Sep 25, 2009 08:53 pm
Re: System requirements
I suspect the breaker size is due to the start-up amperage spike that the motor creates and does not in any way reflect the actual continuous power usage of the machine. I would calculate based on how many times it actually dispenses the firewood.
Let's say that it does 100 per day. Let's round it up to 7 amps that should more than accommodate the bill validator and any other ancillary loads. 100 x 7 amps x 110 volts x .004167 hours = 320.83 watt-hours. Let's add the lights -- 3 x 13 watts x 12 hours = 468 watt-hours. Together, that's 788.83 watt-hours. Assuming 4 hours of full sunlight, you would want a solar panel rated at about 200 watts (cost is approx. $600-$800). Add a 50 to 100 amp-hour sealed gel/agm (to prevent off-gassing and maintenance) battery for another $150 and you can keep your machine working for several days without sunlight. Add a 60 Amp Xantrex or Outback MPPT charge controller for $550 and a Xantrex Prowatt 1kW continuous (2kW/25A surge) inverter for $460, plus some wire, and your total cost comes to around $1,800 - $2,000.
Since I was conservative in sizing this (and especially if you go with a 210 or 220 watt solar panel), you'll likely have many times where you have far more solar than you can store. Thus, I'd recommend hooking up an electric resistance snow melt loop in front of your vending machine connected to your charge controller as a diversion load. It will turn on whenever you have sunlight and your battery is full. This way, your customers will likely deal with less snow and ice when getting their firewood and none of your solar will go to waste.