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The mayor of London, Sadiq Khan, has put air quality and the environment in general at the heart of his term of office; 鈥淲ith nearly 10,000 people dying early every year in London due to exposure to air pollution, cleaning up London鈥檚 toxic air is now an issue of life and death,鈥�. The Greater London Authority has announced a solar strategy and a soon to be formed 鈥淓nergy for London鈥� programme that will be responsible for providing 鈥減ublic sector intervention to help others realise larger-scale decentralised energy projects that the market is failing to develop and deliver.鈥�

The aim is laudable, but it is noticeable that he focuses specifically on current energy policies, which do not actually improve the issue of poor air quality.

In particular, as part of the new programme there will be a big drive on solar power but not solar hot water. On the surface this is logical; London has been criticised as having the lowest amount of energy from solar of any of the 20 largest cities in England and Wales.

But think carefully and there is a good reason why London should not be ashamed. Deploying solar power in London is difficult and inefficient for all the obvious reasons; shading, congestion, heritage, old buildings, small roofs and complex ownership. The same can be said of other cities but it is particularly the case in London. I know of one solar power installer that doesn鈥檛 work in London because of these issues.   

It was suggested before the mayoral election that the candidates should target 750MW of rooftop solar power across London by 2025. Based on our calculations at WSP Parsons Brinckerhoff from projects we have worked on that will cost about 拢2.25bn to deploy. If you approached some of the solar contractors we work with you could get that deployed on a field basis outside London for about 拢650m, about third of the cost, and it would deliver exactly the same benefits in terms of CO₂ emission reductions and energy produced.

It would be much more logical and consistent to prioritise solar hot water over solar power in our cities

In fact, it would be more because field systems are designed more optimally; they face the right direction, avoid shade, and are maintained properly. Remember solar power does not in itself improve air quality as it is simply displacing mains electricity, which doesn鈥檛 emit anything at the point of use.

It would be much more logical and consistent to prioritise solar hot water over solar power in our cities, as this typically displaces gas combustion, improves air quality and produces consistent CO₂ emissions savings. Although suffering from the same difficulties as deploying solar power in cities, solar hot water has to be deployed where it can be used because, unlike power, you can鈥檛 transport long distances.

The other major policy is to require combined heat and power (CHP) systems for new developments. Again, the simple logic is seductive; CHP avoids wasting all heat that is produced when you generate power. But it is now apparent, that over a lifetime they actually increase CO₂ emissions, because our electrical grid is decarbonising, and more immediately they increase local air pollution compared with gas boilers or all-electric systems because they need more gas to make the power and because they operate at higher temperatures.

We need to get past the simple good/bad dichotomies and the idea that doing something is better than doing nothing

Instead it would be more logical to reduce energy demand as this reduces bills, CO₂ emissions and air pollution, and to also start electrifying our buildings as soon as possible. (My previous blog on the topic can be read ).

The key to this debate is policymakers ensuring they are getting good, thought-out advice. We need to get past the simple good/bad dichotomies and the idea that doing something is better than doing nothing.

It is this lack of thinking things through that has led us to the situation where we have diesel vehicles polluting our lungs after they were promoted as 鈥渆co鈥�. Electric cars will undoubtedly improve our environment. We now need the same thinking for our buildings too.

My plea to Mr Khan (and other city authorities): please think about how we can benefit from renewable energy and improve our environment at the same time.

Barny Evans is environmental associate director for WSP | Parsons Brinckerhoff