Hello, I have been trying to go green, I Have purchase somesolar panel they are about 45watts I been putting it against my window and getting ok power out of it enough for my lights and a couple of low watts gadget (cellphone, 2v light, portable dvd) for couple of hours.But its seem to drain the 2v faster then I can charge Am I getting the most power out of my panel?Or should I place it on the roof? I'm in Texas and it gets hot and sunny the sun beam my room windows pretty good during 4pm-6pm.
The MOST efficient placement is on a motorized mounting that constantly moves it to face the Sun directly. Almost nobody does that because it is clumsy and expensive. The best fixed position is facing X degrees due south of straight up, where X is your latitude. I am in Austin, at about 30 degrees latitude, so on the south side of a 30 degree pitched roof would be ideal. The direct south facing it the best average to catch morning and afternoon sun, with most efficient pointing at noon. The tilt equal to latitude is the best average between the high Sun in summer and low Sun in winter, with most efficient pointing in spring and fall.
Solar panel generates fairly low, unreliable source of energy. They are most likely very expensive. Despite all of that, your window may act as a beam filter by refracting the beam or reflects them off trough total internal reflection causing a low yield of sunlight harvest. Sunlight is also necessary to hit the panel 90 degrees to harvest maximum output.
outside is going to be much better. You can't tell but glass is actully opaque to many ranges of 'light'. If you look at advertising for windows you may see claims to reduce sun fading of your carpet/ furniture. That is because the glass blocks UV. Solar panels get some of their energy from UV light. Also some windows are engineered to block IR to help insulate better when the house is cooler than the outside. Again, solar panels get some of their energy from light in the infrared range. And finally if you're charging batteries the 'off angle time' is still important. The amount of light absorbed is pretty closely related to the cosine of the angle that the sun is 'off' of the direct. so when the sun is 45 degrees off of perpendicular the panels still get cos45 =.707 or about 70% of the available energy. (In practice it's a little less than that because not as much energy gets to the panel to be absorbed as at midday). But anyway, you can figure two hours of morning or late afternoon sun will give you as much energy as hour of midday sun. So if the panel is inside, you miss out on that available energy.
It will generate MUCH more current if placed outside of the window. The best position is pointing directly south. Over the period of one day, you will get the most average sunlight pointing in that direction.
