Someone gave me a panel - can I build on it?

One of the neighbors has been watching me build my truck in preparation for my roadtrip through Latin America. The other day he came over and gave me a solar panel and a charge controller that he never got around to using.

The panel is a Unisolar US-21, 20 watt panel. The controller is a BZ Products 240, 14amp controller with a blocking diode.

Score! Now how do I build a solar system around this?

I know from previous experience with a 30 watt Sunforce panel that I can run my Norcold NRF-30 fridge (4.3a @ 12v) for 6 days, if I clean and reposition the panel throughout the day. I measured 1.7a at peak output.

I declined to take that panel on this trip however because of the fragile glass construction. This US solar panel is totally different. It appears to be made from some sort of plastic that seems very durable. 20 watts would help but 80 would probably let me run indefinitely on electric power (stereo, fridge, fan at night).

I don't want to drop a bunch of money on panels (and matching US-21 panels seem pricey) but I'm interested in more power. What are my options? Are there any inexpensive but durable panels I could add on to this setup? I have ~3'x5' of area on my roof rack that I could devote to panels.

Vehicle is a 60 series landcruiser with dual agm batteries on an isolator.
 
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dwh

Tail-End Charlie
Looking at the specs for the PV module, it's got a Vmp of 16.5v. You can parallel that with any other "12 volt nominal" PV module with roughly the same Vmp. Say between 15v-18v Vmp would work fine.

You'll need a charge controller capable of handling the combined amperage of course.

Which you'll need anyway, since pretty much everyone who knows solar and has tried a BZ controller seems to agree - the best use of a BZ charge controller is to strip out the internals and use the metal box for some other project.
 

dwh

Tail-End Charlie
Within 10% is the general recommendation (but it can be fudged a good amount). So 10% of 16.5v would be 1.65v and 17.2v is only 0.7v difference. Well within the ballpark.

Mono- and poly-crystalline PV modules are generally a layer of tempered glass with an anti-reflective coating (don't want the sun's rays to bounce off), then a layer of glass solar cells, then a few layers of rubber and/or epoxy glues. All stuck together under a heavy vacuum. Makes a fairly tough sandwich. Then a frame around that to make it a bit stronger and to give a place to grab it with screws or clamps or whatnot.

Most are also rated for things like high winds and snow loading.
If it's solidly mounted and doesn't flex, it'll almost certainly take a direct (and hard) hit on the glass to break it.
Golf ball sized hail usually won't even break them. Sometimes, but not that often.
 
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Thanks for the info.

Mono- and poly-crystalline PV modules are generally a layer of tempered glass with an anti-reflective coating (don't want the sun's rays to bounce off), then a layer of glass solar cells, then a few layers of rubber and/or epoxy glues. All stuck together under a heavy vacuum. Makes a fairly tough sandwich. Then a frame around that to make it a bit stronger and to give a place to grab it with screws or clamps or whatnot.

How does that compare to what I currently have from unisolar?

UniSolar solar panels uses Triple Junction amorphous thin film silicon cell technology, resulting in a robust and durable but flexible and light-weight cell. Modules are encapsulated in UV-stabilized polmers (includes EVA and fluoropolymer Tefzel similar to Teflon), framed with anodized aluminum, and backed with Galvalume steel for stiffness.

I believe it is a polymer / plastic panel?
 

wrcsixeight

Adventurer
I would not build a system around the free equipment.
I don't know if I'd even use a charge controller with a single 20 watt panel on a vehicle that is running a fridge 24/7. There is no way you will over charge the battery in that situation.

I'd get the biggest wattage panel you can fit in your intended area, as it is really hard to have too much solar. Perhaps 2 panels in case you smash one of them. The faster you can recharge your batteries, the longer they will last. Finding AGM batteries in Honduras might not be an easy task. Easier to do it once right than add more later.

I started with 130 watts, and found after a while that was not enough, now I have 200 watts, and guess what, I could use more if I had it. Especially when it gets overcast.
 
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dwh

Tail-End Charlie
Mono and poly crystalline solar cells are slices sawed off of ingots of silicon glass. Amorphous silicon (thin film) is more like an ink that can be rolled on or sprayed on to a substrate like glass or flexible plastic.

Mono is a single crystal grown in a process that looks similar to something like extruding (actually more like pultruding) . Poly is a bunch of crystals formed when the glass is poured into a mold.

Mono are generally the most efficient in terms of watts harvested per square meter, then poly. Thin film is the least efficient per square meter, BUT often does better in diffuse light such as early morning/late afternoon or hazy/cloudy days.


Unisolar's PV modules are thin film on a flexible backing. They are a sandwich and are very tough and lightweight. You can walk on them in boots. Personally, I think Unisolars are great for trucks except for two things...

A) With the lower watts per square meter, you might cover all the available area, and still not have enough watts (as wrc mentioned, more is better).
B) If you cover your roof with them, it's basically the same as painting the roof black from a heat standpoint.
 
There's a good chance the fridge will be on 24/7 (although it is obviously cycling on and off) but I don't want to count on that so I will use a charge controller regardless. If you guys scare me off the BZ controller I can pick one up at Fry's. I am definitely using this panel unless someone can convince me otherwise. The only reason I'm undertaking this project is the free gear. I don't actually need any solar energy - I can run the fridge for a couple days on battery power alone.

As for turning the roof black, the panels will be mounted on top of my roof rack so there is plenty of gap between the panels and the roof. This will be like bringing my own shade with me wherever I go :)
 

wrcsixeight

Adventurer
I am definitely using this panel unless someone can convince me otherwise. -------- I can run the fridge for a couple days on battery power alone.

How big is the 20 watter?


I could go several days powering my fridge on battery power alone too but I would not expect to get a very long life out of the batteries.

It's not like it is easy to fully charge a severely discharged battery. The alternator does a very poor job bringing a battery above 75% in my experience, and continuous recharges well below 100% can lead to progressive sulfation of the batteries, reducing the capacity significantly, so that couple days will become a few days, and eventually one day, then the search for new batteries begins. Under this sort of use, It is very important to be able to fully charge the batteries at least once every 2 weeks, and this means having access to 110 volts and a battery charger plugged in 24+ hours to insure the batteries are indeed back up to their maximum capacity.

Not sure the temps you camped in that you get several days out of the batteries, but Latin humid america, you fridge will be consuming a lot if it is sitting in a vehicle in the blazing sun.

By all means, use the 20w free panel, but don't rely on it for anything but negating a small percentage of the fridge load. Do consider the hassle of finding replacement AGM's in Latin America, cause even the best batteries are likely to have a very small percentage of their original capacity after running a compressor fridge in Latin America 24/7 without at least coming close to being fully recharged every day.

I'd say you will want at least a 100 watts. If an 80 watt panel next to your free 20 watter fits nicely in your allocated space, great, but if you could get 2 80 watt panels up there your batteries will be so much better off and you can enjoy the lands you visit rather than stress about the food spoiling and searching for new AGM's
 

dwh

Tail-End Charlie
If you guys scare me off the BZ controller I can pick one up at Fry's.

http://www.wind-sun.com/ForumVB/showthread.php?1779-BZ-Controller


As for turning the roof black, the panels will be mounted on top of my roof rack so there is plenty of gap between the panels and the roof. This will be like bringing my own shade with me wherever I go :)

Yea, that was sort of the point. PVs mounted on a rack or otherwise raised off the roof serve to provide a "tropical roof effect". The Unisolars are designed to be stick-on so generally they are just stuck-on to the roof.
 
It is about 16" x 36". It's a unisolar 21, which comes mounted in an aluminum frame. Pretty handy.

My fridge is mainly to keep my film from getting cooked in the sun. Cold beer is a nice ancillary benefit. The fridge will spend most of its time set at ~55f unless I am trying to chill a 6 pack or the occasional perishable. As for battery availability, I can use whatever physically fits in my battery tray, AGM or otherwise, so I'm not too worried about that.

But still, point taken.

I estimated 80watts would overcome my general fridge usage. I'm not opposed to adding another panel to the mix but only if I can do it on the cheap. I am overscoped and underbudgeted as it is :)
 

dwh

Tail-End Charlie
Oh those. I forgot about those. Don't think they make them anymore.

Yea, those aren't the stick-on Unisolars. :)
 
Orientation - on my roof I could install the panel flat on top of my roof rack, removing some of the rack's utility.

Alternatively, I could mount it in front of the rack in which case it would be angled forward slightly - the rear would be ~6" higher than the front.

For a mobile automotive install, I doubt this will make a big difference right? I imagine I'll get better results from the angled install when I park into the sun and worse results when I don't.
 
Ok guys - I bought a morningstar sunsaver ss-10 and an 80 watt panel. I wired my existing Unisolar panel in parallel with the one from solarblvd and connected that to the solar leads on the sunsaver.

The green LED light comes on to say it is charging but I don't get any output if I put a voltmeter or ammeter on the battery or load leads from the controller. Is that odd? I was expecting to see something on the meter. Does this controller only work if connected to a battery?

Should I be fusing cable between the panels & the charge controller or just between the controller & the battery? I'm thinking about a short that might occur where I pass the wiring from the roof of the vehicle into the cabin. I doubt the panels could produce enough current to melt anything but should I be doing anything to protect the panels themselves?
 

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