When wind energy production is high, and electricity demand is low, the laws of supply and demand dictate that the price of electricity goes down. When wind energy production is relatively small compared to "traditional" production, the effect is limited. But when wind energy starts to play a more important role in the Nation's electricity production, the effect becomes more pronounced. In a country like Denmark, with a considerable wind energy production, prices actually drop to very low values when production is high and export cables are already used to maximum capacity. For a wind turbine owner, this sitation is demotivating. Worse, new investors in wind energy production are scared off by this scenario. Therefore, a solution must be offered - and can be offered with the help of electrical energy storage. Ideas for energy storage are currently studied intensively, but most solutions are associated with high costs and with sunstantial energy losses in the storage process.
"Night Wind" is a new concept for storing electrical energy at low costs and practically wthout losses. It makes use of existing Cold Stores, large facilities for storing refrigerated and frozen products. When there is an excess of wind energy, the cold store is switched to maximum capacity. The refrigeration machines will work overtime, and the products in the cold store will be cooled below their normal storage temperature. The effect is that the excess electrical energy is converted into thermal energy, into "cold". When the cold store is "charged" the refrigeration machines resume to operate at their normal level, keeping the products at a constant temperature (which is now below normal). This situation persists until a time comes with electricity shortage. The cold store's refrigerating machines are then switched off - and the elctricity they would normally consume now becomes available to other users on the grid. The product temperatures now will rise, until they reach their initial storage temperature and the cold store is "discharged".
Because the cold stores is using relatively more electricity when there is an excess of electricity and the electricity price thus is low, and uses relatively less electricity when the prices are high, the Night Wind concept is economically attractive for cold store owners.
Night Wind project summary (pdf)
Cold Store economics with Night Wind (pdf)
Night Wind implementation (pdf)
Product Quality during night wind operation (pdf)
Night Wind Control System (implementation)
