Quick question about sizing solar panels (1 Viewer)

[e9999]

before I go and do my usual overanal digging through the web (and Mud) so that maybe I don't need to... , your quick take on this if you know:

what nominal wattage size of panel would I need to take care of my fridge and a bit extra?

So fridge is sucking up about 4.2A when running in normal mode, and let's say it's running about 1/2 the time when it's 90F or 100F or so -which thankfully is also likely when I'd get most of a panel's nominal output, well at least during the day. So that's be 2.1A on average over 24h. Let's throw in a bit more so I can get to play with electronics gadgets too. Say almost 1A more. So 3A average out of the 24h day. But that's really 6A averaged out over 12h during daytime. But the panel would likely not do much early and late in the day. So that'll be what, 9A at noon? When I say hot, let's say desert so good insolation.

So I'd need something like a 100W nominal panel? Then again, they probably lie through their teeth when stating full power.

Anybody has any real life feel for this?

 

[tag3]

I have a Waeco CF-50, run an 85 watt and I forget the amp rating. Might be 4.86 amp. A lifeforce battery. This setup has run the fridge non stop for 3 months straight. Have everything removed now, doing a slide out for the panel.

 

[patrickfinley]

No real life with solar panels, but I think you are about on target. Roughly 80-100w should run your fridge and a few efficient lights and gadgets.

Most people seem to say that for overlanding the flexible or foldable panels are the way to go. The rigid ones just get too bulky or take up too much space. The foldable panels generally come in sizes about 15, 30, 60w and are chainable. You can always start with a 60 see how it works, then add on more as needed.

 

[george_tlc]

Flexible panels are typically less efficient by quite a margin.

Get a decent Mono-crystalline panel (more efficient). I run an 80W nominal panel in oz and it does put out what it is spec'd at. NOTE, if you really want to get the most power from the panel then you want a REAL MPPT charge controller versus the PWM stuff that comes with a lot of panels. The MPPT will get you 5 - 15% more from the same panel (especially on less optimal haze/cloud days).

My old Engel draws close to 5A when running, but even on a 100F ambient day will run <40% of the time and drops closer to 20% during a warm evening.

My panel folds in 1/2, so it takes extra thickness to store, but less area. Works out nicer to have a smaller/thicker storage volume. The panel was <$200 in oz delivered. Pricing seems to have dropped even more since I bought this one 18 months ago. Came with a nice padded cordura type bag with a pouch for cables etc.

Based on a few trips in the oz bush in cool and HOT weather, an 80W panel is just about right to keep up with the demands of a fridge when camping in 100F weather and using/restocking drinks etc during the day. Add some extra insulation around the fridge and keep it out of direct sun to decrease its on time. My 80W panel through my MPPT charge controller puts a consistent 5.5A into the battery in full sunlight while charging. I've seen up to 6A if the panel is cooled down (pour some water over it).

With weather in the 85F or lower range, an 80W panel easily keeps up and you'll have net charge during a 24 hour period. As temps drop, even with more cloud, the fridge draws a lot less average current and even 1 - 2A from the panel is enough over a 24 hour period.

If I was buying a panel again (not like they cost much in oz), I'd likely go for a 120W panel and never worry about fridge/accessory power while camping. Obviously having an isolated aux battery is mandatory for peace of mind.

Note, many MPPT chargers (so claimed on Ebay) are a total Scam - they are PWM chargers. A real MPPT charger will run you at least $100 (Ebay/China) to $300 for US made. Get one rated to at least 15A output if you go with a 120W panel.

Also, the rating of a panel, e.g. 120W, is at MAXIMUM power, it will be LESS at 12- 14V. The MPPT charge controller will extract the 120W (less a few percent loss in its power conversion).

Nov 2012 trip (80W panel in use):

cheers,
george.

 

[TrickyT]

...
Note, many MPPT chargers (so claimed on Ebay) are a total Scam - they are PWM chargers. A real MPPT charger will run you at least $100 (Ebay/China) to $300 for US made. Get one rated to at least 15A output if you go with a 120W panel...

George, Have you looked at Tim Nolan's Arduino-based MPPT charger? (http://www.timnolan.com/index.php?page=arduino-ppt-solar-charger) Just wonder what you think of it.

 

[george_tlc]

George, Have you looked at Tim Nolan's Arduino-based MPPT charger? (http://www.timnolan.com/index.php?page=arduino-ppt-solar-charger) Just wonder what you think of it.

Yes, I have. I went so far as to re-design it and add an LCD port etc etc. But then decided my life was too short to start another software development and mount in a case etc etc....

I found an Ebay MPPT that I've used in Oz this past trip and it appears to work well and actually does implement MPPT hardware inside (real buck driver, with good electronics and conformal coating etc). I just added a bit more weather sealing to the case to deal with rain etc if left out in the weather during a camping trip.

THIS is an example of Junk/Scam and is ***NOT*** an MPPT controller:

http://www.ebay.com/itm/MPPT-15A-12...636?pt=LH_DefaultDomain_0&hash=item3a7d50b9e4

THIS is the same unit that I run and ***IS*** an MPPT controller. There's also a youtube video of a fellow that opens one up and is what convinced me to give it a try. I ended paying something near $100 shipped. It has worked well and I'm pleased with it.

http://www.ebay.com/itm/20A-12V-24V...252?pt=LH_DefaultDomain_0&hash=item2ec5570994

cheers,
george.

 

[TrickyT]

Very interesting, george. Thanks for the links! I have no idea how they can make a quality unit like the one in the second link and only charge US$47, including free shipping. Just the parts for the Arduino-based charger would cost more than that, not counting the time I'd have to put in building it.

 

[e9999]

Yes, I have. I went so far as to re-design it and add an LCD port etc etc. But then decided my life was too short to start another software development and mount in a case etc etc....

I found an Ebay MPPT that I've used in Oz this past trip and it appears to work well and actually does implement MPPT hardware inside (real buck driver, with good electronics and conformal coating etc). I just added a bit more weather sealing to the case to deal with rain etc if left out in the weather during a camping trip.

THIS is an example of Junk/Scam and is ***NOT*** an MPPT controller:

http://www.ebay.com/itm/MPPT-15A-12...636?pt=LH_DefaultDomain_0&hash=item3a7d50b9e4

THIS is the same unit that I run and ***IS*** an MPPT controller. There's also a youtube video of a fellow that opens one up and is what convinced me to give it a try. I ended paying something near $100 shipped. It has worked well and I'm pleased with it.

http://www.ebay.com/itm/20A-12V-24V...252?pt=LH_DefaultDomain_0&hash=item2ec5570994

cheers,
george.

thanks for the links
care to tell those of us who don't know squat about MPPTs how one can tell the difference between real and not?

 

[george_tlc]

thanks for the links
care to tell those of us who don't know squat about MPPTs how one can tell the difference between real and not?

Well, without opening one up to see the 'guts' it's hard to tell. Basically an MPPT charge controller has to be somewhat bulky/heavy to contain the electronics, including a reasonably large inductor that is used to do the power conversion. Also, several high power devices are needed, so usually that means a metal case or at least a heatsink to dissipate the losses in conversion.

Given a 120W or larger panel and a 15 - 20A MPPT controller, even at 95% efficiency we have 5% heat losses of 120W, so 6W and higher yet closer to the MPPT rated output. So, heatsinks are needed to shed that heat. The scam units are just plastic cases and contain a PWM controller which is commonly supplied 'free' with many solar panels.

So, the only way to really know is to buy something that someone has already opened up and confirmed it has real hardware inside versus not much of anything. The controller I linked (that is 'real') has a bunch of electronics and a full buck converter to do the power conversion of the panel to the battery being charged. The LCD panel and menu system allows you to configure the various charging points, i.e. float, bulk etc and the settings are then stored in non-volatile memory. It really does work and is an amazing bargain for what you get. It is well made and the electronics looks to be very good quality. From some web searching (based on the internal design and operating menu system) it appears that the design was a commercial name brand product that likely was farmed out for manufacturer in China and is now being made/sold direct by various ebay stores over there.

Basically MPPT (you can search and read wiki's etc) is an algorithm (plus power conversion hardware, think DC/DC voltage converter) that tracks the maximum power point of a solar panel and then tries to keep the power draw at that exact point while converting that power to a level to charge the battery. As long as the battery is drawing more than what the panel can provide directly, the MPPT algorithm works to extract the most it can from the panel.

Simply put, a solar panel produces a certain voltage at a certain current draw, if you take the product of those values over the full range of no current draw to no voltage output (full current draw) you can plot the power (watts). you'll find that the curve has a pretty narrow peak - that's the maximum power point. If you can keep drawing power at that point you are getting the most out of the panel, of course that may occur at 18V, so you need a DC/DC converter to step that 18V down to the charge voltage (say 14V) and since you have around 95% conversion efficiency you'll be putting out more amps at 14V than you're getting out of the panel at 18V.

So, a solar MPPT charge controller of the type we're discussing does two basic things, 1) it tries to draw maximum power from the panel and the algorithm tracks that point in real time and adapts to variations in the maximum power point depending on the panel output as it responds to the amount of solar input, panel temperature etc and 2) it implements a DC/DC converter whose output conforms to the charging needs of a battery. With a good MPPT charge/controller you can set the threshold voltage that you want to transition from buck to absorption to float so you can tailor it to a particular battery chemistry (SLA/AGM etc).

cheers,
george.

 

[pandasfj]

Good info,just wondering what brand or type of solar panels are good to use with this type of mppt.Are all solar panels the same as far as quality,folding or non-folding?Thanks, gil.

 

[Basie]

Hi

My setup looks he same as george-tlc and consists of two 55w panels. If you have a roof rack where you can store square things it works out very well and is less bulky and less costly than a 120 w flexible panel. I user the CTEK 250S dual as a DC to DC charger for my extra battery and it doubles as a MPPT solar charger as well. During a normal winter day here with outside temps of 28-32C ( not a typo) and with shifting every two or three hours to keep it facing to the sun it runs a 50 litre National luna to deep freeze and with some juice to spare. I tried lots and lots of other ways to keep the extra battery happy, but this is the first one that works for me. You can even ad a wind charger!

 

[LandCruiserPhil]

After several real time test my Waeco CF-50 can run indefinitely on a 55W panel and POS single Checker Auto battery without starting the Cruiser. All test were conducted in AZ and Mexico.

https://forum.ih8mud.com/az-copper-state-cruisers/568756-powering-my-fridge-solar.html

 

[e9999]

all good info, thanks


what's the typical $ premium one would have to pay to go mono over poly or thin film of the same nominal power? The area saved could be significant I suspect but are there also differences as far as thickness and weight?

 

[george_tlc]

all good info, thanks


what's the typical $ premium one would have to pay to go mono over poly or thin film of the same nominal power? The area saved could be significant I suspect but are there also differences as far as thickness and weight?

Time to go and google solar panels etc and do some research of your own

Panel pricing is dropping and certainly in Oz most panels that you can buy on ebay over there are mono and from several I've seen first hand are well built and appear to put out their rated specs.

I personally would go for mono since it's for vehicle use and I have the room to store a rigid panel (albeit folding of 2 hinged panels). Weight, who cares, the vehicle certainly doesn't.

Given you are asking about a solar panel for using with a fridge, size, weight, thickness of the panel is inconsequential versus the fridge So, cost/efficiency is the prime concern. Find a vendor that sells the watts you want for the money you're willing to pay.

Folding panels on oz ebay seem a LOT more popular than US ebay and the oz prices are lower than comparable in the US. I'm guessing there's a lot more demand for folding solar panels over there than in the US where folk typically drive a behemoth RV with generator and hookup at most/every site.

Note: I would assume anything below that says it includes an mppt charge controller is a lie...

US:
http://www.ebay.com/sch/i.html?_sacat=0&_from=R40&_nkw=solar+folding&_sop=1

OZ:
http://www.ebay.com.au/sch/i.html?_sacat=0&_from=R40&_nkw=solar folding&_sop=1

cheers,
george.

 

[e9999]

I was indeed surprised at your stated prices of panels in Oz. They sure seem a lot more expensive here.

 

[patrickfinley]

I was indeed surprised at your stated prices of panels in Oz. They sure seem a lot more expensive here.

Australia has fully embraced Solar power where the US has not. Utilities in the cities are very expensive, making solar attractive. When you leave the cities, there are many regions of Australia that would have little or no power without Solar. The US is just scratching the surface of a "green" lifestyle while the Australians have been living it out of necessity for quite some time.

I would imagine this is why pricing is better down under.