New thoughts on solar... July 24, 2021, 01:51:26 pm Having a solar array on our house for a few months now, I have learned or understood about some issues of significance. As we live in a suburban area, our home solar is grid-tied, which means any energy we produce that we do not use ALL goes back into the grid - a financial credit. In other words, the panels are always producing at maximum efficiency, since the electric energy always has somewhere to go. This is very different from the self-contained system on our LD, which can only produce the power we can use - to power items during the daylight and charge the batteries back up. Since there is no place the excess energy can go if demand is low, it accumulates as additional heat load in the panels and/or dissipates into the environment.Photovoltaic panels when new run from about 14% to 20% efficiency, depending on what generation of manufacture. This means at PEAK efficiency, about 80% to 86% of the incident sunlight gets converted to heat. Panel output is reduced as the panel temperature rises, typically about 1/4% per degree rise above 77F. Rated output is also achieved only at 'one sun' irradiance (about 1000W / sq. meter), normal to the surface of the panel - hard or impossible to achieve with panels flat on a horizontal surface, in North America. For our LD, my solution was simply to keep slapping panels on the roof until the batteries will charge up overnight under 99% of the conditions we encounter. So with an MPPT charge controller, that is the best we can do at the moment, but NOT an efficient way to fully utilize the potential of the panels. A good way to overcome this would be to add more storage devices to take over when our coach batteries are full, such as a lithium battery with integrated inverter module, popular these days.Our home array came with specialized hardware and software that allows me to monitor performance in a way and degree of detail that is impossible with the closed-loop RV setup. One thing I have noticed is that the peak power generated does relate closely with ambient temperature. The rated 7.15kW array has produced a maximum power of about 6.6kW in the late spring when it was in the 70's outside. Now in the middle of the summer, with temps up to 100F or more, power more often peaks in the 5.7kW to 5.9kW range. Total energy produced now is higher, since there are more daylight minutes and the sun is closer to normal to our 20 degree roof angle. Another curious thing is that when clouds temporarily reduce incident light and reduce power, during the subsequent sunny period, peak power rises above 6kW again briefly. Since ambient temps have changed little, this shows the temperature fluctuation due to lower absorbed heat during the cloudy periods. A takeaway for RV use is to make certain the panels are mounted allowing plenty of ventilation to dissipate heat buildup.Steve 4 Likes
Re: New thoughts on solar... Reply #1 – July 24, 2021, 02:07:51 pm Very interesting information, Steve--thanks for posting that."A takeaway for RV use is to make certain the panels are mounted allowing plenty of ventilation to dissipate heat buildup."Heat is definitely a negative factor. I cringe when I see videos where people boast of mounting flexible panels flat on the roof of their RV or boat. It's bad for the panels' output and longevity. And it's equivalent to painting the roof black, guaranteeing higher temperatures inside the vehicle. 3 Likes
Re: New thoughts on solar... Reply #2 – July 24, 2021, 05:32:49 pm Hi Steve; I'm currently (that's a pun!) adding more, new panels to my RV roof and they will be 3 1/4" up to let more air underneath, and avoid some shadows from surrounding hardware. To quote.." keep slapping panels on the roof until the batteries will charge up overnight under 99% of the conditions we encounter." So Arctic polar area with midnight sun? or parking under a street light? Our TK's are deficient in mounting space for more batteries. At least you have a higher weight limit and 6" wider 'box'. I'd like one Lithium, but outside is the wrong place temperature wise. I may eventually do a 'Kent' and go two LiFePO4 some day. Like Larry W. waiting for the prices to settle. The recent addition of a used Tesla car power pack by Joe was interesting.....hmmm. RonB 2 Likes
Re: New thoughts on solar... Reply #3 – July 25, 2021, 12:16:13 pm Quote from: RonB - July 24, 2021, 05:32:49 pmHi Steve; I'm currently (that's a pun!) adding more, new panels to my RV roof and they will be 3 1/4" up to let more air underneath, and avoid some shadows from surrounding hardware. The recent addition of a used Tesla car power pack by Joe was interesting.....hmmm. RonBIt’s well known that panels produce less power when they are hot, nothing new here. Adding panels until you have enough to fully charge year round is how most of us get around it. It works the other way in the winter where cool panels are more efficient, good for maximizing power production when the sun is low inthew sky and the days short.Raising the panels high off the roof does reduce the power loss, by providing good ventilation but the same large gap is also excellant at catching tree pranches large enough to do serious damage. 3-1/4” would allow a big branch to get stuck inbetween the roof and panel. If the RV is moving, adios panel. I have seen it before and the results are never pretty. I prefer to compromise and keep the panels closer to the LD’s roof and accept that the output is going to be less. The heating and power loss issue is a summertime problem, when the days are long and more power over all is available, helping to make up for the loss caused by heat. Mounting panels on the roof of an RV is different than a home system. Home panels can usually be raised safely, they do not have the situation where tree branches are rushing by, assuming nearby trees are trimmed. Concerned about tree damage when adding two 80-watt panels to the nose of our 23.5” FL, an aluminum frame work was built around the panels to protect then, there are scratches on the frame that indicates tree branch hits.Something to think about.Larry 2 Likes
Re: New thoughts on solar... Reply #4 – July 25, 2021, 12:50:01 pm With regards to mounting additional panels on a LD roof, the factory mentions that if you order the additional panel, they add some structural wood bracing to help hold the additional panel. They also state that they don't recommend adding additional panels as they say they will work loose, cause leaks, etc. What experience do people have mounting additional panels? Do you find the wood structural members underneath the alum. roof and secure them to those? (How do you find them?} Or can you use epoxy to mount brackets without drilling? I 'd like to add more panels but don't want to get into leaks, loose panels, etc. Curious what others have done. It seems many people have had good experiences with AM Solar, are they skilled at adding additional panels?thanks,Bill
Re: New thoughts on solar... Reply #5 – July 25, 2021, 01:51:31 pm "They also state that they don't recommend adding additional panels as they say they will work loose, cause leaks, etc."Pure nonsense! Please explain why there are literally thousands of Lazy Daze RVs out there with multiple panels. I have three and could use a fourth.The problem I had, and many others will agree, is the poor factory placement of the one panel they allow as an option. Better to let someone like AM Solar determine proper panel placement, they at least know what they're doing. 1 Likes
Re: New thoughts on solar... Reply #6 – July 25, 2021, 02:29:31 pm Hi Larry; I'm using the brackets I put on for my original 3 small panels to support my new panels. They are behind the escape hatch and in front of the A/C, along with the refrigerator vent on the passenger side. My encounters with low hanging branches is worst on the passenger side, in residential streets. In campgrounds usually taller rigs have taken care of the lower branches. So the hatch will fend off some hits. I will have a 50W panel next to the hatch on the passenger side. It will be lower and have a sturdy deflector in front of it, about 2" above the roof. A still to be decided on additional 100W panel will be prewired aft of the refrigerator vent, and depending on real world input currents to the SB3000i, may turn into a 50W panel instead. So 400 or 450 Watts total. The main array is 3 100W Renogy monocrystalline panels, 42.8" x60" and supposedly 21% efficiency. At 1-1/2" thick they are based on the 2" aluminum angles that held my first set of panels. They were also monocrystalline at 14% and 144 W total. The new panels are more than twice the power in just a bit more roof real estate. (old ones 40" x 51") The 2" brackets were firmly attached with silicone and 26 ss screws 18 years ago. They are still firmly attached and I didn't want to disturb them. A folding tiltable array for these three, weighs less than 60 pounds (with panels). I'll be able to lift them to get to the electrical connections underneath. Clean underneath, and if parked in just the right place (desert, winter) can leave them tilted. Pictures soon. RonB 1 Likes
Re: New thoughts on solar... Reply #7 – July 25, 2021, 02:40:08 pm The factory is somewhat... old-fashioned... in their attitude toward solar power, harking back to the "You don't need that!" days of Ed Newton. Of course it's not unreasonable for them to be concerned about people drilling holes in their nice aluminum roof, but it you don't drill any holes... :-)Many of us have added panels using 3M VHB tape (no holes in the roof). I have yet to hear of one coming loose. There are several kinds of VHB tape. VHB 5952 is the the specific type I've been using, as 3M recommends that variety for painted surfaces. Read their datasheets and follow the preparation instructions religiously.I would definitely not use epoxy to mount solar panels. Remember that the aluminum roof expands and contracts as temperatures vary, and flexes as it does so. Even WestSystem G-Flex might not stand up to that, and more common epoxies are too brittle. VHB is the way to go.AM Solar has done hundreds (maybe thousands?) of solar RV installations, both "from scratch" and add-ons, and they can generally be trusted to do a solid job. Not cheap, but if you don't feel comfortable doing it yourself, that's where I'd go. I recommend staying away from bargain-basement installers of the type found in Quartzsite. 1 Likes As an Amazon Associate Lazy Daze Owners' Group earns from qualifying purchases.
Re: New thoughts on solar... Reply #8 – July 25, 2021, 02:51:18 pm I recently finished a solar install on the boat and purchased all of the pieces from AM Solar and followed their installation and mounting advice. It was worth every penny and I'm really pleased with the performance and finished results. Five days at anchor and I only ran the generator for about three hours on a very foggy day. I usually run it five hours a day. One of my boat buddies is now doing the same after coming over and watching my system recharge the batteries on a cloudy day.AM Solar knows their stuff, has great service and tech support. I did not penetrate the pilothouse roof and exclusively used the VHB tape for the mounting, per their recommendation. (Of course the tug does not drive down the freeway at 60mph.)Harold 1 Likes
Re: New thoughts on solar... Reply #9 – July 25, 2021, 03:00:42 pm I, too, am extremely happy with our AM Solar installation. I find that after several days of low sunlight while camping under the trees, an hour or so of generator time will top off the 5 lithium batts.Next to getting the LD, adding all the extra solar gear is the best thing I have done for our power independence.VHB and no holes drilled makes my heart beat a little easier.Kent 3 Likes
Re: New thoughts on solar... Reply #10 – July 25, 2021, 03:30:05 pm I have installed dozens of panels over the last 20 years, bedding the feet in 3M 5300 and installing a couple stainless-steel sheet metal screws into each foot. AFAIK, none of them have leaked. Panels weight little and do not stress the roof.Several AM Solar installation that I have looked at have used screws along with VHS tape to secure the panels or others have used only the tape. Installing screws into the roof isn’t a hazarious as some people think, the roof already have dozens of screws and several large holes cut through it, none of them leak if well sealed. It’s all about the quality of the work and sealing material.Larry
Re: New thoughts on solar... Reply #11 – July 25, 2021, 04:33:40 pm Thanks to everyone on the great feedback regarding solar panels. Much appreciated!BillPS, Lazybones I hear ya, the evidence out there doesn't seem to support the Factory verbage! 1 Likes
Re: New thoughts on solar... Reply #12 – July 25, 2021, 04:54:48 pm My understanding is that for a long while AM used only tape, then changed and decided to add ss screws on at least the leading edge of their panels. Don't know if this was due to reports of failure or whatever, all I know is that I would be a lot more comfortable with a screw.
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