The cool way to save energy

Lord Redesdale, the Liberal Democrat energy spokesman, tabled The Dynamic Demand Appliances Bill in the House of Lords on 16 January as part of an initiative to urge the UK government to put its weight behind new technology to help curb climate change. If the bill is adopted, it will have implications for the take-up of renewable energy, the operation of some domestic and commercial building services and will pave the way for intelligent electrical appliances to reduce their energy consumption at peak times, helping to reduce carbon emissions.

To see why dynamic device control is useful, it's first necessary to understand how the UK's national grid operates. Because it must maintain its frequency at 50 Hz and electricity cannot be directly stored, the grid has to be continually balanced - ie electricity supply must precisely equal demand, even when millions of customers switch loads on and off.

To maintain this balance, National Grid (the company responsible for operating the grid) has to pay for power stations to continually change their output, using response generators whose output is continuously adjusted, depending on demand. These generators often run at reduced capacity, which is inefficient, hence expensive (the response service costs an estimated £80m annually) and produces vast amounts of unnecessary CO2 emissions.

Intelligent control

The dynamic demand concept is simple. All it would take for a domestic fridge to become "dynamic" is a low cost micro-controller fitted within the fridge to measure the frequency of the grid's alternating current. The controller would turn the fridge on and off according to its internal temperature and the needs of the grid. When there is less power available, it would turn off earlier and when there is excess power, the fridge switches on earlier and stays on for longer. If necessary, the controller will override this, to ensure the refrigerator doesn't stray out of the acceptable temperature range.

Dynamic Demand, a not-for-profit company set up in 2005 by academics, campaigners and engineers to promote the technology, has built and tested a demand control device on a domestic fridge at their London headquarters. It worked successfully, with minimal effect on the chilled food temperature - scientists funded by the government's market transformation programme will now carry out a similar test under laboratory conditions.

The theory is that if millions of electrical appliances were fitted with dynamic demand control to switch them on and off, they would act together and so reduce the need for generators to run at part capacity, cutting their CO2 emissions. In principle, any device that operates to a duty cycle, such as air conditioners, heat pumps and water heaters, could be used.

According to simulation studies undertaken by Dynamic Demand, the combined demand from appliances is far in excess of current levels of response. In the UK, the maximum current response is 1324 MW. The organisation estimates that domestic refrigeration alone has a combined electricity demand of 1900 MW, giving it the potential to replace a large proportion of generator-based response services and their associated emissions of up to 0.6 million tonnes of carbon a year.

That said, the Bill's biggest impact on climate change will come not as a result of running the existing national grid more efficiently, but through encouraging the use of renewables. If the UK opts for more wind or wave power in the future, there are concerns that large amounts of these randomly variable renewable energy sources connected to the grid could make it unstable. By using demand control devices, these fluctuations can be more easily controlled. The technology might also be useful in helping prevent a system blackout if a power station fails or the grid is sabotaged.

The challenge now is making dynamic demand happen. The House of Commons failed to embrace this technology in the Management of Energy in Buildings Bill last November - but the clause was unopposed, so may still find its way into future legislation. Lord Redesdale was impressed with its potential and tabled the private member's Bill in the Lords where it was unopposed. Its second reading is scheduled for 24 March, and the DTI is considering holding a conference on demand side management.