Jeff’s Solar Trailer

How to convert the electrical components of a small camp trailer to run on solar panels

–> Work in progress!

First, acquire a trailer. Jeff’s trailer is a single-axle Sun Valley Road Runner 130, which is a fully self-contained and only 13 feet long.

Here’s the floor plan of Jeff’s trailer (click to enlarge):
Amazingly enough, they managed to cram a shower and a toilet into this tiny trailer! There is also a three-burner propane range, furnace, water heater (for hot and cold running water!), and propane refrigerator.

Jeff took out the flimsy upper bunk that was above the dining table and replaced it with a storage shelf. The dining table makes into a wonderful queen-sized, extra long bed. The shower and toilet are minimal but quite functional!

There were two electrical systems in this trailer: one system ran off standard household 120-volt AC (extension cord from house to trailer); the other system ran off one 12-volt deep-cycle battery that was mounted on the tow bar in the front of the trailer.

Here’s a photo of the original battery placement:

The 12-volt battery was charged when the trailer was towed: the same wiring harness that plugged into the tow vehicle to run the trailer’s brake lights also charged the battery from the tow vehicle’s alternator.

Not too bad a system, but we all know one questionably charged and maintained 12-volt battery isn’t enough electrical current for on-playa lights and sound!

Jeff adds 2 batteries and 2 solar panels to the existing 12-volt system and retains the ‘charge batteries when towing’ system too.

When the sun shines on a solar panel, it produces electrical current. The current flows into 12-volt deep-cycle batteries where it is stored for future use. Current can also flow directly from the solar panel to an electrical device. When you use electrical current to run a fan, the electrical current flows out of the batteries, or directly from the solar panel, to the fan. The electrical current is then ‘consumed’ by the fan.

If you’re gonna go solar, you need to estimate the ‘power consumption’ of all your electrical devices. Next, you must estimate how long you use each electrical device in one day. Add the power consumption of all your electrical devices together: this will give you a rough average of the total amount of current you need each day.

Here is a handy calculator to help you figure out how much power you will need per day. Down at the bottom of the page is a listing of typical devices and their power consumption: http://shop.altenergystore.com/Calculators/OffGridCalculator.html#

How do you find out how much ‘power’ a device consumes? Read its labels, read its packaging materials, research the device on the web, and/or compare it to a similar device.

How big of a solar/battery storage system do you require to provide the total amount of current you need each day? There is nothing mysterious here: it’s just a math problem! Ideally, you want to have your solar/battery storage system ‘in balance’ with your power consumption…so that you don’t run out of power, especially overnight when the sun isn’t recharging your batteries.

Unless you are either a ‘power miser’…or have a trailer and wallet big enough to support a giant solar system/battery array…you will probably discover that the first thing you need to do is to reduce your typical power consumption! Conserve that current!

Jeff started with an inventory of the electrical devices in his trailer: interior lights (with inefficient bulbs!), a small 12-volt fan in the furnace, another small 12-volt fan in the range hood, and a small 12-volt pump to pressurize the water system. There were also several 120-volt outlets inside the trailer to plug in items like a microwave and coffee grinder. The main parts of the water heater, refrigerator, and furnace all run off propane, not electricity.

Next, Jeff upgraded the interior lights to efficient LED bulbs. He found some that plugged right into the same sockets. He also added some 12-volt plugs (like a cigarette lighter) to the interior of the trailer to charge laptops, etc, directly from the 12-volt system.

Hint: you’ll use less power any time you directly use the 12-volt current compared to ‘ramping up’ the 12-volts to run a 120-volt device. Why? To convert 12-volt current to 120-volt requires a device called an “inverter”. And an inverter consumes current to ‘ramp up’ the 12-volt current to a higher voltage. Inverters consume current even if you aren’t using any 120-volt devices, which is why you should turn an inverter off when you don’t need it. Additionally, the bigger the inverter, the more current it consumes when in use: match your inverter to the electrical devices you will use it with.

In Jeff’s trailer, he installed a big inverter to run the microwave and a small inverter to run less ‘power hungry’ electrical devices like the coffee grinder. He also added handy on/off switches to both inverters.

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Related thread on the AEZ mailing list:

Justin Peer wrote:
What would be the minimum recommended panel size for keeping a reasonable gel battery charged for the week, so that you can run some led’s, charge batteries etc. Is 40w reasonable, or do you need to go up to the 80w range.

Jeff replies:
What do you really expect to run with this? Just estimate the watt hours of energy usage per day and divide by about 8 (or 10 if you’re feeling optimistic) and get that size panel.

A watt hour is just what it sounds like: energy used at a one watt rate for an hour. A 2 W light turned on for 3 hours uses 6 watt hours.

Make sure you get a battery that will store that much, too.

Say you want to use 160 watt hours per day. Divide by 8 hours of charge time to get a 20W panel. Now you have to store that 160 watt hours so you get a battery that will handle at least twice that. 160 watt hours / 12 volts = 13.3 amp hours, so get a 28 amp hour battery.

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Here is a ‘flow chart’ showing how the electricity from the sun is used in Jeff’s trailer:

solartrailer.pdf

Jeff had two 150 watt solar panels. These panels came from the factory as 24-volt panels, but Jeff rewired them to 12-volt. Jeff’s solar panels produce more than enough current to keep the batteries fully charged during the day…as long as the sun is shining!

He mounted the solar panels on the roof of the little trailer: they just barely fit! He drilled through the soft top of the trailer into the roof frame, adding reinforcement where necessary to support the extra weight and wind resistance of the panels when towing the trailer. He then carefully caulked the holes in the roof. Here are photos of the panels:
Click on the thumbnail for a large photo.

These panels are permanently afixed flat to the roof. This makes a sturdy mount for towing.

Why aren’t the panels mounted so that they can be tilted to match the angle of the sun? Yes, the panels could produce a bit more current (like 15% typically) if they could be tilted towards the sun. But that would have meant lots of extra engineering to build a tilting mount assembly.

Another complication with a tilting mount assembly is the orientation of the trailer when it’s parked at a campsite: the panels would need to face south or you couldn’t tilt them up! With a flat mount, you don’t need to worry about the orientation of the trailer: park any which way and it’s all the same to the panels! And besides, the two solar panels typically produce more than enough current to power all of Jeff’s needs, even though they are mounted flat.

Some solar trailer owners don’t permanently afix their panels to their roof. Instead they just lay the panels up on the roof or prop them up next to the trailer once they get their campsite. That’s an easy way to do it!

What does a charge controller do? Why do I need one? http://www.enerwest.ca/faq/charger.htm

Jeff purchased a “Solar Boost” Charge Controller: Maximum Power Point Transfer (MPPT) 25 amp Cost: ~$180
http://www.blueskyenergyinc.com/sb2000e.htm

Here are some photos:

The 13.99 you see on the digital display is the charge controller running at its maximum when the sun is shining brightly. The second photo shows the back of the charge controller panel inside the closet.

Jeff decided one 12-volt battery was inadequate to store the electrical current required for life on the playa. He bought two more 12-volt ‘deep cycle’, marine-type batteries, 85 amp for a total of ~255 amps (when all three batteries are fully charged). Cost: ~$50 each

He removed the original battery from the front towing bar and mounted all three batteries in the bottom of the interior ‘wardrobe’ closet in the rear of the trailer. Here are some photos of the batteries before the installation was finished:
The batteries are wired together in a parallel.

Jeff then built a ‘false floor’ in this closet so that the top portion of the closet is still usable. The floor lifts out so that Jeff can add distilled water to the batteries every few months. Otherwise the batteries will dry up and die. Additionally, the battery compartment of the trailer is separated by a panel from the other electrical system components that are in the bottom of the closest.

Note: Lead-acid batteries should not be installed in an unventilated space, especially inside a trailer. Why not? During the charge cycle, batteries can give off hydrogen and oxygen gasses, which, at more than a 4% concentration, is potentially explosive.

“Oxygen and hydrogen gas will be released at recharge voltages between 13.8 V (2.30 volts per cell) and 14.2 V (2.37 vpc). Virtually all battery chargers have output voltages during some portion of the charge algorithm that are higher than the gassing voltage.” http://batterytender.com/battery_basics.php

Batteries should be recharged in an open area with good ventilation, away from any sources of sparks or combustion, like water heaters and electrical motors.

In Jeff’s trailer, he installed a vent in the battery storage compartment: since hydrogen gas is lighter than air, the vent is a large pvc pipe that runs from battery compartment up through the closet and out through the roof of the trailer.

The other electrical system components that are under the false floor also have their a vent (to release excess heat from the inverter) that opens into the interior of the trailer near the floor. This interior vent happens to be next to the trailer’s “propane detector”. On sunny, hot days, the propane detector sounds an alarm even though there is no propane leak. Research shows that propane detectors will detect almost any type of explosive gas. So, possibly, the hydrogen and oxygen gasses released from the batteries during their charge cycle on particularly sunny days is not all vented up through the exterior roof vent. Instead some of it may be leaking out of the unsealed separate battery compartment and triggering the propane alarm.

Although the concentration of gasses is probably too low to be of a concern, it would be better to mount batteries on the exterior of the trailer to avoid venting these potentially explosive gasses into the interior of the trailer. In the future, Jeff plans to move the batteries to the tongue of the trailer.

Another consideration with mounting something really heavy like batteries in a trailer is weight distribution. Trailers with too much weight in the back can “fish tail” when towed. Jeff compensates for the extra weight of the batteries in the rear of the trailer by carefully loading heavy supplies like canned goods and jugs of water as far forward in the front of the trailer as possible.

Sources of battery information: http://www.marine-electronics.net/techarticle/battery_faq/b_faq.htm
http://batterytender.com/technical.php

Since Jeff wants to occasionally run a small microwave in the trailer, he installed a Xantrex 1500 watt inverter. The inverter takes incoming 12-volt DC power from the batteries and converts it into 120-volt AC power for the microwave. Cost: ~$150 Note: Jeff’s model inverter has been discontinued but here’s a similar Xantrex model:
http://www.xantrex.com/web/id/165/p/1/pt/29/product.asp

Here is a photo of the big inverter and its off/on switch:

The inverter is the black metal thing to the right of the battery in the first photo.

Inverters should be mounted as close to the batteries as possible and use a heavy cable. If the cables between your battery and inverter get hot while under heavy load, then you should use a heavier cable.

Remember to ‘match’ your inverter to the watts you need. Here is a table with some estimated watts used by different electrical devices. http://www.invertersrus.com/estimatedwatts.html

Since an inverter uses electrical current when it’s turned on, Jeff installed a switch to turn it off when it’s not in use. When he needs to use the microwave, he pushes the On button, and, assuming the batteries have enough juice, the microwave is ready to go.

Hint: if you have a ‘power hungry’ device like a microwave or hair dryer, use it during the day when the sun can recharge the batteries.

NOTE: You need to be careful about which inverter you purchase: not all inverters will run all electrical devices! Particularly, you should NOT use a “modified sine wave” inverter to recharge the battery on your cordless drill: if you do, you will ruin the rechargeable battery pack on the drill. Need to add information about “modified sine wave” vs “true sine wave”

More information about inverters: http://en.wikipedia.org/wiki/Inverter_%28electrical%29

Notice the speaker installed above the charge controller panel: every trailer needs a decent sound system!

Jeff adds a 12-volt fuse block: the fuse block protects the system components from power surges, etc, like the circuit breakers in your house. This fuse block has six 15-amp circuits. Cost: ~$20

Here are some photos: In the first photo, the fuse block is the black thing with all the wires connected to it. The second photo shows all the components in the bottom of the wardrobe: the three batteries on the right, the big inverter to the left of the batteries, the fuse block and lots and lots of wires. The propane detector is the white plastic box near the floor on the outside of the closet. The third photo shows the false floor being constructed on top of all the components. Jeff thinks it’s really fun to work on delicate carpentry inside a tiny closet.

Small Xantrex Inverter