Features

Renewable energy – particularly the main contenders of wind and solar – may be on the point of moving into the mainstream as governments around the globe look to a clean energy future as a way out of economic gloom and looming environmental catastrophe.

Is renewable energy as good as the hype and ready to deploy? Or are the naysayers who maintain that renewable energy technologies are unproven and unfeasible for large-scale power generation right?
Here we look at the prospects for one of those great hopes – solar power.

Solar power has great attractions – the sun provides an almost limitless resource that could provide more than enough energy to power the entire globe. But that energy has to be harnessed, which is where photovoltaic (PV) technology comes in.

One of the ways in which solar energy can be converted into useable power is through PV devices. There are currently a myriad of competing PV technologies – many of which are already being deployed around the globe – but which, if any, are likely to be major contenders in the future?

The key factors determining the future success of these contenders are the efficiency of the PV devices themselves in transforming the diffuse energy of the sun into usable energy and the cost of those devices.

A recent survey funded by the US National Science Foundation conducted by researchers at Carnegie Mellon University in the US and the University of Calgary in Canada polled 18 experts on the future status of 26 current and emerging PV technologies¹.

The one thing that the experts agreed on is that there is no clear consensus of opinion.

“There was a surprisingly big range of opinions,” says co-author of the study, Aimee E. Curtright, now at the RAND Corporation. “There is a big range of possibilities of what the ‘real answer’ will be in terms of future costs and performance of PV.”

Does deployment lead to cost reduction?

The success of PVs in large-scale applications will depend on capital costs. And the costs continue to be high. Although module prices have fallen by an order of magnitude since the 1980s, a single PV device can still cost over $4.50/Wp (watts peak – the output under standard test conditions equivalent to noon at a mid-latitude site). When installation, wiring and other system costs are taken in account, this price can double.

Although various industry and governmental organisations have set targets such as $1.15/Wp by 2030 (Solar Energy Industry Association) or $1.25/Wp by 2015 (Solar America Initiative), solar power remains one of the most expensive energy generation technologies in terms of capital costs, as well as in terms of the cost of delivered electricity.

The US and Canadian team of researchers calculate that PV, when scaled for availability of the solar resource, costs over $25/W, compared with wind at around $4/W, nuclear at $4.4/W, and even coal-based integrated gasification combined cycle (IGCC) power generation with carbon capture and storage at $4.4/W, when similarly scaled to expected capacity factors.

According to experts surveyed in the study, crystalline silicon, thin-film (especially cadmium telluride) and some solar concentrator technologies have the best chance of achieving module costs of $1.20/ Wp or less by 2030, but beyond that experts are uncertain.

The accepted industry wisdom is that the more PV technology is deployed the cheaper it will become. However, there is no agreement that this will necessarily happen, says Curtright, or in which of the most promising technologies we ought to be investing.

“The talk of ‘if we build enough PV it will get cheaper’ is dangerous,” says Curtright, “both in terms of the over optimism it creates for the industry and potential government expenditure.”

There is no doubt that increased deployment does lower costs, but it still may not be enough for large-scale electricity generation. The cost reductions driven by this approach are likely to hit a plateau, below which they will not be able to fall, she says.

“Our results show that none of the technologies on the table will necessarily get us where we need to go in terms of cost,” she adds.

“If no technology on the table is an obvious ‘slam dunk’ then we should be investing much more aggressively in basic research.”

A disconnect in research

So if deployment isn’t a sure fire route to reducing cost, what is? Research gives you a better bang for your buck, says Curtright.

Research and development is often primarily focused on addressing the other major barrier to large-scale commercial success – efficiency. But the advances in efficiency that arise from research often come at a price – literally – of more expensive materials or complex manufacture.

“Somewhere along the line there is a disconnect in research and policy goals where efficiency is emphasised over price,” says Curtright. “Research efforts needs to be cognoscent of the trade off between efficiency and cost.”

And there is certainly a need for improvement. Most current PV modules offer efficiencies of around 10%. According to solar power proponent Ken Zweibel of the Institute for Analysis of Solar Energy at George Washington University, module efficiencies need to reach around 14% to bring down costs sufficiently for large-scale application². Although much higher efficiencies have been reported on test devices, this has yet to be realised in commercial devices.

A more holistic approach to research is needed, says Curtright, particularly focusing efforts on policy-defined end points such as cost.

Can PV make it on the large scale?

The report’s conclusions may not be what the PV industry wants to hear. The current market for PVs is looking good – according to a recent report from Greentech Media³, venture capitalists alone invested $1.6 billion into solar companies in the third quarter of 2008, more than $1.05 billion invested over the whole of 2007.

Personally, Curtright would like to see PV become a player in the global energy scene, but the results of the study indicate otherwise. Unless there is a surprise on the table in the future, we won’t see PV supplying significant amounts of power without cost increases.

“The main point we’re trying to raise is that PV technology may not become economically attractive for large-scale electricity supply in the near term,” says Curtright. “Many low-carbon technologies will likely be cheaper than PV. If we’ve got limited funds – is PV the way to go?” asks Curtright.

But solar power is riding on a wave of enthusiasm for clean energy technologies. Around the globe, governments are introducing legislation that incentivises investment in and deployment of renewables, including PVs.

“This is a cautionary tale for policymakers,” says Curtright. “We all want PVs to work and we’ve certainly come a long way since the 1980s, but we haven’t thought through the cost implications.”

Despite the fact the PV looks set to remain one of the more expensive players in renewables for the foreseeable future, there may be instances where reasons other than economics could drive adoption. PV could be an obvious winner in some regions such as California or Spain, or in off-grid and high-end back-up applications.

“I’d like to be optimistic, and there is a lot of possibility,” says Curtright, “but we’re not going to be 100% PV anytime soon.”
The challenge is still there though. There is only so much coal, oil or even wind, but the sun’s energy is virtually limitless. Ultimately, we will need to find some way of harnessing its power to meet our growing energy demands.

“Our results indicate that we need to think out of the box if PV is to be a player in the global energy mix on a large-scale – or we need to be prepared to pay more for electricity,” says Curtright.

Cordelia Sealy

Further information

¹Aimee E. Curtright, M. Granger Morgan, and David W. Keith. Expert Assessments of Future Photovoltaic Technologies. Environ. Sci. Technol. (2008), doi: 10.1021/es8014088
²Ken Zweibel, James Mason and Vasilis Fthenakis. A Grand Solar Plan. Scientific American (Dec 2007), www.sciam.com/article.cfm?id=a-solar-grand-plan
³Greentech Media, The Venture Power Report. www.greentechmedia.com/research-venture-power.html

Aimee E. Curtright is currently an Associate Physical Scientist at the RAND Corporation.