Our cities are posing real energy challenges

Around 70% of the energy we use in the built environment goes on space and water heating, and the typical energy source used to generate this is gas. Electricity is important too. One of the expectations of a first world economy is uninterrupted power; some of us can remember the blackouts of the mid ‘70s. So what are the issues now? Well typically, around 35% of our electricity is generated by coal power stations (together with nuclear at 20%, gas at 25%, renewables less than 15% and imported power the rest).

We currently have a margin of about 20% available capacity to meet peak demands. By 2016, the Large Combustion Plants Directive will have closed many of the the coal stations. Renewable energy, principally from offshore wind farms, is expected to replace much of this capacity, but available peak margin will have dropped to around 5%.

So far so good – so what’s the problem? Well the wind does not blow all the time. In fact, in recent years, so called ‘blocking highs’ (high pressure systems) have sat over the North Sea several times a winter. When that happens, the wind may drop for the best part of a week, and wind turbines turn hardly at all. (Ironically, it is likely that blocking highs happen more often as a result of climate change). Under these circumstances, if nothing else is done, power grid controllers may enforce rotating cuts.

Fortunately, if rather late in the day, several remedies may be available, such as grid-scale energy storage and interconnectors to Europe. Currently we have little more than one pumped hydro system in Wales (Dinorwig), rated at 2.5% grid capacity. Recently, the attention of politicians has been drawn to this, and science minister David Willetts announced a £30m investment in capital equipment to support university research in Energy Storage. This should create knowledge leading to new investment in plant. Spot electricity prices (high in times of peak load) are likely to make grid storage an attractive business proposition. High voltage DC (HVDC) links have been established with several counties, and import a few percent of grid capacity.

Of similar importance is reduction in energy demand in homes and offices. This is dependent on measures like insulation and heating controls, and the way people use their houses – remember that more than 70% of energy consumption in homes is used for space and water heating – so while low energy appliances help, the ‘low hanging fruit’ is around reducing heat leaks. Further grid capacity savings are available through smart metering which ultimately will allow supply companies to control appliances with ‘deferrable functions’ (like tumble dryers, freezers, etc.). The ability to automatically switch off such loads can eliminate the need to build reserve power stations to fill in the peaks in demand.

Much electricity is generated from gas, new sources of which may be available through fracking – this will be the subject of a future column.

Professor Jeremy Watson is director of science and technology at Arup