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As news of a now commercially available 100 Ah/day fuel cell has
just been released, and of which more anon, it is timely to review some
of the more important developments over the past few years that affect
campervan and motorhome owners. For buyers of new vehicles, the major
one is probably the widespread usage of small turbo-diesel engines in
campervans and small motorhomes. The marriage of diesel engine and turbocharger
is virtually made in heaven: they are technological soul mates.
Today’s diesel engines are smooth, unobtrusive and restful whilst
driving, and use about 35% less fuel for the same work. Some part of
their output however is spent in pumping in the huge amounts (about the
volume of an average house every three minutes) of oxygen-containing
air that they need for the diesel fuel to burn.
Rather than wasting part of the diesel engine’s power to do the
above, a turbocharger uses the energy otherwise wasted via the exhaust
to drive an integral air pump to do the same job. By doing so this increases
power output and/or efficiency by 10-15%. If this increase is not exploited
by driving faster or accelerating harder – it will be reflected
in a corresponding saving in fuel.
Associated with the above are intercoolers. One of the more fundamental
laws of physics (Charles’ Law) shows that gas heats up when compressed.
Whilst this can be handy (not least because it’s how a diesel engine
works) a corollary of Charles’ Law is that when air is heated it
becomes less dense. This is not useful whilst the air is pumped in (pump
a bicycle tyre with a hand pump and you will have a first-hand demonstration – plus
a not very good pun). So whilst the turbocharger does a good job in pumping
it inevitably heats the pumped air in doing so. An intercooler is simply
a radiator fitted between the turbocharger and the engine that cools
the pumped air. This adds a further few per cent efficiency that may
again be exploited as a power increase (in which case there is no fuel
saving), or driving as before (when there is). A turbocharger and an
(optional) intercooler can be retrofitted, but is a costly and sometimes
mechanically risky thing to do.
Here there are several and ongoing changes. The major one is that solar
modules are progressively decreasing in area per watt. Now, some 120-watt
modules (Kyocera’s is a good example) are literally smaller in
area than some previous 64-watt modules, yet are much the same weight.
Whilst Uni-Solar modules are not heat-sensitive, and far more shadow
tolerant, where RV real estate is short and many watts are required,
it may be more practical to accept the losses of the non-amorphous units
(effectively all except Uni-Solar) if a lot of electrical energy is required.
But if space is not an issue I still prefer Uni-Solar.
A slowly happening change is the increasing use of so-called Multiple
Power Point Tracking (MPPT) solar regulators. These overcome the problem
that solar modules produce maximum power output at about 17 volts but,
if feeding a 12-volt battery and charging at (say) 14 volts, about 14/17ths
of the energy is lost during a fair part of the charging cycle. This
is why solar modules produce that much less than their apparently specified
output when used with 12 or 24 volt systems. An MPPT tracker works a
bit like a torque converter in a car. It takes in volts and amps and
juggles them to optimise power (watts) output. It is likely to increase
output by anything from 10% - 17.5% but rarely the 25%-plus often claimed.
They are currently expensive (a 12-48 volt, 60 amp unit costs about $1200)
but smaller cheaper ones are beginning to appear on the market. They
are however worth considering where a bit more solar is needed but nowhere
to mount the extra modules. In time the technique is likely to be built
into all (around-$300 upward) regulators. I now have one (a 60-amp, 48-volt
output Outback Power unit) in my now- 36-module home system. It typically
increases output by 15%.
An additional benefit of MPPT technology is that the regulator will accept
input voltages up to a typical 120 volts. Thus modules can be wired in
series for high voltage – and thus greatly reduced voltage drop – my
own system now runs with multiples of six series-connected modules (a
nominal 72-volts).
The decreasing size and increasing affordability of solar modules, and
minor improvements in the efficiency of compressor technology, is slowly
increasing the feasibility of using bigger all-electric fridges. Early
editions of my books suggested that 110-litres is about the largest that
can realistically be run from solar. Recent editions extend this upward,
but do be aware that reliably running a (say) 170-litre fridge in the
hotter parts of Australia really needs three 120-watt modules. The increasingly
popular fridge-freezers may need generator backup in hot places even
then.
These are increasingly gaining acceptance, but are being prejudiced by
chain-store specials selling at about 30-40% of their price. The latter
are claimed to do the same job. They absolutely don’t.
A proper three-stage charger utilises a quite different charging regime
that enables it to charge much faster, more deeply, and more safely.
A good (say, 10-amp) example will charge a deep-cycle battery very close
to 100% faster than a 20-amp cheapie will bring the same battery to 70%.
If you try to economise here you are not only being cheated – but
are choosing to be an accomplice.
Contrary to general belief these lights are not efficient: they are little
better than incandescents, and only a third as efficient as fluro's.
However for purposes where light is required in tightly prescribed areas
(such as reading, campfire cooking, narrow beam torches, step lights
etc.) they are very effective. But they are not yet effective for general
lighting unless you accept a very low light level. In effect, white LED's
are a bit like an optical version of a garden hose in that there’s
only so much water coming out, and that can be widely but softly distributed,
or focused into a jet, but cannot flood a wide area.
We are still a fair way off seeing truly convenient and affordable fuel
cells for RV use: but we are now a step closer.
A fuel cell is essentially a device that converts chemical energy (directly
from hydrogen, or indirectly from fuels such as methanol, LPG, diesel,
petrol etc) into electrical energy. It differs from previous methods
in that the conversion does not involve burning the fuel. Because of
this, fuel cells are silent, very efficient (up to 80% instead of 15-25%),
run cool, and produce next to no harmful emissions. A French company
(Max-Power) has now produced the MFC AHD-100 unit - primarily for marine
use. It is a charger/ automatic battery compensator for 12-volt lead
acid batteries.
The unit produces a constant 50 watts (that is about 100 Ah/day) and
consumes 1.2 litres of methanol per 1 kW/h: or about 1.3-1.4 litres/
day if running non-stop.
It is surprisingly small: 380 mm by 260 mm by 155 mm and weighs about
8 kg.
A minor problem (in Australia) is that its operating range only extends
to 40 degrees C. This is a bit too low if travelling up north. A possibly
larger problem is that it may only be fuelled by special methanol canisters
obtainable from its makers or its agents.
This fuel cell is claimed to consume about the same amount of oxygen
as does a human, and exhausts much the same amount of humid air and carbon
dioxide. There is thus no need to ventilate it to atmosphere.
The suggested price is about A$6200 but is expected to sell for less.
At first sight (at this price) it seems a no-goer, but one needs to consider
that the unit is in effect a non-stop battery charger. The output of
100 Ah/day is close to that reliably produced by four 100-watt solar
modules. A battery is still required, but not so much to store energy
for long-term use but rather to cater for short term overloads (the fuel
cell puts out a bit under 5 amps). For many purposes, a 100 Ah battery
would be ample. Thus were the unit to sell for about $4000 it would cost
much the same up front as the equivalent solar output – but there
is the need to buy and store methanol canisters. This is a particularly
unpleasant chemical and very toxic. This unit is however a pointer to
a fuel cell future that may be closer than I had recently thought likely:
an electrical consultant friend is seriously considering one for his
new camping trailer.
If converting a big bus or coach, and still have a year or two to go,
it may be worth putting off any major decisions re power sources until
later. I have no doubts at all that fuel cells and/or ongoing solar technology
are the way we are inevitably heading. Those seeking more info on the
Max-Power fuel cell see www.max-power.com/fuel
cell/faqs.htm
Finally (and non-related) a seriously good tip for those afflicted with
glasses. Modern lenses have a microscopically thin coating that cannot
be cleaned by tissues etc. If mucky (which happens fast and often) these
lenses can only be effectively cleaned by using Windex or preferably
the special cloths available from opticians. OPSM (and no doubt others)
has one that is washable. It makes an amazing difference! Lots of stuff
about things like the above, and heaps more, are in my books.
Collyn Rivers,
W8054
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