[VAC] Re: Sloar, was Equalizer

[Jim Dunmyer <jdunmyer@xxxxxxxxxxx>]

Daisy,
  Here goes:

It appears to me that many, if not most, folks ignore the advice given 
on nearly ALL "solar" sites and just blindly buy panels and bolt 'em to 
the roof. It often leads to disappointment and/or excessive expense. 
Newbys or wannabes usually ask "how many panels do I need?" as their 
first question, which should be the LAST question to be asked and 
answered. Here's the deal if you want the most cost-efficient and 
workable system:

First, you must determine YOUR usage. You can use the worksheets from 
the solar sites or simply do your own. Here's the problem: many people 
don't understand the terminology, especially Amp-Hours (AH). Think of 
"amps" in terms of "gallons per minute" of water flow. If you flow one 
gallon per minute, in one hour, you'll have 60 gallons. If your 
electrical fixture uses 1 amp, it will use 1 AH in an hour. Note that it 
is NOT correct to say, "it uses 1 amp per hour", as an Amp is already an 
expression of rate of  usage. (I spent a couple of hours with our 
neighbor at the Escapade until she finally understood this concept. That 
was AFTER she attended a seminar on the subject!)

You can either MEASURE the current draw (amps) of each fixture or use 
the standard numbers. Most common RV lighting fixtures use #1141 bulbs, 
which draw about 1.5 amps/each. Those fixtures often have 2 bulbs, so 
draw 3 amps when on "high". Multiply the "amps draw" times the estimated 
hours of use to get AH, and put those numbers in a worksheet. It might 
look something like this:

Main light:    3 amps     4 hours/day    12 AH
Kitchen light  3 amps     1 hour/day      3 AH
Bath light     3 amps     1 hour/day      3 AH
pump           5 amps     15 minutes/day 1.25 AH
TV             3 amps     3 hours/day     9 AH

Total usage                               28.25 AH/day

Because MAKING electricity by solar panels is expensive, it's always 
wise to look at possible conservation measures. Replacing the "main 
light" with a flourescent fixture that draws 1.7 amps will save at least 
5 AH/day. Replacing the "low" bulb in a 2-bulb fixture with a #67 will 
give you a light that draws only about 1/2 amp instead of 1.5 amps when 
on the "low" setting. And, of course, don't leave unused lights "on".

So-called "phantom loads" shouldn't be neglected. I have over 5 AH/day 
in our trailer, 1/3 of that is the pilot light that tells us that the 
pump is "on". (!)

Once you have a chart of your usage, take a look at your battery 
storage. Most batteries have an Amp-Hour rating; the common Group 27 is 
rated at 105 AH, the Group 24 is 85, a Golf Cart battery is 200+ (you 
need 2 to make 12 volts) As it's wise to avoid discharging your 
batteries below 50% on a regular basis, you should have a decent reserve 
for the inevitable cloudy day(s). In the case above, a single Group 27 
battery can carry us for at least a couple of days w/o deep discharging, 
but more would be better if we can fit 'em in someplace.

Only now can we look at panels to provide the electricity. A "50-watt" 
panel will provide about 3 amps during the peak 4 hours of the day and 
half that for another 4 hours. A "75-watt" panel will do 4 amps peak. 
Adding the numbers, we see that a 50-watt panel will do about 18 AH/day, 
a 75-watt one will give us 24 AH/day. Looks like 2 50-watt panels will 
do the job.

FYI: a 50-watt panel is about 14" X 48", a 75-watter is 21" X 48". (I'm 
going by memory, so might not be exact)

You should buy only 36-cell panels ("cells" are those dark blue things 
on a panel), don't buy so-called "self-regulating" panels with only 33 
cells. A charge regulator is also required. FWIW: I have a real cheapy 
regulator that cost under $30.00, IIRC, and it works fine. The Solar 
Boost 2000 is very desirable, as it has technology that gives you more 
than rated current from your panels, adding as much as 25% output. (It's 
not magic, but don't ask me to explain it here!)

You'll note in the usage table above that I didn't mention using an 
inverter to provide 115 VAC. The reason is simple: although you can 
install a large inverter to run a coffeepot and/or microwave, you will 
pay VERY dearly for the privilege. I won't go into the calculations at 
this time, but be aware that making a pot of coffee will use at least 
25-30 AH by itself. Popping a bag of corn in the microwave will nearly 
flatten a pair of Group 27 batteries. A small inverter to run your 
laptop computer is OK, we do that all the time.

People with big 5'ers or MHs install a half-dozen GC batteries and cover 
the roof with solar panels. THOSE folks can use an inverter pretty much 
as they please.

An eMeter or equivilant is a very desirable addition to your electrical 
system. Think of it as a "fuel guage" for your batteries, as it tracks 
actual AH use and charging from/to your batteries. An accurate voltmeter 
is a mandatory minimum to get an idea of your battery condition.

The reason many folks don't use solar in the first place ("I'll just buy 
a generator, I understand that") is because they don't do their 
homework. Electrical concepts are pretty foreign to most people, and 
aren't always well-explained in the books and web sites. However, it 
really isn't that complicated, and the usage table (see above) won't 
take you more than 15 minutes to compile for YOUR rig. The biggest 
problem is TRUSTING your calculations. You can't SEE all this stuff 
happening, you have only a fuzzy understanding of what's going on, and 
you're afraid to commit money based on what you know/don't know.

There's several points that might help alleviate the fear of the 
unknown: Many folks are doing it, so it MUST work. And, solar power is 
modular, if one 75-watt panel isn't enough, you can add more. Don't make 
the mistake of covering your (limited) roof real estate with too-small 
panels, however. I'd probably recommend that we try to get by with one 
75-watt panel in the case above and add a second if need be. It'd be 
less finacially risky than installing 2 50-watt panels and finding it to 
be a bit short. Of course, even an "inadaquet" solar system will extend 
your boondocking stays.

If you want to take some of the mystery out of it, get the eMeter first 
and watch it during a weekend of boondocking. Look at some of the web 
sites provided by solar vendors and definitely read Fred's treatise on 
the subject at http://www.phrannie.org

Rest assured that solar DOES work and work well. We've stayed as long as 
3 weeks w/o moving, and had as much charge in our batteries as when we 
arrived. Our usage is pretty light, as we have only a 5" TV that draws 
less than a reading light and our main overhead light is a flourescent. 
I did the calculations above and arrived at 20 AH daily usage for our 
rig. The eMeter confirms it, and the batteries are normally pretty well 
fully charged by 1:00 PM. We have no noisy, stinky generator to fuss 
with or bother the neighbors.

Lest anyone think I'm one of those tree huggers who think we should 
replace nuclear power plants with solar farms, I'm not. Here's some real 
numbers to chew on:

Our little solar system would cost about $1200.00 to buy and it 
generates 30+ AH/day when it's sunny. That amounts to less than 11 KWHR 
(kilowatt hours) per month. We're probably about average in our home 
usage, but we consume about 700 KWHR/mo. in our house. A typical 
home-sized alternate energy system (often comprising solar AND wind 
power) costs about $20,000.00 and provides less than our usage; we'd 
have to do some serious conservation to get by.

If you have any further questions, fire away, I'll try to help.

                                   <<Jim>>