Small solar array on rooftop© Photofusion/Rex Shutterstock

Recent cuts to government support have reduced the attractiveness of large-scale wind and solar investments in the latest Carter Jonas Energy Index, while smaller 50kW rooftop solar is the most attractive.

The index assesses renewable technologies against a range of factors, including financial returns (including available subsidy), development risk (cost and planning risk) and the availability and timescale of securing a viable grid connection.

See also: Planning rules to be relaxed for Scotland’s solar roof projects

While 50kW rooftop solar arrays do not necessarily give the highest rate of return, they are attractive given the Feed-in Tariff support still available, lower risk from generally not needing planning permission and relative ease of grid connection.

The report also says that despite recent cuts to Renewable Heat Incentive payments, biomass systems greater than 200kW are also attractive investments, particularly for properties off the gas grid. But small-scale (sub-200kW) biomass remains “financially challenging”.

For wind, 500kW turbines deliver the highest return on investment for the right site, however the lower planning approval rate, high development costs and risks associated with securing planning make it the riskiest investment, the report says.

“Each opportunity will be driven by site-specific circumstances and we always recommend careful assessment and due diligence of individual projects prior to any investment,” says Andrew Watkin, Carter Jonas head of energy and marine.

A summary of the main risks is shown below.

Carter Jonas Energy Index risks


Grid connection (availability and costs)

Wind speed and obstructions to wind flow

Planning approval

Long development timescale

Rooftop solar PV

Grid connection

Structural stability of buildings

Volatility of support


Volatility of support

Securing fuel supply (quality and price)

High capital cost versus fossil fuel equivalent

Higher maintenance requirements

Fuel storage


Extensive environmental and ecological surveys required

Limited suitable sites

Complex and lengthy planning process

Costs and income very site-specific

Anaerobic digestion

Feedstock availability

Volatility of support

Digestate disposal

Higher operation and maintenance costs

Ground-source heat pumps

Extensive groundworks required

Less effective on traditional buildings/heating systems