I am considering using 2" furniture grade (UV protected, guaranteed for 15 years of direct sun exposure) structural plastic pipe to build a simple rack to mount my large solar panels right down the center of the RV, about 13" off the roof (to clear my ac ducts. I will still have 12ft clearance, BTW). The panels would all be perpendicular to the length of the RV. Has anyone used this material before in this application? If not does anyone make 13" aluminum offsets for racking solar panels?
Thanks for your help,
Chip
LarryW21 said
02:49 PM May 10, 2019
You already have "large" solar panels? With a MH that size you need to put solar panels over the AC etc.?
-- Edited by LarryW21 on Friday 10th of May 2019 02:50:28 PM
Sushidog said
11:45 AM May 11, 2019
Larry, I have not purchased the panels yet. My 50 amp MPPT controller arrived, along with the remote, wiring, breakers, etc, but I plan on going to Northern Arizona Wind and Sun in early June, when I visit the Grand Canyon and Flagstaff, to pick up a pair of these www.solar-electric.com/rec-n-peak-series-320-watt-monocrystalline-solar-panel.html . If I like their performance (which I believe I will) I plan on getting 6 more later, (1,920 additional watts) for my planned 48v system (along with an identical controller) to power this super efficient 48v dc mini-split heat pump www.geinnovations.net/HSAC_Productline.html (that produces 12,000 Btus of cooling using only 560 watts) and for my 110v ac inverter needs. This will allow me to be totally self-sufficient off-grid, power wise, without the need to fire up my 5,500 watt onan except under rare circumstances.
I would like to rack all my panels in a row, crossways, in the center of my roof giving me 17.5" of walk space/access on either side, also for the purpose of mass centralization (for better handling considering I'm adding so much weight on the roof). They are roughly 66" x 40", so 40" x 8 panels = 26' 8" in motorhome length. Because of the spacing of my rooftop AC units I could only fit 5 panels on my roof if mounted port to starboard below the AC shrouds. With a combination of port/starboard and fore/aft arrangement, I could fit 8 on the roof, (3 in the front, 3 in the center and 2 in the rear) but there would be no walkway, compromising roof access and it would not be as aerodynamic as all panels racked in a neat and clean row. With this staggered arrangement I would still need to rack them over my vents (10"), so my thoughts are, why not go 3 inches more and get them above the AC units too? I am also thinking that the more space between the RV roof and panels the more cooling airflow under the panels when parked - like I'm carrying around my own solar powered shade tree. ;)
Chip
LarryW21 said
12:49 PM May 11, 2019
Chip, an ambitious system that’s far beyond my expertise. Please keep us updated.
BiggarView said
03:25 PM May 11, 2019
Chip, it sounds pretty ambitious but my concern if I understand your layout is the 17.5 inch area on each side. Is that from the roof edge to the panel? Too scary for me to even imagine. One false step and it's a real possibility of a nasty fall to the ground. At least with the panels along the edge the danger is reduced and they can be accessed from the roof or from a ladder against the wall. Just my thinking if I understand your idea correctly. Please correct me if I'm wrong.
arcaguy said
09:00 PM May 11, 2019
I have a few of concerns with this set up. First of all I don't think that any kind of plastic will hold up long term in the sun. I know it has a 15 year warranty, but who warrants it against what? The structural PVC I looked at is UV resistant, not unaffected by UV. You might also want to look at the strength of PVC pipe in tension as well a compression. I'm especially concerned about how you would mount it to the roof. If it blows off it will do significant damage to the roof of your coach.
The second thing is the height of your proposed mounting brackets. If you mount them 13" above your roof the structure will be subject to significant racking (diagonal) forces a highway speeds. This would necessitate some type of diagonal bracing for the structure. I don't know what your proposed mounts look like but if you proceed I would mount each panel independently from the others. That way if one of them blows off it won't take the others with it.
Another concern is the air pressure differential that my be created by your panels. If the airflow over the panels creates a vacuum on top of the panels, as it likely will, at merely 1/4 psi difference there will be 660 lbs of upward pressure on each panel or 5,280 lbs of upward pull for the entire array. This type of difference isn't too hard to create at highway speeds. It will not only affect the panels but also unweight the coach by that amount which may affect handling/traction. If this stuff blows off of your rig and injures/kills someone the cost could be very high both financially and emotionally.
Another concern I have is the electrical capacity of your system. You say that you want to add a total of 2,560 watts of power to your system. The panels that you are looking at are 9.55 amps nominal @ roughly 33-34 volts. When you multiply that by 8 you get 76.4 amps of power you need to manage. Your MPPT controller is only capable of 50 amps per your post above, which means you are undersized by about 35% on your charge controller if my math is right. I also think that your building a system way over capacity for your needs. If your proposed primary use is only going to draw 560 watts even with an 20% loss on conversion to 48 volts you only need 2.18 panels to supply that much power during the day, which is when you will likely need air conditioning. What do you plan on using the other 5.82 panels for? You also haven't addressed how you plan to store all of this power you are going to generate. At about $950 per 100 usable amp hours of capacity LiFePo batteries aren't cheap.
Another concern that I have is the how it will affect the air flow to your air conditioners. I'm betting that the air conditioners are designed to have unimpeded air flow, by essentially covering them with a roof you are going to significantly impede air flow to them for heat dissipation.
I'm not saying not to do this, it's your coach and your life/money, but I would proceed with extreme caution and don't get caught by unintended consequences. You've got what appears to be a very reputable supplier for the panels, I'd have a long and detailed discussion with them about what you want to do. I might also talk to Battle Born about their batteries, I know the are expensive but the rest of the system isn't going to be cheap either. Best of luck.
LarryW21 said
09:20 AM May 12, 2019
I find discussing an “ultra” RV solar system very interesting.
Sushidog said
02:35 PM May 12, 2019
Thanks for everyone's replies.
BiggerView, I hear what you are saying about the 17.5" pre side. I could line them up on one side of the coach, giving a more generous 35" (and safe) walkway on one side, but if 1/2 of the 8 panels at 40 lbs each were favoring one side, say the driver's side, that would mean that my weight load on that side would be roughly 200-250 lbs more with the racking. That might actually be a better alternative than the center to offset the 8 GC-2 batteries I plan on adding on the other side 62 lbs x 8 = 500 lbs, so I'd only be favoring the right side with 250-300 more lbs (which is the light side, opposite the slide.)
Arcaguy, you've expressed some of my concerns, mainly the panels acting like a sail, catching the wind, but they will do this whether they are 3 " off the roof or 13' off the roof (if mounted incorrectly, at an angle), will they not? They'll have to be mounted sturdily, for sure. I spoke to Solar Mike at Slab City (an experienced solar RV installer) last week when I was there. He told me he recently racked 4 panels on a motorhome up above the vents with aluminum and recommended that. I don't want to reinvent the wheel, which is why I asked for someone with actual experience using the structural PVC pipe in this capacity. I might end up with aluminum afterall. I spoke with a structural engineer/ designer last night (a family member) about the design asking about the difference in thermal expansion between aluminum and PVC and he assured me that it would be negligible for my project.
I'm not worried about AC venting because the top and front of the AC shroud is solid, blocking all airflow. The back and sides are vented. I have been thinking about removing the AC shrouds completely since I'd have the large solar panels blocking the sun and rain. This would give the ACs even more ventilation for even better cooling that stock.
As far as electrical capacity, when you increase the voltage of a system the current drops. This is one of the reasons for going to a 48v system as it allows smaller wire and controller sizing. For instance My 50 amp controller is only rated to handle 625 watts at 12v but 2,500 watts at 48V because the current at 48v is only 1/4 of what it would be at 12v. www.amazon.com/EPEVER-Controller-Negative-Regulator-Flooded/dp/B07LC657SH Since I will be mounting the panels flat, not angled toward the sun I can only expect about 80% of their rated output at best (less the farther north I go). So those 1920 watts of panels will only be producing a max of that I will be about 1,500 watts in the real world. If I mount 3 in series so have 2 banks in paralel the amperage coming down the wires will be exactly the same as the 2 - 12v panels that will be in parallel wiring. The difference is that the 12v bank will be producing about 34v (under load) into the controller which will convert it to 12v (nominal) and 40 amps, whereas the 48v solar bank will be producing about 102 volts though at the same amperage as before (about 15 amps) which the controller will change to 48v (nominal) and around 30 amps at 48v. Remember, 2 of the 8 panels will be dedicated to the 12v system.
The minisplit I'm looking at draws 11.5 amps (at 48v).So during the daytime, the 48v system this will be enough to run the AC, a 2,000 watt inverter (for occasional microwave and other light a/c use) and still be able to put some current back into the batteries for evening time. My battery bank will have 220 total ah or 110 usable (at 48v) this means I would be able to run my ac unit all night if needed. This type of heat pump uses a rotary compressor which doesn't "cycle" like a traditional AC but scales up and down smoothly and seamlessly, drawing less current as needed without huge start-up power spikes that conventional compressor air conditioners have.
So the next question is if plastic pipe does not prove to be durable, how about a rack make from 1/2" galvanized steel pipe, bolted to the roof with steel flanges. I don't think any cross bracing would be required, just a box shaped rack all tied together and screwed down tightly using 4-1/4" bolts per leg. Sure it will be heavy, maybe 150-200 lbs for the whole rack, but it would be the strongest option, better than aluminum, and I don't have to worry about the effects of sunlight over time. I was just trying to avoid adding that much extra weight to the roof. Surely someone has racked 2,500 watts of solar on their roof and has some real world experience in the matter.
Does anyone have any better suggestions or recommendations?
Chip
-- Edited by Sushidog on Sunday 12th of May 2019 02:38:47 PM
A-S Travelers said
05:55 AM May 19, 2019
First I would say this forum is not the best place to find extensive advice/info about solar/batteries/etc. Not that there aren't good people here, just that the number of people who have installed and use solar is much more limited than on some general RV'ing form with many thousands of forum members.
I think your plans and ideas for building a huge solar array and batteries is a great project. Extremely ambitious though.
Thoughts:
-- I would shift the solar panels to one side, at least a bit to allow at least 24" or maybe as much as 30" for a walkway. 18" is a little narrow for safety.
-- Tilt the solar panels a little. 2-3 inches end to end so the water will drain off. Pooling water greatly reduces the power output. Also standing water collects more dirt, requiring more frequent cleaning.
-- I have experience with large residential solar panels. My panels are 325watt, about 52" x 65". I installed them on my 29" Sightseer Class A and put about 45,000 miles on them, including a 4.5 month trip to Alaska. No problems with them coming loose. My panels were about 1.5" off the roof on one edge and about 4" on the other. I slightly tilted them so the water would not pool on them. I have now moved these panels to our current RV, but only have about 1000 miles on the installation. I fastened the panels on the 4 corners with about a 1.5" by 4" aluminum foot with 3 screws per foot, and Dicor sealant under the foot. If I was to raise the panels to 13" I would add more support and attachment points.
-- Your dedicated battery bank for the air conditioner is 220AH @48V. To make it easier for me to calculate, I am going to make that 880AH @12V. That is 8 Golf Cart batteries at 6V each, or any other combination of battery. I matters little if you go with GC or 4D or 8D the weight and space requirements are all about the same.
-- I would without a doubt go with lithium batteries. Yes they are expensive, but your entire system is expensive. I would use 4 100AH lithium, cost of about $4000. This will give you easily 300-350AH @12V usable power at about 40% of the weight.
-- With lead acid there are 2 or more things to keep in mind. 1) At 60% SOC your battery voltage is now about 12.2V. When you hit those batteries with a load you voltage will probably sag to down into 11.9V or so. That tends to stress your inverter. As you get closer to 50% SOC your voltage sag is going to be more. 2) Charging along with the need to get the lead acid batteries back to 100% SOC as often as possible. Preferably every 3-5 days to keep them from sulfateing. Remember it doesn't matter how much solar you have, charging lead acid the charging current really drops off after the first 1-2 hours and drops down to 10 to 5 amps after 3-5 hours. Makes it hard to keep lead acid charged when going as low as 50% SOC. Only going to 70% or 75% SOC makes it much easier to get back to 100% SOC, but you need quite a bit more battery.
-- Don't overlook the fact that if you DON'T get your batteries back to 100% you no longer have the full 110AH @48V available you are planning on. Or if you do use the 110AH you will drop below 50% SOC.
-- Lithium will charge at a faster rate and doesn't need to be brought to 100% SOC. In fact it is better for the lithium battery if you only go to about 93% SOC.
-- You can mount the lithium inside your rig so they will not be too cold or hot. They can't be charged when the battery is below freezing, discharging (i.e. using) is OK. It is best to keep lithium from going over about 110-120 degrees. Four 100AH lithium only weighs about 130 pounds. You can put that in lots of places. Lead acid is more difficult and has to be AGM if mounting inside the rig.
-- I would use aluminum to build your rack to mount the solar. Here is a possible place to buy larger or heavier duty aluminum than you will find in a big box store: https://www.metalsupermarkets.com/metals/aluminum/ I have no experience with this place, but it sounds legit.
In my current rig I put my 400AH of lithium, a 2000 watt inverter/charger and 60amp solar controller in our bedroom where three drawers used to be.
Neil and Connie said
07:39 AM May 19, 2019
Two items. First, check out www.technomadia.com if you’re considering doing lithium batteries...they put them in their bus and boat and have considerable knowledge about lithium batt. Second...don’t count on getting 80% of rated output...it ain’t gonna happen. First, the panels are tilted relative to the sun and second the sun causes worse tilting effect in the morning and afternoon. You can only count on 4 or 5 hours of max output based on geometry...and the panel efficiency goes down as they get hot. We gave 800 watts of panels and even in southern FL for the winter we o lay get about 400-425 watts max output...and that for only a couple hours a day...in the morning and afternoon it’s more like 250. Make sure you take that into account when sizing panels and batteries for the A/C unit. Chris and heroine (above url) are able to run a sing e unit for awhile but they have way more than my 800 watts of panels.
Bill and Linda said
12:01 PM May 19, 2019
Neil and Connie wrote:
Two items. First, check out www.technomadia.com if you’re considering doing lithium batteries...they put them in their bus and boat and have considerable knowledge about lithium batt. Second...don’t count on getting 80% of rated output...it ain’t gonna happen. First, the panels are tilted relative to the sun and second the sun causes worse tilting effect in the morning and afternoon. You can only count on 4 or 5 hours of max output based on geometry...and the panel efficiency goes down as they get hot. We gave 800 watts of panels and even in southern FL for the winter we o lay get about 400-425 watts max output...and that for only a couple hours a day...in the morning and afternoon it’s more like 250. Make sure you take that into account when sizing panels and batteries for the A/C unit. Chris and heroine (above url) are able to run a sing e unit for awhile but they have way more than my 800 watts of panels.
What Neil said, especially about the temperature. With an almost perfect sun angle, bright, clear day and a very, very cool day I once saw 77% output. But everything has to be just perfect to get the rated output and that number won't last for any extended period of time. 80% is more of a lab / theoretical / standard rating number then an operational design number. Think in the low 60's, or less, percent wise as the peak output for a few hours and I think you will be much more pleased with the results.
zamboni said
05:30 PM May 19, 2019
I used aluminum pipe, sourced from a local fab shop -- I think 1" OD. I didn't have access to a welder so i bought fittings used in building handrails from Wagner (shop.wagnercompanies.com/). They are *not cheap* but they cost less than a welder. Use loctite on the set screws when assembling them. My rack has been holding up 1200W of solar panels for 4 years, including a drive up the Demptster highway. Residential / "grid tie" panels are pretty heavy and you don't want them flexing -- the furniture-grade plastic tubing you found may be UV resistant but i'd worry about how flexible it is.
A-S Travelers said
12:09 PM May 20, 2019
In addition to www.technomadia.com as a very good source for some real world info & experience with lithium, another very good source is Wheelingit Lithium part 1 . There are 4 parts to the info so don't stop with the first. Both of these couples have worked together on providing real world info about lithium batteries and systems.
Sushi Dog, You sound like you are quite committed to running a air conditioner off of battery. That is very ambitious project. I am not aware of anyone attempting to do this in an RV and actually run the A/C for overnight or for 6-8 hours.
From the figures you gave, the mini-split A/C sounds like the best way to go. However I have significant reservations for you to be able to run the A/C 6-8 hours off of 880AH @12V. (Yes I understand your 48V system is 220AH @48V, but everyone is familiar with the amount of AH's from a battery at 12V. It gets confusing to try to equate 48V AH's to what we are accustomed to. )
While I totally agree that it appears the mini-split is much more efficient than the standard RV A/C, I would recommend 880AH @12V of lithium. I really think that 660AH@12V would do just fine, I don't know of a way to use six 12V batteries to get 48V.
In an earlier reply I gave my concerns about trying to run the A/C off of lead acid. The two links above do provide some detail about why they went with Lithium instead of lead acid and the short comings of lead acid.
Sushidog said
01:24 PM May 20, 2019
Thanks for all the feedback! You guys are the best.
I have reconsidered the plastic pipe approach. Instead, I plan on mounting my first 2 panels (the first stage of my system that I will install next month) on an angle so that the first panel attaches to the front of the MH roof along the long 66" side at the 2 pounting points provided for maximum support at about a 9 degree angle to the horizontal roof. This would take care of the water pooling issue, facilitate keeping them clean and productive. I plan on supporting it at the rear of the panel (which will be about 6.5" off the roof) with two vertical mounted galvanized steel 3/4" pipes which will each be screwed into a steel pipe flange and attached to the roof with 4 heavy duty stainless mounting screws. I will attach both panels to 2" angle iron and attach the angle iron to the pipe with 2 horizontal bolts in holes drilled through the pipe. The rear of the second panel will then be mounted to 13" tall pipes in a similar fashion. I checked the wind load at 95 mph and it will be under 1/3 of the panel's rated capacity.
This will act as a wind break for the remaining 6 vertically mounted panels 13" off the roof which will all be attached to the roof similarly. I plan on getting some light weight aluminum bar stock and using them as cross braces in an x pattern, side to side on all 13" high mounts as well as a single diagonal brace fore and aft on all front to rear vertical supports to give the entire structure rigidity.
Thanks for the information on the low real world output of perhaps 60% in flat mounted panels. Instead of the 320 watt panels that I planned on using I will have to look at some more efficient panels. Santan solar www.santansolar.com/deals/ has some used 22% efficiency 360 watt sun panels in a 61" x 41" format for a total of 2160 rated watts. At 60% of rated this equals 1296 watts of usable power for a little better yield than the ones I was looking at. If it looks like I will need even more solar I have considered mounting a few on the side where my slide is I could mount 2 vertically to the roof which would swing out when I extend my slide where my slide topper is. This would add 720 (432 usable) watts, bringing the total to 2,880 (1,728 usable) solar watts, if needed. At that point the battery bank would be by far the choke point in the system.
The roof top ac units are far too inefficient to even considering running even one off of solar, whereas the mini-split I am looking at produces only slightly less cooling (12,000 BTUs vs 13,500 btus but uses only about 1/3 the wattage of a roof top unit to do so. My rooftop units use about 2750 watts to start and about 1250 watts to run vs 560 watts to start and run the 48v DC mini split, with no inverter inefficiencies at all, cause I'll be drawing from a 48v DC bank.
Maybe in a couple years they'll have a more affordable battery option, when I'm ready to buy my 48v panel bank. Perhaps lithium will drop in price by then. I remember reading Technomadia's lithium experiences long ago. If not, I'll have to go with lead acid in spite of the acknowledged benefits of lithium. Now, I can build an affordable lead acid GC-2 bank for 8 x $120 = $960 vs $4,000 for the equivalent lithium bank. True they will weigh almost 370 lbs more, and be worse performers overall, but I won't have to make a loan to buy them. ;)
Chip
A-S Travelers said
08:34 PM May 20, 2019
Well thought out plans. You have done excellent research.
Please come back and update us with how this all works out. I write "how this all works out" because every project I have done changes quite a bit from inception to completion. Even if it takes a year or more before you complete the project come back with an update.
Sushidog said
08:01 PM Jul 21, 2019
I have almost completed phase one of my solar plan, and yes, it turned out quite different than I had in mind.
I decided to mount the 2, 310w panels for my 12v system on the side of my MH. I did this to free up space on my roof for 9 similar panels for my planned 48v system which will be racked above my AC units and vents using sturdy but lightweight aluminum angle and traditional solar rails or rectangular tubing. As a bonus, the side mount allows me to angle the array from about 69 degrees to 20 degrees from horizontal, spending on the latitude I find myself and the season without climbing on the roof. Not only will this will make them more productive, but easier to clean too. The only thing I haven't done to complete this phase is add a couple gas springs to make the array easier to lift. Right now I have to lift about 45 lbs of weight to get them pinned to the angle I want. I'm looking for the right struts now to relieve most of this weight to make setting up easier.
Here's a couple pics of the project so far.
That's my DW doing the Vanna White impersonation.
I'll keep you posted as the project progresses, (which should take some time) but 9 panels x 310w = 2,790 watts for my 48v phase - more than adequate for my anticipated needs!
Good news. I found some breakthrough price point lithium batteries. I think 3 of these with BMS in parallel would be perfect for my needs, and affordable too! That's 198 amp/hrs at 48v - 80% or more usable and only 150lbs for all three battery packs. houston.craigslist.org/ele/d/pearland-48v-3kwh-lithium-ion-battery/6937919504.html These are new 3 kw packs for only $475/pack - that's less than anything I've found, even used.
Chip
-- Edited by Sushidog on Sunday 21st of July 2019 08:01:49 PM
-- Edited by Sushidog on Sunday 21st of July 2019 08:04:45 PM
-- Edited by Sushidog on Sunday 17th of November 2019 09:16:51 PM
-- Edited by Sushidog on Sunday 17th of November 2019 09:20:15 PM
I am considering using 2" furniture grade (UV protected, guaranteed for 15 years of direct sun exposure) structural plastic pipe to build a simple rack to mount my large solar panels right down the center of the RV, about 13" off the roof (to clear my ac ducts. I will still have 12ft clearance, BTW). The panels would all be perpendicular to the length of the RV. Has anyone used this material before in this application? If not does anyone make 13" aluminum offsets for racking solar panels?
Thanks for your help,
Chip
You already have "large" solar panels? With a MH that size you need to put solar panels over the AC etc.?
-- Edited by LarryW21 on Friday 10th of May 2019 02:50:28 PM
I would like to rack all my panels in a row, crossways, in the center of my roof giving me 17.5" of walk space/access on either side, also for the purpose of mass centralization (for better handling considering I'm adding so much weight on the roof). They are roughly 66" x 40", so 40" x 8 panels = 26' 8" in motorhome length. Because of the spacing of my rooftop AC units I could only fit 5 panels on my roof if mounted port to starboard below the AC shrouds. With a combination of port/starboard and fore/aft arrangement, I could fit 8 on the roof, (3 in the front, 3 in the center and 2 in the rear) but there would be no walkway, compromising roof access and it would not be as aerodynamic as all panels racked in a neat and clean row. With this staggered arrangement I would still need to rack them over my vents (10"), so my thoughts are, why not go 3 inches more and get them above the AC units too? I am also thinking that the more space between the RV roof and panels the more cooling airflow under the panels when parked - like I'm carrying around my own solar powered shade tree. ;)
Chip
Chip, it sounds pretty ambitious but my concern if I understand your layout is the 17.5 inch area on each side. Is that from the roof edge to the panel? Too scary for me to even imagine. One false step and it's a real possibility of a nasty fall to the ground. At least with the panels along the edge the danger is reduced and they can be accessed from the roof or from a ladder against the wall. Just my thinking if I understand your idea correctly. Please correct me if I'm wrong.
The second thing is the height of your proposed mounting brackets. If you mount them 13" above your roof the structure will be subject to significant racking (diagonal) forces a highway speeds. This would necessitate some type of diagonal bracing for the structure. I don't know what your proposed mounts look like but if you proceed I would mount each panel independently from the others. That way if one of them blows off it won't take the others with it.
Another concern is the air pressure differential that my be created by your panels. If the airflow over the panels creates a vacuum on top of the panels, as it likely will, at merely 1/4 psi difference there will be 660 lbs of upward pressure on each panel or 5,280 lbs of upward pull for the entire array. This type of difference isn't too hard to create at highway speeds. It will not only affect the panels but also unweight the coach by that amount which may affect handling/traction. If this stuff blows off of your rig and injures/kills someone the cost could be very high both financially and emotionally.
Another concern I have is the electrical capacity of your system. You say that you want to add a total of 2,560 watts of power to your system. The panels that you are looking at are 9.55 amps nominal @ roughly 33-34 volts. When you multiply that by 8 you get 76.4 amps of power you need to manage. Your MPPT controller is only capable of 50 amps per your post above, which means you are undersized by about 35% on your charge controller if my math is right. I also think that your building a system way over capacity for your needs. If your proposed primary use is only going to draw 560 watts even with an 20% loss on conversion to 48 volts you only need 2.18 panels to supply that much power during the day, which is when you will likely need air conditioning. What do you plan on using the other 5.82 panels for? You also haven't addressed how you plan to store all of this power you are going to generate. At about $950 per 100 usable amp hours of capacity LiFePo batteries aren't cheap.
Another concern that I have is the how it will affect the air flow to your air conditioners. I'm betting that the air conditioners are designed to have unimpeded air flow, by essentially covering them with a roof you are going to significantly impede air flow to them for heat dissipation.
I'm not saying not to do this, it's your coach and your life/money, but I would proceed with extreme caution and don't get caught by unintended consequences. You've got what appears to be a very reputable supplier for the panels, I'd have a long and detailed discussion with them about what you want to do. I might also talk to Battle Born about their batteries, I know the are expensive but the rest of the system isn't going to be cheap either. Best of luck.
Thanks for everyone's replies.
BiggerView, I hear what you are saying about the 17.5" pre side. I could line them up on one side of the coach, giving a more generous 35" (and safe) walkway on one side, but if 1/2 of the 8 panels at 40 lbs each were favoring one side, say the driver's side, that would mean that my weight load on that side would be roughly 200-250 lbs more with the racking. That might actually be a better alternative than the center to offset the 8 GC-2 batteries I plan on adding on the other side 62 lbs x 8 = 500 lbs, so I'd only be favoring the right side with 250-300 more lbs (which is the light side, opposite the slide.)
Arcaguy, you've expressed some of my concerns, mainly the panels acting like a sail, catching the wind, but they will do this whether they are 3 " off the roof or 13' off the roof (if mounted incorrectly, at an angle), will they not? They'll have to be mounted sturdily, for sure. I spoke to Solar Mike at Slab City (an experienced solar RV installer) last week when I was there. He told me he recently racked 4 panels on a motorhome up above the vents with aluminum and recommended that. I don't want to reinvent the wheel, which is why I asked for someone with actual experience using the structural PVC pipe in this capacity. I might end up with aluminum afterall. I spoke with a structural engineer/ designer last night (a family member) about the design asking about the difference in thermal expansion between aluminum and PVC and he assured me that it would be negligible for my project.
I'm not worried about AC venting because the top and front of the AC shroud is solid, blocking all airflow. The back and sides are vented. I have been thinking about removing the AC shrouds completely since I'd have the large solar panels blocking the sun and rain. This would give the ACs even more ventilation for even better cooling that stock.
As far as electrical capacity, when you increase the voltage of a system the current drops. This is one of the reasons for going to a 48v system as it allows smaller wire and controller sizing. For instance My 50 amp controller is only rated to handle 625 watts at 12v but 2,500 watts at 48V because the current at 48v is only 1/4 of what it would be at 12v. www.amazon.com/EPEVER-Controller-Negative-Regulator-Flooded/dp/B07LC657SH Since I will be mounting the panels flat, not angled toward the sun I can only expect about 80% of their rated output at best (less the farther north I go). So those 1920 watts of panels will only be producing a max of that I will be about 1,500 watts in the real world. If I mount 3 in series so have 2 banks in paralel the amperage coming down the wires will be exactly the same as the 2 - 12v panels that will be in parallel wiring. The difference is that the 12v bank will be producing about 34v (under load) into the controller which will convert it to 12v (nominal) and 40 amps, whereas the 48v solar bank will be producing about 102 volts though at the same amperage as before (about 15 amps) which the controller will change to 48v (nominal) and around 30 amps at 48v. Remember, 2 of the 8 panels will be dedicated to the 12v system.
The minisplit I'm looking at draws 11.5 amps (at 48v).So during the daytime, the 48v system this will be enough to run the AC, a 2,000 watt inverter (for occasional microwave and other light a/c use) and still be able to put some current back into the batteries for evening time. My battery bank will have 220 total ah or 110 usable (at 48v) this means I would be able to run my ac unit all night if needed. This type of heat pump uses a rotary compressor which doesn't "cycle" like a traditional AC but scales up and down smoothly and seamlessly, drawing less current as needed without huge start-up power spikes that conventional compressor air conditioners have.
So the next question is if plastic pipe does not prove to be durable, how about a rack make from 1/2" galvanized steel pipe, bolted to the roof with steel flanges. I don't think any cross bracing would be required, just a box shaped rack all tied together and screwed down tightly using 4-1/4" bolts per leg. Sure it will be heavy, maybe 150-200 lbs for the whole rack, but it would be the strongest option, better than aluminum, and I don't have to worry about the effects of sunlight over time. I was just trying to avoid adding that much extra weight to the roof. Surely someone has racked 2,500 watts of solar on their roof and has some real world experience in the matter.
Does anyone have any better suggestions or recommendations?
Chip
-- Edited by Sushidog on Sunday 12th of May 2019 02:38:47 PM
The Escapees forum is one place. www.rvnetwork.com/
I think your plans and ideas for building a huge solar array and batteries is a great project. Extremely ambitious though.
Thoughts:
-- I would shift the solar panels to one side, at least a bit to allow at least 24" or maybe as much as 30" for a walkway. 18" is a little narrow for safety.
-- Tilt the solar panels a little. 2-3 inches end to end so the water will drain off. Pooling water greatly reduces the power output. Also standing water collects more dirt, requiring more frequent cleaning.
-- I have experience with large residential solar panels. My panels are 325watt, about 52" x 65". I installed them on my 29" Sightseer Class A and put about 45,000 miles on them, including a 4.5 month trip to Alaska. No problems with them coming loose. My panels were about 1.5" off the roof on one edge and about 4" on the other. I slightly tilted them so the water would not pool on them. I have now moved these panels to our current RV, but only have about 1000 miles on the installation. I fastened the panels on the 4 corners with about a 1.5" by 4" aluminum foot with 3 screws per foot, and Dicor sealant under the foot. If I was to raise the panels to 13" I would add more support and attachment points.
-- Your dedicated battery bank for the air conditioner is 220AH @48V. To make it easier for me to calculate, I am going to make that 880AH @12V. That is 8 Golf Cart batteries at 6V each, or any other combination of battery. I matters little if you go with GC or 4D or 8D the weight and space requirements are all about the same.
-- I would without a doubt go with lithium batteries. Yes they are expensive, but your entire system is expensive. I would use 4 100AH lithium, cost of about $4000. This will give you easily 300-350AH @12V usable power at about 40% of the weight.
-- With lead acid there are 2 or more things to keep in mind. 1) At 60% SOC your battery voltage is now about 12.2V. When you hit those batteries with a load you voltage will probably sag to down into 11.9V or so. That tends to stress your inverter. As you get closer to 50% SOC your voltage sag is going to be more. 2) Charging along with the need to get the lead acid batteries back to 100% SOC as often as possible. Preferably every 3-5 days to keep them from sulfateing. Remember it doesn't matter how much solar you have, charging lead acid the charging current really drops off after the first 1-2 hours and drops down to 10 to 5 amps after 3-5 hours. Makes it hard to keep lead acid charged when going as low as 50% SOC. Only going to 70% or 75% SOC makes it much easier to get back to 100% SOC, but you need quite a bit more battery.
-- Don't overlook the fact that if you DON'T get your batteries back to 100% you no longer have the full 110AH @48V available you are planning on. Or if you do use the 110AH you will drop below 50% SOC.
-- Lithium will charge at a faster rate and doesn't need to be brought to 100% SOC. In fact it is better for the lithium battery if you only go to about 93% SOC.
-- You can mount the lithium inside your rig so they will not be too cold or hot. They can't be charged when the battery is below freezing, discharging (i.e. using) is OK. It is best to keep lithium from going over about 110-120 degrees. Four 100AH lithium only weighs about 130 pounds. You can put that in lots of places. Lead acid is more difficult and has to be AGM if mounting inside the rig.
-- I would use aluminum to build your rack to mount the solar. Here is a possible place to buy larger or heavier duty aluminum than you will find in a big box store: https://www.metalsupermarkets.com/metals/aluminum/ I have no experience with this place, but it sounds legit.
In my current rig I put my 400AH of lithium, a 2000 watt inverter/charger and 60amp solar controller in our bedroom where three drawers used to be.
Two items. First, check out www.technomadia.com if you’re considering doing lithium batteries...they put them in their bus and boat and have considerable knowledge about lithium batt. Second...don’t count on getting 80% of rated output...it ain’t gonna happen. First, the panels are tilted relative to the sun and second the sun causes worse tilting effect in the morning and afternoon. You can only count on 4 or 5 hours of max output based on geometry...and the panel efficiency goes down as they get hot. We gave 800 watts of panels and even in southern FL for the winter we o lay get about 400-425 watts max output...and that for only a couple hours a day...in the morning and afternoon it’s more like 250. Make sure you take that into account when sizing panels and batteries for the A/C unit. Chris and heroine (above url) are able to run a sing e unit for awhile but they have way more than my 800 watts of panels.
What Neil said, especially about the temperature. With an almost perfect sun angle, bright, clear day and a very, very cool day I once saw 77% output. But everything has to be just perfect to get the rated output and that number won't last for any extended period of time. 80% is more of a lab / theoretical / standard rating number then an operational design number. Think in the low 60's, or less, percent wise as the peak output for a few hours and I think you will be much more pleased with the results.
In addition to www.technomadia.com as a very good source for some real world info & experience with lithium, another very good source is Wheelingit Lithium part 1 . There are 4 parts to the info so don't stop with the first. Both of these couples have worked together on providing real world info about lithium batteries and systems.
Sushi Dog, You sound like you are quite committed to running a air conditioner off of battery. That is very ambitious project. I am not aware of anyone attempting to do this in an RV and actually run the A/C for overnight or for 6-8 hours.
From the figures you gave, the mini-split A/C sounds like the best way to go. However I have significant reservations for you to be able to run the A/C 6-8 hours off of 880AH @12V. (Yes I understand your 48V system is 220AH @48V, but everyone is familiar with the amount of AH's from a battery at 12V. It gets confusing to try to equate 48V AH's to what we are accustomed to. )
While I totally agree that it appears the mini-split is much more efficient than the standard RV A/C, I would recommend 880AH @12V of lithium. I really think that 660AH@12V would do just fine, I don't know of a way to use six 12V batteries to get 48V.
In an earlier reply I gave my concerns about trying to run the A/C off of lead acid. The two links above do provide some detail about why they went with Lithium instead of lead acid and the short comings of lead acid.
I have reconsidered the plastic pipe approach. Instead, I plan on mounting my first 2 panels (the first stage of my system that I will install next month) on an angle so that the first panel attaches to the front of the MH roof along the long 66" side at the 2 pounting points provided for maximum support at about a 9 degree angle to the horizontal roof. This would take care of the water pooling issue, facilitate keeping them clean and productive. I plan on supporting it at the rear of the panel (which will be about 6.5" off the roof) with two vertical mounted galvanized steel 3/4" pipes which will each be screwed into a steel pipe flange and attached to the roof with 4 heavy duty stainless mounting screws. I will attach both panels to 2" angle iron and attach the angle iron to the pipe with 2 horizontal bolts in holes drilled through the pipe. The rear of the second panel will then be mounted to 13" tall pipes in a similar fashion. I checked the wind load at 95 mph and it will be under 1/3 of the panel's rated capacity.
This will act as a wind break for the remaining 6 vertically mounted panels 13" off the roof which will all be attached to the roof similarly. I plan on getting some light weight aluminum bar stock and using them as cross braces in an x pattern, side to side on all 13" high mounts as well as a single diagonal brace fore and aft on all front to rear vertical supports to give the entire structure rigidity.
Thanks for the information on the low real world output of perhaps 60% in flat mounted panels. Instead of the 320 watt panels that I planned on using I will have to look at some more efficient panels. Santan solar www.santansolar.com/deals/ has some used 22% efficiency 360 watt sun panels in a 61" x 41" format for a total of 2160 rated watts. At 60% of rated this equals 1296 watts of usable power for a little better yield than the ones I was looking at. If it looks like I will need even more solar I have considered mounting a few on the side where my slide is I could mount 2 vertically to the roof which would swing out when I extend my slide where my slide topper is. This would add 720 (432 usable) watts, bringing the total to 2,880 (1,728 usable) solar watts, if needed. At that point the battery bank would be by far the choke point in the system.
The roof top ac units are far too inefficient to even considering running even one off of solar, whereas the mini-split I am looking at produces only slightly less cooling (12,000 BTUs vs 13,500 btus but uses only about 1/3 the wattage of a roof top unit to do so. My rooftop units use about 2750 watts to start and about 1250 watts to run vs 560 watts to start and run the 48v DC mini split, with no inverter inefficiencies at all, cause I'll be drawing from a 48v DC bank.
Maybe in a couple years they'll have a more affordable battery option, when I'm ready to buy my 48v panel bank. Perhaps lithium will drop in price by then. I remember reading Technomadia's lithium experiences long ago. If not, I'll have to go with lead acid in spite of the acknowledged benefits of lithium. Now, I can build an affordable lead acid GC-2 bank for 8 x $120 = $960 vs $4,000 for the equivalent lithium bank. True they will weigh almost 370 lbs more, and be worse performers overall, but I won't have to make a loan to buy them. ;)
Chip
Well thought out plans. You have done excellent research.
Please come back and update us with how this all works out. I write "how this all works out" because every project I have done changes quite a bit from inception to completion. Even if it takes a year or more before you complete the project come back with an update.
I have almost completed phase one of my solar plan, and yes, it turned out quite different than I had in mind.
I decided to mount the 2, 310w panels for my 12v system on the side of my MH. I did this to free up space on my roof for 9 similar panels for my planned 48v system which will be racked above my AC units and vents using sturdy but lightweight aluminum angle and traditional solar rails or rectangular tubing. As a bonus, the side mount allows me to angle the array from about 69 degrees to 20 degrees from horizontal, spending on the latitude I find myself and the season without climbing on the roof. Not only will this will make them more productive, but easier to clean too. The only thing I haven't done to complete this phase is add a couple gas springs to make the array easier to lift. Right now I have to lift about 45 lbs of weight to get them pinned to the angle I want. I'm looking for the right struts now to relieve most of this weight to make setting up easier.
Here's a couple pics of the project so far.
That's my DW doing the Vanna White impersonation.
I'll keep you posted as the project progresses, (which should take some time) but 9 panels x 310w = 2,790 watts for my 48v phase - more than adequate for my anticipated needs!
Good news. I found some breakthrough price point lithium batteries. I think 3 of these with BMS in parallel would be perfect for my needs, and affordable too! That's 198 amp/hrs at 48v - 80% or more usable and only 150lbs for all three battery packs. houston.craigslist.org/ele/d/pearland-48v-3kwh-lithium-ion-battery/6937919504.html These are new 3 kw packs for only $475/pack - that's less than anything I've found, even used.
Chip
-- Edited by Sushidog on Sunday 21st of July 2019 08:01:49 PM
-- Edited by Sushidog on Sunday 21st of July 2019 08:04:45 PM
-- Edited by Sushidog on Sunday 17th of November 2019 09:16:51 PM
-- Edited by Sushidog on Sunday 17th of November 2019 09:20:15 PM