Microgeneration is classified by ESB Networks as grid connected electricity generation up to a maximum rating of 11kW when connected to the three phase portion of the distribution grid (400V). The vast majority of domestic and agricultural customers are connected to the single phase portion of the distribution grid (230V) and for these customers to be classified as microgenerators the maximum technical rating permitted is 5.75kW. These ratings are in line with Irish conditions prescribed in European standard EN 50438. However ESB Networks accept applications for generators up to 6kW.
The microgeneration section of the SEAI website is a valuable resource which is suggested reading.