What happens when a hectare of UK land is transferred from agriculture to producing electricity from solar panels? This note looks at the impact on energy production, the UK’s trade balance and the productivity of the economy. The numbers show the huge advantage of using land for solar electricity. At current prices the electricity from a solar field is worth at least 20 times the value of wheat produced on the same land.

The analysis is prompted by persistent reports that the British government is intending to block the use of all but low quality land for solar farms.

Map of the south of the UK, with colours reflecting the quality or availability of the agricultural land

A map of the southern UK. The colours reflect the quality of the agricultural land. Under the government’s possible new rules, only yellow and light brown areas could be used for solar. Most of these parts of the country are in national parks, river valleys, uplands or inaccessible moors and are thus unsuitable for solar.

First of all, some numbers on the current state of the UK solar industry.

· Including rooftops, solar capacity is currently about 14 gigawatts.

· This uses about 0.1% of UK land and generates about 4% of all electricity.

· Current plans suggest an active pipeline of around 30 gigawatts or more awaiting permission or construction.

· At current wholesale prices, or indeed at the maximum price caps for renewables recently floated by the UK government of around £50 per megawatt hour, solar appears to be profitable to build across most of the country.

· However the recent rise in interest rates, which will directly affect the costs of solar developers, may reduce the financial attractiveness of solar expansion.

1, Energy productivity

One the roles of agriculture is to convert solar energy into food. When we talk of ‘calories’ we are referring to a measure of energy. So, for example, we can very simply convert the number of tonnes of grain produced on a hectare of land (about 2.5 acres) to megawatt hours.

Let’s use some average UK figures to compare the energy produced by a solar farm and a wheat crop. This will be approximate, of course. Yields vary for both grain and PV in each year and in different parts of the country.

Energy yield - wheat

Typical UK wheat yield About 8 tonnes per hectare

Energy content of wheat About 4 megawatt hours per tonne

Typical energy value of one hectare of wheat About 32 megawatt hours per hectare

Energy yield – solar PV

Typical solar field capacity About 0.5 megawatt per hectare

Capacity factor for a field in southern England About 11%

Total energy produced per year About 480 megawatt hours per hectare.

The energy yield from solar, using these rough approximations, is fifteen times the energy from wheat. Even that number is too favourable to wheat. Fields have to be rotated between crops each year and except in the very best locations need to be rested. So grain is not produced every growing season. Second, I have used the average figure for wheat across the UK. Most planned solar fields are in the less agriculturally productive regions of the country, implying that a conversion to solar results in a lower loss of wheat production.

‘But we can’t eat electricity’ will say the supporters of the proposed new policy. But neither can we power our houses with wheat.

2, The impact on the UK’s trade balance

The UK is a significant net importer of cereals. In the last year for which figures are available, the UK imported over 2 million tonnes were imported while exports were about a quarter of this figure. If a hectare of wheat field is converted to solar, UK imports of wheat will typically rise but energy imports will fall.

Of course wheat prices vary from year to year. The Ukraine war has introduced new instability because the country is a major exporter of grain. I use a figure of £300 a tonne for wheat, approximately the October 2022 level.

Increased cost of importing wheat

Typical UK wheat yield About 8 tonnes per hectare

Price About £300 a tonne

Value of extra imports if field is converted to PV About £2,400 a hectare.

Decreased cost of importing gas

Typical electricity production of solar field About 480 megawatt hours per hectare

Average efficiency of gas power station About 60%

Energy value of gas to make 480 MWh electricity About 800 megawatt hours

Cost of gas (Normal times) About £16 a megawatt hour

(October 2022) About £100 a megawatt hour

Amount of gas imports saved by a 1 hectare solar field

(Normal times) About £12,800 a year

(October 2022) About £80,000 a year

Usually, the saving on imported gas from converting a wheat field to solar PV is about 5 times the cost of importing the grain from that field. At the moment, the multiple is 33 times; every hectare converted would improve the UK’s balance of payments by £77,600.

3, Impact on production.

A farmer growing wheat has to prepare the ground, by the seed, sow it, fertilise and protect the crops, harvest the crop and then dry the grain. A solar farm costs a large sum to install but then very little to maintain each year for the thirty five years or so of its potential existence.

The UK government has recently suggested it may cap the price at which wind and solar farms can sell their output. At the moment, before any restriction, contracts between solar farms and their direct customers are being agreed at prices well above £100 per megawatt hour. But in the analysis below, I have used a figure of £100 for current rates and I assume that any price cap on solar might be around £50 a megawatt hour.

Value of wheat output

Typical UK wheat yield About 8 tonnes per hectare

Price About £300 a tonne

Value of extra imports if field is converted to PV About £2,400 a hectare.

Value of solar output

Total electricity production About 480 megawatt hours per hectare

Value of production

(At £50 a megawatt hour) About £24,000

(At £100 a megawatt hour) About £48,000

Depending on the price assumed, the value of the output of a solar field is therefore between 10 and 20 times the value of the wheat produced.

If economic ‘growth’ is vitally important, as the government asserts, there is no question that solar is far better than wheat for the UK.