Solar 21, the energy group, has written to its investors saying that it “strongly disagrees” with a move by a number of investors to wind up two of its key companies. The winding-up petitions are being taken against two companies being used to fund a new waste-to-energy plant in England at a cost of £275 million, in a project known as EFW P2. Four of the 1,580 investors in this EFW P2 project are behind the petitions.  The petitions are listed for mention on Monday, and are based on a claim that the companies may become insolvent at a “future date.” Solar 21 told…