Mr. Electricity is your guide to saving energy in your home.
We're recommended by the government of Berks County, PA.
Related sites:
Watt Watt. News about efficiency and conservation, written by readers of the site.
Home Power Magazine. All about renewable energy for the home.
Thin House. Blog about a family committed to cutting its energy use by 80%.
No-Impact Man. Blog about a family striving to have no net impact. (i.e., What little they use, they offset.) Inspirational.
Off-Grid. News and resources about living without being connected to a utility company.
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If you like this site, you might also like some of my
other sites:
Battery
Guide
Which battery is best? We cover
rechargeable and alkaline batteries to show you what's hot,
what's not, and the best way to charge them. (visit
now)
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The
Military Budget as Cookies
This excellent animation from TrueMajority shows in
graphic detail (using Oreo cookies) how ridiculously, large
the military budget is, and how we could solve many domestic
problems with a modest 12% cut. A must-see. (watch
it now)
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Solar
electricity:
Finally affordable!
April
2009
How much does a solar
system cost?
A system big enough to supply energy
for an average
home (920 kWh/mo.) will cost $7,000
to $88,000. That compares to $26,500 the
average household would have spent on average
for dirty electricity.
Yes, that's quite a range in prices.
The price is affected by tax credits, rebates,
local prices in your area, and how much sun you
get. Since everyone's situation is different,
the calculator at right will help you figure the
costs for your particular situation.
What you'll see is that in many cases,
solar is affordable
right this very minute. If the
calculator shows that your price per kWH is less
than what you're currently paying per kWh, then
solar is an excellent deal and I recommend you
explore it. If your price per kWh is over what
you're currently paying, then consider whether
you're willing to pay a premium to go green.
Realize that you don't have to get a
system large enough to generate as much as you
use. You can start out with a system that
generates 75%, 50%, 25%, or even just 15% of
your needs to lower your cost. And a 15%
reduction in pollution is better than 0%. Most
people who have gone solar so far have paid a
premium in order to get their energy without
pollution; the environment was their concern,
not money. But as solar is becoming
cost-competitive with dirty energy, people are
indeed going solar to save money.
The 30% federal tax credit is what
suddenly made solar a lot cheaper. Before
2009 the tax credit was limited to $2000. But
now there is no limit. So if you install a
$40,000 system, you lower your tax bill by
$12,000. The credit is 30% of your cost, after
any state/local rebates you get. (Case A in the
calculator assumes a rebate, so the tax credit
in that example is lower.) Note that a tax
credit is more powerful than a tax
deduction. A deduction just
reduces the amount of your income, on
which the tax is based. But a tax credit
comes directly off your total taxes.
State and local rebates can be even more
powerful than tax credits, but they're not
available to everyone. Here are some sample
rebate programs:
- Arizona: $2.50 - $3.00 / watt
- California: $1.90 - $2.50 / watt
- Colorado: $2.00 - $4.50 / watt
- Texas (Austin): $4.50 / watt
- Databases of rebate programs: RecSolar,
DSIRE
If you don't have spare thousands of
dollars lying around, you can always finance the
purchase (i.e., get a home improvement
loan). And if you're in California, you
might be able to rent a system by the month
instead of paying a ton of money up front. Did I
say rental...?
Yes, you might not have to buy a system
outright. A number of companies are now
renting solar systems to California customers,
so you just pay a monthly rate and don't incur
huge startup costs. I'll cover rental programs
below.
Those versed in finance might complain that
I'm not considering opportunity cost, or the
time value of money. They might say you could
take the money you would have spent on solar and
invest it, which earns a return, so the relative
cost of solar is thus higher, because you had to
pay all the money up front. What that idea
misses is that solar is also an investment:
You're locking in your cost for electricity for
20 years, and buying yourself out of
inflationary increases for the price of energy.
If you could get 6% a year with outside
(non-solar) investments but you have to pay 4-5%
more for electricity each year, then your
investment returns are negligible when weighed
against the extra electric cost, and thus the
kWh costs I just quoted for solar are still
pretty accurate. In fact, you might do even
better with your solar investment -- in 2008
dirty electricity costs went up by about 8%.
Incidentally, prices for naked solar panels
run about $4.50 per watt ($222 per kWp), but the
installed cost with all the equipment is around
$6 to $10. (price checked in
9/08; see
current
prices)
|
Price per
kWh
|
Source of
Electricity
|
|
40¢
|
Solar, worst case
($10k install, 105
kWh/mo., no rebate, no tax
credit)
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|
36¢
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Grid energy, Hawaii
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23¢
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Wind turbine, 9mph avg. wind
($3942 installed cost plus
maint. less tax credit, 71 kWh/mo.) (e.g.
Austin/Dallas/San Antonio TX, Mobile AL,
Baltimore, St. Louis, S.F., Denver, SLC,
Wilmington DE, D.C., Miami, Boise, Topeka,
Cincinatti, Lexington KY)
|
|
19¢
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Grid energy, Japan
|
|
17¢
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Grid energy, Alaska
|
|
17¢
|
Solar, average case
($8k
install, 120 kWh/mo., $1/watt rebate, i.e.
$1000, tax credit)
|
|
12¢
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Grid energy, U.S. average
|
|
12¢
|
Solar, good case
($7k
install, 120 kWh/mo., $1.90/watt rebate,
i.e. $1900, tax credit)
|
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10¢
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Wind turbine, 12mph avg. wind
($3942 installed cost plus
maint. less tax credit, 158 kWh/mo.) (e.g.
NYC, Boston, Buffalo, Milwaukee, OKC,
Corpus Christi TX, Lubbock TX, Wichita KS,
Hawaii)
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|
3¢
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Solar, best case
($6k
install, 135 kWh/mo., $4.50/watt rebate,
i.e. $4500, tax credit)
|
|
Sources & Notes:
Prices last sourced or calculated Dec.
2008. Grid energy prices for U.S. from
DOE,
for Japan from OECD.
Solar systems are 1 kWp in size. Solar and
wind systems expected to last for 20
years. Solar tax credit is 30% of
installation cost after rebates. Wind
turbine price of $2775 from
Sundance
Solar, +$86
shipping +35% installation +2% annual
maintenance.
Wind
tax credit is
$1000 per kW of nameplate capacity.
I don't list rental programs like
SolarCity Sun Run in the table because
those companies don't bother to provide
any sample pricing on their websites. As
soon as they're willing to stop being
annoying and clueless, I'll list them
here.
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Why solar is finally
affordable
Before now the biggest problem with solar
systems was the huge upfront cost. The next
problem was that even after 20 years, you wouldn't
make your money back. That left solar only for
people who were willing to shell out the extra cash
required to go green. This explains why only 0.1%
of U.S. energy comes from solar as of 2008.
(source)
For global energy it's even worse -- solar provided
only 0.02% in 2004. That's not two percent, that's
two-hundredths of a percent.
(source)
But solar is finally affordable in many cases
. Here's why.
- Solar gets cheaper every year. It's
not just that every year solar gets a little
cheaper. It's also that every year dirty energy
like oil and gas gets more expensive. And while
that's always been true, what's special about
now is that in many cases those lines have
already crossed, making solar cheaper than dirty
energy. Solar costs have gone down by an average
of 3.5% per year from 1998 to 2007 in real
dollars. (source)
- New tax credit. Before 2009, U.S. the
tax credit for installing solar was limited to
$2000. But now there is no limit. The credit is
good for 30% of the system cost, after rebates.
This tax credit is more powerful than a
tax deduction. A deduction simply reduces
your taxable income, while the credit reduces
your tax bill directly. In plain English, a
$10,000 tax credit reduces your taxes by
$10,000. A tax deduction reduces it by only
$1500 to $3500, depending on which tax bracket
you're in.
- State & Local rebates. Rebates
for installing solar have been around for a
while, but only recently has the cash back been
significant -- enough to often make it solar a
good deal as well as a good environmental
choice. A $3 billion plan in California
unveiled in 2005 aims to put 3,000 megawatts of
solar energy on 1 million homes, businesses and
public buildings over 11 years. And in Austin
the rebate from the city for homeowners who go
solar is $4.50 per watt. Systems generally cost
$6-10/watt to install, so the rebate covers
45%-75% of the system cost. For a small 1 kWp
system on the low end, that's $6000, less the
$4500 rebate, for a net cost to the consumer of
$1500. Have a look at the table at right and you
can see the power of rebates in full force. And
remember, even after rebates you still get a 30%
tax credit.
- Rental Programs. At least three
different companies offer rental programs which
let you rent the panels for a fraction of the
cost of buying the system outright. Another
attractive benefit of rental programs is that
you're not responsible for maintenance. If
something breaks, the company fixes it for free
and you don't have to worry about it. Here's how
the different residential rental programs stack
up.
|
Company
|
Service
area
|
Minimum
use required
|
Min.
Upfront Cost
|
Availability
|
|
SolarCity
|
California only
|
~1250 kWh/wo.
|
$2000+
|
Now
|
|
Sun
Run
|
California only
|
~1250 kWh/mo.
|
$6000+
|
Now
|
|
Citizenre
|
USA except not AK, AL,
KS, MO, MS, NE, NV, SC, SD, TN, WV, and
Austin, TX
|
~250 kWh/mo.
|
$500 deposit
(refundable)
|
mid-2010 at earliest
|
All these solar rental programs are very new,
and I predict solar rental programs will be The
Next Big Thing in solar, or energy production
itself for that matter. Lots of companies will
be offering this type of thing in the very near
future.
Note that Citizenre is just an idea at present.
The company hasn't yet secured financing to
build its manufacturing plant, and it's anyone's
guess when if ever they'll be able to do so.
SunEdison offers a commercial
rental program for business customers.
- Film-based solar cells. A company
called Nanosolar has developed a method to make
solar cells at a much lower cost. Instead of
making big, expensive silicon cells, their
method involves printing a very thin, flexible
film. This makes solar power cost-competitive
with electricity from the grid. The founders of
Google were so excited about this breakthrough
that they invested in the company. Nanosolar is
actually producing product now (this
isn't just a pipe dream), but as I write this
product is sold out through 2009.
(More from Technology
Review and
the
manufacturer)
A similar technology is dye-sensitized
cells, which are supposed to be 1/10th the
cost of traditional cells, but there's no word
yet on when they'll go into
production.
- Plastic solar cells. Like Nanosolar,
STMicroelectronics came up with an alternative
to expensive silicon cells. Their solution
involves making cells out of plastic. It's not
nearly as efficient as silicon, but it's a
whole lot cheaper to produce. Something like
twenty times cheaper. Suddenly this makes solar
cost-competitive with the grid. There are two
downsides: One, because the new cells are less
efficient, you need a lot more space to produce
the same amount of electricity as with
conventional cells. Most homes barely have have
enough roof area to generate all their
electricity from regular solar cells, and with
the less efficient cells, it's unlikely that a
house could go solar for all its needs. (It
could certainly augment its grid usage,
though.) And two, these new cells aren't
available to consumers yet, but I'm guessing
they'll be available by 2010.
(More from CNN
and the
manufacturer)
- Trackers & Mirrors. This is an
old idea but it's taken a while for anyone to
make it easy and cheap enough: Use motors to
keep slightly moving the panels to keep them
aimed directly at the sun, and use lenses and
mirrors to concentrate the sun's energy. And
motors and mirrors are a lot cheaper to make
than solar cells. Many of these products are
available now. (Example:
Energy
Innovations)
Sungevity: Only slightly
cheaper
Readers have been asking why I
haven't listed solar system retailer
Sungevity
on this page, so here's the explanation:
Their systems aren't so much cheaper that they
make solar affordable. They're about 10% cheaper
than competitors' systems, but that's not enough
to suddenly make a huge difference. Their 1.5
kWp system costs $7500 and will save about $292
a year in electric costs, making the payback
time 26 years -- longer than the projected life
of the system. Even then, it's only available to
California residents. Still, if you're in
California, and you prefer to buy instead of
using one of the rental programs mentioned
above, then Sungevity will likely give you the
best price. You can also get a nearly-instant
quote on their website, since they use
satellites to check out your roof remotely to
calculate how suitable it is for solar.
How does a solar energy
system work?
A complete system consists of:
- Solar panels
- Inverters, which convert DC
electricity into AC
- Service panels to tie the output
to your home's wiring, and to let you send
excess electricity back to the utility
 A
system could also have batteries to store
extra electricity. This would allow you to live
completely off the grid if your system were big
enough and if you were good at conservation. But
it also increases the cost and maintenance
requirements substantially, so I recommend you
pass on the batteries. It's easier just to send
the excess you generate back to the utility and
get paid for it.
With a battery-less system, sometimes you'll
be using grid energy and sometimes you'll be
using solar energy. Here's a chart showing a
hypothetical system:
- Red bars.
At night when the sun's not shining,
you'll be getting your electricity from your
local utility.
- Green
bars. During the day, your system
will make some electric and you'll use it
right away.
- Yellow
bars. During the day you'll make
more electric than you need, and you'll sell
that back to the utility.
So as long as you're still connected to the
grid, the size of a system is kind of arbitrary.
You could have a tiny system that simply fuels
part of your needs with green energy, or you
could have a massive system which still won't
fuel all your needs, because it won't run at
night.
How much roof space is
required?
How big a system do I
need?
|
Annual average daily solar
radiation per month
(using a flat-plate
collector facing south at a fixed tilt
equal to the latitude of the site,
which maximizes input). The
scale is the same for peak sunlight
hours. For example, yellow-shaded areas
get an average of 5 to 6 hours of peak
sun per day. (from NationalAtlas.gov)
|
The size of your system is arbitrary --
you can pick any size you want. That's
because in most cases you'll still be connected
to your utility, so you don't have to try to
generate 100% of your needs 100% of the time.
You can get a smaller system to supply 80%, 50%,
or just 15% of your needs, which lowers the
system cost. Even with a small system, you're
still reducing the amount of pollution being
generated at the power plant, because you'll be
using less of their electricity. You could also
go the other direction, getting a system to make
150% or 200% of your needs, selling the excess
you generate back to your utility company. The
point is, the size of your system isn't
something you figure with a calculator, it's
your own personal preference.
If you want to go completely "off the
grid" -- that is, disconnect from your
utility company -- then the cost of installation
soars. The first thing you have to add is
batteries, to store excess energy during the day
so you can use it at night. Then you need a huge
system, to make and store lots of extra energy
to use for other times when the sun doesn't
shine. For most people there's no need to go
this route -- you can just remain connected to
the grid, and then get any size system you
want.
Many people size their system to match the
amount of electricity they use, even though
sometimes they'll be getting some of that energy
from the grid, and sometimes they'll be sending
excess that they generate back to the grid. See
the previous section for
more on that. Let's say you want to go that
route: How big a system do you need? Here's a
rough estimate, based on a typical house.
|
Rough estimate of solar system
sizing to generate 900 kWh/mo
|
|
|
Colored area from map at
right
|
|
|
Light Green
|
Yellow
|
Orange
|
|
Size of system
|
8.6 kWp
|
7.4 kWp
|
6.7 kWp
|
|
Space required
|
860 s.f.
|
740 s.f.
|
670 s.f.
|
This calculator
from Sharp may give you a more accurate
idea, since it's based on your actual zip code
(so they can tell how much sun you're getting)
and how much you're paying for electricity each
month (so they can tell how much electricity
you're using).
kWp is just the units we use to
measure the system. Sometimes it's just referred
to as plain kW. It's not important to
know what kWp means. (But if you must know, it
stands for kilowatt-peak, which is the
maximum possible output of the system at any
point in time.) Each kWp generates 105 to 135
kWh of electricity each month, depending on
where you live on the map.
Here's how you can find how large a system
you need to generate as much energy as you
use:
- Figure your daily usage. If you
use 900 kWh/mo., that's 900 kWh / 30.4 days
per month = 29.6 kWh/day.
- Figure how many kWh you need to
generate each hour. From the map above
you can see that if you live in a yellow area
that you'll get 5 to 6 hours of peak sun per
day on average. We'll call that 5 hours/day
to be conservative. Since you need to
generate 29.6 kwH/day, you need a 29.6 kWh /
5 hours = 5.92 kWp system.
- Add a safety margin. Multiply by
1.25 to account for shading, dust, and bad
feng shui. So 5.92 kW x 1.25 = 7.4
kWp. We need a 7.4 kWp system.
Each 1 kWp of system takes about about 100
s.f. (10' x 10') of roof space.
(source for roof
space)
Note that there's no reason you have to put
the system on the roof. If you're willing to
give up some yard space, you can put the panels
on poles on the ground. This is a good
choice when the roof is shaded by trees and
doesn't get enough sun. Putting the panels on
the ground is also nice because then the panels
can be easily arranged at the optimum angle to
get the most sun, while on the roof you're
limited by the ridgeline of the house.
You can't put panels on every face of your
roof because it's only economical to put them on
the parts that get the most sun. You typically
want the panels facing south. Panels facing east
or west might barely be acceptable, maybe.
Panels facing north are useless.
Remember, if you don't have "enough" roof
space it's not really a problem, because system
size is arbitrary. Whatever system you install
will simply mean that some portion of your
electric needs comes from green energy.
Here are other solar maps and
calculators for those wishing to run their
own numbers:
- Sharp
Zip Code calculator. Enter your zip code
and get more info about a possible system
than you could ever imagine.
- U.S.
Peak Hours map from Wholesale Solar.
- U.S.
Peak Hours map from APS Project.
(kWh/m2 is the same as peak
hours).
- U.S.
Combination Calculator/Map. Lets you
choose Average, Maximum, or Minimum; for the
whole year or just a specific month; and
according to how well your equipment is aimed
at the sun. Wow!
- U.S.
Cities table. Lists summer, winter, and
average peak hours per day for tons of U.S.
cities.
- World
Peak Hours map by month. Nice map where
you can click on the city of your choice and
get a month-by-month listing of peak sun
hours, but unfortunately it doesn't tell you
the average for the year.
- World
peak hours calculator. Choose your
country / city and get detailed info. Takes a
few clicks to get to what you want,
though.
- Word
Peak Hours map for the worst month
of the year. (This is not an average
for the whole year!) Many installers base
their system size on the worst month's sun
output, to be conservative.
How much electricity does
a solar panel generate?
For home energy, it's generally
better to use the method above: Start with
your monthly needs for electricity, then
calculate how big a system you need. But if for
whatever reason you want to know how much energy
you can get from a solar panel, here's how to
calculate it. First start with the number of
hours of "peak sun" you get per day. That's
easy: In our map above, it's 4 hours for green,
5 hours for yellow, and 6 hours for orange. Then
multiply that by the peak output of your panel,
then by the number of days per month. For
example, for a panel rated at 150 watts in New
York, we'd have:
4 hours peak sun
x 150
watts panel
x
30.5 days per month
÷
1000 kWh/watt-hour
=
18.3
kWh/mo.
Solar panels do NOT take
more energy to make than they generate
Somehow the myth got started that it
takes more energy to make a solar panel than you
can get out of that panel. That's just
absolutely not true. The energy payback time on
a panel is 1.5
to 3.5 years, but the panel will produce
useful electricity for at least 20 years. So if
you were worried that solar panels were energy
wasters in disguise, you can breathe a sigh of
relief. They're not.
Google goes solar in a
big way
In 2007 Google built a massive
1.6-megawatt solar system at its headquarters in
California. It generates 30% of Google's
peak demand, and around two million kWH a
year. It's the largest corporate solar
install in the U.S. (There are larger
installations at utility companies, but this is
the biggest for a company generating its own
electric. Here's a good list of the
largest solar installations in the world.)
Google has a page where you can see
how much electricity they generated in the
last 24 hours and the last 7 days. You can also
see a flyover
video of their installation.
The system will take 7 years to pay for
itself, and then will generate free electricity
for another 18. (The lifespan of the panels is
about 25 years.)
It doesn't end with this huge installation.
In late 2007 Google announced
its plans to develop a whopping one
gigawatt of energy from renewable
sources at a cost cheaper than coal, and to
do it "within years, not decades". Wow.!
Other solar
resources
I just found this interesting list of
the
world's 13 largest solar energy plants.
The Wikipedia
article on solar electricity is impressively
comprehensive.
Wind power
compared
Wind power has the same problems as
solar: a big upfront cost, and higher
cost-per-kWh than grid electricity over its
whole useful life. A $16,500 system ($12,500
+ $4000 installation) could generate 74,403 kWh
over its 20-year life. That's 22¢/kWh,
double the cost of grid electricity. But again,
the point of going wind or solar isn't to save a
ton of money, it's to get your electricity
without causing lots of pollution. If you can
afford the price premium, you can go green.
Wind power resources:
Last updated: December
2008
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