Thursday, 1 May 2014

How much more does rooftop solar cost?

The subsidies for solar electricity (PV) panels are currently 5.4p/kWh higher for residential rooftop panels than for ground mounted systems. For large solar farms, the difference is even greater, at 10.4p/kWh. If a quarter of our electricity came from rooftop PV rather than large solar farms then that would cost us £104 on an average household electricity annual bill. This is even worse than the difference between onshore and offshore wind (see How much more does offshore wind cost?). Granted we don't want ugly solar farms cluttering up the countryside - but how ugly are solar farms and how much do we not want them?

These figures are based on the current rates for the Feed in tariffs (FiTs). The FiTs for small rooftop PV are 16.8p/kWh compared to 11.4p/kWh for ground mounted panels not attached to a building [1]. As of February 2014 there was 2 GWp of solar PV installed receiving FiTs of which more than half (1.3 GWp) was for small rooftop systems [2]. For really large scale PV, more than 5 MWp, the subsidy comes from renewable obligation certificates (ROCs) rather than FiTs and currently amounts to only 6.4p/kWh. Subsidy under the ROCs is subject to market forces and only applies to power that the grid suppliers buys - with the FiTs they are obliged to buy all the power exported. So FiTs are a very very good deal.

By the way the largest solar farm in the UK at the moment is 34 MWp on 150 acres at a disused airfield near Wymeswold. There is an even larger system of 200 acres near Portsmouth that has received planning permission.

The government's recent solar strategy report is mindful of the unpopularity of large scale PV.  It says '... the public response to large-scale solar farms which have sometimes been sited insensitively has begun to erode the otherwise record levels of public acceptability the solar PV sector as a whole enjoys.' They are keen to see more PV in small and medium installations - up to 1 MWp [5]. It is predicted they will reduce the subsidy on large scale systems and increase the subsidy on small scale instead [6]. The FiT generation tariff for rooftop installations in the 50-100 kWp range is currently 10.7p/kWh - still 4.3p larger than the ROC level for larger systems.

Building mounted PV reduces the load on the grid if the building uses a significant part of the power generated and particularly if this encourages load shifting away from peak times. However, PV by itself does not help reduce peak demand at all because the peak occurs on winter evenings when the sun is not shining. There are a number of other reasons why the grid operators have said they can only accommodate up to about 10 GWp of PV on Feed in Tariffs without taking special measures. '...above this level would make managing the grid significantly more challenging and costly' [5]. However, the government expects to have 10-12 GWp of solar PV capacity by the end of this decade.

Solar PV farms are not purely industrial - they can accommodate wildlife under and between the panels and pasture for grazing animals - as shown in this picture from a talk on Reach Solar Farm.

Of course we don't have to have PV at all. Onshore wind and nuclear power are both cheaper (see How much more does offshore wind cost?). However, adding carbon capture to fossil fuel power stations is not. Given that we need clean, secure energy the cheapest options are onshore wind, large solar farms and nuclear.

I do appreciate that for people who have chosen to live in the countryside renewable energy brings unwelcome changes to the landscape. Perhaps a compensation system similar to that proposed for fracking would be reasonable. However, it seems to me that this government is keen to promote rooftop solar PV because it is the least unpopular form of all the low carbon technologies, even though it is strategically and financially not the best option.

[1] Calculating Renewable Obligation Certificates (
The figures I have calculated include both the generation tariff (14.38p/kWh for rooftop PV up to 4 kWp and 6.61p/kWh for standalone system) and the export tariff (4.77p/kWh). I have assumed half the electricity from the rooftop PV is exported, so 14.38+4.77/2. I have assumed all the electricity from the standalone panels are exported so 6.61 + 4.77. 
[2] Monthly central Feed in Tariff register statistics (
[3] UK’s Largest Solar Farm Puts Wymeswold on the Map (Lark Energy)
[4] UK’s biggest solar farm will be built between Waterlooville and Fareham ( Dec 2013
[5] UK solar PV strategy (
[6] UK solar farm subsidies to be cut (Guardian) April 23 2014

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