Lazy Daze Owners' Group

Electrical accessories and power balance

March 07, 2001, 11:56:23 pm

Yahoo Message Number: 2521

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Folks here have been helpful while I was deciding what electrical accessories to put into my ordered 26.5 MB. And since I'm quite pleased at the way the ensemble of accessories plays together, I'll make a short note to tell how it came out for me...

Factory doesn't recommend to add solar panels or satellite antenna in the after market due to roof structure limitations, so I was forced to decide if I want these features now. I decide to buy.

So here's the power balance facts as I know them, in rough numbers.

Capacity of the coach batteries is slightly in excess of 200 amp-hours at 12 volts. Say 2500 watt-hours. As rule of thumb, I only want to discharge the batt's 50% before recharging.

Standard 12-volt (13 inch) television draws 4 amps; satellite receiver about 0.4 amps, but at 110 volts. Total entertainment about 80 watts. Couple hours a day is about all the entertainment I can use, so I spent 160 watt-hours per day to chase away boredom.

Other electrical service is roughly same usage per day (say 6 amps of light and 3 amps of furnace at 12 volts for 2 hours per day) total 200 more watt-hours per day.

After three days at this rate - which is fairly profligate of power - the house batt's need a charge, so it's time to run the engine.

Enter the solar panel: rated at 85 watts in full sun, it generates enough in 3 or 4 hours of sunshine to recover what I used the night before. If the sun only half-shines, I still break even.

And if four days go by with no effective sunshine, it's time for me to start the truck and go someplace else!

Make no mistake - your mileage *will* vary, and so will mine. But in my estimate, the LD options provide generous electricity without having to guard every erg.

Best - John

Electrical accessories and power bal

Reply #2 – March 08, 2001, 08:52:35 am

Yahoo Message Number: 2527

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"Enter the solar panel: rated at 85 watts in full sun, it generates enough in 3 or 4 hours of sunshine to recover what I used the night before. If the sun only half-shines, I still break even."

John, I would choose a unit and stick to it!

;^)

My point is that shuffling Watt-hrs and Amp-hrs ends up confusing the issue, particularly when trying to analyse solar panel capabilities.

An 85 Watt panel typically produces 17 Volts at about 5 Amps, at the max power point, in full sun. You will never see this 85W unless you have a power-tracking charge controller, and even then there is a loss due to inefficiency of the power conversion and due to geographical constraints (reality). The panels aren't rated this way to be dishonest, but the figures must be interpreted.

Consider more usefully that this is a 5 Amp panel, with the sun directly overhead on a cloudless day, panel mounted flat.
In the summer in the US Southwest, this might be reduced to 4.5 Amps max, and about half that in winter - if you manage to get good exposure. Over the course of 4-5 hrs charge time - again a cloudless, unshadowed line of sight the entire time - you might average 70% of that output. In other words, your panel could be expected to return a charge of 16 A-hrs in the summer and 8 A-hrs in the winter, on a sunny day.

Convert the rest of your figures to A-hrs to make the rest of your calculations simpler. Note too that there is some excess charge required to restore charge to a battery (lost as heat), but all the solar panel output is efficiently used to directly power appliances when they are run in daylight.

We have two 53W panels, and they are more than adequate to keep up with our modest, conservative uses three seasons of the year. In the winter, they only extend our stays by about a day or so in normal clear weathr camping, and of course are useless in the trees or rainy weather.

Steve