(Image credit: Lisa Blue)

Utility off-takers and regulators are increasing their support for CSP with storage, Scott Frier, COO Renewables of ACWA Power, said.

The storage capacity of Abengoa Solar’s 280 MW Solana project was a key reason the Arizona Public Service (APS) agreed to purchase 100% of the power from the plant, according to Frier.

With a storage capacity of 1,680 MWh/day, the Solana plant represents the largest non-hydro storage power plant in the US.
Frier was formerly Chief Operating Officer of Abengoa Solar in the US and developed the 280 MW Solana project.

The increasing reliance on solar PV plants has raised the need for other units to supply nighttime hours, in particular the evening and early morning periods.

“We are already starting to see and feel the impacts of solar PV penetration, so the big variable for us is how much will get installed in rooftop on our customer premises,” said Brad Albert, the Resource Acquisition General Manager at APS, who negotiated the Solana PPA with Frier.

The increasing deployment of PV on the APS daytime grid is reshaping the load and impacting the wholesale power market there.

"Power prices are no longer lowest at night. Now they are lowest during the day,” Albert said.

Hot and Cold

As more PV is added to the grid, supplying daytime power, the value of CSP storage has increased, because it can shift generation into the evening peak.
Many utilities face evening peak loads as people come home from work.

The differential between the daytime and nighttime supply-demand balance is widened when more solar PV is put on the grid to provide daytime load.

In the Arizona Public Service (APS) area, the number of PV rooftop arrays soared from 900 in 2010 to 18,000 in 2013.

California now supplies 7.4% of its daytime load from solar PV, from behind-the-meter and utility-scale plants.

Desert environments get cold at night in winter. The hour before sunrise is one of the peak demand times for APS. The ability to store power overnight for heating the next morning has become very useful, because APS serves many older homes that depend on electricity for heat, Albert said.

"The most critical periods for us are right after sundown, and in winter; before sunrise as well. Our territory has a very high electric load, versus a lot of places like California, where people use gas for heating," he said.

Hot prospects

In the early years of CSP development in Spain and the US, regulators did not require that CSP include storage.

Now, storage with CSP is commonly favored by utilities with rising PV penetration such as Arizona’s APS, and in countries with the best CSP conditions, storage is often required through legislation.

In South Africa, Morocco, Chile and Saudi Arabia, regulators and off-takers either offer a higher tariff for evening generation or they simply specify a minimum number of hours of storage, which similarly ensures that solar generation can be stored to cover the evening peak demand.

The Moroccan Agency for Solar Energy (MASEN) offers a tariff which is 15% higher after sunset, to power the evening peak demand.

The Renewable Energy Independent Power Producer Procurement Program (REIPPPP) in South Africa pays an even higher tariff for evening solar generation, some 270% of the daytime rate (almost three times higher).

Every CSP project awarded in South Africa has included storage, and storage capacities have increased rapidly in capacity and technological maturity from just two hours per day at Khi Solar in 2011 using steam, to 12 hours daily at Redstone by 2015, using state-of-the art molten salt.

South Africa’s strong storage incentive has sped the rate of its CSP growth. The deployment target is 1.2 GW of CSP by 2030.
In the first four years of the program, South Africa has received bids to meet 600 MW, half its 2030 goal. Once these projects are complete, South Africa will have enough storage to generate 2,500 MWh/day when needed, for example before sunrise or after sundown.

The above graph is from the CSP Today Markets Report 2015 Series- South Africa

In neighboring Namibia, state-owned utility NamPower specified in early 2015 that CSP bids must include six to eight hours of storage to handle its very dominant evening peak.

In the Middle East, a minimum of four hours storage will be required in Saudi Arabia's initial bidding round, and more in subsequent rounds. Although it has yet to offer RFPs, Saudi Arabia has indicated that it favors CSP over PV, targeting 25 GW of CSP by 2040, compared with a PV target of 16 GW.

Chile now leads the world in thermal storage under construction with 3,575 MWh/day planned, from Abengoa's Atacama 1 and 2 and if awarded as expected next April, SolarReserve’s fully permitted Copiapo will add another 3,640 MWh/day.

Chile requires a minimum of three hours of storage at 85% load, and limits the use of backup fuel for keeping thermal fluids from freezing overnight - forcing developers to include storage to at least cover parasitic load for morning startup.

The US state of California, like Arizona, does not specifically require CSP plants to incorporate storage, but regulators and grid operator CAL-ISO have indicated their preference for projects with storage.

California Governor Jerry Brown recently announced a target of 50% of energy from renewable sources by 2030 and the state assembly is now refining new legislative proposals to meet this aim.

“If storage is incorporated into renewable requirements in the US then we immediately become competitive,” said Kevin Smith, CEO of SolarReserve, the California-based CSP and PV developer.

Early contracts awarded under the first Request for Offers to meet California’s mandate for 1.3 GW of storage have largely been allocated to battery technologies and peaker plants using natural gas.
 

By Susan Kraemer