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Panache
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On solar hot water systems
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]
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White Yeti
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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.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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neptunium
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new jersey? lol
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GreenD
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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.
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Endimion17
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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.
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GreenD
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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.
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White Yeti
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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?
"Ja, Kalzium, das ist alles!" -Otto Loewi
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Endimion17
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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?
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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]
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Twospoons
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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.
Helicopter: "helico" -> spiral, "pter" -> with wings
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White Yeti
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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.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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Twospoons
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3/4 of a litre of warm water makes for a very short shower!
Helicopter: "helico" -> spiral, "pter" -> with wings
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White Yeti
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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.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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497
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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]
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Endimion17
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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.
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White Yeti
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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.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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White Yeti
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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.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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Panache
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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.
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GreenD
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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.
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Endimion17
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| 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]
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Twospoons
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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.
Helicopter: "helico" -> spiral, "pter" -> with wings
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GreenD
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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.
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watson.fawkes
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| 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.
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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.
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GreenD
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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.
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White Yeti
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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.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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Polverone
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| 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.
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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.
PGP Key and corresponding e-mail address
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