What advantages are there to using low voltage appliances when using a RAPS system? Obviously, you could get away with a
smaller (and therefore cheaper) inverter as the load from 240V appliances would be less, but what about other
differences such as actual energy requirements? I know they consume less power, but how much less? Obvious candidates
for low voltage are refrigerators and lighting, but what sort of savings would you achieve under typical usage
conditions? Would it mean fewer solar panels and a smaller battery bank would be required, or would you still base your
calculations on the assumption of 100% 240V appliances, and treat the savings in energy requirements as insurance
against a (literally) rainy day, when you might not otherwise generate enough power? And finally, does anyone know of a
site somewhere that already has these answers, to save having to post them here? I'm looking, but it's hard to refine
the search terms enough to get anything genuinely useful! TIA
Damien
I wholeheartedly agree with the other posters here. I bought a house
that started out with 12VDC power only, and then had an AC inverter
added later (all before we took over). An intermediate owner tore out
all the DC sockets, so now, most of my lights are DC, while a few desk
/ floor lamps and most everything else run AC. I get to experience a
mixed voltage system and develop an opinion without having my mind
warped by the original conditions and decisions that fed into it.
Since power is the product of current and voltage (ignoring power
factor for the sake of this discussion), if you cut the supply voltage
by a factor of 10, (e.g. 24VDC vs 240VAC) the current must increase by
a factor of 10 to deliver the same power to the load. If you're
looking at running 12V, then make that a factor of 20.
And, since power can also be expressed as the square of the current
times resistance (again keeping it simple here) that means that wire
losses soar! As other posters have pointed out, that suggests using
larger guage wire to minimize losses. Then there is the need to run
both AC and DC wiring everywhere. Yuck.
DC appliances are *sometimes* more efficient, and it's true that they
can be run directly from the batteries without firing up the inverter
(incurring fixed overhead + conversion efficiency loss therein).
However, unless they draw little power and/or are situated close to
the batteries, your energy savings could quickly be eaten up by
increased wire losses. And from an economic standpoint, DC appliances
are less common and often more expensive. Couple that with more and
bigger wire and it starts to look like a Bad Idea from an economic
standpoint as well.
Since I run a very modest setup and keep a tight control on
consumption, it does annoy me to fire up a big inverter for the sake
of running some little dinky gizmo, especially if the little dinky
gizmo has a wallwart power supply to convert the AC back down to low
voltage DC!
I'm a big fan of redundancy and simplicity, so I must admit really
appreciate knowing that I can still have some DC-powered light to see
my damn inverter if it blows up.
But if I had to do it all from scratch, I would wire completely for
normal line-voltage AC and provide a few emergency DC lights, even if
I was just doing a cabin or something of that nature. For a very
small, simple, compact system (short wire runs, few appliances) I
might still go DC.
BTW, another benefit of sticking to AC distribution is that this
confines the "weirdness" component to the power room. The rest of the
system remains "normal" so far as regular folks, future owners, or
electricians are concerned. Also means that you can upgrade to a
different primary voltage (12V to 24V or 48V) without orphaning a
bunch of 12V gear or having to install a 24V/12V converter to keep it
- which is exactly the decision I'm facing now.
I may well end up completely rewiring this place yet. <sigh>
-=s