Super small solar system on my camper

oly884

Hey guys, been lurking the site for a while and figured I'd post up here to get some expert opinions on what I'm wanting to do.

Right now I've got a small 50 watt Kyocera solar panel on my camper feeding a PWM charge controller which goes to 2-110 amp hour batteries in parallel. The camper runs only off of 12 volts and has no shore power hookup. I also have a battery combiner running to the starting battery in my truck so I'm charging the 2 deep cycles when running the engine.

I'm finding that I don't have quite enough 'juice' with my 50 watt and I've wanted to upgrade it to something that'll keep the batteries charged under normal use on less-than-ideal days. When camping, I usually have to run my truck for an hour or so on all but the sunniest of days to keep the batteries from getting too low.

My rough calculations lead me to believe that a 200 watt solar panel would do the trick, though 2-200 watts wouldn't be too bad either to compensate for the incredibly sunny weather we always have here in the PNW.

My question to you all would be, is a MPPT charge controller overkill for my application, or would a new (higher capacity) PWM charge controller be fine?

Also, I've yet to choose the panels I want to get and I was wondering if there are any brands that seem to hold up better to being placed on campers, or are better suited for vehicle applications?

icarus

Re: Super small solar system on my camper

A pwm controller would be fine, an MPPT would probably not be worth the cost.

Remember the 50%X4 rule of thumb for off grid installations.

Define your loads and see if it fits.

That is, take the name plate rating of the pv, divide by two to account for all cumulative system loses, then multiply that number by four, to represent the number of hours of good sun one might expect per day over the course of the year. Few locations can count on more, and in an RV environment, even that equation is somewhat optimistic since the panels are rarely likely to be optimally oriented.


200/2*4=400 watt/hours/day. So I might look at loading of ~ 300 as a bench mark.

Remember, all design considerations must start with the loads,, if not, one is trying to put square pegs into round holes.

Tony

oly884

Re: Super small solar system on my camper

icarus wrote: »

A pwm controller would be fine, an MPPT would probably not be worth the cost.

Remember the 50%X4 rule of thumb for off grid installations.

Define your loads and see if it fits.

That is, take the name plate rating of the pv, divide by two to account for all cumulative system loses, then multiply that number by four, to represent the number of hours of good sun one might expect per day over the course of the year. Few locations can count on more, and in an RV environment, even that equation is somewhat optimistic since the panels are rarely likely to be optimally oriented.


200/2*4=400 watt/hours/day. So I might look at loading of ~ 300 as a bench mark.

Remember, all design considerations must start with the loads,, if not, one is trying to put square pegs into round holes.

Tony

Thanks Tony, I've gone through a good amount of calc's to figure out what I'd need for my camper:

Engel Fridge: 30 watts (at most) for maybe 8 hrs total a day, and even that's pushing it, under most conditions It'd be far less.
Lighting: (2) 15 watt fluorescent lights, 3 hrs per day
Laptop/misc 120vac loads: ~100 watts a day

So that puts me around 430 watt hours, and I'll round up to 500 watt hours per day to play it on the safe side, so perhaps 2-200 watt panels would be the best bet.

I've also got a furnace, but when I'm camping in the winter time, I'll usually run the truck anyways.

Since I have the truck wired to charge the bank, it's not necessary for me to get a system that will keep the batteries charged under all conditions, mainly just to reduce the time I'm running the truck.

Thanks for the suggestion on the PWM charge controller. I was having a tough time trying to decide if an MPPT would be worth it, but it's good to hear other opinions!

As for panels, any suggestions or am I going to be fairly happy with most offerings out there?

icarus

Re: Super small solar system on my camper

I've also got a furnace, but when I'm camping in the winter time, I'll usually run the truck anyway

A prime example of the third rule of solar power,,, that is loads ALWAYS grow with time.

(Rule number one is that people over estimate how much power they can actually harvest, rule number two is they underestimate their loads (both rules coming into play at the same time quite often.)

T

Cariboocoot

Re: Super small solar system on my camper

Your panel calculations are pretty close: 200 Watt minimum, 400 Watts better.

Why not go for a pair of Kyocera 135W units? They're usually a pretty good value for the $.
http://www.solar-electric.com/kyso130wa12v.html
Three would be better, of course, but then you're in to fusing each panel.

The larger Wattage panels tend to be "24 Volt" and would require an MPPT controller to down-convert to 12 VDC system. They also tend to be physically larger and so may be more problematic in mounting on an RV/camper.

oly884

Re: Super small solar system on my camper

icarus wrote: »

A prime example of the third rule of solar power,,, that is loads ALWAYS grow with time.

(Rule number one is that people over estimate how much power they can actually harvest, rule number two is they underestimate their loads (both rules coming into play at the same time quite often.)

T

Correct.

However, as I stated, solar is not my only source of power, and if necessary, I'll run my truck. It'd be no different than how I run my setup right now, except that I'd be running it far less, if at all, under most conditions. I won't be running my furnace in the summer time, and when I do run it in the winter time, I understand that the lower amount and power of the sun, as well as clouds and all other factors that come into play will have an effect on my system I'm looking at.

I've had my 50 watt solar setup, along with all the same loads in my camper for 4 years now, camped plenty of times, so I've got a good feel for the loads. I also have limited space and weight I can put on the top of my camper, so I'm not able to put any more than 2-200 watt panels on it anyways, so discussing increasing my solar output over 400 watts isn't really necessary.

oly884

Re: Super small solar system on my camper

Cariboocoot wrote: »

Your panel calculations are pretty close: 200 Watt minimum, 400 Watts better.

Why not go for a pair of Kyocera 135W units? They're usually a pretty good value for the $.
http://www.solar-electric.com/kyso130wa12v.html
Three would be better, of course, but then you're in to fusing each panel.

The larger Wattage panels tend to be "24 Volt" and would require an MPPT controller to down-convert to 12 VDC system. They also tend to be physically larger and so may be more problematic in mounting on an RV/camper.

Ah, that's a good call. Thanks for the suggestion!

One question though, why would it be necessary to fuse each panel when using 3 and not when using 2?

BB.

Re: Super small solar system on my camper

The fusing is based on the solar panel's ratings... With two panels in parallel, the one panel cannot back feed a shorted panel with too much current. With three or more panels, the "good" panels can back feed a shorted panel and cause its wiring to overheat and fail.

The MPPT vs PWM controller --- With a MPPT controller you can put the solar panels in series and mount them 50' from your RV (RV in shade, panels in sun) and run a reasonably sized extension cord ( Vmp = 17.5 volts * 3 panels vs Vmp = 54 volts * 1 panel's worth of current).

A couple links about designing small PV off-grid systems. The first is just an emergency power unit. The second is a small RV trailer:

• Emergency Power
• nice thread with video from Kevin in Calgary Canada

And a suggestion to get a small Honda eu1000i or eu2000i genset + a good quality AC battery charger. Will probably be way more fuel efficient and cost effective than idling your truck engine. Vehicle alternators are just not designed to quickly or properly recharge a deep cycle battery system.

If you want to see the gory details of optimizing a small genset + AC charger--Here is a good thread with all of the technical details:

• Selecting a battery charger for a Honda eu2000i generator

-Bill

oly884

Re: Super small solar system on my camper

BB. wrote: »

The fusing is based on the solar panel's ratings... With two panels in parallel, the one panel cannot back feed a shorted panel with too much current. With three or more panels, the "good" panels can back feed a shorted panel and cause its wiring to overheat and fail.

The MPPT vs PWM controller --- With a MPPT controller you can put the solar panels in series and mount them 50' from your RV (RV in shade, panels in sun) and run a reasonably sized extension cord ( Vmp = 17.5 volts * 3 panels vs Vmp = 54 volts * 1 panel's worth of current).

A couple links about designing small PV off-grid systems. The first is just an emergency power unit. The second is a small RV trailer:

• Emergency Power
• nice thread with video from Kevin in Calgary Canada

And a suggestion to get a small Honda eu1000i or eu2000i genset + a good quality AC battery charger. Will probably be way more fuel efficient and cost effective than idling your truck engine. Vehicle alternators are just not designed to quickly or properly recharge a deep cycle battery system.

If you want to see the gory details of optimizing a small genset + AC charger--Here is a good thread with all of the technical details:

• Selecting a battery charger for a Honda eu2000i generator

-Bill

Thanks Bill on the info about fusing. I'll most likely end up with just 2 panels to avoid that mess.

Looks like PWM is the way I'll go. I've got a small camper on my truck:

So it sounds like the space necessary for MPPT just isn't there.

Funny you mention the generator as I've been eying a small trailer to build to carry extra water, fuel (gas and propane), as well as a 1kW or 2kW generator. That's down the road a bit though!

icarus

Re: Super small solar system on my camper

A really nice mate for a small set up is an Honda Eu 1000 genny, weighs ~ 19 lbs and uses practically no fuel. Mate that to a Xantrex TC 20 or an Iota 15 amp charger:

http://www.solar-electric.com/ioen12vo15am.html