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Old 03-22-2015, 12:06 AM   #1
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Solar power

30W 30 Watt Solar Panel 12V 12 Volt Battery Charger Off Grid RV Boat | eBay

I was looking at this solar panel ad on eBay thinking a few of those on the roof could supply all my electrical needs. Comments?
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Old 03-22-2015, 12:56 AM   #2
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It would be cheaper to buy one, big panel than many small ones. Depending on your needs, you might be ok, or you might need a lot more. No one can answer that question without knowing how many watt-hours of energy you need to make per day.
I've had positive experiences with a 100W panel I bought off ebay for something like $160 including a small charge controller. Works great to keep my starting batteries full, and I can run my lights, etc, without fear of the battery being dead the next day.
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Old 03-22-2015, 01:04 AM   #3
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I had two thoughts. One is that with narrower panels I could maintain a walkway down the center of the roof with panels on each side. The other is that if a small panel fails or is broken, no problem. A bigger one is more of an issue.
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Old 03-22-2015, 01:10 AM   #4
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I understand your concerns, but these panels are pretty robust. The walkway is a nice thing to have, but the price on those panels is about double per watt what you would be paying for a 235 watt panel. The dimensions on those bigger panels aren't that bad and you would be able to navigate your roof no problem.
Just my .02
Im putting 4 big ass 315 Watt panels on my bus and I'm not worried about it.
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Old 03-22-2015, 01:11 AM   #5
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In terms of what I'm going to be using... Microwave, steamer, crock pot, chargers (phone, laptop, battery, tablet, mifi), printer, electric kettle, coffee brewer, maybe a 500w heating fan on low in winter, water pump, electric shower, led lighting.
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Old 03-22-2015, 01:40 AM   #6
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I hate to break it to you, but those are all the most power-intensive appliances out there.
there is just no way you could power all that, even if you covered your roof almost completely, you'd still need a massive battery bank to go along with it.
we're talking a couple thousand watts of panels to charge enough battery to run all that.
A system like that would run you at least a few thousand dollars.
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Old 03-22-2015, 02:29 AM   #7
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I'm not going to be running all of that all the time. I use the microwave a couple of times a day. If I use the crockpot, its once a week. Kettle or coffeepot maybe once a day. Chargers don't use much. Actually, I might take a 12v line from the panels straight to my chargers. Shower - as long as the waters not ice cold then I'm happy.
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Old 03-22-2015, 07:25 AM   #8
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I hear ya. I would either do the math myself, or use a calculator to determine your daily energy needs and then size from there. I still think you'll want around 1000 watts on the roof and large battery bank to come close to what you're looking for.
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Old 03-22-2015, 09:18 AM   #9
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The comments so far are spot on. For all those resistive heating devices you'll probably be looking at buying over 30 of those 30w panels to reach a reasonable 900w, not to mention upwards of 6 decent batteries. Running resistive heating devices is a tough chore for a battery bank. They consume a lot of electricity and do it constantly as they run, unlike a motor which will consume much power during starting then smooth out. An electric kettle would be fine since it's only on for about 10 minutes. A heater on overnight will require some serious power reserves, as will an electric on-demand water heater.

If you're serious about boondocking then you may want to look into adding complimentary non-electric options. Are you opposed to propane? It doesn't come freely from the sun, but for cooking and boiling water it works wonderfully. Woodstoves aren't as care-free as simply turning a heater switch to "on", but they provide plenty of heat and a rewarding ambience to the room.

Also, don't buy 12v panels. they're more expensive per watt than grid-tie panels and have more line loss over distance. Look at buying an mppt charge controller and ~36v panels.
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Old 03-22-2015, 09:25 AM   #10
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i agree with charles,and solar power is expensive. cook , heat water and your skoolie with gas,perk coffee over the stove. try to invert the least amount of dc,get down to the basics. my solar system was 5000.00 , 800 watt in 1000 pure sine out.
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Old 03-22-2015, 11:48 AM   #11
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Quote:
even if you covered your roof almost completely, you'd still need a massive battery bank to go along with it.
Speaking of covering things entirely..I've been debating covering my entire bus in these


You can find them pretty cheap on ebay. Nothing wrong with them UniSolar just went out of business (like so many other solar companies).
Unisolar Peel Stick 136W Flexible Solar Panels Home Solar RV Boat Uni Solar Uni | eBay
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Old 03-22-2015, 12:04 PM   #12
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I'm trying to make this an all electric bus. In my house which has a water heater and a fridge constantly on, I pay about $10 a month in pure electricity usage. 100-200 kWh a month. It was 200kwh this February and 43f outside. February I paid more than $10 but most months its only $10 and 100kwh.

How does that translate to solar? Well, I figure if I have a backup generator running on diesel that should do a lot. There is the option of a diy roof mounted turbine too.
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Old 03-22-2015, 12:38 PM   #13
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[QUOTE=Zephod_beeblebrox2;104103]I'm trying to make this an all electric bus. bad idea unless your pluged in. research solar power, lots to it
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Old 03-22-2015, 01:00 PM   #14
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There's nothing that can't be retrofitted. I intend to move into the bus before its completed in order to make best use of my income. The bedroom walls are almost done. Initially water will be from a bucket as will be the toilet. Cooking will initially be a camping stove..

Mind, as I'm parked on my gfs land, I can't imagine needing to rough it before the bus is completed.

I'm going to have to see how far solar will go. Batteries are no problem. They're about $100 each in Walmart for deep cycle 12v. They look big enough too.

Speaking of batteries. What size panel would you recommend for keeping the 2 bus batteries charged? I tend to leave my bus parked for a month or so at a time.
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Old 03-22-2015, 02:10 PM   #15
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200kWh is a lot for a bus-roof sized solar array. It can be done, but it'll take up a good chunk of the space on the roof.

200kWh = 200000Wh

200000Wh per month / 30 days = 6666.67 Wh per day

I'm just guessing here, but I would say that at a suitable North American latitude you may get a couple hours of peak solar charging plus a reduced amount in the morning and evening. For simplicity's sake, let's just say you'll have 5 hours of peak solar charging.

6666.67 Wh / 5 hours = 1333.33 watts

So a solar array of 1333.33 watts could potentially provide you with around 200kWh of electricity, but (as you know) you would also need an appropriate battery bank. Also, this isn't taking into account seriously cloudy/rainy/snowy days.

100kWh a month is reasonable, though. 666.67 watts is easy. 2 or 3 good sized panels can provide that, though I wouldn't expect to be using electric heaters and the like off of this small of a system. The battery chemistry probably wouldn't like it (serious voltage drop) which would also add more heat to the wires.

These are largely made up numbers, but it may give you an idea of how solar panels translate into the type of electricity we use on any given day in a typical house. We use LOADS of electricity in our daily lives without even realizing it.

I have a 600 watt solar array on my roof and a 455Ah battery bank. The system works wonderfully for all the things I do with it: water pump, laptops, phone chargers, lights, fans, tools (even bigger ones like table saws), small 12v refrigerator, stereo. I tried a tiny space heater through the inverter for the fun of it some time back, though, and it imparts a pretty harsh voltage drop. I wouldn't want to run that for long.

Quote:
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if I have a backup generator running on diesel that should do a lot.
Do you have any particular aversion to propane? Nobody is trying to force it down your throat, but my suspicion is that a diesel generator creating electricity to run a resistive device that creates heat would be more expensive (and loud) than a gas that, when ignited, instantly and silently creates heat. There are also some neat little propane on-demand water heaters out there...
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Old 03-22-2015, 02:49 PM   #16
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I am trying to keep sources of fire out of my motorhome. Its kind of important when you also have gunpowder in the mix.

100kwh includes my fridge and water heater. I suspect the water heater burns up more power than an instant hot water setup.

The cables won't like providing so much power to an instant water heater which is why I'm thinking of having an array of super capacitors close to the shower. They can deliver a lot of power quickly. They don't hold much but enough of them should do me for 3 - 5 minute shower. I might do something similar for high surge things like microwaves, kettles etc.

I looked at 12v fridges and decided the way to go with a fridge is a $80 dorm fridge and an inverter. It uses less power and has a lower cost.
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Old 03-22-2015, 03:09 PM   #17
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I looked at 12v fridges and decided the way to go with a fridge is a $80 dorm fridge and an inverter. It uses less power and has a lower cost.
??? Which one did you have in mind? If you can, try to find real-life power consumption of the device. Personally, I have yet to see an efficient "beer fridge". From my previous research, size for size the 12v compressor refrigerators (thermal electric ones are useless) were far more efficient when running off of a 12v battery bank (don't forget the 10%+ inverter efficiency loss).

I tried to get some real numbers quickly, but I should be working so I'm not going to spend any more time on it
Nonetheless, I came across this guy's website: Fridge test 240V - 12V. He did a test of two same sized refrigerators; one purpose built for 12v, the other running off of an inverter.
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Old 03-22-2015, 07:43 PM   #18
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The cables won't like providing so much power to an instant water heater which is why I'm thinking of having an array of super capacitors close to the shower. They can deliver a lot of power quickly. They don't hold much but enough of them should do me for 3 - 5 minute shower. I might do something similar for high surge things like microwaves, kettles etc.
Large cable is a lot cheaper than having an array of super capacitors near anything. Super capacitors are not even cost realistic.

If being able to pull large current draws is important to you, than a good lithium Ion battery bank is the only way. This would be money well spent.

If you want to go completely electric, you need to go do a ton of reading on the electric car forum. There you will learn how to build, charge, and discharge high capacity lithium Ion battery banks.

The yellow ones in this link are the battery cells you need. It takes roughly 4 to make 12 volts. They range in capacity from 40 amp hours to over 1000 amp hours.
LiFePO4 Battery Cell : EV Assemble, LiFePO4, Electric Bike Conversion Kit, EV Charger, BMS, EV Components, EV Parts, All for EV!
Winston LiFeYPO4 3.2V 40Ah Cell [WB-LFP40AHA] - $55.00 : EV Assemble, LiFePO4, Electric Bike Conversion Kit, EV Charger, BMS, EV Components, EV Parts, All for EV!

With solar you don't want flooded lead acid battery's anyway. They are heavy, give of dangerous gas when charging, leak acid, and NEVER GIVE BACK THE ELECTRICITY THAT WAS PUT IN WHILE CHARGING.

Lithium Ion on the other hand returns all of the energy used to charge the battery to the consumer. Loss is almost not there.

It's been 5 years since I researched this. Basics are still the same, but the products will be better.

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Old 03-22-2015, 07:51 PM   #19
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The problem with lithium batteries is they are self contained bombs. Lithium + water = hydrogen. Add air and electricity and you'll see why I really dislike lithium batteries.

Lead acid batteries are cheap. Super capacitors give out high discharges while lead acid only gives low discharges. A pairing of the two seems ideal.

As far as weight, its a bus.

Its all something I'm going to dive into when I've completed the construction and the water supply. I might put a solar panel on the roof to power lights and USB chargers initially while using a camping stove if need be and showering cold.
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Old 03-22-2015, 08:01 PM   #20
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IMO

The percentage of issues consumers have had with lithium Ion battery's is so low your way over thinking this.

I use Lithium Ion battery's everyday as do most people. I may use them a bit more than some.

-My electric shaving razor.
-My cell phone.
-My laptop computer I'm typing this on.
-My Dewalt and Milwaukee hand power tools I use at work. These get used hard.
-The battery in my heated jacket.
-My flashlights

And the list go's on and on. 99% of us use them everyday without even realizing it. There is virtually no risk to using lithium Ion battery's.

Nat
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