Going Solar!

I'm installing a very modest system, 280w/12v, and that will not meet my needs in winter, with heating and extra lighting and such. You are looking at 400w bare minimum, and that solar-ready wiring is the lynch pin. Find out what gauge they plan to install... probably 16-12ga... and ask for a minimum of 10ga, like someone here suggested.

Here's the deal. The higher the voltage, the lower the amperage. Watts = Volts x Amps... so if you double the volts, you halve the amps, and vice versa. (I'm running 6ga for my 12v system, for example, because of the lower volts and thus higher amps). There is a thing called line loss, or voltage drop. This needs to be minimized, and is done so by using large enough wire. With 10ga wiring, you'll likely be best to go with 24v/mppt. And you don't need to spend a small fortune on a controller, but you certainly can if you like.

Your loads will be rather significant... furnace blower and cpap being the biggest power hogs, but don't forget about the fridge controls, and propane detector and such. These things really add up, seeing as they are a constant 24/7 drain on the battery bank. And you may be surprised to know many here use their microwave and TV while boondocking... I know I do.

I prefer 6v batteries, but many here have 12v, and are happy with them. Many times, it's simply a matter of space limitations (two 6v take up more room than one 12v, for example) and there are height issues as well. Either way, it's good to go bigger, i.e; more Amp Hours, rather than smaller, in most cases.

X2 on Handy Bob's Blog... no BS, just straight forward, sound advice.

Vintage465,
I recommend you google Handy Bob's 9 Golden Rules of Solar. Read his entire blog to educate yourself before jumping in to solar. This man has forgotten more than most so called experts know about solar and like he says in his blog, "I'm not trying to sell you anything."

I wonder how every part of this post can be so wrong,.....including the batteries. So far my 12v DC batts are doing fine after 5 yrs.
My 6'ers were great, still doing "not bad" after 8 yrs. I see very little if any difference tween 6 or 12v.

Fishinghat wrote:
First off, almost all solar panels will only produce enough electricity to keep a charged battery charged up, but not to re-charge a run down battery.

Second thing, solar panels are big and expensive. Unless you are willing to spend some serious money on panels that will set out on stands pointing at the sun and storing them when you are not there, forget that option.

Third. I'd suggest what most people who dry camp a lot do. Buy a Honda or Yamaha "quiet" generator and charge your battery(s) for an hour or so in the morning and evening.

Go9ing off topic here, but if you plan to do a lot of dry camping, consider switching to two 6 volt deep cycle batteries if your rig doesn't already have them. They work much better than 12 volt batteries, even if they are marked "deep cycle".

JiminDenver wrote:
Since you are going to spend the money to go MPPT...

He didn't say that. Besides, it sounds like the dealer offers max 150W wiring (and is willing to install only 95W).

Vintage465:
I agree with Pianotuna - with your needs, even without C-pap and humidifier - I would consider at least 200-300W array.

I can't recommend a catalytic heater until the only manufacturer of vented cat heaters - Platinum Cat - will start making it again. They've been out of production for almost a year, don't know if they are making it right now.

Correct me if I'm wrong - the dealer says it is prewired for max 150W, with 10W panel installed and 85W can be added, total 95W. Why not 150W then? The difference btw 80W and 140W is not that big: 12V panels.
Better yet - make them install MC4 cable gauge 10, so that more panel wattage could be added.
Max 150W wiring it's probably gauge 12 or thinner, no UV-resistant cable on the roof, and no weatherproof MC4 connectors. What is the worst, is that you can't add any more wattage in future. I wouldn't like this kind of "solar-ready".

The dealers that you talked to, might be outdoor people, but their system appears to be marginal. Don't get me wrong, I'm coming from years of wilderness tenting and can live for weeks with no energy source other than a few AA batteries. 95W is enough to run a few lights and a radio in a cabin in a bush, but not much else.

PS: Have just re-read your post and noticed that dealer's "fancy controller to convert watts to amps". Couldn't help smiling. There won't be anything fancy for max 150W array, and of course it won't be the kind that converts watts to amps - 12V array doesn't require MPPT controller.

Since you are going to spend the money to go MPPT, why mess with the 12v panels. A 230w panel at solarblvd is just $15 more that a 100w panel. 20a MPPT controllers go from $102 to $250. Need more than that and you certainly want to go with 24v panels if they fit on your roof.

Use Pianotuna's link above to the Excel spreadsheet to calculate power usage. Total evry watt that you use. Example: If you have a radio, it draws power for memory and maybe a backlight. It probably draws 100-300 milliamps. Over a 24 hr period that is 2.4-6.5 amps. In watts--24.5-100 W. Point being, it all adds up to draw on your battery reserve and has to be replenished by the modules. I wouldn't install anything less than 100W panel on an RV.

The reason I would suggest a higher rated MPPT controller is you can add panels as required. If you buy a small MPPT controller than need more panels later you will have another large expense. MPPT controllers aren't cheap. Buy larger than you need so your system can grow.

Vintage465 wrote:
Man! I got tons of info here! OK, got my amps and watts mixed up. That's what I meant...10w is maintenance, like when it's parked at home. Having said that this unit comes prepared for a 150w panel. Yes I said 150w. They stick a 10w on there and call it "Solar Ready". I explained to the dealer what my needs are:
1. We don't watch TV when RV-ing
2. We don't use a micro wave when RV-ing
3. We boil water on the stove to make French press coffee
4. The main reason I want Solar is to replenish the batteries after a night of running the heater.
5. Before you suggest a catalytic heater, they worry my wife to much.
6. This trailer has all LED lighting inside and out.
7. I plan to buy a back up generator to use if there is too much cloud cover.
8. Not really even thinking of an inverter except maybe to run my C-pap at night. If you want the humidifier to work it need 110v. Don't eve know if that is plausible, but as it stands that would be the only reason now.

Talking to the dealer who apparently is a real solar geek, said he would add another 85w panel, 2 6v deep cycle golf cart batteries and the fancy, convert to amp from watt controller. He commented that since this unit comes pre-wired with the quick connects, adding the 85w would be a snap. I think he knows the business pretty well. The other sales man with him said he can power other trailers off his! Both the owner and the sales person at this dealer are avid hunters, fishermen and know their way around a tool box and a test light. I think they sell these rigs to support their habit!

Thanks
V-465

Reading this list of usage I'd want at least 200-300 watts of solar, and the 220 AH 6 volt batteries or more. This is before the C-pap which I have no knowledge of consumption. The furnace can be significant draw in cold weather-especially if you're needing it during the day.

Research your RV furnace consumption. Google model number and look a specs-post the amp draw. Some larger RV furnaces can draw 6-7 amps. Smaller ones like mine are only 3 amps. What thermostat setpoint do you use at night?

I feel 85 watts is inadequate for your proposed usage.

Anyway research your c-pap consumption-post it in watts. Yes you may need backup generator for unusual conditions. And check out the solarblvd.com link posted above. 100 watt panels @ $125. Plus much more.

For professional installation parts and labor check out:
http://www.amsolar.com/
but do have idea of the loads I inquired about to help them size it.

Hi Vintage,

My furnace consumes 9 amps. If assuming an 9 hour night and a 1:3 duty cycle, that works out to 27 amp-hours.

At 85 watt panel based on a 5 hour harvest is only going to "do" about 35 amp-hours. That leaves nothing for lighting, other items and parasitic loads.

I fear your dealer does not really understand much about solar. You need to do a serious energy audit.

Vintage465 wrote:
4. The main reason I want Solar is to replenish the batteries after a night of running the heater.

8. Not really even thinking of an inverter except maybe to run my C-pap at night. If you want the humidifier to work it need 110v. Don't eve know if that is plausible, but as it stands that would be the only reason now.

Talking to the dealer who apparently is a real solar geek, said he would add another 85w panel, 2 6v deep cycle golf cart batteries and the fancy, convert to amp from watt controller. He commented that since this unit comes pre-wired with the quick connects, adding the 85w would be a snap. I think he knows the business pretty well.

Thanks
V-465

Hi,

Welcome to the forums.

Here is a simple flow chart.

Budget-->Energy Audit-->Battery bank size-->number of watts-->PWM or MPPT. What ever type of controller is chosen, make sure it has adjustable set points and a temperature probe that is on the battery.

If you use solar as a battery charger, one rule of thumb is between 60 and 150 watts of panels per 100 amp-hours of storage. The smaller the battery bank the higher the wattage needed (per 100 amp-hours). Here is a link to the rather special spreadsheet which includes an energy audit, that N8GS has created to help size solar battery charging systems!
Solar Spread Sheet by N8GS

If you full time or use an inverter lots, then populate the entire unshaded area of the roof with panels. I'm considering replacing my awning with solar panels.

For a nice explanation of solar, try this link:
Golden rules of solar