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Re: Solar Elec?
Old 05-25-2006, 12:22 PM   #21
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Re: Solar Elec?

Make sure you have adequate soffit venting.

Here in Hades DFW, 100+ days are fairly common. My house has ridge venting, which I may eventually decide to augment with whirly-gigs or the aforementioned solar fan. House has hip-roofing, so any added fans have to pierce the roof deck...

Anywho, since soffit vents run a buck or two, I decided to add some to mi casa. It was amazing to observe the rush of air that occured every time ye old sabre saw cut a new hole... There's some rule-of-thumb for venting, based of attic volume, but I don't remember it off hand.
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Re: Solar Elec?
Old 05-25-2006, 03:26 PM   #22
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Re: Solar Elec?

Rule of thumb for attic venting: Combined venting area (peak + soffit) = 1/300th of the ceiling area if you have a vapor barrier installled in your ceiling (to include 2 coats of vapor barrier paint). If no vapor barrier, combined venting areas should be 1/150th of the ceiling area.
Note that these areas are the "Net Free Area" of the vents, the actual holes will be bigger, but the screens/baffles that keep out the critters decrease their effective area.

This rule of thumb provides enough ventillation to avoid moisture damage. For those in hot areas, more vent area will decrease those temps.

Another note: Some folks who have studied the issue don't think power ventilation of the attic is a good idea. I don't think the small solar fans would be a problem, but the fans that move 1000cfm do a pretty good job of depressurizing the attic, which results in more cool air from the house seeping up there through the inevitable cracks/gaps.

Oh--whirligigs ("turbine vents"): Some folks really hate the looks, and they have a reputation for squeeking in later years (and then they'll leak when it is windy out).
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Re: Solar Elec?
Old 05-25-2006, 04:59 PM   #23
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Re: Solar Elec?

I have a boatload of soffit vents, other gable vents AND the hole I cut in the ceiling in the garage to get access to some pipes is still there.

I thought about putting in ridge venting, as it does work well here, but it would have cost me more just for the couple of pieces of ridge vent than for the solar blower. And then I'd have had to pull up all the ridge tiles, lay and nail the ridge vent, then nail all the tiles back on. Plus fetch up two or three ridge tiles up a 24' ladder to replace the ones I broke with the hammer

Bought the second panel. Definitely a huge change in the volume of air being moved. With the second panel, i'm somewhat believing i'm in the vicinity of the 1100CFM throughput the fan's box claims.

Between the good venting and the only so-so performance of the fan, I dont think i'm getting any significant negative pressure in the attic.

All I have to do now is a slightly better job of mounting the two panels than jamming the little metal mounting tabs under a concrete tile.

Probably a job for november or december when its a little cooler up there...
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Re: Solar Elec?
Old 05-26-2006, 11:22 AM   #24
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Re: Solar Elec?

I am going to bookmark this thread so that when DH gets to the spec'ing the roof materials he can noodle this through.

My take on all of this is that prices for solar electric systems will be going down a lot in a couple years.* Given that the client is financing the remodeling the best return on investment may be to design the potential for solar electric and install a system later.*
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Re: Calculating paybacks
Old 05-26-2006, 05:24 PM   #25
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Re: Calculating paybacks

You business veterans will have to forgive my ignorance if I'm "rediscovering" something that's been known for years in the sales industry. A lot of this is new to me.

I've finished plugging all the solar payback numbers and I've seen three ways to look at a capital investment: dividends, return of your original capital, and the "opportunity cost" of that capital.

As a solar dividend, spending $14K to save $60/month is a 5% yield. Compared to the rest of the S&P500, that's a pretty attractive dividend. When you knock the capital expense down to $7K by adding back the tax credits, it's a great dividend. Maybe PV systems should be marketed to stockbrokers & retail investors who already appreciate dividend math.

As a return of capital, saving $60/month is a 19.5-year payback. That's a tough sell to most customers but, again, after tax credits that can come down to a 9.7-year payback. A lot of customers will consider that, especially if you point out that "At the same time you're earning a 10% dividend!".

"Opportunity cost" is perhaps the most conservative yet most accurate way to look at the expense. $14K spent on a solar array can't be invested elsewhere. If it had been invested then its compound growth sets the pace against which the solar payback is measured. If $14K is compounding at a 6% APY (similar to an equity ETF) then it's earning $70/month. Now spending $14K to save $60/month on your electric bill seems like a bad idea! However that $60/month savings can also be invested at the same 6% return as the original $14K, so eventually the account with the monthly $60 savings deposits compounds faster than the account with the original $14K. When the two lines cross, the payback is complete and you're ahead of the game.

A CPA text might reduce this to a formula, but I crunched the numbers on an "opportunity cost" payback spreadsheet. The first rising curve shows $14K spent buying equipment & labor over the first 18 months and compounding at 6%. The second rising curve shows monthly savings and the tax credits compounding at the same rate. So far the total savings is "only" $3380 but it's adding $60/month and the occasional tax credit-- while compounding at 6%. Projecting monthly solar production of 300 KWHr at 25 cents/KWHr, which seems to be conservative compared to current costs of 20.5 cents/hour, grows the second account to catch up with the first at 15.8 years.

Although it may be the most accurate way to look at an investment, "opportunity cost" sucks as a sales tactic. I added a 5% annual inflation factor to the monthly savings to reflect the rising costs of generating grid electricity. (HECO's actual costs have risen 30% in the last year.) That shortens the payback by a couple months but the effect is a lot less than I expected. I'll have to look up actual energy CPI costs.

So, we'll break even on the opportunity cost in 2021.
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Re: Solar Elec?
Old 05-26-2006, 07:05 PM   #26
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Re: Solar Elec?

I read an article in New Scientist today about some photoelectric breakthroughs that may drastically alter the financials over the next decade. Apparently with current silicon technologies one photon can release no more than one electron. Now using nanocrystals of various substances, scientists are getting up to 7 free electrons from one photon. If the engineers can get the concepts sorted out in the real world we could get much cheaper photo electric and, potentially, a cheap source of fuels (hydrogen for fuel cells and, possibly, ethanol and methanol).
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Re: Solar Elec?
Old 05-26-2006, 07:24 PM   #27
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Re: Solar Elec?

Nords, now you are talking my baby's language!!! *She and her spouse are CPAs, they intend to live in this home for the rest of their lives. *When DH has a couple quotes he can lay down the numbers and let them push them around. *

My gut says that the smart move is to design in conduit for wiring to accomodate a system.* I agree with donheff and others that more efficient systems will soon be on the market and material prices will fall.**Give them ~5 years in the house to pay down the mortgage, then install solar electric.

I forsee solar units that look like shingles or slate tiles that don't take a crane to place on the roof.
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Re: Solar Elec?
Old 05-26-2006, 07:51 PM   #28
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Re: Solar Elec?

Already there...a number of companies make solar units that look like roofing materials...except all the ones i've seen are black, so if you roof isnt black, you're SOL. Maybe someones making other colors by now.
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Re: Solar Elec?
Old 05-26-2006, 08:22 PM   #29
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Re: Solar Elec?

Quote:
Already there...a number of companies make solar units that look like roofing materials...except all the ones i've seen are black, so if you roof isnt black, you're SOL.
Black will do just fine, particularly because they will be on the back side of the house and wouldn't need to match the front (DH might gag however).* The ones I found on the web indicate back orders through 2007!!
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Re: Solar Elec?
Old 05-26-2006, 09:30 PM   #30
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Re: Solar Elec?

Quote:
Originally Posted by donheff
I read an article in New Scientist today about some photoelectric breakthroughs that may drastically alter the financials over the next decade. Apparently with current silicon technologies one photon can release no more than one electron. Now using nanocrystals of various substances, scientists are getting up to 7 free electrons from one photon. If the engineers can get the concepts sorted out in the real world we could get much cheaper photo electric and, potentially, a cheap source of fuels (hydrogen for fuel cells and, possibly, ethanol and methanol).
Remember how long it took to get from the IBM PC to the iPod? I think that's roughly the length of time it'll take for this technology to become an affordable consumer commodity.

Quote:
Originally Posted by Brat
My gut says that the smart move is to design in conduit for wiring to accomodate a system.* I agree with donheff and others that more efficient systems will soon be on the market and material prices will fall.**Give them ~5 years in the house to pay down the mortgage, then install solar electric.
Well, one of the barriers to consumer rooftop solar is that it only pays off if you stay in the house for a while-- which is a lot longer than the seven years that most homeowners stay put. And no homebuyer will pay extra for the array.

Quote:
Originally Posted by Brat
I forsee solar units that look like shingles or slate tiles that don't take a crane to place on the roof.
Ovonics came out with solar roof tiles 10 years ago. Their latest product just popped up a few miles up the road this morning in our local newspaper:
http://starbulletin.com/2006/05/26/news/story04.html
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Re: Solar Elec?
Old 05-27-2006, 09:31 AM   #31
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Re: Solar Elec?

Quote:
Originally Posted by Nords
Remember how long it took to get from the IBM PC to the iPod?* I think that's roughly the length of time it'll take for this technology to become an affordable consumer commodity.
Well, one of the barriers to consumer rooftop solar is that it only pays off if you stay in the house for a while-- which is a lot longer than the seven years that most homeowners stay put.* And no homebuyer will pay extra for the array.
Ovonics came out with solar roof tiles 10 years ago.* Their latest product just popped up a few miles up the road this morning in our local newspaper:
http://starbulletin.com/2006/05/26/news/story04.html
My DH shot down my desire for solar roof tiles last night.. he said that roofing is too important to trust to solar tiles. He believes that a system that is supported on a frame above the roofing is wiser. Solar units on a frame are easier to replace/upgrade.
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Re: Solar Elec?
Old 05-27-2006, 09:53 AM   #32
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Re: Solar Elec?

Depending on your roofing material, you might find the opposite to be the case. In my case, using concrete tiles, the solar panels are a direct replacement for the tile and replacing/upgrading one is as simple as lifting the tile above it, picking it up, and putting a new one down.

In fact, concrete tiles can 'pass' as much as 15-20% of the water that runs over them once they become saturated, leaving the tar paper to do the dirty work. I'd imagine the plastic and metal of the tile are a little more water resistant.

Solar unit on a frame require holes drilled in the roof to mount and put a good deal of weight on a smaller square footage area. And might have to be removed to do any roof repairs underneath. Holes in the roof and heavy stuff putting pressure on the sheeting are both leaks waiting to happen. Good silicone sealer and the wait might be a long time.

Now if you're doing asphalt shingles...I dont think you have an option to use a fake shingle.
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Re: Solar Elec?
Old 05-27-2006, 10:18 AM   #33
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Re: Solar Elec?

The roof is yet to be designed so loading awaits that detail. I asked him the same question about a frame on the roof and he reminded me that it is all in the flashing. The same is true of plumbing vents and chimneys. I think he has standing seam metal in mind for under a solar array (which would face away from the street). That should handle any flex in the underlayment due to wind catching the panels (like a sail) and leaves/needles should sluce under the array easily .
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Re: Solar Elec?
Old 05-27-2006, 12:09 PM   #34
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Re: Solar Elec?

Quote:
Originally Posted by Brat
My DH shot down my desire for solar roof tiles last night.. he said that roofing is too important to trust to solar tiles.* He believes that a system that is supported on a frame above the roofing is wiser.* Solar units on a frame are easier to replace/upgrade.
Tell your spouse from me that he's a killjoy!

I think a standing-seam metal roof is the best roof around if it's put together by experienced contractors. (And yup, flashing will make or break the roof.) If the choice was (1) solar tiles or (2) composition shingles or (3) tiles or (4) wood shakes then I'd go solar. But if you're putting in metal then that's probably better than solar.

Talk to a solar firm and a roofing contractor before you make that standing-seam decision. There may be an easy way to add rack mounts to the roof installation that don't involve drilling additional holes. That'll greatly simplify the rack installation later.

While framed solar units are easier to upgrade, I don't know anybody who upgrades. People get rid of their systems, people replace broken gear, or people expand their systems. There's absolutely no benefit, financial or otherwise, to replace a perfectly good solar panel with one that's a little bit better. (The labor only makes it more painful.) Ovonics has a good niche product that's reliable and as cheap as they're likely to get for some time... so I wouldn't hesitate to put solar tiles on a roof if it seems attractive. There are many cheaper ways to go but I defer to décor issues.
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