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Old 02-02-2009, 12:37 PM   #1
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Solar power and usage

Ok yall, I'm gonna see what you know, I hope. As I have said before I have built a 600w, 120vdc wind turbine and a solar panel that I need to add to for more power before completed. Now since there isn't always wind, I will be relying on the solar for my interior power. The main pcs I'm concerned about is: A full size fridge, Roof mount A/C unit(s) to be used on a regular daily basis. In the evening, a desk top computer (64 bit Gateway system), a television and small lights. Now the fridge (The fridge is a GE TBX18SI top mounted freezer/fridge (15a-120v-60hz) and 1 a/c will probably run full time being in Florida, but at times maybe 2 (roof mount). The computer for about 3 hours a day, the tv about 3-4 hours a night and the lights will be CFC or 12v.

Based on your experiences, how much solar power should I try to put up on the roof to have plenty? I have spoke to a tech person who had some answers that helped but was not a schoolie or RV person so had some "un-sure" answers. So whatcha think??

Thanks.

Scott
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Old 02-02-2009, 01:23 PM   #2
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Re: Solar power and usage

My knowledge is limited, and I'm no expert, but I'd say to run all of that you're going to have the entire roof of your bus covered in solar panels plus a generator on hand to cover what the solar doesn't.

Your AC units and the refrigerator are what will kill you.

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Old 02-02-2009, 05:25 PM   #3
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Re: Solar power and usage

There is a company that sells an RV package called Wholesale Solar. It would only take a few panels. I have taken part of the equation out of the loop as I am building my own panels. The interior lights would be 12 volt so they would not use a lot. I have a wind turbine I built but there is not always wind. I was also told that I could incorporate a battery charger into the loop . That would be weird. The sun charges the batteries which works the invertor, which works the battery charger which charges the batteries. LOL!! I was just looking to find somebody here who may have had some experience with this and their skoolie.
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Old 02-02-2009, 06:17 PM   #4
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Re: Solar power and usage

I think you might be underestimating the power use of the A/C and refrigerator, or else overestimating what you can expect from solar panels.

From a few google searches, it looks like a typical refrigerator might average 400 watts, and A/C is perhaps 1500. This means that you're using 1900 watts constantly, or 45,600 watt hours in a day.

Solar panels only put out their peak rating in full sunlight, and sunlight varies by location. You have to look up how many sunlight hours per day your location gets. This is not the number of hours that the sun is shining, but a number that expresses how many equivalent hours of full sunlight the area gets. Here's one place to find this information: http://www.solar4power.com/solar-power-global-maps.html.

In Florida, it looks like you can count on the equivalent of about 4.5 hours of full sunlight per day. This means that you have to generate 45,600 watts in 4.5 hours, so you need 10,133 watts worth of solar panels. Approximately 10 kW of solar panels.

I know you said you're building your own solar panels, but we can look at commercial ones to get some idea of what's required. Looking at http://sunelec.com/, which seems to have pretty cheap prices, it looks like you can get a 200 watt panel for about $600, and they're somewhere around 3x5 feet in size. So for your 10 kW system, you'd need a total of 50 200W panels, which would cost about $30,000 and take up around 750 square feet. Don't forget that you'll also need a charge controller capable of handling 10kW, and a huge bank of batteries.

Now, these numbers might be a little higher than realistic because you said that you want an air conditioner to run constantly. If you get a high efficiency refrigerator (perhaps look into chest freezer conversions), and you only run the A/C for 2 or 3 hours a day, you may be able to run solely off of a realistic sized solar setup.
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Old 02-02-2009, 06:47 PM   #5
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Re: Solar power and usage

HOLY CRAP!!!! Yeah I had an idea but didn't look at the full numbers I guess. So what do you suggest? A propane fridge? Smaller A/C units, maybe window units instead of roof units? I know my panels would easily run lighting and small things but didn't take in account the massive consumption from the fridge & roof A/C's.

Thats why I love it here. Many minds are better than mine, I mean 1.. .
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Old 02-02-2009, 07:15 PM   #6
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Re: Solar power and usage

I've done lots of reading, but I have no direct experience with any of this stuff, so take what I say with a grain of salt.

For the refrigerator, the usual recommendation is to get a propane fridge. They're supposed to be very efficient in fuel usage. They do have to be level to work though, so either be certain to park the bus on a level surface, or have some way to level out either the bus or the refrigerator.

If you don't want a propane fridge, there are high efficiency refrigerators available that could be powered by a moderate sized battery bank. High efficiency fridges are expensive though; if you want low power use on the cheap, check out chest freezer conversions: http://www.mtbest.net/chest_fridge.html.

The A/C is a little tougher to handle. If you have to have an air conditioner running often, the only solutions I'm aware of are to either stay plugged in, or else to run a generator.

To keep the bus as cool as possible without running A/C, you might want to insulate it well and use things like heat reflecting paint on the roof. Lots of ventilation could help as well, and fans use a tiny amount of power compared to air conditioning.

You could look into heat pumps. I understand that they use a fair amount of power, but not nearly as much as an air conditioner for the same amount of cooling. I think they're on the expensive side, though.

If it's not too humid where you'll be staying, you could also consider swamp coolers. When it's dry, they can do a lot of cooling for a little bit of power and water. I guess you can even get evaporative coolers with a heat exchanger, so that they don't pump humidity into the area you're cooling.
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Old 02-02-2009, 07:17 PM   #7
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Re: Solar power and usage

Conventional air conditioning and alternate power do NOT go together. Air conditioners are power hogs. You can cut down your generator run time with a good battery buffer system, but you will need a genny or shoreline for Air Conditioning. An efficient refrigerator might be do-able on solar.

If you are in a dry climate, you might use a swamp cooler. A fan blows air through water like a home humidifier, and the heat absorbed from the air during evaporation cools the air a few degrees. It won't work in humid climates. Check out a swamp cooler install here:
http://www.macandchris.com/AirConditioning.htm

The mad scientist in me is thinking about trying to design a solar air conditioner using the principle of a propane fridge, with the liquid in a vertical collector in place of the heat tube. You would have to park facing the same direction all the time so the collector got sun during the day. It might work.

To begin with alternate power, you need a usage budget. You must figure your usage in watt-hours per day. Multiply the draw of each device times the time it is on, and add up the results. This is harder to time for loads that cycle like water pumps and fridges. There are plenty of links telling you how to do this, you might want to search this site or solar dealers. [edit: I see this was already posted as I was typing (twice - the first reply was zapped by an errant keystroke)]

For an example to get you started:
You use a 1200-watt microwave 6 minutes a day to make coffee, and 6 minutes for reheating food. You use a 12-volt RV reading lamp with an 1156 turn-signal bulb inside for 5 hours per night.

Microwave: 1200 W x 0.2 hour/day = 240 Wh/day; Light: 27 W x 5 hour/day is 135 Wh/day; total use averages 375 Wh/day.

Batteries:
Multiply the Amp-hour capacity times the battery voltage to find watt-hours. Two 12-volt 220 Ah batteries (at a C/20 rate, or 11 amps for 20 hours) are 12 V x 220 Ah or 2640 Wh each, in parallel they hold 5280 Wh total. Figuring 50% draw-down to extend battery life, you can go 2640 Wh divided by 375 Wh/day, or 7 average days without recharging.

Quote:
The sun charges the batteries which works the invertor, which works the battery charger which charges the batteries. LOL!!
There is no free lunch! However, inverter/chargers usually switch automatically in the presence of shoreline [edit: or generator] power from draining the batteries and powering the load to filling the batteries and passing the load to the cord.
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Old 02-07-2009, 08:22 AM   #8
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Re: Solar power and usage

I've started doing a little research on propane fridges. They are a little expensive but with what I learned are an excellent idea and I like it a lot. Any ideas on where to try to find one used or inexpensive?
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