Ecodyn has been working for several years with the community development company on Fetlar in the Shetland Islands. Grid connections in Shetland are even harder to come by than they are in the Hebrides; the islands are not connected to the UK national grid at all, so connection offers are made under a separate system, called Northern Isles New Energy Solutions (NINES). A connection under NINES comes with a maximum export constraint which can be altered annually, so while you might be able to export all the electricity generated by your community turbine this year, next year you might be allowed to export nothing at all. This means that any installation has to be designed so that it can operate effectively without exporting to the grid, which in turn requires significant investment of time and resources in designing a robust energy management system. It also requires a suitable level of energy demand on site.
While this project has been through various iterations, it is now based around two 25kW turbines which are connected into a new shed housing the export control equipment, as well as the island’s electric bus, which is also charged from the renewable supply. The electrical supply connection to the shed also supplies the local primary school, which is across the road from the shed, and a private residence some 150m away. While these loads all help, the turbines will still normally generate more electricity than can be used on site.
The export control system can be programmed to limit export at any point down to zero, with the excess power being diverted to two 4,000 litre thermal storage tanks. One of these will be connected to the hot water and central heating system for the primary school, the other will supply the private house. In this way, the wind turbines can be run at full capacity, generating as much renewable energy (and income) as possible, without the need for any export agreement from the DNO. The system was commissioned in January 2016.