Help, I am at a total loss....

Re: Help, I am at a total loss....

Okay we got a bit too silly.

So, 3000 Watt hours per day is the target?
What is the maximum you expect to use at any one time?
Is this an RV install, cabin install, home install with/without grid availability?

It all makes a difference on what you select.

About the largest panels you'll find are 250 Watts: http://www.solar-electric.com/sosu250wa.html
Not necessarily the best choice. Usually you want to look at cost per Watt, but sometimes ...
The devil is in the details.

Re: Help, I am at a total loss....

This is going to sound like I'm avoiding giving an answer but ...

What type of loads? Any AC motors like vacuum cleaners or refrigerators? CFL lights? TV/radio/CD?

You can get 1 kW pure sine inverters for quite reasonable amounts these days, but they tend not to have built-in AC chargers. So back-up charging would require a separate battery charger run from the generator.

Magnum makes a 2 kW unit with charger: http://www.solar-electric.com/maenms2020wa.html
Exeltech's non-charger unit is much less expensive: http://www.solar-electric.com/exxp12vol11w.html
Samlex even less so: http://www.solar-electric.com/sa10wa12vosi.html
If the loads can be divided into two separate sources under 300 Watts each you could use a pair of the Morningstar units, but I expect that would get to be too complex.

Also, if you could shave your daily Watt hours by about 600 You could use typical golf cart batteries wired up for 450 Amp hours @ 12 Volts. Very inexpensive power that way, and a good choice for starting out. Otherwise you're looking at a need for 500+ Amp hours, and that gets in to expensive choices (either in individual batteries or the need for 3 parallel sets).

Re: Help, I am at a total loss....

Argh! I knew it! This is what always happens!

"a small, dorm-size refrigerator."

You know what? These things can use as much energy as a full-size refrigerator.

The fans and the 'frige will definitely want the pure sine power: AC induction motors don't like MSW. They "see" it as low Voltage. They'll draw more current, run hotter, and run shorter. In some cases they won't run at all. Why is this important if I've already suggested several PSW inverters? Because that refrigerator (or any refrigerator) will have a big start-up surge which a 1 kW inverter, even pure sine wave, may not handle. If it was a big, non-inductive load you could select from quite a wide array of MSW inverters with high power ratings for very low cost.

Okay, so here's what you do if you can: get a Kill-A-Watt meter and run everything you want to use at the cabin through it and collect some real-world numbers. If you haven't already bought the equipment, start thinking about alternatives.

First alternative: propane refrigerator. If this is an occasional use cabin buying one of these, especially used like an RV unit, can save you a lot of money over a solar electric set-up capable of powering an electric 'frige. The more time you spend there, the more viable the electric becomes. Making this one change will allow you to "shift down" substantially in power needs. It's the difference between the big batteries, large array, and over-sized inverter and one set of 225 Amp hours, 400 Watts of panel, and a Morningstar 300 W inverter. Ask Icarus: that configuration is about what he lives on, full time. The difference? He uses a propane 'frige.

Meanwhile I and all my necessary AC induction motors have 320 Amp hours, 700 Watts of panel - both of which are marginal for performance - and a 3.6 kW 24 Volt inverter which produces less than 200 Watts most of the time. But when the motors kick on that big capacity is needed, even if only momentarily.

Re: Help, I am at a total loss....

It still comes down to the same calculations from loads. Eliminating the refrigerator will take at least 120 Watts off the maximum (down to 630 from 750) and probably 1000 Watt hours off the daily total. Just guessing here, but you can see it will be significant.

Even at 600+ Watts peak you'll need larger than the Morningstar 300. The fans won't draw much (depending on size and how long they are on), neither will CFL lights. But you will need to get some idea of what you're left powering; it's easier to come up with the power you need than to figure out what to do when it runs out at 2:00 AM because the system is too small.

A small system as an example only:

Two 6 Volt golf cart type batteries for 12 Volts @ 225 Amp hours gives 112 Amp hours maximum, or about 1344 Watt hours daily @ 50% DOD. At 25% DOD = 672 Watt hours - usually a better target.
432 Watts of panel to get 10% charge current @ 14.8 Volts using 77% efficiency factor. Should produce 864 Watt hours daily factoring in all efficiency losses and figuring on 4 hours of "equivalent good sun" per day. Will need a charge controller capable of up to 30 Amps, either PWM or MPPT (the latter especially if planning further expansion but there's a big price difference).
An inverter suitable to the maximum load. This will still be under 1 kW, and could go as low as 300.
Back-up charging system for when the sun doesn't shine. A small generator like a Honda EU1000i and a good battery charger.

If you need more daily Watt hours you increase the battery bank and the panels/controller accordingly. It can be advantageous to up the system Voltage to avoid too many parallel battery connections (becomes problematic in keeping the current flow even through all batteries). Also, the same "30 Amp" charge controller can be used at higher system Voltages to handle more over-all power, rather than having to up the current capacity: 30 Amps @ 12 Volts = 360 Watts, but 30 Amps @ 24 Volts = 720 Watts - on the same controller.