At the end of my recent post on the National Grid’s energy future scenarios I mentioned that I was working on a plan for decarbonizing the UK electricity sector that works in practice and which gets the UK least some way down the road towards an increasingly elusive green energy future. The work is now complete, and here I present five future energy options that employ nuclear, gas and variable amounts of wind to achieve large reductions in CO2 emissions while at the same time meeting UK demand in a typical winter month.
The options are designed to meet hourly electricity demand in February 20XX, where XX is an unspecified year in the future. Basic assumptions are:
- Demand in February 20XX is the same as it was in February 2013. (The February 2013 generation data are from Gridwatch.)
- Wind conditions in February 20XX are the same as they were in February 2013, allowing hourly wind generation in February 20XX to be estimated by factoring February 2013 wind generation.
- Hydro and “other” generation is the same as it was in February 2013.
- 20GW of the 28GW of the nuclear capacity currently in operation, planned or being considered will be on line in 20XX. Operating at a capacity factor of 90% this delivers a constant 18GW of baseload power.
- Gas-fired capacity remains substantially the same as it is now.
- All existing coal-fired capacity is decommissioned.
- In February 20XX there will be no significant amount of electricity available from imports, CCS, biomass, biogas or solar and no significant amount of energy storage capacity.
Generation mixes for the five options are quantified as follows:
- Nuclear plus hydro/other generation is the same for all options.
- Wind generation is progressively increased.
- Wind generation is added to nuclear plus hydro/other generation. If the sum exceeds hourly demand the surplus wind generation is curtailed. Shortfalls are filled with load-following gas and “peaking” generation.
Installed wind capacity increases from 10GW in Option 1 to 20GW in Option 2, to 50GW in Option 3, to 100GW in Option 4 and to 200GW in Option 5 assuming a capacity factor of 20%. Increasing wind capacity does not lower the requirement for gas capacity because peak load for gas is about the same in all five options.
Generation mixes, emissions reductions and percent renewables generation for the five options are summarized in Figure 1:
Figure 1: Generation mix, emissions relative to 2013 and percent renewables generation by Option
Option 1, which replaces coal-fired generation with nuclear generation and expands gas generation, achieves a 55% reduction in CO2 emissions relative to 2013 levels without expanding wind capacity. Options 2 through 5 show emissions continuing to decrease as installed wind capacity increases. In Option 5 they are cut by over 90% relative to 2013.
Increasing wind generation, however, comes at a cost. Figure 2 shows how wind and gas capacity factors decrease as wind capacity increases, to the point where in Option 5 they are down in the 10% range, which is hugely inefficient. Accompanying the increase in wind generation is a rapid increase in the percentage of wind generation that has to be curtailed. It is in fact impossible to increase renewables penetration much above 50% by increasing wind capacity because almost all of the wind generation added above the 50% level gets curtailed.
Figure 2: Gas & wind capacity factors and wind generation curtailments by option
Another problem is the erratic and largely unpredictable shape of the gas generation curve needed to match demand in the higher-wind cases. Figure 3 shows the generation curve for Option 5. The operators of the CCGTs, OCGTs and “peakers” that have to follow it will insist on being well compensated before agreeing to subject them to this level of abuse and underutilization:
Figure 3: Gas generation needed to match demand, Option 5
Figures 4 through 8 show generation by source for the five options. Option 1 (Figure 4) shows actual February 2013 generation with coal replaced by nuclear. The impact is to cut CO2 emissions to 43% of 2013 levels with renewables generation remaining at 8% of total generation:
Figure 4: Top graph: Monthly demand & generation by source for February 20XX. Bottom graph: Gas generation needed to match demand (hourly data) – Option 1
Option 2 (Figure 5) doubles wind generation over February 2013 levels. This Option cuts emissions to 38% of 2013 levels and increases the percentage of renewables generation (wind plus hydro/other) from 8% to 13%.
Figure 5: Top graph: Monthly demand & generation by source for February 20XX. Bottom graph: Gas generation needed to match demand (hourly data) – Option 2
Option 3 (Figure 6) expands wind generation by a factor of five. This Option cuts emissions to 27% of 2013 levels and increases renewables generation to 26% of total generation. At this level, however, curtailment of surplus wind generation becomes necessary. (Note that the gas generation curve assumes complete shutdown of gas-fired capacity during wind surpluses. If an operating reserve is maintained the level of wind curtailment during surplus periods increases.)
Figure 6: Top graph: Monthly demand & generation by source for February 20XX. Bottom graph: Gas generation needed to match demand (hourly data) – Option 3
Option 4 (Figure 7) expands wind generation by a factor of ten. This Option cuts emissions to 16% of 2013 levels and increases renewables generation to 39% of total generation, but 24% of total wind generation now gets curtailed:
Figure 7: Top graph: Monthly demand & generation by source for February 20XX. Bottom graph: Gas generation needed to match demand (hourly data) – Option 4
Option 5 (Figure 8) expands wind generation by a factor of twenty. This Option cuts emissions to 7% of 2013 levels and increases renewables generation to 50% of total generation. Wind curtailment, however, is now up to 50% (the light green “curtailed” areas on the Figure go way off scale).
Figure 8: Top graph: Monthly demand & generation by source for February 20XX. Bottom graph: Gas generation needed to match demand (hourly data) – Option 5
Some future energy scenarios make copious use of solar. I do not. As well as being inefficient at high latitudes – particularly in the winter when the power is most needed – solar roughly doubles the number of hoops the gas plants have to jump through to balance generation against load. This is illustrated in Figure 9, which shows Option 3 with approximately 20GW of solar added. Compare the gas generation curve with Figure 6, which shows Option 3 without the solar:
Figure 9: Option 3 with solar generation added
UK Energy Policy:
Any future UK energy scenario should conform with established UK energy policy, and with the current fixation on wind and solar it’s easy to forget that UK energy policy statements heavily emphasize nuclear and gas. The July 2011 National Policy Statement for Nuclear Power Generation, for example, considers nuclear to be “vitally important”:
Any new nuclear power stations consented under the Planning Act 2008 will play a vitally important role in providing reliable electricity supplies and a secure and diverse energy mix as the UK makes the transition to a low carbon economy.
And in his introduction to DECC’s 2012 “Gas Generation Strategy” paper Ed Davey acknowledges that gas is “crucial” to keeping the lights on and the economy working:
Gas – as a flexible source of generation which emits half the CO2 of coal – will be needed to help balance the relatively inflexible and intermittent low-carbon generation our policies will bring forward. It will provide crucial capacity to keep the lights on and the economy working.
So nuclear and gas are acceptable future energy options.
All options depend on having 20GW of operating nuclear capacity in place by 20XX. Can this be done? Without specifying what year XX refers to the answer is of course yes. But according to the 2014 DECC report New Nuclear in the UK five proposed nuclear plants with a combined installed capacity of 15.4GW have firm development plans and scheduled completion dates, and adding them to presently-existing nuclear plants still in operation would give ~19GW of installed nuclear capacity by 2027. Three other designated nuclear sites could add ~9GW more, giving a total of ~28GW of installed nuclear capacity by, say, 2030. Adding 20GW of nuclear capacity over the next fifteen years is therefore not only feasible but also in accordance with existing plans. And all it will take to add it is a firm commitment on the part of the government and maybe a little less messing around with experimental reactor designs.
The gas generation curves peak out around 30GW in all cases, meaning that roughly 35GW of installed gas capacity would be needed. The UK presently has about 30GW of installed CCGT capacity, so this should not be a problem either. There would even be time to modernize or replace some of the more inefficient older plants.
Replacing coal with nuclear will eliminate the UK’s dependency on imported coal, much of which has been coming from Russia in recent years. Gas imports will either increase or decrease depending on the level of wind generation, with the gas plants burning 80% more gas than they did in 2013 under Option 1 but 70% less under Option 5. I haven’t looked into the situation regarding security of uranium imports but assume that it will not be a problem.
I haven’t looked into this in any detail either, but 20GW of nuclear at £5,000/installed kW will cost £100 billion, and to this we can add maybe £5 billion for additions and upgrades to gas plants. Spreading this £105 billion over 15 years gives £7 billion/year, less than the £9 billion/year the UK is projected to be spending on renewable energy subsidies by 2020. Moreover, roughly 50GW of offshore wind capacity would be needed to match the 18,000GW average output of the nuclear plants (although delivery would of course be intermittent), and at £3000/installed kW this would cost about £150 billion, 50% more than the nuclear plants.
The five energy options described above actually define a continuum of possibilities where nuclear generation is held constant, wind generation is progressively increased and decreasing amounts of gas generation are used to match wind generation to demand. The best choice of options occurs at the point where the advantages and disadvantages balance out, but exactly where one picks this point depends on what one considers most important. Being more concerned with system reliability and efficiency I would be inclined to pick Option 2, which cuts emissions by over 60% below current levels but includes only 13% renewables generation. Those more concerned with emissions and sustainability might prefer Option 4, which cuts emissions by over 80% below current levels and includes 39% renewables generation, but at the cost of a significant decrease in system efficiency and reliability. I doubt that anyone would go for Option 5.
Finally, all the options presuppose a continuing supply of fossil fuels. A fully-sustainable, zero-emissions energy system powered dominantly by intermittent wind and solar will not be achievable until energy storage can be commercialized on a large enough scale.
Footnote: Comparisons are invited with Euan Mearns’ July 2013 post Energy Matters 2050 pathway for the UK, which I note with interest includes over four times as much nuclear as I do.