Some Basic Questions Re Solar - Fiberglass RV



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Old 06-12-2019, 12:43 AM   #1
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Some Basic Questions Re Solar

Hi all.
It’s time to go solar. I’ve done everything I can to conserve energy: I have 2 deep cycle batteries which support all LED light bulbs, a 12 volt stereo system, a 12 volt ceiling fan. The refrigerator is propane powered. We try to be good about turning off the water pump. we charge our mobile devices using 12 volt outlets in the cabin.

I believe that I initially need to determine my energy requirements. And i’d appreciate some suggestions on how I can go about this.

Most of our energy consumption takes place in the evening. During the day, we’re out and about till late afternoon. So, unless we leave something on by mistake, there’s a minimum amount of demand.

I’m thinking that during warmer weather the ceiling fan will be going all night long. The audio system is turned off at bedtime. We really don’t have a lot of lights going even at night. We do need to power a CPAP unit.

Should I get a voltage meter? How best to connect it inside the trailer? How do I collect & analyze usage info?

Is there another device I should use?

Once I get the information, how do I translate it into solar panel wattage needed?

Do I even need to bother calculating my energy needs? I see that manufacturers, such as Escape, install a 160 watts. That seems to be the sweet spot. Should I just get a system with couple of 80 watt panels, and see if the batteries will last the night, and add more panels if need be?

What say you?





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Old 06-12-2019, 02:35 AM   #2
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Hi Jane, you've ask a lot of questions but you didn't say if your power use has ever run your batteries down enough to make your items unusable. I'm not going to get into the ins/outs of solar as others have all the specs and they will chime in soon. If your batteries are working for you with the draw you use, it may just be a matter of adding a small portable/suitcase type solar panel to top them off and you're good to go, the kiss thing .
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Old 06-12-2019, 02:52 AM   #3
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Originally Posted by Borrego Dave View Post
Hi Jane, you've ask a lot of questions but you didn't say if your power use has ever run your batteries down enough to make your items unusable. I'm not going to get into the ins/outs of solar as others have all the specs and they will chime in soon. If your batteries are working for you with the draw you use, it may just be a matter of adding a small portable/suitcase type solar panel to top them off and you're good to go, the kiss thing .
I can go several days without having to recharge. I added the second battery to run the CPAP machine. The ceiling fan is new, and I don’t know how it will effect the batteries. I’d like to expand my entertainment capabilities with a TV.
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Old 06-12-2019, 07:18 AM   #4
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jane, how are your batteries wired? are they connected to each other?

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Old 06-12-2019, 07:26 AM   #5
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Solar

I also would suggest you get a portable solar setup. One with an extension cord that will allow you to park in the shade and still charge the battery.
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Old 06-12-2019, 08:05 AM   #6
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Originally Posted by Jane P. View Post
... We do need to power a CPAP unit.

Should I get a voltage meter? How best to connect it inside the trailer? How do I collect & analyze usage info?

Is there another device I should use?
See this recent post:
Understanding the the battery power levels

If I needed to power a medical device on my RV battery then I would opt for a good battery monitor that uses a shunt. I use the Trimetric but there are less expensive options. In its most basic mode it is like your car's gas gauge, showing percent full. (Except be sure to stay about 50% at the very minimum).

The shunt is wired in series (in line) with the negative side coming off the battery so that all current goes through it, then the meter detects, measures and records the current (both charging and discharging). It should be installed by someone who has an understanding of proper DC wiring practices. Refer to the device installation instructions - for the Trimetric see:
http://www.bogartengineering.com/wp-...ions062017.pdf

Those instructions are good to review for any similar device. The web site also has much more helpful information.

Living with a meter like this over a period of time will give you a good feel for how much power you use, how much charging takes place, how long you can go with little sun or no charging, etc.
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Old 06-12-2019, 08:06 AM   #7
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We placed a 90 watt panel on the roof, and have another 90 watt panel that is movable if we need to chase the sun. Normally the rooftop panel is all we need and we only have one 12 volt 155 amp hour golf cart battery.
I don't use the humidifier with my CPAP so mine only uses about 7 amp hours per night, but I suspect everyone has different draws depending on settings.
Our fan uses about 3 amp hours at max speed, but we rarely ever use max speed.
The disadvantage of rooftop solar is that you can't aim it directly at the sun if stationary, and you might be parked in the shade. One of the pros is that it's always there, and it's unlikely anyone can walk off with it.
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Old 06-12-2019, 08:36 AM   #8
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There are a few ways to do it. Depending on how much power you use and where you live (how much sun), often just buying a 100W panel will do it. Done.

But if you want to make sure you get what you need, there are a few options. There are online solar calculators (google that phrase) that have general estimates of what some common appliances draw. You enter how many of them you have and how many hours you plan to run them, and it tells you what it thinks you should buy. These are pretty nice if for no other reason to that look at the gigantic draw of some appliances. It may make you decide they aren't worth it. Go Power. Play around. I've found the results tell you to buy way more system than you need. They are trying to sell you something.

I don't have the actual solar charging figured out yet, but for determining your draw, things to know:

It's easy to find the watts of most appliances, either on the item itself, in the owners manual, or online. Take the watts for the device, multiply by how many hours you run it, then divide that number by the volts (12vDC or 120vAC). That's amp hours. Add all those up per day and you know your power draw each day.

Batteries should not be drawn below 50%. So you need to decide how many days you think may go by with no solar charging (rainy day etc). Your battery capacity (in amp hours) needs to be double what you use for that amount of time. If your calculations from above say you'll use 70 amp hours per day, and you think you ought to be able to go 2 days without a charge, that means your needs for those two days are 140 amp hours. So you need 280 amp hours of battery.

There are also monitors that will tell you exactly what you're using, which you mentioned. I don't have experience with those yet.

My power needs are so low, I've gotten away with winging it. I have a 90W panel and one 12V battery usually between 80-100 amp hours. I didn't do any calculations, I just keep my use low and keep the panel out and it's been fine. But I'm going through the process above, the "right way", right now. I want to put panels on my roof and figure I should do this right, if no other reason than to learn the right way.
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Old 06-12-2019, 08:50 AM   #9
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Originally Posted by starbrightsteve View Post
I also would suggest you get a portable solar setup. One with an extension cord that will allow you to park in the shade and still charge the battery.
While I love to have a portable along as a backup for conditions like you mention, I would always first go with a roof mount so the charging happens all the time and there is no need to set up the portable all the time.

Mind you, my trailer was recently broken into and they stole my GoPower portable panel, so I need to get another.
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Old 06-12-2019, 09:09 AM   #10
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Ooh, that's too bad to hear.

I agree and disagree...for charging purposes, rooftop is the best start. They're always there, charging, and then if you need more you can supplement with portable. For dipping your toes in the water of solar, portable panels are an easy, no-installation introduction. No permanent mounts, no holes, no paying anyone. But I agree, it's just one more thing to haul, one more thing to set up and break down every time.
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Old 06-12-2019, 09:38 AM   #11
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Jane,

You already, sort of, know what your consumption is. If your batteries are discharged in a couple of days, with careful use, for instance, that is your consumption.

Get a simple digital volt meter that plugs into the cigarette lighter (Walmart is a good place to find these). When the batteries get to 50% discharge, or about 12.2 volts, you have reached your battery capacity, which equals your combined loads for that amount of time.

Determine what your battery capacity is, as listed on the battery. Use 50% of that number and you then have your use over time.

Try to size the solar to make that much power, plus about 25%, in the period it took to discharge the batteries, say, two days, or whatever it is.

Rooftop solar will produce less than half of its rated power if placed flat on the roof. A suitcase system can be manually tracked, but required more work and attention. So, for a rooftop system, you would need a system that had an output equal to your consumption, plus 25% for charging losses, and a system about 60% bigger than it's listed output because it is placed flat on the roof. These are rough numbers, but get you in the ballpark.

Solar output varies continuously all day and does not work even with a small bit of shade on the collectors. Early and late in the day, the output will be less than in the middle of the day, so it's a bit of a guess on sizing. Also, there is only so much room on the roof. So, go as big as practical. Or, get a suitcase system and see how it works out for you. Then you'll know if you need twice as much, or if you have enough, or what, and you can adjust the size as needed. Having a rooftop system is nice, even if it doesn't produce it's full rated output, because it is always there doing something, whereas a suitcase system only works when you get it out and set it up.

What size batteries do you have? Are the batteries in good condition?

It sounds like you are being very careful with your usage. That's good, but not always fun or practical. Usage is bound to go up if you have the capacity, but you must first meet the load requirements you have. Then, if you have some reserve, you can be less careful, or use it in other ways. So, try to go big with the solar, if you have the room.

Keep in mind that with a rooftop system, you will have to park in the sun to make it work and you will have to keep the panels clean to get the best performance.
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Old 06-12-2019, 09:59 AM   #12
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I think your camping habit is a big consideration. I'm on the move a bit, and the camper recharges from the tow vehicle. So for simplicity I just got a portable solar panel/charger. Yes its another thing to setup, but if I'm only on site for a night or two I don't need to bother. If you are in one location for extended periods of time (without hookup) then getting the right size is more important. There is a lot of arithmetic you can do to figure out the right size, or just start with a small portable one, from a company that has the accessories to expand it, and permanently mount the panels when you have enough.

Or just go big from the start and get a few hundred watts all at once.

I'd start with a smallish portable one and expand as necessary, then mount on the roof when you know it works out.
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Old 06-12-2019, 10:11 AM   #13
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My usage is significantly higher in cold weather when I'm running the heater. It's a big draw.

We just got back from Yellowstone. I left the generator at home. We had reservations, but all the sites were taken and ours was in the shade.

I hooked the truck up to the batteries with jumper cables, as I usually do when we are getting low on battery power, and idled the truck for a while. Along came the "volunteer" and told me they do not allow trailers to be charged from the tow vehicles. Running a generator is OK, but not an idling TV. So, that night I left the heater off and we left the next day, as scheduled.

By the time we got to the next stop, the batteries were charged from the seven pin. We get by just fine for a few days, in reasonable weather, just by towing. But even in warm weather, a week or longer stay requires us to do something.
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Old 06-12-2019, 01:52 PM   #14
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jane, how are your batteries wired? are they connected to each other?

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Wired in parallel

They’re 12 volt batteries.
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