Solar collectors

Factual Questions
1

I was going to put this in MPSIMS since that is really what it is but, due to the topic, I think it fits better in GQ. I know we’ve had a few threads about solar power. I was tempted to resurrect Solar Economy or Whatever happened to Solar Power? or Whatever happened to affordable solar electrical power?. In a way this is a continuation of those threads. But just to comply with the letter as well as the spirit of this forum, i’ll make it a question… Let’s see… the question may be “What am I missing here?”

Being an engineer I enjoy tinkering with numbers and I love the idea of solar panels. I am the proud owner of a house with solar collectors for domestic hot water.

I have put the house up for sale and I was hoping the solar panels would be a plus but after talking to many buyers most of them do not seem impressed or even interested. Where are all the ecological types who would like to have an eco-friendly house? Send them over! I got a great deal for you!

Since I do not expect to sell my house through the SDMB I guess I can share my experience here…

Last week I got an offer and Saturday was inspection day. When the prospective buyer and the inspector arrived it was pouring like heck. The type of downpour you get very seldomly.

I had been having problems with leaks in the back porch so a few months ago I had the roof replaced for a couple grand. I casually mentioned this to the inspector. A while later he came back to me and said “you better have that new roof checked; it’s leaking”. Shoot! It was leaking in the same place as before!

Today I got notice they cancelled their offer. Probably the roof leak was a very minor part in that decision so I am not blaming it on that but still…

Today I went up there with a can of that black tar cement and even though I could not see any obvious cracks, I tarred all around the panel supports, where the pipes go into the roof etc. I have been doing this for all these years but it still leaks ocassionally. The roofer couldn’t find anything obvious either…

So, if you enjoy messing with tar up on the roof, then solar panels are for you. Luckily I am comfortable on the roof and maintaining the system but if you had to pay for the maintenance it would cost you way more than you would ever save.

Another problem is the panels cover quite a bit of roof so you have to remove the panels before you replace the roof or if you need to do any roof maintenance. Every support for the panels, as well as the pipes, is a potential source for a leak.

After messing on the roof today, and getting some tar on my clothes and hands, I have had a sudden new idea which might explain the leaks. Because the pipes are insulated the roof is well caulked to the insulation but if water gets between the insulation and the pipes, then it will just run down inside unimpeded.

If I do not sell the house my next step would be to remove the insulation where the pipes enter the roof and caulk up against the pipes themselves. This may solve the leak or it may not. Who knows? I’ve been messing with this since I bought the house.

I have owned this house for 15 years now and the solar collectors have not saved me a cent and just been a PITA generally. They are nearing the end of their useful life and I’d have them removed if it weren’t so expensive. I don’t know how I could get them down…

In the winter they provide so little heat it makes no difference. The circuit has to be filled with special propilene glycol antifreeze which is pretty expensive. In the summer, if you do not consume enough hot water, the antifreeze solution overheats which is bad for it so I find myself flushing the toilet with buckets of hot water just so as to use up unneeded hot water. If I leave the house for a few days in the summer, when I come back the water is close to boiling and I figure I’ll have to replace the antifreeze sooner.

If you figure out the cost of installation, the cost of maintenance, the hassle factor, the cost of removing the system at the end of its life, the cost of repairing roof leaks, the ocassional person who hurts himself or falls from the roof… there is no way in the world these solar panels make any economic sense.

I think the future for solar collectors may be in large installations (manufacturing plants, etc) who already have maintenance people on site and who can have large installations with economies of scale. But for now, having a couple panels on your roof is going to cost you way more than you will ever save. And we’re talking about heat collectors. Electric PV panels make even less sense.

But if you know anyone who likes the idea of solar panels… please send them over. Have I got a deal for you!

Or maybe I could make money from the evil oil and gas monopolies by becoming their poster boy. Maybe there is money to be made with solar panels after all.

2

Hmm, interesting.
Thing is, my mother-in-law had solar panels on a house she owned in Fla for a few years. She used it to heat the pool water. She never had any trouble with roof leaks, and she swore by the system because it saved her a ton of money in heating bills and allowed her to use the pool almost year round.
Could be that north of Fla solar panels don’t make any sense.

3

pantom, leaks are not an inherent characteristic of the system but they are definitely a risk. I suppose you can lower the risk by getting a good installation to begin with but unless you are an expert the risk is there. A single well-placed leak can wipe years of savings on energy.

You are right that a solar collector in FL will collect more heat than one up here in DC so it will be more cost-efficient. At the same time heat is not as valuable in Fl as it is in DC.

4

One thing you should know, and that I thought about after I posted, is that she replaced the roof almost immediately after buying the house. She didn’t get an inspection, and so didn’t know about the condition of the roof until after she moved in. (a cautionary tale about getting an inspection for all those considering buying, BTW.)
Anyway, the solar system was installed shortly after the roof was replaced, so it was being placed on a spanking new roof. This may have helped.
It was effective in raising the temperature to the mid 80’s in the early spring and late fall, when the unassisted temp would otherwise have been in the 70’s somewhere. (This was in Venice, which is about an hour and a half south of Tampa.) Against this relatively modest boost you have to weigh the sheer volume of water the system was handling. I don’t know how much water the average-sized pool has, but I know it amounts to the thousands of gallons. Someone out there I’m sure can do the calculation as to how much energy it would take to raise the temperature of so much water about 10 degrees.

5

An old friend of mine had a pool, which was too cold even in summer. (Not uncommon, as this was in Sweden). However he noted that the black roof of the garage constantly had hot air simmering above it, so he did something which I thought was a stroke of genius:
He took tens of meters of garden hose and laid it out on top of the (flat) garage roof, and connected a small electric pump to circulate the pool water through this set-up. In a few days the water was much nicer!

caveat: It was a very small pool, and a long time ago, so I’m not sure how much energy he did get out of the system… I know one thing though. It was dirt cheap.

6

pantom, while a new roof may help avoid roof problems, the supports for the panels and the pipes may be the cause of leaks even in a brand new roof. They shouldn’t but they can be.

In Florida and tropical settings solar collectors may yield the most but they are also needed the least.

tc, makeshift things like that often work pretty well within their limits, of course. They sell a “solar water heater” for boats and campers which is basically a black plastic bag which you fill with water and leave in the sun for a while. It works pretty well.

7

http://www.cetsolar.com/sunhourmap.htm#Continental United States

Outside the US scroll down.
In sailors case when you only have an average of 3 hours of sun a day you probably shouldn’t expect to use solar for your sole heating source.

8

justwannano, my solar collectors are for domestic water, not space heating. They would be very useless for space heating as in the winter they collect close to zero heat. But even for domestic hot water they are inadequate for the following reason:

In winter the water arrives very cold and the heating needs are greatest but the solar panels collect very little heat. Then in the summer the solar panels collect a lot of heat but the water arrives pretty warm already and you have more heat than you need.

The only way around this would be to have a huge, insulated, storage tank which could store enough water for many months. Then you could heat it in the summer and still have heated water in the following winter. The obvious problem is the cost of the storage but it may work out for huge storage tanks since the cost of the storage tank rises with size in less proportion than the amount of water it can store. So it may may make economic sense in a condominium where it can serve the entire community…

I figure a cube of 21’ 6" on the side could store enough water for a small family. But if you triple the dimensions you multipy the surface by 9 but the volume by 27 so the cost per volume is much lower.

In my case most of the summer heat is wasted as I find myself dumping hot water just to drain heat out of the system.

9

Salior,

You are pretty cranky about your solar hot water heater. I have seen your posts on the other threads when they were current. I have a friend in San Diego and he is very happy with his solar hot water setup. It wasn’t working when he got the house due to a failed diode. Once fixed he says his backup heater is hardly ever on. I would install one but my summer gas bill is about $20 a month. So just the pain it would be to have the system hardly justifies it.

As for the coiled hoses on the roof the heat the pool. It seems to me that about 1/2 or more of the home pools I know about in San Diego are heated in pretty much this way to what I believe would be great savings.

As far as your specific problem. The setup for the solar hot water that my friend has it is as follows:

Panels on the roof with a pipe going in and a pipe coming out. Solar hot water tank in utility room with cold water going in. Hot water going to the hot water heater and then the two pipes to the panel. Water is pumped from the tank to the panels when the panels are hotter than the tank. This keeps the solar hot water tank hot then when somebody uses hot water from the regular tank more hot water comes from the solar tank to refill it. Is this similar to your system?

10

gazpacho, I am not sure “cranky” is the right word. My point is that solar collectors are much less of a solution than many people would think and that the reason the market has not adopted them more widely is they really are not such a great idea as some people would have you think. Of course, it is not a black OR white issue and I recognise that they may make sense in some situations, especially where energy is very expensive.

>> I have a friend in San Diego and he is very happy with his solar hot water setup.

Well, I do not doubt that but it proves nothing. I am glad your friend is very happy but that is not how I would measure the cost-efficiency of a system. I need numbers to do that. I have posted in other threads some numbers of my own which pretty much prove my system is not cost-effective. Now, I am not saying they are never cost-effective but the fact that your friend is happy really does not prove anything. If he has not done a cost analysis then he may be fooling himself into believing he is saving money. I find this to be the case very often.

My mother is very happy with a number of things which are so foolish they are beyond belief. For one thing she is happy with a Mazda with a Wankel rotary engine. What does this prove other than my mother is highly suggestible? Rotary engines failed in the market because they were plagued with problems. Even my mother’s is plagued with problems but she is predisposed to discount them because she has already decided she loves it.

>> I would install one but my summer gas bill is about $20 a month. So just the pain it would be to have the system hardly justifies it.

Hey, you are making my point. Forget about the pain of installing and maintaining it. My point is that you would never recover the initial investment and the maintenance costs and what is true for you is true for very large numbers of people.

My solar system is probably past it’s life expectancy and should be removed pretty soon. My assessment is that it is not worth replacing it with a new one. If anyone has numbers which would show otherwise, I’d like to see them.

The owner of one single installation being happy really does not prove the system. You need to take large numbers. How many will develop problems and how much will they cost? etc. One single leak or one single fall from the roof of the guy maintaining it is enough to wipe out the savings of many installations. You have to use big numbers.

And yes, as I explained, my system is the standard type with a water storage tank in the basement heated by an antifreeze solution which circulates through the panels.

These summer days I am back to flushing the toilet with buckets of hot water just to relieve heat from the system.

In conclusion: I would like to see numbers showing where and when solar systems may be cost-effective.

11

Forgive me for seeming dense, but why not just place a large aluminum sheet over some of the panels, to reduce the radiant heat flux? The father of a guy I used to know had a system like yours, and in the Summer he would take this 8 by 4 foot sheet of shiny aluminum and place it over some of the panels, and bungie cord it into place. I suppose someone could be neat and have it attached with C-clamps or something…have you considered this approach?

12

Anthracite, I guess you are right, I never really thought of that… I don’t know about buying a big aluminum panel as it would probably be a bit expensive and especially difficult to handle and may be a risk to handle on the roof and also may be at risk of flying away. A better idea may be some kind of shading mesh which could be handled more easily and not such a risk… Still it is ironic I need to cover the panels. And being the way I am it would probably be half way or more through the summer before I installed the shading and the following Spring before I removed it… (It has been two winters now that I never got around to covering the boat)

Aside story about handling things on the roof. Quite a few years ago I lived in a 7th floor apartment with not too good water pressure and I decided to jury-rig a water tank on the (flat) roof above. I made a cheap tank by welding together two 55 gallon drums, placed it on the roof and connected it with a copper pipe. The weight of the water kept it in place… until one day I got home to find a bunch of people on the sidewalk looking at my tank which, serving its function had released a lot of water to my apartment… and was blown away by the wind. Very luckily for me it did not hit anybody when it landed on the sidewalk… It is amazing it did not hit a person or a car.

13

Sailor:
If you installed your solar panels, you may have goofed. The panels on my shed are on the roof, yes, but the pipes (heavily insulated)travel down the slope of the roof and enter through the wall below the eaves. The support brackets slide up under the shingles where they are nailed, no exposed holes in the roof. If it’s not a BIG deal, you might consider this re-plumb. Also: If you make a “dip” in the pipes befoere they enter the wall, any condensate or rain drips off the pipes at the “dip”.

The system I have, I made out of old flat steel radiator panels. pretty crude, pretty inneficient, but it keeps the paint etc. in the shed from freezing.

Good luck with the house- hope it sells soon.

b.

14

Billy Rubin, nope, the panels were here when I bought the house, installed by “professionals”. I have no doubt it could be done better. Yes, I can see that taking the pipes around the eaves, rather than through the roof, would save some leaks but it would look pretty bad, at least in my house.

15

You could build a sensor system to detect the changes in temperature and automatically roll the shading in or out, of course! :slight_smile:

Well have fun, I am off to stare at the mess in my room and hope that will make it disappear.
Britt

16

gazpacho said:
>> I have a friend in San Diego and he is very happy with his solar hot water setup.

Salior responds:
Well, I do not doubt that but it proves nothing. I am glad your friend is very happy but that is not how I would measure the cost-efficiency of a system. I need numbers to do that. I have posted in other threads some numbers of my own which pretty much prove my system is not cost-effective. Now, I am not saying they are never cost-effective but the fact that your friend is happy really does not prove anything. If he has not done a cost analysis then he may be fooling himself into believing he is saving money. I find this to be the case very often.

Gazpacho continues the conversation:
I went on to say that his normal hot water heater almost never comes on. I have seen similar systems to his for $750. Lets assume that the total cost of such a system is $2500 including installation. I just got my power bill today and I find that the cost of natural gas has gone up and my bill is $30. I run only the water heater off of gas this time of year so assuming I get as good of results as my friend I can save 30*12 or $360 a year or pay off the system in about 7 years maybe 10 to 15 years if you count the time value of money. That is a somewhat reasonable time to pay off a power system. However as you pointed out I am not going to install such a system because it does not save me very much and I have no real desire to invest money for 10 years to get into the power generation business.

I think a real case can be made that it is cost effective to install solar hot water heaters in the southern US. But it is also cost effective to cook your meals at home all the time but I don’t do that either. I don’t install solar power at my house because I want to relax at my house not come home and run my small power company.

So to a large extent I agree with you that home solar power is more trouble than it is worth. But my friend has real success with solar hot water which from your description you are not having with your system.

17

Gazpacho, I have to insist that “the heater almost never comes on” is meaningless. I would need numbers. How much does such a system cost to install and what are the measured and tangible savings? That is what we need to know to make any reasonable asssessment.

Assuming a 60 ft2 system like mine costs about $3000 to install and delivers 80 therms per year, it does not make economical sense to install. Let us assume a 15 year amortization which I think is a reasonable lifespan. Even at zero interest, the system would have to deliver about $17 /month for me to recover the invested money.
If I invest the $3000 at 8.75% it will bring back $30 every month for 15 years so that the solar system would have to yield more than that value in energy savings to make sense. Delivering less than 7 therm /month it does not come even close to that. Using a gas water heater (which I have anyway) the net cost of that energy would be under $7 (about $1/therm, net). My money will yield four times more if financially invested. If the water heater is electric the difference is not so great but still much in favor of electric power.

A system that yields about 8 MBTU/Yr ($80 - $100 / Yr) would have to cost no more than $800 - $1000 to install to make financial sense. And these figures do not take into account maintenance and removal costs which would make the picture even more favorable to conventional systems.

Maybe in rural locations where there is no gas or electric supply and the cost of these or other forms of energy are much more expensive a system of solar collectors will make sense financially speaking. Or maybe large installations for hotels or other large buildings can be installed at lower cost per unit (square foot of collector, gallon of tank, etc.)

You can see in my case I could install the system for $3000 and be so happy “the heater hardly ever comes on” which is true but but I’d be fooling myself. The gas heater would be cheaper than the solar panels as I have shown.

Some people can jury-rig cheap installations themselves but this is not the majority. These people are not counting their work. I rig temporarily, in the winter, a wood-burninhg stove and it works for me. Does this means it would work for most people? NO! What I do is dangerous unless you know exactly what you are doing. I have plenty of wood at hand. And most important: I am not counting the work of installing and maintaining the stove and cutting the wood. So, it works for me but this is something which would work for only a very small number of people. I think solar panels fall into the same category.

18

sailor, where do you get a guaranteed ROI of 8.75%? I need to get in on that… :wink:

Not that it changes your overall result, but it’s probably more fair to assume a lower rate - like 5.5%?

19

Numbers for salior.

Get a $2,500 home equity loan at 7% I get these offers in the mail all the time. 15 year term is $22.47 a month. If we take my case of $30 a month for hot water. And say the solar cut my bill by 80% my combine bill is now $6 bucks for gas $22.47 for loan payment giving us a savings of $1.53 a month. I think my friend is doing much better than 80% but sailor wont believe this unless I get actual numbers I will try to do this next week. With 90% savings you get $4.53 a month.

Is this worth the trouble of being in the power generation business? Not to me and obviously not to Sailor. But then Sailor’s solar power system does not really work so he only gets expenses.

20

Anthracite, not being a banker nor an investor I got that number some time ago in another forum talking about long term investments (which solar panels are). I have no idea what would be a reasonable return to assume for long term investments. While I would not want to sidetrack this thread into discussing this, I will be happy to do the analisys with whatever figure we find most likely. Any millionaires who can inform us? :slight_smile:

gazpacho, (I love that name) I am not trying to be difficult but rather to shed some light on this issue. I am not asking for notarized affidavits, just reasonable numbers we can discuss. Again, what might not make sense to me might make sense to someone living in the Arizona desert. That’s what I would like to determine.

The example I gave was from an exchange I had a few years back with an installer of these systems here in DC and we pretty much agreed on the figures: a 60 ft2 system like mine costs about $3000 to install and delivers 80 therms per year which to me is worth about $80/year or $6.67/mo. Let’s assume Anthracite’s 5.5% return: $3000, 180 mo, 5.5% = $24.51. Add another $5.49 /mo to take care of removal and disposal at the end of its life. Add $3 /mo for maintenance. Add the cost of leaks, accidents etc.: I think $5 /mo is a reasonable figure. Some installations will have none and some will have some.

Note also that is you use natural gas or electricity, you pay what you use. If you leave your home this summer for an extended vacation in Europe, you will save on electricity and gas but not on solar panels. So, furthermore, you would have to increase the monthly cost by a usage factor, let’s say another couple of bucks.

So, I say $40 / month ($480/year) is a reasonable figure to assume for the cost of having your typical home 60 sq ft system. Now, if it gives me 80 therms per year, the cost per therm is $6 which is about 6 times what it costs me with natural gas.

Now, to make it worth the while some things would have to change:

  • As I pointed out before, larger installations could probably lower the cost per therm obtained we would have to determine how much lower).
  • Sunnier places can get a higher yield of therms (we would have to determine how much more)
  • And, probably most importantly, isolated places where energy is more expensive (like in the middle of the dessert) may make a solar system cost effective.

So my point is: I am quite sure solar panels make NO sense in this part of the country with energy prices being what they are. Even if they are given to you for free they are probably not cost-effective if you consider the cost of maintenance, leaks, accidents, removal etc.

Now, maybe we can determine a different scenario. Say a system 50 times the size of mine can be built, maintained, removed etc for a cost of only 25 times the cost of mine. If it is located in a sunnier part of the country let’s assume it collects 20% more heat. So now we have a system which costs $1000/mo and yields 400 therms/mo. That is $2.5 /therm, still 2.5 times more than I am paying here. But if the cost of energy there at that time is over $2.5 / therm, then it would make sense. This may be the case is some tropical third world countries or even in some remote areas of the US.

Gazpacho you make a good point in that if the investment is cost effective, you could borrow the money and pay the loan back with the savings. This is the best way to analize this. Assume no money out of pocket. Borrow the money needed and see if your monthly payment is less than what you are saving on energy.

Ideally a company would say to you: We will install, maintain, remove the system and pay for any damage or accidents or liability in exchange for X dollars a month for 15 years. You have to do nothing but pay the monthly fee and, hopefully, you would save on energy. Now, I am saying I doubt the monthly payment would be under $40.

But I have to stop you when you say: If we take my case of $30 a month for hot water. And say the solar cut my bill by 80% my combine bill is now $6 bucks for gas $22.47 for loan payment giving us a savings of $1.53 a month.

Where do you get those numbers from? I do not think there is any way in the world they can be real. My numbers are actual numbers discussed with a professional installer. Let’s see your numbers: you are saving $24/mo, which is about 24 therms/mo or 288 therms/year.

I say there is no way, no how, no place in the world where a $3000, 60 sq ft panels will collect 288 therms per year. Mine are rated at 80 therms per year so you are claiming yours would collect 3.6 times as much. No way.

Well, either that or you are paying 3.6 times more than I am for energy. Where do you live? How much are you paying per therm?

Note that if you provide a location and panel area it is very straightforward to determine the yield in therms/year. Now give me the price of energy there, multiply the two figures and you have your “savings”.

I know the figures you gave are just off the top of your head but I say the figure you assume for cost is too low and the figure you assume for yield is way too high.