How CPV trumps CSP in high DNI locations

High solar irradiation is not just ideal for CPV, but for solar thermal development as well. What advantages can concentrated PV offer to sway developers in its favour?

Thinking of developing a solar project in the Chilean Atacama Desert or South Africa’s Northern Cape? If so, you will probably want to extract the maximum value from the high levels of direct normal irradiance (DNI) available. And that means you have got a couple of obvious options.

On one hand there is CPV, the most efficient form of photovoltaic energy around. And on the other is concentrated solar power (CSP), or solar thermal energy, which has a very different set of characteristics. Choosing between the two is not straightforward.

“With CSP, whilst it is still arguably in its infancy, it is arguably much more easy to demonstrate it being a technical solution that works,” says Charlie Richardson, class underwriter at the renewable energy insurer GCube.

“The Spanish market has been there for a long time, operating without too many problems at a commercial scale. And when you look at the main generating equipment, the steam turbine and the boilers, it is commercially available equipment which isn't prototypical at all.”

All this adds up to powerful reasons why solar developers might pick CSP over CPV. “It's a no-brainer, really,” Richardson says. “If you're going to build commercial-scale solar then CSP, particularly parabolic trough, is the obvious solution.

“CPV is a great idea, great potential, but still very much the baby of the group.” This does not mean CPV is without its merits for a wide range of projects, though.

A potential drawback for CSP is that you cannot build a solar thermal plant piecemeal, says Tim Keating, vice president of marketing and field operations at Skyline Solar.

Water use

“The beauty of Skyline’s solution is you can build modular plant systems, whereas with other solutions it’s all or nothing,” he says. “You don’t know until it’s commissioned what you’re getting.”

CSP also loses out to CPV on water use, which is potentially an important consideration in many desert regions. “High DNI and fresh clean water are mutually exclusive,” notes Keating. “They need thousands of tons of water per megawatt, and we don’t.”

Finally there is the levelised cost of energy (LCOE). CPV already beats CSP on this measure and analysis by GTM Research indicates it could reduce its costs more quickly than any other solar technology.

CPV’s LCOE is already on a par with other PV and solar thermal energies and is expected to overtake them, and natural gas, during the course of this year.

Meanwhile, bringing down the cost of solar thermal is difficult because of the relatively immovable price of major items such as steam turbines. “It’s a technology whose time came and went,” Keating says.

Brett Prior, senior analyst at GTM Research, agrees that CPV has an advantage over CSP in terms of cost, water use and modularity. The minimum project size for solar thermal is about 50 MW, he says, whereas CPV projects can be brought on line in 5 MW to 10 MW stages.

In addition, CPV does not take up as much land as CSP, which may not be much of an issue in deserts but could be in some solar markets, such as Italy.

Cost and modularity

In fact, although the key factors are “mostly cost and modularity,” Prior says, in a study last year GTM Research found CPV compared favourably to other solar technologies on six measures: LCOE, modularity, water use, capacity factor, solar-to-electric efficiency and land use.

“Where CPV loses out it is because [the industry is made up of] smaller companies, so bankability can be a problem,” says Prior.

Although Keating contends that Skyline’s products use tried-and-tested components, this could be a bone of contention with investors who see CPV as a new technology and feel more comfortable with the good-old-heat-and-steam engineering approach used for CSP.

Finally there is the issue of storage. Newer CSP projects are increasingly being equipped with heat storage to allow the plant to provide base-load power around the clock, something that CPV just cannot match at the moment.

However, says Keating, storage “is not an Achilles heel for CPV, it’s an Achilles heel for all renewables. And I wouldn’t even say it’s an Achilles heel. It’s a limitation.”

In that sense, he says, there is a pressing need for the development of mechanisms that counteract the variable nature of renewable energy, either through storage or through more intelligent power distribution, and these will presumably one day overcome PV’s shortcomings.

For now, what is clear is that CPV has all it takes to be a serious contender for solar projects in high DNI locations. That might explain why one of the world’s top solar thermal companies, Abengoa, has recently added CPV to its portfolio.

After all, says Prior, the most serious challenge to CPV is not CSP. “I think the real competition is PV,” he says.