Posted by Ecnerwal on September 2, 2005, 9:18 am
After a couple of years of construction and recovering finances, I'm
getting nearer to buying significant parts of my off-grid system. Some
parts will have to be staged purchases as more money comes in, but the
initial chunk of battery, first inverter, charge controller, one string
of panels, and all that interconnection NEC meeting "stuff" that ends up
costing a lot more than it seems like it should.
At present my offgrid system consists of an unsuitable generator (3600
RPM welder/generator, air cooled) and a bank balance.
As far as I can tell, an installation in Vermont which is off-grid gets
diddly for rebates, tax breaks, etc. Location is SW Vermont, wind
potential stinks (84 foot straight-growing trees), likely solar + fuel
for a good long time since solar alone would blow the budget (though
fuel prices are right up there at the moment with no signs of dropping).
Going to have to lay waste to more trees than planned (not a big lawn
fan) to get sun in for panels. Only hope for microhydro would be very
micro - if the gravity well pans out and has noticable excess water.
Good or bad experiences with cut-rate internet dealers welcomed - good
experiences with dealers local to me also welcomed - I may well have
missed some. Cash is definitely a limiting factor - the budget for the
inital phase is probably not much more than $12,000, assuming no
surprises with other aspects already budgeted. I admit to being somewhat
bemused by the wealth of PV cells which tout being cheaper to make, yet
which cost more per watt than other products they are supposed to be
cheaper than (eg, Unisolar, Evergreen).
My inital application is a bit odd .vs. typical offgrid houses - the
first building up is the shop. It will have need of some pumping
capacity for radiant heat (probably a couple of ~125 watt pumps, duty
cycle not certain), and sporadic use of up to 3-4 HP worth of motors,
along with as much as a kilowatt+ (even if it's _very_ efficent,
slow-starting metal halide - a few dim CFs just won't cut it) of
lighting. It might sit for most of a week (or longer) doing nothing but
running the heat, and then get used for several hours of motor-heavy
work - a low average, but high peak use. Over time more typical house
loads will be added. I'm strongly considering DC pumps for the heat, but
that might limit me to 24V (or needing to fiddle about to get 24V from
48V).
Thus far all motor loads can be run 120V (3-4hp is multiple motors at
once). While many could be switched to 240V for less amperage, messing
about with balancing 240/120V seems more complex than just sizing the
wiring correctly for 120V.
General thoughts are 48V battery bank, with a dedicated "power house"
including a nice basement/vault for them to hide from the winter (and
summer) in. All reading indicates that I should try to make the battery
as big as I need for the next 10 years right off the bat, and that the
ideal situation would be 2V individual cells in a single series string.
Of course, many people seem much happier having switched to AGM or gel
batteries (which don't appear to come in 2V cells) and the lowest
starting cost option of golf cart batteries is 6V and high maintenance
with a likely need to run several parallel strings, with associated
equalization headaches.
A liquid-cooled diesel generator has been in the plans, but is becoming
more questionable as the price of all forms of petroleum shoots up.
I will no doubt start undersized for panels, and then have to plan to
add them in chunks over time as more money comes in (I have a practical
aversion to loans if they can be avoided - saves a lot of money on the
long run). Presumably this will mean needing to run the generator to top
up the battery some, as well as to support the major loads if run for
much length of time in the early phase.
PVWatts indicates that Nov/Dec are the worst months - sounds about right
for the cloudy VT weather.
I'm mostly looking for ideas about what you would do differently if you
were starting with a blank slate, within the context of the general
background information I've provided to make it less a purely vague
question. Aspects like detailed system sizing are inherently somewhat
vague, as it's not just a matter of household appliances with
predictable use times and power draw, nor much room for "reduce power
use first" with motors that inherently need a good deal of power (even
if they could be 100% efficient, which they cannot).
--
Cats, coffee, chocolate...vices to live by
Posted by Harry Chickpea on September 2, 2005, 10:17 am
>My inital application is a bit odd .vs. typical offgrid houses - the
>first building up is the shop. It will have need of some pumping
>capacity for radiant heat (probably a couple of ~125 watt pumps, duty
>cycle not certain), and sporadic use of up to 3-4 HP worth of motors,
>along with as much as a kilowatt+ (even if it's _very_ efficent,
>slow-starting metal halide - a few dim CFs just won't cut it) of
>lighting. It might sit for most of a week (or longer) doing nothing but
>running the heat, and then get used for several hours of motor-heavy
>work - a low average, but high peak use. Over time more typical house
>loads will be added. I'm strongly considering DC pumps for the heat, but
>that might limit me to 24V (or needing to fiddle about to get 24V from
>48V).
That usage pattern sure sounds like it calls for a diesel generator,
and in Vermont I would sure want a way to scavenge the heat from the
exhaust and the generator itself.
I'd be looking for a generator, a bank of cheap golf cart batteries, a
few solar cells, a charge controller and an inverter. Why cheap golf
cart batteries? Because batteries take care and feeding, and I'd feel
a lot more comfortable shortening the life of cheap short life
batteries when getting used to that routine than killing more
expensive ones. Why just a few solar cells? Because they will be a
cost effective way of maintaining a charge or float charging during
the low usage periods, but wouldn't be a cost effective way to build
up a charge for the type of usage you plan when working in the shop.
Why diesel for the generator? Slower speed, better construction,
possibility of vegetable or bio-fuel use. Why scavenge the heat?
Vermont winters - and springs - and falls - and sometimes summers
(although not this year).
I'd have a sound-insulated generator room within the shop, and in
southern Vermont I'd be looking for a source for waste marble grout or
concrete waste to use as a thermal mass, rather than using water.
One idea might be constructing a large bin in the shop area on top of
an EDPM lined pan, using hardware cloth and rebar to contain the small
angular rocks that make up most grout. This bin would then be sealed
with a layer of gunnite over the hardware cloth, and the exhaust stack
at the top would have a safety interlocked fan powered by the
generator to insure a negative air pressure when the generator was
running. The bin would receive the exhaust gasses at the base through
a manifold. The rocks would absorb the heat and condense out the
water while the generator was operating. When the generator was
stopped, the fan would continue for a few minutes then stop and a
stack seal would drop. The bin would then slowly release the heat to
the shop during the rest of the week. A shunt would be needed to move
the exhaust directly to the outside during the summer month, and
obviously a couple of CO detectors would be required.
Using marble grout eliminates any possible freezing problems and the
need for pumps, thus minimizing the standby electric usage. The
downside is that it does take up some space. I suppose in theory, you
could use the grout under a false floor for a heated floor, but
columns would be simpler and cheaper.
To simplify drainage from the rocks, the bin or bins might be
constructed on shower pans plumbed to a drain or enclosed sump.
Posted by nicksanspam on September 2, 2005, 12:36 pm
>One idea might be constructing a large bin in the shop area on top of
>an EDPM lined pan, using hardware cloth and rebar to contain the small
>angular rocks that make up most grout.
Sounds great :-) So this "grout" is pieces of marble...?
>This bin would then be sealed with a layer of gunnite over the hardware
>cloth,
How about a simple EPDM cover?
>The bin would receive the exhaust gasses at the base through
>a manifold. The rocks would absorb the heat and condense out the
>water while the generator was operating...
The rocks could provide lots of surface. The box might also have a few
hollow concrete blocks to lessen the airflow resistance and a few plastic
55 gallon water drums to store more heat in the same volume...
>The bin would then slowly release the heat to the shop during the rest
>of the week.
This box could do a good job of collecting heat, but the rate of heat
distribution might be increased and controlled with another room airpath
inside the box to extract heat, vs just letting heat leave via the walls.
Nick
Posted by nicksanspam on September 2, 2005, 11:52 am
>At present my offgrid system consists of an unsuitable generator (3600
>RPM welder/generator, air cooled) and a bank balance.
You can quickly convert that pesky bank balance into PVs :-)
>...wind potential stinks (84 foot straight-growing trees)...
Aka "towers"?
>My inital application is a bit odd .vs. typical offgrid houses - the
>first building up is the shop. It will have need of some pumping
>capacity for radiant heat (probably a couple of ~125 watt pumps, duty
>cycle not certain), and sporadic use of up to 3-4 HP worth of motors,
>along with as much as a kilowatt+ (even if it's _very_ efficent,
>slow-starting metal halide - a few dim CFs just won't cut it) of
>lighting. It might sit for most of a week (or longer) doing nothing but
>running the heat...
>I'm mostly looking for ideas about what you would do differently if you
>were starting with a blank slate, within the context of the general
>background information I've provided...
How about a sunspace over the insulated south wall of the shop, or some
polycarbonate "solar siding" to make an air heater to lower the heating
fuel bill, with a few small windows and lightshelves near the top of the
south wall to provide light? Full sun is about 10K footcandles.
A well-lit office is 50, 200X less.
Nick
Posted by Gary on September 2, 2005, 12:58 pm
Hi,
...
>
> My inital application is a bit odd .vs. typical offgrid houses - the
> first building up is the shop. It will have need of some pumping
> capacity for radiant heat (probably a couple of ~125 watt pumps, duty
> cycle not certain), and sporadic use of up to 3-4 HP worth of motors,
> along with as much as a kilowatt+ (even if it's _very_ efficent,
> slow-starting metal halide - a few dim CFs just won't cut it) of
> lighting.
You might take a look at this scheme -- it results in the best lit
shop I have ever had. During the day I don't use any other light --
its much better than the half dozen fluorescents I have on the
ceiling. It also does a very good job of heating the shop:
http://www.builditsolar.com/Projects/SpaceHeating/garcol.htm
The combination of the roll-up door plus the glazed doors really makes
a difference thermally, in that the roll-up door greatly reduces heat
loss at night.
Gary
--
Gary
www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects
----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----
XML site map
>first building up is the shop. It will have need of some pumping
>capacity for radiant heat (probably a couple of ~125 watt pumps, duty
>cycle not certain), and sporadic use of up to 3-4 HP worth of motors,
>along with as much as a kilowatt+ (even if it's _very_ efficent,
>slow-starting metal halide - a few dim CFs just won't cut it) of
>lighting. It might sit for most of a week (or longer) doing nothing but
>running the heat, and then get used for several hours of motor-heavy
>work - a low average, but high peak use. Over time more typical house
>loads will be added. I'm strongly considering DC pumps for the heat, but
>that might limit me to 24V (or needing to fiddle about to get 24V from
>48V).