Solar power questions

OK, went through the forum, but didn't find out quite what I needed.  Here is my situation:

We have a small 5th with 6 GC-2's (new 6 months ago), a 2500 watt pure sine inverter (for the trailer as a whole), a 1000 watt pure sine inverter (for outlets on the table for electronic devices only), and a Honda 2K generator.  Converter is a 60 amp Xantrex that I installed several years ago.  We use the generator when drawing heavily, like for toaster, waffle iron, or microwave.

The idle current on the 1Kw inverter is about .36 amps according to what I could find online.  Lets call it 0.4 amps.  The larger Sunforce 2500 watt I am going to guess takes 2.5 times more, or about 1 amp (I've seen 0.8 listed, but can't confirm that).  Even if I left both running (which I don't) 1.5 amps x 12 volts gives me idle current drain of 18 watts x perhaps 8 hrs/day for 144 watt hours.

32" Flat panel TV takes about 70 watts for perhaps 2 hrs/day for 140 watt hours

17" Dell computer takes about the same for about the same amount of time for another 140 watt hours.

140 plus 140 plus 144 = 424 watt hours

Now, am I correct that one calculates about 5 hours/day (average) of full output from a solar panel given that the sun is not always as strong during the 10 hours or so of daylight that one gets in Quartzsite in December and January?  If so, then an 80 watt solar panel would give 5 x 80 watts during a whole day for 400 watt hours.

In other words, an 80 watt solar panel should cover the day to day 'extras'.

My goal is to just  reduce the amount of times we use the generator while parked in the quiet, not to replace it totally.  The 6 GC-2's run the furnace on their own for a couple of weeks in the desert, but I am finding that the electronics we are adding as time goes on mean that I have to run the generator more than I want to.

I can get an 80 watt portable solar kit for about $450 (in Canada).  I'm willing to spend that much.  I am not interested in loading the roof of the trailer with solar panels as we just don't use it enough in a year to justify the cost and hassle.

Anyone see any major faults with this so far?

Thanks.

Frank.

Hi Frank...

I'm literally right in the middle of writing an article for the forum library about RV solar power so I have some helpful information right in front of me. The five hour figure you mention is an average that's used throughout the US, throughout the year. Go to this link  https://tools.carmanah.com/src.web/GoPowerCalculator.htm?state=RvDiv  and click on the "ENERGY IN" tab and then the "SOLAR MAP" link, you'll see how much solar energy is available for solar panels in different parts of the country, at different times of the year. In Quartzsite in December, there's about 3 kilowatt hours of useful sunlight each day.

An 80 watt solar panel will produce about 4.5 amps per hour under ideal conditions, which almost never exist. And remember, a panel's output is measured at the panel itself under ideal environmental conditions. You're going to lose a little power in the wire run from the panel to the batteries, your panel may not always be perfectly perpendicular to the sun and higher surface temperatures on the panel will cause it to produce less power. In reality, you're probably only going to get about 3.5 to 4 amps per hour out of an 80 watt panel - best case scenario.

I would strongly recommend that, if you're only going to have a single 80 watt panel, don't spend money on a solar "kit" that contains a charge controller - just buy the panel and good wiring. The primary purpose of a charge controller is to prevent the panels from overcharging your batteries. Between the parasitic loads of your 5th wheel, the size of your battery-bank and the power you'll be drawing from your batteries while you're camping, a single 80 watt panel will not generate enough power to overcharge your batteries - far from it.

Kev

Kev:

Between the parasitic loads of your 5th wheel, the size of your battery-bank and the power you'll be drawing from your batteries while you're camping, a single 80 watt panel will not generate enough power to overcharge your batteries - far from it.

Seems reasonable.  Now I have to decide how much I want to spend, I guess.

Thanks for the comments on the lack of need for a charge regulator.  That may save me some bucks.

Frank.

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Kev:

So, in shopping around, I found this item right here in Calgary.

It appears to come without a charge regulator, and the price looks right.  In fact, at that price, I might be able to afford two of them.

It is small in size compared to some other units I have seen, so I wonder if it will produce what it is said to produce.

Do you have an opinion?  I would probably just be propping it up on the ground and running a cable to the batteries for a portable external setup.

Frank.

Hi Frank. The panels you're looking at look fine. They have the older style method of connecting to the wiring (a junction box vs. MC4 connectors), but there's nothing wrong with a junction box - in fact, some might prefer it for portable installations like you're talking about.

Before you buy them, you might take a look at the "Sale Tools" website (Sorry, the device I'm typing on won't let me copy or paste links.) They're advertising Grape 100 watt mono panels for $99.00 right now, or $130.00 if you want black frames. They have slightly better performance specs than the panels you're looking at but, honestly, I don't think you'd ever notice the difference. Grape panels consistently get excellent reviews and they're priced pretty reasonably. Let me know if there's anything I can help you with.

Kev

I use portable solar, except I use the big 200w+ panels. We can take three for up to 720w

First thing I suggest is to get Poly crystalline panels over Mono crystalline if you can. Polys do better in less that optimal light.

Two of the 100w panels would be a nice portable but you will need a charge controller.  A inexpensive functional PWM controller can be had for around $30. MPPT would get you a bit more but the controller would be $100.

My three portables have 25-50 ft cords that allow me to move them around avoiding the shade.  I use 10 gauge solar cable but I've seen people use a heavy extension cord for smaller set ups.

I would suggest ebay where the 200w kits are $300 or less with everything you need and free shipping, but with you in Canada I don't know how the shipping works.

The performance differences between mono and poly panels are, essentially, a wash - too small to differentiate between on RV sized arrays. Poly panels have a slight edge when it comes to less than ideal lighting conditions, but their solar cells have a peak efficiency rating of 18% vs. mono's 22%. Poly pannels tend to run a bit cheaper than mono panels but they aren't rated to live as long as mono panels. In either case, the gaps are closing in all those areas.

My recommendation is to buy from a reputable manufacturer. A lot of Chinese panel manufacturers have popped up in recent years, only to go out of business soon thereafter due to cut-throat competition. So much for their warranties.

With only two 100 watt panels, I wouldn't buy a charge controller. With the amount of draw you potentially have and nearly 700 AH of useful battery power, two 100 watt panels will be little more than a trickle-charger to a battery-bank that size. If you have plans to expand the size of your array, however, a controller may eventually become necessarry - it depends on how big you want to go.

Kev

(Oh yeah, if you decide not to buy a controller, make sure you wire the panels in parallel - not series. If you decide to buy a controller, we can go over the benefits and drawbacks of each.)

Kev

I have three different type/brand panels. The mono's are a CanadianSolar 220w and two Bosch 245w. The Poly is a Scottpoly 230w.  I have used the 245's and the 230 camping and all of them yard testing as I learned about solar. That gave all the numbers, formulas and theories some understandability.

Now Mono's are the latest tech, more efficient in bright light and have the smallest footprint of the three major types. They are great if you are in a area with lots of clear skies. Let even light cloud cover come in and their Voc and Isc drop like a rock. This isn't a problem when you are grid tied and have a back up but in a RV it's charge or run the generator. My 245w mono's will drop from 17a to 2.38a in light cloud cover. The Canadian solar will drop to .78a and will go to sleep.

Polys are larger, in fact my 230w poly is bigger than my 245w mono. It has a lower Voc but a more stable one. Light clouds will drop it a few amps to 14, the monos will be asleep when the poly is still pushing 8a and in clouds so thick you can barely tell where the sun is, 4a.

When I first started reporting this 3 years ago, I was told oh no, Mono's are the best. Such is the hype. Of course not many people get to test multiple panels side by side with identical controllers etc. Since then others have confirmed my findings with other mono and poly panels.

So if you are in a area with LOTS of nice clear skies, go with the monos. Here in "Sunny" Colorado we get 6 hours of sun in the morning and then clouds most days. There have been twin monsoon seasons this year land last and I can remember only three full days of sun. I'll be selling all three of my mono's for two more poly's.

Hi Jim...

Don't get me wrong, I'm not suggesting that mono panels are always a better panel, but all six of ours are mono and they don't drop off anywhere near that much in Iight cloud cover. In fact, they do quite well, but detetmining what "light cloud cover" is would be rather subjective. We live in the San Diego area so we usually get a lot of sun.

Poly panels are larger, because of the way their silicon cells are made. They're less efficient so they have to be physically bigger to produce the same power. Both types of panels have made strong gains in recent years but mono panels are now generally considered to be better performers in cloudy conditions. That hasn't always been the case.

Here's some info from a couple recent articles... Eco Alternative Energy, a Canadian Solar Company. "The benefit of mono cells is that they perform slightly better under low light conditions equating to better production on cloudy days versus polycrystalline panels. How much better? Well that is a topic for discussion as there has been little local data to prove this here in Ontario. Suffice to say, you may get up to about .5% better production per annum using mono cells versus using polycrystalline."

There's also this from Energy Informative, "Monocrystalline panels tend to perform better than similarly rated polycrystalline solar panels at low-light conditions."

Virtually all the recent publications that I've found, that had compared newer mono and poly panels, gave mono panels the edge in lower light conditions. I've never done any side by side testing (and I doubt I ever will), but it's pretty consistent info. Polys are still (usually) cheaper but they're narrowing that gap too.

Kev

Kevin Means:

With only two 100 watt panels, I wouldn't buy a charge controller. With the amount of draw you potentially have and nearly 700 AH of useful battery power, two 100 watt panels will be little more than a trickle-charger to a battery-bank that size. If you have plans to expand the size of your array, however, a controller may eventually become necessarry - it depends on how big you want to go.

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OK, my situation has changed already.  We bought a different unit - a 2010 Arctic Fox 30U TT.  We are in Palm Desert with it at the moment.  It came with a single 150W solar panel as part of a factory installation, and it has a Specialty Concepts Mark PV Controller as part of the kit.  So, now I have new questions:

I still have the 100W panel I bought, and was going to use on the previous trailer.  Now I'm looking at adding the 100W panel to the 150W panel that is already installed.  What is involved in adding a 'mis-matched' panel?  Can it be done?  What do I need to do?  Can I add yet another 100w panel for a total of 3?  I think there is enough room on the roof for that many.

I understand this controller to be good for 30 amps.  Two panels are well within its capability.  Not so sure about 3 of them.  In the full sunlight at the moment, I get a maximum of just under 5 amps from the single 150W panel currently on the roof, which is mounted flat and is not adjustable.

Thanks.

Frank.

The only problem is if the panels have different voltages - the number of cells connected in series.  For example, adding a 32 cell panel to a 36 cell system (16 VOC vs. 18 VOC) will pull the system's voltage down to the level of the 32 cell panel.

This can affect the operation of a MPPC controller because there will be less excess voltage for it to convert into current, or if the lower system voltage affects the battery's charging rate.

As long as the panels have the same number of cells in series (i.e. the same open circuit voltage) you can mix and match all you want.

Kevin

The same test results were out there when I started, so was the response to my side by side testing. I have heard my mono's must be damaged or the cheap MPPT controller was the issue. I thought I'd get the chance to test that concept with a local that has the same pair of Bosch 245w mono's that I had but he uses a expensive Morningstar controller.I told him my peak was 34.2 amps and he backed down, never telling me what his peak was. Sometimes side by side is better than relying on the test result provided by a company trying to sell you something. ( or even a testing facility the gets it's money from said company)

Lou:

As long as the panels have the same number of cells in series (i.e. the same open circuit voltage) you can mix and match all you want.

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OK, I'll see if I can obtain the specs from Northwood, or another Northwood owner may want to step into the discussion here.

One can determine the voltage of a battery by counting the cells.  Can the same be done with a solar panel?

Thanks.

Frank.

It's not just the number of cells, it's the type of panel too. Even in 12v a mono has a slightly higher Voc and lower Isc than the same wattage in poly. With 24v panels Voc can vary greatly, so can the response to different amounts of light.

In a 12v PWM system, most mono's I've seen lately have a Voc of just over 22v and just over 21v for poly. The voltage difference doesn't seem to have a huge effect like it would if I mixed my 24v panels in MPPT.

JimInDenver:


Though I linked it further up in this thread, here is the panel I bought.  It claims 21.6 Voc.


I am trying to determine what is already mounted on this unit.  IIUC, if they are close to one another in specs, then they should work together.


Another possibility is to just wire the 100w panel directly to the batteries with crocodile clips, and stand it up in the sun.  Again, IIUC, both the roof mount 150w and the auxiliary 100w panels should get loaded down to the same voltage when connected to the big battery bank I have, with each doing 'what it can' to charge the batteries.  I don't see the 100w panel, even if unregulated, doing any damage to a battery bank that size.  I doubt if both of them TOGETHER can keep up with what we use in a day, in any case.


Frank.

Can you? Yes but YOU become the controller. It is what a PWM controller does until the battery voltage reaches a certain point and then it starts turning on and off the power. Allow the voltage to get too high and you may damage the battery or your rig systems that can only take so much. I wouldn't risk it for the few bucks a small PWM controller runs.

My systems have been portable so far. That gives me the peak of what I can get from first light to last light. My batteries are in float earlier and once there the solar becomes a power source. A load wont touch the battery until it exceeds the 50a being put out by the system. A mixture of mounted and portable is something I'm seeing more often as usually the mounted handle it but the portable helps out in a pinch OR they want to park in the shade and run the portable out to where the sun is.

Hi Frank.

Yeah, you could alligator-clip your 2nd panel directly to the battery terminals and it would charge the batteries just fine. Lou's explanation of solar panels with different output voltages is correct. You can do it but it's not the most efficient way to wire a solar system.

There's a lot of discussion here about minor voltage differnces, PWM vs. MPPT, the differnces in types of panels, how they're mounted etc. Jim seems to have had some problems with his mono panels. I suspect his particular panels may have something wrong wth them or they are older, because what he's experienced does not jive with, not only with what we've experienced, but with what has been published in the last few years about recently manufactured panels (The technology has advanced quite a bit in recent years).

When it comes to deciding whether or not you need a controller, there is no "one-size-fits-all" answer until your array starts to get relatively big. Otherwise, it depends on things like, the size of your battery-bank, the amount of power you normally consume, your parasitic loads, where you are in the country, the time of year and on and on. In the end, we have to consider all those factors and decide on the likelihood of the solar panels being able to overcharge our batteries. With "typical" RV power use and a 700 AH battery-bank, I think it's highly unlikely that 250 watts of solar panels will be able to recover all the power that's been consumed in 24 hours and then overcharge the batteries.

As a frame of reference, our six 160 watt roof-mounted panels (960 watts total), wired two in series and three pairs in parallel, supply 42 volts to the controller in direct sunlight in the summer in San Diego. With that, the Outback Flexmax 80 MPPT controller can put 48 amps per hour into the batteries. That's with 8 guage wire on the roof, 4 guage wire to the controller and 2 gauge wire to the batteries. We've got an 840 AH battery-bank and, between our large residential refrigerator, TV use, phone charging, parasitic loads etc. that's barely enough solar power to keep up with the loads. Throw in a cloudy day and we're running the generator.

If you decide that you want a controller, which certainly wouldn't hurt anything - other than it's another power-consuming device, (not a lot though), you should read about the pros and cons of both types. There's a lot written online about them. A PWM controller will work just fine for smaller arrays, or even larger arrays if the battery bank is never drawn down very much - but that's not typical for most boondockers. Most of us draw our batteries down a lot through the late afternoon, night and early morning hours. If the array is wired correctly, an MPPT controller is able to extract power from our panels both sooner and later into the day than a PWM controller. It can also convert excess voltage from the panels to amps - a PWM controller cannot.

So, if we're trying to squeeze every amp possible out of our panels, we could be meticulous about every little detail. We could learn about voltage loss in various thicknesses of wire, wire lengths vs. voltage loss, crimped vs. soldered connections etc. Or we could keep our blood pressure down, drink a refreshing beverage and make sure our alligator-clips are still hooked to the battery terminals.    

Kev

Oh yes, my panels are bad.....Interestingly enough my 720w system peaks at 50a but I suspect you will find lower Voc and higher Isc translates to 12v better than higher Voc, lower Isc. You guaranty a higher Voc in lower light but it's inefficient.

True - solar panels are constant current devices - they put out about the the same current into a short circuit as they do at the Maximum Power Point and the panel won't be harmed in either case.

Contrast that to a traditional power supply where a short circuit will make the current skyrocket and cause damage if it's not protected by other means like a fuse.

Jim, what I said was not meant as a cap on your system. Rather, it was based on your previous post of how you said your mono panels perform in "light cloud cover" compared to poly panels. That is not typical performance for recently manufactured mono panels, although, like I said earlier, judging cloud cover thickness would be very subjective and it's only one factor that will affect panel peformance. Perhaps your panels are more than a few years old?

JiminDenver said:

Kev

I have three different type/brand panels. The mono's are a CanadianSolar 220w and two Bosch 245w. The Poly is a Scottpoly 230w.

My 245w mono's will drop from 17a to 2.38a in light cloud cover. The Canadian solar will drop to .78a and will go to sleep.

Since then others have confirmed my findings with other mono and poly panels.

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My statements about the performance of mono and poly panels weren't based on anything other than the performance specs/data sheets of the panels I looked at less than a year ago, as well as several reports published by different entities on the matter in the past couple of years. Virtually all of them reported different findings than what you experienced. I doubt that the companies that test mono panels would be more inclined to fudge their test results than the companies who test poly panels.

Kev