The mayor of London wants large projects in the capital to generate one-fifth of their own energy from renewable sources. Is there a snowball’s chance in hell of this happening?

Ken Livingstone wants large developments to generate 20% of their own energy; at present they must generate 10%. It is a commendable aim, given that buildings are estimated to be responsible for 70% of London’s carbon emission. Unfortunately, the policy won’t change that for a long time: in 2050, 60% of the built environment will have been in existence today and 40% will predate 1985, when Part L of the Building Regulations was introduced.

One of the risks with this strategy is that it could draw attention – and funds – away from other measures for reducing emissions. The London Plan sets out a hierarchy of energy-saving measures to be addressed by developers. At the top of the list is passive design, such as natural ventilation, night cooling and passive solar heating. These can be achieved with clever design at little cost. Indeed, if air-conditioning can be designed out, significant cost savings can be achieved.

The only criterion for which the mayor has set a benchmark is the proportion of total energy generated by on-site renewables. There is no clarity as to what is considered an acceptable baseline for this or how it should relate to the revised Part L of the Building Regulations. Part L2 – which applies to buildings other than dwellings – also includes a 10% renewables element that might be interpreted as being the same 10% presently prescribed by the mayor. However, should the London Plan merely be reinforcing Building Regulations or should it be encouraging an enhancement?

It is my view that the plan should set benchmarks that relate to Building Regulations. If the mayor wants all large projects to perform better than Part L, he should specify by how much. If he requires an element of renewables but would also like his hierarchy to be applied, why can’t he specify benchmarks for passive design measures, combined heat and power plants, tri-generation and low-energy services design? The problem is deciding how this relates to Part L and what constitutes a reasonable baseline carbon emission – bearing in mind that all designs will include an element of passive design and some applications don’t lend themselves to CHP.

If there is a significant heating load, biomass fired boilers might be able to cater for more than 20% of energy demand

In other words, it is not a good idea to be too prescriptive.

The big question is whether the 20% rule will make projects unviable. There is no simple answer to this. For example, if a development is to sit on a large plot, has significant cooling requirements and bore holes can be drilled economically into a productive aquifer, then the requirement could be met at a reasonable cost. Or if there is a significant heating load, biomass fired boilers might be able to cater for more than 20% of energy demand. On the other hand, a tall office located on a tight site may not be suitable for either option, and solar photovoltaics will be too expensive and wind turbines are likely to provide only 2-4% of demand.

A solution for these developments might be to tap into local energy networks, as planned by the London Climate Change Agency and EDF, although these are not going to be available overnight.

So my answer to the question “20% renewables – can it be done?” is “sometimes”. However, another question has to be asked: “Is this going to divert funds from more cost-effective measures for reducing carbon emissions?” I would like to see a coherent strategy that relates to Building Regulations and encourages passive design, efficient services design as well as on-site renewables, while recognising the potential for connection to off-site energy networks in the long term.