The BusinessGreen.com beginners' guide to solar tech

Anyone who has spent any time looking at the potential for renewables will have surely stumbled across one of those maps of North Africa displaying the relatively tiny area of a few hundred square miles where scientists have calculated enough solar energy falls each day to power the entire global economy.

But if you do happen to find yourself in a desert, or indeed anywhere where the sun is shining, which of the many solar technologies promises the best returns?

BusinessGreen.com travelled to Abu Dhabi's World Future Energy Summit – where solar was unsurprisingly something of a hot topic – to weigh up the pros and cons of the four main technologies now jostling for dominance of this potentially world-changing market.

Concentrated photovoltaic

A relatively new technology that uses mirrors to concentrate the sun's rays on to PV cells. Advocates claim it has a relatively high field durability and about 25 per cent efficiency and as such it is good for regions with direct light and high temperatures, such as deserts.

Conversely, it is inefficient at converting indirect light into energy and is therefore not particularly suitable for areas with a high chance of cloud cover.

Concentrator panels consist mainly of aluminium and glass, while the PV cells can be gallium indium-based so construction of the technology is not necessarily reliant on currently stretched silicon supplies.

Supporters claim it is already relatively cost competitive, generating energy at less than 15 US cents per watt, and consumes no water, making it ideal for desert conditions.

"We are looking to drive down prices and we hope to achieve grid parity – the point where we can compete on costs with grid electricity – in about 2012," says Roberto De Diego, president of Solfocus Europe, a manufacturer of concentrated PV panels.

Solar thermal

Solar thermal technologies use a series of panels to concentrate solar energy to a level where it can heat water to boiling point. The resulting steam is then used to drive turbines.

One of the main disadvantages of solar – and most renewables – is that it is difficult to guarantee regular supply to the grid. Supply drops off at night and at times of cloud cover, meaning that even in the sunniest desert there are no 100 per cent guarantees of regular supply.

Solar thermal technologies can increasingly get round this problem by either using molten salt to store the sun's heat overnight, using it to create the steam and power the turbines long after the sun has set, or by integrating a biomass or even fossil fuel generator to power the turbines when weather conditions mean the the solar panels fail to generate enough energy.

Advocates of the technology also insist that despite the high upfront construction costs, desert solar thermal farms promise to be far more cost effective than PV systems. "We hope our solar thermal technologies will reach grid parity before standard photo voltaic solar," said a spokesman for solar thermal developer Abengoa Solar.

Crystalline photo voltaics

Crystalline PV panels are arguably the most widespread, long-established, and consequently cost-competitive solar technology currently available.

Used widely used for decentralised installations, home generation and commercial rooftop installations, silicon-based crystalline solar panels are still the dominant technology in the solar market, regardless of the fact that newer rivals are coming up fast.

Prices for panels are low relative to newer technologies and while there have been widespread fears that silicon supply constraints will push up prices, experts counter that moves by manufacturers to increase control over their supply chains and improve manufacturing techniques mean prices should in fact continue to fall in the long term.

The panels have a uniform black appearance and are often favoured for rooftop installations. They are reliable for about 20 years and have about four per cent degradation. They are also more efficient in terms of space-use than thin-film solar panels and advocates insist that if installed in the right position and climate, they can offer payback periods over five years.

"This is one of the most established solar technologies, having been around for 30 years," said Peter Ushumbeier of leading manufacturer Sunpower. "We continue to have about a 20 per cent price reduction every time production capacity is doubled."

Thin-film photo voltaics

Thin film is a relatively new solar technology, but many observers believe it represents the future of solar energy and some expect the sector to grow to account for a third of all PV production by 2012.

A wide range of different thin-film technologies are now available, ranging from more traditional silicon and glass-based systems to cutting-edge copper indium gallium selenide cells.

What thin-film cells tend to have in common is that they are particularly efficient at converting indirect light – this is the technology used in solar-powered calculators – and so are therefore suitable for locations that have a higher chance of cloud cover.

They can also be produced using printing press-style manufacturing techniques, which means that in theory they could be produced far quicker and cheaper than their more established rivals.

Meanwhile, the light and flexible nature of many thin-film technologies mean that they have the potential to used in a huge number of different applications, ranging from solar windows to solar clothes.

Thin film may be relatively expensive and not very efficient at the moment, but millions of dollars have been invested in firms that promise to take the technology into the mainstream.

"This is one of the technologies of the future and prices will come down as we gain economies of scale," said Joachim Nel, chief operating officer at Masdar PV.