heating, but the ability of a storage heater system to use electricity at times when, for example, wind generated electricity could not otherwise be used, may in conjunction with a smart grid give storage heating a new role in the future. In some countries, the current design of the electrical generating system may result in a surplus of electricity from base load power stations during off-peak periods, and storage heaters may then be able to make use of this surplus to increase the net efficiency of the system as a whole. However, future changes in supply and demand—for example as a result of energy conservation measures or a more responsive generating system—may then reverse this situation, with storage heaters preventing a reduction in the national base load. Other technologies may incorporate demand response electronics to sense when there is a change in supply and demand. Thereby, they ensure that these loads only use off-peak electricity. Further advances in supply technology could provide for a more bespoke 'supply and demand' tariff system to make smart grid sensing technologies like dynamic demand a more viable financial prospect. Compared to other forms of electric heating, storage heaters are cheaper to run and they impose lower peak loads. The highest peak loads come from instantaneous electric heating, such as immersion water heaters, which create heavy loads for short durations, although instantaneous water heaters may use less electricity overall. High-efficiency ground source heat pumps are able to use up to 66% less electricity than storage heaters in heating by recovering heat from the ground, and are regarded as preferable even though they use electricity throughout the day. Air source heat pumps give similar efficiency increases and are generally easier and cheaper to install for domestic use. These are not to be confused with air conditioning (A/C) heat pumps which provide cooling with an increased carbon footprint and are now considered to be an environmental liability in some, (in particular hotter climate), countries. Where alternatives to electricity exist, hot-water central heating systems can use water heated in or close to the building using high-efficiency condensing boilers, biofuels, heat pumps or district heating. Ideally hot water heating should be used. This can be converted in the future to use other technologies such as solar panels, so also providing future-proofing. In the case of new buildings, low-energy buildings such as those built to the Passive House standard can