CSP plants store heat for up to nine hours

CSP plants store heat for up to nine hours

Supporters of concentrated solar power (CSP) are working hard to secure what they regard as their technology’s rightful place in the sun.

Government has allocated a relatively minor role to CSP in SA’s future energy mix. This is mainly because CSP is more expensive than other renewable energy technologies such as solar photovoltaic (PV) and wind.

What this overlooks, says the CSP lobby, is that the technology is the only form of renewable energy capable of supplying electricity during peak demand times – when Eskom needs additional supplies to keep the lights burning.

CSP, they point out, has the ability to store heat energy, which is then used to create steam to drive a turbine and to generate electricity during cloudy periods or after sunset.

"CSP costs more because it delivers more," says Jonathan de Vries, CE of the Southern Africa Solar Thermal & Electricity Association (Sastela), which represents the CSP industry.

CSP, he says, also creates more construction, operation and manufacturing jobs than other forms of renewable energy. That is a major contribution to the development of a manufacturing-based green economy sector, which government hopes will create about 460000 jobs.

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Government’s Integrated Resource Plan (IRP), which projects SA’s energy mix until 2030, has allocated only 1200MW of the 21500MW of renewable energy the country will need to CSP. This is equivalent to 1,5 units of a major six-unit Eskom coal-based power station – such as the 4800MW Medupi plant under construction in Limpopo.

Wind power has been allocated 9200MW and solar PV 8400MW, with the balance made up of biogas and imported hydro power.

Of the initial 3725MW of clean electricity government is procuring under its Renewable Energy Independent Power Producers’ Procurement Programme (REIPPPP), CSP has been allocated 200MW. Three CSP projects, all in the sun-drenched Northern Cape, have been given preferred bidder status. The first two are scheduled to come online by mid-2015 and will sell electricity to the national grid at R2,60/kWh. The third will sell electricity at a marginally lower R2,51/kWh.

By comparison, the price of solar PV under the REIPPPP has dropped from R2,70/kWh in the first round to R1,64/kWh in the second, and wind from R1,14/kWh to 89c/kWh. The Eskom average standard tariff is about 60c/kWh, but this is expected to rise above R1/kWh over the next five years, while costs of renewable energy technologies are likely to decline significantly.

Part of the reason for CSP’s higher cost is the addition of heat energy storage facilities. The first two stations will have between two and three hours of storage, and the third as much as 9,5 hours. This will enable the third CSP station to approximate the generation capability of an Eskom coal-fired power station, says Michael Goldblatt, a member of the consortium that will build this CSP plant.

The intermittency of wind, and the inability of solar PV to include mass storage means that "only CSP with storage can provide electricity at peak times, when the national grid needs it most", says De Vries. "The costs of CSP will also continue to decline as the technology gains traction and improved economies of scale as well as new efficiencies are built into it, while the Eskom tariff will continue to rise sharply, making CSP increasingly competitive."

An issue of great concern to Sastela, he says, is the fact that the IRP has allocated about 5000MW of additional open cycle gas turbine (OCGT) capacity that operates on imported diesel – and which Eskom currently operates as an emergency back-up during peak-time generation.

According to information given to parliament by the minister of public enterprises, Eskom’s two OCGT plants generated electricity at an average cost of R2,47/kWh and consumed R1,55bn worth of diesel over a seven-month period from August 2011 to March 2012.

"The first CSP power stations in SA will generate electricity at between R2,68/kWh and R2,51/kWh, which is on a par with the OCGT power stations," says De Vries. "And instead of using diesel as their fuel, CSP power stations use the free energy of the sun. CSP can provide clean, environmentally friendly electricity to support peak-time generation, support local manufacturing and generate jobs."

In addition, he says CSP can help to reduce SA’s excessively high carbon emissions from coal-based electricity generation, of which Eskom accounts for 220Mt, or about half of the country’s total emissions. Spanish company Abengoa estimates that its Khi and KaXu plants will reduce carbon emissions by about 500000Mt/year.

De Vries says Sastela is engaging government and other interest groups to increase CSP allocation significantly.

Sastela chair Ayanda Nakedi, who heads Eskom’s recently formed Renewables Business Unit, which is developing the utility’s own CSP plant, says: "CSP with storage can go a long way to addressing our country’s peak demand. We need to embrace CSP and allocate it a greater role in our energy mix."

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