Escapees May June 2015 Demo

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16 .ESCAPEES |May/June 2015 |
or more. A good size for a full-time
RV used for many continuous months
of living off the grid, even in winter, is
500 watts or more.
Solar panels come in many sizes,
and the limiting factor on RV roofs is
physical space. It is vital not to let any
shade fall on the panels from rooftop
appliances like the air condition-
ing unit or trees or buildings. A few
square inches of shade on a panel can
shut the entire panel down.
A typical full-time RVer choice
is four 140-watt 12-volt panels. An
alternative is to use fewer, but bigger,
24-volt panels, for instance, two or
three 255-watt panels. Smaller 12-volt
panels fit into smaller spaces on the
roof. Bigger 24-volt panels can be in-
stalled using thinner gauge wire, which
is cheaper and easier to cut and bend.
A general rule of thumb is to
“match” (roughly) the number of
amp-hours in the battery bank to the
number of “watts” in the solar panel
array. For instance, 600 watts of solar
power would be matched with 600
amp-hours of battery storage.
Charging the Batteries—
Charge Controller
The solar panels will send as much
current to the batteries as the sun al-
lows, but sometimes this is more than
the batteries need. A charge controller
protects the batteries and ensures they
don’t get overcharged. Similar to turn-
ing the knob on the tub’s water faucet
to make the water flow either at full
blast or at a slow trickle, the charge
controller controls the flow of current
into the batteries.
Charge controllers are rated in
terms of the maximum amount of
current they can control and the
maximum amount of watts in the solar
panel array, and they must be installed
as close to the batteries as possible.
For small weekend/vacation RVs,
a 10-amp or 20-amp charge controller
will do the trick. For full-time RVs
camping off the grid long term, a
60-amp or larger charge controller is
needed. Buying a larger one allows
for the addition of more solar panels
down the road.
Larger charge controllers use a
multi-stage charging system for the
batteries. First thing in the morning,
when the batteries are most depleted
(perhaps around 12.3 volts), they put
the batteries in a bulk charge state, let-
ting the current flow from the panels
at full blast. Of course, until the sun is
high in the sky around noon, full blast
may not be that much.
“...hair dryers, toasters, small pancake com-
pressors and power tools, vacuums and
microwaves can all be powered with an
appropriately sized inverter, battery bank
and solar panel installation.”