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Can we manufacture renewables without fossil fuels?

Posted by Alex Barrett on 20 September 2016 at 10:05 am

In order to capture energy from renewable sources we need the right technology. But solar panels and wind turbines are very energy intensive to manufacture. Unfortunately the energy that is used to make renewable systems usually comes from fossil fuels. So can we produce enough renewable electricity to sustain the renewables industry? Or are some of our sources of green energy themselves unsustainable?

The good news is that the solar industry is now making more energy than it consumes, although it has only reached this threshold relatively recently [1]. It is estimated that it is only since 2010 that this has been the case. As the share of renewables grows this will improve. Green sources will provide an ever increasing proportion of the electricity that is required for the construction of additional panels. Unfortunately electricity isn’t the only type of energy which is needed for industry to function.

Heat accounts for 47% of the world’s energy consumption. It is reported that nearly 90% of the thermal energy used in industry comes from the direct burning of fuels, the remainder is produced using electricity. Some of this electricity will be produced by renewables, but most comes from fossil fuels. Biofuels can account for around 11% of the direct fuel used in industry, but fossil fuels still predominate [2].  

This is unsurprising, as industry is rarely considered to be green. The industrial revolution was kick started by coal, and fossil fuels remain the go to energy source for most high temperature processes. Some renewables, such as solar thermal and geothermal plants produce heat, but most renewable energy is in the form of electricity. We can certainly use this electricity to produce a high temperature. However doing so is much less energy efficient than burning a fuel source directly and is as much as two to three times more expensive [3].

Making a solar panel involves numerous high temperature processes [4]. The main component is silicon, which is extracted from quartz. Leaving aside the energy cost of the mining operation, melting quartz requires temperatures of over 1600 oC [1].  The process of turning silicon from a raw material into a working semiconductor then requires the use of numerous chemicals, all of which need to be produced industrially. Other components of the panel may be made of plastic, or metals such as steel and aluminium, all of which require very high temperatures to refine.

It is easiest and cheapest to get these high temperatures with fossil fuels but could we use solar thermal technology instead?

The maximum temperature produced by solar thermal is generally in the range of 80 - 120 oC, depending on the type of system, and the location in which it is installed. They are generally used to produce hot water. The International Energy Agency (IEA) has estimated that 30% of industrial heating demand in Europe could be met by these fairly low temperatures [2, 3].

Another option is the concentrating solar power plant. These consist of a series of mirrors which focus sunlight onto a small area. They are currently used to generate electricity by boiling water, the steam from which turns a turbine. Concentrating solar plants produce temperatures as high as 250 oC and can get much higher. They generally don’t produce enough heat to make metal or melt quartz, but a further 27% of industrial processes need heating in the range of 100-400 oC which the IEA believes could be provided by concentrating solar plants [2, 3, 5].

This means that more than half of all industrial heating demand could be met by renewable energy. Unfortunately melting quartz and forging steel is still beyond their reach [3, 5]. Higher temperatures would require the use of a “solar furnace”, far fewer of which have been built. These can theoretically reach temperatures of up to 3,500 °C [6]. Solar furnaces work on similar principles to the concentrating plant, albeit with a far greater intensity. This technology is ancient, Archimedes is believed to have used an array of mirrors to set fire to roman ships in antiquity. The Odeillo solar furnace in France is shown below.

There aren’t many working solar furnaces yet, but they are the best option. The heat produced by a furnace would be more than sufficient to fuel most industrial processes, including those required to manufacture solar photovoltaics. The technology exists, but phasing out fossil fuels in favour of a more sustainable option won’t be a cheap solution.

References

  1. Popular Science: Solar panels now make more electricity than they use
  2. Environmental and Energy Study Institute: Solar Thermal energy for industrial uses.
  3. Low Tech Magazine: The bright future of solar powered factories.
  4. IEEE Spectrum: Solar energy isn’t always as green as you think
  5. International Energy Agency: Solar heat in industrial processes
  6. Wikipedia: Solar Furnace

Image: Odeillo solar furnace in France

Odeillo Solar furnace by H. Zell CC BY-SA 3.0 via Wikimedia Commons

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