Concentrated solar booster projects for coal-fired power stations in South Africa can be constructed within about 18 months, can provide about 10% extra electricity and can be constructed using more than 60% local content, says French nuclear firm subsidiary Areva Solar business development lead Mikael Hajjar.
The solar boiler uses compact linear Fresnel reflector (CLFR) technology, which consists of a solar array field of low-iron flat mirrors that focus sunlight up to a central receiver in which water boils into super-heated steam (up to 482 ºC). This steam is then injected directly into the coal-fired power station’s boiler to generate additional power without added emissions.
Further, the system is compatible with the dry-cooling designs of the Matimba and Medupi coal-fired power stations, in Limpopo, and can be used in a closed-loop system to conserve water.
“The advantage of the CLFR technology is its small land footprint. One booster will require about 6 ha, which, under Matimba’s sun, is above 7 MW electric or 22 MW thermal.
“Further, from the moment we receive notice to proceed to the final commissioning date, it will be reasonable to achieve completion within 18 months to deliver a 50 MW boost to Matimba, for example,” says Hajjar.
The boiler design has American Society of Mechanical Engineers S-stamp certification and is similar to a conventional boiler, which means it fits into South Africa’s skills profile.
“The carbon steel piping and the frame structure for the booster can also be sourced locally relatively easily and our estimates indicate that we can easily reach above 60% local content, and that 80% local content is reasonably achievable,” he adds.
Over the longer term, Areva Solar aims to grow local capacity and, once South African industries can provide supplies more readily, it will be able to lower costs and progressively achieve standalone stations with a competitive price tag, compared with standalone photo- voltaic (PV) stations.
Areva Solar was the first to successfully augment a coal-fired power plant using its CLFR system. Its integrated solar steam generator performance has been proven at the Liddell facility, in Australia, since 2008. The company is currently constructing a 44 MW solar augmentation facility at another coal-fired power station in Australia and recently announced a partnership with US utility Tuscon Electric Power to build a solar booster at a duel-fuelled generating station in Tuscon, Arizona.
“It is a proven and simple technology with more than 500 MW electric under construction, under contract or in advanced development in India, Australia, North Africa and the US.”
The technology was designed as a conventional boiler for hybrid application. However, Areva Solar will deliver the first of several 125 MW standalone concentrated solar power (CSP) plant units late next year.
However, a lack of policy framework for the technology is preventing it from competing effectively against other renewable technologies, such as PV and wind.
“Until policymakers have modified regulations to support steam tariff booster applications, which will enable us to compete on price with PV, currently our only way to compete is through a smaller land footprint and high local content,” he notes, adding that the technology offers up to 20 minutes of thermal inertia under cloudy conditions, which reduces its variability and which has not been addressed by government policy frameworks.
Areva Solar’s CLFR technology is able to reliably produce super-heated steam at 370 ºC through partial cloud cover. Further, the arrays are aligned south-to-north and the single-axis mirrors track the sun east-to-west. In its technology development roadmap, Areva Solar also has both a short-term and a longer-term storage solution for CSP standalone product offerings.
“AREVA Solar responded to the South African Depart of Energy’s request for information for over 150 MWe net of Solar Thermal Co-Generation Energy Projects with both State-owned power utility Eskom and independent power producers (IPPs).
“After the flue gas desulphurisation boilers technology currently under installation at Kusile Power station and before the future carbon capture and storage technology can be deployed, solar boosters represent the lowest hanging fruit for Eskom toward a clean coal fleet and it should set the example and lead the way so that prospective IPPs are incentivised to carry on similar development efforts.”