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Henning 4148
06-19-2008, 04:16 PM
Thermal solar panels collect a lot more energy than electrical solar cells for the same surface. But - you only need that energy for heating in spring, autumn and winter. In summer, most of that wonderful energy is wasted with thermal solar systems, unless you can convert it to electricity or have a pool to heat.

What I am thinking about is a stirling with an alternator, one side heated by the fluid from the panels, the other side cooled with well water. Are there solutions on the market yet?

StevenBauer
06-19-2008, 04:24 PM
Don't you use hot water for bathing? Many solar systems around here are geared toward domestic hot water heating.


Steven

Dan McCosh
06-19-2008, 05:21 PM
The basic concept is sound, but as Norman said, a stirling engine takes a larger temperature differential to operate than a simple hot-water solar collector. A stirling can operate on a solar collector, however, and what might work better is using the excess heat from that operation to heat water. There is considerable research being done on these concepts, but nothing in production that I am aware of.

willmarsh3
06-19-2008, 09:22 PM
Here's one that will work on the heat of your hand;

http://www.discoverthis.com/head-hand-stirling-engine.html

There are many makes and models of stirling engine fans that work sitting on top of a wood stove such as this one:
http://www.lehmans.com/jump.jsp?itemType=PRODUCT&itemID=6921

Perhaps something like this could be made to work on the heat from the solar panel.

David G
06-19-2008, 09:30 PM
I think the problem is that solar-heated water is 'low grade' heat; there's a lot of it, in terms of BTU's, but the temperature differential isn't big enough to make conversion worthwhile. I've always thought that it made sense to use this low-grade heat to 'pre-heat' water, or air, before it enters a hot water heater or furnace... thereby reducing the fuel costs of those two systems.

Mr. Bernstein - That's exactly the system we have on our home. Collector on S. facing roof heats liquid. Photovoltaic panel adjacent powers a pump which moves liquid to a transfer coil in a secondary hot water heater. Primary hot water heater pulls this pre-heated water from the secondary tank. Obviously, it takes less energy to bring the preheated water up to proper temperature.

I find that - even here is drizzly Portland - the flowmeter shows heated liquid moving in the system at the slightest hint of sun. Projected payback (after tax credits) was 5+ years. Current projections - after 2 years - is actual payback of 4.66 years.


"Efficiency is intelligent laziness"

PeterSibley
06-20-2008, 04:26 AM
I think the problem is that solar-heated water is 'low grade' heat; there's a lot of it, in terms of BTU's, but the temperature differential isn't big enough to make conversion worthwhile. I've always thought that it made sense to use this low-grade heat to 'pre-heat' water, or air, before it enters a hot water heater or furnace... thereby reducing the fuel costs of those two systems.

If you have sufficient panel area for the quantity of hot water required , there is no need for secondary heat on a sunny day .140 F / 60 C is easily available .

Ron Williamson
06-20-2008, 05:09 AM
Here,on a sunny -10C day in February,Mike got 69C water out of his new evacuated tube collector.
They are talking about an insulated heat sink under his garage floor for long term storage of summer heat.
R

Ian McColgin
06-20-2008, 05:41 AM
Dad's solar hot water system (preheat style) paid for itself in about 2 years when he installed it in '74 and lasted trouble free as long as they had that place, up to '97. This in central Connecticut.

huisjen
06-20-2008, 07:16 AM
I was looking here (http://www.stirlingengine.com/bboard/q-and-a.tcl?topic_id=4&topic=Power%2dproducing%20Stirling%20engines) a few months ago. There are lots of people poking their heads in there, asking for a domestic sized stirling generator, but not much response.

Rigadog
06-20-2008, 07:35 AM
We don't need solar, we need more oil wells, on shore, offshore on the moon if need be... We can drill ourselves out of this mess those meany Arabs have foisted on us, and you won't need any of that solar crap.

Dan McCosh
06-20-2008, 08:06 AM
Here's one that will work on the heat of your hand;

http://www.discoverthis.com/head-hand-stirling-engine.html

There are many makes and models of stirling engine fans that work sitting on top of a wood stove such as this one:
http://www.lehmans.com/jump.jsp?itemType=PRODUCT&itemID=6921

Perhaps something like this could be made to work on the heat from the solar panel.

I didn't know a stirling engine would work with such a low temperature differential. Still, the basic concept requires a much higher temperature differential to produce a reasonable amount of power. As I noted, using a solar collector that basically is a lens concentrating the heat of the sun has been demonstrated, and has some potential. Hot water systems are similar to a tank painted black and left in the sun. The water gets hot, but not much useful energy is available for power.

Henning 4148
06-24-2008, 01:19 PM
Dan, I did some figures today and it's all a bit frustrating. With well water to cool at estimated 15 C and water from the panels at say 85 C, you end up with a thermodynamic efficiency below 20 %. Put on top the efficiency of the engine and alternator and you are probably around the 10 % mark. Pretty similar to solar electric cells. As it is benefit in addition to reducing the heating bills, summer only, it is still of some interest, but thermodynamics are a shame for offering such low efficiency only ...

If it was easy, someone would already be doing it though.

George Roberts
06-24-2008, 03:29 PM
Most computations of "pay back" times are at best defective.

Our hot water costs us $120/year. 10% return on investment seems reasonable - 20% is preferable. I don't think it is possible to get an adequate solar hot water system for $1200.

---

As Henning 4148 points out - thermodynamics is to blame for many ideas not working out as planned.

PeterSibley
06-24-2008, 06:22 PM
Actually , what is to blame is the very low price of coal produced power . It tends to make any other form of electricity production seem expensive.....unless of course here is a carbon price .

Rigadog
06-24-2008, 09:06 PM
The man who posted # 14 is an authority on hot water, being in it himself.

Tylerdurden
06-25-2008, 05:15 AM
I would like to see somebody build Pelitier junctions into solar panels for solar cooling. It would eliminate normal air conditioning or heating
While generating electricity. You never see much movement on that technology except for small portable coolers.


http://en.wikipedia.org/wiki/Thermoelectric_cooling

http://www.melcor.com/ptseries.html

Frank Wentzel
06-27-2008, 07:06 AM
Peltiers are about 1/8th as energy efficient as compressor based refrigeration systems. Its not for lack of trying. Semiconductor manufacturers know that an efficient peltier would be a gold mine but pesky physics keeps getting in the way.

/// Frank ///

carioca1232001
06-27-2008, 08:17 AM
In the early 70īs, my employers in Rio were approached by an Israeli outfit - ORMAT TURBINES - that specialised in manufacturing power plants for radio-communications stations where the cost to install a power distribution line would be prohibitive.

Power output for the basic plant was limited to about 1 kw and the fluid used in the closed-cycle turbine system was top secret.

Needless to say, , the sunīs rays acted on the fluid in the absorber, the fluid expanded through the turbine which turned an electrical generator, following which the fluid was cooled, transferred by a pump to the absorber, repeating the closed cycle (standard procedure).

The key to harnassing power at any temperature ............ is quite often .....concocting the adequate fluid

Ron Williamson
06-27-2008, 04:24 PM
Propane fridges have no moving parts besides the refrigerant,the flame and the door.
Why can't solar heat be used to replace the flame?
R

ljb5
06-27-2008, 04:58 PM
The house I grew up in had solar panels for the hot water -- not just as a pre-heater, but as a stand-alone system. Paid for itself many times over in 25 years.

I can see on Google Earth that they're still there.

carioca1232001
06-27-2008, 05:06 PM
In the interior of Brazil, they have used in the past a similar set up but the heat source used was a kerosene/parrafin burner.

Why canīt solar heat be used to replace the flame ?

To answer that, one would need to know at least the heat required per unit mass of the refrigerant per unit change of temperature, in addition to the initial temperature of the refrigerant and the final (target) temperature that is to be attained.

Then one would look at the figures for solar radiation in oneīs part of the world....and take it from there.

At the end of the day (sunset!) there could be a problem, though !

paladin
06-27-2008, 05:28 PM
kerosene/propane refrigeration units have caused many, many fires.....they are generally left unattended...open flame with liquid or gaseous fuel......and BOOM!

carioca1232001
06-27-2008, 06:34 PM
Just curious, Paladin, but does your comment in relation to the fire hazard posed by inflammable fuels, reflect the general viewpoint on this issue in the US?

Could this be why one never sees a gas-fired cooker in an American kitchen ?

paladin
06-27-2008, 06:53 PM
No Cedric, I don't think so.....it was an observation. In many areas those systems are used. Just as they may be in Brazil, we do still have some areas of "country" that is relatively undeveloped/underdeveloped. We still have telephone service on party lines, but I think those will be gone in 2-3 years, most areas have electricity, but some areas still use gas/propane/kerosene for heating and cooking. The same systems that were used 20-40 years ago are the same systems in use today, the demand is declining as electricity becomes available.

Rigadog
06-27-2008, 10:17 PM
Are we, the greatest nation ever placed on earth, to now follow the lead of the Brazilians? Would it not be better to saw the ice from the lakes and keep it in an icehouse? If you long for fewer moving parts, there's the solution.

carioca1232001
06-27-2008, 11:03 PM
Paladin thanks for your input.

The US and Canada use electricity for powering the great majority of household appliances, except for space heating when oil-fired furnaces are also used.

In Britain of the 60īs gas was used to power cookers and the hot-water supply. When residential premises were equipped with central-heating, these were run on gas, but such systems were rare in the 60īs. Paraffin-powered heaters were commonplace then.

It is staggeringly expensive to install electricity distribution lines to remote communities in Brazil, whose hinterland in terms of sparsity of population will beat the US hollow. It would be much cheaper to build isolated electric systems for such places, run on bio-fuel, say.

What is not publicised much now that China is growing so vigorously into a world player, is that bio-digestors using human and animal waste provided the main source of energy in the interior. They do not talk about it too much, but these could still be running at full blast for all we know !

Just a thought !

BTW, do not Internet Highways also use a similar idea to party lines, except that the technology is impressive (space-age) ? !

Henning 4148
06-28-2008, 02:26 AM
The first thermoelectric converters seem to be sold now for excess solar heat. Which sounds good. The downside is,that they do not readily (at least where I have looked) give efficiencies but only tell how much cash they will generate. From that, I would say certainly below 10 % ... Somewhere else I read it used to be typically 4%, perhaps they get a bit more now. But there is research going on again on the topic. If they get 10 % or more, it will become interesting.

Ron Williamson
06-28-2008, 06:02 AM
Carioca
There are plenty of natural gas/propane stoves or cookers in this country,but regional differences abound.
R

carioca1232001
06-29-2008, 12:19 PM
Carioca
There are plenty of natural gas/propane stoves or cookers in this country,but regional differences abound.
R

I should have said ...'in the Toronto, Ottawa Valley and Montreal area ...... places I have been to '. !

pipefitter
06-29-2008, 03:42 PM
In most of these discussions, the topic of needing to create electricity for homes and appliances but in most ideal situations, it is about physical comfort over survival and avoidance of what it is we are actually contemplating trying to perpetuate here. The thought of making an entire space in which our bodies take up such a small part of it climatically ideal and convenient, seems that the numbers of probability are right up there with the concept of a usable perpetual motion machine.

If the resources on this planet were to accommodate more to the scale of size of it's inhabitants, the numbers of efficiency and the supply/demand efficiencies increase exponentially. I bet as a conservative estimate of individual efficiency concerning waste alone, 50% of people are unaware of their individual waste output of resources used and it wouldn't take any technology to invent a process for reducing that alone.

In that respect, climate controllable clothing would make more sense than an entire space having to be that way. Bedrooms the size it takes to actually be able just to sleep there would be another and a much more efficiently sized space to control. Books with print that glow in the dark as a loose example for making a point.

The concept of man making himself 'immediately' comfortable within his default environment has been working for eons and I would think with just the technology we have for our toys and how fast the technology evolves around such amusements, I would say we are much more capable of reinventing the necessities on a much smaller scale of solvable physics and with portability, over trying to tweak the laws of physics of a fixed environment that by natural considerations, doesn't even belong there in the first place. I mean, just think of the basic capabilities of even the crudest individual by instinct alone, knowing what to do when it gets cold or hot out. I would think there is efficient, available, technology that already at least, almost exists for such concepts of creating efficient and convenient individuals over convenient and efficient wasted spaces and appliances.

I converted solar and wind power to electricity this weekend. The included motor boat kind of makes it an oxymoron but I tried at any rate. :D

http://i99.photobucket.com/albums/l309/tigmaster/P6280026.jpg