Beware of Blind Alleys in the Search for the Sun

The world has been obsessed with solar photovoltaic power – but salvation could actually lie in the direction of solar thermal power.

Two years ago, Prime Minister Narendra Modi drew praise from the world by taking the lead (with France) in forming an International Solar alliance of tropical countries to harness the Sun’s energy. On March 4, that initiative took concrete shape in Delhi. The Indian media treated this as a diplomatic coup for Modi, and the international media took it as a sign that India, the second most populous country in the world with energy consumption expected to rise by 4.2% a year until 2035, was taking its responsibility seriously.

However, these expectations will only be fulfilled if New Delhi and Paris are able to steer the alliance away from the blind alley into which “green” corporations and powerful governments have been dragging the world for the last five years. This is the frantic promotion of solar photovoltaic (PV) electricity, lithium-ion battery storage and electric cars, the increased neglect of concentrated solar thermal power (CSP) and biomass-based transport fuels.

This has been so effective in the field of power generation that virtually every advertisement of solar energy anywhere in the world shows only solar PV panels – despite the fact that PV power simply can’t meet more than a small fraction of the world’s need for electricity. There are two reasons for this, one well-known and the other only just coming to light.

Issues with photovoltaic power

The first is that sunlight can only be tapped when the Sun is shining in the sky and is some distance above the horizon. This limits direct energy production from it even in the best of circumstances to about eight hours a day. Allowing for the 30 to 90 days when clouds, haze or dust storms obscure the sun, this allows solar PV plants to supply power for no more than a quarter of the 8,760 hours in a year.

The only way to extend this is through batteries. But battery storage is very expensive today. The proponents of solar PV power point out that this cost is falling dramatically. But a report published by the World Energy Council in 2016 has shown that this will only drop from the 2015 level of 12-80 ¢ a unit to 6-23 ¢ by 2030. If solar PV has to be synchronised with wind and other forms of renewable energy, the cost of the “smart” grids that will be needed will take even more of the shine out of solar PV power, and in all likelihood make it uneconomic.

PV power’s insurmountable barrier is not, however, the cost of storage but the scarcity of the metals needed to make the panels and batteries. These are cadmium, tellurium and lithium. The current generation of PV panels uses a thin film of cadmium telluride to achieve its near-20% conversion efficiency. One megawatt of solar PV generating capacity requires 90.38 kg of tellurium and 83.51 kg of cadmium.

Tellurium is a byproduct of copper mining, and about 420 tonnes of it was produced in 2017. The precise amount of tellurium in Earth’s crust is not known but it is estimated to be around the same as platinum, which is three-times rarer than gold. That would make it around 70,000 tonnes. The US Geological Survey thinks tellurium is eight times rarer than gold in Earth’s crust.

Cadmium is extracted from zinc ores, of which it makes up 0.03-9% by weight. Its total mineable reserve is therefore estimated to be around 570,000 tonnes.

The world consumed 22 billion MWh of power from 6.1 million MW of generating capacity in 2017. To supply the two-thirds that is now generated from coal, oil and gas with solar PV power will require installing around 7 million MW of solar panels. These panels will require 650,000 tonnes of tellurium and 580,000 tonnes of cadmium. This is all the presently accessible cadmium and up to ten times the accessible tellurium in Earth’s crust.

Lithium is relatively more abundant. Till last year the US Geological Survey had placed the mineable content in Earth’s crust at around 14 million tonnes but has now raised it to 53 million tonnes.

Now, the total number of cars on the road crossed a billion in 2010, and is expected to reach 2.5 billion by 2050. The batteries powering battery electric cars like the Tesla Roadster require about 12.7 kg of lithium each to make (hybrid electric vehicles require 0.09 kg each). With country after country announcing that it will replace liquid fuel-driven with electric cars, it is worth remembering that – even with a 25% increase in battery efficiency – an all-electric global fleet in 2050 will require over 30 million tonnes of lithium.

Enter thermal power

These calculations show that, as has happened with ethanol, not long after the world starts shifting to these technologies, the rising demand for these metals will push their prices into the stratosphere and bring the shift to a halt. By then another decade will have been lost – time that the world can no longer afford.

Salvation lies not in solar PV but solar thermal power. CSP power plants require only mild steels, aluminium and silver-backed mirrors to generate power. Solar thermal power has a big advantage: by using molten salt instead of water to capture the Sun’s heat, it can provide steam to turbines at up to 1,000º C, far higher than the 593º currently needed by advanced supercritical boilers in the conventional power industry. (Higher the temperature, greater the efficiency of heat transfer.)

More importantly, when stored in well-designed tanks, a mixture of molten sodium and potassium nitrates has been found to lose 3% of its heat in 24 hours. As a result, solar thermal power plants in Spain, Morocco, Dubai, Saudi Arabia, South Africa and elsewhere are now supplying up to 20 hours of guaranteed power from solar heat alone.

Best of all, CSP power prices are also plummeting, from 15.9 ¢ (Rs 11.60) a unit in the third phase of the 580-MW plant completed at Ouarzazate, Morocco, only a year ago to 7.3 ¢ (Rs 4.90) for a 700-MW plant to be constructed in Dubai by 2020.

While Modi has been making grand promises about what India will do in the solar energy sector, India has fallen steadily behind even small developing countries in performance. In 2013, there were 50-100 MW CSP plants power plants on the drawing boards. Today only two are operational, and there is not a single solar thermal power plant, large or small, in the works.

The reason is that while CSP plants can deliver up to four times as much power as solar PV plants, they also cost nearly four times as much to build. This makes the cost of the plant highly sensitive to interest rates and delays in the provision of infrastructure by the state. India’s prohibitive interest rates (11% against Dubai’s 4%) and the delays that the bureaucracy has imposed on the pioneers in this field have made sure no one will venture into CSP power plants. This is despite the fact that India has more than 50,000 km2  of hot and cold desert available for setting them up.

Prior to launching its 700 MW project, the Dubai Electricity and Water Authority divided its detailed planning into four parts: legal framework, infrastructure, finance and skill-building. Construction began only after all four were in place. India could learn from Dubai’s example.

Prem Shankar Jha is a journalist who lives and works in Delhi.