Possible hybrid PV/hot water panel product?

Gooserider · May 2009

I posted on this a while back, as one of my earliest questions, and one that still bugs me...

How come it seems like nobody makes a "hybrid" panel that can make both PV and hot water at the same time? I keep hearing that cooling panels can be a challenge and that the cooler a panel is, the more juice it will make... It seemed to me like it would be a logical combination to put a hot water collector on the back side of a PV panel, and get the advantage of cooling the panel and collecting the waste heat it produces. I understand that the hot water production might not be as good as with a pure HW panel, but that could be made up just by increasing the HW hybrid area, and besides "half a loaf beats no bread..."

This would seem especially helpful for those with limited panel space.

I've run into a fair number of people that seem to have had the same thought, but wasn't aware of any commercial products that did this, and could understand why people might be worried about doing attempts at home brew with an expensive commercial panel...

I went to an "alternative energy" show in Boston a week or so ago, and ran into a solar outfit that pointed me at a company called "Sun Drum Solar" that seems to be working on this idea...

They have made a hot water panel that is designed to fasten into the back of several different standard commercial panels (list includes models from Evergreen, Sanyo, SunPower, Sharp and Solar Power) and put out 500w of hot water w/ 1,000w solar input, giving a net "per-panel" total efficency of about 55-60%. This includes a 10% boost in the PV output... Once the Sun Drum panel is installed, the panel mounts in the usual way to standard PV racking, obviously with added plumbing. Since their panels don't get quite as hot as a standard HW panel, the claim is that you could plumb them with PEX, though I'd be inclined to use copper on general principles. Cost was said to be comparable to a standard HW panel of similar size.

I have no association with the company at all, but thought it was interesting - and glad to see both that someone is finally doing something with the idea, and that (judging from the claims at least) it works as I expected...8) I haven't tried it, but if I do solar stuff, I'd be strongly interested in the product.

I'd be interested in what others think of the approach...

(Feel free to move to a different area if this is the wrong spot for this...)

Gooserider

BB. · May 2009

Re: Possible hybrid PV/hot water panel product?

Partly, depends on how hot you want the water... If you want 120-160F--that means the panels may be operating near "normal" temperatures--and a lot hotter in cold/windy weather.

Square area wise--most people only need about 20 gallons of hot water a day--depending on climate and collector type--that is only about 10 square feet per person--or 40-80 square feet for a family of 4.

For Grid Tied Solar--panels on the order of 3,500 watts or larger--they require about 270 sq.ft. of solar panels--so there is a big miss-match in area requirements for Grid Tied systems.

Another issue may include orientation to the sun... Solar PV--you want them always gathering as much sun as they can. Solar Thermal tend to favor winter tilt/orientation. Normally, you want more heat in the winter, and in the summer, you actually want less so you don't overheat the panels (too much sun, may boil the water/heat transfer medium).

200+ Watt solar panels are already getting difficult to manage with just one installer on the roof--add the weight with a thermal collector--your manpower costs for an install may go up too.

In the end--the added cost and complexity of wiring and plumbing your solar panels and the mix of solar PV and solar PV+Water setup just does not make sense for large PV systems...

The above is just my opinion--Always happy to hear from others with different (and possibly better) ideas/experiences.

-Bill

Gooserider · May 2009

Re: Possible hybrid PV/hot water panel product?

Well, we probably aren't terribly out of line on our hot water needs, though the GF and I are both fans of hot showers... However, I was hoping to generate enough hot water to put at least a partial dent in our heating bill - with balance to come from wood burning.
DHW should be just over 120*, and I'm planning on doing the in-floor radiant heating system to run on 120* water during "design day" demands (less the rest of the time) so winter temps shouldn't get that high.

Mount angle will be 45*, as that is the pitch on our roof surfaces, which is about optimal for year round at our latitude (about 20 miles north of Boston)

Summer time is also not an issue, as we have a 17kgal in-ground pool, currently not heated, that could REALLY benefit from being used as a "heat dump"

I would agree, it might not be an ideal solution for everyone, but it might work well for those with limited mounting area that want to get the absolute most out of their setups.

If roof area isn't a limiting factor, then I agree it might make more sense to do a separate panel design...

dwh · May 2009

Re: Possible hybrid PV/hot water panel product?

BB. wrote: »

200+ Watt solar panels are already getting difficult to manage with just one installer on the roof--add the weight with a thermal collector--your manpower costs for an install may go up too.

I don't think this is much of an issue, except perhaps for DIY people. Professional installers are almost certainly going to have a "helper" on the job anyway, PLUS with that extra set of hands the job will take less time (possibly less than half the time) than it would with just one person working solo.

In the end--the added cost and complexity of wiring and plumbing your solar panels and the mix of solar PV and solar PV+Water setup just does not make sense for large PV systems...

The above is just my opinion--Always happy to hear from others with different (and possibly better) ideas/experiences.

-Bill

Personally, I think that adding heat reclamation is a great idea. Even just that one application - dumping the waste heat into a swimming pool - is a great idea, if for no other reason than simply keeping the temp of the PV down.

I also think that having the liquid system integrated into the panels will go a long way toward making the install quicker and easier.

As for the benefits with a large array, the problem seems to be where to dump so *much* waste heat. Obviously, in the desert in the summer, if there is no swimming pool or other large water reservoir, then the heat can be dumped via geothermal - but that is a waste.

What about running the hot water through some sort of geothermal heat pump electric generator?

Or, some other fashion of converting the excess heat into electricity?

I haven't thought much about this, but just offhand I will note that Peltier junctions can use electricity to create temperature differences, but they can also use temperature differences to *generate* electricity.

(Though yes, most peltier junctions are optimized to use electricity to move heat, rather than being optimized for moving heat to make electricity...but they don't *have* to be.)

Attaching the Peltiers directly to the back of the PV might be better from an electrical generation point of view, but you wouldn't get the hot water with that.

How about putting peltiers *between* the PV and the attached liquid system?

Gooserider · May 2009

Re: Possible hybrid PV/hot water panel product?

The numbers I've seen on Peltiers is that while yes, they will generate electricity from heat, they are not very efficient at it... (Nor are they all that good at moving heat when fed electric...) They also need to have a heat differential driving them, not just being heated... IOW, you need to put a heat source on one side, and a significant heat dump on the other, with the amount of power being generated being a function of how big the differential between them is. Putting a Peltier between the panel and the water collector wouldn't give much of a differential unless you had a really serious heat dump somewhere else in the system (and if you did, why not put the Peltier there?) Pelts are also quite expensive...

I would tend to say that a heat dumping a large array would be a problem in the summer unless one had a pool or other similar high heat demand thing to use as a heat dump.

While there are a few "bottoming cycle" engines that could be driven by 120-140* water, I don't know of any that are both sufficiently economical, and capable of making enough power to be useful - after all in the general scheme of things, 120* is relatively low grade as heat energy goes... The laws of thermodynamics come into play here, it would be a challenge to pump that 120* water into a more useful form of power such as electric - you would be far better off to find a way to use it as heat...

Gooserider

Gooserider

BB. · May 2009

Re: Possible hybrid PV/hot water panel product?

Peltier devices (really the Seebeck effect) need a relatively large temperature differential to generate much power. Overall, they tend to be very inefficient

You are only talking about a 5-10% efficiency of the devices... Of course if it is "waste energy"--then 5% of "free" may be worth it.

From the Wiki--they said that BMW made a 600 Watt device that would improve mileage by 5%...

An interesting article about RTG (Radiological Thermal Generators). They average 3-7% efficiency.

It appears that a Stirling based (mechanical) thermal generator may be in the 20% efficiency range.

And there are a few propane fired TG's that have been used for remote installations where reliability is more important that fuel efficiency (and, at times, they have been replaced with solar+diesel gensets).

Here is a website with a whole range of fuel fired TGs. It is out of the Ukraine "Institue of Thermoelectricity".

Notice that none of them are very large (milliwatts to 100 watts). And the larger units seem to require around 250C temperature differentials to achieve the higher output.

I don't think thermal electric generators will ever make it into mainstream usage.

-Bill

dwh · May 2009

Re: Possible hybrid PV/hot water panel product?

Gooserider wrote: »

you would be far better off to find a way to use it as heat...

Well sure, but in a desert with a large array, what you probably don't need more of is heat (at least during the day).

So while yes, using the heat directly as heat would definitely be more *efficient* than converting it to electricity, converting it to electricity would likely be more *useful*.

Efficiency is good only as long as it's useful.

As I said, most junctions available today are design optimized to *use* electricity, not to *make* electricity - making them somewhat more efficient at generating electricity is only a matter of stating a different design goal.

How about using them to generate some electricity during the day with a temp differential between the PV and the liquid, and again at night with a temp differential between the liquid and the air (desert nights are more often cool than they are hot).

Gooserider · May 2009

Re: Possible hybrid PV/hot water panel product?

As per the prior post, I don't think there is much hope of an efficient thermoelectric generator... If they can't make one that is very efficient at cooling, I doubt they could do much better producing one that does very well at making electricity...

If I was stuck in a desert situation, what MIGHT work is to use the collected heat to charge a thermal storage tank (could be any medium, but big tanks of water tend to be the best bank for the buck(pun intended)) during the day, then use the stored heat to drive a radiant heating setup at night... Of course this assumes the night is cool enough to need heat, but.

My basic bottom line is I don't see a cost effective way to make enough power to make a salvage heat water system worth while...

OTOH, it MIGHT (emphasis on the "MIGHT") be workable to do a really high temperature solar steam generation setup that could make useful power, but that has it's own dangers and engineering challenges - Solar PV is probably more straightforward.

Gooserider

Gooserider

icarus · May 2009

Re: Possible hybrid PV/hot water panel product?

I had the Tg brain storm a number of years ago. I used about 30 of the small ones wired in series,, hot side on the wood stove,,, cold side with a bucket of ice. (Got lot's of ice in our neck in the winter. (I was going to run a ceiling fan) By keeping the bucket full of ice, and the fire roaring,,, I could get 12 vdc,,but not enough to run a 5 watt fan. Never put a meter on it,, as it seemed kind of silly to have to keep shoveling ice into the bucket for the sake of a fan that didn't even work!

T

BB. · May 2009

Re: Possible hybrid PV/hot water panel product?

I guess I should add this disclaimer--Thermopiles are in the mainstream--they are used in Gas furnaces to control MilliVolt gas valves and as part of IR Thermometers.

And, of course, they are used for small cooling applications (labs, portable coolers, Computer Processor Coolers, etc.).

They just will (probably) never make where 100's of watts or more are needed to be generated around the home/off-grid living.

-Bill

Gooserider · May 2009

Re: Possible hybrid PV/hot water panel product?

BB. wrote: »

I guess I should add this disclaimer--Thermopiles are in the mainstream--they are used in Gas furnaces to control MilliVolt gas valves and as part of IR Thermometers.

And, of course, they are used for small cooling applications (labs, portable coolers, Computer Processor Coolers, etc.).

They just will (probably) never make where 100's of watts or more are needed to be generated around the home/off-grid living.

-Bill

Actually Bill, I believe what you will find in those small cooling applications are Peltier junction devices, not thermopiles... It is worth noting that while those small coolers DO work, my impression is that they burn an awful lot of juice for the amount of cooling you get... The big advantage that they have for portable coolers is that they are pretty much position independent, and don't mind movement but my understanding is that the high efficiency types prefer a compressor driven heat pump unit for getting the maximum cooling per watt...

The computer cooling application is (or used to be) popular with the overclocker crowd, but in that case you are looking at a SERIOUS power hog application which shows a big limit of the PJ device - it uses a great deal of energy to move the heat, and that extra energy must also be dealt with... I never did Overclocking myself, but looking at the boards for folks that did, it seemed like the typical Pelt used on an overclocked Athlon32 was around 1-200W, PLUS the 100W from the processor meant that you had to put 300 watts of cooling power on the "hot" side of the Pelt - which often meant liquid cooling or refrigerator systems - so you ended up spending 4-500 watts of power in total to drive a processor that normally would have taken 70-80 Watts...

Gooserider

BB. · May 2009

Re: Possible hybrid PV/hot water panel product?

Yea--you are right, it is the Peltier devices that are used for cooling (same physical materials--just one you pump electricity to move heat/cold; the other you pump heat/cool to produce electricity).

And, yes, thermoelectric coolers are just as inefficient as thermoelectric generators. The more expensive portable coolers use refrigeration compressors (they can move more BTU's and cool to a higher differential temperature than "simple" thermoelectric coolers).

I was just trying to do the disclaimer thing--broad/blanket statements are always wrong (well--almost always wrong except where they are right--including this one :roll: ).

-Bill

dwh · May 2009

Re: Possible hybrid PV/hot water panel product?

How about this gadget?

http://www.youtube.com/watch?v=SVRBKhK-jYU

BB. · May 2009

Re: Possible hybrid PV/hot water panel product?

Not very efficient (3.5-7%?). As solar PV panels have come down in price--I am not sure that this Hydrogen/Hydride technology would be very cost competitive.

The company has been around since the 1970's in one form or another.

Ergenics Home Page

They seem to be doing OK at making speciallized hydrogen storage "cells".

-Bill

stephendv · May 2009

Re: Possible hybrid PV/hot water panel product?

I think the main problem with integrating hot water and PV is that you're chasing a very small efficiency gain with large expense and difficulty in construction.

Also, bear in mind that in most solar HW systems the incoming "cold" water from the tank is anything but cold. The coolest part of the bottom of the tank could be between 50 - 90 degrees C (for a vented tank) depending on hot water usage. So you may even be heating the PV panels!

Gooserider · May 2009

Re: Possible hybrid PV/hot water panel product?

Actually, while there is a lot of debate in this thread about efforts to convert the hot water output of a hybrid panel to electricity, which I keep saying is a BAD idea because of it's low efficiency, a hybrid panel if used properly is FAR more efficient than a plain PV panel...

According to the guy from Sun Drum, (one could question his numbers, but I will assume they are accurate in the absence of contrary data) typical PV panel efficiency is on the order of 17% - or you get 17 watts of juice for every 100 watts of solar energy that falls on it. He claims that water cooling the panel improves it's efficiency 10% of that number or 1.7watts, so you would get a net panel efficiency of about 18.7% or 18.7 watts per 100 watts of solar. I would totally agree that this tiny gain hardly seems worth it.

However, you also get an ADDITIONAL 40 watts worth of hot water at 120-140*F - for a net panel output of 57 watts out of every 100 watts of solar input. IMHO this is a quite significant gain, IF, and ONLY IF, one can make good use of this energy in the form which it is produced

120-140*F water is quite useful for DHW pre-heating, if not full heating. It is useful for home heating in a properly designed in-floor radiant system (and designing for 120* water has a lot of other benefits for an in-floor system, regardless of heat source) indeed a radiant system can use water as cool as 80*F on less than "design day" circumstances. This temperature water is also very useful for pool heating, so it can be used by some people year round.

Gooserider

Dave Angelini · May 2009

Re: Possible hybrid PV/hot water panel product?

A pessimistic opinion of what you propose would be something like, solar hot water is extremely easy to do already and why would you want to have a photovoltaic exposed to the huge temperature extremes when the water in the panels is in a state of flux? The number of panels water verses electricity is not even close to the same these days so you would have panels that are only photovoltaic. Service of the panel would be a nightmare! It seems like an idea with good intentions but remind me, what is the benefit?

BB. · May 2009

Re: Possible hybrid PV/hot water panel product?

Gooserider,

There may be something "wrong" in your panel output estimates...

A solar PV/Electric panel is around 12-17% efficient. But, at least for a decently made solar thermal panel, they are around 80% efficient.

So, on a square unit per square unit comparison between solar PV, and solar thermal:

100 watts for solar electric
100 watts / 0.12 = 833 watts of "sun" on panel
833 watts of sun per sq. * 0.80 = 667 watts from equivalent thermal panel

Even if a solar PV + solar thermal panel was only 40% efficient for solar thermal collection--you would still see, very roughly, 333 watts of solar thermal.

40 watt of solar thermal output per 100 watts of solar panels sounds way to low (5% thermal efficiency per square).

If the combo panel thermal efficiency was this low--I would fear that system losses (pumping, thermal "leaks" through piping / tanks / cold day solar thermal panels / etc.) would swamp the 5% thermal energy collection rate.

Also, the claim that the panel electrical efficiency is improved by 10% would increase the output by 7-10 watts (not 1.7 watts).

But, I would guess that this 10% improvement would be based on heating pool water (to 90F or so)--not to 140F--which is getting pretty close to the operating temperature of a solar pV panel on a typical hot day any way (which--means very little solar thermal energy collection anyway--to heat water to 140F, the collector assembly has to be able to get even hotter for thermal transfer from the solar PV section to the solar thermal section).

From the www.SunDrum.com website, the PDF brochure says several things:

Capatures 3x more solar energy than Solar PV alone.
Captures 50-60% of sun's energy vs 12-18% for PV only solutions.

So... From the 3x claim--a 100 watt solar panel should provide ~100 watts of electricity and 200 watts of solar hot water (numbers are marketing numbers--A "100 watt" panel really only averages closer to 80-85% of panel rating in real life use).

From the 50-60% claim--then my guess of 40% of solar thermal efficiency would be about right, and ~333 watts of solar thermal would be expected. So--I would guess they told you 400 watts of solar thermal collection, not 40 watts (they claim 422 watts of solar thermal on a 943 watt/sq.meter solar day).

The solar thermal panels have a 6 psi max pressure rating, require distilled water or anti-freeze mix, and a 10 year warranty.

So--you have to have a closed looped system (a bit of a pain). 6 psi is equivalent to about 12' of water--so you would have problem if you installed panels on both a 1st and 2nd story roof home (plus pumping pressure).

Also, would you want to bolt a 10 year warranty thermal collector on the back of a 25 year warranty solar PV panel (with 40+ year expected life)?

Going through their site--I am not sure I trust their data collection (numbers, graphs, and panels supported don't seem to line up)... In any case, the efficiency thermal energy collection is very dependent on the amount of thermal insulation and ambient temperatures. Is this thing "60%" efficient on a 100F day or a 32F day?

Still not convinced it is worth the hassles/costs.

-Bill

lorelec · May 2009

Re: Possible hybrid PV/hot water panel product?

Gooserider wrote: »

According to the guy from Sun Drum, (one could question his numbers, but I will assume they are accurate in the absence of contrary data) typical PV panel efficiency is on the order of 17% - or you get 17 watts of juice for every 100 watts of solar energy that falls on it. He claims that water cooling the panel improves it's efficiency 10% of that number or 1.7watts, so you would get a net panel efficiency of about 18.7% or 18.7 watts per 100 watts of solar. I would totally agree that this tiny gain hardly seems worth it.

These numbers don't seem right. For simplicity, assume a square meter of PV with 1kW of insolation. At 17% efficiency, that's going to give you 170W -- now this is the PV's maximum rated output under standard conditions. Assume that the PV heated up 40degC above rated ambient. Power at that increased temp will be roughly {170 x [1 - (.004 x 40)]} = 142.8W -- 84% of rated output, or 14.3% efficiency. Assuming we were able to cool the PV back down to 25degC, we'd be able to recapture that 16% loss, not to mention heat some water at the same time if we used it to move the heat away from the PV. Seems worth the trouble, especially for larger arrays. If you don't have domestic water to heat, or your DHW is already too hot, sink it into the ground.

Marc

Gooserider · May 2009

Re: Possible hybrid PV/hot water panel product?

I will admit that I may have borked the numbers in my earlier posts... They do give some estimates on the SD website, which might be better than my memory and fuzzy math

I will totally agree that the SunDrum product is in many ways a compromise - it WON'T put out as much hot water as a dedicated HW panel, and the amount that it claims to boost the output of a PV panel hardly seems worth it (and my in my conversation with the SD guy, he said as much also)

Some of your other objections are also quite legitimate, but...

I don't see the closed glycol system idea as a major problem. Yes, it has it's negatives, but if you want to run a HW system in New England, your choices are drain-back or glycol, as you MUST have some sort of freeze protection at night. Given that I have a roughly 30-40' distance between the peak of my roof and the basement floor, a drainback system would require a relatively HUGE, power hungry pump to overcome the head loss, and have significant plumbing design constraints in order to get a good drain. With a closed glycol system, most of the plumbing design issues go away, and the circ requirement drops to just enough to overcome the piping resistance head loss. Yes, I'd have to add a (relatively small) expansion tank and a relief valve, but I'd lose the much larger drainback tank... IMHO the tradeoff is well worth it.

The typical SD install for just a DHW system would only involve putting SD panels under some of the PV panels (as shown on the SD website) - perhaps one more SD panel than you would otherwise use in a dedicated HW panel system. I would try to put all the SD panels on the same PV string, though I don't know how much difference that makes.

I am more or less inclined to agree that the ideal approach given the available mounting space, etc. would be to have a dedicated PV array, and a separate dedicated HW array, but not everyone is going to have enough roof space for both.

Given that the SD panel is supposed to be comparable in cost to a standard HW panel, the only savings would be in the cost for the racking and mounts for the separate HW panels. I will admit I haven't priced the mounting hardware, but I've gotten the impression that in the overall system cost, the mounts are a relatively trivial part of the total, so I don't think there would be any real cost advantage to going with SD.

Thus (and I think I've said this before) the ONLY real reason to want to go SD is if you have a shortage of mounting space and can't fit two dedicated systems of the desired size in the available space...

In my case, I suspect that would be likely... Our current electric consumption is probably on the average of about 12-1500KWH / month... (and I don't see much in the way of "low hanging fruit" to trim it...) That would take a LARGE PV array to cover most of it. I would also like to have enough of a HW array to cover not just our DHW consumption, but also put a dent in the winter heating bill, and also warm the swimming pool in the summer. It is entirely possible that we wouldn't have enough room to do both with dedicated arrays...

Actually, I should correct the above - I had been working off a bill from 12/07, and my numbers were from that bill - I've just dug up one from 12/08, and we are doing better... In 08, our highs were 2103KWH in July, 1630 in Aug, and 1127 in Sept. The rest of the year was all under 1,000; mostly in the 5-800 KWh range, with an average of 927kWh...

Looks like the "low hanging fruit" that I've already grabbed has paid off...

Thus my personal interest in hybrid panels...

Gooserider

cow_rancher · June 2009

Re: Possible hybrid PV/hot water panel product?

icarus wrote: »

I used about 30 of the small ones wired in series,, hot side on the wood stove,,, cold side with a bucket of ice. (I was going to run a ceiling fan) By keeping the bucket full of ice, and the fire roaring,,,

you had the right idea, wrong energy conversion, check out this Utube video:

http://www.youtube.com/watch?v=D7NV38Ymep0&feature=related&pos=1

You can go to this site to get building instructions... I'll leave the translation up to someone else...

http://mywebside.extra.hu/keptar/keptar.php

And check out that solar power station!!!

Rancher

niel · June 2009

Re: Possible hybrid PV/hot water panel product?

that's a neat toy, but putting it under a prescribed load would differentiate that from a toy as anybody can spin wheels. pun intended.

cow_rancher · June 2009

Re: Possible hybrid PV/hot water panel product?

niel wrote: »

that's a neat toy, but putting it under a prescribed load would differentiate that from a toy as anybody can spin wheels. pun intended.

Always a critic in the crowd, OK how about this one, I'm sure it would work on a wood stove...

http://www.youtube.com/user/nitrozil

Rancher

BB. · June 2009

Re: Possible hybrid PV/hot water panel product?

cow_rancher wrote: »

Always a critic in the crowd, OK how about this one, I'm sure it would work on a wood stove...

Only one? That is not how I see it... :roll:

-Bill

icarus · June 2009

Re: Possible hybrid PV/hot water panel product?

Sterling engines are not thermo-electric devices in the strict sense.

There is no argument that Sterling engines do indeed work,, but in the link you provide, :

"you had the right idea, wrong energy conversion, check out this Utube video:

http://www.youtube.com/watch?v=D7NV3...=related&pos=1"

Energy to power the Sterling engine far exceeds the energy that it puts out.

Icarus

Gooserider · June 2009

Re: Possible hybrid PV/hot water panel product?

As a moderator on a major wood burning website, I can comment on driving fans, etc. off the stove... Lots of discussion and user reports over the years

Anybody wants gory details and links, etc. go over to Hearth.com and use the search...

Essentially right now there are two major designs for stove powered fans, one using a thermo-electric generation effect to drive an electric motor, and the other using a sterling engine design...

There are two sizes of the thermo-electric fan, and most people that have tried the smaller one say that it works, but doesn't really move enough air to make a difference. The larger unit gets more positive reviews, but even there the reports describe it as being about the equivalent air moving power of a large computer cooling muffin fan - you can feel it moving the air around, but it doesn't really do a lot - although some reported it was just enough to get the room air circulating.

The bigger problem is that the thermo-electric units had a fairly narrow operation band - you needed to get the stove fairly hot in order to get it to do much, but if you accidentally over-fired, it was easy to fry the unit from overheating it...

The stirling engine unit seemed to be a bit stronger as a fan, and was more robust about it's operating temperature range - overheating didn't destroy it the same way. Most complaints were sort of aesthetic related - the unit comes with a nice cover for the mechanical bits that made the unit quite reliable when used. Trouble is that with a stirling engine, there is a lot of fascination with being able to watch all the whirly bits, so most people would leave the cover off, and the unit would get gummed up and need cleaning every month or two...

However if I had to draw one conclusion, it was that most people seemed to find the units more useful as a visual / kinetic indicator of stove temperature (the hotter the stove, the faster the units spin...) - if you REALLY wanted to move more than trivial amounts of air, the answer is an electric fan...

Gooserider

cow_rancher · June 2009

Re: Possible hybrid PV/hot water panel product?

icarus wrote: »

Energy to power the Sterling engine far exceeds the energy that it puts out.

Icarus

Oh by all means that's true, I was just providing you a solution to using your wood stove heat to move some air around, I am going to check out the hearth.com site, I may have to have one...

Rancher

icarus · June 2009

Re: Possible hybrid PV/hot water panel product?

If all you want to do is move air around on top of the stove,,:http://www.wttool.com/landing/caframo_ecofan.php?utm_medium=cpc&utm_source=EcoFanLanding

There is also a Sterling engine fan for a stove.

What I was trying to build was a themo-electric generator that I could wire to a ceiling fan,,,

TXony

Gooserider · June 2009

Re: Possible hybrid PV/hot water panel product?

icarus wrote: »

If all you want to do is move air around on top of the stove,,:http://www.wttool.com/landing/caframo_ecofan.php?utm_medium=cpc&utm_source=EcoFanLanding

There is also a Sterling engine fan for a stove.

What I was trying to build was a themo-electric generator that I could wire to a ceiling fan,,,

TXony

Yup, that's the thermo-electric type fan that I mentioned earlier... The stirling engine versions are made by a different company, but look sort of similar with the cover on them. Without the cover, obviously the whirly bits show, but it is still about the same size and general configuration.

They both do about the same amount of work, i.e. about what you can get with a $10 electric fan from Wal-Mart :roll: IMHO they are more interesting from a "cool toy" factor than as a value approach...

I have never been all that tempted by either one, but if I had to make a choice it would be hard... The engineering side of me likes the simplicity of the Caframo units, and the fact that they have only one real moving part (the fan blades). OTOH the "gearhead" side of me likes the idea of seeing all the moving bits in the stirling engine, and the sort of "steampunk" look...

I don't think it is practical to make a unit big enough to power a ceiling fan for a number of reasons, but it's a fun thought.

Gooserider

icarus · June 2009

Re: Possible hybrid PV/hot water panel product?

The thermo-electric stove top fans move a huge amount of air,,, with no noise. I keep one on all my stoves.

The real reason they work well, is that when properly installed on the stove top,, the bottom top keeps cool by having the fan draw cooler air off the back of the stove,, while the hot side is on the stove,, leaving a pretty proper Delta T.

Tony

stephendv · July 2009

Re: Possible hybrid PV/hot water panel product?

Came across a commerical hybrid PV and hot water panel which is already being used in the UK and Germany: http://www.solar-energy-systems.eu/EN/index.html

Possible hybrid PV/hot water panel product?

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