Solar Energy Perspectives - IEA

Chapter 5: Industry and transport
in a significant amount of so-called “still gas”, which is recovered and burnt. Machines are
powered by electricity, often cogenerated with steam in the refinery. In 2000, purchased
natural gas accounted for 28%, and purchased electricity for only 4%, of the needs of the
refineries. The availability of still gas restricts the possible role of renewables in refining
petroleum.
Hydrogen used for synthesis of fertilisers and cleaning petroleum products could be produced
either from water electrolysis using excess wind or PV power, or from steam reforming of
natural gas. In this case, it would use concentrated solar heat as the energy source, instead
of burning natural gas (on top of the “still gas” produced in the refineries themselves).
Preliminary indications suggest that the second option would be three to four times less
costly but is only available where high DNI permits. Solar heating of the water could,
however, be used extensively to reduce the amount of electricity required by electrolysis.
Apart from a few direct industrial uses of hydrogen, solar hydrogen could be mixed in various
proportions with methane, transported as such and ultimately burnt in combination with
natural gas.
Desalination
Arid regions are both blessed by good DNI resources and cursed by water shortages.
Desalination techniques are expected to continue expanding, particularly in the Middle East.
Two main techniques exist: distillation and reverse osmosis. Distillation requires large
amounts of thermal energy, while reverse osmosis consumes large amounts of electricity. It is
tempting to think that CSP plants, which generate electricity from heat, could have an
important advantage in combination with multi-effect desalination plants in “cogenerating”
electricity and the heat needed for the desalination process.
A closer examination, however, suggests that such an advantage does not exist. The diversion
of low-pressure, low-temperature steam from the turbine to serve the distillation plant would
reduce the electricity generation. Coastal areas often enjoy lower DNI than more inward sites.
The choice of desalination process may primarily depend on the salinity of the marine or brine
waters. More saline waters increase the electricity loads of reverse osmosis plants and may lead
to a preference for distillation plants, while less saline waters may lead to a preference for
reverse osmosis technologies run on solar electricity from concentrating solar power plants.
If this sort of “cogeneration” exists, it should paradoxically be sought for in the combination
of CPV systems and distillation plants. CPV systems may need or benefit from cooling, and
the heat removed by this cooling process may serve the purpose of distillation while
increasing, even slightly, the efficiency of the solar plant, not reducing its electric output.
In any case, however, the co-existence of fresh water shortages and excellent direct solar
resource certainly offers many opportunities for this growing industry sector to be powered
by solar, whether heat or electricity.
Similarly, the potential for water detoxification by solar light is important in sunny developing
countries and to some extent already mobilised in conventional open-air wastewater
treatment plants. It can contribute to provide clean water to people and combat water-related
diseases in the developing world. Research and development in this area is part of the scope
of the IEA SolarPACES programme.
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© OECD/IEA, 2011