When it comes to carbon emissions, electricity production is just the tip of the iceberg.

Written by David Watson

June 3, 2019

Just as the bulk of an iceberg hides beneath the waves, more than half of our carbon emissions do not come from electricity production. In the US, emissions from transport outweigh those from electricity. CO2 produced by industry follows close behind, with buildings (prinicially heating & AC) and agriculture the other major contributors.

So if we are to really drop our carbon emissions, we need to deal with CO2 from non-electricity sources as well as decarbonise our grids. Not only that, but we must do so in a world with up to 10 billion human beings. Most would agree those 10 billion people deserve to enjoy at least the standard of living currently experienced in developed countries.

This makes one thing clear: we’re going to need more energy. Lots of it.

And it better be clean.

In this 10 billion-person world where we all experience European-level prosperity, decarbonising all our energy — not just electricity — with water, sun and wind energy alone would be a mighty challenge indeed.

With fossil fuels out the question, most scientists believe using 100% renewables to supply all our energy needs would bring unacceptably high costs, both financial and environmental (think land usage and mining impacts of solar panels and batteries).

And there’s one type of energy that wind turbines and solar panels are really bad at replacing: high-grade heat.

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Nuclear’s potential to decarbonise heat (and transport)

Heat, just like electricity, is a form of energy. Sometimes we consume energy directly in the form we find it. For example, we can warm ourselves with heat if we stand in the sun. We can also convert energy to a different form, sometimes storing it and consuming it at a later date. For example, plants convert energy from the sun into chemical energy stored in leaves, fruits and vegetables that humans harvest and eat at their leisure.

Human society needs energy to function, but what forms of energy, and in what proportions? As my personal hero David Mackay put it:

You can’t power a TV with cat food, nor can you feed a cat from a wind turbine. Energy exists in different forms — chemical, electrical, kinetic, and heat, for example. For a sustainable energy plan to add up, we need both the forms and amounts of energy consumption and production to match up. Converting energy from one form to another — from chemical to electrical, as at a fossil-fuel power station, or from electrical to chemical, as in a factory making hydrogen from water — usually involves substantial losses of useful energy.

Converting energy from one form to another is wasteful.

When we say we need “energy”, sometimes we mean “electricity”, sometimes we mean “heat”, and sometimes we mean portable fuel that can be converted to either electricity or heat when we need it (such as the fuel in a car).

Industries such as steel manufacturing or petrochemical production are heavy consumers of high quality heat. Hydrogen production is most efficient at high temperatures. Commercial and residential buildings require heating through colder months and the boiling of hot water all-year around.

Currently, almost all this heat comes from the burning of fossil fuels such as natural gas and fuel oil (although Russia, Ukraine, the Czech Republic, Slovakia, Hungary, Bulgaria, Sweden and Switzerland have all used nuclear-powered district heating at some point, and Iceland geothermal).

So why don’t we use solar panels and wind turbines to produce heat, you might ask? The quick answer is, we do! Using renewable electricity to run heat pumps is an efficient way to heat your home. But heat pumps can only produce heat at temperatures up to 100 degrees Celsius. Something goes wrong when we try to go hotter.

Wind turbines and solar panels produce electricity, some of which would have to be stored in batteries to ensure a constant supply. To get temperatures above 100 degrees Celsius, this battery energy would then be turned back into electrical energy, then converted into heat using e.g. an electrical resistance element.

All these conversions mean using wind turbines and solar panels to produce heat is highly inefficient. What are our alternatives? The best candidates for the production of low-carbon, high-quality heat are carbon captured and storage fossil fuel plants, concentrated solar power and high-temperature nuclear reactors.

Carbon capture and storage (CCS) means developing ways to capture the emissions from burning gas or coal (or maybe biomass, but that brings its own land use and habitat destruction problems). CCS is still in its infancy, and even if perfected would require the extraction and transporting of large amounts of fuel, the managing of waste streams, and the sequestering (storing) of carbon dioxide in e.g. spent oil wells.

Concentrated solar means using thousands of mirrors to focus sunlight to heat a fluid that is used to store heat. This heat can then be used to produced steam and turn an electricity-generating turbine, or else used in industrial processes. Concentrated solar is likely to take off in parts of the world with guaranteed sunshine, which is why most developments have so far been in the south of Spain or in southern US deserts.

The technology is not without its detractors, most of whom highlight the large land area required and the potential to damage habitats which have so far escaped large-scale human development.

In parts of the world with large populations and heavy industry but little sunlight, such as northern Europe, concentrated solar is not an effective option. We need a source of heat which works whatever the weather, 24 hours a day.

And we might just have it…

Advanced nuclear reactors.

Many advanced nuclear reactors are specifically designed to produce high temperature heat such as in the British-Canadian high-temperature gas-cooled U-Battery design.

Others, such as Moltex, plan to use “solar salts” (liquid salt technology pioneered in concentrated solar power plants) to store heat that can then be called on as required to match demand. As well as being used to produce electricity, heat from these salts could also be turned to producing hydrogen, chemicals or heating for local homes.

If nuclear reactors are used to make clean hydrogen, we can decarbonise transport by powering vehicles using fuel cells; out the tailpipe would be released only a harmless trail of water vapour. The United Nations is seriously considering this as a viable option to decarbonise transport and heat.

Decarbonising heat is an essential step on our path to a carbon-neutral future. It’s a big challenge but is entirely achievable with a mix of research, engineering and government policy.

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