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Old 09-21-2008, 03:34 PM   #15
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There are some here who have gone into solar having no clue how much power they use, or how little they can get by with. You don't have to be one of those. With a multimeter that has a 10 amp or higher DC measuring capability, you can get an idea.

To get started, unplug from shorepower, turn everything off in the trailer (don't forget the antenna amplifier) and disconnect the cables from the battery negative posts. Put the black meter lead on one battery's negative terminal and the positive (red) meter lead on the cable that went to that terminal.

Don't be surprised if you see current being drawn. This is the sum of your phantom loads, the LP, smoke, and CO detectors, the radio remembering its settings, and any control circuit boards in appliances. This is your base load in amps and you can multiply it times 24 hours to get daily base amp-hours. Amperage (aka amps) is an instantaneous measure of current, amp-hours is the current used over time.

Now turn on one thing at a time, note the meter reading, and subtract the base load to get the amperage that thing draws. Multiply that times the number of hours per 24 hour period you think you will use that thing. Go through the trailer making an electrical use inventory. If you have Fantastic Vents, check them on each speed.

Don't forget to do this with the refrigerator and the water heater. Although they run on gas, they have circuit boards and ignitors, and possibly an electric gas valve. These cycle on and off and you need to measure their draw in each condition. You'll have to estimate how long each will be on vs off over 24 hours to calculate the total use for the day. Personally, I turn our water heater off until about 1/2 hour before it's needed.

I do NOT recommend doing this measurement with an inverter or the furnace fan on. Even if they aren't rated as high as the multimeter's maximum DC current, they have a start-up surge that may exceed a 10 amp DC meter's rating. For the furnace, you can use the manufacturer's rating.

For the inverter, you can use the wattage rating of the 120VAC appliance it will power, divided by 10 (that accounts for less than 100% efficiency) to estimate the instantaneous amperage the inverter will draw from the batteries. Note that the power drawn by an "X" cooking power microwave can be 1.5 times "X". Look at the data plate.

A total instantaneous amperage draw in excess of the sum of your batteries' 20 hour rate requires special handling. For example, a 100 amp-hour 12 volt battery will last from full charge to a defined full discharge 20 hours at the 100/20 = 5 amp rate (or two in parallel, this is a 10 amp rate).

But this does NOT mean it will last 100 amp-hours/25 amps = 4 hours at a 25 amp discharge. At that rate, which is the one used to establish the Reserve Capacity rating, the battery will only last roughly 180 minutes or 3 hours. One way of looking at this is that a battery that's rated 100 amp-hours at a 5 amp draw is only a 75 amp-hour battery at a 25 amp draw. Another way of looking at it is that a 25 amp draw is like a 1.33 x 25 = 33 amp draw when it comes to calculating use out of 100 amp-hours. This is due to something called the Peukert Effect. I won't go into the calculations, but will say that the higher the draw, the worse this effect is.

Two paralleled 12 volt batteries, each supplying 25 amps, is about what it takes to power a little 500 watt inverter supplying its rated 120VAC output. A 2000 watt inverter can draw as much current as an automobile starter and many know how quickly that can drain a battery.

I am not a fan of inverters, but there are some things that need them. Such things are laptop computers and LCD TVs for which there are no 12VDC adapters, satellite receivers, etc. Fortunately, these are low draw items. On the high draw side, I'll include vacuum cleaners. I've never found a 12 volt vacuum that works worth a darn. Just minimize the time you use a 120VAC model on an inverter, or better yet on hard-surface floors, use a dust mop or broom.

The worst thing one can use battery power for is making heat. If you do the math, the effective amperage drawn for a coffeemaker or toaster is mighty high when the Peukert Effect is considered. Fortunately, a pop-up toaster isn't on very long, but I prefer to use a camping toaster over a gas burner.

I'd rather you use an inverter to power an electric coffeemaker than power up a generator right next to me early in the morning. If you're smart, you'll shut the inverter off as soon as the coffee is done and pour it into an air pot thermos. But if you're smarter, you'll boil water for coffee on the stove and pour it into a Melitta or Dripolator, or use the Coleman drip coffeemaker on the gas stove.

When taking inventory of electrical use, you can see how much these high draw of inverter-fed applications increase your expensive solar requirement. You may also be surprised at how much long-duration, low draw things use over a day. Over 24 hours, Fantastic Vents can use much if not all of a large panel's daily output.

Once you've done your inventory, consider the rule of thumb that a horizontally mounted solar panel typically provides 1/4 of its wattage rating as amp-hours per sunny day in the summer. To account for cloudy or rainy days, you may want some reserve capacity, or you may just choose to carry a small generator to augment your solar setup.

By doing these measurements, you can make an informed choice about how much capacity you want AND how much value conserving electricity has for you.
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Old 09-21-2008, 07:33 PM   #16
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Flexible Solar Panels.

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Originally Posted by dufferin View Post
I myself start to look at solar. I am interested in flexible solar panels if they are any good.

Any thought on that?
Hello,
I have used the Unisolar Flexible Solar Modules. They are 15" wide and about 9 feet long and are rated at 68 watts. They are much more tolorant of shading, self stick, very durable, light weight and they can conform to the radius of an airstream. I first mounted them on an airstram about 8 years ago. I used a flat piece of aluminum threshold bedded in silicone and rivited to hold down the leading edge. I am very happy with them. I can't provide you with any photos but you can go to gosolar.com and see them mounted. Good luck.
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Old 09-21-2008, 07:41 PM   #17
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To Road King Moe

Don't know you, never read your posts. Never read such a detailed and accurate description and recommendaton about how to get into solar. Great Job!
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Old 09-21-2008, 07:51 PM   #18
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Quote:
Originally Posted by joecolao View Post
Hello,
I have used the Unisolar Flexible Solar Modules. They are 15" wide and about 9 feet long and are rated at 68 watts. They are much more tolorant of shading, self stick, very durable, light weight and they can conform to the radius of an airstream. I first mounted them on an airstram about 8 years ago. I used a flat piece of aluminum threshold bedded in silicone and rivited to hold down the leading edge. I am very happy with them. I can't provide you with any photos but you can go to gosolar.com and see them mounted. Good luck.
How much does GoSolar.com sell those for do you know?
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Old 09-21-2008, 08:16 PM   #19
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1,500th post



Great 1,500th post RoadKingMoe!
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Old 09-21-2008, 08:36 PM   #20
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Don't know you, never read your posts. Never read such a detailed and accurate description and recommendaton about how to get into solar. Great Job!
joecolao,
Those of us who have been on the forum for years realize that RoadKingMoe is pretty sharp on his electrical/generator /solar info.
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Old 09-21-2008, 08:39 PM   #21
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Thanks Mike! You too Joe and Craig.

Here's a picture of the flexible panels on an Airstream from GoSolar.
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Old 09-21-2008, 10:19 PM   #22
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Mo,
How about a shopping list for what a guy would need to get from them to almost duplicate your setup there,

Thanks, Kevin
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Old 09-21-2008, 11:04 PM   #23
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136 Watts of solar does not get you a whole lot of...
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Old 09-22-2008, 06:31 AM   #24
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Solar stuff

Mo, great picture! That picture is my trailer, a 1977 31 foot. I usually recommend the Blue Sky mppt charge controller, used to like the SCI with the graphics. It too was pretty good and gave my wife a good education at a glance. She got real good at knowing the conditon of our bank. She was able to predict the charge - and adjust the voltage to the power coming in and the load to get a pretty close to the SOC.

LI Pets - I think he charges around $6-7 per watt, I am not sure. I know they are hard to come by.
Joe
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Old 09-22-2008, 09:10 AM   #25
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Kevin,
As Joe says, that's a picture of his setup. It looks like it would be easy to get four of those on most larger Airstreams.

After all the analysis, we decided to forgo solar and put under $1,800 into a pair of Honda 2000s and interface. Our 2001 34 has a lot of phantom loads and we run the Fantastic Vents a lot, both during the day, one at night (with the windows closed and the other vent open unpowered). With AC, two skylights and two Fantastic Vents, there's less room than you'd think for panels. Physically, I could fit longer ones (i.e. 110W) on either side of the AC, but about the longest that would work without shading by the shroud were four 40" long Kyocera 80 (now 85). Even a little shading kills mono or multi (aka poly) crystaline panels (regardless of marketing hype). On top of that, we prefer to park in the shade whenever possible.

We run one of the generators for four hours each day from about 5 to 9PM when the weather isn't too hot. When it is, we have the option to fire both up and run the air-conditioner. The generators have been useful for running tools down at our boat (no power on the docks), and they've been great to have now that we're in our eighth day without electricity at home courtesy of Ike's remnants!

In that daily four hours while the 60A 3-stage converter is charging the (now Lifeline AGM) main batteries, and powering lights and other 12V items, we use 120VAC to charge batteries in the camera, cell phone, FRS and ham radios, and computer. We vacuum if necessary, and used to watch a little satellite TV before we mostly gave up TV. No inverter necessary. Other than the fans, most of our 12V use occurs during that time, coming out of the converter instead of the batteries. We make coffee in the mornings on the gas stove and if we want toast, use can use either the oven broiler or better yet, a camping toaster like we use on the boat.

Just because I believe solar wasn't the best option for us, doesn't mean it isn't for many others. It's absolutely ideal for powering vent fans during the day in a geographic area where there is no shade to park in. It's great for trailers without as many phantom loads, which is especially true of older ones. And it's great for those who don't like generators.
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Old 09-22-2008, 09:31 AM   #26
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Solar is not for all...

I have just installed two 115watt panels (230 watts total) on my Safari 30 and have had the unit out twice since. In full sun I have seen 15-16 amps available (only charging about 2), so I am getting a respectable performance. However, as Lewster said inverters really drink the juice and with a modest solar array it is really suited for the conservative user. We are minimalist, not turning on lights unless really needed and only two fantastic fans at a time etc so it works great for us. We end up keeping our charge above 13.2 all the time which is great.

From a accounting standpoint most would argue that the twin Hondas are a better return on investment. I have the two 2000i's as well, but prefer the clean quiet no gas alternative as it is more why I go camping anyway.
I think to each to his own, but folks need to do the homework on their needs and back into the best off-grid solution.
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Old 09-22-2008, 11:23 PM   #27
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Good Points and thanks Mo and SafariSS for the replies, I have a 5kw generator, so for now I will continue the search for my first A/S. (I sold my 38' Class A Motor coach) and keep reading and getting more selective on what I am looking for :-)

Kevin
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Old 09-23-2008, 09:24 AM   #28
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We have gone as long as 5 1/2 months without electric using solar. We power a laptop computer, 2 lcd tv, vcr, dvd, satellite rec. and dome, vacuum cleaner, microwave and more.
Our converter has been disconnected for about 2 years. Sometimes we will run our rear tv, dvd, vcr with a tiny plug in type inverter instead of the 1750 watt inverter.
I think if you do the math and the long term numbers solar is actually cheaper.
When you buy a generator you still need a gas can and funnel and gas and maintenace.
When you buy solar, your batteries are always up - with a good charge controller you lose less water too. I topped off water to my batteries in 2006 before our trip to Alaska. I had not added water for 3 1/2 years before that.
In my mind solar provides more independance, less maintenance, higher quality charging, improved battery life, achieves a higher capacity charge in the batteries and I don't have to chain it up or drag it out or drag my tow vehicle alternator while trying to charge a couple of 27 series that are dead.
I think if one were to take into account all the hidden costs and inconviences of a generator - solar might be a better option.
The only thing I really cannot run for any legnth of time is the AC. It won't run that or resistive loads ie. electric heaters for any length of time
We use a perk pot for coffee, my wife insists on using the toaster instead of the stove top toaster and her hair blower.
I guess it is all a compromise.

Joe
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