Renewable alternatives to nuclear in the UK

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As of mid-2020 the building of two new nuclear power stations are being proposed the UK: Sizewell C and Bradwell B. Sizewell C would comprise two EPR reactors, like the two currently being built at Hinkley Point C, with a combined capacity of 3.2 GW. Bradwell B would have two HPR1000 "Hualong One" reactors with a combined capacity of about 2.2 GW[1]. These new reactors will not increase the UK's clean electricity generating capacity when the imminent retirement of our existing nuclear fleet is considered.

Some critics, especially those opposed to nuclear energy, argue that these projects should not be built and the energy they would produce should be supplied by renewables such as wind, solar or avoided by improved energy efficiency and/or reduced use of energy overall.

Whilst the efficiency with which we use energy should be improved where possible, there are limits, as discussed by David MacKay in Sustainable Energy Without The Hot Air. Also many of the ways in which we can decarbonise our energy uses involve switching from fossil fuels to electricity, e.g. electric vehicles, for which we will need significantly more electricity which we need to be carbon zero or carbon negative. So improved efficiency and energy reduction don't seem promising ways of substituting for the roughly 10 GigaWatts of clean nuclear energy from our existing nuclear fleet which is due to be retired, let alone to supply increased needs.

Wind

See also Wind + battery

The UK has some of the best potential wind resources in the world, and wind already contributes about a fifth of our electricity,[2] similar to the contribution of our existing nuclear fleet[3]. Couldn't we substitute wind for nuclear?

In terms simply of energy output it would require that we more than double our existing wind fleet which we have built up over several decades. How many wind turbines would we need to substitute for just one of the proposed new nuclear power stations, and how quickly could we build them?

Taking the case of the proposed Sizewell C, we need around 3.2 GigaWatts of average power. The biggest wind farm in the UK is the Walney Extension,[4] which has a peak (or nameplate capacity) output of about 660 MW. The capacity factor of offshore wind is about 40% so Walney's average output is about 264 MW. So we need about 12 Walney Extension-sized wind farms to replace one Sizewell C-size nuclear plant.

Build time

Walney extension was approved in late 2014, construction started in August 2015 and completed in June 2018,[5] a period of 34 months for actual construction. At a similar rate of building it would take around 34 years to build a Sizewell C-sized wind farm, although it should be possible to shorten this considerably by building many turbines simultaneously (subject to sufficient production rate of turbines and blades, and availability of sufficient jack-up rigs and other machinery needed for construction).

It is not possible to significantly speed up construction of a single nuclear power plant since most of the work has to be done in a sequence e.g. initial ground work, concrete for the "nuclear island", installing the pressure vessel followed by other equipment, constructing the containment vessel, and various stages of testing, fuel, loading and commissioning. There is however scope for reducing the average build times of a series of similar reactors when they are built sequentially, as the crew doing e.g. the ground work and initial concrete pour can move on to the next site while the crew doing the next part of the project starts work.

Intermittency

The average rate of energy generation is not the only factor to consider. Whilst nuclear supplies energy constantly, 24*7, for a year or more at a time, wind is intermittent and may vary between its full "nameplate" capacity and zero. We can compensate for this in various ways:

  1. we could have another source of energy to make up shortfalls; this could be
    1. a generator that doesn't rely on wind, that can be turned on and off when we need it, or
    2. another set of wind generators located far enough away that variations in wind at the separate sites are uncorrelated,
  2. we can try to store enough electricity to provide a supply when wind is insufficient,
  3. we can try to reduce demand to match reduced supply.

Clearly the last option - reducing demand, to zero when there's no supply - is not compatible with our modern civilisation which depends on having electricity available for everything; keeping us warm in winter and able to see what we're doing in the dark, pumping our drinking water and sewage, keeping our food and medicines cool and safe, running our hospitals, trains, businesses, etc.

Building a duplicate wind generator possibly thousands of kilometres away where wind conditions are guaranteed to be radically different not only doubles the cost of the generators themselves but adds the cost of building extremely long, very high power transmission lines, and diplomatic challenges in persuading other countries to co-operate in such a venture. (In Germany local opposition has for years prevented the building of transmission lines from the wind-rich north of the country to the energy-hungry south; one may imagine the response of EU countries if the UK wanted to build thousand of pylons across their countries so that we could get power from north Africa or eastern Europe.)

So we need either a backup generator we can turn on when we need, or storage.

Storage

How much storage would we need?

Worst-case scenarios for wind outages in times of critical demand are stable winter anti-cyclones which can give periods of up to 3 weeks[6] of still air, clear skies, and freezing temperatures: high demand with no wind and very little solar[7]. To cope with that we would need to store 3.2 GW * 21 days * 24 hours-in-a-day = 1613 GigaWatt-hours of electricity. How could we store that much?

Britain has about 30 GWh of pumped storage[8] which could no doubt be increased somewhat, but it would be a huge challenge to reach 1600 GWh, let alone to do that multiple times over to replace other planned nuclear power stations with wind.

What about batteries? Tesla's original GigaFactory can in theory produce 35 GWh of batteries in a year[9] so one factory would take 46 years to produce enough batteries. We could build, say, 5 GigaFactories and reduce the time taken to produce enough batteries to 10 years — after we've built the factories, of course, and they take a few years, and cost around $4bn each.[10][11] And how much would the batteries themselves cost? The "holy grail" of battery costs is reckoned to be $100/KWh.[12] At this price our 1600 GWh of battery storage would cost $160 billion. For comparison Hinkley Point C, which is widely regarded (even by nuclear advocates) as overpriced[13], looks like costing around £20 - 25bn.

Backup

This is effectively the situation we have at present for wind and solar: we have a fleet of gas, coal, and biomass power stations which supply the electricity we need, less what these intermittent renewables are able to supply at any given time. But of course these generators emit CO
2
(albeit that those burning biomass should end up being closer to carbon neutral in several decades when the trees which they mostly burn have been replaced by re-grown ones). If we want to reduce our emissions to zero we need to convert or replace these generators with ones which capture and store the carbon they release.

Solar

We have seen that combining wind with gas, coal, or biomass, with Carbon Capture and Storage, could functionally substitute for the new nuclear power stations we are planning to build. How about solar?

The biggest solar farm currently planned in the UK is Cleve Hill solar park in Kent. It has a nameplate capacity of about 350 MW, about half that of the Walney Extension wind farm. However the capacity factor of solar in the UK is about 10%, so its average output will be about 35 MW and we would need almost a hundred such farms to equal Sizewell C. The cost of Cleve Hill is about £450m[14] so to total cost would be around £45 billion.

Cleve Hill will cover 360 hectares (890 acres) and a hectare is a hundredth of a square kilometre so we would need about 360 km2 of land, equivalent to a circle of about 20 km diameter. That's like the area of London within the North and South Circular roads, and more than the built-up area of most British cities.[15]

And that's just to replace one new nuclear power plant with solar.

Intermittency

Dealing with the intermittency of solar is far more of a challenge than for wind. The problem is not storing energy from daytime to night-time, but that during winter time the output from solar is negligible.[7]

If storing energy for 3 weeks of wind drought is impracticable, storing it for approximately 6 months is clearly not worth even thinking about. Thus the only possible backup mechanism for a zero-carbon solution is fossil fuel (or biomass) with CCS. And due to the low capacity factor of solar, for every unit of electricity supplied by solar our "backup" generator actually has to supply 9 units!

Footnotes and references

  1. Hualong One Wikipedia
  2. Wind power in the United Kingdom Wikipedia
  3. Nuclear Power in the United Kingdom World Nuclear Association, June 2020
  4. List of offshore wind farms in the United Kingdom Wikipedia
  5. Walney Extension Project Summary Walney Extension website via Internet Archive Wayback Machine
  6. See page 10 of Managing Flexibility Whilst Decarbonising the GB Electricity System - Executive Summary and Recommendations (pdf) by Energy Research Partnership; Aug 2015
  7. 7.0 7.1 The amount of energy supplied by solar PV in Britain over a year can be seen from this display from Sheffield University's Live PV generation web pages: Power supplied to from solar over a year
  8. Sustainable Energy Without The Hot Air pp191
  9. Tesla battery partner Panasonic sees higher Gigafactory output, cites Model S/X demand increase by Simon Alvarez in Teslarati on 10 May 2019
  10. Tesla was ordered to stop work on its $4 billion Berlin Gigafactory over environmental concerns by Isobel Asher Hamilton in Business Insider on 17 Feb 2020
  11. Note however that the Berlin factory is intended to produce cars as well as batteries, so this figure may be different from what a battery-only factory would cost. However we are interested only in a rough order-of-magnitude estimate of the costs so this inaccuracy should not be particularly significant.
  12. The Holy Grail of Battery Storage by Roger Andrews in Energy Matters on 18 Aug 2016
    referencing Holy Grail of energy policy in sight as battery technology smashes the old order (paywalled) by Ambrose Evans Pritchard in The Daily Telegraph on 10 Aug 2016
  13. Hinkley Point C cost breakdown pie chart.png
    Note however that approximately two-thirds of the price of Hinkley Point C appears to be its financing costs under the UK government's Contracts for Differences scheme used at the time; see The Hinkley Point C case: is nuclear energy expensive? by Joris van Dorp; Medium; 23 Dec 2019
  14. Britain's largest solar farm poised to begin development in Kent Jillian Ambrose; The Guardian; 24 May 2020
  15. List of urban areas in the United Kingdom Wikipedia