# Remedial question on grid tied solar panels



## Jokarva (Jan 17, 2010)

We'd like to have solar panels at our retirement home in W NC - have never lived there (it's been a rental since we bought it 5 yrs ago) so not sure how feasible this is. Anyway, if we do get solar panels we'd need them tied to the grid since we know NOTHING about storage batteries, etc. 

So - if you tie to the grid, are you actually using your own electricity as you produce it and only dip into the grid if you don't produce enough? Or is all the electricity you produce going straight into the grid and just financially offsets the amount you use? Hope I'm making sense here...

Thanks for any input - but if you use complicated terms you're likely to lose me!


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## J2E1 (Oct 15, 2009)

You'll use what you generate and from the grid if you need it. If you don't need more from the grid and generate more than you use, your meter will run backwards.


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## Jokarva (Jan 17, 2010)

So *our* electricity goes to power *our *stuff and goes off into the grid only if there's an excess? So if the grid is down *our *solar will still power *our* home, we just won't have the elec co as a backup?

Sorry to be pesky, I'm really trying to understand how this works.


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## wy_white_wolf (Oct 14, 2004)

NO - PV systems without a battery bank will shut down when the grid goes down.

there are 3 basic types of PV systems-

Off-Grid 
Grid-tied
Grid-tied with battery back-up (the most expensive)


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## TnAndy (Sep 15, 2005)

Electricity flows to where ever there is a need calling for it.

If your panels are producing, and you have something requiring power, it flows to you first, otherwise it flows out to the grid.

It may or may not turn your meter backwards.....that depends on how your local power company deals with solar.

It would keep you from having to buy the amount you produce, so you would have the "avoided" cost advantage, but you may or may not get credit for any excess.

For what it's worth, unless you have a pretty decent sized system, you likely won't HAVE any excess.

And as white wolf said: with a simple, no-battery-backup type grid tie system, when the grid goes down, so does your power production....all grid tie inverters must meet a UL standard ( 1741 ) so that the inverter senses grid power, and shuts down if it can't find grid power.....this prevents you from backfeeding the grid and possibly injuring a power company person working on what they thought was a dead line.

If you put in a grid tie with battery backup type system ( which is what I have ), there is an extra set of contacts in the inverter.....when the grid tie contacts go open ( for lack of grid power ), the other set closes, and diverts your solar production to you....you also need a transfer switch located at/near your main panel, just like if you put in a whole house generator, so it can isolate out certain circuits and not back feed the utility line.


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## Jokarva (Jan 17, 2010)

Thank you all! That was clear enough even for me.

The solar panel with battery backup sounds like what we're aiming for, I'd like at least minimal power if grid power is out. DH wants a whole house generator, but I'm not comfortable storing large amounts of fuel on the property. 

We have lots of homework to do before we retire.


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## Mickie3 (Aug 28, 2010)

TnAndy said:


> If you put in a grid tie with battery backup type system ( which is what I have ), there is an extra set of contacts in the inverter.....when the grid tie contacts go open ( for lack of grid power ), the other set closes, and diverts your solar production to you....you also need a transfer switch located at/near your main panel, just like if you put in a whole house generator, so it can isolate out certain circuits and not back feed the utility line.


We are getting ready to build a rural home and have just began to look at systems and have been thinking about grid-tie with battery backup. It appears that the only real differences are in that you get a different inverter and buy batteries (deep charge marine type is what they appear to be). Is that all the difference is, when it comes down to it (bypassing all the hype the sales reps put out)? 

Any idea of how much more this costs for a medium sized system, around 40 panels or so? I had been thinking of putting in a nearly "all house" (100 amp) generator for use during outages, but if it won't cost a lot more to use batteries, would rather go that route. (Generator looks to be about 3,500 installed. The one that I currently have is a manual system, that is why I am looking at alternatives, hate to get out in storms and power that up like I did the other night.)

Thanks!


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## wy_white_wolf (Oct 14, 2004)

Mickie3 said:


> ...(deep charge marine type is what they appear to be). Is that all the difference is, when it comes down to it (bypassing all the hype the sales reps put out)? ...


There is a difference (internally) but marine batteries will work about the same as using 1/2T pickup to do the work of a 3/4T pickup. It'll get the job done but also wear out faster doing it.

Look at the differences in jobs:
Marine - Needs to be portable and easy to hook up and disconnect. Cycled only a dozen or so times a year.
Solar (industrial) - stationary and connections only messed with during maintance. Cycled daily.

internally - marine batteries will not have as thick of plates as industrial batteries and they will have some way to stabilize the plates during transport. They are also generally 12v where industrial type are commonly 2, 4 or 6 volt (just more batteries in series) Thicker plates on industrial batteries means they can last more cycles without wearing out, but they also can not handle short bursts of high amp loads (relative to size).

http://www.windsun.com/Batteries/Battery_FAQ.htm has a good FAQ page on batteries.

WWW


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## TnAndy (Sep 15, 2005)

Mickie3 said:


> We are getting ready to build a rural home and have just began to look at systems and have been thinking about grid-tie with battery backup. It appears that the only real differences are in that you get a different inverter and buy batteries (deep charge marine type is what they appear to be). Is that all the difference is, when it comes down to it (bypassing all the hype the sales reps put out)?


You'll also have to have at least one charge controller ( mostly likely with 40 panels....you don't mention wattage, so it's hard to say....2 or more ), and a good one is about 600 bucks. Plus you'll need a bit more wiring, and disconnecting means ( one on either side of the charge controller, for example ), and you'll need a rather large disconnect ( fuse or breaker ) between the battery and inverters.

You're most likely looking a two ( or more ) inverters, plus a "brain" unit to put out 120/240....

You'll want some kind of battery monitor, like a Trimetric.....

So, all in all, yes, there is quite a bit more stuff to a grid tie with battery backup than a plain Jane grid tie.

No WAY is this type of system going to compete with a 3500 buck whole house generator, money wise.

What you DO have to look at is:

How often will you use it ?

Does your utility pay decently for solar infeed ? Ours does....12 cents/kwhr over retail.

Do you live in a State where you can sell the renewable energy credits ? They can REALLY make a solar power system pay off quick.....up to 50-60 cents/kwhr !

What do you think the future holds about fuel being available for the generator....or the grid in general.


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## wind power (Sep 29, 2010)

Here in SC you can grid tie solar two ways...you can net meter for an even KW for KW excahnge...in other words you use 4 kw's but make only three kw's you're in the hole to the power company for 1 kw.

Or you can net meter and they buy it back at wholesale prices....my power company only offers 4-5 cents a kw....for me its best to net meter for a KW to KW exchange rate.
if you go battery back up, be prepared to monitor them closely they are expensive and dont tolerate over charging or dropping the voltage too far too many times very well......now you need to thinking of a charge controller and possibly some kind of dump resistors.


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## TnAndy (Sep 15, 2005)

Two points on the above:

You don't need dump loads on a PV system.

The batteries are rarely used on a grid tie w/battery backup, since they ARE backup, so the batteries tend to last a long time, as they are rarely even cycled. If you use wet cells, you do have to keep an eye on the electrolyte levels.


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## Jim-mi (May 15, 2002)

My sister has a phobia about Propane tanks..
But you will have to admit that there are untold tens of thousands of folks with propane tanks . .and NO problems..........
So.........
A good propane powered generator is, IMHO the best way to go.
They have very Clean running engines.
Diesel . .alge and gelling with age...
Gasoline goes punky real fast.....for "long term" do not consider.
Propane stores for years...........Safely


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## wind power (Sep 29, 2010)

Thanks TnAndy,
I'm learing as I go, I was thinking along the lines of my wind generator with the charge controller and dump load.
Duh... I was thinking the batteries are the first source of power than the grid as a backup as in my setup....Doh!

Thanks for clearing that up for me!
All the best,
Gavin


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## TnAndy (Sep 15, 2005)

No problem.....none of us was born knowing this stuff, all have to learn it from scratch.


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## WisJim (Jan 14, 2004)

A couple of things to consider about a battery back up grid tied system. First, it makes sense most if you know you will have frequent outages. If you have a history of few outages, it might make more sense to have a standby generator instead of a battery system. Batteries need maintenance!!! and they have a limited life, and most people ruin their first set of batteries through lack of knowledge and experience. Next, if building a new house especially, it is cheaper to save energy than to produce it. Almost anywhere in the country you can design and build a home that doesn't require central heating or air conditioning--but finding someone to design it and build it properly can be hard. So make sure your house and appliances are as energy efficient as possible, even if you need to spend thousands of dollars on improvements, because (as a rule of thumb) every dollar spent on reducing energy consumption saves four dollars in the hardware needed to produce the energy.


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## Mickie3 (Aug 28, 2010)

wy_white_wolf said:


> There is a difference (internally) but marine batteries will work about the same as using 1/2T pickup to do the work of a 3/4T pickup. It'll get the job done but also wear out faster doing it.
> 
> Look at the differences in jobs:
> Marine - Needs to be portable and easy to hook up and disconnect. Cycled only a dozen or so times a year.
> ...


Thanks for the info and the link. Loads of good info there. Also, talked to the dealer where I had been looking at getting a small wind turbine generator and the estimated cost of the battery array for being totally off-grid is about 15k from their estimate. There is no way I can afford to do that, but may look at getting a smaller battery backup setup. (Propane is expensive from the specs I have seen to run the generators I am looking at - GenRac.)



TnAndy said:


> You'll also have to have at least one charge controller ( mostly likely with 40 panels....you don't mention wattage, so it's hard to say....2 or more ), and a good one is about 600 bucks. Plus you'll need a bit more wiring, and disconnecting means ( one on either side of the charge controller, for example ), and you'll need a rather large disconnect ( fuse or breaker ) between the battery and inverters.
> 
> You're most likely looking a two ( or more ) inverters, plus a "brain" unit to put out 120/240....
> 
> ...


Am currently in KY, moving to NE Indiana, and I thought KY was cheap in their support of alternative power, but Indiana has nothing, even the net-metering seems to be mostly unfavorable to the consumer.  In spite of that, I am still planning on going solar and using wind if there is enough wind there (going to wait until we actually move there to do the study and see about the wind-power, the data I have been getting is not for the area we are buying / building.) We are doing this as we wish to be independent of the grid to an extent while being eco-friendly at the same time. 



wind power said:


> Here in SC you can grid tie solar two ways...you can net meter for an even KW for KW excahnge...in other words you use 4 kw's but make only three kw's you're in the hole to the power company for 1 kw.
> 
> Or you can net meter and they buy it back at wholesale prices....my power company only offers 4-5 cents a kw....for me its best to net meter for a KW to KW exchange rate.
> if you go battery back up, be prepared to monitor them closely they are expensive and dont tolerate over charging or dropping the voltage too far too many times very well......now you need to thinking of a charge controller and possibly some kind of dump resistors.


In Indiana, its totally dependent on what the power company wants to do. With some, its a total joke, but with the Rural Co-op where we are headed, they will buy your excess power for 3.8 cents per KWh, if you produce more than you use, and sell you power for that same cost if you use more than you produce. Their tariffs are a bear to read, but that is what it looks to be at this time, have to talk to them about that.  



Jim-mi said:


> My sister has a phobia about Propane tanks..
> But you will have to admit that there are untold tens of thousands of folks with propane tanks . .and NO problems..........
> So.........
> A good propane powered generator is, IMHO the best way to go.
> ...


We currently have a gasoline generator and I have to add stabil (I think that is the name) to keep gas OK, but it works. Will use that one till everything else is working, but then, for a permanent backup, looks like propane is the answer for us, the folks who sell the windmills and solar and battery backups recommend propane backups interestingly enough. 



WisJim said:


> A couple of things to consider about a battery back up grid tied system. First, it makes sense most if you know you will have frequent outages. If you have a history of few outages, it might make more sense to have a standby generator instead of a battery system. Batteries need maintenance!!! and they have a limited life, and most people ruin their first set of batteries through lack of knowledge and experience. Next, if building a new house especially, it is cheaper to save energy than to produce it. Almost anywhere in the country you can design and build a home that doesn't require central heating or air conditioning--but finding someone to design it and build it properly can be hard. So make sure your house and appliances are as energy efficient as possible, even if you need to spend thousands of dollars on improvements, because (as a rule of thumb) every dollar spent on reducing energy consumption saves four dollars in the hardware needed to produce the energy.


That much we have been prepared more so for than anything else. The builder we are working with is a "certified green builder" and his homes are "Energy Star certified" (the homes are all built with geothermal heat pumps, extra insulation above Energy Star standards, etc.) Also, where the ES standards are for dual pane windows, we are going to go with triple pane, etc. to try and cut the consumption down so that we need to produce less for our needs. 


Sorry for the long post, but I really appreciate the input and wanted to address the things completely.


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## WisJim (Jan 14, 2004)

A well insulated and designed new house shouldn't need a geothermal heat pump system. That is a lot of money to spend on a heating system that should be avoidable by adequately insulating and siting the house. For the cost of a ground coupled heat pump, you could add insulation and energy saving features that would avoid the cost of the heat pump system, and you should be able to heat with a combination of active and passive solar features.


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## Mickie3 (Aug 28, 2010)

WisJim said:


> A well insulated and designed new house shouldn't need a geothermal heat pump system. That is a lot of money to spend on a heating system that should be avoidable by adequately insulating and siting the house. For the cost of a ground coupled heat pump, you could add insulation and energy saving features that would avoid the cost of the heat pump system, and you should be able to heat with a combination of active and passive solar features.


Where I am now (KY), I have a air-source heat pump and it works great until the outside temps fall below 40 degrees F, then the high efficiency gas furnace kicks in, as the ASHP is no longer doing much good Where we are moving to (IN, near MI border), the average winter temps are about 10 degrees F lower than here and will not have natural gas available. Even though we are going to build an energy efficient home, the numbers I ran show a GSHP being paid back in a few years (under 5) when comparing to electric heat and even shorter than that when comparing to propane due to the prices for both there.


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## SolarGary (Sep 8, 2005)

Hi,
I'd very carefully consider whether adding battery backup to a grid-tie system is really going to be worth it to you.
We went through the same decision a year ago when we put in our grid-tie without backup system in.
The batteries, more expensive inverter and charge controller add substantially to the the cost of the system. Battery replacement costs substantially reduce the return on the system, which is already quite low.

For us, grid power is reliable and we have a 2K watt Honda generator to cover outages -- in the 5 years since we got the generator for outages, its total run time has been less than 15 minutes. It seems like when the power goes down here by the time I get the generator out and gassed up, the power is back on. But, this varies with location.
I just use extension cords -- no whole house generator. I changed the furnace hookup so it will must plug into the generator.

If the main objective is saving money, just using less electricity is usually the way to go. 
For us, we started at 1000 KWH a month -- spent about $1200 getting that down to 500 KWH a month via efficiency changes:
http://www.builditsolar.com/References/Half/ProjectsConservation.htm
This is falling off a log easy and very cheap.

We added the PV system, which cost us $6500 after rebates ($3 per watt), and it saves us 250 KWH a month. This is with me doing all the work.
http://www.builditsolar.com/Projects/PV/EnphasePV/Main.htm

So, conservation savings cost $2.40 per monthly KWH saved.
PV cost $26 per monthly KWH saved.
For us, conservations was about 10 times more cost effective than PV.

All that said, I do love my PV system 

Gary


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## TnAndy (Sep 15, 2005)

Mickie3,

Something you need to investigate are SREC's. Solar Renewable Energy Credits.

IF you can sell your SREC, they can be worth a WHOLE LOT MORE than anything the utility company would probably pay you.

For example, selling them to Pennsylvania, or Wash DC can get you 35 cents/kw/hr....which makes the ROI on solar drop way on down there. I'm only getting 12 cents from TVA, and by generating 1/2 our needs, eliminates all our bill.

We don't have the ability to sell them here, yet, but if it comes, I'm dropping TVA like a hot potato !

check it out, good page on SREC's for Indiana:

http://www.srectrade.com/indiana_srec.php


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## Mickie3 (Aug 28, 2010)

Gary - I am finding that out. Was at Costco and saw they have a 100 AMP propane backup system for under 2k, so looks like that will be the most cost-effective route for us to go. The only way I can see that I will end up with the batteries is if the interconnect into the power company there is anywhere the cost of the batteries, however, I cannot see where they could be that high (per what I have read from their tariffs.)


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## Mickie3 (Aug 28, 2010)

Andy - Thanks for the info on SRECs. It appears that Indiana will not be in that program any time soon, but would encourage people if they were. Will check into whether you can actually sell to other states, like that site implies. If so, I will look into doing it, but if not, we are still intending to be as carbon-neutral as we can be.


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## Mickie3 (Aug 28, 2010)

SolarGary said:


> Hi,
> So, conservation savings cost $2.40 per monthly KWH saved.
> PV cost $26 per monthly KWH saved.
> For us, conservations was about 10 times more cost effective than PV.
> ...


Gary - That is why we have picked the builder that we have. He is a "Certified Green" builder and his homes go way beyond the "Energy Star" standards (i.e. minimum of R-45 in ceilings with R-38 being the ES standard there, triple-glazed windows instead of double-glazed, etc.) The incremental costs at time of construction of many of the things you can do is so small, the state building codes should be updated to make them mandatory in all new homes, in my opinion. We are supposed to be meeting with him tomorrow at the site we are negotiating to build on and I want to run a list of additional features past him while we are making changes to the specs we have preliminarily looked at for new house (several of which I have found on your web site.)

PS: We do intend to do as much PV as we can when building, however, I am going to estimate on the low end for consumption as the power company on grid-tied will not buy back any excess and, also, wife wants me to put in a wind turbine system in the future as well, so may as well not cover all demand at once. (We are doing this to hopefully offset the carbon for our kids and grand-kids.)


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## SolarGary (Sep 8, 2005)

Mickie3 said:


> Gary - That is why we have picked the builder that we have. He is a "Certified Green" builder and his homes go way beyond the "Energy Star" standards (i.e. minimum of R-45 in ceilings with R-38 being the ES standard there, triple-glazed windows instead of double-glazed, etc.) The incremental costs at time of construction of many of the things you can do is so small, the state building codes should be updated to make them mandatory in all new homes, in my opinion. We are supposed to be meeting with him tomorrow at the site we are negotiating to build on and I want to run a list of additional features past him while we are making changes to the specs we have preliminarily looked at for new house (several of which I have found on your web site.)
> 
> PS: We do intend to do as much PV as we can when building, however, I am going to estimate on the low end for consumption as the power company on grid-tied will not buy back any excess and, also, wife wants me to put in a wind turbine system in the future as well, so may as well not cover all demand at once. (We are doing this to hopefully offset the carbon for our kids and grand-kids.)



Hi,
That sounds like a very good approach.

One thing I would do if building new is to review every single item that goes in the house that uses electricity. The best time to control electricity use and avoid building in phantom loads is during construction. 

Gary


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## Mickie3 (Aug 28, 2010)

Gary,

We are doing that as well as looking into designing to make use of CFL and LED lighting throughout the house. The builder was well aware of what I wanted when I was asking about design considerations for use of LEDs in places like kitchen work lighting, so made me feel better with the choice of him to work with. (We are using a LEED architect for actual design of the house, pond, etc.) Hopefully, between all of us, we can minimize our impact that this house will have on the environment of the rural area we are moving to.
-Mick


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## wind power (Sep 29, 2010)

Hi Folks,
FWIW, I have a wind generator and I supplement my grid power with it....while its not a typical grid tie inverter...... I use a battery bank and a transfer switch panel which allows me to flip from grid to battery/inverter power. So when the battery bank drops enough, I simply go back to grid power at the flip of a switch. But I also have a generator too, for when the grid is down and the batteris are too low.

In all honesty, If I had a solar system, I would consider grid tying it before purchasing a large battery bank...batteries are expensive!
Now if you are off the grid and to have a line ran to you would be costly...well that is another beast all together concerning a battery system.

If possible, I would simply grid tie the solar and have a generator just large enough for the back up power for a few "essentials". 
This setup would be a good deal easier if your power outages only last from 2-4 days.
However, many offgriders' have multiple layered systems; solar, wind, generator, aladdin lamps, wood stoves...lol... etc etc

Currently I'm dabbling in LED's, at first it appears they sure are a good choice....real low watt use but the darn light does not bathe an area like CFL's do. You have to be right under it or next to it...and some of these bulbs I have have about 60-80 leds all over it!
I'm about ready to trash the whole LED adventure and go with the old Aladdin lamps as a reliable source of alternative lighting.


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## Mickie3 (Aug 28, 2010)

wind power said:


> If possible, I would simply grid tie the solar and have a generator just large enough for the back up power for a few "essentials".
> This setup would be a good deal easier if your power outages only last from 2-4 days.
> However, many offgriders' have multiple layered systems; solar, wind, generator, aladdin lamps, wood stoves...lol... etc etc


This is sounding like what I am finding that we may well need to do.



> Currently I'm dabbling in LED's, at first it appears they sure are a good choice....real low watt use but the darn light does not bathe an area like CFL's do. You have to be right under it or next to it...and some of these bulbs I have have about 60-80 leds all over it!
> I'm about ready to trash the whole LED adventure and go with the old Aladdin lamps as a reliable source of alternative lighting.


Also, the cost of LEDs is extremely high for now. Home Depot had the *new low cost* of about 40$ per bulb (60 W equivalent) last time I saw them in the store.


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## redwall (Mar 10, 2007)

they are 9 bucks at ace the led lights


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## Mickie3 (Aug 28, 2010)

redwall said:


> they are 9 bucks at ace the led lights



Which ones? 


Per their websites: 

Home Depot 15 watt LED - 40$

Ace Hardware 10 watt - 46$ 

Which bulbs are 9$? That is a lot cheaper than what I have seen, excepting nightlights.


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## TnAndy (Sep 15, 2005)

If you're using any recessed ( "can" ) lights, check out the CREE LR6 bulbs. Not cheap, but WOW the light they put out is INCREDIBLE compared to CFL's. And if you figure they only take 12w of power, and are supposed to have 50,000hr life, they actually work out cheaper than a CFL over time. We just re-did our kitchen and put these in the whole thing....LOVE 'em ! Bright as a 75w incandescent and you can put a dimmer on them ( unlike a CFL )


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## redwall (Mar 10, 2007)

hum it might be just local sales. it puts out 40 watts of light. we use that all though our house no matter what the type


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