How big of a PV system do I need.

Help me understand what capacity a PV system would need to be to power my house. Here is what I get from the electric company: Days Consumption Units 28 1953 KWH 30 3180 KWH 32 4493 KWH 30 4130 KWH 33 4493 KWH 29 2201 KWH 29 1367 KWH 33 1289 KWH 30 1092 KWH 33 1731 KWH 31 1562 KWH 31 1264 KWH 29 2929 KWH 30 4033 KWH
Would a 6kwh system be sufficient? Do I take the consumption/days/24 to calculate the per hour need?
Thx D

On Mon, 27 Oct 2008 17:39:45 -0700 (PDT), DavidIa wrote:

Help me understand what capacity a PV system would need to be to power my house. Here is what I get from the electric company: Days Consumption Units 28 1953 KWH 30 3180 KWH 32 4493 KWH 30 4130 KWH 33 4493 KWH 29 2201 KWH 29 1367 KWH 33 1289 KWH 30 1092 KWH 33 1731 KWH 31 1562 KWH 31 1264 KWH 29 2929 KWH 30 4033 KWH
Would a 6kwh system be sufficient? Do I take the consumption/days/24 to calculate the per hour need?
Thx D

You don't provide sufficient information. Since a PV system requires the SUN to generate power, you need to know how much sunlight you will get at the location and orientation of your PV panels.
If you are in the US, you can use the PVWATTS (google for the URL) calculator to estimate electricity production for different sized arrays.
The very basic calculations go something like:
Days Total: 428 Consumption Total: 35,717 kWh
Your Average daily consumption: 83.45 kWh
For a grid-connected system, you would then divide that value by the hours of FULL sunlight per day, averaged over a year. That is considerably less than the time from sunrise to sunset, by the way. And it may have to be adjusted if you cannot optimally orient your array.
Assume for this exercise that you have 5 hrs of full sun equivalent (also called ESH for effective sun hours, or insolation) per day.
83.45 / 5 = 16.69 kWh.
But the manner in which PV arrays are rated does not usually reflect "real world" electricity generation. There will also be losses in your inverter.
So your hypothetical system my have to be sized as a 20+ kWh array to replace all of your generated electricity. The cost to do that would probably be on the order of 160,000 USD.
You may want to consider other alternatives to reduce your electric bill. --ron

"DavidIa" wrote in message

Would a 6kwh system be sufficient? Do I take the consumption/days/24 to calculate the per hour need?
Thx D

No. Your consumption must be reduced, probably by a factor of 10.
In Iowa, the average daily insolation over the year is less than 4kWh per square meter per day. In December to January it will be around 2 kWh per square meter per day. Thats solar. Photovoltaic panels are about 10 to 15 percent efficient. If you purchase 10 panels rated for 100 watts, then you will harvest about 4 kWh-e per day for your total system. You are using over 10 times that amount of power. In winter you are using 50 times that amount. Thats a one kilowatt system in Iowa.
If you purchase a 6 kilowatt system you will harvest 24 kWh-e per day on average but only about 12 kWh per day in winter. Still not enough at six times the initial cost. It can't be done.

On Mon, 27 Oct 2008 22:36:39 -0400, Ron Rosenfeld wrote:

On Mon, 27 Oct 2008 17:39:45 -0700 (PDT), DavidIa <xlfiles@gmail.com wrote:
Help me understand what capacity a PV system would need to be to power my house. Here is what I get from the electric company: Days Consumption Units 28 1953 KWH 30 3180 KWH 32 4493 KWH 30 4130 KWH 33 4493 KWH 29 2201 KWH 29 1367 KWH 33 1289 KWH 30 1092 KWH 33 1731 KWH 31 1562 KWH 31 1264 KWH 29 2929 KWH 30 4033 KWH
Assume for this exercise that you have 5 hrs of full sun equivalent (also called ESH for effective sun hours, or insolation) per day.
83.45 / 5 = 16.69 kWh.

Actually, if you cancel your units properly, that's 16.7 kilowatts and not kilowatt-hours.

But the manner in which PV arrays are rated does not usually reflect "real world" electricity generation. There will also be losses in your inverter.
So your hypothetical system my have to be sized as a 20+ kWh array to replace all of your generated electricity. The cost to do that would probably be on the order of 160,000 USD.

Again, it's 20 kilowatts and not kWh.
Of course, with that kind of consumption variability, I'd never even remotely consider recommending a system large enough to pick up all the peak load. Without any more information at hand than what was given, I'd probably go for something in the 5kW range. Enough to handle all the load on the low consumption months, most of the load on the medium consumption months and then I'd find out how to trim the high consumption months.

You may want to consider other alternatives to reduce your electric bill.

Yes, I agree. Further I have some questions. Your usage varies over a 4:1 ratio, especially if the numbers are normalized to constant days.
Assuming this is a domestic situation, what are you doing to vary your usage that much? That would be the very first thing I'd want to investigate. You didn't put any months next to the readings but still, I don't see a seasonal pattern there.
If this is a heating application such as a pool or hot tub then it would foolish to spend money to turn radiant energy (sunlight) into electricity, only to turn it back into heat. You'd be MUCH better off collecting the solar energy, including the infrared that solar cells don't do anything with, with solar-to-water collectors and using that flow to heat your pool or tub directly. Solar water heater panels cost a tiny fraction of solar electric panels and can easily be home-built if you're the type to do that.
If you're comfort heating your house then again, solar heat collectors are a much more sensible way to go.
Please do tell us what causes these huge consumption swings. Of course, if the load involves lots of big ole grow lights, never mind..... :-) That would be a great application for solar light ducts. Home Depot has 'em.
John
-- John De Armond See my website for my current email address http://www.neon-john.com http://www.johndearmond.com <-- best little blog on the net! Tellico Plains, Occupied TN No one can be right all of the time but I'm getting close.

DavidIa wrote:

Help me understand what capacity a PV system would need to be to power my house. Here is what I get from the electric company: Days Consumption Units 28 1953 KWH 30 3180 KWH 32 4493 KWH 30 4130 KWH 33 4493 KWH 29 2201 KWH 29 1367 KWH 33 1289 KWH 30 1092 KWH 33 1731 KWH 31 1562 KWH 31 1264 KWH 29 2929 KWH 30 4033 KWH
Would a 6kwh system be sufficient? Do I take the consumption/days/24 to calculate the per hour need?

NO, because the sun don't shine 24 hrs a day ! You need an insolation map to see how much it does shine and when it's cloudy, you'll get bugger all electricity.
PV Solar is INSANELY expensive and unless you're off-grid and have no choice your best way of going 'green' is to invest in some insulation to lower the amount of electricity you use in the first place. Actually you should insulate heavily in the first place especially with new build. That attacks the CAUSE. PV can only influence the EFFECT. Plus it's maybe 20-30 times more cost effective to insulate.
See "Price of Solar" and "More info prevous Solar question" threads in alt.solar.photovoltaic
Graham

Neon John wrote:

Ron Rosenfeld wrote: DavidIa wrote:
Help me understand what capacity a PV system would need to be to power my house. Here is what I get from the electric company: Days Consumption Units 28 1953 KWH 30 3180 KWH 32 4493 KWH 30 4130 KWH 33 4493 KWH 29 2201 KWH 29 1367 KWH 33 1289 KWH 30 1092 KWH 33 1731 KWH 31 1562 KWH 31 1264 KWH 29 2929 KWH 30 4033 KWH

Are the high kWh hours due to A/C or heating ?

Assume for this exercise that you have 5 hrs of full sun equivalent (also called ESH for effective sun hours, or insolation) per day.
83.45 / 5 = 16.69 kWh.
Actually, if you cancel your units properly, that's 16.7 kilowatts and not kilowatt-hours.

And 5 hours peak equivalent is a LOT. Certainly won't get that in New England. And doubly not in winter.
Oh he's in Texas. At least that won't be a problem then.
Graham

On Tue, 28 Oct 2008 01:41:16 -0400, Neon John wrote:

Again, it's 20 kilowatts and not kWh.

You're absolutely correct. And I do know better. But sometimes, typing late at night, errors occur. --ron

On Tue, 28 Oct 2008 01:41:16 -0400, Neon John wrote:

Of course, with that kind of consumption variability, I'd never even remotely consider recommending a system large enough to pick up all the peak load. Without any more information at hand than what was given, I'd probably go for something in the 5kW range. Enough to handle all the load on the low consumption months, most of the load on the medium consumption months and then I'd find out how to trim the high consumption months.

As I wrote, since the OP is grid connected, the sizing was based on average annual load. At least in many parts of the US, net metering allows the user to use the grid as a battery. Many places do the reconciliation on an annual basis.
Now, if he were off-grid, then the sizing would be based on insolation and load during the worst month. But he is not.
Obviously, with that kind of load, as I suggested, he might be better served by finding other methods of reducing his bill. --ron

On Oct 28, 6:35�am, Ron Rosenfeld wrote:

On Tue, 28 Oct 2008 01:41:16 -0400, Neon John wrote: Of course, with that kind of consumption variability, I'd never even remotely consider recommending a system large enough to pick up all the peak load.. Without any more information at hand than what was given, I'd probably go for something in the 5kW range. Enough to handle all the load on the low consumption months, most of the load on the medium consumption months and then I'd find out how to trim the high consumption months.
As I wrote, since the OP is grid connected, the sizing was based on average annual load. �At least in many parts of the US, net metering allows the user to use the grid as a battery. �Many places do the reconciliation on an annual basis.
Now, if he were off-grid, then the sizing would be based on insolation and load during the worst month. �But he is not.
Obviously, with that kind of load, as I suggested, he might be better served by finding other methods of reducing his bill. --ron

Thank you all for your responses. Yes I am in Texas, Dallas. And the high consumption months are the summer (cooling). I guess the 4:1 swing is due to our mild winters were neither cooling or heating is necessary (almost). The highest consumption months are June and August (I was out of town in July :)).
I am learning a lot, and than you again for your responses...please add more knowledge to the thread!
David

"DavidIa" wrote in message I am learning a lot, and than you again for your responses...please add more knowledge to the thread!
I suspect that you are asking the wrong question. Perhaps a better question should be: "Based on this data, how can I invest to decrease my monthly energy bills?"
1) Take a hard look at your central AC system and the way you use it. The new inverter central AC systems are a true quantum leap in efficiency. Also, there may be strategies to reduce your use of cooling such as programmed thermostats. Is your house properly insulated? Windows shaded?
Since my wife and I (south Florida) are empty nesters, we rarely need to cool the whole house at once. Daytime we run just a small high-efficiency AC unit in the study, and nighttime we do the same in our bedroom. It cuts our electric bill to half of what it could be if we just turned on our central AC and "let er rip". As a side benefit, our central AC unit is 20 years old, and still looks and runs like new.
2) Take a hard look at your other appliances. Does it make $en$e to invest in Energy Star appliances?
3) Do you have electric or gas hot water? What does it cost you per month for those hot water BTUs? Solar hot water gives a far better "bang for the buck" than a PV system.
4) (Probably should be #1) Get an energy audit.
5) You have already gotten rid of all your incandescent bulbs...right?
None of the above things are a sexy as a big new PV system, but you should do all of the above before even thinking about investing in PV. If you can reduce your electrical usage by 50%, then you are reducing the potential size of your PV system by 50%.
Vaughn

DavidIa wrote:

On Oct 28, 6:35 am, Ron Rosenfeld wrote: On Tue, 28 Oct 2008 01:41:16 -0400, Neon John wrote: Of course, with that kind of consumption variability, I'd never even remotely consider recommending a system large enough to pick up all the peak load. Without any more information at hand than what was given, I'd probably go for something in the 5kW range. Enough to handle all the load on the low consumption months, most of the load on the medium consumption months and then I'd find out how to trim the high consumption months.
As I wrote, since the OP is grid connected, the sizing was based on average annual load. At least in many parts of the US, net metering allows the user to use the grid as a battery. Many places do the reconciliation on an annual basis.
Now, if he were off-grid, then the sizing would be based on insolation and load during the worst month. But he is not.
Obviously, with that kind of load, as I suggested, he might be better served by finding other methods of reducing his bill. --ron
Thank you all for your responses. Yes I am in Texas, Dallas. And the high consumption months are the summer (cooling). I guess the 4:1 swing is due to our mild winters were neither cooling or heating is necessary (almost). The highest consumption months are June and August (I was out of town in July :)).
I am learning a lot, and than you again for your responses...please add more knowledge to the thread!

Since your major needs are clearly A/C, look at how the heat gets in. Consider reflective glass for example (i.e reduce solar gain) and reflective roof tiling.
Serious loft/attic insulation will also stop that heat radiating down from the ceiling too. Esp look at some of the 'silvery' reflective insulation on top of fibreglass/rockwool. Helps stop IR radiation as well as air based thermal conduction.
A lot will also depend on the construction of your house and its amentity to installing such measures. Surely there must be experts in your area who can advise sensibly too ?
Graham

Thanks again for all the responses
I think 'improving' the current house will run somewhere around $40-50k (insulation, windows, roof, more efficient A/C, etc..etc..)
I have keep going back and forth, improving this house (originally built with no regard for energy consumption) or building a new house with a re-newed appreciation for smart building (PV sys or not). It's like throwing good money after bad...if you know what I mean. Of course this is not the time to be selling any houses so...:)
Thanks again, David

� �1) Take a hard look at your central AC system and the way you use it. �The new inverter central AC systems are a true quantum leap in efficiency. �Also, there may be strategies to reduce your use of cooling such as programmed thermostats. �Is your house properly insulated? �Windows shaded?

I will look into new AC systems. Got the programmables. The house is not properly insulated in sections where we have no attic space.
� � �Since my wife and I (south Florida) are empty nesters, we rarely need to

cool the whole house at once. �Daytime we run just a small high-efficiency AC unit in the study, and nighttime we do the same in our bedroom. �It cuts our electric bill to half of what it could be if we just turned on our central AC and "let er rip". �As a side benefit, our central AC unit is 20 years old, and still looks and runs like new.

I wish I could do that. Kids running/using the entire house...

� �3) Do you have electric or gas hot water? �What does it cost you per month for those hot water BTUs? �Solar hot water gives a far better "bang for the buck" than a PV system.

Gas hot water....will look at solar hot wafer...

� �4) (Probably should be #1) �Get an energy audit.
� �5) You have already gotten rid of all your incandescent bulbs...right?

Yes.

None of the above things are a sexy as a big new PV system, but you should do all of the above before even thinking about investing in PV. �If you can reduce your electrical usage by 50%, then you are reducing the potential size of your PV system by 50%.

Got it.
Thanks!
D

DavidIa wrote:

Thanks again for all the responses
I think 'improving' the current house will run somewhere around $40-50k (insulation, windows, roof, more efficient A/C, etc..etc..)

Insulation is CHEAP !

I have keep going back and forth, improving this house (originally built with no regard for energy consumption) or building a new house with a re-newed appreciation for smart building (PV sys or not). It's like throwing good money after bad...if you know what I mean. Of course this is not the time to be selling any houses so...:)

You know it may be cheaper to knock the house down and build one that's energy efficient at this rate.
Graham