Please tel me this is not correct, and why!

[Alan Combellack]

I live near Ottawa in Canada. We receive, in December, about 1.2
kWh/day/m^2 on a horizontal surface (annual average about 3.5). A system
with the angle of the cells tracking the sun will receive a maximum power in
December of about 3 1/4 kWh/day/m^2. A fixed system, optimised for
December, would receive about 2.2 kWh/day/m^2. I would like to generate 24
kWh/day from PV cells and want to draw 1 kW continuously so I need
batteries. I would
need, say, two days reserve to carry over overcast days. I therefore will
need about 70 kWh of storage capacity. Batteries have a limited life so
will need replacing every, say, 6 years. PV cell probably last about 25
years so we will need to replace the batteries 3 times meaning we will need
210 kWh of batteries over the life of the system. The questions are:- "Is
this worth doing? If not; what cost levels are needed to make such a system
economically feasible?"
The first guesstimate is done using car batteries at today's prices which
may be $100 C per kWh. The total battery cost will therefore be about
$21000 C. Not negligible. No doubt there will also be maintenance costs as
well as environmental control of the significant volume the batteries will
require. There are probably less expensive options for the batteries, such
as those used in telephone Central Offices which are also much longer
lasting than car batteries. For now I will go with $20k for the batteries,
which is a somewhat alarming start.
As stated previously I can expect to receive about 2.2 kWh/day/m^2 with a
fixed panel optimally set for December. Over the whole year the average
insolation would be about 4.3 kWh/day/m^2.
Since solar cells are around 20% efficient at present and I want to be
able to use 24 kWh/day I would need a minimum of 24/(.2*2.2) = 54.5 m^2 of
panels. If I start from scratch in December (not a good idea) I would need
much more area so as to ensure that the reserve batteries become properly
charged. In any case it is quite likely that the batteries could become
discharged during long cloudy periods. It seems to me that I would need an
area of at least 3 times the calculated area, i.e. 164 m^2.
I know of one panel which produces 190 W from irradiation of 1 kW/m^2 and
which costs, on special, $840.00 US. It covers an area of 1.4 m^2. We will
probably never get 1 kW irradiation in December but the figures might give
me a rough estimate of panel cost. This would total about 164/1/4*840 =
97425 dollars US. Add that to the battery cost of about $20000 we have a
cost of around $117425.
Over the life of the PV panels this system might produce a total of about
1.3 million kWh of useable electricity. My cost for a kWh is, at present,
about 11 cents (Canadian) so the value of the electricity produced might be
$141569. This suggests we just about pay back the installation cost in the
25 life span of the system.
I don't think I would be interested unless I could get pay back in much
more than 5 years so it appears I will have to wait until PV cells and
batteries become very much less expensive, say by a factor of about 5.
No doubt I have made errors in this analysis and I would be very happy to
receive any and all comments and criticisms
Thank you,

Alan C
[email protected]

 

[SJC]

I assume that you do not want to use grid netmetering. Here in California that
seems to be the way to go. I think you have pointed out the high costs and long
payback of this method rather well.

I live near Ottawa in Canada. We receive, in December, about 1.2
kWh/day/m^2 on a horizontal surface (annual average about 3.5). A system
with the angle of the cells tracking the sun will receive a maximum power in
December of about 3 1/4 kWh/day/m^2. A fixed system, optimised for
December, would receive about 2.2 kWh/day/m^2. I would like to generate 24
kWh/day from PV cells and want to draw 1 kW continuously so I need
batteries. I would
need, say, two days reserve to carry over overcast days. I therefore will
need about 70 kWh of storage capacity. Batteries have a limited life so
will need replacing every, say, 6 years. PV cell probably last about 25
years so we will need to replace the batteries 3 times meaning we will need
210 kWh of batteries over the life of the system. The questions are:- "Is
this worth doing? If not; what cost levels are needed to make such a system
economically feasible?"
The first guesstimate is done using car batteries at today's prices which
may be $100 C per kWh. The total battery cost will therefore be about
$21000 C. Not negligible. No doubt there will also be maintenance costs as
well as environmental control of the significant volume the batteries will
require. There are probably less expensive options for the batteries, such
as those used in telephone Central Offices which are also much longer
lasting than car batteries. For now I will go with $20k for the batteries,
which is a somewhat alarming start.
As stated previously I can expect to receive about 2.2 kWh/day/m^2 with a
fixed panel optimally set for December. Over the whole year the average
insolation would be about 4.3 kWh/day/m^2.
Since solar cells are around 20% efficient at present and I want to be
able to use 24 kWh/day I would need a minimum of 24/(.2*2.2) = 54.5 m^2 of
panels. If I start from scratch in December (not a good idea) I would need
much more area so as to ensure that the reserve batteries become properly
charged. In any case it is quite likely that the batteries could become
discharged during long cloudy periods. It seems to me that I would need an
area of at least 3 times the calculated area, i.e. 164 m^2.
I know of one panel which produces 190 W from irradiation of 1 kW/m^2 and
which costs, on special, $840.00 US. It covers an area of 1.4 m^2. We will
probably never get 1 kW irradiation in December but the figures might give
me a rough estimate of panel cost. This would total about 164/1/4*840 =
97425 dollars US. Add that to the battery cost of about $20000 we have a
cost of around $117425.
Over the life of the PV panels this system might produce a total of about
1.3 million kWh of useable electricity. My cost for a kWh is, at present,
about 11 cents (Canadian) so the value of the electricity produced might be
$141569. This suggests we just about pay back the installation cost in the
25 life span of the system.
I don't think I would be interested unless I could get pay back in much
more than 5 years so it appears I will have to wait until PV cells and
batteries become very much less expensive, say by a factor of about 5.
No doubt I have made errors in this analysis and I would be very happy to
receive any and all comments and criticisms
Thank you,

Alan C
[email protected]

 

[Anthony Matonak]

I live near Ottawa in Canada. We receive, in December, about 1.2
kWh/day/m^2 on a horizontal surface (annual average about 3.5). A system
with the angle of the cells tracking the sun will receive a maximum power in
December of about 3 1/4 kWh/day/m^2. A fixed system, optimised for
December, would receive about 2.2 kWh/day/m^2. I would like to generate 24
kWh/day from PV cells and want to draw 1 kW continuously so I need
batteries. I would

24kWh/day is rather a lot of electricity. Are you really sure you need
this much? Conservation (using less) is one heck of a lot cheaper than
buying bigger systems. Even if you don't go with solar, reducing your
power consumption will save you money in the long run.

need, say, two days reserve to carry over overcast days. I therefore will
need about 70 kWh of storage capacity. Batteries have a limited life so
will need replacing every, say, 6 years. PV cell probably last about 25
years so we will need to replace the batteries 3 times meaning we will need
210 kWh of batteries over the life of the system. The questions are:- "Is
this worth doing? If not; what cost levels are needed to make such a system
economically feasible?"

A good set of batteries might last 10 or more years, if you don't abuse
them. PV cells are warrantied for 80% power at 25 years but they can be
expected to continue to generate power for 50 to 100 years. At 50 years
they may only produce 64% and at 100 years 51%. So you can figure you'll
need to add roughly 50% more PV panels every 100 years.

In any case, if you are looking at off-grid PV then the economic
comparison is against running grid power to your property. If you
are already connected to the grid then it's much cheaper to go with
a grid-tied system that has no batteries.

If you are looking to generate power cheaper than the grid then
just forget about it. Power companies generally generate power
cheaper than anyone can at home and lots cheaper than using PV.

The first guesstimate is done using car batteries at today's prices which
may be $100 C per kWh. The total battery cost will therefore be about
$21000 C. Not negligible. No doubt there will also be maintenance costs as
well as environmental control of the significant volume the batteries will
require. There are probably less expensive options for the batteries, such
as those used in telephone Central Offices which are also much longer
lasting than car batteries. For now I will go with $20k for the batteries,
which is a somewhat alarming start.

Why car batteries? They aren't very cheap and don't work well for deep
discharge. Look at golf cart batteries if you want cheap or large lead
acid batteries like the Rolls if you want long lasting.

Since solar cells are around 20% efficient at present and I want to be
able to use 24 kWh/day I would need a minimum of 24/(.2*2.2) = 54.5 m^2 of
panels. If I start from scratch in December (not a good idea) I would need
much more area so as to ensure that the reserve batteries become properly
charged. In any case it is quite likely that the batteries could become
discharged during long cloudy periods. It seems to me that I would need an
area of at least 3 times the calculated area, i.e. 164 m^2.

Solar cells are really around 10 to 12% efficient in the real world,
mostly. Insolation is also more likely to be closer to 900 W/m^2 than
1000W/m^2. Also you should probably discount the STC ratings on the
panels by as much as 80% due to temperature effects. Batteries are
only around 80-90% efficient themselves and if you use an inverter then
it also is in the 80-90% efficiency range.

To provide 24kWh/day you would then need (roughly) 24kWh/.8/.9/.9=37kW
of PV panels. At 12% efficiency and 1000 W/m^2 these panels would have
to be (37,000W/.12/1000) 308 m^2.

You might find it cheaper to install somewhat less PV than you need and
supplement your power with a wind turbine or generator.

Anthony

 

[Alan Combellack]

Ron and everyone else who replied,
Many thanks to everyone who replied. I like this group.
My estimates were deliberately simplified and I do know that I left out
many areas of inefficiency. I was just looking for a ball-park figure to
see if the thing is feasible at all.
My existing house is a very old log farmhouse on a fairly well treed 3/4
acre lot which has a decent southern exposure. I do have access to utility
power and everything in the house; heating; cooking; lighting; clothes
washing and drying; water heating; TVs etc. and even water pumping is
powered by electricity. The average electricity use between April 2000 and
April 2001 was, believe it or not, 3.65 kW continuously so my target figure
of 1 kW continuous was reasonable I think (although present consumption
certainly isn't).
It seems that to replace all of this power would cost about three times
the current value of the property which is clearly not sensible, even if it
were possible.
I have done a lot of calculations about insulation improvement as well as
assessing the advantages of adding thermal solar panels for the heating.
Very much better value can be obtained by going these routes, if the local
municipality could be persuaded to allow it.
The heating model shows payback of about $20k in around 8 years. This
would replace about 60% of the heating and I would also have a new 2 car
garage; greenhouse and large spare room. I think this is nearly
economically sensible but I am still trying to convince myself to go ahead
with it. I don't have $20k lying around unused unfortunately.
I'll keep my eye on PV panel prices and when (if) they fall to something
like 1 or 2 dollars per Watt I may try and build a smaller system.
Thanks again everyone although I do wish I had made some serious errors in
my simple calculations.

Alan C

 

[[email protected]]

I have done a lot of calculations about insulation improvement as well as
assessing the advantages of adding thermal solar panels for the heating.
Very much better value can be obtained by going these routes, if the local
municipality could be persuaded to allow it.

For the same heat output, a sunspace or polycarbonate "solar siding" can be
a lot less expensive than solar thermal panels...

Nick

 

[Steve Spence]

There is no "netmetering" in Ontario and may never be
any the way our government has their heads up their
asses.

None in Upstate NY (National Grid) either.

 

[SJC]

Here is some info on Net Metering and other energy issues in NY.
http://www.dsireusa.org/library/includes/map2.cfm?CurrentPageID=1&State=NY

Are they talking about it incessantly in NY?

 

[Steve Spence]

Are they talking about it incessantly in NY?

not a whisper.

 

[Alan Combellack]

Nick,
I haven't been keeping up to date on solar matters for a couple of years
so know nothing about this solar siding stuff. I will certainly look into
it and would appreciate any links you care to suggest. My previous
conclusion was that it was nearly, but not quite, an economic proposition,
provided I did most of the building myself, so any significant reduction in
costs are of great interest to me.
Thanks,
Alan C

 

[[email protected]]

I haven't been keeping up to date on solar matters for a couple of years
so know nothing about this solar siding stuff...

It's a single polycarbonate layer of clear Dynaglas greenhouse roofing with
90% solar transmission and R1 insulation value, applied in lieu of house
siding with horizontal corrugations and an airspace over a dark surface.
Sun heats air which circulates between the airspace and the living space
during the day. Airflow stops at night, with a one-way plastic film damper.

The polycarb costs about $1/ft^2 and should last 20 years. Where I live near
Philadelphia, 1000 Btu/ft^2 of sun falls on a south wall on an average 30 F
January day, when 80 F airspace air might lose 6h(80-30)1ft^2/R1 = 300 Btu,
for a net gain of 600 Btu/ft^2 per day. In peak sun, the output would be
about 250-(80-30)1ft^2/R1 = 200 Btu/h-ft^2 (59 watts), or about $0.017/PW.

Nick

 

[daestrom]

None in Upstate NY (National Grid) either.

AFAIK (I'm also a National Grid customer), they *do* allow net-metering on
PV only. They don't allow net-metering on any other form of private
generation.

daestrom

 

[SJC]

In California, I guess we figured out a watt saved is a watt earned.
We also have a rebate program that pay about $3 a watt for PV to
help offset the cost of the system.
This rebate is paid for by putting a small fee on everyones bill every
month. This fund will work as long as only a small percentage of the
people actually do install a system in any given year.
It helps to create more solar homes every year, so in the long run
we all can benefit.

A local (to me) utility here has advertised net
metering upon request. After a call to their metering
guys about it, turns out they put a mechanical meter
with no detents on your house, which most already have.

This is not only very inaccurate for light loads in
reverse but illegal to bill on also. The alternative is
a true netmeter and mass memory for dial up
interrogation costing about $3-4K for the home. I doubt
the PV owner wants to pay for the difference they can
charge.

The solution is coming soon though once the gov. makes
up it's moronic mind which way to go.


message

 

[[email protected]]

A local (to me) utility here has advertised net
metering upon request. After a call to their metering
guys about it, turns out they put a mechanical meter
with no detents on your house, which most already have.

This is not only very inaccurate for light loads in
reverse but illegal to bill on also.

Would you have any evidence for these articles of faith?

Nick

 

[daestrom]

A local (to me) utility here has advertised net
metering upon request. After a call to their metering
guys about it, turns out they put a mechanical meter
with no detents on your house, which most already have.

This is not only very inaccurate for light loads in
reverse but illegal to bill on also.

While very light loads do lead to some inaccuracies, turning your meter
backwards with generation is not illegal in net-metering states. That's
what net-metering rules are all about, making it legal to turn your meter
backwards with home-grown generation. Some states (such as NY) go into more
detail and only make it legal to turn your meter backwards with certain
types of generation. And your generation has to be 'registered' with the
utility so they can set up the proper accounting to recognize the unusual
meter readings.

Spinning mechancial kwh meters backwards was available (and legal) in many
states long before electronic/digital units were available (circa 1970's).

daestrom

 

[Alan Combellack]

Thanks again Sir,
My house has white aluminum siding. Could I paint some of it black and
get this effect or do I need to remove the siding and put up something else.
If so what material is best?
I like the prices you mention so, while it isn't a total solution, it does
certainly look very useful.
Alan C

 

[daestrom]

Not the "generation of reverse power" is illegal.

It is the "billing" using a meter going backward that
is illegal. It has never been calibrated, inspected or
approved for reverse consumption metering.

Maybe you should qualify your statements as 'illegal in Canada'. But in the
US, it is perfectly legal, and done in a large number of states.

daestrom

 

[[email protected]]

My house has white aluminum siding. Could I paint some of it black and
get this effect or do I need to remove the siding and put up something else.

Painting it darker will help, but it will work a lot better with an air gap
and glazing and airflow through the house during the day. You might paint
the aluminum siding darker and a) build a deep picture frame on the wall
with 2x6s on edge and polycarbonate over that, or b) make a sunspace that's
4' or 8' deep with a dark mesh curtain (eg 80% greenhouse shadecloth) 1'
behind the glazing, which adds useful floorspace to a house.

Nick

 

[SJC]

Nick,
I haven't been keeping up to date on solar matters for a couple of years
so know nothing about this solar siding stuff. I will certainly look into
it and would appreciate any links you care to suggest. My previous
conclusion was that it was nearly, but not quite, an economic proposition,
provided I did most of the building myself, so any significant reduction in
costs are of great interest to me.
Thanks,
Alan C

I imagine that it would look something like this:
http://urbanoptions.org/SustainEdHandbook/BuildYourOwnSolarAirCollector.htm
Cool air goes in the bottom, warm air comes out the top.