How to assess whether rooftop solar is right for your farm

With equipment costs at historic lows and a favourable government policy towards renewables, now could be a good opportunity to invest in rooftop solar photovoltaic (PV) panels.

However, this is only the case if systems are designed carefully to meet the needs of your business, cautions Savills senior energy consultant, Henry Cody.

See also: 157 solar farms approved amid food security fears

“The past couple of years have seen incredibly low equipment pricing for solar PV, but there are signs that certain factors are starting to push prices up.

“If you are considering investing, there might not be a better time,” he reckons.

One potential inflationary factor is the recent rise in the precious metals markets, particularly silver, which is used in PV panels.

This could add “a couple of percent” to the capital expenditure for projects, although it is unlikely to be a definitive factor in determining whether a project goes ahead or not, Henry says.

Assessing costs

With farm margins already squeezed, investing in solar is not a decision to take lightly, so good homework is crucial, says Henry.

Farmers should start by carefully evaluating if solar is right for the broader aims of the business, for example:

• How much generation capacity is required?
• Is battery storage needed to balance differences in generation and demand?
• What is feasible within the budget available?

“These are long-term, 25- to 30-year investments, so there needs to be foresight to plan what’s needed now, and in the future,” Henry says.

“Batteries, for example, can serve a fantastic purpose. But depending on the size and type of batteries used they can almost double the capital expenditure of some projects, so won’t be for everyone.

“There are things you can do to future-proof designs to take batteries at a later date, such as fitting a hybrid inverter or planning for AC coupling, but this will still add some cost.”

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With so much variation in the characteristics, constraints, and pre-installation work required for farm rooftop sites, he says it is hard to give reliable estimates of cost and payback without knowing all of the details.

Figures of £800-£1,200 for each kW of installed capacity are often quoted, which may be a reasonable ballpark cost for a straightforward project (for example, fitting solar to a new barn roof), but figures can look very different for more complex projects, he says.

“Payback can be anything from a couple of years to a couple of decades. If anyone is quick to promise you a certain payback without doing due diligence and assessing your site, I’d be very cautious.”

Henry says an assessment of site constraints and remedial costs must be part of the feasibility process for rooftop solar. Key considerations include:

• Electricity supply (age, size and condition) – for single-phase supplies, an export limit of 3.68kW applies. Upgrading to a three-phase electricity supply will increase costs.
• Does the potential solar site contain asbestos? Any removal should be done professionally.
• Structural integrity – is the building and roof suitable for solar PV or is structural work needed?
• Building orientation and pitch – generally a south-facing roof, at a 30-40deg angle is optimum, and variations around that will affect electricity output and payback.
• Roof area required – as a general rule, 5sq m of roof area is needed for each 1kWp of generation capacity, but this varies depending on the type/size/wattage of panels and other factors.
• Grid availability – are new connections permitted by your local distribution network operator?
• Aesthetics and planning – rooftop solar generally falls within permitted development, but some projects may require full planning (for example, if they are within an area of outstanding natural beauty, national landscape, national park, or near airports), so check with your local authority what is allowed.