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Old 09-27-2017, 08:15 PM   #1
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Join Date: Sep 2017
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Question about power draw

Hello, I'm new to the skoolie forum and I'm considering building one as an "apartment" while i'm at school.

My question is about the ball-park power consumption of the project.

The most demanding condition the bus would see is as follows: Running electric heat continuously for 12 hours, an apartment sized refrigerator, a hot water heater, an oven for 1 hour and also running a few LED light bulbs and a computer. Does anyone have a ballpark estimate on how much draw that might be? Looking to go 100% solar (but I may need to compromise on that... may go for propane/fire heat instead)

Thanks for any input!
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Old 09-27-2017, 08:22 PM   #2
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if tyou are going to be in an area thats cold enough for electric heat for 12 hours a day.. you are looking at being way up north in the winter.. which you have much less daylight hours, and a sun angle thats meager in december and january for sure... seems like solar in those conditons would need to be huge..

contrasting with summer where you have very long days with strong sun... its actually easier to A/C solar simply for that reason you have much more utilization of your system. I would want some type of fuel heat.. esp if you find yourself in an area with lots of winter cloudy days.. cloudy days in sumnmer still yield decent output.. in winter not so much...

-Christopher
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Old 09-27-2017, 10:32 PM   #3
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The conversion efficiency proposition for hydronic solar heating might be feasible.. ie solar water heating panels and a lot of thermal mass, probably just water tanks, stored inside. And a lot of insulation and really good air sealing too.

But like cadillackid says, heating has its greatest demand at times when there's the least energy available from a solar PV system. Rent would save a lot of money.

As for data: yes, I do have a little. A couple years ago I ran an overnight heat loss test in my bus. At the time it was very much stock; I hadn't removed any windows nor added any insulation. It's a transit style Blue Bird, 38 feet long. It was parked outdoors and had 5 kW of electric baseboard heater laid in the aisle on the floor in the middle of the bus. I wired the heater to be always on; there was no thermostat. As I recall the numbers, the outdoor temperature got as low as 14 F and the bus temperature, measured at just one point, was 54 F. I don't recall where I left the temperature sensor but I expect it was somewhat central in the bus, maybe 5-6 feet away from the heaters. The ends of the bus must surely have been colder.

Working with really rough numbers: 5 kW continuous all night long managed to hold about a 40 F temperature differential. Things warm up fairly quickly when the sun is out. If we say that energy draw was continuous from 7 pm to 7 am it's 12 hours: 60 kWh of energy to be collected on an array and stored in a battery every day. And not even all that comfortable as indoor temperatures go.

We won't say it's impossible, but most probably would say it's impractical. Deleting windows and adding insulation certainly will help.
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