veryone wants to know about solar power and what they can do to
create a power-independent RV.
The secret is all in the planning.........
You need to work out exactly what you want
to run off DC power and how many batteries
and solar panels you’ll need to handle that
load. And that stuff ain’t cheap.
First thing to do is sit down and work out the
consumption of all the stuff you want to run.
You can measure this in whichever unit suits
you (amps, watts or volts), and virtually all
appliances have a plaque stating their
consumption. It sounds obvious but add them
up using the same unit of measurement. We’ve
decided to go with watts as it’s how the output
for most panels are measured.
Make yourself a list (called a load chart – see
breakout) of what you want to run, writing
down their consumption in watts. This will
provide you with an accurate and realistic
assessment of how much electricity you can
expect to consume daily so that you can then
determine the size, and nature, of the solar
panel(s) you’ll need to maintain power supply.
Refrigeration: this can be written out of the
electrical equation if you run a three-way fridge,since they run off gas when stationary. A three-
way running off 12 volts will consume 140-180
watts per hour. Compressor fridges will
consume between 36 and 48 watts per hour for
a top-loading unit up to 110 litres, 40-70 watts
for small front door opening units, and 70-95
watts for larger units.
If you’re in a camper trailer you may get away
with gas lighting and/or portable battery-
powered units some of the time, but most
people require, or desire, more convenient
lighting around cooking areas and after dinner.
LED lights are much more efficient and use
much less power; halogen lights are energy
consumptive.
Incidentals: DC water pumps, an inverter to
charge mobile phones, portable radios, or run
laptop computers. Also, for an inverter, add 15
per cent to the wattage consumption. There are
loads of other things you could include besides
the above. An LCD TV can easily consume
around 60-75 watts.
Stereos or videos usually
swallow around 20 watts each.
A microwave, on the other hand, can gorge on
a massive 1500 watts.
Get the ‘rated wattage’ of each appliance and
work out the length of time each day that they
are used. Multiply these numbers together for
each item; this gives you the total watts per day
for each item. Add all the total watts together
for total power consumption per day.
Now divide by 0.7 for panel efficiency and
divide by the number of peak sunlight hours
for area travelled (about five hours or so median
average for Brisbane). This will give you close to
the panel size required.
The ‘number of peak sun hours per day’ is
determined, basically, by the latitude and the
season, though it’s not quite that straight
forward. This is not the number of hours
between sunrise and sunset, as the earlier and
later hours have diminished energy input.
We are talking of peak sun hours, and that can
range from as low as three in Tasmania to over
six in parts of QLD, NT and northern WA. See
breakout for the monthly peak sun hours for
various locations in Australia.
Solar Panel Choice
Once you’ve worked out how much juice your
appliances will be sucking down, you can then
set about choosing the right solar panel.
The glass-based panels are divisible into the
newer technology multicrystaline, the older polycrystalline and the more expensive
monocrystaline. All of these panels are smaller
and lighter per unit of power output than the
amorphous panels. The downside, however,
is that they really struggle to generate anything
when there’s cloud cover or shadows.
“There are some exceptions to this,” says
Jamie Hazelden from Dynamic Solar Solutions,
in Moffat Beach, Queensland. “For example,
the Kyocera glass panels are in the multi-
crystalline category and have some shadow
tolerance built into them making them the
most efficient panel.”
The Triple Junction amorphous panels have
a textured surface and aren’t seriously impacted
by shadow; they’ll only drop output proportional
to the area of the panel covered by shadow.
However, the biggest output available in this
grouping is 64 watts and at that they are bigger
than a 130 watt glass-based panel in physical
size.
Amorphous panels are more heat tolerant
and can be produced in a flexible form to fit a
curved surface, but they rarely operate at their
full potential when configured this way.
Now, whatever you figured you needed to
meet your electrical consumption needs you
must be aware that all solar panels will only
output around 70% of their ‘rated capacity’, for
reasons which are too detailed to go into here. We have allowed for this by dividing our
accumulated consumption by a factor of 0.7.
Portable Panel PackS
There are many options in folding
solar panels that are actually
just pairs of panels wired
together, hinged at one edge,
with a latch and handle at the
opposite edge. These are handy,
easy to store and, though solar
panels are much tougher than
many people think, a good way
to protect them when packed for
transport. Just be careful of some
of the cheaper set-ups on sale as
these are often of lower quality.
Making Best use of your
Panels
Solar panels function at their best when facing
directly towards the sun.
That means unless you have an automatic
tracking system you are going to have to adjust
the panel’s position every hour or two if you
want to maximise input. For this reason, having
panels fixed to the roof of your camper loses
you 10-20 per cent of input, but you can
compensate by allowing for this when planning
for capacity.
You also need to allow that some days will be
cloudy or wet, and this will impact upon the
efficiency of your system. Most solar panels
decline in output once temperatures rise above
25 degrees Celsius so, on a 35 degree Celsius
day, you can knock off about 15 per cent from
your expected output. On the other hand,
amorphous panels actually show a slight
increase with rising temperature.
For those seeking flexibility there are some
very neat folding packages available today,
supplied with a regulator, stands and lengthy
cabling which permit you to locate your panel
where it will do the best job. Solar panel set-ups
are relatively expensive and desirable,
so don’t leave them unattended.
Above: By remotely locating the panels, this camper is able to best adapt to the sun’s motion in the sky and changing circumstances.
Above: Some camper trailer manufacturers, such as Trak
Shak, offer serious solar arrays with their trailers, although
you wouldn’t normally align them with a large tree.
Controlling the Power
You are also going to need a regulator to
control the flow of your generated electricity
into your storage battery(s). This is to prevent
your solar panel overcharging your battery(s)
and, if you choose an appropriate regulator,
tapering off the charge rate as your battery
approaches full charge.
As with everything in this area, these come in
a variety of forms. Forget simple (read cheap)
regulators. A recharging battery will take power
at the bulk rate until it reaches 70-80 per cent
capacity, and then the remaining 20 per cent
should take as long to be delivered as the first
80 per cent did.
A quality regulator will give you a range of
information on the system and how it’s
operating, so they are definitely worth spending
money on.
To determine the size of regulator you need
(in amps) for your chosen system, take your
total solar panel wattage and divide this by the
voltage of your system at full charge (for a
12-volt system this is effectively 15; for a 24-volt
system this will be effectively 30).
It’s worth seeking out a professional to make
sure you link your batteries correctly.
A quality regulator will give you
a range of information on the
system and how it’s operating...
Above:Even the humble camper trailer can
require serious battery storage capacity under the
demanding situations at the high dollar end of the
market. In such cases, a bank of AGM batteries
may be required as shown here.
Above: The Unisolar brand amorphous panels are not
as heavily impacted by shadow as the crystalline
units but they are bigger and bulkier.
Storing that Power
Deep-cycle batteries are the only way to go
when it comes to storing power – these have
the capacity to handle constant discharging and
recharging. The less you discharge it before
fully recharging it, the longer (in terms of the
number of cycles of discharge/recharge) the
battery will last.
Storage batteries are designed for slower
release of direct current, and starting (cranking)
batteries for short sharp discharges. Battery
capacity for a storage situation such as we are
referring to is measured in amp/hours, the
higher the rating the more power you are
storing.
The idea is to choose the highest
storage capacity, taking into account your
budget, carrying capacity, ability to recharge in
a reasonable time and needs. When choosing a
battery, you’ll need to take into account factors such as physical storage/mounting space and
weight, as storage batteries can be heavy.
A 100
amp/hour deep cycle battery will weigh around
35kg, and a suitably strong mount that can
restrain such
a mass in a moving environment such as a
caravan or camper will thus also be heavy.
Deep-cycle batteries can be divided into two
camps: wet cell and absorbed glass matt (AGM).
I’m going to jump straight to a
recommendation and encourage you to buy
a sealed battery in most cases.
Though AGM batteries are more expensive,
they do not give off excess amounts of highly
combustible hydrogen gas, can be mounted in
any orientation (even upside down) and in the
unlikely event that they may be ruptured, they
don’t release nasty gases. They will recharge
more quickly, are maintenance free, they will
self-discharge at a slower rate if in storage and
can then be recharged with no loss of efficiency
and their robust construction makes them good
for rough terrain travelling.
An automotive recharging system is not
designed to recharge the battery over 70-80 per
cent of a battery’s capacity, simply having to top
up a relatively small amount of power lost in
starting and then keeping up with the demands
of running the car.
However, with an appropriately sized solar
system with a quality regulator constantly able
to top up that last 25-30 percent of capacity,
your battery will last much longer and give you
more usable power at any time. A well-balanced
system will finish charging to 100 per cent
capacity by the time the sun goes down in the
late afternoon and not go much under 80-85
Load chart
Work out how much energy your camper uses daily to determine what solar panels you’ll need.
a p p l i a n c e
w a t t a g e
X
Hours Per day
=
Watt-Hours Per day
Fridge
40
X
8
=
320
Interior light
4
X
3
=
12
Reading Lights
10
X
1
=
10
Exterior Light
11
X
2
=
22
Phone Chargers
7(+15%)
X
2
=
16
Lap Top
70(+15%)
X
1
=
81
TOTAL
461
Factor (Watt-Hours/0.7)
658.5(F)
F/Sun Hours
Estimate 5.2
126.6
+ FAST FACTS
You can convert
the different
units by
applying Ohm’s
Law, which
states: Amps X
Volts = Watts.
Make Hay while the Sun Shines
The dual panel set-up at left, in shade, will now be dropping
off its output, very dramatically if a glass-based unit, while the
units in the sun at right will still be drawing the best possible
output from the late afternoon sun.
Above: One of the advantages of AGM batteries is that they can
be mounted on their side, as in this Aussie Swag camper van.
Above: One option would be to mount your panel on
an arm above the draw bar.
