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Time For Solar, Have No Idea Where To Start.


Incurable Wanderlust

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Hello Dear Toyota Motorhome lovers!

The next step for my motorhome is to add solar to it so I can run the basic appliances without using my car battery. Since I am living in it, I am not driving my motorhome for long distances so the battery does not fully charge or stay charged very long.

The main things I would like to use it for are the water pump and "cigarette lighter outlet" to charge my phone etc. I have solar lights inside, so that's fine and i'm not worried about having the refridgerator or convection oven running regularly. Really, I would just like to be able to flush the toilet with water and use shower and charge my phone.

So where do I start? Specifally, what kind of watts should I be looking to buy? Do I need a whole kit or would a trickle charger be sufficient? Seems like all I need to do is keep the aux battery charged right? Currently, there's about 12 hours of daylight and I'm parked in a place with lots of sun exposure. I won't be running the appliances for hours on end, but would really just like to have a fully charged battery. Any info, please share!

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IMHO 100w is the minimum needed for true boondocking. Your refer should be on propane and a convection oven is a non-starter. A larger battery is very desirable, it will store any excess solar power for cloudy days. Basically the size of battery determines how long you can run your stuff and the size of the solar panel determines how fast the battery gets recharged. A 100w panel will average about 4 amps of charge over a day. So 4 amps x 10 hours give your about 40 AH of power. Figure out how much power you will be using and go from there.

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A 100 watt solar panel will not average 4 amps over day anywhere I go. Maybe in the sunny southwest. In the northeast the best sun is only 4 hours a day. That equates to maybe 5 amps per hour for 4 hours in a best case. That is unless you make the panel track the sun and follow it all day long. Tracking will give some gain. But still - peak time is the only time a solar makes near it's rating. The rest of the day you're talking 1-2 amps IF the sun is shining. That's around 1.5 amps per hour, average, for a 24 hour day in GOOD sun. Here in NY we have 4 peak hours per day. In the SW some areas get 5.5 peak hours.

My entire home and farm is run on solar. 5400 watts of solar panels and it makes, on average, 11.5 KWh per day. Better said - I have twenty-seven solar panels and each is rated 200 watts. All those 27 panels, in total, make on average 34 amps @ 14 volts for a 24 hour day. That means that one 200 watt solar panel has an average output of 1.25 amps @ 14 volts, all the time averaged over a year. That's with winter taken into account when sun is much less.

As far as what is needed for an RV? All depends if you actually want to run off of solar - or just supplement charging to your battery bank. A high-efficiency refrigerator like a 5.8 cubic foot Sundanzer with 4" of foam insulation can be used with just one 120 watt panel and one 110 AH battery.

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So where do I start? Specifally, what kind of watts should I be looking to buy? Do I need a whole kit or would a trickle charger be sufficient? Seems like all I need to do is keep the aux battery charged right? Currently, there's about 12 hours of daylight and I'm parked in a place with lots of sun exposure. I won't be running the appliances for hours on end, but would really just like to have a fully charged battery. Any info, please share!

Any solar panel over 20 watts needs a "controller." The controller is the only special piece of equipment you need to hook a solar panel to your battery or battery bank. No place in the contiguous USA gets more then 5.5 peak sun hours a day and those are the only hours a panel will make near it's max rating. The other daylight hours IF sunny will have panel making 1/2 to 1/3 it's rating. You can buy controllers for less then $20. All depends on the size. Just like the isolators in RVS, the controllers must be matched in output. Better said, the controller must be rated at max panel rating or more, in amps. I've been buying these lately because they are cheap and have free shipping. Main thing is - the amp rating must be the same or more as the panel. You have can four panels each rated 7 amps and each having their own 10 amp controllers - or have all four hooked to just one controller rated for 30-40 amps. Makes no difference.

http://www.ebay.com/itm/12V-24V-5-10-15-20-30A-PWM-Solar-Panel-Battery-Regulator-Charge-Controller-/351004581852?pt=LH_DefaultDomain_0&var=&hash=item51b980dfdc

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I was in Harbor Freight yesterday and they had a complete 3 panel 45 watt system for $200. The collector had connections to hook up 8 sets of panels for a total of 24 panels if you need to go that far. I don't know about the quality of them but they have either a 30 or 90 day return policy that they have always honored for me. I would give them a shot but I just can't bring myself to drill holes in the roof of my RV.

Edited by JUSTABANGER
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Why would you want to spend $200 on just 45 watts worth of solar? 80 watt panels typically sell for $100 or less shipped to anyone's door in the USA. Controller less then $15. For $215 you could have 200 watts of solar.

That price that HF is charging is what solar was selling for 10 years ago before the prices came WAY down. Noting against Harbor Freight by the way. Their prices are great for some things. Not for solar though.

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=80+watt+solar+panel&rt=nc&LH_BIN=1

http://www.ebay.com/itm/20A-12V-24V-Solar-Panel-Charge-Controller-Battery-Regulator-Safe-Protection-/301218792237?pt=LH_DefaultDomain_0&hash=item46220a032d

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I didn't know what they were going for I just happen to run a crossed it a H F and thought I'd share.

10 years ago solar panels were $4 to $5 per watt. Now they are down to 50 cents per watt if you buy in bulk. Shipping is often the killer. Ebay seller often have free shipping and if you can find a panel shipped for free priced at $1 per watt - it's good deal.

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It is a very completive business shop around. You can buy a whole lot more than 35 watts for $200.

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12 volt panels are usually the most expensive per watt. Higher voltage panels 30-60 volts being sold for grid-tie systems are usually the lowest price. Some around now for 30 cents per watt.

There are trade-wars going on over polysilicon (to make solar panels) with China and Korea in front. I don't know how long these low prices can last. It's not due to any sort of normal competition or to higher production. It's more about companies dumping solar panels on the market priced below production cost. China has done it over and over and many of their companies are surviving it. US companies do it for awhile, then beg for government bale-outs, and then disappear. Like Evergreen in Massachusetts, or Obama's Solyndra started by a guy in Oklahoma..

15 years ago a 12 volt panels could easily sell for $6 per watt. Now they can be found for around $1. All the other equipment, e.g. inverters, controllers, etc. have gone up in price for the higher-quality equipment certified for grid-tie hook-ups. The non-certified stuff used on 12 volts systems in boats, off-grid homes, RVs, etc. can be found cheap since the Chinese and Koreans seem to be dumping the stuff on the American market. I've been buying in bulk from Sunelec in Miami for years. Here's a history of their prices they published. The problem with big sellers like Sunelect is - you have to buy entire pallets of the stuff to get the real savings. Thus the nice thing about Ebay where some sellers have already bought pallet loads - and then sell one at at time on Ebay.

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I'm looking for solar panels for a solar boat project. I need them to be as light as possible and not too large and these are the best I have found so far. I would love your opinion JD. I have no knowledge of solar at all. Planning on having 2 of them.

http://www.ebay.com/itm/100-W-Watt-12-V-Volt-Semi-Flexible-Mono-Monocrystalline-Silicon-Solar-Panel-/331257054540?pt=LH_DefaultDomain_0&hash=item4d2075854c

Linda S

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I don't personally know anybody who has used flexible panels. Looks like a great way to directly install on curved surfaces with glue. Unisolar was one of the biggest sellers for a few years and is now gone. They were prices around the same as the ones you linked to. The only "fear" I heard expressed with them was overheating. Usually solar panels have to be mounted with air-space underneath them so they don't overheat. Obviously - with the glue-on flexible panels - there is no air space. I don't know of any failures or success stories with them. I DID notice that many newer RVs with factory installed solar are not using them - but I don't know why. My guess would be they were be fine as long as installed on fiberglass and not metal.

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I wouldn't trust glued-on-the-roof solar panel mounts. A traditional 120 watt solar panel with aluminum frame and tempered glass weighs 26-30 lbs. That is a lot of mass to have clinging to a roof on a hot day when you slam on the brakes. Makes me of the "Big Dig" in Massachusetts where all those concrete panels came down and killed people after the engineer-certified epoxy glue came loose. Obviously the solar won't kill someone unless some poor guy is behind you and your panel flies off and goes through his windshield. I'd be worried about just the wind pushing on it at 60 MPH. Lots of holes in the roof anyway. No big deal to me as long as they get sealed with Quad sealant or equivalent. The key thing to me - with solar mounts is you want them two-piece. This way you can quickly remove a panel without disturbing the mount-holes that are sealed to the roof.

Roadtrek has their new E-tek RV with one big panel and I can't make out how that thing is mounted. Mounts seem to be kind of hidden.

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I have been told that MPPT charge controllers will allow you to save to your batteries more of the energy you collect than PWM controllers. Any thoughts on that? Are MPPT controllers worth the extra cost?

MPPT= Multi Power Point Tracking

PWM= Pulse Wave Modulation

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  • 2 weeks later...

Here is a folding 120 watt panel at a good price...I made my own up before I saw this one. I have 30 foot #10 marine wire off panel to controller mounted close to my battery. This way I can park in the shade and put the panel in the sun.

http://www.ebay.com/itm/80W-100W-120W-watt-12V-poly-folding-foldable-portable-solar-panel-kit-for-RV-/171311780467?pt=LH_DefaultDomain_0&var=&hash=item27e2fa5273

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I have been told that MPPT charge controllers will allow you to save to your batteries more of the energy you collect than PWM controllers. Any thoughts on that? Are MPPT controllers worth the extra cost?

MPPT= Multi Power Point Tracking

PWM= Pulse Wave Modulation

I've had both versions for years. I've never noticed any substantial difference in small setups like you'd have on a RV. On large solar arrays - the MPPT units are better because the input voltage does not have to match the output voltage. With a MPPT controller - you can take 30 solar panels and wire them up to make 120 or 240 volts (series-parallel connections) to the input of the controller. This allows the wire size to be much smaller. The output can be set much lower, i.e. to 12, 24, or 48 volts to charge a battery bank. On the other hand, a PWM controller usually has to have the input voltage and the output voltage matched. On an RV where the wire-distance is short - it's no big deal to have the solar input wired for 12 volts, along with the charge output also set at 12 volts.

Long story short . . if you want to stick a few 120 watt solar panels on your roof of your RV - a PWM controller will work just as well as a MPPT controller. With the PWM - you'd hook multiple 12 volt panels in parallel to keep the voltage at 12 volts. If you were using a MPPT controller- you could hook them in series and have a higher input voltage or even higher voltage 24 volt panels. For that short distance though- the end result will be the same. The 12 volt panels will just need larger wire.

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Here is a folding 120 watt panel at a good price...I made my own up before I saw this one. I have 30 foot #10 marine wire off panel to controller mounted close to my battery. This way I can park in the shade and put the panel in the sun.

http://www.ebay.com/itm/80W-100W-120W-watt-12V-poly-folding-foldable-portable-solar-panel-kit-for-RV-/171311780467?pt=LH_DefaultDomain_0&var=&hash=item27e2fa5273

I purchased one of these last year and have had good results so far. I do wish the cables were a bit longer, but otherwise I'm happy with them.

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