (for the molten salt circuit), making it about a tenth of the price of Tehachapi on a like-for-like basis. And that is on present-day costs.

In the near future, however, CSP plants could become much cheaper. SolarReserve estimates that compared to Crescent Dunes it can reduce the cost of its upcoming Redstone project in South Africa by 20% through heliostat design advances alone.

Many CSP observers agree that it makes sense to see CSP as complementing rather than competing with other renewable generation sources, including wind.

In a LinkedIn debate sparked by a CSP Today story on competition between CSP and wind, for example, a number of experts came forward to defend putting the two together and in particular making better use of the heat output from solar thermal plants.

“Wind and CSP are two different forms of energy which can be used for different applications,” said Michael Goth, general manager at STEAG Energy Services in Germany.

“Developers need to determine the best mix to maximise these resources and perhaps storage is the meeting ground for the chosen systems,” chimed Nigel Spink, a former senior project manager with ABB.

“The output, whether it is electrical energy, heating, cooling on a local or district level, or desalination, may depend upon the location.”

Hybrid projects

Despite this apparent level of appreciation for the synergies between CSP and wind, developers have yet to propose any hybrid projects of note. But it is worth highlighting that some major CSP players also have significant experience in wind power, particularly in Spain.

Acciona, for example, is known for its expertise in wind as well as PV, hydro and biomass project development. FCC Energy, meanwhile, has a portfolio of 14 wind farms with an installed capacity of almost 421MW on top of its two 50MW CSP projects.

Grupo TSK and Ibereólica are among other Spanish firms that have significant track records in both CSP and wind project development.

What these companies perhaps lack is SolarReserve’s track record in molten salt power tower designs, which are arguably the best in terms of storage capability.

But the Spanish companies are catching up fast: at Ouarzazate in Morocco, for example, Acciona and TSK are working with Sener and Aries on a project for ACWA Power that will include a power tower with molten salt storage.

Given the diversity of project experience in these companies, it is perhaps just a matter of time before one of them proposes a development combining CSP with wind.

“One may expect that local communities in desert countries will actively drive small wind and solar energy applications,” confirmed Paul van Son, country chairman for RWE in the Middle East, North Africa and Turkey.