How Clean and Renewable are Wind and Solar?

This post looks at how wind and solar perform in two important environmental dimensions.

renewable versus clean

Lets start with some definitions

• renewable = not depleting a natural resource
• clean = not contributing to negative environmental effects such as climate change, poisoning of rivers or loss of biodiversity

There’s a third dimension we could look at here – sustainability. Sustainability is meeting the needs of the today without compromising the ability of future generations to meet their own needs.

While I like the idea of sustainability applying it is difficult. What are the needs of today? Are our needs different from the needs of future generations?

Now let’s look solar and wind in the context of the definitions above. We will take a look at both the operation and manufacture of wind and solar.

solar

Operating solar plants uses the sun for fuel and water to wash panels. Both are renewable (water might not be in some areas!) and the use of the sun as a fuel is clean.

The negative environmental effects of generating water for panel cleaning are site specific. Best practice for generating this water will most likely have minimal environmental impact. The operation of solar panels is therefore renewable and clean.

The manufacture of solar panels involves processing of quartz in electric furnaces to remove oxygen. The electricity used in silicon production today is non-renewable. Where the silicon production occurred will determine how non-renewable those solar panels are.

Silicon tetrachloride is a hazardous chemical that is a by-product of silicon purification. Production of hazardous wastes is not unusual in chemical processing. Best practice for disposal or reprocessing will limit environmental damage.

Solar panel manufacture uses rare earth elements such as silver, tellurium or indium. Unless we are at a position of 100% recycling then use of these will be depleting the natural resource. This makes solar panel manufacture non-renewable.

The use of carbon-intense electricity will solar panel manufacture unclean. While this may change in the future with high levels of renewables penetration it’s not the case today – and probably won’t be for a long time.

wind

Operation of wind plants appears renewable. Yet Vaclav Smil notes in his excellent book Energy Myths and Realities: Bringing Science to the Energy Policy Debate:

…very large-scale extraction of wind (requiring installed capacities on a TW scale needed to supply at least a quarter of today’s demand) reduces wind speeds and consequently lowers the average power density of wind-driven generation to around 1 W/m² (from 2 W/m²)

If Smil is correct then by our definition the operation of wind turbines is not renewable. Large scale deployment of wind depletes the resource.

How clean large turbine scale deployment is an unknown. Changing wind speeds may do environmental damage but who knows?

Now let’s take a look at wind turbine manufacture. Wind turbine blades are made from fiberglass. Producing fiberglass requires non-renewable petrochemicals.

A significant amount of steel and concrete is used in building wind turbine plants. Fossil fuels are used in the production of both.

It’s not only the energy content of fossil fuels that is required. Fossil fuels are an inherent part of the chemistry of steel and concrete manufacture.

In steel production fossil fuels are required for iron smelting. Concrete production uses coal to remove carbon from calcium carbonate.

Fe₂O₃ + 3CO → 2Fe + 3CO₂ CaCO₃ → CaO + CO₂

In both reactions above carbon dioxide is produced. Not only is wind turbine manufacture non-renewable it is also inherently unclean.

what does this actually mean?

All energy generation technologies have their problems.

In choosing a way forward, it’s not about if a technology has problems. It’s about what those problems are versus the alternative.

This is a function not only of the problem but of societies attitude towards the problem. Perhaps we don’t mind depleting our resources of rare earth elements if it means reducing carbon emissions.

To quantify the environmental benefit of renewables versus fossil fuels is a project with a massive scope. The analysis is full of uncertainty and is location & time specific.

Yet but only highlighting some of the inherent problems with solar & wind we can think about ways to address them in the future.

Perhaps we need to focus on understanding what impact large-scale wind deployment will have on wind speeds, or what quantities of rare earth elements we have left for use in solar panels.

By addressing these issues we can move forward into a brighter (but maybe less windy) future.

Thanks for reading!