Sciencemadness Discussion Board - On solar hot water systems

On solar hot water systems

Panache - 24-1-2012 at 19:58

Having now thoroghly researched this advanced incomprehensible human technology can someone tell me why some old radiators sprayed matt black, a tank in an esky and a small thermostated thermovoltaic pump/battery combo can cost around $100 and probably be equivalent or better to the ~3K commercial units.

[Edited on 25-1-2012 by Panache]

White Yeti - 25-1-2012 at 10:48

There's no reason for those things to be as expensive as they are. I think most of the cost comes from the actual idea and the concept rather than the cost of production itself. The raw materials are cheap as dirt.

I wish I could make one for myself, but I live in a magical land where the weather is perpetually overcast and the sun rarely comes out, let alone high enough in the sky to heat even the slightest amount of water.

neptunium - 25-1-2012 at 10:58

new jersey? lol

GreenD - 26-1-2012 at 07:15

cuz greenies are stupid - especially the rich ones.

just buy black rustoleum paint, spraypaint some copper tubes or even aluminum, or like you said - recycled materials. voila. its better to incase the unit of course.

Endimion17 - 26-1-2012 at 08:11

Well, those things are certainly overpriced, but they're not so cheap as one could imagine. Of course, you could use cheap materials and end up with a nice homemade heater, but how long will it last? Also, will it be a system with a heat exchanger, a heat tank, a pump, a thermostat etc., or just a bunch of pipes suspended on the roof that can heat few liters of water to ensure one person gets a nice shower after work?

Those things are exposed to the weather conditions. Now, if your climate if arid and hot, let's say Middle East, pretty much the only thing you have to worry about is sand erosion.
But if you live in Italy, you get scorching heat in the summer, quite cold weather in the winter, with rain distributed during the entire year. Imagine what that does to the materials.

Solar hot water systems (part of solar thermal energy usage) have to endure all that without getting damaged well over the time of cost amortization. I'm not sure how long does it take for a commercial system to become viable (I think it's 5-10 years in my region which has great insolation), but you certainly don't want cracked glass or leaking silicone seals after 15 years.
Also, it's not like the system is "press button and enjoy". It mainly uses water as a heat transfer medium, meaning there'll be time for maintenance which costs money and time.

So yeah, commercial units are often overpriced, but you can't really install things like this expecting you'll spend few coins.

GreenD - 26-1-2012 at 10:05

Sure you can.

I would say all in all a complete sytem would cost (using scavenged tubes) 300-500$. Thats with a thermometer, pump, housing, silicone, etc.

I doubt even the commercial models won't need repair after 15 years.

White Yeti - 26-1-2012 at 10:32

Just wondering...

Why do people go solar rather than geothermal? I understand that geothermal is not available everywhere, but solar isn't much better. Besides, you cannot heat water with solar power alone, you can only pre-heat water, you'll have to use a burner of some kind to get the water to the desired temperature.

As mentioned earlier, I live in a perpetually overcast state (NY), would it make more sense to dig a geothermal well for preheating water rather than using solar power? Does anyone happen to know how deep a well has to be dug in order to reach ground that is 40 degrees centigrade or hotter?

Endimion17 - 26-1-2012 at 11:02

Quote: Originally posted by GreenD

Sure you can.

I would say all in all a complete sytem would cost (using scavenged tubes) 300-500$. Thats with a thermometer, pump, housing, silicone, etc.

I doubt even the commercial models won't need repair after 15 years.

Umm, no, you can't. I live in a region with high insolation and know people that tried that. The amortization period is long and you don't really get what you want.
It will cost much more if you do it yourself than buy it. Of course, I'm talking about exact systems, not comparing naked boiled vessel painted in black and suspended on the roof with professional system that offers a lot more.
If you want something pro, you buy it. It's cheaper on the long run.
But if you want few liters of hot water per day, you invest 50 € in cheap pipes and black spray and that's it.

Solar water heating systems are used to lower the electrical/gas bills. They can not substitute those sources.

Quote: Originally posted by White Yeti

Just wondering...

Why do people go solar rather than geothermal? I understand that geothermal is not available everywhere, but solar isn't much better. Besides, you cannot heat water with solar power alone, you can only pre-heat water, you'll have to use a burner of some kind to get the water to the desired temperature.

As mentioned earlier, I live in a perpetually overcast state (NY), would it make more sense to dig a geothermal well for preheating water rather than using solar power? Does anyone happen to know how deep a well has to be dug in order to reach ground that is 40 degrees centigrade or hotter?

Because it's extremely expensive for most habitable parts of Earth.
In addition, there are cases where you've got exploitable conditions, but nobody lives there, or few people at most.
For example, there are few geothermal hotspots in my country, but there aren't many people living nearby, and you can't make a thermal facility of any kind far from people's houses. It isn't economic because of the heat loss during the pipe transfer. That's why heating plants or cogeneration plants (fossile fuels) are built close to the cities, often on their edges. Sometimes there are heating plants that are built for one large part of the town, etc.

You can either exploit hot water wells, or dig deeper, where the ground is very hot, and place heat exchanger inside.
Either way, 40 °C is way too low. The temperature difference between outside temperature is around 30 degrees on average, which is laughably low. The only application would be a spa center.

Geothermal potential is something that each country's energy department craves for, and be sure that it's all mapped and written about somewhere. It's a resource that can lower some state project costs.
The same thing goes for hydroelectric potential, potable water wells, fossil fuel reserves, ore deposits. Those things are of each country's primary interest.

[Edited on 26-1-2012 by Endimion17]

Twospoons - 26-1-2012 at 14:55

Where did you get the idea that painted radiators are better than evacuated glass tubes with heat pipes and selective absorbers? You might come close on a bright sunny day, but on an overcast day those fancy tubes will beat painted metal hands down.
If you want cheap you go directly to the Chinese tube manufacturers - they sell for ~$10 each.

White Yeti - 26-1-2012 at 15:56

Here's something I found out by accident, I left a glass mason jar outside filled with water and stuffed with a couple of sticks and sealed with a lid. On a cold sunny day, the jar would feel very warm to the touch (think of a comfortably warm cup of tea/coffee) even though the surroundings were as cold as 5 degrees centigrade.

I don't think you even need evacuated tubes or what not, a simple jar and a couple of sticks can warm three quarters of a litre of water remarkably well.

It's actually snowing right now

so I can't repeat this set-up let alone make any measurements.

Twospoons - 26-1-2012 at 18:49

3/4 of a litre of warm water makes for a very short shower!

White Yeti - 26-1-2012 at 19:23

Quote: Originally posted by Twospoons

3/4 of a litre of warm water makes for a very short shower!

Yep, but scale it up to 1x2 metres and you'd get about a fifth of a cubic meter of warm water- that is, if the sun decides to show up. You'd need a pretty sturdy roof to hold all that water.

497 - 26-1-2012 at 22:42

How about throw a layer of glass on top of a sheet of black painted steel roofing (the kind with angular ridges), then circulate water through a gap between it and second sheet underneath? Silicone the edges to seal the cavity, put some free salvaged insulation on the back and you're almost done. Then a small solar panel powered pump and insulated holding tank (which need not be on the roof) would complete the system. What is so complicated about that?
I believe such a system would collect around 1kwh/m^2/day depending on how hot you get the water.

[Edited on 27-1-2012 by 497]

Endimion17 - 27-1-2012 at 05:31

If you don't mind using water that smells like mold or corroded metals, and if you don't mind climbing the roof every now and then, spending on detergents to clean the roof glass panels from the crap buildup that reduces radiation transmission, that's fine.
I'd do it too. Actually, I'm planning to do it one day, just to get smaller amounts of hot water during the summer which is just blazing heat where I live. But if you want to make something more complicated, you'll end up with a deficit in your pockets.

Guys, the whole premise "I'm gonna get loads of energy for free" is bogus. Remember - people want to make money. Companies want to make money even more. When a concept is brought up, someone's gonna eventually turn it into a product. So people are employed to do calculations, and to make their product very cost effective when produced on a mass market.
You can't beat that. Two things will fuck up your plans: thermodynamics and economy.

The more complicated and demanding the system is, the less cost effective it is, if made for individual purposes, and at some point, it becomes cost-prohibitive. In today's modern society, that point is quite low, because buying is cheaper than producing for pretty much everything.

Also, if you live in places like Great Britain or Norway, you can forget about solar thermal on a small scale. The energy density during the peak insolation is ridiculous compared to the density in the Mediterranean.

White Yeti - 29-1-2012 at 08:43

Quote: Originally posted by White Yeti

It's actually snowing right now

so I can't repeat this set-up let alone make any measurements.

It's a nice sunny day today (with a few scattered clouds), I set up a jar filled with water and piece of black paper outside. It's 3 degrees centigrade right now, perfect to test out the losses associated with this system.

I'm waiting for the water to warm up, I'll post again when I get results and pictures.

White Yeti - 29-1-2012 at 09:28

DAMMIT! It got cloudy again -.-
Here's what the weather turned into:

It's not bad enough to call off the experiment, but not good enough to get good results.

Just a few days ago, this was what the weather was like:

This is why I'd rather go geothermal than solar.
Better luck next time, I hope.

Panache - 30-1-2012 at 05:40

i was being flippant in my opening post, however it's rather disgusting looking at how simple and effective measures that have been around for almost a century have not been adopted into building codes. i'm definitely not a conspiracist and have no intention of wanting a political argument in this thread but the effect of the energy lobby has not been one that has benefitted society very much.
Geothermal and simple solar, where appropriate should be in the building code . in australia we didn't even have insulation in the building code until the nineties, just ridiculous, did we think carbon based energy would just never run out? i don't get it other than to explain it via the argument in the first paragraph.

GreenD - 30-1-2012 at 11:33

I don't know about geothermal, something about it smells of a future catastrophe, can't put my finger on it.

Solar water heating is a no-brainer. The water isn't going to smell or stink any more than the water from your faucet.

The installation of solar water heating can be a pain (modification of existing house). If you build a new house however, the process is seemingly simple.

Somewhat off topic, but I have a 15 or 20W solar panel in my backyard. I charge my Ipod, camera, phone, my room mates phone, and various other things on it. Its nice. 20W will get you a long way, unless, of course, you have a 500W computer, 200W TV etc. But apparently - reading a recent article, by using "efficient" phone chargers and laptop chargesrs, california plans to save 309$ million a year by implementing new efficiency laws on cwall adapters.

Endimion17 - 30-1-2012 at 14:23

Quote: Originally posted by GreenD

I don't know about geothermal, something about it smells of a future catastrophe, can't put my finger on it.

What catastrophe? We might puncture out hollow planet?

Quote:

Solar water heating is a no-brainer. The water isn't going to smell or stink any more than the water from your faucet.

Yes, it will, if you use the heated water directly, and not as a heat transfer medium. Pipes corrode and get filled with microorganisms. Ever hear of iron bacteria? Cool creatures, benign and passive, but make the water turn yucky.

Quote:

The installation of solar water heating can be a pain (modification of existing house). If you build a new house however, the process is seemingly simple.

Somewhat off topic, but I have a 15 or 20W solar panel in my backyard. I charge my Ipod, camera, phone, my room mates phone, and various other things on it. Its nice. 20W will get you a long way, unless, of course, you have a 500W computer, 200W TV etc. But apparently - reading a recent article, by using "efficient" phone chargers and laptop chargesrs, california plans to save 309$ million a year by implementing new efficiency laws on cwall adapters.

California? Sounds much more reasonable than stories about people in Ireland. I just hope your panels will last long enough to pay themselves off. They usually don't, at least not the ones with a reasonable price so far.

But that's not solar thermal, which is much more efficient and not borderline like PV.

[Edited on 30-1-2012 by Endimion17]

Twospoons - 31-1-2012 at 00:22

Used to be that PV cells needed as much energy to manufacture as they could produce in their lifetime. I don't know if that is still true.

GreenD - 31-1-2012 at 07:20

I'm sure it is... silicon from silicon dioxide is a very intense process. Like making carbon from carbon dioxide.

Still - you can use wind, or once you have a start of PV cells, you can continually crank them out in an ideal world.

watson.fawkes - 31-1-2012 at 07:52

Quote: Originally posted by Twospoons

Used to be that PV cells needed as much energy to manufacture as they could produce in their lifetime. I don't know if that is still true.

Not true any more. Fabrication technology is better. But that's not the main economic driver.

There's no intermediate grade of refined silicon that's suitable for solar cells that's too impure for semiconductors. So there's always been competition for silicon supply between these two, and semiconductors are far more valuable per unit mass. What's changed recently is that the Chinese government purchased a number of silicon refineries. (Four, as I recall, not completely sure.) There's an excess supply of silicon now for semiconductors, so the cost of solar cells has been dropping as a result. It was part of a strategic plan to make China a leader in the solar industry.

I am not as a rule in favor of government industry, but silicon refineries have such a huge leverage that I'm willing to make an exception. They're expensive enough that financing new ones is a relatively high-risk venture, given that you have to gauge medium-term demand for silicon pretty accurately. Government financing of such refineries would not have this risk. With the twin goals shifting demand away from carbon and energy independence, this seems like a pretty good option. In the USA, the main difficulty is political ideology. Since we're no longer fighting communism and socialized industry, it seems like fighting the last war to make an objection on ideological grounds only.

GreenD - 31-1-2012 at 08:38

Watson, good post.

I laughed quite a bit in the republican debate when the runners kept saying China was "Cheating" in the economics of silicon. I couldn't help but think of corn.

The US subsidizes corn. China subsidizes solar energy. Go figure.

White Yeti - 31-1-2012 at 16:53

Quote: Originally posted by watson.fawkes

Quote: Originally posted by Twospoons

Used to be that PV cells needed as much energy to manufacture as they could produce in their lifetime. I don't know if that is still true.

Not true any more. Fabrication technology is better. But that's not the main economic driver.

Not only that, but the dye sensitised solar cells and thin films are becoming more and more efficient and cheap. That being said, we're not quite there yet, but at least they don't use silicon.

I read here that 70% of the energy used in western industry is used in the form of heat. I don't believe that most of it should come only from nuclear, or only from solar or geothermal, we need a little bit of everything.

But I think we should stop turning heat into electricity and electricity back into heat. It doesn't make sense thermodynamically, but we do it anyway because we don't yet know how to store and transport heat energy efficiently over long distances.

Polverone - 31-1-2012 at 18:10

Quote: Originally posted by watson.fawkes

There's no intermediate grade of refined silicon that's suitable for solar cells that's too impure for semiconductors. So there's always been competition for silicon supply between these two, and semiconductors are far more valuable per unit mass. What's changed recently is that the Chinese government purchased a number of silicon refineries. (Four, as I recall, not completely sure.) There's an excess supply of silicon now for semiconductors, so the cost of solar cells has been dropping as a result. It was part of a strategic plan to make China a leader in the solar industry.

This is half-true. Chinese producers have ramped up recently, but so have foreign producers. The foreign producers can offer purer product than what domestic Chinese producers can offer at a corresponding price point. A purer product is in high demand because it enables PV makers to produce more watts of cells without any additional labor or capital costs; the gain is purely through light conversion efficiency. The end result is that China is the world's largest net importer of refined silicon, even though it is the largest net exporter of PV modules, and domestic Chinese silicon doesn't chase foreign silicon from Chinese PV cell factories. Naturally this has led to trade disputes, with China claiming that American companies are dumping silicon in China much as American companies have claimed that China dumps PV modules in the US.

IrC - 1-2-2012 at 00:18

Endimion17 you sound pessimistic about DIY. Living for over 30 years in Arizona I saw many, these setups numbered in the thousands. Radiators were loved in these, in the era of the 70's you could collect many for very low cost and flat black paint was cheap. One I knew of used crushed granite for near zero cost from an open pit Cu mine. He had a setup with pipes running through rock for storage, a little bleach in the water stops mold. Not to mention a percentage of antifreeze and rust inhibitor from Checker Auto was also unfriendly for bacteria. Or have you never slept for years on a water bed with the same water in it. No it never got moldy. He never turned on heat in the winter his system did it all. Decently warm showers and never the need for a furnace. In January it typically gets to 19 at night but back to the 60's in the day with strong solar radiation normal every day. In a quarter century I don't recall any times he was out repairing things nor did I ever hear complaints about maintenance. That was one of his bragging points, he never had to muck with it much at all ever. I cannot fathom where you are getting all your negative waves about home built solar in the desert it has been popular for decades.

GreenD - 1-2-2012 at 07:40

Quote: Originally posted by IrC

Endimion17 ...

Good points.
If you use water from your pipes, why would the water be any different than if it were coming from your faucet?! If you build the setup correctly, there should be no more "Stink" or "mold" than from your kitchen sink.

White Yeti - 15-2-2012 at 13:18

As a side-note, I compared my original jar filled with sticks and it was getting much warmer than my control set-up. I wondered why...

As it turned out, the warmth was due to the anaerobic digestion of the sticks in a warm environment. The sun was providing the "activation energy", but the decomposition that was happening inside was what held the internal temperature close to 28-30C while the external temperature was 10 degrees centigrade.

I wonder if this would be a controllable way to harness biomass energy on small scales. If you get a biomass-sun hybrid system to heat you house, the sun heats the biomass and all the bacteria, those bacteria produce useful co-products, heat, biogas and fertiliser.

That way, you can break down wood more efficiently than if you burned it in a fireplace. Here's a more extreme example of heat generation from biomass.

Endimion17 - 16-2-2012 at 04:38

Quote: Originally posted by IrC

Endimion17 you sound pessimistic about DIY. Living for over 30 years in Arizona I saw many, these setups numbered in the thousands. Radiators were loved in these, in the era of the 70's you could collect many for very low cost and flat black paint was cheap. One I knew of used crushed granite for near zero cost from an open pit Cu mine. He had a setup with pipes running through rock for storage, a little bleach in the water stops mold. Not to mention a percentage of antifreeze and rust inhibitor from Checker Auto was also unfriendly for bacteria. Or have you never slept for years on a water bed with the same water in it. No it never got moldy. He never turned on heat in the winter his system did it all. Decently warm showers and never the need for a furnace. In January it typically gets to 19 at night but back to the 60's in the day with strong solar radiation normal every day. In a quarter century I don't recall any times he was out repairing things nor did I ever hear complaints about maintenance. That was one of his bragging points, he never had to muck with it much at all ever. I cannot fathom where you are getting all your negative waves about home built solar in the desert it has been popular for decades.

I'm pessimistic for a reason. Of course, you can build it yourself correctly, but the price jumps up the better you do it.
There are essentially two ways you can do it - with and without secondary heat loop. AFAIK, only the latter systems give you potable water.
The main issue is the local climate, of course. I can totally see DIY one-loop systems working (and paying off in a few years!) in my area, and that's why I'm planning to do it one summer.
Two-looped DIY systems... I'd say the time to pay it off would be short enough in the equatorial zone. Mediterranean area and Florida, I hardly think so. That's why people buy them, and yet it's still expensive.

Dr.Bob - 27-2-2012 at 13:13

There is some confusion around the original question. If you live in FL or Hawaii, you can just paint a tank black and put it on the roof. But if you live in most places, it would freeze and burst at night, or at least lose most of the heat to the cold air. So most people put in a heat exchanger solar system, and since that requires a fair amount of pumping, piping, and other stuff, the costs go up.

The cost of the actual collector is not that much wholesale (under $1000 each, most areas would need 2 for enough hot water for 4 people), so that part you can save money on, but the quality won't be as good. If you already have a lot of copper tubing and such, you can build one, but that won't save so much. The largest cost is the labor of installing the rooftop part, running the pipes, and connecting it all to a water heater tank, which will cost about $500-700 or more itself, for one with a heat exchanger built in. But the parts are getting cheaper to buy pre-built everyday, even for decent quality.

On the other hand, a heat pump water heater is more appropriate for some areas with mild climates, and can be either stand alone, or part of a geothermal heat pump system. I have three friends with these systems and they are interesting solutions.

One has the stand alone heat pump water heater, which is in his garage in a warm climate, so it actually air-conditions his garage while moving the heat into the water tank. That is a great solution. The other two people bought whole house geothermal heat pump systems, and one has broken even (compared to natural gas, which is available in his area, and prices are falling), and the other; who lives in an all electric neighborhood, is seeing a large cost savings over his old heat pump, which was already 15 years old and needing replacement. It provides cooling and heating to the house, as well as pre-warmed water for his water heater. That aspect only works really well in the summer, the rest of the year it does not provide substantial preheating.

I have also seen a number of solar thermal installations. They pay off quickest when you have a large hot water consumption, as they are cheap to scale up. So if you have a large family, solar thermal hot water will pay off. If you are single, it might not make any sense to do anything, unless you take really long showers, and for 2 people, the stand alone heat pump water heater is probably the best solution.

497 - 29-2-2012 at 17:09

No need for copper tube for DIY setups. That crap is expensive.

White Yeti - 1-3-2012 at 14:49

Quote: Originally posted by 497

No need for copper tube for DIY setups. That crap is expensive.

If you'd make it out of anything, galvanised steel. I agree copper tubes are waay too fancy for this kind of thing.

Would PVC deteriorate under the heat? That's the cheapest tubing material I can think of.

Endimion17 - 1-3-2012 at 15:56

Quote: Originally posted by White Yeti

Quote: Originally posted by 497

No need for copper tube for DIY setups. That crap is expensive.

No, it wouldn't deteriorate from the heat. But it would deteriorate. UV rays would degrade it a lot after just one season.
Copper is expensive, though I'd use it in some parts of the system, just to give a hard time to any bacteria inside. If you use steel only, iron bacteria would proliferate.

Dr.Bob - 2-3-2012 at 12:25

PVC would not do great in the heat that can occur in a solar thermal system, they can easily get over 180F in the summer, and that is getting to be way above the reasonable working temp for PVC. As well, iron or steel pipe heated to 140-180F exposed to water will corrode very fast. There is a reason that most solar collectors use copper, and that is because it will last years, even if allowed to overheat or build up pressure.

http://www.harvel.com/pipepvc-sch40-80-derating.asp:
"THE MAXIMUM SERVICE TEMPERATURE FOR PVC IS 140°F."

While it is not difficult to build a decent solar water heater, it is not trivial, and I have friends who have spent a lot of effort fixing systems built by home owners or even some "professionals" which were built cheaply or poorly, and they failed quickly, many from freezing or a leaking pipe. A water leak in your attic or walls can cost way more to fix the damage from than a well built system. If you want to build on, just buy one of the better books on the subject and read it well.

Depending on your climate, there are a few various design choices, but if you buy the parts as a kit, you can build a good system for $2000-4000 yourself, and get one that will last a lifetime as well as provide hot water nearly year-round. But I would still suggest a heat pump design unless you have a large family, based on my analysis of the payback and costs. Of course tax credits and rebates can change that dramatically.

497 - 5-3-2012 at 13:12

Iron bacteria in glycol? That would impressive. Corrosion of steel is not impossible to prevent if you try. http://onlinelibrary.wiley.com/doi/10.1002/jctb.5010091103/a...

Endimion17 - 5-3-2012 at 15:40

When did you mention glycol?

497 - 5-3-2012 at 15:48

A closed loop system may be cheaper, and prevent freezing corrosion, etc. Why not use a closed loop? The heat exchanger isn't that hard.