David Mackay Highlighted Problems With Solar Power In 2013
By Paul Homewood
h/t Joe Public
Back in 2013, the late David Mackay, at the time the Chief Scientific Advisor to DECC, wrote a paper called “Solar energy in the context of energy use, energy transportation and energy storage”. He went into a lot of detail evaluating solar potential, and his Abstract found that “in a decarbonized world that is renewable-powered, the land area required to maintain today’s British energy consumption would have to be similar to the area of Britain”.
But there is one particular section which caught my eye:
For solar photovoltaics to supply 6 per cent or more of today’s average electricity demand in the UK would involve some technical challenges. The UK’s National Grid (2012, personal communication) has advised me that, if 22 GW of solar capacity (370 W of capacity per person) were attached to today’s grid, then the system would, at some times on some sunny summer days, be unacceptably challenging to control and unacceptably lacking in robustness to a sudden fall in demand: the control of the grid’s frequency relies on having sufficient inertial generators on the system; in its advice to me, National Grid reckoned that 40 per cent of demand at any time should be served by inertial generators, and it assumed that solar and wind generators would contribute no inertia. This constraint could in due course be relaxed if additional inertial services could be supplied (e.g. by wind generators that incorporate energy stores and can therefore synthesize inertial properties) or if control-commands could when necessary be issued to solar generators to instruct them to reduce their output. (Future generation codes in the UK will require solar generators to have the capability to respond to such signals.)
Last year, in comparison, solar supplied just 2% of the UK’s power.
But then he continues:
Let us assume that these technical constraints can be solved. What if solar photovoltaics supplied 11 per cent or more of today’s average electricity demand in the UK? Figure 11 shows the time variation of the output of a simply-modelled fleet of 40 GW of solar panels in the UK (670 W of capacity per person), whose average output (4.4 GW, if we assume a load factor of 0.11) would equal 11 per cent of current electricity demand. The total output is occasionally close to the total electricity demand; at these levels of solar capacity, peaks of solar output would certainly cause electricity supply to be shed, unless our electricity system is enhanced by the addition of (i) large pieces of flexible demand; (ii) large interconnectors to other countries willing to buy excess electricity; or (iii) large-scale energy storage.
Electricity demand in the UK and modelled solar production, assuming 40 GW of solar capacity. (a–c) The upper curves show Britain’s electricity demand, half-hourly, in 2006. The lower data sequence in (a) is a scaled-up rendering of the electricity production of a roof-mounted south-facing 4.3 kW 25 m2 array in Cambridgeshire, UK, in 2006. Its average output, year-round, was 12 kWh per day (0.5 kW). The data have been scaled up to represent, approximately, the output of 40 GW of solar capacity in the UK. The average output, year round, is 4.6 GW. The area of panels would be about 3.8 m2 per person, assuming a population of roughly 60 million. (For comparison, the land area occupied by buildings is 48 m2 per person.) (b,c) The lower curves show, for a summer week and a winter week, the computed output of a national fleet of 40 GW of solar panels, assuming those panels are unshaded and are pitched in equal quantities in each of the following 10 orientations: south-facing roofs with pitch of (1) 0°, (2) 30°, (3) 45°, (4) 52°, and (5) 60°; (6) south-facing wall; and roofs with a pitch of 45° facing (7) southeast, (8) southwest, (9) east and (10) west. On each day, the theoretical clear-sky output of the panels is scaled by a factor of either 1, 0.547, or 0.1, to illustrate sunny, partially sunny, and overcast days. Note that, on a sunny weekend in summer, the instantaneous output near midday comes close to matching the total electricity demand. Thus, if solar photovoltaics is to contribute on average more than 11% of British electricity demand without generation being frequently constrained off, significant developments will be required in demand-side response, large-scale storage, and interconnection.
This is an issue I have raised previously with regard to wind power. In other words, that a large scale build of wind capacity would lead to a lot of surplus electricity on windy days.
What Mackay’s analysis shows is that, without large scale storage, even relatively low roll out of solar and wind capacity will lead to underutilisation of that capacity. This, in turn, will drastically increase the cost of solar and wind power.
The Mackay paper is here.