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Discussion Starter #1
Hi! I'm new to this forum. I signed up because I have an idea, but I need help figuring out if it will even work the way I would hope.

My idea is to build a solar-electric powered sheep wagon, such as the one pictured below:



The reason being, I love the idea of camping in one of these, but I don't want to use a horse to pull it. I want to build a more modern yet still antiquated version of my own design, with help and knowledge of experts.

If you're wondering, I would add a driver's seat/cab to the front of the wagon.

So here's the rough requirements:
Total weight of wagon (not including batteries): 5000 lbs.
Top speed: 5 mph.
Duration of travel: 5 hours per day
Charge system: on-board solar array and optional gas generator.
Type of travel: off road/hilly terrain.
Axels/wheel hubs: 2x 4000lbs rated axels.
On-board electrical: pumps, lights, fans, refridgerator/freezer, tv, etc.

So! Can it be done? What kind of batteries would I need, and how many? What kind of motor would I need? How many, and what kind, of solar cells would I need? Would an AC or DC system be better? How do I measure the amount of energy I would need, do I measure in watts per hour? Please, any help would be greatly appreciated! My building skills end at the frame and body, I know nothing about the electrical requirements... I will hire an electrician to help install things and make things safe to use, by the way.

Thanks for your input!
 

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Roughly:

2 kW motor
10 kWh battery
200 W worth of solar panels
10 days to recharge, after which you can go another 5 miles

Based on my experience with the Solar Sparrow
 

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Hey, it's physics. Not much you can do about the laws of nature.

If solar power were practical for vehicles, you would see it used, wouldn't you?

As it is, I may be the only fool who drives a 100 % solar powered car. After parking it in the sun for 1 or 2 months, I get 70 miles.

Totally impractical. But, just like you, I like the principle of it.
 

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Discussion Starter #5
Maybe if I added a wood gas generator, and forgo the solar/batteries? Check this out:



This way I would have an ample supply of fuel... I could even use straw as a fuel source! Truthfully, I like the solar idea, but this seems cheaper and maybe less expensive.

Any other ideas? Can wood gas be easily converted into electricity? Should I still use batteries if I use a generator? Should the propulsion be electrical or with a gas engine?

I guess these are all questions I need to think about further.
 

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Discussion Starter #6
I'm allergic to horses... the last few times I've tried riding a horse, any contact resulted in painful swelling, particularly in my hands.
 

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Some rough calculations using my http://enginuitysystems.com/EVCalculator.htm:

For a 1% slope:
330 Wh/mile
2.2 HP (1.6 kW)

For a flat road:
219 Wh/mile
1.5 HP (1.1 kW)

So for 25 miles over fairly flat terrain you will need about 6.25 kWh. You can get a 280W solar panel from Home Depot for about $400:
http://www.homedepot.com/p/Grape-Solar-280-Watt-Polcrystalline-Solar-Panel-GS-P-280-Fab1/202959966#.Ud2YZ53D_IU

It's about 40" x 80" so it should easily fit the roof of your buggy. Optimistically, 3 or 4 of these should give you the 6 kWh you need with 8 hours of good sunlight. Or you could run a 3-4 kW generator for a couple of hours.

You might be able to use deep cycle lead-acid batteries. A 100 Ah 12V battery is about $80 and weighs 65 lb. So 6 of these will give you 7.2 kWh capacity at 72V, although at 1.6 kW power you will draw about 25 amps and the Peukert effect will give you an effective 70 Ah (5 kWh) rating and about 3 hours of run time, maximum. For a 5000 lb buggy an extra 400 lb of lead isn't bad and $480 won't break the bank. The same effective capacity with LiFePO4 will cost about $2500 and will last about 10 years, compared to 2-3 years for the lead. So the long term cost is similar.

My personal choice for a motor would be three phase AC and an industrial controller. A 3 HP motor and controller would be about $500. You can get three 1000W 24V to 220V inverters for about $50 each and they can be modified to give you 270 VDC for the link.

You could also use SLA batteries, in which case there are 12V 12 Ah batteries for about $25 each, and you can use 30 of them for 360 VDC and 4.3 kWh. This eliminates the inverters and you can use regen to get a little better range. Cost would be $750 and weight about 240 lb.

Good luck!
 

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Discussion Starter #8
So you're saying it would work!? Wouldn't I need to to charge the batteries for 10 days to get 5 miles?
Also, I really get confused over the numbers and units. Does 6.25 kWh mean 6,250 watts per hour? Doesn't a solar panel rated at 280 watts provide that amount for every second? So wouldn't my motor need only 1.7 watts every second?
 

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I believe this idea is doable. No need to wait for days until battery is charged.

280W for one hour makes 280Wh. For 6250Wh (6.25kWh) you need over 22 hours of theoretical maximum output from panel. This is the scenario from 0% to 100% full. Not good. You need more panels.

You could make a folding rack for multiple panels and not have them on top of your wagon all the time. Four 280W panels would give ~1kW charging power which would mean about 6 hours charge time. In theory. www.ev-power.eu sells 290W panels for 230$ each.
 

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You might consider building an electric tractor to pull the wagon. There have been quite a few successful conversions, and you can usually find a good size garden tractor with a blown engine for a couple hundred dollars or less, and it would have a multi-speed transmission and be designed for pulling using a standard hitch. Then when you have parked the wagon for camping, you can take the tractor for a ride using much less energy. You will probably want to put batteries on the tractor as well as the wagon. You'd only need maybe 2 kWh of energy to run the 500 lb tractor for a couple of hours.

Maybe you could put a horse costume on the tractor to complete the 19th century or Amish image. Sort of like this in reverse:

http://horsefancydress.blogspot.com/2009/07/tractor.html
 

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Discussion Starter #11
ha, funny! the thought of using a 'disguise' to hide a tractor came to mind actually. I have nothing against tractors, but the sight of a tractor pulling a stagecoach somehow doesn't work. I do like the idea though, because all the mechanics can be in one place. However, if the tractor was ever lifted off while I was sleeping, I'd be in trouble!
I think having an electric motor inside the wagon, and doing something like an inboard motor on a boat to get the drive shaft to the differential would be best. Being that I'm kind of designing from the ground up, the drive shaft wouldn't have to be very long, the electric motor could even sit right next to the differential, or drive it directly (if I was using a DC motor).
Thanks for your thoughts and consideration! This is very helpful!
 

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So here's the rough requirements:
Total weight of wagon (not including batteries): 5000 lbs.
Top speed: 5 mph.
Duration of travel: 5 hours per day
Charge system: on-board solar array and optional gas generator.
Type of travel: off road/hilly terrain.
Axels/wheel hubs: 2x 4000lbs rated axels.
On-board electrical: pumps, lights, fans, refridgerator/freezer, tv, etc.
If you work the numbers like a car then

25 miles range at 5000 lbs means you need at least a 12.5kwh battery. You will want it to be larger than this so you can operate your accessories at night and during periods where the sun isn't really there. Because your speed is low you might need less than this but because you are off road you might need more. You will also want more so you dont wear the batteries out too fast. But lets just use that number.

In the best places in the US you get an average of 5 hours of sun a day and in the worst about 3. (Look up the solar insolation value for your area). That means you need between 2.5 and 4.2 kw of panels to make this work. You can get about 800 watts off of a panel the size of a sheet of plywood (4x8 ft). So you need between 3 and 5 sheets of plywood worth of panels minimum. Only problem with all this is that this is optimistic because you don't get 3-5 hours of sun every day, this is an average. You are going to have days where you essentially get no sun. You are going to want both more batteries and more panels to last through those stretches.

Is it possible? Sort of but I dont think you will be able to engineer a system which will allow you to go 25 miles every day. You might have to sit a couple of days to charge when the weather is poor in the winter. You can't really charge while moving either so you will lose some charging time while traveling.

Is it practical? Not really but people do a lot of things that are not practical so I certainly wouldn't discount it on the basis of practicality. You will most likely end up with around $15k in stuff to make all this work.

Good luck!
 

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The 5 mph is the key. My guess is that you need not more than 1kW to propell such a vehicle at that breath taking speed. And not the dozens of kWatts that's needed for a normal car at higway speed.

The 5 hrs a day gives it a range need of 25 miles. But that's not important, you'll need only 5kWhrs. That's a relatively small pack.

And playing with this site:
http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php#
You'll need aprox 2kWp of solar power to charge 5kWh in a day, very much depending on where you are and at what time of year of course.

That's with the better panels to date you can buy, aprox 10m2. With 5m2 you'll need 2 days to recharge. 5m2 seems to me close to the roofsize.
 

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I really like the idea, but one practical aspect I've not seen anyone mention is that those wagon wheels aren't designed for traction, they're meant to be pulled. If you drive through the wheels isn't there likely to be a problem with grip on offroad/hilly terrain, especially when wet?

I'd look at building an "iron horse" rig equipped with offroad tyres, something like this, but without the ICE:

 

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I'd definitely buy a plastic mannequin horse and add wheels to it (and enough power for highway speeds), it would be so cool to ride it on the highways! (And get a speeding ticket, how cool would that be.)

Sorry, went offtopic.

Yes, there is a lot of energy in sunlight, but there are two problems:
1) Current solar panels are not efficient enough
2) Sun doesn't always shine, and the orientation is important.

Solar makes a lot of sense in stationary installations, but not much so in vehicles.

You can add some solar for looks but you need a small gasoline engine. In your case, a cheap 3 kW genset would be enough.

Any chances of charging it from the grid? Any public wall sockets (or private you could use with a permission / small fee) near where you tend to stay? Your power consumption at that speed would be relatively small so that you could use a standard 110V plug.
 

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Does 6.25 kWh mean 6,250 watts per hour?
This is a good opportunity to purge "watts per hour" from your brain. No such unit exists in a meaningful sense.

--Energy is measured in joules.

--Power is the time rate of energy. It is measured in joules per second, or Watts.

--You can multiply power by time to move it back to energy. If you multiply Watts by seconds, you are back to joules. But we like to run our vehicles for more than a second, we multiply it by hours. And since 1 Watt isn't enough, we multiply them by 1000. That give us the familiar unit of kilowatt-hour or kWh. This is a measurement of energy--enough energy to provide 1 kilowatt of power for a period of 1 hour (or 2 kilowatts for 30 minutes, or 500 watts for two hours, etc etc).

--kilowatts per hour would tell you how fast your power consumption is changing. No one uses that.


Hope this helps!
 

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Some numbers for Solar:

--The solar insolation in direct sunlight with no clouds is taken to be 1000 watts/m^2

--The most efficient panels are 20% efficient. The more common and affordable panels are 15% efficient.

--Typical location in the US receives about 5 hours "peak sun equivalent" per day. That takes into account weather and the movement of the sun through the sky, and puts it in terms of how long of 1000w/m^2 light would be equivalent.

Based on this, the best you can get for energy out of solar panels is 1000w/m^2*.2*5hr/day = 1kWh/m^2/day of energy. Not much to work with.
 
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