OT...Help with solar hot water

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Chubby Hubby and I have decided we are going to go with solar hot water heating. Since we have two large HW heaters, we feel this would be a good investment. We have the book, "Who Owns the Sun" and while it is very interesting, it is not a manual on how to do solar hot water... or solar anything. I went to Amazon and did a search and came up with 15 books....14 are out of print and the one in print is about all solar power. Those out of print were all published in 1980, so you can see how the interest in solar has decreased during the cheap oil years. Can someone point me towards a good UP TO DATE manual on solar hot water and its installation? In Gainsville, Fl, just up the road, there is a solar company and we will probably contact him to do the work. He does solar stuff all over the world it appears, and especially in Fl and the Carib. But we would like to be armed with lots of info before we go shopping for a system. Thanks Taz

-- Taz (Tassi123@aol.com), February 04, 2000


You might try talking to the Tech team at Real Goods?


Good luck.


-- Diane J. Squire (sacredspaces@yahoo.com), February 04, 2000.

Bravo! Applause for your courage to try to eliminate the "hook" in your lip from the "powers that be."

"Who Owns the Sun" is definitely not a "how to do it book." Instead it is a rather tedious (but important) diatribe describing how the hook got there.

Unfortunately, solar power in most any of it's forms is it's own "snare." Those who put themselves out on the marketplace in the solar field don't do it for the fun of it (although most start with high ideals.) Rather they do it to make a living and "improve their condition" and they are not bashful in having you pay for it.

This is one of the problems with making anything that is "solar powered" economically viable. The expertise and labor to make a "engineered" system that will work and provide your needs is expensive.

Consequently, the most economically viable solar systems are those that are "home brew." Solar Hot Water is one of the most easily mastered of these "home brew" setups, once you do some self educating.

See www.homepower.com where you can "download" for free the bimonthly magazine of the same name. Also, from the site you can order online CD ROMs which include all the previous issues of the magazine. (About $89 for the three CD set - a worthy buy and several hours or days of good reading.)

There are lots of other free downloads at the site if you look around.

Mother Earth News also used to be a good source of information but as they have changed hands in recent history, they are more the "glossly newstand" magazine of the "yuppie/enviro wannabees" They now have a chat forum at the magazine website (www.motherearthnews.com) that you may be able to make an inquiry on some current information sources.

The website for the printers of "Who Owns the Sun" (www.chelseagreen.com) may have some more books of this ilk. Last time I checked they had some excellent "discounted" books of environmental interest.

Hope this all helps. I myself have been trying to get that hook out of my lip for years now.

Best regards,

-- Joe (KEITH@neesnet.com), February 04, 2000.

Taz, I ran a company from 1975 to 1985 selling and installing solar heating systems and have used solar for years myself. I have many books from that era which are now probably out of print. Please feel free to e-mail me with ANY questions you have on Solar Hot Water heating. I would be happy to review any proposal that you get from your local solar company to see if it is technically sound and economically reasonable. -Mark

-- Mark (mpmayer@powerway.com), February 04, 2000.


Does it ever freeze where you are? There are
two types of systems. One that just preheats
the water before it enters the water heater,
and one that is filled with anti-freeze and
heats the water by convection. The second one
is necessary for areas that reach freezing
temperatures. The first one is more efficient.

In the anti-freeze system, there needs to be
double insulation between it and your water
to prevent contamination.

Most installers will opt for putting the
panels on your roof. I prefer keeping them
off the roof. If you are using the direct
preheat method, they can be put lower than
your water heater and transfer the heat
without a pump.

Sorry, all my solar links failed.

-- spider (spider0@usa.net), February 04, 2000.

Hi Taz,

Homepower magazine is probably the way to go. Our local solar guy mentioned before the rollover that apparently the best way to do solar water heating is a parabolic set up rather than the flat panels which are more common. Apparently, there are some new manufacturers out there now. Of course, it is likely to cost a lot up front, so you may have to sell some of your gold. ;^)

-- nothere nothere (notherethere@hotmail.com), February 04, 2000.


Check out Thermomax at http://www.thermomax.com/. These hotwater panels boast an 85% efficiency using vacume technology. A little expensive but probably the best on the market. The site also includes alot of very good technical information as well as sizing for you location.

-- PA Engineer (PA Engineer@longtimelurker.com), February 04, 2000.

Taz, While vacuum tibes and parabolic reflectors have their purpose, it is NOT to heat water to 120 degrees which is what you want for a solar hot water heater. You want a SIMPLE flat plate collector. If you need an anti-freeze system or single or double glass covers will all depend on your physical location. I have installed over 100 systems and believe me SIMPLE IS BETTER!

I live in Indiana where it freezes. My system uses antifreeze and a heat exchanger in the solar pre-heat tank and flat panels with a single sheet of glass. It heats the water in the tank to 100 degrees above outside air temp.

Let me know if you need any help.

-- Mark (mpmayer@powerway.com), February 04, 2000.

Here are a few "Solar Water" bookmarks I've collected:

Home Power Magazine

Solar Water Heater Project

Popular Mechanics: Solar Hot Water

Good luck!

-- DeeEmBee (macbeth1@pacbell.net), February 04, 2000.


I am curious what your issues are with the Thermomax vacuum technology. I have examined a few of the installations locally (very cold winters) and am budgeting for a 30 tube installation this summer. You state "it is NOT to heat water to 120 degrees which is what you want for a solar hot water heater". I think you may want to review the site technical information since domestic hot water (DHW) is one of the primary applications of this unit. If you know of any technical faults such as reliability issues I think many of us would like to hear of them.

-- PA Engineer (PA Engineer@longtimelurker.com), February 04, 2000.

PA Engineer.

Several years ago I went to the Florida Solar Energy Center with guy from France wanting to sell his Vacuum tube collector here in the States. Their (FSEC's) complaint with it was at intercept (and I don't have the formula with me now)and out to 150 degrees F the vacuum collector performed no better than a regular flatplate copper collector. After 150 - 155 degrees the flatplate bottomed out and of course the vacuum collector keeps going out beyond 200 degrees. Their (FSEC's) point was that if the vacuum collector didn't do any better than the flatplate at 150 degrees - why bother paying more money for the vacuum collector. Performance may be different in other areas of the country especially in the colder climates. And for information on that I have a friend of mine up in Maine who used to work with the Thermofax collector who could give you some more information and more details. If you want his phone number just e-mail me and I'll send it to you.

My advice to any one buying solar is to check with your state's energy office about what's best, get at least two bids and check out the solar contractor who's doing the work.

BTW I am not in the Solar business.


-- Bookworm (bookworm_2@hotmail.com), February 04, 2000.


Thanks for the valuable info. Do you have a link to the FSEC site and reports? Have you heard of any reliability issues with a closed loop Thermomax installation? Again thanks for the input. I will save this thread and may contact you later about your friends email if my digging turns up empty.

-- PA Engineer (PA Engineer@longtimelurker.com), February 04, 2000.

Ah shucks gang...Thanks for the "flowers". As a member of the Home Power Mag crew we sincerely appreciate folks spreading the word about our efforts. I write for them and produce the Solar CD-ROMs. Do visit the website, lots of great info there.

We have run articles on solar hot water systems, including some home- brew pieces on building your own. In our strawbale bathhouse we've installed 2 almost identical DHW systems, the only difference being one is sourced by a flat plate collector and the other by Thermomax tubes. Both use a glycol mix thru a heat exchanger next to the tank. We should be running an article soon about our performance experience with these. Thermomax tubes work great in cold temps, know a number of folks who use them and swear by them.

I'm really fond of breadbox "batch" style water heaters (ie., big black tank to preheat water). These work well in conjunction with a normal water heater to lighten it's duty load or can be used by themselves if you don't mind tying your hot water useage to time of day and weather considerations. These can only be used year round in mild conditions.

Smitty and the gang at AAA Solar in New Mexico (they have a website) offer good prices on DHW solar gear and have a very informative catalog.

-- Don Kulha (dkulha@vom.com), February 04, 2000.

-- Don

Thanks for the post. I live in an area of the country that can be best described as "Langley Challenged" (Western PA). I am looking forward to your article.

-- PA Engineer (PA Engineer@longtimelurker.com), February 04, 2000.

Thanks for all your work with Home Power, Don. My two teens have started using up hot water at an alarming rate, so I'm current researching a way to augment the current supply. Have enjoyed your articles very much.

-- DeeEmBee (macbeth1@pacbell.net), February 04, 2000.

Saw a short article recently about a combined system with Amorphous Si PV panels (to get a little power from the same glass that covers the hot water system) and a hot water heater system.

I agree that the outdoor conditions where you are will determine the best system: a two fluid is best in colder areas - the outer fluid (antifreeze or a specialized mix) heats your potable water. Depending on design, the outside (primary) fluid is either automatically drained at night, or is able to resist destructive freezing down to the lowest expected. (Even then, emergency freeze portection is needed under worst case conditions.) The secondary (potable) water stays indoors and doesn't need freeze protection.

Another option is pre-heating the water going into a regular water heater. (That also requires two heaters and two sets of piping = the inlet water heater and a regular water heater, but the money to build a pre-heat water system is usually less than to do all the heating with solar.)

As mentioned above by the Homepower editor, an even simpler system uses a large black-coated receiver outside (drained or isolated at night) that doesn't require any "panels" at all. The result reduces your water heating bill, but doesn't eliminate it. You still require some power from the utilities.

Am-Si is coated glass PV system, not the usual crystal silicon system where individual little sections of Si are placed into an aluminium boarded tray. The amorphous Si PV's are much lower in cost, but a little less efficient that the classic crystal Si arrays. But at 2.00/watt wholesale, 3.00 per watt retail - they're "almost" less than grid power....but when you factor in the charge controller expense to get the 12v batteries recharged, it adds a bit back. (On the other hand, at 45-60v from the array and with power point tracking in the charge controller, you get better overall efficiency than from classic crystal arrays.

You can get a payback in less time...though solar still is a little expensive, at least your money isn't being thrown away to the power company.

Important thing with a combined power + water system is the lower cost of the shared array mounts, lightning ground system, and arrays themselves.

More data later, I've got to look up the details - I think in "Solar Today" magazine. Email me if you've got more questions, or are interested in combining your generator with a (silent) emergency battery "plug-in-play" backup system.

Found a company near here with a neat pre-packaged backup system. (Much more professional assembly than the one I put together for myself in case of y2k-induced power problems.)

-- Robert A. Cook, PE (Marietta, GA) (cook.r@csaatl.com), February 04, 2000.

Ok...I have read and reread all that is on this thread, plus whatever else I could find on the net and in solar catalogs that I had. Here is my question. I am not planning on getting off the grid. Just want to cut the bills some. Why can't I just put a black barrel of water inline between well's pressure tank (P is at 70psi when pumping and then falls off to 50psi) and my electric hot water heater. Leave the electric heater on so that if the water coming into it is now up to the set temp, the heater will turn on and bring it up to temp. Won't that pressure tank push that water from black barrel into the hot water tank in the house? Won't just the sun heating that water in the black barrel cause a pressure increase in that tank and the water will go to the area of least resistance, the same as a gas does? (Isn't that Boyel's law?...pun intended) And wouldn't that be the hot water tank or otherwise the P tank wouldn't be functioning now? OK...fire away! Taz

-- Taz (Tassi123@aol.com), February 05, 2000.


A better low cost solution would be to
coil a black 3/4" rubber hose on your
roof to preheat the water before it enters
your water heater. There is more exposed
surface area than just a black tank. This
presents problems if there is wind or
freezing temperatures. It must be attached
firmly and have an option to bypass and
drain in cold weather.

-- spider (spider0@usa.net), February 05, 2000.

Your proposal will work exactly as intended - when the well pump is running and the weather hot and hot water is being used (water tap open), but let me think a bit about a few other conditions and cases:

Since your water supply is affected, you've got to be sure everything is okay under all conditions...you want to be sure the pipes are not over-stressed, you want to be sure you get hot water when desired (the pipes aren't empty, nor filled with ice! even if the pipes don't burst), and you want to save some dollars - so exotic solutions aren't really a solution.

Right now, your pipes are protected (underground?) against freezing. Obviously, the water in the well itself isn't freezing (too deep), and the ground will keep a steady temperature (in your area) of about 60-65 real degrees all the time. So the water gets to your house also at 65 degrees, and you spend a lot of money heating it up to 130-140, storing it at the hot temperature until needed (while it looses heat than must be replaced with more energy), then sending the hot water itself down the pipe to the tap.

So overpressure protection of the cold water is limited by the max pressure of the well pump (which the pipes are sized to accept), and overpressure protection of the hot water is by the air bubble (and relief valve) in the hot water heater.

Second, IF the hot water collector is ever COMPLETELY isolated on a hot summer day - the water will heat up (obviously!) and have no place to expand to (since the water tap in the tub is closed) - and will increase water pressure in the piping between the pump and the tap.

This overpressure - if there is no closed valve between the current hot water heater and the collector, hsould be sensed by the current relief valve on the current hot water heater and relieve the pressure.

BUT - if there is a vlave that could be accidently or deliberately be left closed between the collector and currenthot water heater, then those pipes might be overstressed. (Some stress is okay - both copper and steel pipes accomodate a certain amount of overpressure with no problems.)


Cold weather is worst.

When you add a solar collector into the piping system: you introduce the probability that this "always 65 degrees" cool (protected by the ground) water from the well is going to be exposed to the freezing air temperature in the solar collector (coiled pipe or black barrel) long enough to freeze.

Freezing isn't catastrophic - if the frozen codition -

= isn't long enough to block delivery of water - or can be by-passed with the current underground pipes until warmer weather returns.

= doesn't overpressure the pipes/collector and cause them to rupture. For example, if there were always a air chamber or vent in the top of the barrel, or if the coiled spool of plastic pipe just expanded a little when ice forms inside (like a garden hose left outside does) - then there is no problem.

What you don't want happening is a solid mass of water in the collector that could break the collector when it expands as it freezes. You don't want a solid mass of water in the collector or any above-ground pipes blocking all water flow in the winter time. Also, you don't want your current "cool" water to be replaced with "very cold" water going into the hot water heater - since it obviously costs more to heat 35 degree water (from a non-frozen but exposed-to-the-cold-air water pipe) to 140 degrees than it does to heat 65 degree water (from an underground pipe) up to 140 degrees.

All of these concerns are only applicable IF the collector or above ground pipes freeze. Under warm conditions, or under conditions where there is a constant (small) stream of water through the exposed pipes, the well water pressure simple flows exactly as you described. The well pump will "push" the cool well water to the collector (connect inlet to the lower past of the collector), the water in the collector will heat up (in daytime), expand a little, and rise to to the outlet pipe, flow to the inlet of the current water heater, and then contiue to rise (if needed) by the electric heater, then flow to the water tap.

So, your plan will work as long as air temperature stays above freezing, or (if freezing) as long as water flows.


Many solar water users avoid this problem, and maintain the previously heated water in the hot water heater hot through the day, by adding a small (sometimes dc solar powered) circulating pump between the outside solar collector and the house water heater. Thus, if at 12 noon, when the tap is closed but the collecor is hot up on the roof (and getting hotter) - but the electric water heater is loosing energy through its insulation inside the house (and so running up the electric bill)... the little 12v dc water circulating pump runs "cool" water from the water heater up to the collector, through the collector, and forces the newly re-heated water back inside to the (storage) water heater.

In winter, this flow prevents freezing in the pipes exposed to air.

-- Robert A. Cook, PE (Marietta, GA) (cook.r@csaatl.com), February 07, 2000.

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