The current vogue for PV on domestic roofs needs to be extended to the nation’s commercial building stock

Barny Evans

Rooftop solar is very much the flavour of the month. The government has removed Renewable Obligations Certificates (ROCs) support for large ground mount systems so they aren’t viable at the moment. Meanwhile, rooftop solar up to 1MW will generally be designated as a “permitted development” and finally the so-called “lift and shift” right (removing them from one place and putting them somewhere else) has been approved.

A combination of these factors means that rooftop solar is now a lot simpler and more secure as an investment but also that an industry that delivered 2.8GigaWatts, the equivalent to 5% of peak UK power demand, of (mostly ground-mount) solar last year now probably has to refocus that capacity on to roofs.

And why not? Although solar farms are more efficient - in terms of per kWh generated - than rooftop systems, they are generally of less benefit to our overall electric system. They don’t help make our businesses more competitive and arguably reduce CO2 emissions by less. Conversely rooftop systems are normally installed where at least some of the powercan be used.

This has the benefit of reducing the cost of electricity for the factory, office, or home that it serves and also has the benefit of not exporting power onto what is an increasing full electrical network. As a technology they are silent, emit no air pollution, do not interfere with other technologies, and are relatively uncontroversial.

There are challenges. Rooftops are increasingly contested spaces, whether for recreation, flora and fauna, plant or power generation

We held an evening seminar on the subject last week and both the number of people who attended and the discussions afterwards testified to the fact that people from all angles are very interested in the subject.

However, although domestic rooftop solar is going well, commercial roofs have been a slower burn. This is despite non-domestic roofs being generally better suited to solar as their demand tends to follow that of the solar power generation  i.e. they are busy in the middle of the day when the sun is out and power is being generated. The power they generate can be huge, particularly on buildings with large roof to floor area ratios.

The benefits are obvious regardless of your motivation: they reduce CO2 emissions, reduce bills, and give greater price security and improve Energy Performance Certificate ratings (this is very important as a building can’t be let from 2018 if it has a rating of F or G.

We worked on a recent project where our energy efficiency team demonstrated how an office could improve from an an F to an E rating with a relatively small solar array. For new buildings with increasingly challenging regulatory compliance and local authority targets, rooftop solar is the obvious first port of call.

There are challenges. Rooftops are increasingly contested spaces, whether for recreation, flora and fauna, plant or power generation. In addition, as mentioned above, the national grid is increasingly full, contractual and structural issues are potential obstacles so disruption to operations must be minimised. Even the sizing calculations must be carefully considered to optimise returns, roofspace, and on-site demand profiles. Finally there are a range of different funding options and incentives out there to be considered. There are answers to these challenges, they just require robust analysis.

Rooftop solar will increasingly become not just ubiquitous, but crucial for new and existing buildings. All companies and homeowners should be considering how it can benefit them now.

Barny Evans is associate for energy and sustainability, at WSP | Parsons Brinckerhoff