And there is a set of slides that gives you a more detailed description:

CLICK HERE for the slides

I made it from an old rectangular plastic kitchen garbage container. On the 2 large sides I cut a hole app. 12″ square, and covered the hole with replacement pads from an evaporative cooler. A small fountain pump and some clear tubing runs water over these pads. The top of the garbage can is covered with a piece of plywood with a hole cut in the center, and over this hole is mounted a 12V fan (either large computer muffin fan, or a salvaged ventilation fan from an old car). This fan is set up so it pulls (exhausts) air from the trash container, pulling it over the wet pads. A piece of dryer vent hose directs this air into the vehicle, tent, or whatever space you want to cool. The whole thing is powered by a solar panel. The fountain pump draws less than an amp, so size your fan based on the amount of solar power you have available.

The key to making this work is to pre-treat your greywater. I collected the shower water in a blow-up kiddie pool, and then transferred it to a 5 gallon bucket. I treated the water in the bucket with Alum (a flocculant) and bleach. The alum causes the suspended particles of playa dust to clump together and settle to the bottom, and the bleach sterilizes the water. After a little experimentation, I found that a teaspoon of alum and about 15 drops of bleach per 5 gallons worked well when allowed to sit overnight. After the water has settled, it can be transferred to the swamp cooler. Be careful not to stir up the water while transferring it, and you can get almost all the clear water leaving only a couple of inches of muddy water in the bottom of the bucket.

Alum can be bought in small containers at the grocery store (look in spices, it’s used for pickling) or in larger containers at swimming pool supply stores.

I probably won’t be at BM 2007, but would be happy to loan my prototype to someone, or to answer questions.

Steve steve_susswein@hotmail.com

On the playa, “graywater” or “grey water” are terms for water with contaminants that make it unsatisfactory as drinking water, but that wouldn’t normally require a septic waste system for disposal. Graywater includes ice-melt in coolers, shower water with soaps and cosmetics, kitchen waste including dishwater and scraps from food preparation (including raw meat), and toothpaste and saliva. Also a good bit of playa dust.

“Evapotron” is a highfaluting term, coined for Burning Man, for graywater evaporating devices suitable for use and operation by members of a camp. The term “evap-o-wheel” has also been used for an evapotron using rotating evaporative surfaces.

Three of my designs relied on wind power, and for them the corral was great for public attention but not for evaporative performance, because the wind and sun were often blocked by nearby structures. Non-wind-powered devices were no doubt affected as well. To get reliable estimates of performance we need to evaluate all the evapotrons in a more typical camp environment with fuller wind and sun exposure.

Each of the devices stood over a “pond” of on-edge 2×4s surrounding a plywood floor, about 24×48 inches, covered with black plastic sheet. I built the ponds and fans (salvage bike wheels with aluminum-sheet blades attached to the spokes) at home. The devices were brought to the playa as almost-flat components, then assembled.

“The Clothesline”

This design focuses on ease of construction. It is nothing more than an evaporation pond, and fabric that hangs above the pond and dips into the water. One end of the clothesline is easily detached from its support, to permit dunking the fabric fully into the water, then lifting it again to dry.

The clothesline would be a good solution for a small camp. Building it requires little construction skill or time, and in use it needs attention for a few seconds a few times a day, to dunk the fabric. The pond walls need to be taller than 3-1/2 inches; my device’s pond was too shallow to fully dunk the fabric.

“The Nonokini”

The Nonokini is a single bike-wheel fan with fabric wrapped around its nine blades. As wind rotates the fan, the fabric on each blade in turn is wetted in the pond, then lifted to evaporate or to disperse droplets downwind. The intent was to exploit the useful properties of bike wheels, without needing much mechanical tinkering.

Although the low wind made judging performance difficult, I think the Nonokini design would not perform well. The evaporative surface is relatively small, and the side of the fabric that touches the blade can’t evaporate at all. The water released as droplets may land on the ground or may annoy people downwind.

“Archie”

The Archie evapotron uses a bike-wheel fan to drive a bidirectional pair of Archimedes’ screws made of vinyl tubing wrapped around an inclined length of plastic pipe. Water lifted to the top of the screw is dispersed onto several sheets of fabric, to evaporate.

Archie was the most intriguing device to watch, but had several problems. The fan is close to ground level and therefore in very low wind; it is also tilted and shielded from the wind in one direction by the evaporative fabric. These problems could be overcome by making the screw longer; the fan could be elevated to 6 or 8 feet, where it would be in full wind, with a screw 12 to 15 feet long.

Another problem was that after a few days, the fabric became coated with playa dust and graywater contaminants. It lost virtually all its absorbency, and water released at the top ran straight downward without spreading within the fabric by capillary action. Evaporation diminished to near zero. I think the reason that only Archie was affected this way is that the other devices all had fabric moving in the water; contaminants could dislodge, to settle at the bottom of the pond.

I speculate that the evapotrons in several camps that trickle water over hardware cloth, rather than fabric, are successful because the metal mesh is so coarse that contaminants can’t form a continuous coating, as they do over close-mesh fabric. Perhaps a tall Archie using hardware cloth would perform well.

“Old Number One (rev. 2.2)”

Old Number One will in time get a more descriptive name. It’s a redesign of the evapotron I built in 2005. A fan carrying a clothesline pulley is mounted above a fabric-covered drum that is partially immersed in a pond. A drive belt from the fan causes the drum to rotate, dipping into the pond and carrying wet fabric up into the air and sunlight for evaporation.

To save travel space, I assembled the drum onsite. The drum ends were bicycle wheels, held apart by an 18-inch-long plastic pipe with ends notched where spokes touched. #12-24 allthread through the wheels’ hollow axles clamped the assembly together. String laced zigzag from rim to rim supported the fabric and also strengthened the assembly. In attaching the fabric, the ends were left free, which produced flaps that scavenged water from the bottom of the pond.

I made the drive belt from lengths of stockings or pantyhose legs. A very tidy knot for connecting them exploits the “hose” of the hosiery: tie an overhand knot in the end of one length; slide it into the end of another length; tie cord around the end of that length, to capture the overhand knot within. The drive belt is, naturally, very stretchy. Wet it, then stretch it substantially as you decide on the length you need.

Because a bicycle wheel rim looks like a pulley, I tried to use it as one for the drive belt. The belt repeatedly fell off the rim, requiring me to tinker with wheel alignment and belt tension. In hindsight, I realized the drive belt could have traveled on any part of the fabric drum; it didn’t need to ride on the rim.

This evapotron design was the most effective of the four. In sufficient wind, my 2005 device evaporated (or dispersed as droplets) as much as two gallons per hour. “Rev. 2.2” raises the fan from ground level to about 40 inches, where it catches more wind. The drum fabric is old sheets; I think it’s an open question whether using a more-absorbent or faster-drying fabric would make a significant difference.

Additional notes

Evapotron designs must consider disassembly and disposal as well as operation. Unevaporated water must be disposed of; this means getting it out of the pond, straining it (if that wasn’t done already), and scattering it or packing it out.

Once they were dry, I removed the fabric strips and black plastic and packed them out in my trash; apart from that, the devices were relatively clean and could be disassembled and packed out. I burned the wood of most ponds rather than taking them home to store.

Treating (disinfecting) graywater is important for camp safety, but reliable guidelines have not yet been established. Clorox is readily available but may not be the best approach. Its effectiveness is significantly reduced in water carrying suspended solids, so a concentration appropriate for purifying drinking water may be insufficient. Whenever more graywater is added, more disinfectant must also be applied.

Lining an Evapotron Tray

To hold their water, many evapotrons use a shallow tray with a floor of plywood and a rim of 2×4’s standing on edge. To make it waterproof, it’s lined with a sheet of black plastic. I wrote this to remind myself how to do the lining.

To begin with: the one important function of the plastic is to hold water. It doesn’t need to be tidy and unwrinkled, but it does need to be free of holes. Use new plastic sheet fresh off the roll, or check re-used plastic very carefully. What thickness? Thicker than a typical plastic bag, so it’s not fragile. It doesn’t need to be strong enough to support the water’s weight. The wood does that.

You will also need scissors and a stapler, the kind that can push staples into wood.

Determine the length and width you need, and cut the plastic sheet a couple of inches longer and wider. The length is the length of the plywood floor (outside measure), plus twice the height of the rim (twice 3-1/2 in. for a 2×4 rim.) Thus a floor 48 in. long requires a sheet length of 48+7 = 55 in., so cut 57 in. Similar math determines the width.

Now you will staple the plastic to the top of the rim only, but don’t start by stapling! Almost any mistake you make in positioning the plastic means a hole in the wall or floor, and you get to start over with a new sheet. Instead,

Place the plastic in the tray with a weight holding it down at each corner. Adjust the position so the plastic covers the rim tops and is fairly flat across the floor. Don’t worry yet about the plastic bunching up in the corners. Staple the sheet to the rim tops starting 3 in. from the corners, with whatever staple spacing you like.

To get tidy-looking, waterproof corners, grasp a corner of the plastic and pull upward and slightly inward. The plastic will form a fold in a straight line from your fingers down to the corner of the floor and rim. Now pull the plastic outward over the outside of the rim corner. With a little tucking, the formerly bunched-up plastic will form a neat squared shape on top of the rim corner. Staple it twice, once on each side of the diagonal. Repeat on the other three corners.

Trim the excess plastic along the rim’s outer edge, and you’re done.

In 2009 I had just published (on Instructables.com) a construction guide for building Gray-B-Gon evapotrons.  Since then, I’ve held five construction workshops in the SF area, and last year evapotrons on the playa consumed 500-1000 gallons of wastewater PER DAY.  I have built a website for evapotrons:  the easy-to-remember URL is  evapotrons.info, which forwards to the real URL,  https://sites.google.com/site/evapotrons/home .  You’ll find pix and words about every practical or intriguing evapotron design I’ve come across; also a dauntingly detailed guide to putting on a workshop in your own locale.  (Don’t be daunted!  It’s not that hard, really; and I’ll help.)

The Gray-B-Gon itself has many minor improvements (colllapsible drum; wheel balancing; belt traction; Clorox info; easier knots etc.)  which are recorded in the Instructables guide and in the same document, freely downloadable, on the website.  This year I will be testing a redesign that I expect to give a 2x performance improvement.  Residential evapotrons don’t need this — they usually run dry already — but I have my eye on the lucrative industrial market:  big camps using giant, inefficient evaporation ponds.  HeeBeeJeeBees tried a GBG last year, saw the effect, and asked for another.  The high-performance model, code name Jumbo, has the same footprint as always.  It just drops into an evap pond and goes to work with three times the evaporative surface area.

This is a HUGE photo of the inside of the BRCMUD dome: you can see all the plants they watered with the reclaimed grey water. They also sprinkled water on the dome’s burlap cover for cooling.
http://www.anybodyburns.com/2003/wallpaper/domelife.jpg

photo is worth 1,000 words.

–> 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.

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.

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

http://calsolarsolutions.com/rvandcabin.html

To summarise, you should know the following :

• Voltage is variable, it is like water pressure, devices can handle changes in voltage as long as it isn’t too much or to little.
• Amps are also variable, it is like the speed of the water flowing through a pipe.
• AmpHours is a rating of how long you can maintain that speed, it’s the bucket of water that will eventually get empty.
• Watts is the overall ‘usage’, Watts = Volts x Amps

Batteries

• Batteries are a 12V DC system, but they are really closer to 13V
• You need more than 17v or more to get a good charge into a battery
• Batteries do not like to be discharged below 12V, or 50% of their capacity
• A 50AH battery can give 1A for 50 hours, or 2A for 25 hours

Panels

• Panels are rated for their perfect conditions (midday, full sun, 25 deg C)
• Heat (aka the playa) reduces a panels’ output
• The angle to the sun reduces a panel’s output
• An 18V,75W panel really only puts out 15V,60A on average

Charge controllers

• 3-stage or PWM controllers are better
• controllers stop overcharging the battery
• controllers have a load (Amps) rating, if you panel has too many Amps, it will blow out the controller