Questions about solar power

[Briantb]

Originally Posted by carlkeigley

WOW............LOL
And I was hoping there would be a one size
fits all system out there somewhere.....lol.

It can be as simple or complicated as you want to make it but in the end it comes down to how much power do you use, can you conserve any and what are you willing to spend to spend on your solar. If you spend a couple hundred dollars on your solar system most times you will need to dump or get fresh water before you run out of power.

[MCDenny]

Originally Posted by padlin00

Unless I missed it, it looks like Renogy panel doesn't come with a controller so you'll have to account for one. I like the idea of the semi flexible panels, any idea if they need an air space behind them like the rigid ones for cooling?

It doesn't include a controller but I see that as an advantage. I want to get a name brand controller, probably a Morningstar, instead of the $30 controllers the Chinese panel kits come with. This way I don't have to pay for the $30 controller I don't want.

[blodn1]

I like the a la carte method of buying - whether to buy an MPPT or a PWM, size of panels, etc. because everyone has unique needs. And you can start small and add to the system in the future, as needed.

[peterh]

McDenny, if I were looking at a use case and really calculating out my energy consumption and solar panel power production, and found (using round numbers) I'd use 30AH daily and my solar panels would produce 21-33AH (-25 to +10% of my 30AH consumption) daily, I'd go ahead and pop for the MPPT controller because that's right in the range where it'll do me the most good.

If my numbers for the panel output were low, I'd probably spend more money on panels or buy a bigger battery before investing in an MPPT unit.

If my panel numbers were high, I'd either scale back my solar panel wattage and get the MPPT controller, or I'd just go ahead and buy the cheaper PWM unit and call it good.

That's if I were carefully calculating it all out. If the price difference between good PWM and MPPT units was $50 or less, I'd say "to heck with it, I'll just get the MPPT controller." :-)

About those flexible panels: I looked at them and thought they look nifty, but they haven't been around all that long and I don't how durable the technology will be. A few campers have installed them in the last year or two, and all of them were happy with them last time we talked. That suggests the technology may be quite good, but I still have nagging reservations about long-term durability.

In the end I decided I didn't want to drill holes in my roof for the newer, not-quite-proven technology and go with the tried and true. I bought a $125 100w traditional polycrystalline panel from SolarBlvd.com, painted the frame white to match our trailer, then mounted it on my roof. I like roof-mounts: they're hard to steal, easy to set up (like, they're always set up), and just driving down the road seems to dust them off and keep them nice and clean.

We also have a separate, suitcase-like panel set I built using two identical 20w monocrystalline panels and a cheap (Harbor Freight) 3-wire 120v extension cord so we can augment our system when we're in a shady spot, winter camping, or experiencing a string of bad weather days. The stand I made is simple, lightweight PVC tube and fittings that can be assembled in a minute or two when we're on-site.

No pics of the suitcase, but here's our roof installation.

Installed:


I integrated these teardrop-shaped standoffs to mount the panel and allow air circulation (for cooling) underneath. I used neoprene washers to make the mount waterproof.


And made a matching terdrop structure to house the wirefeeds through the hull.


With the wire through-ways raised above the roofline, butyl tape packing, and cap, it should be pretty leak proof.

[blodn1]

Peter - that's beautiful work. I'm looking at the flexible panels so I don't have to put but one hole in the roof. With the all electric trailer, I'll probably get 4 panels (~400W). The claim is that they don't break, even when walked on, and that they work better than the polycrystalline ones in shade and at different sun angles. Have no verification of the claims, though.

[MCDenny]

Thanks for those great pictures Peter. Beautiful fiberglass job.

What has your experience been with shading from parking the trailer under trees? We live in Michigan and camp in Florida, both places have lots of trees. Maybe not so much if you camp in the west?

PS: Why two wires penetrating the roof?

[Raz]

Originally Posted by MCDenny

I appreciate all the discussion too. Maybe the people who really know this stuff could comment on what I envision my scenario to be:

Start camping with a full battery. During the day my (didn't buy it yet) 100 w panel will put out about as much energy as I consume. Load is intermittent 4a draw from the fridge (maybe on 1/3 of the time) and (worst case) a couple of hours of 6a draw to charge the computers. Assuming a 12 hr day that's 28ah consumption. The panel should give me exactly that "on average" in S Fl in the winter. So I'm thinking I'll still have a full battery when the sun goes down. Night time use would be fridge on 1/4 of the time, 12ah and maybe another 2ah for lights. I'll get up in the morning with the battery at a soc of around 92%. Every day my soc will drop another 8%. After a week I'd still be at 44% and be thinking about plugging into shore power somewhere.

Does this sound right? Would PWM or MPPT make much difference?

Thanks.

Bearing in mind I'm an old and often skeptical engineer: I've seen increased efficiency claims for MPPT controllers ranging from 2% to 40%. Much like the label on the cereal box that says 50% more, I have to wonder 50% more than what? Who did the measurements and how did they do them? If I had money to spend, I'd put it on the sure thing, increased panel wattage. If you go the MPPT route I hope you will share your experience, good or bad. Raz

[peterh]

Originally Posted by MCDenny

. . . What has your experience been with shading from parking the trailer under trees?

. . . Why two wires penetrating the roof?

Some parks are very shady. Some Olympic National Park camping spots are completely shaded (gloomy, even) even an a clear summer day.

The two wires are the positive and negative leads from the panel.

Originally Posted by blodn1

. . . I'm looking at the flexible panels so I don't have to put but one hole in the roof . . . The claim is that they don't break, even when walked on, and that they work better than the polycrystalline ones in shade and at different sun angles. Have no verification of the claims, though.

Let us know how that works out. I'm very curious to see out how well these new, flexible panels work in the long term. (I just posted my doubts, so I won't redux.)

There have been some interesting innovations in solar panels over the last several years. Amorphous silicon panels, like the ones Harbor Freight sells, are made by spraying a silicon layer on a substrate. They used to be the cheapest technology on a per-watt basis on the market, but the competition in the mono-and poly-crystalline panel market from China have driven those technologies down so much that they're actually cheaper than amorphous.

Amorphous panels are the shady-spot champions for producing power from scattered and indirect light. They're also the least space efficeint and least durable, consuming about twice as much rooftop space per-watt as competing mono- and poly-crystalline panels. Their performance also deteriorates much more quickly over time, further increasing the amount of space required to get the same power output, though some new production techniques have cut that deterioration rate down.

Monocrystalline panels have been the best-performing "conventional" solar technology when you have direct sun. They take up the least amount of space, per watt and per unit of weight. Until recently they were about 25% more space efficient when compared to similar polycrystalline panels and performed better than poly in scattered light, but both these factors have changed.

A new production technique, one that has come into wide use since the German company that invented it went bankrupt, acid-etches the sunward side of a poly solar cell and substantially increases their performance. Modern poly panels are less expensive to produce than mono panels, have comparable scattered light performance, and now take up only about 10% more space than a mono panel with a similar output.

Then there are these new, flexible mono panels that are mounted on a sheet of flexible aluminum. I just plain don't know what to think of these panels. They look like they might be a great new tool for boaters and RVers, but I've never seen real-world durability or output studies on them.

I guess the point is, the world of solar panels is still evolving, and sometimes you have to just make your best guess as to which technology will work best for your application.

[Carol H]

Peter I like the roof connection you made. As usual you have come up with a great solution! How did you make that?

One question I have in regards to upgrading to the MPPT controller that I still haven't seen answered is in regards to the fact you will get a higher battery charge out of it. But how many more years of life could i expect to get out of my group 27 deep cell battery as a result? Also how would the fact that I do camp on and off the grid 50/50 and only have a pretty inexpensive power converter ($150) all be it a popular one, with a simple smart charger on it impact that situation. As been discussed here more than once even with the smart charger the battery isn't getting a real full charge from the converter I & many others are using. Seems I would need to upgrade to a converter worth about 5X that to get the real full charge if I am not mistaken. I do know I could change the set up of the trailer and eliminate the converter & go with an inverter set up but not really wanting to do that at this time.

I guess my question is what longevity differences to the life of the battery could I expect if I was only able to obtain a full charge when on solar & less than full charge when plugged in due to the converter charging restraints?

[MCDenny]

Originally Posted by peterh

Some parks are very shady. Some Olympic National Park camping spots are completely shaded (gloomy, even) even an a clear summer day.

The two wires are the positive and negative leads from the panel

Duh! I thought they looked like duplex cable.

[blodn1]

Add to the mix the new technology of printing solar panels.
This solar panel printer can make 33 feet of solar cells per minute | Grist
Don't think they're ready for prime time, yet, but that could make solar very cheap in the future.

[Raz]

Originally Posted by Carol H

I guess my question is what longevity differences to the life of the battery could I expect ......

That's the million dollar question isn't it. How much to spend on a charging system if you have an inexpensive battery and a trailer you may not own 5 years from now. Of course in the case of solar you can take the system with you.


Oh, and in terms of charging methods don't forget your tow vehicle. Raz

[Carol H]

Originally Posted by P. Raz

That's the million dollar question isn't it. How much to spend on a charging system if you have an inexpensive battery and a trailer you may not own 5 years from now. Of course in the case of solar you can take the system with you.


Oh, and in terms of charging methods don't forget your tow vehicle. Raz

I have always assumed that my tow vehicle charge is not going to give me the max charge possible either - assuming of course its actually has left over power to send out to the trailer battery and I have not maxing out the cars ability to supply power with all the other stuff running (GPS, MP3 Player, AC, back up camera etc running) and charging of phones & IPads while heading down the road. I already know it can't keep up with the fridge consumption if I was to run with the fridge on 12V even when not charging up phones or running with the GPS on.

Even if the tow did have the DC power does it have the capability/technology with the simple wiring charging system it uses to give it the ultimate max charge?

[Raz]

Originally Posted by Carol H

Even if the tow did have the DC power does it have the capability/technology with the simple wiring charging system it uses to give it the ultimate max charge?

How long does the tow vehicle battery last? Don't run it down by leaving your lights on, 5 years?

[Carol H]

Originally Posted by P. Raz

How long does the tow vehicle battery last? Don't run it down by leaving your lights on, 5 years?

Even without ever leaving the lights on, 5 years seems to be about the norm - that is if I want to be sure the battery is good enough to crank over at -30 on a ski hill. I guess if you stick to warmer climates you might get more years out of one.

The good news is my new tug is a bit fool proof in regards to leaving lights on when its not running. It shuts them off itself after 5 min. Which reminds me I have to check to see if it keeps charging the trailer if I leave it plugged in while parked.

[MCDenny]

My jeep grand cherokee puts 13.0 volts on the trailer battery whether idling or running 2000 rpm. Not enough oomph left after running through the vehicle to the plug and another 5' of 10 gage wire to the battery. Towing with the fridge running doesn't seem to run down the battery but towing with a partially discharged trailer battery won't recharge it either.

[Carol H]

Originally Posted by MCDenny

Towing with the fridge running doesn't seem to run down the battery but towing with a partially discharged trailer battery won't recharge it either.

I suspect you have a bit better results with the fridge on 12v than I do as your fridge if I am not mistaken is of better/newer 12v design/technology. Unfortunately my fridge is a bit of a 12v hog so the few times I did try running it on 12v while driving the trailer battery suffered a deficit.

[Carol H]

So I am guessing by the lack of responses to my question as to whether or not adding a MPPT solar controller will improve the life of my trailer battery if I continue to run the basic consumer grade simple power converter with a smart charger will remain an unknown?

[Jon Vermilye]

And, just to throw another option into the mix, Bogart Engineering is expected to release their SC2030 Charge Controller, a PWM controller that ties to their TM 2030 battery monitor in March.

I haven't seen the manual or specifications, but the preliminary description gives the impression that the two devices communicate to give the solar controller real battery status, something that most PWM and MPPT controllers don't actually do since most controllers don't actually measure the amp hour status of the battery.

[multi-task]

Originally Posted by Carol H

So I am guessing by the lack of responses to my question as to whether or not adding a MPPT solar controller will improve the life of my trailer battery if I continue to run the basic consumer grade simple power converter with a smart charger will remain an unknown?

Personally I'd go with the controller & panel that can reach the bulk charge voltage for your battery specs, preferably in one day. Either controller type will accomplish this.

If your panel is undersized and it never raises the voltage above float I'd expect it's not helping your batteries longevity or properly charge them. Of course I'm hesitant to mention this in case the thread turns into one of the others that was closed because of the arguments However there are a number of good controllers which allow you to set your set points which is something that's missing from converter style chargers.