Blasphemy..... Solar power.

[Tom]

There are new water heaters that work like a heat pump that will maximize the hot water per kw you get. As a bonus you can duct the cold air into the house in the summer.

[BruceM]

I think DIY solar flat panel collectors is the way to heat water.  Buiditsolar has the details.  My 4x32 foot panel is copper with aluminum fins per builditsolar.  I have endless hot water via 180 foot (4- 45' coils in parallel) of 1/2'' copper heat exchanger in my home built 800 gallon insulated storage tank.  The same tank is used directly for my home in-floor heat. 

[Tom]

DIY may be cheaper, but for a purchased system in HI Casey may do better with something like this. http://www.homepower.com/articles/solar-water-heating/domestic-hot-water/heat-pump-water-heaters To heat water and cool/dehumidify the home is a 2fer. When the tank is hot the electricity from PV panels can be used for other things. 

[BruceM]

It's true that flat panel solar panels, which are easy to build your own, don't work at all on overcast or cloudy days.  But if you look at the price of the evacuated tubes, and consider the amount of them to equal my 4 by 32 foot flat panel, you see why compromising on cloudy days is not a bad compromise.  My homebuilt EPDM lined 800 gallon insulated tank lets me ride through cloudy days, even in winter.  Domestic hot water use has no appreciable impact on my hot water storage temp.  Heating the house does!

[LowGear]

Gosh glort,

You whipped out all the reasons that PV hot water is becoming "The" choice here in Hawaii.  Two PV panels with micro inverters can be purchased here for under $1,000 while a water collector system is going come in around $6,000 but that would be installed and all new.  Of course getting micro inverters to fire without a grid tie hasn't crossed my desk as of yet.

Because I've got a flat panel water collector already on the roof I'm going with the DIY lines in the drain plug hole.  Sort of like this only without the cold water supply.  http://www.solardirect.co.nz/scv.html.  (You'll need to page down once.)

Casey

[BruceM]

You can build a flat panel collector for much less than PV, and there's the matter of 85% efficiency for hot water direct heating vs 16% for PV.
Check out the variety of diy flat panel designs at builditsolar.com.

[LowGear]

Wow.  I've decided to read your novelettes one paragraph at a time.  Reads like you're having a lot of fun.  Normally I'd mention thermos to someone that is hot water fixated But I respect the learning that is happening in your journey.  And then it struck me.  There is a correlation between caffeine abuse and hyper-keyboarding. 

We have some visitors from central Washington, USA and live about a 100 miles from Grand Coulee dam.  They pay 2.6 cents a kilowatt.  How'd you like to sell solar panels in that town?  Grand Coulee is one of the early 20th century make work projects sponsored by President Roosevelt.  I wonder what the return on investment that federal program has returned to the people.  I wander.

Thanks for the update glort,

Casey

[buickanddeere]

You can build a flat panel collector for much less than PV, and there's the matter of 85% efficiency for hot water direct heating vs 16% for PV.
Check out the variety of diy flat panel designs at builditsolar.com.

In locations with freezing weather using a PV system can eliminate the complexity of draining, pumping and complex valving.

[BruceM]

Single tank drainback systems have become the new standard because they eliminate freeze/antifreeze and stagnation issues.  If the circ pump fails, the system is automatically safe. 

Certainly PV is at the point where it can be used for water heating and such. for retrofits. It just doesn't hold a candle to direct water heating for BTU's per square meter of panel.

My home (1100 SF superinsulated) heating and domestic hot water are heated by a single 4x32 foot homebuilt copper and aluminum fin panel. My backup propane was $60 a year last winter.  It would take about 6x the PV area in panels to match that winter performance.  That would be a hell of a lot of panels, racks, and wiring and electronics.  The average time between repair for the current transformerless grid tie inverters is 3-4 years.  They also put a lot of high frequency EMI on the home power which some independent researchers think is a serious health stressor.

[BruceM]

Glort, take a look at drain-back hot water systems at builditsolar.com.  I built one of his copper with aluminum fin designs.  Quite easy to construct.  Mine is a Hizer setup- horizonal "risers".  With drain back systems, you use a controller with a themistor attached to the solar panel close to the exit, and one at the bottom of your drainback/storage tank.  The pump only starts when it's hot enough, and stops when there is no net gain or with a max tank temperature.  The solar panels are designed to be able to stagnate without water in them.  Mine are tilted for best winter gain, when I'm heating the house.  It's shaded in the summer by a small roof overhang (intentional design) until afternoon to reduce excess capacity in summer and avoid extended stagnation.  I only have my backup hot water propane on for Dec-Feb.  It still carries all but $60. worth of propane a year. 

[carlb23]

I built a drain back system into the wall of a my shed when i was constructing it.  The south facing wall is at a 35 degree angle to the sun for best winter performance for me.  The collector has vertical risers and is 8 x 12' for a total collector size of 96sf.  I use a controller that cost about 100 dollars and it has 3 sensors one at the collector one at the bottom of the tank and one at the top of the tank.  I also built a parabolic reflector that tracks the sun.  It is 4 x 8' and is a single axis design angled for winter performance as well.  both are drain back both work really well.   If you have the room they really do work great and produce a lot of hot water.   I use mine to preheat my domestic water.  Normal tank temps in the winter are 124 degrees and in summer i have it shutoff at 130 degrees.  I use two hot air heaters for aux heat in the winter one is 48sf the other 100sf and these also work great.  All are controlled by a simple snap switch. on at 120 degrees collector temp off at 90 degrees collector temp.  they have been running for over 10 years with 0 maintenance needed.   

[buickanddeere]

I think DIY solar flat panel collectors is the way to heat water.  Buiditsolar has the details.  My 4x32 foot panel is copper with aluminum fins per builditsolar.  I have endless hot water via 180 foot (4- 45' coils in parallel) of 1/2'' copper heat exchanger in my home built 800 gallon insulated storage tank.  The same tank is used directly for my home in-floor heat. 

Not enough sun here for such a system from November through February. 

[BruceM]

Hi Carl,
I'm not surprised that you have a DIY, technically savy solar hot water setup; your projects are always smart, and technically impressive.  Reflector systems have the advantage of being able to produce useful temperatures on hazy or cloudy days (at reduced rate), which my flat panel doesn't. 

What did you use for reflector material, and did you glaze over the parabola or leave it open?  Did you use evacuated tubes?

Bruce

[carlb23]

Hi Carl,
I'm not surprised that you have a DIY, technically savy solar hot water setup; your projects are always smart, and technically impressive.  Reflector systems have the advantage of being able to produce useful temperatures on hazy or cloudy days (at reduced rate), which my flat panel doesn't. 

What did you use for reflector material, and did you glaze over the parabola or leave it open?  Did you use evacuated tubes?

Bruce

The reflector is made from 4 2x4' mirror grade stainless steel sheets. the parabola is not covered and i couldn't get an 8' long evacuated tube so i encased the receiver in a Borosilicate Glass tube sealed it up good at both ends  and vacuumed the air out with a air conditioner vacuum pump to 10" of vacuum.
i has leaked some of the vacuum out but it seems to have stabilized at 6" which is fine by me.  I am using a simple cheap Chinese pump (12 dollars) with a cheap adjustable voltage regular (less than a dollar) to adjust the dc pump speed for optimal heat transfer and flow. a simple old laptop power supply is more than enough to supply the pump.

[LowGear]

Is it a full moon?  So many contributions in only one night.

I think the saving grace of using PV for hot water is that they also produce electricity when your tank comes up to 160 degrees or so.  How many showers can you take in the Summer?

Hey glort:  Thanks for being a good sport and taking my posts as intended.

Too bad photos are a bit tricky here as I'd like to see carlb23's system.