How to measure how much solar we need?

[path1]

(hope this is right section) Brought home TT last month and now have basics taken care of and RV is road ready. Now starting to think about bigger long term projects.

One project is, we would like to get some solar. Which I know nothing about. I suspect the first step is figuring out a starting place for this project. So I'm assuming that finding how much we actually need might be a good starting spot.

Is there any meter or way to measure to figure out what we need? I'm thinking, if we know how much we use, we could determine how big or small of solar project would be. Thinking in my mind about some type of elec meter that we see how much we use in a week.

Or maybe better yet; how did you figure out how much solar you needed?

Anybody care to pass on any good links or info on RV solar?


Thanks

[ewarnerusa]

Sounds like the OP hasn't even taken their camper out camping yet, so it is impossible to know how many AH they'll use and need to replenish daily. Solar is a great DIY project and you'll get the most out of it by learning how every component contributes and can be maximized, including the batteries. So I suggest basically as pianotuna mentions as a rule of thumb => 100+ watts of solar per battery for a starting point, but build your system capable of expansion.

I installed solar before I ever took our TT out for the first time. I installed 280 watts of 12V panels and have only upgraded the 2 12V batteries to 2 6V GC batteries.

[NinerBikes]

Alternative method.


Charge your batteries fully, 100% before leaving on a trip. Measure voltage disconnected. Measure the specific gravity after doing so, and log it down per cell. Note the time you arrived at the campsite and started running strictly off the batteries.

24 hours later, shut all electrical off, take a specific gravity reading, and take a voltage reading with everything disconnected. Compare. That will give you a rough State Of Charge from 100% down to 50%. Your specific gravity will tell you more, % wise, what you've consumed, based on the total Amp hour ratings of your batteries.

Go from there...but first, if your unit does not have all LED lights inside, change those all out first from incandescents. Next might be a no fan heater like a Olympic Solar 6 or solar 3 or solar 8. Next after that might be a low amperage draw LED TV. Plenty of ways to cut amps consumed, though in the end, its probably way cheaper to just add more watts in solar panels. However, LEDs are best bang for the buck in dropping your amp hours consumption quickly and effectively. Do a search here on ¨48 SMD warm white LEDs¨

120 to 200 watts of solar panel is a good start if you are going through 25 -45 amp hours in a 24 hour period. You;ll burn a lot more than that in winter time if you keep those stock incandscent bulbs, though. Those bulbs are pretty much a ''Must go'' item if you want to keep consumption down on long fall, winter and early spring nights.

[jrnymn7]

My power needs are constantly changing; heating and air conditioning being the biggest game changers; so I'm trying to plan for both the bare minimum, and absolute maximum power requirements. I'm going with two (portable) 140w panels for four 6v batteries, so I have options... use one or two panels, on a small or large bank.

I determined my energy needs using a kill-a-watt meter, trimetric meter, and some simple calculations based on manufacturers' ratings.

[Snowman9000]

Agree with Rjsfishin's first post. In earlier times, solar was very expensive, it made sense to do an audit and a lot of figuring. Now, you can install a pair of 100w 12v panels, mounts and hardware, 8 AWG wires, fuse or better yet an audio supply breaker you can trip for service, a cheap PWM controller (read and or ask here), some terminal ends for wiring, and a cheap meter, all for less than $400 DIY.

If down the road you feel the need to go big, the 8 AWG wire, breaker, and controller will be replaced. You'd be out say $50. IF.

That's my generic recommendation.

[RJsfishin]

I guess I did solar for a hobby, or just a project.
It is absolutely worthless here in OR on the coast,....even in the summer
we lucky to get a 1/2 day of sun.
But for 3 months each year in AZ, it not only works superbly, it lets me park w/ "The Big Boyz":)

[path1]

OP here.... Thanks for all the input. I've got a lot of reading to do.

Do you even camp in the sun up there in the PNW?

Well, I think we do. But there has been times that we drive 2 hours to the other side and camp 2 or 3 days. Can say that we have a very small 5 watt on top of the a/c cover that doesn't keep up with the battery drainage with nothing on (except c/o alarm).

This solar set up would be for when we go south or east

I do remember chuckling about an old article of how we have disproportionate amount of sales of sun glasses. Turns out it is not from to much sun. It's people forgetting where they put them, as they are not needed that much. So they end up buying another pair for the next time the sun comes out.

[mena661]

smkettner wrote:
Consider 100 to 200 watts as minimum for the effort. Do you even camp in the sun up there in the PNW?

X2, if you have little to no sun, don't bother with solar. You'd have to size it on the huge side to get the small amount of sun you would get.

[time2roll]

Consider 100 to 200 watts as minimum for the effort. Do you even camp in the sun up there in the PNW?

[2oldman]

Forum members solar
Solar basics

[MEXICOWANDERER]

I remember my "careful calculations" changing maybe 120 times the first two months I started using solar. I added. I found ten excuses as to why I just had to use something else, so more panels, and more justifications. I remember doing an Easter Egg Hunt to find more places to stuff batteries.

Mr Wizard's meter idea is tops. But don't fool yourself into kneeling before the altar of amp hours - you'll never live that way. Live normal, have a heart attack when you read the amount of amp hours you use, then go with the flow.

[donn0128]

Lots of opinions, so heres mine.
250 watts of panels, 4 to 6 golf cart batteries should allow you to sit, even on the wet side 3 to 4 days using the furnace sparingly, a little TV watching at night and lights as necessary. The key is not how much, but how well balanced your system is.

[SteveAE]

Path,

Here is a link to AM Solar's education pages that you may want to look though.

Steve

[pianotuna]

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.

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 N8GS

For a nice explanation of solar, try this link:

Golden rules of solar

[korbe]

In conserve mode, we use about 20a per day. That is what I would start with. A number.

[RJsfishin]

You can't depend on the sun.
In full sun like AZ, a couple 3 hundred watts goes a long way.
Start small, 2-3 hundred watts, keeping the plan so you can easily add a couple hundred more if needed (wanted)

I am not a "more battery" fan ! They are very heavy, and are like horses eating hay.