I'm afraid this isn't a very happy post. This is why I don't encourage my clients to put solar panels on their roofs - so far I haven't met anyone who wants to reduce their house size to under 1000sf, or who doesn't want to experience summer from indoors at 78d.
From the Small House Society discussion list, at Yahoo!:
Like they say in the article, economics is not the reason to go solar.
However if you want autonomy, and the ability to move your house (if it is
on a trailer for instance) going solar is a great option.Lets crunch some numbers. First I will make an estimate of a tiny houses
electrical need.First there is the draw
Refrigerator
Microwave?
Hot Plate?
Coffee Maker
Fan(s)
Laptop
Radio (or speakers)
DC pump for water
NiMH battery charger
Cordless phone
Lights (hopefully fluorescent)(actually this is what I have, so I happen to have the numbers for their
electrical consumption)fridge consumes 331 KWh/year (so that equates to about 900 watts/day)
Microwave 2000 watts actual times however long it takes the popcorn to pop
--about 10 minutes a day -- 333 watts per day
hotplate 1000 watts times however long it takes the eggs to cook over hard
I would guess about 1/2 hour a day --500 watts per day
Coffee maker -thermal carafe by the way, so it just takes power during
brewing- about 1000 watts times about 12 minutes to brew a pot = 183 watts
per day
Fans about 120 watts times however long you leave them on, maybe 2 hours a
day--240 watts per day
Laptop about 40-60 watts usually times 24 for me--about 1200 watts per day
1000 watt speaker system (usually draws about 100 watts) only when I am
jamming out or watching a movie, I'd say 6 hours a day 600 watts per day
DC pump for water pressure 84 watts times about 1 to 2/60 of an hour
1.4-3watts per day
battery charger (almost nothing) but lets say if you are charging batteries
everyday 5 watts times 24--120 watts per day
cordless phone 6 watts times 24 -- about 144 watts per day
lights each bulb about 30 watts times how many hours you are a night owl
(one bulb per person then the difference between when there is usable light
inside and bedtime) guessing here at 6 hours--- 180 watts per day
Wireless router about 150 watts per day
DSL modem about 130 watts per dayLets add this up
I get 4683 watts per day as what I need for my electric hungerI have 8 Kycocera 120 watt panels on a Zomeworks passive tracker
that means I get 960 watts in full sun (in my dreams you actually get about
80% of that)
so I get about 760 watts when the sun is shining
so if you do the math the sun needs to shine a little over 6 hours to supply
my need
which is about how I figure it, I actually don't get that many average "sun
hours" in my location due to clouds, my northern location, etc....year
round. However I track the sun so when the sun is out my panels are facing
them, so that helps a lot. About 40% more power in the summer and 15%
better power in the winter, average of about 25% more output from stationary
mounted panels. Also it doesn't make sense economically to track until you
get to about 1000 watts of solar, it is cheaper to buy more panels instead
of making the ones you have more efficient. However I lost two panels to
the ex-wife in the separation, I used to have 10 total. I personally like
tracking, because the tracker uses less resources than the panels do and it
is a great demonstration of a wonderful technology that is simple and works.
( www.zomeworks. com)So you wanted to know about economics, life span we will discuss next
Life span of the panels --about 40 years-- most manufacturers guarantee
output for 10 years, the panels make the energy it took to create them in
the first place in about two years depending on how they are installed (see
http://www.homepowe r.com/files/ pvpayback. pdf) the other components in the
system might not last as long. I am a big fan of lightening protection and
recommend www.deltala. com delta lightening arrestors for that reason.
Assuming you don't have a catastrophic failure to your inverter (about
1500-2000) the rest of the components are not as big a pill to swallow if
they fail on you. Batteries are the shortest lived part of a Renewable
Energy system, if they are properly maintained you can get a good 10 years
of performance from them, if you abuse and neglect them quite a bit less. I
use 6 volt deep cycle batteries that are rated at 350 amp*hrs, I have 8 of
them. They are arranged in two banks of 4 so that I have a series-parallel
configuration. It is best to not arrange battery cells in parallel if you
can help it. In hindsight I would have set up my system to run at 48 volts
instead of 24 (would have saved me a few hundred dollars in wire from the
wind tower-miscommunicat ion from the vendor caused that one) My total
battery storage is 24 volts and 700 amp hours (you only can draw the
batteries half way down so I actually can only use 350 of those amp*hrs) you
multiply those numbers and you have 8400 watt*hrs (that is only two days of
autonomy from the sun--not good--however I don't like the thought of
replacing all those batteries every 7-10 years at a cost of about 1200
dollars, which is why I use wind as well. It tends to fill in the gaps
between sunny days and has a longer lifespan than a battery.Payback time, well assuming you have an option of going on grid and going
off grid, it is cheaper to go on grid. However there is a warm, fuzzy
feeling about knowing blackouts don't affect you (after all after a few days
of no sun, you have a brown out anyway, so your used to it) However lets
look at the numbers, grid power costs about 8.35 cents / KWhr in Arizona so
that if you had a 1000 watt solar tracking system it would cost you roughly
9000 in parts (using the calculator at
http://rredc. nrel.gov/ solar/calculator s/PVWATTS/ version1/ ) you will make
about 2178 KWhrs a year which worth about $185.13 at the current price of
grid power (but that is sure to go up in price in the next 40 years, that
you can count on) then it would take you roughly 50 years to pay for your
system (not counting battery replacement costs) which would be a sizable
portion of your continuing costs. However that is at the current price of
power, If the cost of electricity doubles then you would have made a good
investment in an uncertain future. Not to get into the science of
non-renewable resources but they will eventually run out, and when that
happens you won't be able to buy power at any cost, but then again if that
happens electricity is the least of your worries.
Thanks to Tim Johnson - understanding this stuff is not included in architecture school.