Commercial solar cost in South East

In South East, solar systems of 10-50 kW cost an average of £1,330 per kW in 2025/26 (DESNZ). A south-facing kW at Reading generates about 851 kWh a year (PVGIS). A 30 kW system would cost about £39,900 and, used on site at 28.59p per kWh, pay back in about 5.5-10.9 years.

By system size in South East

System size	Typical cost	Generation a year	Value a year, all used on site	Payback (all used / half used)
10 kW	£13,300	8,510 kWh	£2,433	5.5 / 10.9 years
20 kW	£26,600	17,020 kWh	£4,866	5.5 / 10.9 years
30 kW	£39,900	25,530 kWh	£7,299	5.5 / 10.9 years
50 kW	£66,500	42,550 kWh	£12,165	5.5 / 10.9 years

Payback is the same at each size because DESNZ gives one average cost per kW for all 10-50 kW systems. In practice larger systems usually cost less per kW, so they tend to pay back sooner.

How this is worked out

Cost: DESNZ mean cost per kW of Total Installed Capacity for 2025/26, from MCS-certified installations. It includes equipment, installation and connection. DESNZ only covers systems up to 50 kW; larger systems usually cost less per kW.
Generation: PVGIS (European Commission) for 1 kW facing south at the default tilt, with 14% system losses.
Value: generation × the share used on site × the DESNZ price for small businesses (28.59p per kWh incl. CCL, 2026 Q2). Exported power is counted at nothing, so payback is conservative if you are paid for exports.
Not included: maintenance, inverter replacement, panel ageing, finance costs, grants and tax relief. These are averages for planning, not a quote.

Sources

Solar photovoltaic (PV) cost data: Total Installed Capacity, Department for Energy Security and Net Zero (data from the Microgeneration Certification Scheme)
Photovoltaic Geographical Information System (PVGIS), European Commission Joint Research Centre
Prices of fuels purchased by non-domestic consumers in the United Kingdom (QEP 3.4.1 and 3.4.2), Department for Energy Security and Net Zero