WHILE shale gas has grabbed most of the headlines in recent months, another form of unconventional gas has quietly been establishing itself in Scotland. Scotland’s first “gas to grid” anaerobic digestion project in Coupar Angus, Perthshire, came on line towards the end of 2014 and a number of others are currently in various stages of development. There is no doubt that commercial scale anaerobic digestion gas-to-grid has arrived in Scotland. Anaerobic digestion (AD) is a natural process where, in the absence of oxygen, organic material is broken down by bacteria to produce biogas. The technology is not new. AD plants producing biogas have been widely used for some time. The gas produced was typically used for on-site heating or for the production of electricity. However, if there is no on-site or neighbouring demand for heat, then using the gas to solely produce electricity only uses around 30-35 per cent of the energy in the gas. A far more efficient method of harnessing the energy content, and one with reduced emissions, is to clean up the gas and inject it into the gas grid – into the pipeline networks that supply our homes and businesses, bringing green gas to all. By selling into the grid, developers of projects create a market; no longer are they concerned with the financial stability of a single on-site user of gas. It also has a number of other potential benefits.