Thoughts on solar water heaters?

My friend has been talking about making a solar hot water heater.  I know very little about them and it seemed like every question I asked about it, he was unsure or didn't know.  So here are a few solar hot water heater questions before I spend a weekend helping him make one.  
Are they worth it?  DIY or purchase a pre made kit.  My buddy wants to make one, I've seen fully instructed heaters minus the install for around 200$.  Not sure what parts would cost but if it takes a day to make with 2 guys it seems like maybe buying one for 200$ might be the way to go.
Can these be used year round in the northeast (NJ) where we can be at or below freezing for 3 months of the year?  
How much can this actually save?  Heating a home not hot water is usually the bulk of most people's energy consumption.  Would it make more sense to do one of those solar air heater glass box type things?  

Those were my main questions.  Curious to hear everyone's thoughts and ideas.  

A solar water heater can make most or all of the hot water you need for three seasons, which could eliminate a lot of electricity or gas expense. You would need to isolate and drain any simple solar water heater before freezing weather, though, to avoid burst pipes. There are systems that can handle cold weather, but they will not be simple and passive.

A batchbox-type heater may be the simplest, and if you have a metal tank that can handle water pressure and not corrode, the rest can be easy and cheap.
"Bread Box" Solar Water Heater
DIY Batch Water Heater

One of the cheapest systems you can make if looks are not at issue and you have space would be a coil of black HDPE plastic tubing. It can't handle high pressure when hot, but you could use it unpressurized to heat a tank of water, with a coil of copper tubing carrying potable water inside the tank.

If you have a south-facing wall that is not visually important. you can do a solar air heater pretty easily.
Thermosyphoning Air Panel (or Solar Chimney)
Solar DIY Space Heating Projects
$2K Solar Space + Water Heating -- One Simple DIY System

Just wanted to add a quick mention about a recent book review thread:
Solar water heater plans - safe and easy to build

Hi Dave

In my opinion solar water heaters are the best! They can do awesome things - check out this cool project in Canada where they are basically heating an entire community pretty much on solar heating....

http://www.dlsc.ca

also excellent stuff for individual dwellings - I have it on my house and we turn off all other heating from Apr-Oct pretty much.

Can be done DIY but also for not much more very good quality products are available which will probably work better.

Of course, covered in my book.....

http://www.energyrevolution.solutions

Hope that helps

Howard

Some stuff.

Dont hesitate to build or buy, depending.

For diy, Rodale institute had excellent designs, explanations and examples. These can be replicated by the type of person who is handy and has access to a workshop or workspace and a few specialty tools.

For the interwebs and homebrew-ability I like build it solar and Home Power Magazine diy sections. Im sure there are many others.
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

Parts are available, AAA Solar in New Mexico was great. They may be gone.
AET and a couple others if i remember right. Sunmaxx. A quick search found this.

http://www.aluminum-solar-absorbers.com/

Hydronic collectors are probably the toughest diy for building a project that has store-bought performance, much less that and good looks. Kinda like diy pv modules that i have seen, you might make it compete but ohh, ugly.

The enclosure is easy enough to make from wood, rodale has construction detail.

Absorbers and other types of heat exchanger are a simple concept and an effective one can be done by most people if you follow rules of thumb and engineering disipline, sometimes just rule of thumb depending on the cost or desire.

A high performance absorber with waterways and proper build for long term survival with extreme temp swings and varying humidity, is a work of art and understanding like pv modules.

I have seen decent hand built collectors. There are rules of thumb for plates or sheets of copper or aluminum. Copper is the most likely material for the home builder and is sure to be long lasting.

Tempered glass, even if its not low iron, obscured or diffused.
Not a show stopper, 3/16 is plenty especially if tempered.
Doorwall glass replacements are $40-$50 and are cut apart and butyl scraped yielding 2 sheets of 34" x 72" or other standard size.
Base your box on available glass unless you need to fit an available absorber, then comprimise the glass.

Bead blast the face of the absorber and coat with proper paint or lamp black. These are insulators but will work and are widely used. Quasi selective properties. Surface prep (cleaning) is paramount.

Metals deposited by exotic means or black nickel chrome plating is among the best available but has environmental issues (may be solved?) And titanium compounds are right up there or better. These are selective surfaces.

Blueing or controlled corrosion techniques may be known dy copper artists or crafters here.

The box insulation can be polyisocyanurate sheet 1-1.5 inches common. 2" back sheet to da nort, Eh!? They also use binder free ceramic, binder free fiberglass and non binder rockwool, no binder!

A rabbit cut into wood box sides face and back will allow an inset of glass and back sheets and will help keep water out of the back, especially if co ered in light gauge sheet metal. Battens and caulk or rubber or epdm if you got it. Rodale always caught the fact that you should bake the assembled collector to evaporate voc's from coatings. Cover with a sheet of mylar or clean the glass really well. Some chemicals will etch glass with vapors so sacrificial material, old glass, etc., is preferred.

Unions are great but not a must, especially to keep cost down.

Another tact is to build an air heater and use an air to water heat exchanger.

WWWSunsiarray.com cant find him, he is a great guy and i toured his manufactury. He uses an aluminum 6",8", or larger in line, round exchanger from a common manufacturer. Hayden or other.

I have repaired systems by a famous michigan installer of the 80's, who used hvac A frame type for space heater and dhw. Cant remember his name but the people were reverent and i should find out for historical purposes locally.

A perfect "donor" would be a cheap or free used air heater, likely the best box you will find. Extrusions from the recycling/scrap center can work too, but i lean toward a used air heater.

Shelf beams 4" to 6" tall x 6'-8' or rectangular c- or ship channel of light to medium gauge. You COULD make it or trim for wood on a brake with  coil stock for seamless gutters. Try a pro shop, the thin stuff is not what you want. Advantage is a range of residential colors and about $.45/foot 12-14 inches wide.

Rivets and stainless or painted screws.

Weep holes!!

Hope you guys build it.

If you want a world class collector, this is what i install, even though i have second hand reynolds aluminum ones.

http://www.heliodyne.com/

Caleffi, steibel eltron, aet, bosch, i think even lg has them, sunmaxx, solarskies has exotic tanks and collectors.

Steel is inexpensive, aluminum is almost forever, and wood is good if maintained and proper details for water exposure are followed.

Freezing is usually addressed by draining fluid back inside the house or with the use of antifreeze. In batch heaters, you can shutter them with an insulated cover at night or on very cold and over cast days, they can be freeze tolerant (ambient temp)  without the insulating cover.

One of my favorite schemes as far as enginuity is the Zomeworks beadwall.

They do window treatments too, but the beadwall was for trombe walls. It was a space behind glass that uses and arrangment like a whole house vac system. When the sun goes down the vac blows the space full of insulating beads and when there is sun available, the vac sucks them all back into a container.

Not used on water heaters as far as i know and im sure that if it was workable someone would. Still, on a batch box, it could be done as an experiment...Dale Hodgins?...

For hydronic solar collectors, its easy to let the water back in by gravity. If your pump is pv driven, it cannot not fail in pump mode and run all night in freezing weather and destroy stuff. Antifreeze is most common in the north.

http://www.zomeworks.com/about-us/

In climates where freezing is a concern, a drainback system, where the water only gets pumped up into and through the collector when the collector is warmer than the storage tank, is probably the simplest and most failsafe option once you go beyond a cheap weekend project. It requires no particular chemicals or antifreeze mixture and won't burst if the power goes out or controls fail.

frank li wrote:Freezing is usually addressed by draining fluid back inside the house or with the use of antifreeze. In batch heaters, you can shutter them with an insulated cover at night or on very cold and over cast days, they can be freeze tolerant (ambient temp)  without the insulating cover.

For hydronic solar collectors, its easy to let the water back in by gravity. If your pump is pv driven, it cannot not fail in pump mode and run all night in freezing weather and destroy stuff. Antifreeze is most common in the north.

Yeah, i was being nice because a batch box was mentioned, usually not recommended in areas with sub zero winters. Freeze tolerant in not freeze protected though.

Early delta t controllers had a freeze protection mode that actually was an issue.

Also, it is rare, but controls that connect power to a pump through a relay can and do sometimes fail in the on (pumping) condition, especially if that power is available at night or during extreme temps on a dark overcast day.

In a good scenario there is enough storage to keep everything ok...until the heat radiates off!

This is not an issue though, just a possibility.

Its true, you do not require any chemical antifreeze for total freeze protection, its just most common to have the collector loop a closed loop protected by antifreeze.

I prefer purified water as a heat transfer fluid. I have removed some pretty nasty looking and quite acidic fluid from antifreeze protected systems! Yuck.

Some people can keep antifreeze good and in operation for 20-30 years but it required special care of the fluid relating to loop volume. An anti freeze protected drainback is done sometimes but these guys were letting air expansion force fluid back out of the collector to limit high stagnation temps and allow antifreeze to last much longer than usual without radiators and valving geared at cooling transfer fluid.

Xkeep it simple

I've lived with a solar water heater for 5 years, and it is an adjunct at best.  It never eliminated the need for some other source of water heater, even in the summer.  Solar is solar is solar, if it's overcast it's not going to heat much of anything, and that can go on for days, even in the summer.  

Heating water takes a minimum of 6 hours of direct, hot, uninterrupted sunlight.  Not 3 or 4 on a partially sunny day.  

It's a lot more work for the sun if you are heating 20 gallons or heating 40 gallons, and how many people are using the system.   Is the heated water going into a hot water tank that is being heated by some other means and the savings comes from it not having to heat from scratch?  

Spring and fall have more storms, lower temps, sometimes freezing depending on where you are, and absolutely need some backup source of water heating, unless you are in San Diego or Mexico near the ocean, or someplace where there are moderate temps and overcast is rare.

Thanks everyone for the great info.  I really appreciate all the tips and suggustions.  I passed the link to the thread along to my buddy.  This gives him a ton of stuff to read thru and research.  At least this way now I know he getting the right info for the project.  Which will make me feel better about helping him with the project!
I'll keep you updated with what he ultimately decides.  Thanks!

I have used a flat plate solar water heater for 28 years or so.
It heats about 200L of water and operates by thermosyphon with 1 inch pipes between the storage tank and the collector.
Freezing is sorted with a valve device.
It is useful all summer, and partially for spring and autumn, it save a tremendous amout of energy in our household.

Dave Hunt wrote:...How much can this actually save?  Heating a home not hot water is usually the bulk of most people's energy consumption.  Would it make more sense to do one of those solar air heater glass box type things?

I would say that is a misleading question.  Why should solar H2O and a solar air heater be an "either/or" proposition?  Particularly since solar air heaters are SO easy to make!  I totally plan to have both, and to DIY both.

As for the solar H2O and how much can it save?  I couldn't tell you that from experience, but there are surely resources online that will provide you an estimate based on your geographic area.  Do a search for "solar calculator" and work from there.  These resources are likely provided by the people who sell you solar systems, so beware that they may present an optimistic picture.

As for myself, I already have photovoltaics, and though I am currently grid-tied, I might well decide to go off-grid in the future.  Thus I am unconcerned by exactly how much $ solar H20 would save me today.  Rather, I think in terms of every kWh saved will help me live within the means of my small solar PV system's capacity if I do end up relying solely on that for power tomorrow.

Several posters above have given some very good advice.  I will cherry pick and elaborate on what I think are the best pieces of advice...

Keep your system as simple as possible.  Opportunity for simplicity #1: don't mess with antifreeze.  Not when a drain-back system using pure water is so simple to design.  In the event of a cold collector, or if your storage water gets too hot, or if the system looses power, the pump turns off and everything drains back inside your storage tank inside the house.

And if you're going to have a drain-back system, that big interior storage tank is a convenient place for a water-to-water heat exchanger.  So, opportunity for simplicity #2: don't mix your potable water with your collector water.  Just divert the plumbing for your potable water through a bunch of copper coils - they sell these for heating/cooling the wort in homebrew set-ups - through your storage tank and out the other side.

Opportunity for simplicity (and safety) #3: operate your collector system at regular atmospheric pressure.  Your water mains run at 80psi or more, but there is no need for your solar collector to do so, since we've determined that your collector fluid need only be a warm bath through which your sealed drinking-water pipes can run.  Keep the lid of your water tank loosely fit, rather than screwed down.  In an overheat scenario, it can vent steam rather than allow pressure to build inside your collector piping.  To be totally safe, include an actual steam release valve somewhere else in the system as well.

Opportunity for simplicity (and practicality) #4: don't plan to rely on your solar H20 for 100% of your hot water needs.  It is much more realistic to use your solar H2O simply to pre-heat the water heading to your conventional water heater.  This could still noticeably reduce your energy consumption, but it also takes a lot of pressure off of you while designing your system, and it won't leave you taking cold showers on cloudy days.

Opportunity for simplicity #5: DIY'ing an insulated box to be your storage tank, all the piping, and even the electric pump controls are easy enough tasks using largely off-the-shelf components.  But DIY'ing the solar collector itself strikes me as a much greater challenge.  Do yourself a favor and look to purchase a (used?) commercially-built collector to integrate into your otherwise-homemade system.  If you can afford it, or if the opportunity arises for a good deal on a used one, you might then consider a vacuum tube-style solar collector.  These are really nifty, but impossible to DIY!  Then your system could supply you with a substantial portion of your hot water even during the winter months.

Mathew

#4: don't plan to rely on your solar H20 for 100% of your hot water needs.  It is much more realistic to use your solar H2O simply to pre-heat the water heading to your conventional water heater.  
Opportunity for simplicity #5: DIY'ing an insulated box to be your storage tank, all the piping, and even the electric pump controls are easy enough tasks using largely off-the-shelf components.  But DIY'ing the solar collector itself strikes me as a much greater challenge.  Do yourself a favor and look to purchase a (used?) commercially-built collector to integrate into your otherwise-homemade system.  If you can afford it, or if the opportunity arises for a good deal on a used one, you might then consider a vacuum tube-style solar collector.  These are really nifty, but impossible to DIY!  

SOLAR HOT WATER
Please dont think of solar hot water as a pre heater;
- In Australia at 38 deg latitude i get 200-300L of 65 deg Celcius all day.
- Remember its 2-300L of very hot water which is diluted for use.
- there is no need for preheating it for about8 months of the year.
VACUUM TUBES
IMO they are shocking to use;
- cannot be repaired
- claims to be more efficient dont cover periods when hail has broken them
 Birds eat the wiring- and generally need a pump 24/ 7
FLAT PLATE COLLECTORS
- Can be home made
- manufactured ones are better built
- generally do not get hail damage
- work very well with thermo syphon systems