[MsNomer]

I give. KOV and RD convinced us at our gathering. We are adding solar.

Contrary to RD's protestations, we will use the PWM controller which mates with our TriMetric meter. We love the meter and are impressed by Bogart Engineering. Because it mates with the meter, this controller is smarter than most PWM controllers, but still cheap and simple.

We will have 200AH of AGM battery--the price was so good on the second 100AH Trojan that we felt like we stole it, and no sales tax in NH. I'm not looking forward to remaking the battery box, though.

We are contemplating 300W of panel--haven't decided whether two 150W or three 100W.

Question: What is the minimum distance between panels? With two 150W, we would be pushing the limit lengthwise, but we like that the 150’s would be farther in from the sides. Three 100’s would have to be crosswise, thus 48" wide instead of 39".

Question: When batteries are full, where does all that energy go? I assume it is converted to heat--does that heat stay outside on the panels? Do they heat up the roof?

 

[Zyzzyx]

Good call on the Bogart hardware. Really like that stuff myself. The TM and SC pair real well together.

I would recommend the two panel setup. Generally easier to mount fewer panels. And as you mention, farther in from the edges to be visible. There is no minimum distance between the panels. Just bump them right together. Depending on how you have them mounted. I have four 160w panels up top. 2x2 layout. I have a crossbard in the middle front to rear, but side to side the panels are abutting each other.

And as for length, do what you need to. I have the Maxxfan all the way at the rear of the roof. My panels are nearly 10' long total and go from just in front of the fan to just behind where the roof ribs start on the flat part of the roof. Definitely visible, but no problems with them.

And as for the 'energy' of when the batteries are full, its just an energy potential, not something that needs to be shunted off. If the panel is in open circuit, there's no power flowing, so no heat to deal with. An unplugged solar panel sitting in the sun just... sits there.

And some folks have theorized that although solar panels are black and do heat up in the sun, they could possibly help cool the van since the roof is effectively shaded. Though it does pick up more radiant heat from the back of the panels. Question is, does that account for less heat than the infrared of being directly in the sun. Dunno...


If you're looking for panels or other solar stuff, I highly recommend AM Solar, in Springfield OR. They have been beyond wonderful to work with as I did my installation with parts purchased through them. May not be the least expensive, but I have found it worth a bit extra in the customer service provided.

 

[keeponvaning]

I would (did) go with the 2 150's they are about 41" sq and less wiring connections and mounting problems. I have to agree with RD tho about the controller!

The controller allows the batteries to only receive the max charge the extra voltage goes to the same place it goes in the electric grid I imagine - don't worry about it

 

[RDinNHandAZ]

Well KOV and Msnomer I did due diligance witht the controller once you left and I agree with Msnomer that the Bogart PWM controller is the way to go with your meter. Your TriMetric monitor seems to be a great product but Bogart's site put me off a bit with some of their claims which were a bit like hype. Oh well I don't have their stuff nor reason to doubt them really. The 300 Watts is going to be so much solar a caveman switching it on and off would work too. You do know with your Engle refrigerator 100 watts would be enough? You'll be able to use the microwave for everything!

Zyzzyx, I once saw an old VW Kombi with a desert top that worked on this principle. Just a sheet of tin raised a few inches above the roof to keep the van cooler in the Serengetti or Tanami Desert. Very effective if you are moving. You are right about the power as there is electrical potential (voltage) but no current (amps) so Power (loss) is V*A which is zero! No heat produced, had to think about that one!

 

[proeddie]

Ms,

I will be very interested in the cost, and how close to the roof you can mount the panels!

They wouldn't do me much good under my carport (most of the time) but would be a great asset on the road.

Ed

 

[Zoomyn]

When sun hits a solar panel? Whether the panel is electrically active or not might add 10-15% heat if it is open circuit, after the following...

If* the sun is perfectly square overhead and/or the panel is angled to match the suns position above the horizon about 5-7% 'sunshine' is immediately reflected off the outside glass surface, then about another 5% gets reflected back from the inside surface of glass, and the PV cells surface itself reflects back 2-3% of the light striking them. So instantly 15% of the suns energy is beamed back upward without being converted into either electricity or heat, and more, even much more, is lost if the panel is mounted horizontally.

So now it's the PV cells themselves being solar heated. If there is electric load being supplied from the panel that is 13-20% of sunshine energy transported from the local area. So 65 to 75% of the suns 'shine & warmth' is being absorbed & converted into heat and that heat moves in three ways: conductance, convection, radiation.

Conductance: Unless it is a frame-less surface mount flex panel there is little surface area to conduct heat into the supporting structure even with aluminum being a great conductor of heat, yes the hot aluminum channels heat into the mounts but it's a small percentage since glass & the plastics used conduct heat very poorly.

Convection: Between the front/back/sides of the solar panels there is not much 'texture' to help it shed heat by acting as a finned heat sink to warm air as fast as possible and so create its own 'smokestack' draft but there is a bunch of surface area that is wafting up blobs of hot air as they form.

Radiative: Here is where it gets fun, the high energy sunlight (visible, IR and ultraviolet) gets absorbed and warms up the PV panels which then 'glows' in infrared wavelengths, throwing about 60% skywards and 40% downward, the glass holds most of the heat and the plastic backing being so lightweight it stalls the heat moving through it.

So.... 40 to 45% of the 65 to 75%, or 25% to 35% of sunshine radiating down towards the van converts to infrared and it 'lost' with maybe another 5% being conducted by the panel mounts. Anyhow, it sums up to glass-faced solar panel shade having a cooling effect even if the airspace beneath them stagnates - The surface mount non-glass panels are likely break even on heating up the RV roof versus bare roof with their 2mm of plastic backing insulating the van roof, and likely a cooler situation when their 20-23% efficient solar cells are carrying off chunks of sunshine energy.

If there is no current flowing the PV panels are nearly inert, that energy available is potential only. Most panels are labeled as rated to 600 or 1000V, say 30 to 45 panels in series, before there is concerns on electrical leakage making tracks where it shouldn't.

 

[Steve]

Can't see any bad info from the previous posters (good thing I wasn't the first to respond). The ONLY real consideration in size/number of panels is what will fit best in relationship to what you already have on your roof. RE: the heat issue - I'm in the "they shade the roof" camp, although mine are mounted on the Fiamma roof rack, so they a 3 inches above the the roof.

I would second Zyzzyx on his recommendation of AM Solar - they know their stuff.

 

[MsNomer]

Steve, how much wind noise do you get with that set-up?

 

[Hein]

We have a 300 watt layout for the Sprinter that would work just as well on a Promaster. It utilizes our tower brackets and 3 Renogy Eclipse panels. These are black panels so we have towers in black to match and the 8020 is available in black also. Looks pretty good, imo.

On the Promaster without roof rails we would use our ABS mounting pads with metal threaded inserts. These have a very large area of VHB to securely hold our tower bracket which support the 8020 crossbars holding the solar panels. There would be 6 of these with 3 crossbars for this 300 watt install. The crossbars can be either square or 1/4 round (1517 LS) profiles.

Here is the 300 watt layout shown on the Sprinter:
http://www.impact3d.com/fiama_with_3x_eclipse100w.pdf

Here is a layout showing how the towers and 8020 crossbars fit on the Promaster using the mounting pads: www.impact3d.com/Ian_promaster_solar_layout.pdf

We have some other options for less panels and shorter vans.

 

[keeponvaning]

Just screw the two 150w panels to the roof with stainless self tapping screws a dab of sealant and simple aluminum mounts about and inch off the roof. Simple, cheap, not very visible and very efficient. Solar isn't rocket science, although some would like to think it is. Once you've done it you will ask yourself "Why does everyone make this out to be so hard to figure out and do?".

End of today's rant

 

[RDinNHandAZ]

Hein,
That is a beautiful thing!

KOV,
Mine are on the simplest brackets cut from 2" lightweight aluminum angle and have been fine too.
http://www.promasterforum.com/forum/attachment.php?attachmentid=15033&d=1443224750

 

[keeponvaning]

I learned everything I need to know (about solar) from you, RD, not to mention a few other things

Now, if only that Leatherman I ordered several months ago would arrive...

 

[MsNomer]

Can I borrow the Leatherman to attach the panels?

 

[keeponvaning]

Certainly but only after RD certifies us as competent users.

 

[RDinNHandAZ]

STOP. No Leatherman for any of YOU! NO Certify! Stop thanking KOV and MsNomer too. They thrive on it. We must not do it! STOP! STOP! STOP!
NO LEATHERMAN FOR ANY OF YOU!!

opps did I yell again?
(coments credit to "the soup nazi" -Sienfield Nov. 2 1995)

 

[keeponvaning]

RD has spoken!

 

[Steve]

Steve, how much wind noise do you get with that set-up?

None that bothers me, but I've always had all that "stuff" up there (roof rack, two awnings, two MaxxAir fans, and the three solar panels) so I don't have anything to compare with.

Another questions I usually get is "doesn't your mpg suffer?" - I've always gotten 17mpg, don't know if that's good or bad.

 

[keeponvaning]

Mine are mounted on brackets about an inch off the roof. No noise and my mileage has stayed steady at 17 mpg also since installing the panels.

 

[twicken2]

I am designing my solar right now and have settled on a similar setup:

3 x 160W Grape Solar panels mounted width-wise. Will mount with simple 2" aluminum angle mounts.. sikaflex the mounts to the roof (is that what you used RD?) + one self-tapping sheet metal screw, then seal the screw with more sikaflex or dicor sealant. I was considering 4 x 100W Renogy as an alternative, but have decided on the 3 panels to limit the number of holes in the roof.

Inside, I'm going with the Bogart combo - TM-2030 and SC-2030, Magnum MMS1012 inverter/charger, 2 x 155AH vmaxtanks AGM batteries, and a battery isolator (battery doctor?) to enable charging from the alternator. This setup will likely be bumping up against the SC-2030's 31 amp maximum during the peak hours on sunny days, but I am really enticed by the integration and price point of the Bogart stuff!

I ordered the rhinorack 2-bar setup planning to mount the panels on that, but have scrapped that plan since seeing how "high profile" the panels would be and deciding to add an extra panel.

It's a lot of solar and storage, but we will be chasing snow in the winter, and I will be running a decent sized monitor and multiple laptops most days in addition to the normal stuff.

 

[RDinNHandAZ]

Tyler, I used double sided High Bond 3M tape covering the 2X4 inch surface of the angle pieces. I had been led to believe that would be enough to keep the panels on the roof but I chickened and set a self taping screw through a hole I had made in the brackets JIC. Dicor lap seal bonds the screw head.
If you keep the panels clear in the winter length of day decreases a lot but solar cell efficiency increases as it gets colder, perhaps gaining >20% on a below zero day compared to a hot summer day. It won't overcome the loss of daylight but it helps.