According to the best medical research available, the only
sure cure for these fatigue and 'googly eye' afflictions is
a few days of fishing. Since Dan's Dad has a vintage 1968
Starcraft pop-up camping trailer available for use, Dan
figured that installing a simple solar power system in the
"Sally Ann" and writing a web page about it would be a great
way to catch the late summer damselfly hatch near Walden,
Colorado and the October caddis hatch in Lowell, Idaho and
still pretend that he was actually working the whole time!
System design considerations
How much power do we really need?
(and how we addressed them)
Not a whole lot for us--we go camping so we can flyfish,
and get away from all the modern contraptions and their
noise. We need lights at night, a portable radio/CD boombox,
and battery chargers for our 2-way radios, digital cameras,
and GPS units. Bright lights are essential if we are tying
trout flies in the evenings. If we bring our vintage Grumman
canoe, we do use some serious power with the electric trolling
motor--more on that later.
There have been other people at certain campgrounds we've
stayed at recently who seem to need satellite television
dishes, big screen TVs, electric Mister Coffee machines,
electric refrigerators, and all kinds of other stuff that
we are trying to get away from. They put all this stuff
right in their campers! We are boggled by this attitude
towards wasteful power use, and the noise, fuel cost, and
maintenance factors of running an infernal combustion engine
at the edge of the wilderness. Perhaps we are Luddites, but
we do like our peace and quiet. That's why the 'Sally Ann'
is powered only by (silent) solar power, with the option
of a (again, silent) shore power connection.
12 volt DC versus 120 volt AC power systems
A few years ago, just about everyone that powered a camper
(or small cabin, for that matter) from solar used a 12 volt
DC (12 VDC) system--that's a direct feed to your
cigarette-lighter-plug gadgets off of a 12 V battery or
bank of batteries. Problem is, 12 volt power has lots of
losses in the transmission, and to reduce the losses things
need to be wired with very thick, expensive wire that's hard
to work with. That's why most 12 VDC lights and appliances
are very small...a typical car cigarette lighter plug and
outlet can't handle much power before becoming hot from
electrical resistance and melting your dashboard, or
(hopefully) blowing the fuse first.
In the last 5 years, 'power inverters' have dropped
dramatically in price and become widely available--the
internet, truck stops, the local NAPA auto parts shop,
everyone sells these gadgets now for cheap. Most are
around $150 or less. They convert 12 volt DC power into
120 volt AC power, also known as 'house current.' That's
what's available at every electrical outlet in your house
in town! If you are not in the USA, inverters are available
worldwide for every different electrical scheme, you just
have to buy the right one for your country. With an inverter,
instead of buying all new light bulbs, boom boxes, toasters,
radio/GPS/camera battery chargers and such for your 12-volt
camper, you can use the stuff you already have, or buy new
ones from K-Mart for cheap. A typical (and highly efficient)
compact fluorescent (CF) light bulb for 120 volt AC house
current will cost you only a couple bucks at Home Depot or
the local supermarket. A 12 volt DC version will cost you
at least $10 per light bulb, be available only online or at
a specialty RV shop, and probably won't be built by a major
US or European manufacturer from whom you can obtain a refund
if it doesn't work right.
We decided to go with 120 volt AC inverter power for the Sally
Ann. A quick trip to K-Mart, and all our lighting and appliance
needs were met at low cost. Buying all those gadgets again for
12 volts DC would have cost far more than the cost of the
inverter! We ended up with a 1500 watt Whistler inverter,
much more than we need, but it was available cheaply used.
If we were to actually RUN a 1500 watt load from it, our
little marine deep cycle battery would be dead in less than an
hour. To pick the correct size of inverter, total up the power
draw in watts for all the lights, appliances, and other gadgets
that you might be running all at the same time, and pick an
inverter with a 'continuous' power output of a couple hundred
watts above that. 'Surge' power output that's advertised is not
a useful spec--if you ever reach this number in the power you
are using, your inverter is too small. Also, be sure to follow
the inverter manufacturer's recommendations for wire size from
your battery to the inverter--this wire needs to be both thick
1500 Watt Whistler inverter installed under counter, to keep
it safe from water drips, bourbon and beer botches, chili spills,
and tipsy flyfishermen.
Power versus Work
Folks often get confused about the correct units in which
to measure power consumption. Volts, Amps, and Watts
measure work, not power--power is measured over time. It
doesn't matter that the big TV in your camper uses 200
watts. The real issue is how many hours per day you have
the thing on! So, the proper units to use are watt-hours
or amp-hours (A/H), not watts or amps. Ten amp-hours of
use means that you ran your boombox that draws one amp
for 10 hours--or that you ran your big TV that draws 10
amps for one hour. You get the idea.
Appliances and lights are always rated in watts, and they
are always marked on the back for how many watts they draw
at full power. Batteries are rated in amp-hours of capacity.
The only math you need to do for designing a simple RE system
is converting watts to amps. Then you multiply by time to get
amp-hours. Watts = amps x volts, and amps = watts / volts.
So, a 60 watt light bulb powered from your inverter will
use 1/2 amp at 120 volts AC (60 watts / 120 volts =
0.5 amps). But your battery is 12 volts! So to power this
bulb, you need to do the math for what's really coming out
of your 12 volt battery-- 60 watts / 12 volts = 5 amps.
Choosing the battery
The Trojan CB-27 battery we installed in the Sally Ann stores
100 amp-hours of power. BUT you never, ever want to take any
battery down below 50% of its capacity--most batteries can
only do this for you a couple dozen times, then they are
ruined. For long battery life (2 years or more) don't take
your battery down by more than 30% of capacity. If you can
afford to replace your battery every year or two, you can
be more abusive.
The 30% discharge guideline says we can frequently draw down
the battery on the Sally Ann by 30 amp-hours, with occasional
drops to 50 A/H (half capacity). So, for decent battery life
we could run that big 60 watt light bulb for at most 10 hours
to take our battery down to half capacity (100 amp-hours / 5 amps = 10
hours.) If we ran our cute little 1000 watt electric heater
from inverter power, the math would be: 1000 watts / 12
volts = 83 amps-- a bit over half an hour to the
'battery critical' condition of 50% discharge. Cold Cranking
Amp (CCA) ratings on batteries are useless for measuring
storage capacity. CCA is for car engine starting batteries,
not RE systems. The number you need to look at is amp-hours
(A/H). You might have to ask your battery dealer for this
information--it may not be printed on the battery.
You can combine multiple batteries for more capacity, if
you have the space. Standard 'marine deep cycle' batteries
are a good choice for a tiny system, they withstand deeper
discharge much better than car engine starting batteries.
For a larger camper or a cabin, you might consider golf
cart batteries (T-105s), which have to be installed in
pairs because they are 6 volt, not 12 volt. Home or cabin
power systems often use 6 volt L-16 batteries, which have
lots of capacity and are extremely durable--but they are
large, heavy and expensive, and usually much more than can
be fit into a camper. So-called 'gel cell' batteries have
the advantage that they can be tipped over without losing
electrolyte, but in general they are much more expensive
and fragile than the run-of-the-mill 'flooded lead acid'
battery we used in the Sally Ann.
Trojan CB-27 battery in the battery box, with lid removed.
Inverter is mounted above it. 100 amp-hours capacity. Note
how thick the inverter wires are -- this is essential. The
battery box is screwed to the floor so that nothing can move.
A 60 watt incandescent light bulb wastes more power as
heat than it turns into light. Think of any incandescent
bulb as a space heater that produces light as a byproduct!
Fluorescents (FL) and compact fluorescents (CFs) are FAR
more efficient, and they should be the only bulbs you even
consider for an RE power system. LEDs are also an option--they
are not very efficient (despite many advertising claims),
but they do emit most of their light in one direction,
eliminating the need for reflectors. Our lights are a
pair of 7 watt compact fluorescent (CF) bulbs, plus a
CF fly tying lamp that uses 13 watts, for a total of
27 watts with all lights on. That's 2.25 amps at 12 volts,
so we could then run all these bulbs at the same time for
13 hours without damaging the battery (30 amp-hours / 2.25
amps = 13.3 hours.)
The solar panel
We didn't want any glass in our solar panel because of
long drives on bone-jarring dirt roads, so that ruled
out all the normal models intended to be mounted on
houses. My remote house in the mountains runs on such
solar panels, but we feared breakage during our driving.
We also did not want to permanantly mount the panel to
the roof of the trailer--we're lucky the old girl doesn't
already have a leaky roof, and putting holes in it sounded
like a bad idea. Plus, a flat mounted solar panel doesn't
do much good unless you are near the equator--for maximum
power generation, solar panels should be facing directly
at the sun.
There are some really cool flexible solar panels available--you
can roll them up for storage, and even mount them on the
upper deck of boat and walk on them--but they are much more
expensive than standard models. For solar panels, it all
boils down to dollars per watt. Standard, 'single-crystalline'
or 'poly-crystalline' panels mounted under glass for homes
run about $5 per watt right now. 'Amorphous' panels are up
around $6-8 per watt, and flexible amorphous panels can reach
$10-12 per watt! Amorphous panels have the disadvantage of
making much less power per square foot than single or poly
crystal, but have the advantages of not being so brittle and
fragile, can be built into flexible panels, and are affected
less by partial shading.
We couldn't see the logic in paying more for one flexible,
roll-up solar panel than what the pop-up camper cost us
in the first place! So, we compromised--our solar panel,
made by Innergy and mostly used in remote river gauging
stations and other telemetry applications, uses single
crystal cells embedded in fiberglass instead of under
fragile real glass. It gives 30 watts of power in full
sun, and is only 19" x 36". It came in at $5.97 per watt,
much better than roll-up models, and it makes more
power for its size than amorphous designs. We built a
simple aluminum frame for it that we can prop up near
the camper after we arrive at a remote campsite. Shading
is a big factor in solar panel output, even one branch
shading part of a solar panel reduces output to nearly
nothing. With the 25 foot extension cord, we can
put the camper in a shady spot and set the panel in the sun.
Our glass-less, fiberglass embedded solar panel with homebuilt
aluminum frame. The tree shading shown in the picture is
BAD--the panel is hardly putting out any power because of
Solar panel wire sizing
Remember that we discussed earlier how difficult 12 volt DC
electricity is to move around compared to house current?
Proper wire thickness is essential in connecting solar
panels or else much of the power coming in will be lost
as heat (just like in a toaster, only the solar panel
wire won't even feel warm to the touch.) Wire losses
of around 5% of your panel's output are acceptable. Rather
then go into all the math, the easiest way to do it is Google
up 'wire size chart' online, or get a printed one from any
large renewable energy dealer's catalog. Simply look up
your panel's output in amps at 12 volts, and read the
maximum distance you can go on certain gauge of wire.
Extension cords are great for this, but be sure to check
on the package what the actual wire size inside the cord
is. Generally, 10 or 12 gauge is the largest available at
the hardware store...get the best and thickest you can
afford. The more power your panel puts out, the thicker
the wire you need and the shorter the distance you can
go. For us, a nice 25 foot, 10 gauge extension cord cost
about $25 and has very little loss at only 2.5 amps from
our solar panel--we could add a couple more solar panels
later and still be able to use this cord with under 5% loss.
Solar panel controllers
Large home-sized solar power systems always have controllers
to keep the battery bank from overcharging. In our tiny system,
we did not include a controller. The reason is that standard
'flooded lead-acid' batteries are not damaged at all by
'overcharging' -- defined as continuing to pump electricity
into the battery after it's full. All that happens is that
the battery electrolyte level drops more rapidly as the
battery bubbles. If the electrolyte level drops below the
top of the plates, the battery is ruined. It's important in
any RE power system, with a controller or without, to check
the battery electrolyte level monthly and refill it with
distilled water when it gets low. In our case -- we'll
never have that battery bubbling on a fishing trip, we
use too much power every night. When the trailer is parked
at home waiting for the next trip, we plug in the solar
panel for a day or two each week to keep the battery
topped off. If your battery is bubbling, it's no problem --
but don't smoke around it, and be sure the hydrogen is
properly vented to the outside. In a camping trailer power
system, the only time the battery might be bubbling is when
the trailer is in storage for the winter with no power usage.
If you for some reason chose a gel cell battery, a controller
is REQUIRED, and will cost you $50-100.
Back to input vs output
We just did all that math about how much you can draw down
a battery. Now look at our input from the solar panel (30
watts, 2.5 amps) versus the output from our lights (27 watts,
2.25 amps.) Here in Northern Colorado, a good clear day gives
an average of about 6-9 full sun hours on a panel, it varies
greatly by season. Multiply that by the amps output of the
panel to figure how many amp-hours are coming in. 30 watts =
2.25 amps x 6 hours = 13.5 amp-hours (winter), and for 9
hours of solar exposure (summer) it's 20.25 amp-hours. That's
not too bad--we could run our 27 watts of lights for 6-9 hours
at night after a sunny day. What if it's overcast, or rainy?
Solar panels put out nearly nothing unless they are in full
sun. After a few cloudy days, we'd be dipping deep into the
batteries capacity to run our lights for 6 hours a night. That's
where shore power can be handy!
Renewable energy versus shore power
In a house in town, you'd call it 'grid power' instead of 'shore
power.' It's your basic electrical outlet into which you can
plug your camper electrical system. Most campsites that provide
shore power also provide shore water pressure. This is absolutely
worth the small amount of money it costs per night! Besides
having potable water under pressure hooked right into the
trailer, a simple 10 amp battery charger from the auto parts
store can be running at any time we are connected to shore
power -- that 10 amps coming in is like having 4 of our 30
watt solar panels running at once. Even so, the cute little
1000 watt electric heater we carry along to warm up the camper
while making early-morning coffee is simply NOT feasible to
run off of a renewable energy system, no matter how many solar
panels and batteries were installed. We run it off of shore
power only. It's the same in town--electric ranges, water
heaters, space heaters and such use far more power than
even a large renewable energy system could provide.
Is a transfer switch needed?
All a transfer switch does is switch your electrical outlets
from shore power to inverter power and back again. Some are
automatic, some are manual. All are expensive. To save money,
we simply wired up a pair of outlets in the Sally Ann--one
is for shore power (if it's available) and one is for inverter
power. Simple, cheap, and can cause no confusion if properly
labelled. The only thing an inexperienced operator would have
to remember is to NOT plug the 1000 watt electric heater into
the inverter output--shore power only for that power hog of
a (very handy) gadget!
I already have a generator, will it help?
You bet! In a remote campsite where there's no shore power,
a generator could be really handy. And the battery system
means that you might not have to run your generator late
at night to watch TV--you could instead boost your battery
with the generator during the day, and keep a silent
campground at night by running your TV off of the inverter.
In our case we'd simply plug the generator into our shore
power input, and both run loads directly from it, and use
the remaining generator power to charge our battery with
the standard NAPA battery charger we haul along with us.
Get the biggest battery charger your generator can handle
and that you can afford. Generators give you the most
watt-hours per gallon of gas when you run them at 50% of
their rated load or more, and run time will be much less to fill
your battery when using a big charger.
How about water pressure?
Once again, we kept it simple. There was already a standard
camper-style water faucet over the sink in our camper. If
there's shore water pressure available, we push down on the
handle to get water. If we are using water from our
self-contained water cistern (a new, clean, food-grade,
white 5-gallon bucket) we pump manually from it via the
same handle. An electric water pump would have been an
option, but adds more electricity use and possible
reliability problems to the water system. It would be
irritating to be without water just because the battery
was low, with no sun or shore power to charge it back up.
What about the trolling motor?
On some lake fishing trips, we bring our vintage Grumman
canoe and small electric trolling motor along. It's easy
to drain that battery way down with just a few hours of
flyfishing, especially in windy conditions. So, we chose
exactly the same battery for the trolling motor as we did
for the trailer -- they fit in the same battery box and
hook up the same way, so we can quickly exchange the
trailer battery for the troller. Shore power with a
battery charger or a direct connection to the solar
panel are the best ways to charge up the trolling
motor battery. Don't try to run your 120 vac battery
charger from the inverter to charge the trolling battery!
You'd be converting 12 vdc to 120 vac back to 12 vdc for
charging, with losses every step of the way. It's much
more efficient to charge the trolling battery from shore
power or direct solar...that's the main reason we made
it easy to swap batteries between the canoe and the camper.
You could spend lots and lots of money on a solar power
system for a camper. In fact, I wish some of those folks
with noisy generators on our last fishing trip had done
so! The problem is, they would HAVE to spend a lot of
cash to run all those power-hogging gadgets off of solar.
The same problem crops up in designing a renewable energy
system for a home or cabin--the more kilowatt-hours of
power you use each day, the more batteries and solar
panels you need. Conservation is the key--it's estimated
that for every dollar you spend on energy conservation,
you save $3-5 on the cost of the RE equipment needed to
power your stuff. If we'd used incandescent light bulbs
in the Sally Ann, our possible run time before the battery
was empty would be about 6 times less! The same for TVs,
computers and anything else you need to run in the backcountry.
LCD screen TVs have very low energy draw compared to normal
models, as do laptop computers. Use an old-fashioned stove-top
toaster instead of an electric one. Install a propane fridge
instead of an electric one. Pick which appliances you use on
a trip, depending on whether you are hooked into shore power
or not. The electric toaster oven is FINE on shore power, but
not on solar! Microwave ovens are surprising --- they use
lots of power (800-1500 watts) but are only on for a minute
or two, so a small microwave is perfectly feasible on solar
The key to using renewable energy, and one great benefit, is
that you MUST be aware of your power usage at all times! When
you return home, you'll suddenly be aware of all the power you
are wasting every day. You might even turn into a 'power ogre'
like me, roaming the house finding TVs and lights that were
left on and shutting them off!
Irritated rainbow trout. I released him.
~ Dan Fink - (DanBob)