Weighing up the pros and cons of Solar PV

Renewable energy technical consultant, Joe Fergusson, gives his thoughts on the current state-of-play in the solar PV and battery storage markets, and on the feasibility of these technologies in light commercial situations.

Anticipating the UK economy emerging from pandemic induced ‘intensive care’, there are loud calls from a range of pressure groups for the ‘rebuilding’ policies that will lay the foundations for our route to a Carbon-neutral Britain to be legally enforced.

As these policies very slowly take shape it is hoped that the waning direct support schemes for low-carbon heat and power technologies might be ‘re-loaded’, giving a much-needed boost to the heat pump, hydro, solar, biomass and small wind industries. However, the only support so far under consultation is a £4,000-perinstallation Clean Heat Grant to replace the Renewable Heat Incentive when that finally dwindles to nothing in March 2022.

Solar PV is evidently considered a mature technology, sustainable without further state subsidy. The installation cost of the panels, inverters and mountings is not changing much over time but the price of those components has now fallen to a point where, even without the feed-in tariffs that drove the market between 2011 and 2018, it is now cost-effective to install a system of an appropriate size, ie. Such that the majority of the power generated is consumed on site, displacing power that would otherwise be purchased. With the electricity price now risen to 15-17p per kilowatt hour (kWh), the payback can be attractive, especially when carbon savings are a consideration.

Output from solar PV systems is highly variable on a daily and seasonal basis.  For an example, on a cloudless May day with a cooling breeze in central Scotland, a 90 module (panel) PV array covering 150m2 of roof, or ground-mounted, might generate 200 kWh over the day.  Some of the output, up to 25 kW, could be used by machinery or by heat pumps heating a building, and some stored in a battery bank. The surplus would be exported, earning a guaranteed minimum export tariff. On a dull day in November or February this same system might generate just 20 kWh in the day or less.  The annual total should be around 21,000 kWh.

Depending on many factors the value of this system’s generated power, in savings and exports, could be in the region of £3,000. The installation of such a system (not including battery) may cost in the region of £30,000, giving a payback period of about a decade, before allowing for any future electricity price increases.  The system should last at least 25 years, the output diminishing only very slowly over the long term.

Where there is significant onsite consumption during the hours of darkness it is worth considering the feasibility of storing surplus power in batteries sized to suit normal overnight consumption. This is likely to rise with the fast-growing uptake of electric vehicles. A commercial battery system appropriate for the PV installation described above, storing 30-40kWh, might cost £15-25,000 at the moment.

The efficiency of panels and batteries may rise slowly and Government support could possibly return, but whether these factors will overcome the savings lost to delay is the moot question.

Exciting developments in ‘smart tariffs’ that reward those making battery capacity momentarily available to the National Grid for frequency and voltage balancing purposes could accelerate investment paybacks considerably. As these systems continue to fall in price our advice is to at least ‘future-proof’ any new building development or PV system by ensuring that battery banks and the associated control hardware – and also EV charging equipment, benefitting from 3-phase power supply – can be easily retrofitted in years to come.

Independent advice on the ideal system sizing and configuration will ensure the best outcome.

Article posted on 01/11/2021