Solar Power System for RPod 171

Originally posted by Tars Tarkas Originally posted by Rustler   Yes, I'm obsessive about maximum efficiency.  It makes perfect sense to me to try your best to minimize losses due to wire length, gauge, connections, etc., but it seems to me that the bottom line is to get enough juice to recharge your battery.  So if, say, a 100w panel is what you need to do that, but it loses 5% or 10% of it's output to all that resistance, why not just go with a 120 panel?  I know you can continue to worry about the 5% to 10% loss with your 120w panel, but you're getting everything you need, and a little more. Of course one of the reasons to strive for maximum efficiency with your set up is to try to counteract the things that are much harder, or impossible, to control, like a cloudy day, or not wanting to hang around the campsite all day to turn your panels to follow the sun. TT

One of the things that might not be intuitively obvious is that when using an MPPT controller, you can go for maximum voltage. You could string together a pair of small 75 watt 37-volt panels in series for ~~ 74 volts. Sounds ridiculous, but the two panels could be getting partial sun and only putting out 18 volts each (total of 36 volts), yet because of the MPPT controller, you can still be getting a decent charge to your 12 volt battery. If you had a 300 watt 18V panel and use a PWM controller in the same circumstance, the panel would only be running about 8 volts, and you'd get zilch to the battery.

Originally posted by GlueGuy Originally posted by Tars Tarkas Originally posted by Rustler   Yes, I'm obsessive about maximum efficiency.  It makes perfect sense to me to try your best to minimize losses due to wire length, gauge, connections, etc., but it seems to me that the bottom line is to get enough juice to recharge your battery.  So if, say, a 100w panel is what you need to do that, but it loses 5% or 10% of it's output to all that resistance, why not just go with a 120 panel?  I know you can continue to worry about the 5% to 10% loss with your 120w panel, but you're getting everything you need, and a little more. Of course one of the reasons to strive for maximum efficiency with your set up is to try to counteract the things that are much harder, or impossible, to control, like a cloudy day, or not wanting to hang around the campsite all day to turn your panels to follow the sun. TT One of the things that might not be intuitively obvious is that when using an MPPT controller, you can go for maximum voltage. You could string together a pair of small 75 watt 37-volt panels in series for ~~ 74 volts. Sounds ridiculous, but the two panels could be getting partial sun and only putting out 18 volts each (total of 36 volts), yet because of the MPPT controller, you can still be getting a decent charge to your 12 volt battery. If you had a 300 watt 18V panel and use a PWM controller in the same circumstance, the panel would only be running about 8 volts, and you'd get zilch to the battery. Even if you're only using one 37 volt panel under similar circumstances, the 18 volts would still be enough to juice up your battery. So it's not just efficiency, but also being able to squeeze out some power under not-ideal solar situations.