re: economics of pv
25 dec 1997
tom gray quotes randy udall's inspiring essay, to which
i'll add a few quibbles. for instance, his email bounces...
>date: wed, 24 dec 1997 11:07:46 est
date: thu, 25 dec 1997 08:35:58 -0500 (est)
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>...a grid-tied pv system will be more efficient, arguably greener,
>and certainly cheaper than a backwoods one. more efficient because
>the inverter can track the modules' "maximum power curve" rather than
>the lower voltage needed to recharge batteries...
it seems to me there's no reason a standalone system can't track a
pv power curve, although off-the-shelf hardware may not exist now.
conceptually, this might be an extra box between the pvs and the battery
charger, given a large enough number of batteries, which decides how much
current to draw from the array depending on solar intensity and makes a
constant voltage output for the charger, using some sort of switching power
supply. power is voltage times current: draw 0 current from the array, and
there's no useful electrical output, just a warm pv panel (or free-spinning
windmill) with a high open-circuit voltage. draw too much power from the
array, ie something like a short-circuit, and the output voltage is 0, so
again there's no useful output, just i^r losses inside the array (or a
stalled windmill), so there's an "optimum power point" in between.
for a human analogy, consider the work a person does pushing a boxcar.
huffing and puffing doesn't count. if the boxcar doesn't move, no useful
physical work (= force x distance) results. if a person pushes a tiny wagon,
the resulting useful work is again small, because the force is very small.
so there's an optimum load for the person, which depends on circumstances,
eg the person's condition.
>...with the grid as backup, you don't have to buy batteries, charge
>controller, control panel, or generator. right there, you've knocked up to
>$5,000 off a typical stand-alone system.
the grid may be a fine battery, but it isn't a "backup" in the sense of
adding any reliability in this case. better to buy a few batteries, maybe
enough for a 24 hour outage. one consequence of electrical deregulation
is likely to be a less reliable grid. for instance, peco now undersizes
pole transformers to save money, and fuses them at 10 times their power
rating to save money and make higher profits. so in the statistically
unlikely event that several neighbors on the same transformer all turn on
their hair dryers and toasters and electric ranges at the same time, the
pole transformer will catch fire before its fuse blows. peco loses little
by this, economically, just the opportunity to sell a few kwh to a few
customers for a few hours...
>to sell grid-connected pv systems you've got to get the price down
>and then help prospective customers understand that solar is to coal
>as a croissant is to a twinkie.
"solar" what? why make a mountain out of this electrical molehill, when
oil and energy used for heating are much larger problems? doug balcomb says
(in "solar energy houses," 1996, james and james) that a typical house uses
172 kwh per square meter per year of energy, 97 of those for heating and
34 for hot water, with only 38 kwh (22%) for "other electrical usage." he
describes iea energy-improved houses as only using 44 kwh/m^2-year, 14 for
heating (a 7-fold improvement :-), 11 for hot water and only 18 (41%) for
"other electrical usage."
if electrical energy usage is such a small part of our household energy pie,
and it's so easy to cut it in half, using cfs and so on, and if the cost
of electrical energy is falling under deregulation (assuming no rps), why
focus first on the tiny electrical fraction of energy that we use? let's
heat houses and water with the sun first. adding a sunspace on to a house
to heat it (which also provides more floorspace) can be 100 times more
cost-effective than adding pvs.
>...the 800 watt system--a solarex prototype subsidized by the
>u.s. department of energy--cost $4,200 installed...
part of that money came out of my pocket. can everyone do this,
as in a marx brothers movie? :-)
>a contract from sandia national laboratory covered our logistical costs.
more money out of my pocket. congratulations on your successful theft, but
how can we run a whole country this way, picking each others' pockets?
>...much of the gear we installed in 1997 was unavailable
>or unaffordable in 1987.
i'd say it's unaffordable in 1997. and not likely to become a lot
cheaper soon, since oil companies make pvs, and a lot of people have
been trying to make pvs cheaper since 1930.
>...is a pv system more or less "cost effective" than a suburban?
less so, for most people, since the suburban has other more interesting
uses than the pvs, which just make electricity. most people just want to
use electricity, not make their own, which they see as an expensive and
boring hobby. and a kwh is a kwh--just something to make a toaster work--
they all look the same, and they all taste the same.
>it's not cost-effective
>gag me with a spoon. if i heard it once, i heard it a dozen times:
>"what's the payback?" i heard it from an architect, rancher, engineer,
>and electrical inspector. dividing my system's price by its production
>gave my brother-in-law his bottom line: "it's not earning its keep."
that's the way many people think. whining won't help...
>why pay 25 cents a kilowatt-hour for solar power when you can buy
>coal power for 7? are you brain-dead, a moon rock? pv is
>cost-effective for cannabis growers, dirt-poor haitians, soviet
>cosmonauts, everest climbers, indonesian peasants, and the mars
>rover. as for the rest of you, forget it.
exactly, although i think haitians and indonesians might be
more cost-effectively served by some larger-scale grid system.
>relative to cheap coal (and ignoring global warming), solar may
"solar" what? solar house heating seems cheap to me.
>...daily production from my system will average 8 kilowatt-hours.
>each kwh costs me 25 cents, compared to the 7 cents i pay for coal.
>the difference--=9718 cent--s=97is my added cost. it works out to
>$1.44 a day, $42 per month, $518 per year. that's what it's costing me
>to get 75% of my electricity from the sun... break the bank? hardly.
>my family of five spends almost fifteen times that much on food,
>five times that on automobiles, almost twice that on piano lessons.
>any family that can afford cable television or the internet, could
>probably afford to get some power from the sun.
so energy is too cheap in this country? how do you heat your house?
>to move pv into the mainstream, we need ready financing. many
>homeowners have (or qualify for) 9% home equity loans. but zilch
>(zero-interest) loans would be even better.
sure, but who's going to pay for that?
>there's some talk that low-interest loans may become available through
>the million solar roofs program.
more money out of my pocket? hey, i want to get on this bandwagon. can
i take money out of your pocket faster than you take it from mine? :-)
>let's hope so, for nothing would do more to catalyze that program and
>the feds should put money where mouth is.
let's hope not. the last solar tax credits were a disaster. it seems
to me that individual people should decide where to put their money.
>rebates would also jumpstart the market. the $3/watt buydown now
>available in california should unleash a torrent of orders.
where does that money come from...?
>an average american home produces 25,000 pounds of co2 due to its
i wonder if you are only counting electrical energy.
>before the retrofit my house used approximately 7,000 kilowatt-hours
>of coal power per year. after the retrofit, the house is on pace to use
>just 1,200 kwh, a 83% reduction. daily co2 emissions have been lowered
>from 38 pounds to 6.5 pounds. over their 20-year lifetime, the solar water
>heater and pv system will avoid 230,000 pounds of co2.
and how do you heat your house? with propane, like amory lovins?
>theoretically life on the grid should be less arduous for an
>inverter than life off, since the grid can easily provide the
>heavy surges of power needed to start a refrigerator, vacuum,
>table saw, or all three at once.
that doesn't seem clear to me, since an inverter can be designed to
handle those predictable "power surges," but a grid connection adds
more risk of unpredictable lightning damage.
>in japan, 10,000 people are on a waiting list to buy subsidized
so some lucky 10,000 people get to pick every one elses' pockets :-)