An energy future dominated by renewable energy will require large areas of land to be devoted to solar and wind farms, both onshore and offshore. Some people, such as the late David MacKay, think that this poses substantial challenges. A recent article in the Financial Times also quoted an estimate that 23,000 sq km of land (almost 10% of the UK’s land area) would be needed just to provide the energy to replace oil.[1]

This article provides an estimate of land and sea areas of the UK needed to provide all the country’s energy needs, not just electricity. Much of the electricity will be directly used but large percentages will be devoted to making hydrogen, both to be used directly but also to be converted into synthetic hydrocarbons, such as aviation fuel.

It assumes the electricity is provided by these extra capacities[2]:

Offshore wind - 250 gigawatts ( in addition to about 10 GW in August 2020)

Onshore wind - 120 gigawatts ( +about 14 GW in August 2020)

Solar - 250 gigawatts (+ about 13 GW in August 2020)

This renewables fleet would require approximately these areas

Offshore wind - 41,000 sq km

Onshore wind - 30,000 sq km

Solar - 5,000 sq km

These figures represent the following percentages of the maximum available area

Offshore wind - 5.3% of the UK’s EEZ[3]

Onshore wind - 12.5% of the UK’s land area

Solar - 2.1% of the UK’s land area.

The calculation

The UK currently uses about 1873 terawatt hours (TWh) of energy each year.[4]

Oil - 756 TWh

Natural Gas - 872 TWh[5]

Coal - 59 TWh

Electricity from non-carbon - 186 TWh (renewables, nuclear, hydro, imports)

Full decarbonisation requires us either to continue using fossil fuels but to capture all the resulting CO2 or to move all our energy needs to renewables. I believe that this second strategy is cheaper and easier to achieve. The rest of this article analyses this route and estimates the capacity of renewables that we will need and how much land and sea area that this will entail.

How do we move to using renewables as our complete energy source?

Many activities that use oil and gas can be easily transferred to electricity. Personal cars, for example, can shift to batteries while much domestic and other space heating can be carried out by electric heat pumps. Other energy uses, such as aviation, cannot be switched to using electricity, despite what the airlines sometimes tell us. In these cases electricity will need to be used to make hydrogen using electrolysis. This hydrogen will either be employed directly, to make steel for example, or will be used to provide the critical component in the manufacture of synthetic hydrocarbons.[6]

To summarise: we can use electricity as the raw material for all energy needs

· As electricity itself, usually to power an electric motor

· As the energy source for making hydrogen, either to be used directly as the energy source;

· Or as the critical ingredient in the manufacture of synthetic fuels.

Renewables in combination with hydrogen can do almost everything fossil fuels can do. An energy strategy based on huge amounts of renewables, combined with turning excess electricity production into hydrogen is therefore possible.

Calculating how much electricity we will need to replace fossil fuels.

The UK uses three principal fossil fuels: coal, oil and gas. The government data on the consumption of each fuel gives figures for how each is used. In the case of oil, it is employed to make vehicle fuels, aviation fuels and plastics, among other uses.

In the case of each specific use for each category of fuel I have taken the figures from official statistics to estimate the electricity equivalent.

· Domestic cars, for example, required about 22 million tonnes of oil in 2019. The energy value of that oil was equivalent to approximately 256 terawatt hours. However a car is a very inefficient converter of the energy in oil into motion. Over three quarters is wasted as heat. So my calculation (which probably needs refinement) is that domestic cars might only use 67 terawatt hours of electricity to charge and drive. This is an example of a direct switch from a fossil fuel to electricity.

· Many commercial vehicles will also use batteries but expert opinion suggests that some bigger trucks will need to use fuel cells as the power source. In this case, they will use hydrogen, made from electricity, which the fuel cell will convert back into electricity to drive electric motors. Because of the substantial conversion losses, this will require us to generate much more original electric power. This is an example of the second category of switch: movement from fossil fuel to hydrogen

· The third category of switch is the replacement of a fossil fuel with a low-carbon synthetic equivalent. Aviation fuel will be made using electricity to make hydrogen which will then be combined with carbon molecules in relatively simple reactions to make long chain hydrocarbons that chemically identical to conventional fuels.

In each of 23 separate energy uses, I estimate how much renewable electricity will be needed to power the activity. In each case I first make an assessment of what percentage of each category of energy use will move to using direct electricity or hydrogen or synthetic fuels. I then estimate the conversion efficiency of all the processes needed to create the fossil fuel substitute, enabling me to calculate how much renewable electricity will be needed to completely substitute for existing sources.

Adding up all these 23 figures gives me an estimate of the amount of electricity that will be needed to replace all fossil fuel use. It amounts to 1,710 TWh, or just over 90% of existing total energy use. (For comparison, total electricity production today is just over 300 TWh). I was surprised this number was so high. I expected that the efficiency gains of moving to electric cars and electric heat pump heating would significantly reduce total primary energy demand. I had forgotten that other energy uses, such as making synthetic aviation fuel, will be considerably less energy efficient.[7]

Will 1,710 TWh of new renewable electricity be sufficient to cover all the UK’s needs? Not quite. We will still have to ensure that we have enough electric power at all times to provide for all the needs for reliable electricity. Let me explain this a bit more. At the moment, we get about 60% of electricity from low carbon sources. When the wind and the sun aren’t performing, the UK is able to revert to gas generation. Under the route proposed in this article, this will have to stop.

But we will be needing to expand renewables capacity by approximately 17 fold to get all the power we require. This means that even on relatively dark and still days, we will get enough electricity to cover all the ‘undelayable’ needs for power.[8] During periods of high wind and sun we can convert all the surplus power to hydrogen. Current electricity demand peaks at around 50 gigawatts. But in my estimates we will need over 600 gigawatts of additional renewables capacity so it would have to be a very poor day not to provide today’s levels of power need.[9]

In the hours that renewables do not provide enough ‘undelayable’ electricity, we should plan for it to be provided by gas turbine power stations powered by hydrogen. This is inefficient because it requires us to store surplus electricity in the form of hydrogen (80% efficiency) and then converted back to electricity at times of urgent need in a gas turbine (60% efficiency). I have budgeted just over 100 Terawatt hours of extra electricity from renewables to pay for this inefficiency.

How much space will be needed?

In my simple model we will need a total of just over 1800 Terawatt hours of extra renewable electricity. (This is approximately the same as our total requirement today). We can provide this by a mixture of onshore and offshore wind plus solar power. Each of these power sources has its own space requirement.

My calculations suggest the following approximate electricity production estimates for these three technologies:[10

· Offshore wind - 3.4 watts per square metre

· Onshore wind - 1.4 watts per square metre

· Solar - 5.5 watts per square metre [11]

(As background, today’s energy consumption for the UK, in terms of watts per square metre of land area is just under 1. Therefore we would be able to provide all the energy needs of the country by putting just less than 20% of the UK under solar panels.[12] Of course we will probably choose not to do this.

I guess that the most likely approximate outcome will be as follows

· Offshore wind - 250 gigawatts

· Onshore wind - 120 gigawatts

· Solar - 250 gigawatts.

We could decide to use a different balance but this combination gives us the overall amount of electricity we need. As I said in the introduction these figures represent the following percentages of the maximum available area:

· Offshore wind - 5.3% of the UK’s EEZ[13]

· Onshore wind - 12.5% of the UK’s land area

· Solar - 2.1% of the UK’s land area.

Is this plausible?

· Offshore wind - David MacKay estimated that the total UK sea area with a water depth of less than 50 metres was about 120,000 sq. km. (50 metres is used as an approximate figure for the deepest water in which fixed foundation offshore wind can be installed). My estimates are that the requirement is about one third of this space. However the demand is actually less than this because some power, possibly huge amounts, can be provided by ‘floating’ offshore wind turbines. There is only one large such commercial installation in the UK today but it is proving productive. The floating wind variant may become cheaper than fixed foundation turbines.[14]

· Onshore wind – 12.5% of the UK’s land area is probably the most demanding of the three targets. But onshore wind can co-exist with solar and, of course, with conventional farming. It will need to be concentrated in areas close to the coast all around the country, but the results will be best if the focus is on the northern half of the country and the south west of England. It may be that solar and onshore wind should take a larger share of the target to avoid over-crowding.

· Solar. 2.1% (about one fiftieth) of the UK seems quite easy, but the capacity should probably be concentrated on the south coast and, of course, on all buildings with roofs facing between east and west. (An east facing roof produces maximum power at a different time to one facing west, which is an important advantage of diversity in how solar is oriented). Solar can, of course, be combined with the grazing of some animals.

The cost

Before counting in the cost of electrolysers, new pipelines and electricity transmission grids, the capital cost of a 100% renewables plus hydrogen economy will be as much as £700-800 billion, or around 40% of 2019 UK GDP. Carried out over 20 years, this means devoting 2% of national income to investment in renewables, or around £40 billion a year. But at the end of the process the UK will have effective self-sufficiency in energy at a reliable and steady cost. Hundreds of thousands, perhaps millions, of jobs will have been created and emissions driven to near zero. Now is precisely the time to do this.

Conclusion[15]

Full decarbonisation is possible using renewables that occupy a manageable fraction of UK land and sea areas. And which provide reliable, dispatchable power.

[1] https://www.ft.com/content/763b96c3-438f-4f5b-b6cb-f94f4dbfbaf2 (Paywall)

[2] Other proportions could be used.

[3] Exclusive Economic Zone

[4] I used the figures from the quarterly Energy Trends for 2019, published as provisional figures in March 2020. https://www.gov.uk/government/statistics/energy-trends-march-2020

[5] Much of the gas is used to make electricity.

[6] I define a synthetic hydrocarbon in this context as a replacement for a fossil fuel. Using hydrogen and a source of carbon (either captured from the air or from the exhaust gases of processes such as cement manufacture), relatively simple chemical engineering can be used to generate products that can function as near-perfect substitutes for oil and gas derivatives, such as petrol or aviation kerosene.

[7] Aviation fuel will be made from electricity which is converted to hydrogen (80% efficiency) and then to hydrocarbons (50% efficiency). So making chemically similar fuel will require input energy of two and a half times the energy value of the aviation fuel used today.

[8] My need for electricity for the lights in the house is ‘undelayable’. On the other hand, charging the car can usually wait for a few hours, or indeed a few days. So we don’t have to have power immediately available to meet all our electricity needs.

[9] Nevertheless, we do need to take into account the need for ‘undelayable’ heating, which is heavily concentrated into colder days in mid-winter. This will significantly raise peak electricity demand.

[10] For information, these are the estimates in David MacKay’s Sustainable Energy – without the hot air. Solar, 10 watts/m2, onshore wind 2 watts/m2, offshore wind 3 watts/m2.

[11] Future advances, such as the use of perovskite tandem panels may push this up to more than 7 watts).

[12] This sounds impossible, or at least very difficult. I don’t think it would be. Over 20% of the UK’s land area is given over to unproductive grazing of animals on rough pasture. This is concentrated in Scotland. However the total amount of all grazing land just in England would be almost sufficient to provide the total space required for the UK.

[13] Exclusive Economic Zone

[14] One of the reasons for this is that the North Sea is relatively unusual in having large amounts of space with less than 50 metres water depth. Other parts of the world will largely have to use floating turbines to achieve significant offshore wind capacity. This emphasis will help push costs down.

[15] The Excel worksheets which provide the backup calculations for this article are available from me. I will try to post them in a freely accessible place as soon as I have tidied them up to make them legible. Many of the calculations are necessarily approximate but I believe the figures in this article are broadly accurate.