Energy storage thanks to refrigeration

Electrical energy is notoriously difficult to store, especially on a large scale and this can be particularly problematical when dealing with irregular sources such as wind power for which there can be a great mismatch between energy supply and demand. The Night Wind Cold Store project aims at storing wind power at night. The principle is simple: to cool the cold stores and products (as if charging a battery) to a greater extent when the energy supply exceeds demand and energy prices are lower, and to release this energy during day time peak hours. In the case of frozen foods, slight temperature variations do not entail important efficiency losses. The temperature variations should not exceed the frozen foods temperature range (-18°C to -27°C) limit. However, it is essential for the proponents of the system to certify that the "Night Wind" battery operation has no adverse effects on the quality of the stored products. Tests conducted over 8 months with 10 different food samples showed that the attributes of foods stored in frozen state at variable temperatures were comparable but generally slightly inferior to those of foods maintained at a constant temperature. It is also necessary to develop a specific control system to operate a cold store as a Night Wind "battery", taking into account parameters such as input of wind energy predictions, energy cost predictions, calculation of time-series for lowest costs or optimal grid control, control of the capacity of the refrigeration compressors, measurement of air and product temperatures, adjustment of the dynamic cold store model in order to optimize (future) temperature predictions, etc. The differences in the time scales of the air temperature (minutes) and the product temperature dynamics (days) make it very difficult to perform optimization of compressor-capacity time series, but recently a fast control system was developed and successfully tested on a small storage facility with success. From Cold Storage of Wind Energy - Night Wind, September 2008, by S.M van der Sluis, President of IIR section D and project coordinator, www.nightwind.eu