Their charges for electricity supplied from the grid are set to match those of the major suppliers in a given area. I'm currently paying 13.85p/4.45p on my Economy7 tariff. The first 900 day-time units per annum are charged at 29.14p.
Not necessarily the cheapest supplier, but they are a superb company to deal with and have always been extremely helpful on all matters relating to home generation. They have been particularly helpful in the changeover from ROCs to FITs, providing all the necessary forms and instructions on what needed to be done.