evacuated tubes Vs. Flat plates again url comparsion

jrc2905

The only thing left to do is to give the armor flex on the roof some UV protection. I started to wrap it with foil insulation wrap but having silver pipes on the roof looked lousy. I am think of using some flexible black drain pipe if I can locate the right size.

WV EGBERT_2

Armaflex UV

is available, I had a heck of a time getting it, but I got it.

Just getting back from a manufacturer's solar class yesterday.
We went through some math and worked out that the payback was 20 years for their two flat panels, solar controller , tank etc.. Efficiency of the array was factored in. When compared to oil at current price of $4.75 a gal. DHW only, add panels for heat and the payback is non existent..
At least they were honest !! People buy into solar for the "green" save the polar bears factor, just the same as people buying a hybrid car, payback is well after the life of car.
BTW, the price of their two flat panels system vs one evac 30 tube array system totaled to less than $2000 difference. At a 20 year pay back for both,doubt if really makes a difference what type you choose.

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Unknown

what efficiency were they assuming for oil fired DHW?

more than, say, 60%?

michael_34

solar heating tilt

I believe the best way to combat any overheating is the tilt of the collector. The company I worked for in Santa Fe(yes Santa Fe gets really cold and snowy too!) the tilt was 85* for heating systems. This gets all the winter sun and eliminates the chance for overheating in the summer. Figure the latitude change for northern climates and cloudy days and get your tilt. Here in Ithaca NY, I don't go below 65*. And do well with winter heating and summer overheating. What you folks think?
Michael

michael_34

armflex UV is it

High temp? Man that would be great. A HT armflex with UV. If you have any leads I would be awfully thankful (how's that for kissing a**)
Michael

Unknown

levelized cost vs. simple payback

I'm also a bit suspicious of the economic viability of active solar heating especially here in the northeast where solar resources are less than stellar.

Bob makes a important point about operating temperatures and efficiency, there are times when a low temperature heating application can make much more efficient use of a collector than DHW can.

There will probably be times during shoulder season or when there is no dhw load when it makes sence to stop loading the preheat tank at say 95 and divert to a low temp heating load. However the added cost and complexity of such a design may not justify it's cost.

Solar involves some things that are not generally part of the average heating guy's work flow, for this and other reasons I can see how making money on solar and still presenting a good economic proposal to a client is going to be tough. Like you said there are those who are interested for other reasons, the green is the new black types.

The wild card on efficiency/solar investment is energy markets. If, as some believe current escalations reflect deep structural problems with production capacity (peek oil) then $5 gas may seem like the good old days in the all to soon future. At that point the Prius WILL make economic sense and that 20year solar payback starts to shrink fast. Who want's to be the Doomsayer salesman

From a sales point I think a good aproach is to market the payback in terms of an energy pre-buy. Calculate the lifetime generating capacity (easer said than done) Divide the installed cost plus operation and maintenance expenses (generally 1-2% of installed cost) this gives the cost per unit of energy btu's or KW. I like KW because it has a clear market value with no need to adjust for fuel conversion efficiency( ie. it converts to heat at basically %100 eff.)

I think offering someone a fixed price on a fuel for 20 years may be more compelling than saying it's going to take 20-years before this thing will pay for it's self. As long as that price ends up at or below current market price

WV EGBERT_2

Well said Scott

Exactly what the solar instructor said yesterday.
Sell solar as a pre-payment for energy, not for payback.

Good tip on the KW comparison.

Rob, no 86 % afue boiler with indirect was figured.
For DHW figure btu's needed per day, this will be constant for the year (if no new additions to family !)
A family of four using 20 gals. per day per person x diff of incoming cold water temp to 120* x 8.33 = btus
(80gals)(120-50)(8.33) = 46,468 per day x 365 days.
now figure how many gals of oil need per year, knowing that 1 gal = 140,000 btus, correct for effciency of appliance, and current price per gal for fuel oil = how much it will cost to heat DHW with oil for the year.
Lets say the solar array system will cost $12,000 divide that by yearly oil cost should give how many years until ROI.
This does not include any solar rebates, maintenance costs ,nor adjustments in oil prices if oil goes up lets say an average of 10% (conservative I know).



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WV EGBERT_2

Yes hi-temp uv resitant

Actually my supplier ended up getting me Nomaco (I think) insulation, same as Armaflex.
I still have 30' left of 1/2" nom. I know he had to buy entire box, but was kind enough to sell me pieces, maybe he still has some.
Let me know if I can help.

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michael_34

HT armaflex UV

If you can pass on his number that would be helpful. Thanks again.
Michael

Darin Cook_5

$$$$$$

I am thinking that without incentives such as tax credits, we would not see alot of solar thermal installs going on.
I also believe that alot of the old solar "specialists" gave away alot of their work, dollar wise, making it seem more cost effective to customers. I know that we do not like to talk dollars on the Wall but when you price out a solar thermal install just as you would a boiler install or the like it not a "cheap" system and you will not be in and out of a house in a day as some solar marketers would have you believe.
Now I believe that solar is a great way to supplement your domestic hot water. The higher fuel costs go the more sense it makes. I believe it can seriously make a dent in our national energy dependancy. The majority of systems themselves are plug and play making the systems installer friendly. Seeing how Solar has gone mainstream with the Plumbing and Heating industry it will keep growing.









Darin

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Ron Huber_2

One more factor on efficiency

Not easy to figure, but, when that 500 or 600 lb boiler shuts off after heating either an indirect tank or tankless coil, how many btu's are wasted to the boiler room. From May to October there is not much call for heat (like none) so x number of lbs of mass and water, also include boiler piping and manifold losses,are wasted, now the efficiency is not the 86% according to the combustion analyzer. That is where the solar with electric back up kicks butt, the times of the year when solar is good and you do not need the Incredible Hulk cycling on and of for a little DHW

WV EGBERT_2

True Ron

Not easy to figure in piping losses.

But think of the family of four coming home in the evening after the solar has been supplying DHW during the day. Now the dishwasher comes on, a load of wash, showers or baths are drawn, the next thing the tank is depleted and boiler back up furnishes its btu's to replenish tank since sun is down and is no longer effective.
This is when solar pre heat with a tankless electric kicks butt !

Oh, what a tangled web we weave!

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Unknown

right, that was my point. cast iron oil is not a particularly efficient way to generate hot water, indirect or not. a company around here data logged such boilers and figured out actual oil to used hot water in such configurations can be as low as 30% efficiency.

That can halve your payback calculation in a hurry. it's not that bad if the boiler is already hot for heating purposes, of course.

Solar DHW preheat with electric on demand can be fairly good payback. but then, $12k solar DHW only is probably an evac tube system

Ron Huber_2

mute point

So they have used all the btu's from the solar, it did it's job of supplying whatever it could that day, 20%, 50%, 90%, and now it is time to use the back up, we are not trying to supply or promise 100% solar contribution here. If I have a tank of 80 gallons of 120 degree water at the end of the day and I used it up that night, that is 80 gallons deliverd and if the back up kicks on, so what? What more can you ask for?

WV EGBERT_2

Maybe Summer

You can get to satisfy 80 gals with 120*,
Even so,at night the boiler WILL fire.
And the remaining 10 months it will fire longer to make up the difference where solar does not produce.
So if your paying for oil anyway, ... and if it will cost $800 a year in oil to produce DHW only no matter how "inefficient" it will still beat out solar @ $12000, which ,btw Rob was a hypothetical number, email me, I can tell you what the real costs for tubes are vs. two flat panels.

And, although not controlled ,that cast iron mass is lossing heat within the house in the winter and will probably still do better adding heat, while we can imagineer fancy and expensive ways to suck out every available btu to integrate solar and radiant heat. The law of diminishing returns will always win. If oil doubles in price, yes it gets closer, but not much.
Look at the UK and France, they have had high oil for a while now they are focusing on Nuclear. The only reason why Germany is big on solar is because the gov is subsidizing solar. I heard around 80%.

Lastly, the reality of an arrays ability to capture, and maintain all the yearly solar energy that makes it pass our atmoshpere is what 35%, while the rest bounces off the glass, and the remaining is loss, there is a reason snowmelts off FP. It would be interesting to factor that against the cast iron beast in the basement.

I'm home today, It's 73* and sunny today and my gauges show I'm pulling 90* so far from the roof, and it's not even noon yet, later tonight my electric tankless will be happy. : )



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Darin Cook_5

Another thought

Many new appliances have timer features built-in, so a washing machine or dishwasher could be run during the day maximizing the solar collection and decreasing the possibility of stagnation and then still pulling energy out of the sun for showers when the occupants come home. The more hot water that you use during the day accelerates the savings.






Darin

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Metro Man

Or...

> Many new appliances have timer features built-in,

> so a washing machine or dishwasher could be run

> during the day maximizing the solar collection

> and decreasing the possibility of stagnation and

> then still pulling energy out of the sun for

> showers when the occupants come home. The more

> hot water that you use during the day accelerates

> the savings.

>

>

>

>

>

> Darin

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 509&Step=30"_To Learn More About This

> Professional, Click Here to Visit Their Ad in

> "Find A Professional"_/A_



Install a drain back water system and never worry about it again.

Metro Man

hot_rod

Why leave out the $2000.00 rebate?

it is real and available, at least to years end. And it does make quite a difference in payback numbers considering a solar DHW system in the 8K installed price range.

I predict this program will renew possible get better with the next adminstration.

Seems every day various states are upping the ante on solar incentives. Didn't colorado this week pass the Homeowners Association bill, preventing HOA form restricting the installation of energy "devices"

Them energy price increases predicted by the EIA need to be considered also. Although an exact number is hard to predict I suspect all forms of energy will continue to increase in cost.

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