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re: a simple starter pv system
7 may 1997
don kulha posted with permission from home power magazine,
>solar power can be confusing.
agreed. for instance, to some people "solar power" means "photovoltaics."
>the user becomes his own power company
that's confusing. a little crazy, even...
>fortunately, pv systems are ultrareliable...
oh?
>the four major components in a pv system are: energy
>source (the pv modules), energy storage (battery),
>energy processing (inverters, controls, instruments, and
>such), and loads (appliances).
a non-redundant system is no more reliable than any one of its parts, like
a chain with a weak link. leaving aside the appliances, which may be
"ultrareliable" (?), what about the rest of that stuff? what's the mtbf of
a trace inverter?
>so, country folks and city dwellers, here's a guide to
>the basic concepts involved in a simple starter pv system.
one guide, for country and city dwellers?
>the need is for electric power
or maybe also house or water heating, or electrical energy conservation?
>what do you want to power with the system?
manhattan. or perhaps just brooklyn. would you believe a newstand? how about
one of those solar pith helmets, with a little pv and motor and fan?
>for our purposes here, consider a small system as one that uses between one
>and four pv modules. such a system will use between two and four small
>lead-acid batteries like the trojan t-105 (220 ampere-hours at 6 vdc).
why do city dwellers need batteries? for that matter, why do they need pvs?
>energy processing may or may not include an inverter (like the small trace
>612 or powerstar models), a simple charge controller (like the trace c30a),
i>and a voltmeter.
or a grid-tie only integrated inverter? this might be a fine yuppie toy,
on a small scale. or an expensive money-losing business, on a larger scale.
>typical loads appropriate to the small starter system are: lights
>(high-efficiency fluorescents), electronics (tv, stereo, vcr, computer,
>etc.), kitchen appliances (blenders, juicers, & mixers)...
and hair dryers and espresso machines?
>allow one 50 watt pv module for each person in the household. this means
>that each person can use, each day, the energy produced by a single
>module about 250 watt-hours.
about 0.25 kwh per day, worth less than 1 cent, at today's electrical energy
prices, or 15 kwh per month for a family of 2, vs a typical frugal household
electrical energy consumption of 500 kwh/month, today?
>cost is about $370 per installed module.
that's $370, so far, to make 90 kwh/year, worth about $9.
>battery cost will be about $170 for two batteries...
$540 invested so far, to save $9 per year...
>using an inverter will add about $600 to the system's overall cost.
$1140 invested so far, to save $9 per year...
>controls
>a control is not necessary if the system is
>continually occupied. if you go on vacation
>simply disconnect half of all of the pv modules.
ok, let's omit the controls, to save money.
>instruments
>for economy and flexibility, buy a digital
>multimeter (dmm). the dmm can make most
>essential voltage and current measurements...
>if bucks are tight, go to radio shack and spend about $60...
that makes $1200, to save $9 per year, a 0.75% return on investment.
>installing the starter system
>mount the pv modules on metal racks or even wooden ones.
free racks, or were they included with the panel price?
>wire the modules with 10 gauge wire...
>bring the pv power to the battery with 10 gauge wire for less than 25 feet
>(one way between the modules and the battery), 8 gauge for about 50 feet,
>6 gauge for 75 feet, and 4 gauge for 100 feet...
wire is also included?
>locate the batteries where they are warm, dry, and not in
>human living spaces. build a battery box...
also included?
>the important thing is to get started. don't wait until you
>can afford a megasystem...
it seems to me this may be an affordable money-losing hobby on a small scale,
but we cannot afford to do it on a large scale, unless we are doctors or
lawyers, or public utilities selling "green power" at public expense.
nick
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