The 4WD Solar Fridge Project
Note: this is an archive of a 1996-2004 page of solar system "notes" and journalism from my old website. I'll update it with the new modifications to the new solar Trooper system when I have time... December 9, 2018.
Freedom to live where you want—up a desert wash, far from civilization, for days, for two weeks—with fresh cold food and drink, without having to go to town for ice or deal with sloshy ice and water.
Your own independent power source for laptop computer, video camera, lights, etc.
Here's the vehicle in-situ in the Anza Borrego desert (January 1996). The panels are obviously in the up position. I actually found that they did not need to be raised to get adequate power. I just parked and left them where they were in a horizontal position. The solar radiation in the desert is more intense because their is less moisture in the air, and of course there is usually very little cloud cover.
You can just see the refrigerator inside the vehicle, to the left of the deep cycle battery on the right. The raised sleeping bed above it is in the tilted-up position to allow access to storage and the fridge underneath. You can just make out the wire going from the vehicle towards the tent. (More detailed photos of these features are on the next 3 pages).
They Said it Couldn't Be Done
Everyone I talked to was quite pessimistic – they thought I would need a $1000 worth of panels, or that it just wasn't practical to run a fridge off solar in a vehicle. I had a feeling I could do it though, and they were just basing their estimates on what had been done in the past, or on average conditions and typical scenarios. But I was doing something relatively unique, with a particular set of hand-picked parts. It's called thinking outside the box. Or how to make cold inside a box in the middle of nowhere in this case.
The selection of the refrigerator was a critical part of the picture. After some research, I came up with this small, low-duty cycle, 12V RV refrigerator made by NORCOLD (see photo below).
The NORCOLD Tek II (with Rowan my Queensland Heeler posing for scale) uses only about 2.5 to 4 amps (when running), with less than a 50% duty cycle (how much the cooling pump is actually running). They are made for motorhomes and the like - and this is the smallest unit they make. They run on both 12V DC and 110VAC, and are relatively efficient in terms of cold storage. The estimates of the duty cycle the manufacturer gave I found to be very conservative. These things are not cheap though -it was over $600.00 I believe. But this is a real refigerator, not a wimpy thermoelectric unit. We've also used this as an overflow refrigerator in the house at Thanksgiving time. The efficiency of this fridge together with the intensity of the desert light in the dry air made it all a possibility. I could come back to my locked truck after a hike on a hot day, and the truck would be like an oven inside. This little fridge would be purring away, nice and cool inside, no problem. And since the sun that was heating the vehicle was also hitting the panels at full force, there was enough current, and no over-drain on the battery.
I looked into the little electric coolers that you can pick up for around $50. They are basically styrofoam ice chests with a Peltier element (a solid state heat pump) with a large heatsink and fan. The problem with them is that they are 1, horribly inefficent, and 2, noisy. If you wanted to cool down some beer and sandwiches for example, you'd have to either cool them down in your real fridge and then put them in the cooler that has been running for a while, or if you put the stuff in warm, run the cooler for something like 6 or 8 hours. This NORCOLD unit however, could make ice in the middle of the Mojave in short order. Just park in the sun, crank the dial to "5", and come back from your hike to frozen beer (well, OK, it's just an example). It's also very quiet. I'm very sensitive to noise, and often slept in the Trooper in the desert silence, and was not bothered by the noise it made when it switched on.
This system consists of a solar electric panel, a storage battery, a voltage regulator/diode, electrical wiring, various mounting hardware, and modifications to the vehicle to mount the hardware and allow sleeping and storage.
These pictures were taken on the day I "de-commisioned" the system from the vehicle (March 17, 2001). The solar system had been up and in use off and on since January 1995 (6+ years) without any problems except for the battery. The vehicle on the other hand (a 1986 Isuzu Trooper) had seen better days, and was too old to take to the desert anymore.
The panel is made from 4 surplus photovoltaic panels bought from Solar Electric, Inc. They were only $50 each if you bought four, for a total of only $200. If you've ever priced photovoltaics, you'll know this is very cheap. These tempered plate glass panels were originally part of a solar demonstration project put on by Arco in the Arizona desert in 1984. They were apparently used in conjunction with mirrors that concentrated the sun to a degree, which accounts for the brown color. They only lose a couple of percentage points in efficiency from being browned - no big deal. I built a frame from wood, wired the 4 panels in series, and sealed and glued it up with some non-acidic black silicone sealant (Dow 739). The sealant was also used to seal the holes I drilled where the wires entered the roof of the truck. The wood was given a coat or two of spar varnish (what you use on boats).
In the photo above you can see where the positive and negative wires enter the roof and were sealed with silicone. You can also see some of how the panels were mounted: the luggage rack hardware was modified to hold the panels. Holes were drilled in the mounts, and custom fittings made from wood and brass were put in place to hold the long brass bolts that served as the mounting point and hinge for the panels.
The original machine screws that held the luggage rack mounting hardware on the roof were not strong enough to hold the panels firmly while driving over rough, rocky desert roads I discovered, so I drilled larger holes in the roof and used brass bolts. I had to cut through the ceiling liner to get at the bolts from inside the truck
The original machine screws that held the luggage rack mounting hardware on the roof were not strong enough to hold the panels, so I drilled larger holes in the roof and used brass bolts. I had to cut through the ceiling liner to get at the bolts from inside the truck (see photos below). Not a pretty sight, but who cares. It was worth it.
For almost any kind of solar electric power system, you need some way to store the power when the sun is not out, and this usually means a battery. You also need some way to regulate the current going to the battery, and a diode to keep current from going back through the cells. I used an inexpensive ($49) electronic solar charge controller/voltage regulator made by Specialty Concepts, Inc.
The charge controller (above) was easily mounted to the side rail in the back of the truck with two machine screws. I could also see the charge light from anywhere. Notice the in-line fuse on the wire – very important.
This battery was kept under the bed next to the fridge. Deep cycle marine/rv batteries come with threaded posts that make it simple to hook up multiple wires.The cover was made from a plastic storage box. I had a long wire with in in-line cigarette lighter type connector on the end that could hook up to a laptop computer or light, and sit in a camp chair away from the vehicle, or in the tent. I also charged video camera batteries, cell phone batteries, and flashlight batteries off the system. All you need are the right adapters or connectors, which are not hard to find.
I got the idea of a raised bed in the Trooper from a friend of a friend who spent a lot of time living in his truck. He had built a raised bed system for himself. The storage space created underneath meshed nicely with the solar powered refrigeration system, since I could place the fridge and batteries underneath. (Fridge not shown – it was kept just to the left of the battery).
In the picture below you can see the bed in the raised position. This allowed access to the refrigerator - somewhat of an inconvenience, but you get used to the routine of raising the bed and putting it on the hook quickly.
The mesh hammocks I found at a boating supply store. They are a great way for keeeping stuff off the floor, and keeping it in place as the vehicle traverses rough terrain. They just swing as the vehicle rolls. Boat people need to survive out on the wilds of the sea, tossing to and fro and so have good stuff for vehicles and people that want to survive moving out over the wilds of the land.
I sure drilled a lot of holes in this truck! The bed was attached with large hinges using machine screws. The supply hammocks were attached to screw eyes that were bolted into holes.
Above and below views of the attachment of the bed. What would I do without titanium drill bits?
A view of the supply hammocks on the left side. My girlfriend made curtains that I attached with velcro that was attached with epoxy to the window trim. No, I'm not a very good candidate for leasing a vehicle!
The (New) 4WD Solar Fridge Project: V.2 (2006)
Got a new (used) 1991 Isuzu Trooper in 2000. Finally, in late November 2006, bought a new UNI-SOLAR panel from Affordable Solar Group in Albuquerque, NM (Model US-64 64W PV M). Cost at that time was $319. (This was a higher than I expected to pay: the story was there was a shortage of panels in the market because the Japanese and Europeans were buying them up). They still show the panels on their site, but as of this writing (3/17/10) they've been discontinued.
Solar Panel Specs:
Model: UNI-SOLAR US-64
Rated power: 64 Watts
Operating Voltage: 16.5 Volts
Operating Current: 3.88 Amps
Open Circuit Voltage: 23.8 Volts
Short Circuit Current: 4.80 Amps
Bypass Diode Included: Yes
Blocking Diode Included: No
Minimum Blocking Diode: 8.0 Amp
Length x Width: 53.8" x 29.2" (1367 x 742 mm)
Weight: 20.2 lbs. (9.18kg)
Warranty on Power Output: 20 yr
Model: Interstate SRM-29
12 Volts - Deep Cycle/ Cranking
CCA: 675 MCA: 845
RC: 210 minutes
Warranty: 30 months
Dimensions (in): 13 x 6.75 x 10
Weight: 61 lbs. Terminal: Auto/Stud posts
Hours @ Ampere Load: 21@5; 6.4@15; 3.4@25
Norcold 330, 3.5 Amps at 12 Volts.
This panel has some advantages over the old system. These glass-free panels are extremely durable. You could shoot a bullet through them and they would still work. Or be hit by a rock (a more likely scenario). They are good in high temperatures (like the desert), and are extremely shadow tolerant. They supposedly work well under various lighting conditions such as cloudy days, because of having different layers that absorb different frequencies. And they came pre-framed.
You can just make out the fridge in the photo below (same old Norcold 330D - takes a licking and keeps on ticking). I covered it with silver insulated mylar from a windshield shade to keep it cooler.
Took it for a "shakedown cruise" in the Anza Borrego Desert starting March 5, 2007. Camped out in a little wash. Used the same Norcold fridge, which is amazingly sturdy and reliable. Replaced the old RV battery with a larger, higher capacity model.
Below is a closer view, showing the mounting brackets. I decided not to use a hinged mounting system this time, because I ended up keeping the old system flat, and it's vastly simpler. These are also very secure brackets: they mount underneath the panel, in a slot in the aluminum where you can't get to them, and on the roof of the vehicle, four bolts and silicone hold them down (plus a acrylic plastic spacer on the right hand side).
You can also see the windbreak I put on the front. Without it, the panels make a funny low wooshing noise above about 20 mph speeds while driving. The windbreak is made from a piece of wood, but was later replaced with aluminum bar, bent around the sides.
Took apart the back where the condenser is. Vacuumed and cleaned out, including coils.
Checked functioning with A/C at 5, 4, 3 setttings using thermometer. Got down to around 20 degrees F.
Replaced rubber bumpers (they'd pretty much dissolved) on top that stop the lid when opened.
Replaced Norcold fridge (which was getting loud) with Dometic CF-25 , which is narrower, higher, and more advanced electronics with some useful features.
- SPECIFICATIONS: Dometic CF-25 CF-25 "COOLFREEZE" Portable Fridge
- CAPACITY: .9 Cu. Ft.
- WEIGHT: 26.5 lbs.
- POWER CONSUMPTION:
- RUNNING TIME PER HOUR:
- TI = 41° F, TA = 68° F: 11%
- TI = 41° F, TA = 89° F: 16%
- NOMINAL CURRENT 12V DC: 6.8A
- MATERIALS: Injection molded housing with integrated rollbond evaporator; blow molded lid; PU foam insulation
- COMPRESSOR: Fully hermetical Danfoss BD35F compressor with control electronics and integrated
low voltage protection for 12V and 24V DC. Dynamic ventilated condenser,
aluminum rollbond evaporator, electronics reverse polarity protection, adjustable electronic thermostat
- BATTERY CONTROLLER: The coolbox is equipped with a battery controller cutting the compressor in or out in order to protect the battery and the compressor.
- CUT OUT VOLTAGE: low 10.4 med 11.0 high 12.0
- CUT IN VOLTAGE: low 11.2 med 12.0 high 12.9
Replaced the old old charging system with a SunSaver 6 (series instead of shunt, PWM), installed a wiring block, replaced battery.
Did some work on the fridge. Replaced the fan a few months ago (some of the blades broke off and it was generating an error). Found a replacement fan by matching model numbers, on a website from a company in Singapore. Turns out to be a server fan. Installed it and seemed to be working but was fairly loud – I did not transfer the thermistor from the old fan over since I couldn't see a way to do it. Starting getting errors and the fridge just not keeping cold –seemed to be when the air was warm and/or when the sun was hitting it. So it may need that thermistor. Unfortunately the elctronics were re-designed, and I could not find an equivalent connection on the new fan's circuit board for the thermistor.
So yesterday I made a Frankenstein fan by taking the old fan housing & electronic and sticking in the new fan blades/axle with it (plus a little spring from the new that pushes it out - without which it made scraping noises).
Also accidentally blew 20 amp inline fuse on the positive lead that goes from the battery to the wiring block, but that wire was warm to the touch I noticed. Pulled out old fuse and saw the contacts were corroded. So put in a 10 amp fuse since that's what I had (other than a 30 amp one). Better too small than too large: don't want to start a fire!
Went on desert trip to Anza Borrego. It had been a while since I'd been out – this was a kind of "shakedown cruise" – and the first night, the fridge stops working: does its error light deal, cycles off and on without cooling to any significant degree. I thought it was only that the fridge was not working properly.
Turns out some of the wiring came loose, from the battery moving back and forth when driving on rough roads and pulling on wires – so came up with the idea of using a battery tray! – but also some wiring was not of adequate gauge. Also I hadn't realized that the fridge has a function that cuts it out when it senses the battery is below a certain voltage, and there is a Low Medium and Hi setting for that, plus the fridge is getting old, beat up (for example the lid doesn't fully close after I, like an idiot, stored leftover dry ice in it!) and not working up to spec.
All in all I decided to:
• Upgrade the wiring with heavier gauge (less resistance).
• Upgrade the charge controller with a newer and higher capacity model (more indicators of battery status too).
• Get a new, more efficient and slightly larger fridge, with updated electronics
• Install a battery tray.
New charge controller (Amazon): Morningstar SS-10L-12V Sunsaver-10 Amp With Lvd.
New battery connector wires.
New, better quality cigarette lighter adapter cables (which is how everything is connected to solar power system).
Battery Tray: Attwood Corporation with 29/31 Series Strap.
Been doing some upgrades on the electrical aspects of the solar system lately. These were to address some problems and needs I realized from forays camping in the desert:
Had to pull out the voltmeter every time I wanted to know what the exact status of the battery, and what the panel output was, etc. The SunSaver 10 only has LED lamps that indicate by Red/Yellow/Green the general status of the battery, and a small greenish LED that lights (and is hard to see) when the battery is being charged by the system.