Sailor
It looks to me that you are comparing the total cost of the solar heater but just the cost of the energy to run the others. There is also maintenance, cost to install and remove for the others. You speak of leaks in the solar heater but not in the conventional.
I don’t think you’ve done all your homework.
If you had bothered to read the thread you would have seen I am about the only one who has done some homework here.
If you would bother to read the thread and to know the basics of what we are talking about you would know that a solar system does not replace the conventional water heater, only supplements it. The cost per Therm from the solar system should include everything as that is your cost of producing that therm but that therm applied to preheating the water only saves you the variable cost of fuel and does not save you any maintenance on the conventional heater. In other words, your analisys is faulty. Did you do your homework?
Well maybe I can learn something here.
Is it your opinion that you cannot cost effectively supplement your hot water heater with an expensive state of the art solar water heater in the northern 2/3 of the USA?
And among the reasons are:
it might leak because yours does
someday it will wear out and need disassembly
somebody might fall off the roof.
justwannano, I am not sure if you are serious or not but I am going to assume you are serious. I have pretty much summed it up in my previous posts. Yes, it is my experience that a domestic system like mine is not cost effective even in the best of circumstances. If you add the several things which can go wrong then it looks even worse. These are things you should take into account but, as I say, I believe even if the initial installation is given away for free (mine was installed when they were heavily subsidised, I believe) they are still not worth the trouble and expense.
I doubt they would make sense even in sunnier parts of the country. I think the main factor which might make them cost-effective is high energy prices so I’d be interested in hearing experiences from other users of these systems.
The way I see it right now is that solar collectors might be cost effective in tropical countries where energy is very expensive and where, conceivably, they could be manufactured locally, cheaply.
Another aspect I would consider is the visual-aesthetic. My three panels are on the roof and, while they are visible and not pretty, they do not bother me too much. OTOH, my mother has a large installation of solar panels (for space heating) which are installed outside, at ground level, and the whole thing is so ugly and so in the way…
We have heard about your system two times this past year. Once in the dead of winter when you say it doesn’t work well enough and in the summer when you say it works too damned well.
You haven’t said ,at least that I remember, weather you have tried to use it in the winter to preheat the water going to the conventional water heater. Which would make it partially effective.
You have already stated in this thread that you haven’t tried to shade it in the summer so it wouldn’t be so effective.
So can we determine from what you have said that it does do what it was intended to do at some time? If so when, and for how long?
Oh I so like these guys that like to play with numbers.
I would also guess that your engineering specialty has nothing to do with thermodynamics.
We also haven’t heard any clever engineer
justwannano, I am trying to be constructive in my posts but you are not bothering to try to understand the least of what has been said already. You are just posting negative stuff which comes from nowhere else but your total lack of understanding of what we are talking about.
>> You haven’t said ,at least that I remember, weather you have tried to use it in the winter to preheat the water going to the conventional water heater.
WTF are you talking about? That is exactly what it does as has been explained. Will you please read and understand what has already been said? This is the second time I ask this from you.
>> I would also guess that your engineering specialty has nothing to do with thermodynamics.
While my specialty is in Electrical Engineering, I have studied in depth heat pumps, HVAC (Heating, Ventilation and AC) and worked (sized, drew up specs, etc) for industrial water chillers. I am quite capable of holding my own in this field as I think Anthracite and other “clever engineers” might attest.
Now, please stop posting nonsense and wasting our time. I am trying to have a meaningful discussion about solar collectors and when and where they may be cost effective and when and where they are not. If you have something useful to contribute I and others will welcome it. If you have questions, I and others will do our best to answer them. But your posts up to this point are really not helping in any way.
Quote justwannano
So can we determine from what you have said that it does do what it was intended to do at some time? If so when, and for how long?
So just exactly what about this question don’t you like?
You’re the one saying that it isn’t worth it’
Show us some charts showing what you say is so.
You are the one that said I wasn’t reading the posts.
I read every word I just didn’t put much faith in your numbers. Your negativeness once again slants your reasoning.
Honestly sailor I don’t know what your purpose is in going through all this just to show your dissatisfaction with a system that is over 15 years old. BTW when was it installed?
I also don’t know you seriously have looked into the possibilities of using the hot water for some other purpose.
quote websters
thremodynamics
the science that deals with the relationship of heat and mechanical energy and the conversion of one intothe other.
underlining mine
What ideas do you have in mind? You’d think that with all that energy available in the hot water, there’d be some use for it rather than dumping it down the toilet, right? But…as I think about it, I am having trouble thinking of uses for it…at all…unless one had a swimming pool or jacuzzi that needed heating. Or a Turkish bath/sauna, which I really don’t like using in the Summer anyhow. ANy heat engine you use from water that cool (relatively speaking) is going to have a hideously low efficiency.
I’m just surprised that pouring hot water into the toilet has not resulted in a hideous explosion of porcelain, rendering poor sailor into some sort of hideous, scarred beast… 
Quote Anthracite
ANy heat engine you use from water that cool (relatively speaking) is going to have a hideously low efficiency
Probably true. I don’t know what temperature it takes for any kind of efficency.
We haven’t heard anything in his 5 or 6 posts about his system that says sailor was contemplating any use of the hot water other than to continue using it as an excuse to continue this rant.
How hot can he get it? He never mentions this either.
He also doesn’t mention what months it does work. You have already mentioned a way he could turn down the temperature during the summer.
During the winter or maybe just a couple of months during the late fall,early spring he might be able to add reflectors.
One thought maybe the heat engine doesn’t have to be very efficent if it is used to pull down the shades ,so to speak.
I think sailor is probably frustrated and just doesn’t want to screw with it.
Well, let’s get an idea of what the maximum possible efficiency of a heat engine would be. This is assuming no heat losses, frictionless components, etc.
Let’s assume that sailor’s system could heat water to a certain temperature, use all of its energy, and exhaust it to a cold reservoir. Let’s also consider two cases - an “ideal” case, and what I consider to be an “actual” case.
Ideal Case:
Water is heated to 212 F (liquid), and is able to be cooled to 55 F (groundwater temperature).
Actual Case:
Water is heated to 180 F, and is able to be cooled to 90 F (assumed environment temperature).
Let’s also assume his system can heat 1 gallon/minute at this temperature, and 1 gal/minute is equal to 8.3 lbm/min.
Let’s examine the Carnot efficiency of a heat engine operating between these hot and cold reservoirs, effectively. A Carnot cycle device is by definition the most perfect heat engine that can operate between two reservoirs. Thus, no other device can be more efficient.
Carnot efficiency is given by:
Carnot efficiency = 1 - (T[sub]L[/sub]/T[sub]H[/sub])
where T[sub]L[/sub] is the absolute temperature of the cold reservoir (Low-temperature) and T[sub]H[/sub] is the absolute temperature of the hot reservoir.
Looking at our fluid properties:
Temperature, F Temperature, R Enthalpy, Btu/lbm
55 F 515 R 23.06
90 F 550 R 58.02
180 F 640 R 148.00
212 F 672 R 180.17
Working through our equation, we get Carnot cycle efficiencies of:
Ideal: 1 - (515/672) = 23.36 %
Actual: 1 - (550/640) = 14.06 %
This means of all the heat difference between the two reservoirs, only 23.36 % of it can be converted to power at the most in the ideal case, and 14.06 % of it can be converted to power at the most in the actual case.
So…how much power is that, anyhow? Well…assuming our 1 gallon/minute at 8.3 lbm/gallon, and looking at our enthalpy change, we get:
At 100% efficiency, Ideal case: 8.3 lbm/min(180.17-23.06) Btu/lbm = 1304 Btu/min
At 100% efficiency, Actual case: 8.3 lbm/min(148 - 58.02) Btu/lbm = 746.8 Btu/min
At Carnot cycle efficiency, Ideal case: 1304 Btu/min * 0.2336 = 304.6 Btu/min
At Carnot cycle efficiency, Actual case: 746.8 Btu/min * 0.1406 = 105.0 Btu/min
Converting this to power in terms we can understand, we get:
At Carnot cycle efficiency, Ideal case: 304.6 Btu/min = 5.36 kW
At Carnot cycle efficiency, Actual case: 105 Btu/min = 1.85 kW
So…taking the Actual case of a perfect heat engine, we have a maximum power output at 1 gallon per minute, with the assumed temperatures, of 1.85 kW. Since sailor can likely buy his power at around 7-10 cents/kW per hour, this perfect system would have to be cheaper to operate than about 13-18.4 cents/hour.
Now…what is the actual efficiency of a real system going to be, in this case? Let’s put in some inefficiencies and find out.
Assume this is used to generate electricity. Assume a small generator/transformer/wire loss of 5%.
What are our heat losses of the engine itself? A good, well packed steam turbine can lose a bit of heat. Let’s say 5%.
What are our pressure losses in the piping? Heat losses in the piping? Another 5%, let’s say.
Frictional losses of the steam engine/heat engine? Well, if it uses pistons this might be as high as 20%. A turbine set up of some sort might be as low as 10%. Let’s say 10%.
And, of course, this all still assumes that the engine is exhausting the water to the low-temperature reservoir at either ambient or sub-ambient. IRL, that would never be even close to the case. You might expect a 180 F system to exhaust at…120 F? If so, the Carnot efficiency drops to 9.4%. And our power output above drops from 1.85 kW to 1.23 kW. Adding up all the losses above, and assuming a actual 120 F outlet temperature, we get:
1.23*(1-0.05-0.05-0.05-0.1) = 0.925 kW per gallon per minute.
And I still think this is high. At this rate though, sailor is receiving between 6.5 to 9.3 cents per hour of benefit. While the sun shines.
What does this all mean? Damned if I know. But you can see the process, at least.
Is there anything preventing you from just unfastening them and letting them fall? That’d be cool to watch.
If you’re looking to cut your energy costs, wouldn’t photovoltaic panels be a much better choice? Not only do they generate power that you can appreciate year-round, but in some areas the distributors will buy surplus power when you aren’t using all that you generate. Some states even let you deduct part of the system’s cost from your taxable income.
Anthracite, some things about solar collectors: One is that their efficiency drops very sharply as you demand higher output temperatures. They are most efficient at lower temperatures. So if you want to use them for any kind of heat engine their efficiency would be much lower and still the output temperature would be very low for an engine. I have never seen them used like this and they wold not be cost effective.
Another is that they heat only about 1/10th of the time and do not heat about 9/10ths of the time. In other words, my panels might generate 3Kw during 1/10th of the time and close to nothing the rest of the time. Not only that but I do not get to choose the time. This is not a good use of investment.
If you use solar collectors to heat water you use 100% of the output as heat gained in your water and , as I have shown, it is not cost effective. Any further transformation would just decrease the yield. Trying to convert heat from water at, say, 180F into mechanical energy is a losing proposition. I do not think you could get above 15% or 20% efficiency, which in effect means your cost is multiplied by 5 or 6, at least.
Anthracite, also note this: you can expect a system like mine, with 60 sq ft of collectors, to yield about 80 therms/year of heat, which is low quality energy. That is equivalent to 2350 Kwh / year. If you are heating your domestic hot water with electricity then the value of your savings per year would be about $235. If you are using gas then the cost is much cheaper and your savings would be half that.
As you can see, using the heat directly is already a losing proposition. If you then want to convert that heat into mechanical energy your costs per KWh would be staggering as your efficiency is, again, just a fraction of your input.
In other words, suppose my 60 sq ft provide 3Kw of heat in full sun. From that I doubt you could obtain 600 w of mechanical energy and that would be for about 3 or 4 hours a day in the summer and nothing in the winter.
If just the solar system costs about $3000, if you add whatever machine you need then you are talking quite a bit more. It clearly makes no sense to invest $4 - $5000 in a system that will give you such a low output, for a very small fraction of the time. I have never heard of this even being tried. Not even as an experimental viable unit. At this point I think Photovoltaic would be more cost-effective.
I have heard of some experiments done using solar collectors for A/C using absorbtion cycle heat pumps but, as you know, this is so inefficient that you need massive systems to provide any usable refrigeration. I do not think these experiments have come to anything useful.
In summary: using the heat from solar collectors directly to heat water is the most efficient use of that energy and even then it is not cost effective. There is a very good reason why these systems do not sell: they do not save money.
Anthracite, I did some research online and learnt a few things. Solar installations for heating pools in Florida have several advantages over solar domestic water installations.
- They are located in the south where solar irradiation is more constant year round and heat needs are also more constant. By contrast up north, heating needs skyrocket in the winter due to water being much colder, and yet this is the time when solar irradiation is the least.
- Solar collectors for swimming pools work at much lower temperatures which makes them more efficient. The models used for this purpose have no glazing which makes them much cheaper. By contrast my panels have double glazing.
- Systems for swiming pools do not require a storage tank or heat exchanger which is a major part of the cost of a system like mine.
- Those systems do not require a separate circuit with antifreeze.
In other words, you start with a much lower cost and you get a much bigger yield.
Most vendors claim yields of 600 - 900 BTU per day and sq ft but I find this wishful thinking. Yes, if per “day” you mean “sunny day”. My estimate is that in real life you get about half that but, of course, it depends a lot on location, system use etc.
Some sites look very amateurish. Some have their energy units all mixed up. This first one looks a bit outdated as their prices for energy and systems look a bit too low. http://www.ecs-solar.com/
This one has some collector specs in PDF format.
http://www.ips-solar.com/solarheating/heliodyne.htm
This one has an interesting concept: non rigid collectors which you can lay on the roof. I have no idea pf pricing but I guess they might be a bit more expensive than the rigid kind. They are only good for swimming pools (low temp) as they have no glazing.
I took a solar systems course in undergraduate school.
We were, unlike your case, supplementing the heating system of a house. We drew locations to design a system for the final.
I drew Fargo, North Dakota. Or South Dakota, whatever. Winter average temp of 20 F. We bought the system and compared money saved on heating oil to paying off the loan. At twice the design load, it lost money out the kazo. At the desing load it lost money. At 1/4 the load, it made money.
Quote anthracite
What ideas do you have in mind? You’d think that with all that energy available in the hot
water, there’d be some use for it rather than dumping it down the toilet, right? But…as I
think about it, I am having trouble thinking of uses for it…at all…
If I were so lucky to have a heat source at my disposal right now, and that source would
not cost me one red cent more if I used it than if I didn’t use it what would I do with it?
Several uses of heat come to mind . Most of these are probably silly and not thought out
completely but hey Anthracite couldn’t think of any uses for it and I’ve only had a few hours.
Food preparation
At 200 degrees bread can be baked.
In canning the temperature for the hot water bath is 212 degrees,the boiling point of
water.
The temperature of a dehydrator is not very high. Probably only 150 degrees.Beef Jerkey
anyone?
Mfg
paint can be cured at low temperatures.
with the additional use of a dehumidifier and an insulated room and maybe a fan,herb
and spice leaves can be dried.
I believe slip , the clay like stuff that ceramic figures are made of , needs to be dried
before firing.
Just a few things.
How about Corn Likker;)
Dried flowers
Clandestine Meth Lab:(
OK enough of this
When life deals you lemons make lemonade.
>> At twice the design load, it lost money out the kazo. At the desing load it lost money. At 1/4 the load, it made money.
carnivorousplant, I do not understand what you mean. Can you explain?
Questioning the safety of baking at 200 degrees?
How about this?
Specially baked in our nations capitol
GORMET
Dog Biscuits
Specially baked just for you by unemployed Democrats.
------Our extra special recipe-----------
CONTAINS PORK____
Need a recipe
here is a site-----http://www.mamastable.com/links/biscuits.htm--
OK enough fun.
Sailor here is a site where the people that really know about solar hang out.
As promised I have some numbers from my friend with the solar hot water. He is an engineer, like me, who has been keeping track of the energy situation in southern California, unlike me. So he has been measuring all of his energy costs to try and figure out how much things cost. Any way he has as a backup an electric water heater. He put a logging device on it to see how long it ran because he wanted to see how well the solar worked. His numbers are:
June - 30 hours
July - 20 hours
Aug - 20 hours
Sept - 30 hours
He has two panels that are about 4x7.
This is a 1200W heater. Lets assume $.14 a KWh which is what I pay when you include the distribution charges. This gives about $3.30 to $5 for heating water. If we assume that he would be charged $30 without the solar. I assume this because that is what I pay for heating my water. I have gas so his would probably be higher but oh well. We both are married with no kids.
So continuing with the assumption of $2500 over 15 years the loan payment is 22.47. $22.47 + $5 is $27.47 for about a $2.50 savings a month.
Now we can quibble about the $2500 for this system. I do not have great numbers to back this up but I have seen systems like my friends for less but I doubt that included installation. But if you are going to install solar bite the bullet and put a little sweat equity into it. You will never get a deal like sailor wants someone who will refund you the cost and remove it if you are not satisfied.
Now lets try and add in inflation. Say 3% after 10 years my gas bill would be $40.31 the extra cost for backup would be $6.71 The loan payment would still be $27.47. So now we are saving $6.13 a month.
Once the 15 years are up the cost of gas would be $46.74 the backup power would be $7.79 and there would be no payments.
Now I have not included maintenance and things like that but beyond the initial debugging of the system when he moved in my friend has not had to do anything to his system. So considering that he bought it anyway with the house he is saving money.
So you can make the case that you save money but it is not very much money.
Gazpacho, thanks for your post. Some comments: As I said before, electricity is quite a bit more expensive than natural gas so, a solar system will be cost effective as an alternative to electricity before it is cost effective as an alternative to natural gas.
While your numbers can serve as a rule of thumb, they cannot really be analyzed because they are just vague estimates and there is too much room for error. I have records of all my gas and electric bills going back 15 years and they vary quite a bit between the same months of different years even with the same system. There are too many variables (water usage, water input temperature, etc) You cannot use such numbers as a solid basis, only as numbers to play around with (which is, of course, better than nothing). These numbers are really of any value if you average large numbers of households over many years and compare with similar households without the systems.
On the other hand, if statistics tell you that in San Diego, over the last 50 or 100 years, you get an average of X hours of sunshine which yield Z number of Therms per sq ft of panel, that is something much more reliable on which you can base an investment decision.
Another point about sweat equity is that you are “saving money” by working which I would say is cheating. I am not saying you shouldn’t do it, I am just saying you are comparing different things which is not fair. Most people are not qualified, willing nor able to install a solar system… much less for a perceived savings of $2.50 a month.
As I said, I rig a wood-burning stove and save a lot, but I am not fooling myself: heating a house with wood is very expensive. If the work I put into making firewood was put into productive, billable, work, I would get much more heat then paying for natural gas. So, what I mean, is that the fact that burning wood works for me, does not mean it is a viable alternative for most people.
Likewise, solar panels may be attractive in very specific situations (like heating pools in very southern latitudes) but, for now, are not a cost-effective alternative to natural gas.
In summary: your numbers show a solar system may be marginally comparable to electricity. I think a closer look would probably show the solar system is probably even less efficient than that but we do not have enough information to demonstrate that. We would need to know the area of the panels, how much heat gain he claims, etc.