By Sam Phipps
The price imperative is crucial. CSP costs are forecast at around $208/MWh in 2015, according to the International Energy Agency’s Technology Roadmap – double the rate for onshore wind and more than three times the cost of biomass.
Increasingly, innovators are responding with bespoke solutions that combine CSP with a range of other fuel sources, from coal and gas-fired plants to biomass. The most obvious initial saving is through joint use of equipment such as steam turbines and condensers.
At a stroke ISCC (integrated solar combined cycle) plants can cut LCOE in this way by up to 30%, depending on size and location, as well as soothing the worries of investors and technology providers who might otherwise be fazed by the notion of an all-new construction. This in turn will tend to mean faster implementation.
Converting open cycle gas turbine (OCGT) and combined cycle gas turbine (CCGT) plants to ISCC ones can also bring relatively high capacity without capital-intensive storage. Moreover, an ISCC plant has a lower DNI (direct normal irradiance) requirement and can easily compensate DNI variations, meaning CSP plants can be sited closer to load centres.
Biomass
CSP-biomass hybrids offer an attractive alternative to thermal energy storage in locations where long hours of power generation are demanded. They can thus bring consistent energy supply for industrial processes and power generation.

The use of biomass can also deliver economic and employment benefits in local economies.

The first CSP-biomass hybrid plant, Termosolar Borges, near Lleida in Spain, opened in December 2012, with a peak capacity of 22.5MW of which up to 12MWe is from biomass.

Termosolar Borges is 90 miles west of Barcelona, in a region rich in agriculture and horticulture, which provides an abundant biomass resource to complement the high levels of sunshine.

The 150million Euro investment uses parabolic troughs with thermal oil as the CSP component while the biomass component consists of two grate type boilers/heaters.
Both biomass boilers/heaters are integrated into the thermal oil loop of the parabolic trough system; gas firing is available for back-up. The solar field generates saturated steam at 40 bar and the biomass boilers superheat this steam to 520°C. The plant will create 30 direct and 150 indirect jobs over its 25-year lifetime.

Researchers at the University of Technology Sydney are investigating whether such technology could be successfully applied in many areas of Australia, using optimal CSP-biomass plant configurations to suit the similar regional conditions.

Waste biomass is available in almost any environment for CSP but a plant has to be sited close enough to the source to make it economical. BraxEnergy has done that in north-eastern Brazil, planning its first CSP plant in the town of Coremas, Paraiba state, within 30 miles of multiple coconut farms that have few secondary markets for their shells.
Australia could also be ripe for many ISCC plants, according to some scientists, because of its abundant natural gas reserves and excellent solar conditions.

A DNI of ≥2,000kWh/m2/year is usually needed for standalone CSP plants but ISCC cost reduction benefits, such as joint use of equipment, can bring regions with a DNI of ≥1,700kWh/m2/year and natural gas resources into consideration.

In Australia several locations in New South Wales, Queensland, Western Australia and South Australia fit that bill. Most of them are remote or off-grid with far higher electricity prices than the national average, which is among the OECD’s lowest.

In addition natural gas prices are expected to rise sharply in the coming years owing to large LNG export facilities coming on stream. This could favour the use of CSP systems as fuel saver systems.

One UK company at the forefront of CSP innovation is 20C, which is developing a hybrid system that would combine CSP and ISCC plants with existing gas pressure reduction sites. The aim is to provide a much cheaper and more effective form of condenser cooling than the vast amounts of water that are usually needed, according to Andrew Mercer, its CEO.

“Condenser cooling is a major challenge for CSP and ISCC plants, since such plants are typically located in arid desert areas. It represents one of the significant barriers to the growth of CSP as a renewable, low carbon technology,” he said.

20C’s iQuadgen® Hybrid CSP would raise output, improve electrical efficiency and cut capital costs.

“It would reduce the development cost for a typical CSP plant from $17.5 million per MW to $5.4 million per MW at today’s prices for a typical sized plant,” Mercer said.

Adding a fuel cell or engine, running on bio-energy, to provide heat when the solar heat source is not available, could further reduce this to $4.3 million, although with increased operating cost to reflect the fuel needed to run the engine.

iQuadgen® Hybrid CSP also provides a heat source for the pressure reduction station.

Baseload tracking means iQuadgen® CSP will balance the generation of solar electricity with the generation of electricity from the turbo expander and, if necessary, from a bio-energy based heat source to meet the demands for electricity irrespective of the time of day or time of year.

A 20C spokesman said a team of Swiss consultants NEP had analysed a solar-only plant in southern Spain and an ISCC plant in North Africa with iQuadgen® applied and found “very low condensation temperatures can be achieved without external water cooling”. Electricity yields were also 20% higher than with air-cooled condensers.

In summary, hybridisation looks set to play a key role in the development of CSP.

To comment on this article please contact the editor, Jenny Muirhead