Dublin-based renewable firm Solar 21 is to write off more than £43 million of investors’ money as part of an orderly wind-down of its business aimed at warding off insolvency proceedings. The company, which has been experiencing significant cash flow problems for some time, apologised to investors for the “reset” which will involve the divestment of its assets.  “Solar 21 acknowledges and sincerely apologises for the stress and hardship that this difficult news has caused to our valued investors and broker advisors who have supported us over the years and wishes to assure brokers and investors alike that the Group…