Choudhury explains: “Solar thermal systems do not use ‘panels’ per se. They use mirrors, usually, to focus the solar (heat) energy onto pipes that have a heat transfer fluid, which converts water into steam, thereby running a steam turbine. In other scenarios, the solar heat energy can be used to directly run a Sterling engine without the need for intermediate conversions.”
“Since the price of mirrors has largely remained the same, the price of solar PV panels (which contribute about 50 per cent to the project cost) has dropped significantly due to the global supply glut. This drop in price is due to a supply-demand mismatch rather than the cheapness of the technology as such,” he adds.
Further, considering that the global appetite for solar thermal is much lower than that for solar PV, there are very few players in that space and it is only logical that it will suffer from mismatches in economies of scale.
Raghunandan feels that it’s not right to compare solar PV and solar thermal. “Both are different approaches and have their own engineering approach. The conversion efficiency of PV is very less compared to thermal conversion efficiencies. In PV, only a part of sunlight can work in generation while the other is converted into heat or lost. So research work is going on toward building panels that can generate electricity and heat. The industry is still working in this direction,” he shares.
Stefan de Haan points out that concentrated solar power (large-scale solar thermal) has the potential to become cheaper than PV in the earth’s sunbelt. However, progress in the past years has been minimal. The technology is not yet mature and might not fulfil its promises. The progress of PV on the other hand is overwhelming.
“For typical residential rooftops, small-scale solar thermal is not cheaper than PV anymore. Not too far from today, it will even be the other way round: PV electricity will be used to heat water,” he adds.
Effectiveness of PV panels
Suppliers are actively working towards increasing the effectiveness of PV panels.
Raghunandan notes: “The crystalline efficiencies mostly depend on cell efficiency. At module level, we are only trying to see how we could reduce the temperatures of the modules to increase the efficiencies. The cell efficiencies have reached over 20 per cent and there is a possibility that these efficiencies would reach around 30 per cent in future.”
Therefore, can PV systems operate normally in grid-connected mode and still operate loads when the utility service is disrupted?
Choudhury answers: “Yes, they can operate normally in both modes. Modern inverters have controllers built into them that choose the cheapest source of electricity available at all times. Further, in the absence of the grid, the solar PV installation and loads are usually ‘islanded’ and the solar PV system proceeds to act much like a diesel generator.”
Raghunandan adds, “Grid-connected ones work only when the grid is available. For grid failure, we must go for off-grid type of systems.”
The key is cost-effective storage solutions, according to Stefan de Haan. That would solve many issues. “We see progress here, but it is still the one and only missing component,” he adds.
Finally, it will be interesting to note IHS iSuppli’s forecast for India for 2013. It expects the Indian market to surpass the gigawatt mark in 2012 and continue to grow strongly in the years after. About 1.7 GW is expected for 2013.
The author is an executive editor at EFY