having solar panels under your grow lights is definetly not worth the money/loss of energy and frankly makes no sense.keep in mind that energy cannot be created or reused, a self sustaining growhouse is against almost every rule of physics there is, so if you can do that then congrats and here is your nobel prize So say you have a 1000w HID running. Also consider that no energy is being wasted in the form of heat. You pay the electric company for 1000w to run your light. You then recapture the 100w that you have not hitting your plants and convert the light to energy and inefficiently return it back to electricity to power a fan. Why not just plug the fan into the wall? The energy has to come from somewhere. Another point is that in an efficient grow room you should have little to no wasted light and only wasted light can be reused by a solar panel. Mylar/hoods should focus as much light as possible on the plants. So basically the bottom line is this, go spend $50 on making your grow light efficiently use all of its energy on your plants and just plug your fans/pumps/whatever into the wall. The energy has to come from the electric company at some point