How much PV would I need?

S-F · 03-14-11, 06:35 PM

Just checked my last electric bill and it was about 400 KwH. They are all about that much. Last summer it was hot enough to set the House on fire so we used an AC unit some and then it was a little higher but it's usually around 400. I'm pretty new to the whole solar power world so I also need to know what I'd need to get grid tied. I'm in western MA also. I imagine that makes a big difference.

Xringer · 03-14-11, 08:07 PM

Have you been following the 'cheap panels' thread?
http://ecorenovator.org/forum/solar-...eap-panel.html

I'm inept with simple arithmetic, so you might want to check my figures.

It sounds like your load is about 550 watts 24/7. So, if you had 3 or 4
200w panels with Enphase GTIs, you could power your average daily load,
during the 5 or so hours of each sunny day.
But, more is better..

400kWh/30 days=13.33 kWh per day being used.
To make 13.33 kw each day, (quickly) in about 5 hours,
you would need to make 2.66 kwh per hour.

About 14 200w panels?? Wow! That's a few bucks.

Anyways, my guess is.. Use between 1 and 16 (200w) panels.
Depending on southern facing roof space and bank account.

Just so you know, unless they start charging us 50 cents per kwh,
breaking even on solar PV takes a LOT of years..
Just look at the price and do the math. It's scary.

Cheers,
Rich

03-14-11, 08:09 PM

400kWh/28Days/8Hours=~1.8kW of solar But that's assuming no cloudy days year round so around 2.5kW may be better.

Here's a map of solar radiation to give you an idea of how much power you could make.

Ryland · 03-14-11, 09:14 PM

You do not get 8 sun hours per day of sun in many states other then Arizona and even there I think it's about 7 hours per day so your first step, if you don't want to have a site assessment done (required for most grants) is to figure out how many sun hours per day you have, then figure out what your shading is for your exact location for your panels, subtract the losses from inverter and wiring.
A site assessment gives you all of that info along with suggestions for panel locations, an estimate on cost, output and pay back.

Piwoslaw · 03-15-11, 01:23 AM

S-F, the first step to going solar is to reduce your electrical usage. Investing $1 in energy reduction saves $5 in energy generation.
(I'm assuming you're already saving, so that was for any n00bs that may stumble along.)

What kind of water heater do you have? On-demand or tank? Electric or gas? Switching to a tank and investing in a solar hot water set-up will be more efficient ($$$-wise) than PV.

gasstingy · 03-15-11, 08:11 AM

It also depends on what you are trying to accomplish, and depends on the way your area treats renewable energy. I've been fighting with the local electric utility for ~ 2 1/2 years and they almost came into the 20th century last year. It may take a while for them to get there, much less the 21st century. They changed their mind and are still refusing renewable energy.

Sorry for the detour.

Are you trying to produce what you use? There are charts that can estimate the average sun hours available for your location so you can base your PV array on that.

Are you trying to eliminate your electric bill? TVA {in my area} will pay 12 cents above retail for all the KwH of renewable energy I produce. Our base rate is $0.085 per KwH. My average useage ranges from 300 KwH in the colder months to 450 KwH in the warmer months to 600 or so in the truly hot months. Using that as a guide, and adding in the $25 base charge from the power company, I could figure what I'd need to eliminate my power bill completely.

S-F · 03-15-11, 02:48 PM

So it's looking like if I went with the recommendations of xringer I would need about 5 - 8 K in panels. I'm assuming that there is also some other equipment needed to tie it to the grid. So maybe we should say 10 K? With my electric bill being about $60 a month it would take me about 14 years just to break even!
Now I see why every house doesn't have these.

Xringer · 03-15-11, 07:25 PM

If you used Enphase GTIs (Grid Tied Inverters), you would need one for each panel.
They cost around $1/per watt. Which isn't too bad.
I think the system cost might be as low as $3 to $5 a watt, if you did most of the work yourself.

The dealers & their suppliers can charge a lot, because the state & federal government
is footing a good portion of the cost. The installers can also make a killing.

When last I looked, the install labor cost was the same or more than the hardware cost.

When I say " state & federal gov", I mean us taxpayers who don't own subsidized solar.
It's kinda funny, working people who can't afford PV on the roof, pay to put panels on rich people's roofs.

If Home Depot could get a DIY system down to $3 a watt, they would be the king of solar sales.

But, things like this
Mighty Mule 10-Watt Solar Panel Kit for Gate Openers - FM123 at The Home Depot
are discouraging.
$239.00 /EA-Each for a 10w panel? Mine came from Ebay for about $25..
Then I got two more for free with my UL panel order..
They are the three little panels on the top right..

Ryland · 03-15-11, 08:46 PM

Funny thing is, most of the people I know who put solar panels on the homes are not rich, they do however tend to spend their money wisely when they've saved enough up, the people who have alot of money don't tend to care about something that has a 15 year pay back.

Xringer · 03-15-11, 09:52 PM

IMHO, buying a Prius or Fusion hybrid would be a better use of my moola..

03-14-11, 06:35 PM	#1
S-F You Ain't Me Join Date: Nov 2009 Location: Northampton MA Posts: 662 Thanks: 6 Thanked 71 Times in 58 Posts	How much PV would I need? Just checked my last electric bill and it was about 400 KwH. They are all about that much. Last summer it was hot enough to set the House on fire so we used an AC unit some and then it was a little higher but it's usually around 400. I'm pretty new to the whole solar power world so I also need to know what I'd need to get grid tied. I'm in western MA also. I imagine that makes a big difference.

03-14-11, 08:09 PM	#3
Angmaar Guest Posts: n/a	400kWh/28Days/8Hours=~1.8kW of solar But that's assuming no cloudy days year round so around 2.5kW may be better. Here's a map of solar radiation to give you an idea of how much power you could make. Last edited by Angmaar; 03-14-11 at 08:17 PM..

03-15-11, 01:23 AM	#5
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	S-F, the first step to going solar is to reduce your electrical usage. Investing $1 in energy reduction saves $5 in energy generation. (I'm assuming you're already saving, so that was for any n00bs that may stumble along.) What kind of water heater do you have? On-demand or tank? Electric or gas? Switching to a tank and investing in a solar hot water set-up will be more efficient ($$$-wise) than PV. __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

03-14-11, 08:07 PM	#2
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Have you been following the 'cheap panels' thread? http://ecorenovator.org/forum/solar-...eap-panel.html I'm inept with simple arithmetic, so you might want to check my figures. It sounds like your load is about 550 watts 24/7. So, if you had 3 or 4 200w panels with Enphase GTIs, you could power your average daily load, during the 5 or so hours of each sunny day. But, more is better.. 400kWh/30 days=13.33 kWh per day being used. To make 13.33 kw each day, (quickly) in about 5 hours, you would need to make 2.66 kwh per hour. About 14 200w panels?? Wow! That's a few bucks. Anyways, my guess is.. Use between 1 and 16 (200w) panels. Depending on southern facing roof space and bank account. Just so you know, unless they start charging us 50 cents per kwh, breaking even on solar PV takes a LOT of years.. Just look at the price and do the math. It's scary. Cheers, Rich

03-14-11, 09:14 PM	#4
Ryland Master EcoRenovator Join Date: Mar 2009 Location: Western Wisconsin. Posts: 913 Thanks: 127 Thanked 82 Times in 71 Posts	You do not get 8 sun hours per day of sun in many states other then Arizona and even there I think it's about 7 hours per day so your first step, if you don't want to have a site assessment done (required for most grants) is to figure out how many sun hours per day you have, then figure out what your shading is for your exact location for your panels, subtract the losses from inverter and wiring. A site assessment gives you all of that info along with suggestions for panel locations, an estimate on cost, output and pay back.

03-15-11, 08:11 AM	#6
gasstingy Journeyman EcoRenovator Join Date: Feb 2010 Location: Arab, AL Posts: 491 Thanks: 109 Thanked 49 Times in 43 Posts	It also depends on what you are trying to accomplish, and depends on the way your area treats renewable energy. I've been fighting with the local electric utility for ~ 2 1/2 years and they almost came into the 20th century last year. It may take a while for them to get there, much less the 21st century. They changed their mind and are still refusing renewable energy. Sorry for the detour. Are you trying to produce what you use? There are charts that can estimate the average sun hours available for your location so you can base your PV array on that. Are you trying to eliminate your electric bill? TVA {in my area} will pay 12 cents above retail for all the KwH of renewable energy I produce. Our base rate is $0.085 per KwH. My average useage ranges from 300 KwH in the colder months to 450 KwH in the warmer months to 600 or so in the truly hot months. Using that as a guide, and adding in the $25 base charge from the power company, I could figure what I'd need to eliminate my power bill completely.

03-15-11, 02:48 PM	#7
S-F You Ain't Me Join Date: Nov 2009 Location: Northampton MA Posts: 662 Thanks: 6 Thanked 71 Times in 58 Posts	So it's looking like if I went with the recommendations of xringer I would need about 5 - 8 K in panels. I'm assuming that there is also some other equipment needed to tie it to the grid. So maybe we should say 10 K? With my electric bill being about $60 a month it would take me about 14 years just to break even! Now I see why every house doesn't have these.

03-15-11, 07:25 PM	#8
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	If you used Enphase GTIs (Grid Tied Inverters), you would need one for each panel. They cost around $1/per watt. Which isn't too bad. I think the system cost might be as low as $3 to $5 a watt, if you did most of the work yourself. The dealers & their suppliers can charge a lot, because the state & federal government is footing a good portion of the cost. The installers can also make a killing. When last I looked, the install labor cost was the same or more than the hardware cost. When I say " state & federal gov", I mean us taxpayers who don't own subsidized solar. It's kinda funny, working people who can't afford PV on the roof, pay to put panels on rich people's roofs. If Home Depot could get a DIY system down to $3 a watt, they would be the king of solar sales. But, things like this Mighty Mule 10-Watt Solar Panel Kit for Gate Openers - FM123 at The Home Depot are discouraging. $239.00 /EA-Each for a 10w panel? Mine came from Ebay for about $25.. Then I got two more for free with my UL panel order.. They are the three little panels on the top right..

03-15-11, 08:46 PM	#9
Ryland Master EcoRenovator Join Date: Mar 2009 Location: Western Wisconsin. Posts: 913 Thanks: 127 Thanked 82 Times in 71 Posts	Funny thing is, most of the people I know who put solar panels on the homes are not rich, they do however tend to spend their money wisely when they've saved enough up, the people who have alot of money don't tend to care about something that has a 15 year pay back.

03-15-11, 09:52 PM	#10
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	IMHO, buying a Prius or Fusion hybrid would be a better use of my moola..