is solar thermal dead?

jumper

Since photovoltaic keeps getting less expensive?
Has anyone compared cost of more photovoltaic powering resistance heat versus less photovoltaic powering heat pump?

Eastman

I expect photovoltaic to dominate.

Leonard

Think photovoltaic is only 10% efficient at turning sun into power, not sure how good conversion efficiency is with thermal .
But bigger issue seems with photovoltaic you can sell power to utility during summer when you wouldn't need heat, Can use it to save money the WHOLE year, that should offset it's lower efficiency.

Neice in-law has 5kw of solar on small roof in Maine , net metering almost eliminates their yearly electric bill. They are conservative but have electric water heater, drier, well, and A/C. KWHs get "banked" on long summer days and used on gloomy short winter days when solar isn't making much. Have to use KWHs banked with utility by end of the year or loose them, so in December they started using electric heaters for heat. Selling excess power to utility effectively eliminates need for large $$$ thermal banks. But I think selling excess all summer is biggest financial plus. Set it upright and won't need a generator and FUEL for power outages.

As always install labor is a large part of the cost ,her father was a carpenter and mounted them on roof. Electrician he works with wired it at trade pricing. It's the boonies of Maine, wood is plentiful, so they burn it for heat and sell the solar. If that work way up in the winter gloomy north it should work anywhere

hot_rod

Far better efficiency from thermal collectors, the exact number depends on the operating condition you drive them at.

A thermal pool heater for example can be 90% efficient on days where the ambient temperature is close to the pool water temperature. The collector loses very little energy to the air around it.

Running a collector at 95°F when it is 20° outside and expect around 43% efficiency. If you drive it to a 160 temperature on a 20° day, 16% of the energy is converted to useful heat.

The main issue with thermal is what to do with that energy all summer when there is no load to be had, the load is lopsided.

Electricity is used most every day for some load in a home. Stored, or sold back to the utilities.

Leonard

Summer pool heating is a very good use for thermal solar, I only thought of house heating in winter. Cousin had in ground pool, spent $1000 for propane one summer~ 25 years ago, and pool liner was insulated.

Summer domestic water here is ~ 45-50 degs . So to fill and heat a small 8ft blow up pool on 80 deg summer day I slow flowed water thru ~ 900 ft of garden hose laid 1 ft apart on hot sunny gray pavement the whole day. Water came out a nice ~ 100 degs FREE. Think it took ~ 4 hours to fill ~ 1 ft deep. Had an old 20k BTU A/C and wondered if condensor coil would heat water faster. Calculated solar heated it ~ 3X faster, and free. Would think a real solar panel would collect more energy/sq ft.

Next time to speed it up I pre-heated the 45-50 deg domestic water with a repaired car radiator and box fan before the 900 ft of hose, summer was 80-85 deg air

Neighbor used real solar factory sections of simple black plastic tube/mat tied on roof in summer for thermal solar pool heating , 8ft dia 5ft deep pool/hot tub. Worked great, free heat, cheap collectors. It's a cost/benefit ratio thing.

hot_rod

Interestingly enough un-glazed black rubber mat pool collectors end up being the most efficient in summer pool heating conditions. Without the glass covering additional radiation gets to the water.

Performance drops like a rock as ambient drops about 15- 20 below fluid temperature, however.

My mother used the same garden hose in the sun trick to fill our kiddie pool. The use of solar energy use dates to the cave men years. KISS And the heat goes on "Nancy Sinatra"

Leonard

My attic is real hot, thought about moving radiatior into it. But wondered if heat transfer thru roof and decking would keep up with it , or cool down. Didn't want to bother with all the pipes, only a few days of real hot weather here in NH to need a pool (have lot of tree shade in my yard.

Plus car rad was only rated for 15 psi and I'ld have to remember to drain it before winter. Plus maybe set up a condensate pan of some sort.

TheLeakyTub

Build it solar had a ton of DIY stuff. These are somewhere between black plastic and vacuum tubes. Lots of data, plans and even a guy who fabricates aluminum backing parts.

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Example1KSystems

If you want some serious heat here a DIY parabolic tracker.

http://georgesworkshop.blogspot.com

BobC

The very best steam turbines can achieve close to 40% efficiency with 500C steam so they would be better than the best voltaic panels that are a little over 20%. That said the gas turbines are very large and even more expensive.

Bob

Mark Eatherton

Biggest problem with Solar T is that it can't spin the gas meter backwards. It can only stop it, and with todays greedy society, they want to spin their meters backwards, hence PV and the DOE pushing PV's. I think drain waste heat recovery should get a better subsidy than ANY of the solar systems. A 50% recovery reduces energy for heating hot water by 50%. Pure and simple.

ME

Leonard

Drain heat recovery might be high % , but showers don't run long so small number of BTUs. All that copper sounds $500, I wonder what break even point is . Guessing yearly clean outs.

Hummmm my house two 10 minute shower /day. 1.1GPM oil nossle and ~ $2.50/gal oil, so ~ $.90/day fuel cost. Or ~ $330/year. So 50% savings = ~$164/yr. Assume $500 cost so breakeven in ~ 3 years. Hummm not so bad.......maybe ....

hot_rod

There should not be much to clean out? it's just a straight piece of copper DWV with a rectangular copper coil wrapped around?

Although a couple Webstone purge balls would allow you to de-lime the coil if ever that was a concern. At low temperatures mineral scale should not be a big concern.

I see they offer horizontal versions now, wonder what the difference is?

It should be an easy project for a DIYer, wrap some parallel 3/8 soft copper loops, for adequate flow, solder to the 3" DWV.

I suppose you could build 1-1/2 or 2" versions for showers and sink drains if you have access to the piping.

Mark Eatherton

Leonard said:

Drain heat recovery might be high % , but showers don't run long so small number of BTUs. All that copper sounds $500, I wonder what break even point is . Guessing yearly clean outs.

Hummmm my house two 10 minute shower /day. 1.1GPM oil nossle and ~ $2.50/gal oil, so ~ $.90/day fuel cost. Or ~ $330/year. So 50% savings = ~$164/yr. Assume $500 cost so breakeven in ~ 3 years. Hummm not so bad.......maybe ....

Yeah, now run the numbers on a solar thermal system. Say $10,000 installed costs... Even with tax credits, the numbers don't pencil out in the theoretical life expectancy of the equipment.

BTW, there is no maintenance to a DWHR system. None...

http://www.swing-green.com/index.php/green-products/greenfox-dwhr

ME

hot_rod

Mark is correct, unless you have a consistent DHW load, or get bargain prices and install it yourself the SDHW numbers don't often work out for residential. When you could scrap together 50% in incentives it started to look better.

There are some good commercial loads where it can pencil out.

Bottling companies, brewing operations, ice rinks. It depends on their fuel costs also.

No question pool loads in warm climates make sense. Fly into Florida and see how many pool solar systems you see below. that is still the largest market and the reason companies like AET and Sun Earth manage to stay in business, they locked up Florida, So. Cal and Hawaii.

It's an inexpensive collector, and you already have the pump

Leonard

I'ld GUESS the waste water flow has mostly air in it. The vertical ones likley have baffles to slow waste water instead of letting it free falling thru quickly. Give it more contact time to transfer it's heat thru pipe wall. Baffles likely have to be removable for cleaning. My shower drain catches hair a lot on drain mechanism and plugs up as it is.

I suppose if pipe the vertical exchanger on one side of a U shape could keep it 100% loaded with water you wouldn't need baffles. Kinda like a P-trap. Need a sludge trap at bottom, my shower 4inch dia x 9 inch tall one was filled with muck after ~ 30 years and coating in the pipe

hot_rod

I've seen cutaways of several brands at trade shows, no baffles I could see? Something to do with the "film" transfer?
There may be other types with some technology inside.
http://renewability.com

Leonard

I suppose falling balls of water might touch one surface, drag and roll. And maybe grab onto it, and slide/film down the pipe

Just seems lot of water would also be falling down center and not touch walls much. Industrial heat exchangers with "clean" liquids have baffles to enhance contact with walls. With shower water: hair, bits of bath tissue and other junk likely would foul any baffles, and need periodic cleaning. But with house waste water, shower is about your best target for free BTUs, so maybe experiment with copper baffles and put up with cleaning them.

Jamie Hall

On solar thermal for space heating (not domestic hot water) the best and most efficient designs are passive or semi-passive and architectural, involving proper use of glass, building orientation, and interiors -- and in some designs a fan to provide warm air movement to storage media (that's where the semi-passive bit comes from). They also involve a large amount of storage built in.

Properly designed and sited, they can approach meeting all of the heating load of a reasonably sized residence or even some commercial applications, even in some pretty beastly climate conditions. I have seen successful designs along these lines in all the New England states -- though not, I have to say, in the wilds of northern Maine!

Sadly, it is not feasible to retrofit most of these techniques to existing structures -- but for new construction I wish that we'd see more of it.

Domestic hot water is another problem; as other posts here have noted, efficiency drops as the temperature of the heated medium increases, and there are some rather difficult problems with managing the system as a whole at night or cloudy conditions in colder weather. There are a number of ingenious solutions, but they have booby traps in one way or another.

Compared with either one, though, the efficiency of photovoltaic is abysmal, although advances are being made in multi-layer conversion devices which can improve efficiency a lot. They aren't cheap... the biggest advantage I can see of PV, though, is that it's easy to measure -- and make money off of.

Leonard

Vertical shower drain exchangers ...... Seems a few vanes or tangent entrance will give water a swirl so it would stay in contact with walls more.

Horizontal shower exchanger....... Finally dawned on me, just install it about 4-6 inches below the existing drain line, have tees pointing up at both ends. Tees, so you can open both ends and ram out clogs if need to. That way it stays filled with water at all times. Stops water from only staying in contact with bottom of pipe, longer contact time and higher efficiency.

Baffel (stationary) on horizontal install ...... might not need to improve things too much ,but could try a simple long strip of copper sheet metal and twist it into a slow spiral , to increase turbulence. Like those "twirling" strips that spin in the wind. Might not catch much hair and debris, size it so can pull it out the clean out tees at ends.

Mark Eatherton

Leonard said:

I suppose falling balls of water might touch one surface, drag and roll. And maybe grab onto it, and slide/film down the pipe

Just seems lot of water would also be falling down center and not touch walls much. Industrial heat exchangers with "clean" liquids have baffles to enhance contact with walls. With shower water: hair, bits of bath tissue and other junk likely would foul any baffles, and need periodic cleaning. But with house waste water, shower is about your best target for free BTUs, so maybe experiment with copper baffles and put up with cleaning them.

It is called the gravity surface effect, and it has been proven that it works quite well. Like most things mechanical, it goes against your personal intuition. The water does in fact cling to the outside of the drain pipe. In fact the original name of the GreenFoX was the GFX, which stood for Gravity Effects. Carmine Vasile is the patent holder on this particular device. His daughter has taken over the company.

ME

hot_rod

I visited a Energy Research center in Ontario a few years back. they had one installed and data logged, I think the info was online in real time. Now I have to remember the name of the facility
I took pic when I was there, he had all sorts of unique products, a prototype Baxi modcon that generated electric as it fired, many other energy products, some made it to the market, others not.

It would not be hard to put a BTU meter on the water side and let it log for a few months or a year.

Leonard

I don't see the cold water pipes soldered onto center drain pipe. I wonder what they are using to improve heat transfer between the pipes, air gaps are a very poor thermal conductor.

Surprised they issued a patent, must be more to it than just cling effect. Although the cling effect might not have been fully realized until recently. The effect has been happening in vertical exchangers long before people realized what's going on, so that part seems to fail the required patent novelty test , of not being done before patent holder did it. So I wouldn't want to be the one defending that "patent" against patent infringers.

Larry Weingarten

Hello, There's a lot going on in this discussion! I met Carmine Vasile long ago, while he was still trying to get his GFX off the ground. It was tough with so many questions like what I see here. My understanding is that GFX stands for "Gravity Film eXchange". About the issues of fouling, it's been demonstrated over a longish time that it isn't a problem. Even the horizontal units made by David Velan (Eco Drain) have simply a wide flat copper plate that drain water flows over, so there isn't much to catch on, or stick to.

About the solar side of things, if you use "inefficient" collectors similar to pool panels, you can get around both of the issues of overheating and freezing, so the system can be much simpler and cheaper. I've got a system I built a few years ago that is providing 90% of the client's hot water need and the cost was far less than going conventional solar thermal.

Yours, Larry

Mark Eatherton

I stand corrected on the name. Thanks Larry.

ME

WillyP

Like all things solar, it is all about the storage. You can build a heat sink and store a lot of hot water all summer. If it is in an insulated bunker under ground, you can store a lot of that energy. This allows you to keep it hot in winter. But the cost of doing that can be so high that you never see a return. But it works great if you are off grid in the great white north.
But it is much cheaper to just put up PV and use that to run a hot water heater, with grid storage.

Jamie Hall

I hope it's not dead. Only -- why not use it directly for space heating? This is, of course, only really feasible for a new build, and it does place a few restrictions. However, if one is willing to compromise a little and use a wood stove to take the edge off, even those restrictions are minor. The house I built before I took over Cedric's home looks almost completely conventional -- just a rather nice saltbox with a 1200 square foot foot print, two stories in front and one in back, on slab, in the hills of northwestern Connecticut. And uses half a cord of wood a winter to heat it. The rest is entirely passive solar. My father-in-law, now deceased, built about a dozen passively heated solar houses in southern New Hampshire and north of Boston; the early ones had some air quality problems (too tight), but the later ones use HRVs and don't have that problem. None of them are anything unusual to look at -- except, perhaps, more south glass than one is used to.

The two biggest problems are storage -- getting a week's thermal storage at a small delta T is not simple -- and overheating in late winter -- but that's easy to fix: open a window...

jumper

Solar thermal and passive don't mean the same in common useage.

Solid_Fuel_Man

I think PV is really the best bang for the buck. I believe that's a big reason solar thermal has fallen out of fashion. Glycol, drain back, controls.....any of which fail and you end up with a mess. 

PV, cant freeze (works better in the cold), has no moving parts, keeps getting cheaper/ watt output to buy. 

Jamie Hall

jumper said:

Solar thermal and passive don't mean the same in common useage.

Quite true. And for some reason -- which I simply don't understand -- passive direct solar heating doesn't ever seem to be considered.

Why?

jumper

Jamie Hall said:

jumper said:

Solar thermal and passive don't mean the same in common useage.

Quite true. And for some reason -- which I simply don't understand -- passive direct solar heating doesn't ever seem to be considered.

Why?

Just too sensible? A Canada2000 house with a solarium on south side?

Jamie Hall

Something along those lines...

Here's one, in Weston, MA. Built in 1964. Not in such good shape now (essentially abandoned for the last three years, but restorable -- and for sale.

WillyP

Leonard said "Have to use KWHs banked with utility by end of the year or loose them, so in December they started using electric heaters for heat. "
How des that work? If they make you blank out your wattage bank in December, does that mean you have to pay for electricity in January until you get more watts in the bank?

GW

I think thermal died out years ago. What’s the average monthly bill to run hot water? Small money

hot_rod

Plenty of excellent thermal solar opportunities. You need a year around load to make it pay out. Rarely do residential applications pencil out unless you have about a 60% incentive offset. Water parks, hotels that have laundry and restaurants on site, heated pool.
I think Hawaii requires a solar component on all new buildings. Pricey electricity over there, not many other fuel options.

Sun Earth, AET and Heliodyne are 3 US solar companies that are still in business, have been for 30 plus years.

Plain water drainback systems are pretty simple, less components than a hydronic heating system actually

Robert O'Brien

It's dead. The cost of the fuel being displaced is the issue.

Larry Weingarten

Hi, I don't think solar thermal has to be dead. Here is an article I helped write about finding ways to cut energy use at a friend's place. https://www.homeenergy.org/show/article/page/3/id/2303/viewFull/ Solar thermal was about half the cost of what you would expect, does 90% of the domestic water heating and is paying for itself at about 25% per year. It's alive!

Yours, Larry

PerryHolzman

I also don't think solar thermal is dead. It's rare because few heating contractors are willing to educate themselves about it and are willing to service it.

When the 1st answer the contractors give you when they see a strange system is that it has to be replaced with whatever they are most current on.... Nothing will be maintained; and nothing actually pencils out financially either (mod-con boilers being a current example because they have to be replaced because the contractors don't know how to service most anything over 5-7 years old unless they are working with a lot of a specific model).

Solar thermal is best when designed in up front by someone who really understands things. Passive solar works in some cases too; and again needs to be designed in up front.

Retrofit of Solar thermal to an older house often runs into economic considerations at those tend to be pricey for what you get - and are often over complex with too many active components for long term low cost reliability (although a few cases do work out).

However, its the 1st point of this post that's the biggest reason solar thermal is relatively stagnant - even though it makes a lot of sense (and financial cents) for many places.

I note that steam heat is also considered dead for very similar reasons - although there are many advantages in the most cold climates (and your pipes & radiators won't freeze and crack if its done right in the event of a loss of heat situation in winter).

jumper

Solar thermal is most economic when you have a use for relatively low temperature medium. I remember a company that used solar air heaters for industrial buildings where 55° was acceptable. Mornings and late afternoon gas fired radiant fired up.