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

[NinerBikes]

RJsfishin wrote:
Thinking in terms of "reality", I love your wording, "possible" 52 amps
But then, I love the 14 hr days too:B.

I saw, for real, a 50 amp day on my 120W portable solar panel. It was June 10th, and I was camping in Montana on the Madison River. I had to leave my bathroom fan on all day, just to make it possible, but, past May through August, if you camp in northern latitudes in the summer, on a sunny day, it can happen with portable aimed panels moved 3x a day.

OP needs to tell us more about the rig he is in, what they use that sucks power, and wifey habits. Obviously, hair dryers, and A/C's and microwaves may be out of the picture, without a generator if in a smaller rig.

[BFL13]

You can get your theoretical AH daily haul for any solar wattage amount for a location and time of year, but that is normally way more of an AH haul than you will use, mostly due to the way battery charging works.

The batteries get high in SOC later in the day and then the only way to get at the solar "going to waste" is to run other loads besides battery charging.

When I did my AH haul testing, I ran loads the whole daylight time so the batteries could not reduce the recorded haul. With MPPT, that also keeps battery voltage low all day further enhancing the amps and so the AH haul. In real life you would not do that since you do want to charge those batteries up before dark and solar shuts off.

In theory or during such a test, the afternoon AH haul is a mirror image of the morning haul. So you can actually just run the test from solar wake-up till high noon and double the haul. But then you have different horizons at dawn and dusk such as mountains or trees that can spoil the perfect mirror image too.

With 130w at 49.3N in May testing, I got 56AH flat, 70AH tilted, and 90AH tracking. It is all proportionate so with 230w now, I would get
99AH flat, 124AH tilted, and 159AH tracking.

All those numbers are good for is comparing set-ups. Then you could say, whatever the actual cloud amount vs sunshine in any day, which set-up would get you more AH, but not be able to say how many.

[jrnymn7]

RJsfishin wrote:
Quote:
the 5-600 AH the panels can do tracking on a good summer day
--------------------------------------------------------------
How does one do this w/ 700 watts of panels ?
My 100 watt panels put out 5 amps max while tracking on a good day.
7 panels x 5 amps = 35 amps max.
35 amps x 8 hrs = 280 - 300 AHs per day,.....a very far cry from 5 - 600.

Where did I go wrong ?

Let's see if I've learned anything regarding solar?

RJ, you are thinking in terms of paralleling 12v panels, whereas Jim is talking about paralleling 24v panels. The difference, the 24's can be bucked down to produce more current, where as the 12's, using pwm, cannot.

[JiminDenver]

What are your sun up and down times mid summer? Ours would be longer but the mountains tend to cost us some day light.

Maybe available 50a would have been better than possible. The only time we can use that level of power is when running the microwave or some other high powered load so I know the 50 amp is possible/ available any time the sun is shining. (again it's only 35a or so the first and last hours)

BFL reports close to the same amps tracking from his 230w/ Eco-w set up. Altitude gives me a few amps advantage but not that much. Amps times the hours of sunlight = man these big panels are sweet.

[RJsfishin]

Thinking in terms of "reality", I love your wording, "possible" 52 amps
But then, I love the 14 hr days too:B.

[JiminDenver]

RJsfishin wrote:
Quote:
the 5-600 AH the panels can do tracking on a good summer day
--------------------------------------------------------------
How does one do this w/ 700 watts of panels ?
My 100 watt panels put out 5 amps max while tracking on a good day.
7 panels x 5 amps = 35 amps max.
35 amps x 8 hrs = 280 - 300 AHs per day,.....a very far cry from 5 - 600.

Where did I go wrong ?

Yeah, those little low watt, low voltage panels are cute, aren't they. 😉

So lets run some numbers. My three panels put out 50a. (17a, 17a, 16a) A good summer day starts at 6 am and ends around 8 pm for me. tracking allows me to take advantage of all of it. That's 14 hours at a possible 50a. That is closer to 700 ah but I trimmed off some for good measure since we will only be getting 35a or so the first and last hour.

Now you might improve your situation by running those 100 watt panels in pairs with a MPPT controller. 😉

[RJsfishin]

Quote:
the 5-600 AH the panels can do tracking on a good summer day
--------------------------------------------------------------
How does one do this w/ 700 watts of panels ?
My 100 watt panels put out 5 amps max while tracking on a good day.
7 panels x 5 amps = 35 amps max.
35 amps x 8 hrs = 280 - 300 AHs per day,.....a very far cry from 5 - 600.

Where did I go wrong ?

[Almot]

pianotuna wrote:

Solar Spread Sheet N8GS

Yes.

Estimating often works better than measuring because measuring needs to be averaged. On estimates you can throw, say, 20% up-margin, and if you're reasonable, it will work.

Some things need to be measured though. Like DC draw of your LP fridge.

If you don't know much about solar and need to ask "how to measure", you probably don't have much general electrical knowledge either. Then you will need - very likely - services of solar installer. They are to be kept a close eye on, the industry is not regulated and many are simply hillbillies with multimeter and pair of pliers, minimal skills and no professional ethics. The best you can do is to figure out the approximate values for total solar wattage, battery bank, inverter, recommended brands and models for those (not for panels - here brand and type are not important) - and put these requirements before the installer.

One good advice was there - if you want to stop making guys in turbans rich, max it up. There is no such thing as too much solar. If 1000W array fits, then put it. Solar guidelines of 60-100W per 1 AH of battery bank are just guidelines. You can't have too much solar. You can always set a limit on solar charger to prevent the current from spiking too high on a bright day. OTH, on a dark day a 1000W array will work as 100W, supplying just enough to get by. Consequently, a 100W array on a dark rainy day will work as a 10W, supplying almost nothing.

Battery bank size is a slightly different matter, they are heavy, need to be taken care of and need to be replaced from time to time. You can't carry more battery bank than you can, anyway. If the goal is living generator-free, then for long-term living your battery bank should be big enough to prevent the charge from dropping below 50%. So with battery bank you also should try and go big, - within a reason.

path1 wrote:
Wife on "power diet". Yep, been discussed many times. "why bother having an RV if we aren't going to use what the heck is in it?" She's got a point...

This is a flawed logic. Like saying "why bother going shopping if you can't afford spending a few grand in one day" (or 10K, or 50K, whatever number describes your situation best).

For some people solar Rv-ing is simply impossible, as you've probably realized. Not because they always camp where it's dark and rainy, but because they want RV to be what it is not - carrying items that don't belong in RV, in terms of size and energy use. This isn't a shore home, you can't have 9000W solar farm there. RV manufacturers aren't helping much, either. They make RVs unbelievably energy-inefficient, with prehistorical lighting, heating and ventilation.

[NinerBikes]

path1 wrote:

smkettner wrote:
Wife runs the battery down? Want to get rid of the gasoline?

Max it out. Post a pic of the roof and figure out how to get 500+ watts up there :B

can't post pic's, haven't sign up yet.

I will measure the space on roof that I have and see what will fit. So far I don't even see a way to run the wires.

(minor side note)...I know this is not good for batteries, but when we do long dry camps in our small Class C, I bring my 6 batteries (all charged) 2 batteries hooked up in RV and my 4 spares and change them out when the little light says they are on 1/4 mark. If we run out of batteries then we live like the chickens in daylight only till end of trip. Sort of fun actually. But that's in the summer not when it's cold. Think hard sided tent.

Wife on "power diet". Yep, been discussed many times. "why bother having an RV if we aren't going to use what the heck is in it?" She's got a point, just wish the power problem could be solved easier.

I use everything in my 21 foot travel trailer... in moderation. Key words, in moderation. They can be taught.

[JiminDenver]

AHA

You DO have an idea of how much power you use. How long did each pair last you? What were you doing to drain them and at what times of the day? What kind of batteries were they?

A power diet, the poor thing. We did that one trip, not acceptable. Nor was listening to a generator everyday. Having the solar means if it has a button and you feel like pushing it.... Well in fair weather anyways. In bad weather we trim back on the big loads and ride the batteries until we have to use the generator.(hasn't happened yet) When the sun does peak out again our three 24v panels tracking are good for 40-50a any time the sun shines.

Even running things like the the furnace every night, microwave, coffee pot, TV all day, even a small air conditioner we are only using a portion of the 5-600 AH the panels can do tracking on a good summer day. It will less once mounted but still more than we can use.

Power diet...heheheh

[mena661]

path1, energy is the easiest thing to supply in a RV. The real problem is water. With enough battery capacity, you can power anything. When I had my 5th wheel, we didn't have a generator. Never needed one. We never camped where it was that hot and we had enough battery capacity to last 10 days without a recharge and we were not power misers either. With solar we could've stayed out indefinitely (well at least as long as the water would last). But most people are willing to haul around 400 lbs worth of batteries nor are they willing to spend the money on them or they don't think that much capacity is needed (ie they'd rather have a generator).

[path1]

smkettner wrote:
Wife runs the battery down? Want to get rid of the gasoline?

Max it out. Post a pic of the roof and figure out how to get 500+ watts up there :B

can't post pic's, haven't sign up yet.

I will measure the space on roof that I have and see what will fit. So far I don't even see a way to run the wires.

(minor side note)...I know this is not good for batteries, but when we do long dry camps in our small Class C, I bring my 6 batteries (all charged) 2 batteries hooked up in RV and my 4 spares and change them out when the little light says they are on 1/4 mark. If we run out of batteries then we live like the chickens in daylight only till end of trip. Sort of fun actually. But that's in the summer not when it's cold. Think hard sided tent.

Wife on "power diet". Yep, been discussed many times. "why bother having an RV if we aren't going to use what the heck is in it?" She's got a point, just wish the power problem could be solved easier.

[NinerBikes]

path1 wrote:

ewarnerusa wrote:
Sounds like the OP hasn't even taken their camper out camping yet.

Absolutely true. Got in home and took care of big stuff... changed out tires, pulled hubs and bearings, load up wives stuff and about ready to use first time.

My posting was an interest in solar because wife runs down batteries in our little Majestic when it's cold out. It is like 1 night 1 battery. This newer TT (her RV) is going to need something because our generator (older Honda) runs on gas and our tow vehicle is diesel. So now I'll have to carry along gas and if we stay longer (1 week is about our camping time at one place) I'll be bringing lots of gas and cans. Solar would solve some of that situation.

NinerBikes said... if your unit does not have all LED lights inside, change those all out first from incandescents."

Yep, bank account shows I did that. But those LED's must be one of the best things that happened to RV's, after installing them.

I did not know solar was as cheap as people commented here, that's a good thing IMO.

Thanks

You may have to go the route some of us went that camp off grid, off pedestal, and dry camp... get a separate charge controller that charges at a 14.8V charge rate, bulk, mount it as close to the batteries as possible with fat gauge wire, and run the device first thing in the morning off the generator, to get the easy bulk charging done quickly before letting the solar panel take over and finish off what the bulk charging PSU or charge controller that the generator started.

Lots for you to learn about recharging batteries, state of charge, and how to measure properly your batteries to determine their health. '' Search'' is your friend.

Put your wife on a power diet.

[time2roll]

Wife runs the battery down? Want to get rid of the gasoline?

Max it out. Post a pic of the roof and figure out how to get 500+ watts up there :B

[path1]

ewarnerusa wrote:
Sounds like the OP hasn't even taken their camper out camping yet.

Absolutely true. Got in home and took care of big stuff... changed out tires, pulled hubs and bearings, load up wives stuff and about ready to use first time.

My posting was an interest in solar because wife runs down batteries in our little Majestic when it's cold out. It is like 1 night 1 battery. This newer TT (her RV) is going to need something because our generator (older Honda) runs on gas and our tow vehicle is diesel. So now I'll have to carry along gas and if we stay longer (1 week is about our camping time at one place) I'll be bringing lots of gas and cans. Solar would solve some of that situation.

NinerBikes said... if your unit does not have all LED lights inside, change those all out first from incandescents."

Yep, bank account shows I did that. But those LED's must be one of the best things that happened to RV's, after installing them.

I did not know solar was as cheap as people commented here, that's a good thing IMO.

Thanks