How much energy could a community generate itself?

In a talk I addressed the topic ‘Greening Our Energy: How Soon?’, using recent research [1] to show that the UK could be self-sufficient in energy using wind and solar alone, along with significant levels of long-term energy storage to ensure energy security. The talk also discussed  how electrification of much of our energy use reduces the overall energy demand, something that Mackay and others have talked about for years.

A question raised by an audience member was ‘How much energy could a community generate itself?’. This essay aims to answer this question, using my home town of Nailsworth as an example. As I said in the talk, the focus is on wind and solar.

When considering the total carbon emissions we are responsible for (so-called ‘consumption emissions’) studies [2] include literally everything. Including imported goods and produce. However, in terms of future UK generation, it is better to consider just the energy produced and consumed in the UK (the so-called ‘terrestrial emissions’).

We can narrow the scope further by considering those forms of energy consumption that are truly local and therefore best considered as being potentially met in whole or in part by community energy.

The two big ones are: 

• electrified private cars and public transport (we’ll call these simply ‘transport’).
• heat pumps used to heat our homes and offices.

In terms of carbon emissions, these two represent 60% of Nailsworth’s terrestrial emissions, and 40% of our consumption emissions, so highly significant, however they are viewed [2].

According to Mackay [3], these would require energy consumption of 18 kWh and 12 kWh, respectively, per person per day in this electrified future world. The total including all energy needed would be 68 kWh/p.d and this is the figure used in the Oxford study referred to in my talk. So these two uses of energy would account for 44% of the total consumption of energy used.

The total of 30 kWh per person per day for transport and heating implies an average delivered power supply from community energy of 30/24 = 1.25 kW per person in Winter. In Summer we still need hot water but the great majority of heating is for space heating so we’d need about 12/24 = 0.5 kW per person in Summer for transport.

Nailsworth has a population of around 5,500, so let’s assume a future population of 6,000, which would imply a power supply required (for transport and heating) of 1.25 kW x 6,000 = 7,500 kW = 7.5MW in Winter, and 0.5 kW x 6,000 = 3,000 kW = 3MW in Summer.

Now the capacity factors for wind and solar in England [4]  are on average, respectively, about 40% and 3% in winter and 20% and 20% in summer.

The winter solar generation depends a great deal on the orientation of the panels – much more so than in summer. I have taken a relatively pessimistic figure, assuming on average East/West orientation, which still provides some energy in Winter but I have based estimates assuming wind alone meets the required demand in winter.

So let’s start with winter where we will discount solar [5]. Applying the capacity factor of 40% (in this case, dividing by 0.4) the 7.5 MW delivered energy would require 7.5MW/0.4 = 18.75MW of wind energy capacity to meet it. Let’s round that up to 20MW. 

For onshore wind turbines, we cannot use the largest ones available and are potentially restricted to say 5MW turbines. Only 4 of these would meet the power requirement of 20MW. Currently we have one 500kW wind turbine high above Nailsworth owned by Ecotricity.  Having established this precedent, and given changing public attitudes, and both Stroud District Council and Nailsworth Town Council having declared a climate emergency, one would hope this could be implemented, especially if it is a community energy scheme. 

Now, should we increase the capacity to deal with peaks in demand or lulls in wind? No, in my view. Community energy will be connected to the grid. When Nympsfield above Nailsworth is having a lull, other community sites around the country, and indeed large resources such as North Sea wind farms, will be able to take up the strain. 

A national energy storage strategy would deal with more extreme lulls that cover most of the country, as discussed in the talk.

Moving now to Summer, the four wind turbines proposed would deliver (now multiplying the wind capacity by the summer capacity factor), 20MWx0.2 = 4MW, so we’d need solar to deliver the remaining requirement of 7.5-4 = 3.5MW. Using the capacity factor for solar in Summer (at 20%, twice as good as the average for the year, 10%), that gives us a required solar PV capacity of 3.5MW/0.2 = 17.5MW. 

The average domestic solar PV installation in the UK has been 3.5kW, but with improved panels let’s round this to 4 kW. Assuming that the average home has 3 occupant, we anticipate 2,000 dwellings. They could provide a capacity of 2,000 x 4kW = 8MW, or about 45% of the solar capacity required. Yes, I know many live in flats, but the goal here is to look at broad brush feasibility. 

Ground mounted solar would then need to deliver 9.5MW. It’s been estimated that “Approximately 25 acres of land is required for every 5 megawatts (MW) of installation while 6 to 8 acres will be needed for a 1MW farm” [6]. So lets assume 1MW parcels at average of 7 acres each. We’d need 9.5 x 7 acres or about 70 acres. 

To give a sense of scale, Minchinhamption Common is 182 hectares or 450 acres, so we’d require the equivalent of 15% of it’s land area. This is not a proposal to use this common I should stress, just to give a sense of scale and feasibility. Nevertheless, shade (for our grazers and humans alike) will come at a premium by 2050 [7] so who knows?

This feels like a doable number.

To the extent to which domestic solar cannot be fully deployed, then ground mounted solar could be increased, or solar on commercial or civic buildings could take up the strain. I haven’t included these but they could make a substantial contribution (actually, are already making a contribution), albeit not necessarily being able to be classed as ‘community energy’.

The question naturally arises as to whether Nailsworth could use small hydro power using its streams, or as a mini Dinorwig, for energy storage, harking back to the Mill Ponds used during the 19th and 20th Century, when they provided some energy resilience to the wool mills of the town. It could of course play and role, and even if at a scale which is less significant numerically [8], could help in enabling local energy resilience [9]. There is strength in diversity, as nature teaches us.

Research on renewables offers up some pleasant surprises in how different forms of it can complement and support each other [10]. All of this is detail to explore of course.

My main goal in this essay was to establish if Community-based renewables – and specifically wind and solar – could compete in relevance with the large national assets such as North Sea wind, and thus provide a strong case for Community Energy schemes.

The answer is a definite yes.

Community Energy could provide a significant percentage (over 40%) of the terrestrial energy demand of a town like Nailsworth, throught the year. This would shift the control of energy, to a significant extent, away from large commercial assets, and could have untold benefits for local communities [11]. Nationally, such diversified and highly dispersed resources would enhance energy security for the whole country.

Richard Erskine, 6th March 2024

NOTES

[1] ‘Greening Our Energy: How Soon?’, Richard Erskine, Nailsworth Climate Action Network, https://www.nailsworthcan.org/blog/greening-our-energy-how-soon 

[2] IMPACT: Community Carbon Calculator, Centre for Sustainable Energy and the University of Exeter, https://impact-tool.org.uk/ 

[3] Mackay (2008), Sustainable Energy without the hot air, http://www.withouthotair.com/ 

3.1) Note that 68 kWh/p.d for a 70m population, say, in 2050 would amount to a UK energy demand per year of 68 kWh/p.d x 60m p x 365 d/y = 1,489 TWh/y – the total energy requirement that the Oxford Study shows can be achieved with wind and solar (actually, they show we could do double that quite feasibly with out excessive use of land or sea area).

3.2) Note that the (18+12)/68 = 0.44 or 44%

But be careful not to assume that means 44% of our consumption emissions being eliminated by transport and heating as it depends on the carbon intensity of different processes. It could be more or less. Actually, due to relatively efficiencies, moving to electrification of heating in particular and also transport, make very good contributions to displacing carbon-creating energy usage. As a percentage of our terrestrial emissions, transport and heating amount to about 60%.

[4] Estimating generation from Feed in Tariff installations, James Hemingway, DECC, December 2013, https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/266474/estimating_generation_from_fit_installations.pdf 

[5] For example, see https://leoht.co.uk/pages/how-much-do-solar-panels-generate-in-the-winter-  and also Sam Jeans, How much electricity will solar panels generate?, Federation of Master Builders, 6th November 2023, 

https://www.fmb.org.uk/homepicks/solar-panels/how-much-electricity-will-solar-panels-generate

[6] Everything You Need to Know About Solar Farm Requirements, Richard Burdett-Gardiner, 26th July 2023, The Renewable Energy Hub, https://www.renewableenergyhub.co.uk/blog/everything-you-need-to-know-about-solar-farm-requirements 

For ground mounted solar the area used has to take account of the spacing of tilted panels to allow for shadowing etc.

[7] Heatwaves such as those in 2022 will become much more common by 2050 on our current trajectory https://www.bbc.co.uk/news/science-environment-62207466 

So who know what solutions will be needed to provide shelter from the heat?

[8] I’m emotionally attracted to the gravitational storage / micro hydro idea. After all, the Mill Ponds around Nailsworth kept the mills running when the streams ran slack. It’s part of our history. But then again, Dunkirk Mill needed only about 16kW to run, a thousandth of what we are now considering, and even 20 of these would match the vastly greater energy footprint of modern society. The Centre for Alternative Energy’s Zero Carbon Britain report includes an estimate of 8 TWh of generation from hydro (including large and micro) for UK, so about 1% of the total.

[9] Assuming 20 reservoirs at 100m above their twins on valley floor, each holding 10,000 cubic metres of water, and a round trip efficiency of 75%, one could store about 40 MWh of energy, a not inconsiderable amount. If each reservoir used a 100 kW turbine (not the largest micro turbine but illustrative) then they would generate in total 2 MW, or nearly 30% of the Nailsworth average power demand, although at full power, the reservoirs would be exhausted in 20 hours. If larger turbines were used, the duration at full power would decline in proportion (eg. if 500 kW, then in 4 hours)

For storage, Micro hydro would have to compete with (or maybe, collaborate with!) domestic or small scale batteries. For example, if each household had a battery with 100kWh storage, then 2000 of these would equal 200 MWh, and would be equivalent to 200MWh/7.5MW = 26.7h, so about 1 day’s worth of storage. That again is pretty significant local resilience to augment a national massive (30 day) storage capacity discussed in the essay.

[10] While either micro hydro or batteries may have limited capacity, they could make an extremely significant contribution to balancing the local grid over a day or so, and that could in its turn relieve pinch points in the distribution grid when there are short term mis-matches between supply and demand. Indeed, I wrote a piece – Small Is Beautiful – local renewables and storage can catalyse the greening of grid – based on some modelling in the USA that showed that even small amounts of local solar could have a disproportionately large impact in enabling increasing grid-scale wind resources. Similar modelling of a diverse array of renewable assets could reveal other pleasant surprises.

[11] A Community Energy scheme could, if setup right, ensure that it incorporates energy security for all as a founding principle, using profits to help fund the restrofitting (insulation, solar, heat pumps, etc.) of poorly built or maintained accommodation and social housing, for example.

THE END