Four Gigawatts of Illusion , Or One Reactor of Reality?

Britain has just awarded 4.9 gigawatts of new solar capacity under the latest Contracts for Difference round.

On paper, it sounds vast. Gigawatts always do. The language of scale is politically intoxicating. Ministers speak of transformation. Press releases speak of progress. Campaigners speak of momentum.

But electricity systems do not operate on press releases. They operate on delivered energy ,  particularly in winter.

Under Allocation Round 7a, approximately 4.9 GW of solar PV secured contracts. � That figure represents theoretical maximum output under perfect sunshine. It does not represent what Britain will actually receive over the course of a year , or, more critically, on a dark January evening when demand peaks.

According to the Department for Energy Security and Net Zero’s own load factor analysis, the median solar load factor in 2024/25 was 9.2 per cent, with a weighted mean of 8.3 per cent.¹ In plain English, 4.9 GW behaves more like 0.4–0.45 GW on average across the year.

That translates into roughly 3.6–4.0 terawatt-hours annually.

Impressive? Perhaps.

But now look at winter.

DESNZ data shows that in the October–December quarter, the median solar load factor falls to 4.7 per cent.¹ During that period, all 4.9 GW combined will produce approximately 39 GWh per week.

And during the winter evening peak , the hours between 4pm and 7pm, when households cook, heat and light their homes , solar contributes effectively nothing at all.

This is not ideological. It is astronomical. The sun sets.

Now consider the alternative.

The British-designed small modular reactor being developed by Rolls-Royce is rated at 470 megawatts electrical output.² Assuming a conservative 90 per cent capacity factor , standard for modern nuclear plant , one such unit would produce around 3.7 TWh per year.

That is roughly the same annual energy as the entire 4.9 GW solar award.

In winter weeks, however, the contrast becomes starker still.

One SMR would deliver approximately 71 GWh per week — nearly double the winter-week energy of all AR7a solar combined.

Solar, by contrast, drives expansion outward. It requires reinforcement of 132kV and 400kV lines. It necessitates inverter-based stability solutions. It increases curtailment risk when supply outstrips demand in summer and vanishes in winter.

This is not a cultural debate between “green” and “grey”. It is a systems question.

What delivers adequacy per acre?
What delivers reliability per pound?
What reduces the need for ever-expanding transmission corridors?

When measured honestly, the arithmetic becomes uncomfortable.

Four-point-nine gigawatts sounds revolutionary. Yet in delivered energy terms, it is equivalent to roughly one 470 MW nuclear unit operating continuously.

The political class continues to celebrate nameplate capacity as if it were achievement. But households do not heat their homes with nameplate capacity. Hospitals do not power operating theatres with theoretical maxima. The grid does not stabilise itself with sunlight after sunset.

Britain faces a simple choice.

Continue multiplying intermittent capacity across vast swathes of land  and then spend billions reinforcing the network to manage its volatility , or build compact, firm, synchronous generation that stabilises the system at its core.

The first option expands complexity.
The second reduces it.

If winter security and land stewardship matter, then delivered energy must become the metric   not headline gigawatts.

Until then, we will continue mistaking scale for substance, and illusion for infrastructure.

References

1.  Department for Energy Security and Net Zero, Feed-in Tariff Load Factor Analysis 2024/25 (median 9.2%; Oct–Dec 4.7%).
2.  Rolls-Royce SMR official specification (470 MW electrical design output).