 LaST WEEK's letter "Renewables will pay rich rewards", from David Nussbaum, Dale Vince, Ben Caldecott and Juliet Davenport, illustrates the blinkered thinking of some renewable energy groups.  Let there be no doubt, the main purpose of solar and wind farms is to grind out cash for landowners and investors; whereas the public, including the very poor, are compelled to pay.  There is nothing wrong in making money - it's a question of how it is done. In these cases, electricity companies are forced to pay the investors whether the unpredictable levels of electricity produced are used or not. Huge amounts of wind power in particular are wasted in the small hours. The single greatest reason for an average bill increase of ?200 a year per household is to pay for these inefficient wind farms.  Efficient renewable energy can be excellent. There is, for example, enough wave and tidal energy surrounding Britain to supply our energy needs five times over. That is where our investment should go.  Philip Sullivan Frolesworth, Lutterworth