Right now, we are seeing truly major changes
in solar cell technology. Our still mainly siliconbased
(commercial) solar cells were about 6%
efficient in 1954. The best are now 20%-22%
and not expected to exceed that.
Amorphous solar panels are flexible panels
that can be rolled up or installed on a curved
roof. While convenient, they are only about
14% efficient.
PURCHASING TRAP
There is a trap when buying, in that the
claimed output is not of the overall output. It is
the most typical output of the 36 or so
individual cells that make up a typical 12-volt
solar module. All are individually joined endto-end
by soldering. There are inevitable
losses. All (silicon-based) solar modules lose
output when they become hot. Total panel
efficiency is measured under standard test
conditions based on a cell temperature of
25°C, not ambient temperature. In practice,
that cell (in the sun under hot glass) will reach
25°C at only 50°C ambient temperature.
An excellent general guide to a solar
module’s realistic maximum output is to
assume about 71% of what is claimed in the
module’s promotional material. This
corresponds to the solar industry’s nominal
operating cell temperature.
INSTALLATION
In practice, it is extremely important to ensure
at least 50mm of free air space beneath all
silicon-based solar modules, and to use
adequate cable size to connect them to your
solar regulator and batteries. For most RVs,
use a minimum of 6.0 square mm cable.
HOW MUCH SOLAR?
As noted above, the price of solar has
substantially fallen in the past eight years.
Battery capacity continues to rise. The best
thing to do is to maximise solar capacity, using
the most efficient solar modules you can find.
This will ensure that your battery bank
receives some charge even when it is overcast.
It also necessitates using AGM or lithium
batteries, because deep-cycle lead-acid
batteries cannot absorb a high current charge.
In essence, use as much solar as feasible. As
long as you also use an adequate solar
regulator, there is no risk of your battery
overcharging.
The writer says this is one of the earliest
known uses of RV solar. This image shows
his wife, Maarit, and his 1974 Westfalia
VW Kombi in 1994.