Originally Posted by jam0o0
ok i'm new. i've been researching all the ins and outs of building your own rv. this seems to be the place to get good answers. my background is mechanical engineering and design. but i could use some guidance with this electricity stuff.
so 1000W A/C,... 7 hours a day... i'll get 5 hours of peek sun per day
Here are a few things to think about when designing a Photovoltaic system:
You only charge during daylight hours. You have to get all the power you need in that time. One commonly overlooked factor is how quickly you can push that energy back into the batteries. Here's a good rule of thumb: the fastest you can charge a battery bank is 1/10 the total Amp hour capacity.
You said 1000Watts 7 hours per day. To make that 110V alternating current power to run the A/C you need an inverter. Let's say it's a REALLY nice one and it 90% efficient. So you need to make 7hrs * 1000W * 1.1 = 7.7 Kw-hours of power and get it into your batteries.
7.7kw-hrs = 640 Amp-Hours in a 12 Volt battery. Now keep in mind you can only run the battery down 50% AT MOST (better to stay above 80%) so you should have a battery bank capacity of at least 1300 Amp hours. Let's say you use Trojan T-105 Batteries (a common choice) which have 220 Amp-hours. So you need 6 pairs of batteries. (it takes two batteries in series to make 12V and capacity only adds in parallel).
12 batteries at $140 each. Now how fast can you charge them? Max charge rate is about 1300 * 1/10 or 130 amps. You need to replace 640 amp-hours so you'll need to charge at the max rate for 640/130 = 4.9 hours.
Oh, good we have 5 hours of daylight! Seems doable right? But wait, let's look at battery charging a bit more carefully. When you first start charging a "dead" battery, the battery will take lots of energy (the full 130 Amps) but as it charges it will take less and less. This is because the difference in voltage get smaller and smaller. In reality, it will take MUCH longer to get you batteries back to full charge. So you need to push even MORE current. That means a more batteries and a bigger charger.
So right now we have $1700 worth of batteries, a single 130 amp voltage controller or, yes, multiple 70 amp controllers and finally enough PV panels to push 130 Amps at 15 volts (14.4-14.8 is the charging voltage) That's 15Volts*130Amps = almost 2000 Watts worth of solar panels! We're talking over 15 big panels at $500-600 each. That's at least $7500 worth of panels (way conservative estimate on panel price).
When you add up wire, fuses, bus bars, charge controllers, charge status monitors, bla bla bla We're talking at least $12000 for the whole system. (Don't ask me where you'll put 15 120 Watt PV panels on an RV).
And all that will build you a system that runs it's batteries down too low and can't charge them in the available daylight.
Can you build a PV system to run your AC? Yes. Is it hard? Yes. Is it expensive? Yes. The biggest danger is spending thousands (even 10's of thousands) and still being hot with no AC.
Originally Posted by jam0o0
is there a generator that isn't gunna bother the tent campers in our group? it's gotta be VERY quiet and i haven't found one yet.
Honda and Yamaha make generators that are 60dB, I don't think you can get much quieter. But you pay for quiet. Still cheaper than the solar.