Avoid hang-time, attach ladder to gutter nail using piece of wire 
Solar collectors at Amazon

Should you buy solar water heater

Solar water heater review
Applies to recirculation type system
Electric solar PV panels not covered here... but some information applies
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Solar water heater
Cirrex with electric back-up

Includes solar pump station, 2-3 collector panels, 80-120 gallon storage tank, and plumbing for heat transfer fluid.
Other materials not included are expansion tank, air vent at top of circulation loop, drain pan, pipe insulation, discharge line from TP valve, mixing valve, additional drain valve on circulation loop, etc
1) Collect solar heat using 2-3 panels located on roof of house. 2) Electric pump circulates distilled water or propylene glycol from solar panels into large tank. 3) Solar heat is transferred into water using a heat loop or heat exchanger located inside tank.
Is a solar water heater worth the investment?
.... depends on cost of system and other factors... read more
Rule of thumb:
Don't buy expensive water heater that you cannot maintain yourself:
Applies to solar water heater, heat pump, hybrid, tankless, condensing etc..
All costs and decisions are energy. Keep it simple.
Consider all costs
Federal Residential Renewable Energy Tax Credit is worth 30 percent of the cost, including labor and installation costs of a solar water heater. So your system net cost might be 12,500 less 30% = $8750? for a water heater that lasts 12-14 years
AO Smith Solar
Sell sheet
Solar manuals
DIY solar collector 2'x2'
Read about new federal water heater energy standards
solar water heater
See detailed illustration
Pipes are oversized in this illustration... actual pipes are smaller, and amount of fluid is small
Storage tank has 1 element for back-up heat
Tank has heat loop coil built into tank
The collector loop is closed, and is filled with antifreeze or water that does NOT mix with water stored inside tank
Bottom element port usually has temperature sensor mounting plug.
Tank has 1-2 ordinary anode rods that are cut off short so they do not touch solar heat loop
Otherwise tank is typical electric water heater with anode rod, dip tube, thermostat, electrical connection. See
Closed loop recirculation design, reviewed here, some say... 'provides most reliable source of hot water vrs other commercial designs'
Recirculation design uses pump to circulate distilled water or glycol.
Recirculation system requires electricity to run 30 watt, 1/25 Hp motor
Different system or do-it-yourself system may fit your situation better than this design... but this design is generally  most reliable for producing hot water.
Every locale and situation is different. Every budget is different.

Circulate heat-transfer fluid/ or circulate water into storage tank
AO Smith Cirrex uses non-toxic freeze-protected heat-transfer fluid. Fluid will not freeze down to -30F in some conditions.
100% Propylene Glycol mixed 50/50 with demineralized water.
Propylene Glycol prevents water from freezing
Heat transfer fluid contains corrosion inhibitors. Not corrosion proof.
Do NOT use tap water... only demineralized or distilled water.
Water-based system: 
Water systems will freeze and must be drained in freezing weather.
Water does not contain corrosion inhibitors.
Water that circulates must be treated to prevent deterioration of closed circulation system
One back-up element
Typical storage tank for recirculation system is 80-120 gallons and has 1 back up element located in upper element port, typically ordinary 240 volt, 4500 watt element available local store.
AO Smith manual says: Solar water heater will work with 'one voltage only'... do not connect to any voltage other than voltage listed on rating plate located on side of tank
Condensation/ drain pan required
Solar tank will have condensation. Insulate pipes can reduce condensation.
TANK must be set in drain pan with 3/4" line going to appropriate drain
The conversation below is between 2 people in 2015, compares PV electric vrs glycol collection system and is not comprehensive of all people's experience and may not reflect prices and results in your area.
Information from local users is best source.

Q. $28,000 for PV photovoltaic solar water heater? That's high.
I assume the price was not DIY?... and price included batteries, inverter, everything normally associated with converting DC to AC.
A. It was for a PV electric system installed package that didn't include batteries. The government tested the FP panels I got independently for SRCC rating and from their rating mine produce 21,450kW per day after inefficiencies which should translate into a 6700 watt PV hot water system. Per the government most PV systems people install are 4kWh with an average price of $32,500 per install. My coworker has a 16kWh system he did and it was $86,000. My other coworker is getting a PV system over $40,000 on his house.
PV is spreading like crazy here because they don't pay for a dime of it: with the state incentives + the installing company sells the excess and leaves the homeowner paying for nothing in the end. My state I think is going to go bankrupt if they keep this up.

Commentary: PV photovoltaic provides electricity to entire house... not just water heater. PV has come down in price from $4-5 per Kw to near $1 per Kw 2015 with 20-25 year warranty on power output. Read the warranty on any solar product carefully. product and installation have different warranties. Different parts have different warranties.

Glycol system:
Q. Are glycol solar water heating incentives still in effect?
A. I did the 3 panel glycol system with 120 gallon tank and after buying it got around $3,500 back from incentives. To see if there's solar incentives for your state (Federal should be 15% on entire project) you can check out http://www.dsireusa.org/

Q. After incentives, can I ask what was final cost for your glycol system 5 years ago in 2010.
I assume the installation was not DIY?
A. $3,000 after incentives. Total $6500 up front 5 years ago. It's a DIY kit, has everything needed to DIY except pipe (pick up at local store), fittings, and insulation. Total cost after incentives was just under $3,000 for everything and I mean everything. But, $1000 of it was for electrician and plumber because in my state you have to be licensed to do any electrical or attach to drinking water.

Q. Approximately what area of world do you live?
Warm climates favor glycol circulation collectors?
While cold climates favor PV energy collection because hot panel causes less output?
Windy location favors PV electric because it cools panels, while windy location is not best for glycol collector because it cools panels.
A. Yes cold PV panels produce more electricity. I live in the cold parts of Massachusetts (far away from Boston). Cold doesn't affect my solar glycol much, just wind. It can be -5F and sunny and my solar glycol will have the bottom of my tank over 120F. If 20F and very windy I can expect around 90-100F. Even so that's the very bottom of my 120 gallon tank. My solar is designed since we have 2-3 days of clouds/rain a week typically one day of sun and my solar turbo heats enough water for 2-3 days of coasting. Mine is not meant for day after day of sun, though it includes overheat protection.

Q. An important price consideration is durability...
Glycol systems last about 12-14 years? And that lifespan includes collection panels and storage tank... the entire thing.
While PV electric panels last about 25 years? But that doesn't calculate replacement of storage tank, batteries, etc for converting to DC to AC.
A. There's 2 kinds of Glycol systems I suspect you're thinking of the evacuated tube kind. Flat Panels are strictly made of glass, copper, and aluminum and the lamination technology binds the coating to the aluminum so it can't delaminate. If you saw todays Flat Panels you'd have a hard time finding any thing that can fail before 40 years, just the fluid running in the pipe over decades causes the pipe to get thinner and thinner and eventually it will fail. My house has original copper pipes and is 1962 and they're still going should be more than 50 years.

Q. I would estimate the cost comparison between glycol and PV is about 1:1.6. So if glycol system lasted 1 year... the PV system would last 1.6 years. Total cost comparison should consider this?
A. As mentioned I see no reason why a glycol FP system would fail within 40 years. The reason I chose FP's was because my in-laws have a solar house from 1983 with factory made FP's (not home made of wood, screws, see-through fiberglass, etc.). So far in 32 years they have had to replace a pump which was easy enough, otherwise their solar FP's are still going strong heating their house and hot water.

Commentary: Soldered copper joints exposed to constant temperature change might not last as well as indoor copper pipes. There is no 40 year warranty. 12 year warranty is standard. (compare 25 year for PV electric panel). Product warranty and installation warranty are usually separate. Some parts may have different warranty than other parts. Solar water heater tanks are probably not going to last 40 years. There are products that out-perform expectation if anode rod is changed and native water supply does not have heavy mineral content. Panels lasting 40 years: Cool region that only gets sun 1 out of 3 days like areas of Mass, the panels will probably last longer than intense-sun states like Texas. Technology is always changing. Government website shows 12-14 year lifespan for glycol product.
Note: The anodes may not bet standard for your tank. Certainly they must be shorter so they do not come in contact with solar loop, and generally two anode rods are used.

Q. Glycol system generally must be located near to water heater, for example on rooftop.
A. All the solar installs here the water heater is in the basement and we run glycol pipes up to the roof through the panels and back into the basement. Attics here are ventilated to prevent ice dams so attics are typically the same temp as outside which can get below 0F... terrible place for a water tank Everyone puts them in the basement and pipes the glycol up through the panels on the roof.

Commentary: Pumps must match the load. More elbows and distance increase friction in the line. 85 watts, 110 vac  is standard. They also sell DC pumps (3 watts) for regions like Hawaii that are connected to a 10 watt PV panel, but there is no switch or thermostat to control it.  The pump works faster when the sun is hot, but slower on cloudy days or not at all at night or extremely cloudy. 

Q. PV panels are more numerous and can be located farther away... on the ground... but greater distances causes more power loss... and PV panels consume a lot of space if located on the ground.
A. You can put hydronic anywhere as well it's just pipe (though must be copper). PV system does take up a lot of room I calculated one would need a 24 panel PV (420 sq ft system) to heat as well as my 3 panel glycol (96 sq ft).

Commentary: More distance = more heat loss along length of glycol pipes. Do not assume your location requires 3 panels. Estimate of 24 PV panels does not specify the Kw rating of each panel. For example they make 100 Kw and 270 Kw panels

Q. PV electric systems must accommodate resistance changes as solar output changes... while glycol systems just heat or don't heat depending on solar output?.
A. In short you can do PV, not saying it won't work just that it's almost certain you'll end up with a lot more parts, complexity, price, space, and failures sooner than the alternative.

Commentary: PV has more parts and complexity. PV supplies electricity to entire home, and not just water heater
Solar water heater
See detailed illustration
Solar water heating seems simple
Can be complex.

Freeze prevention unless unit is glycol
Storage tank
Heat exchanger
Seasonal temperatures
Secondary heat source

Damage to roof
Insurance coverage
Storms, lightning
Resale of home
Local codes
Expected life vrs future Replacement cost

Part replacement
Solar water heater Solar loop inside water heater can be single-wall or double wall
Solar water heater
Larger image
Another image
Solar water heater can be complex & expensive
Solar panels integrated with gas water heater and tankless.
Tankless uses solar heat to preheat incoming water.
WHY make a system so complicated? It cannot save money.
BUT tankless cannot be easily integrated with other heat sources

Solar water heater can produce 180 degree water midday on hottest day. Special tank is needed to handle expansion, or mixing valve to add cold water into pipes.
Water confined to a storage tank or piping system, when subjected to a temperature rise of 10F (increasing from 75 to 85),increases pressure from 50 psi to 250 psi

180 degrees is very hot. Storage tank must be well insulated. If the system recycles water continually, then the 180 degree water will only be available for short period of time, and water cools quickly once it circulates outside the insulated tank.

Other parts not shown:
Solar Pump
Tankless circulating pump
Air vent
Vacuum relief valve
Bolts drilled through roof
How does that save money?
Payback 25-35 years

How to save hot water using mixing valve
There is NO magic water heater... reduce consumption is best answer. 
I prefer ordinary electric water heater since it can be repaired and maintained DIY to last forever using simple generic parts. But new energy standards 2015 will change the landscape. Read about new energy standards
Numbers on chart below may not be most current information for your area. Cost of maintenance and repair not included
solar water heater cost
Payback depends on total cost
Typical saving might be $12-20 per month depending on many factors
Payback depends on total cost
Payback $12-20 per month maximum
Use this page to help research total cost of solar system.
Use this page to consider other factors.
Are you going to use back-up electric heat elements? Or go off-grid?
When do you consume hot water? Morning, evening? Or afternoon?
Maintenance, parts, repairs, warranty, people with similar system in your area, cloudy days, wind, shade, storms, local codes etc
Jose Alano solar collector
Solar collector made from plastic bottles
Do it yourself  might be better?
Do it yourself solar at Amazon
Resources: Do some reading, and make choices:
Long list of do-it-yourself solar projects
Convert old water heater into solar water heater
DIY solar collector 2'x2'
Set 2 gallons water in the sun inside glass-covered box, and have hot water at dinnertime.
Put solar heated gallon in styrafoam box, Check if water is still warm one hour after removing from direct sun.
If you shower late in evening, solar heated water has cooled, so solar heater is only saving water heater standby costs during day ... which is small amount.
solar water heater collector Try small DIY do-it-yourself solar collector
Recirculate water from panel into small water heater
Solar collector at Amazon
2x2 panels at Amazon
Compare small water heaters
Solar water heater project
Larger image
PV solar panel powers pump/ solar panel heats water
Must use water filter and air vent when connecting to plumbing system
Do the homework.... make sure PV panels and pump work together.... make sure pump will circulate the water enough distance
This pump will probably not work with long distances... use 120 volt pump
Use any water container... not necessary to connect to water heater
Filter the water using hose washer... innovate

Solar collector at Amazon
2x2 panels at Amazon
Pump at Amazon
Compare small water heaters
Water heater terminology and formulas
Water pump information
Heavy-duty recirculation pumps at Amazon/ solar systems use pumps
Use recirculation pump for DIY solar
Works for any recirculation system or solar project
120 volt, 1/25 HP, 30 watt
New line of lower Hp pumps introduced by Grundfos for PV solar-power homes.
PV is photovoltaic... where solar panels produce electricity

Grundfos recirculation pump at Amazon
Cast iron flange set for flanged pumps
Compare recirculation pumps
Photovoltaic water heater
PV solar voltaic produces electricity
Photovoltaic electricity/ not a recirculation system
Can photovoltaic DC electricity be connected directly to water heater? Maybe.
Electric Solar panel connected to electric water heater
Ordinary water heater elements will work with DC power
BUT water heater thermostats will melt with high voltage 200+ VDC power, however you can accomplish the goal.
You can also get some water heating using low voltage 12-24 VDC and using a single-U or double-U DC element
Buy from my associate links:
DC Element at Amazon
Single U element at Amazon
Double U element at Amazon

How to convert AC water heater to DC/ high voltage
Convert AC water heater to DC/ low voltage Using U elements
Information on elements
wrap water heater     dripping faucet Easier ways to save money?
3) There are many low-cost ways to save with a water heater, including behavioral changes.
Reduce consumption. Insulate pipes and water heater. Maintain water heater. Do not turn on hot side when using cold.
Read 9-ways to save with water heater
How to maintain water heater
Solar water heater
Solar water heater collectors near water heater
Requires 2-3 panels to circulate water into storage
Proper tilt angle for solar collectors is latitude plus 15.
Performance suffers little when collector oriented no more than 45 East or West of True South.

Compare: with photovoltaic array
Photovoltaic array
Photovoltaic array uses more panels, produces electricity, panels located on ground, can be further from home
Larger image
Resale of house/ appearance
4) Call real estate agent about solar rooftop systems.
Agent can tell you if solar must be removed before resale
Some areas, solar will increase resale value of home
Appearance of home can be altered with panels and pipes. Visit another home with similar solar installation.
Solar investment is not mobile
If family moves frequently, can you afford to invest in expensive water heater?
Local codes
5) Contact permit board to see what permits are needed.
Local neighborhood may not permit solar panels.
Reason, solar panels on roof can detract buyers or attract buyers depending on market.
Solar collectors on roof
Usually the recirculating solar system [being reviewed here] requires 2-3 collectors located close to storage tank.
2 panels for Hawaii. 3 panels for less temperate regions.
Proximity to water heater is important so small pump can circulate the water.
Rooftop installation not required... but hot water rises, so elevating panels above storage tank is better.
PV electric collectors on ground
PV electric systems usually require more collectors, or more panels, but collectors can be on the ground farther away from water heater. PV electric loses power when more distance is added. Use larger wire for panels located farther away.
On average, PV systems last longer than solar thermal systems. PV lasts about 25 years.
PV system works better in cold weather than warm weather. Reverse of recirculation systems.
Lightning/Storms/High winds/ 
6) Do you have lightning rod?
Copper pipes and metal on roof attract lightning
Use lightning rod system in areas where lightning is common.
Risk of lightning is higher when home is near pond, high elevation, or sitting alone.
Higher structures or multiple structures nearby, will reduce lightning risk.
Lightning within 100 feet can damage any home not protected by lightning rods.

Lightning safety
Move indoors and do not stay on roof, or move metal ladders, or touch anything made of metal when lightning is within 5 miles or can be heard or seen.
Baseball/ Tornado/ water leaks/ are additional risks
How to install whole house surge
Bond solar panel to ground rod Ground wire/// this information applies to all water heaters and appliances
All solar system must be grounded. Check local electric codes.
What does this mean? Drive ground rod 8-10 feet into soil. Bond #6-8 bare copper wire to ground rod and to solar panels and pipes on roof.
Do NOT ground electric system to water pipes. Ground must be connected to ground rod. Stray current corrosion can cause pipes to deteriorate. Uncertain bond to ground because of plastic pipes.
Ground rod and clamps at Amazon
Bonding lugs
Bond all ground wires together to help prevent surge & lightning damage
Bonding all grounds together will help prevent damage from lightning strikes beyond 100' away...
Strong lightning strikes within 100 feet must be handled by lightning rod
Local code requires bonding: this includes all ground rods for satellite, TV, phone, solar, electric panel, subpanels (within 100 feet) etc must be connected together and bonded to main electric panel ground rod driven into soil at correct depth to meet local code. Consult local electrician.
Codes for grounding depth vary: loose rocky dry soils are less conductive than dense wet soils
No system other than lightning rods will protect against direct lightning strike or strike within 100 feet.
Move indoors and do not stay on roof, or move metal ladders, or touch anything made of metal when lightning is within 1 mile or can be heard or seen.
Clean solar panels

Old ropes are NOT safe
Always use new ropes.

8) Ask seller and installer about required maintenance. Maintenance is required.
Solar panels do not clean themselves. And solar panels are located on roof.
Dirty solar panel will absorb less heat.
Trees, leaves, roof repairs
Do NOT believe salesman who says no maintenance needed
Can you maintain the system yourself? Can you find somebody locally who can maintain the system?
Do not buy complex systems if local area does not have affordable, experienced service people.

Roof leaks
We occasionally fixed roof leaks caused by solar panels
Contact local roofing company and ask their experience
Roof replacement
If roof needs to be replaced, then work has to take place around panels
This increases cost, chance of leak, damage to panels
Solar panels on roof
Move indoors and do not stay on roof, or touch metal ladders, or touch anything made of metal when lightning is within 1 mile or can be heard or seen.
7) Call insurance company and ask if homeowner insurance covers external solar panels.
Do you need special insurance?
Are the installers insured?
Who will repair and maintain system, how much will it cost, and are you covered from liability?
If you are climbing on roof once each year to clean solar panels, what is cost of one broken leg?
Do you have to buy ladders?
Take apart extension ladder, and you have 2 ladders
We use two aluminum ladders chained together to climb down sides of roof.
Best way to get on roof is along the pitched side. Set ladder at angle, as illustrated with wooden ladder, so both ladder feet are flat on ground, then set ladder at angle until both rails are flat against roofline.
This is counter-intuitive to set ladders this way, but very effective and safe.
We also used ropes to secure ladder from falling over, we also made one ladder leg longer on aluminum and wood ladders by adding stout 2x4 or 1x4 yellow pine.
When setting ladder against gutter... use wire to tie ladder to gutter nail. Set bag of dirt behind ladder feet.
When setting ladder on grass or dirt, turn the feet so they stab into soil. Dig small holes for feet.
Choose grass-dirt over concrete surface when setting ladder.
Never set extension ladder on wet concrete, or concrete that slopes away from ladder. Sweep surface clean.
Never set extension ladder on tile surface without full bracing behind feet. Higher person climbs, less stable ladder.
Always make sure 4 points of ladder touch... 2 feet firmly at bottom and 2 rails firmly at top
Ladder safety How to check extension Ladders
Extension ladder has several parts: 1) Rung locks, 2) anti-slip safety feet, 3) Slide rails, 4) Base rails, 5) Rungs etc
Do not use ladder that is bent.
Check the bolt that connects rung lock to ladder. Look for cracks in aluminum rail... add fender washer to strengthen
Check if bolt is bent excessively. Must use hardened bolt.
Always check that rung lock is over both rungs.
ALWAYS make sure both rung locks are in place.
Treat your ladder like it was airplane... you are the pilot... inspect plane BEFORE flying
Ladder replacement feet with hardened bolts
Aluminum ladder leveler for uneven ground
Safety step ladder
Ladder parts and stabilizers at Amazon

Galveston 2015
Solar panels block sun from hitting roof
Solar panels on roof will reduce temperature of roof in winter
Attic is cooler in winter. Furnace runs more
Warm attic helps keep house warm for many hours after sun sets in winter climates
Tropical climates such as Malaysia and Hawaii might benefit from reduced solar on roof, while homes in Indiana might not benefit
Wind blows away solar heat Wind
Windy location will cool the glycol solar collector.
Result less solar heat/ less hot water circulates into storage tank
Manufacturer's glossy brochure does not consider heat loss from wind
Compare: PV photovoltaic panels, that produce electricity, benefit when wind cools the panel
Wind damage
Surprisingly, panels located on ground are more susceptible to wind damage and wind effect from many directions
solar water heater pipe
Use new pipe
Use as few elbows as possible
Keep solar panels close to water heater

Distance between collector and storage tank
Locate collection panels as close as possible to storage heater.
Longer distance means loss of efficiency when pump is circulating water, and loss of heat along length of pipes.
Heat travels upward, so best if panels are located above storage heater.
Number of elbows
Number of elbows and bends in pipe affect efficiency of recirculation pump.
Use long sweep elbows.
Diameter, condition, distance, and configuration of pipe effects overall efficiency
Prevent electrolytic corrosion/ deterioration of galvanized pipes and clogs. Use brass and stainless when connecting copper and galvanized pipes. Use 6 wraps teflon tape on threads
Brass nipples at Amazon
Brass elbows at Amazon
Stainless nipples at Amazon
Stainless elbows at Amazon
Water pump and pipe distance information
water heater sediment Heated water and sediment deposits
All heated water leaves behind mineral deposits.
Higher temperatures, and harder water cause more deposits.
Water heated in excess of 140 will percolate many minerals out of water
Heated glycol does not leave behind deposits in the collector.
Water circulation system will leave behind deposits in the collector and heat exchanger.
Storage tank and heat exchanger can become coated with sediments using either water or glycol system
Treating hard water costs money
Water softener may be required, or other water treatment.
For example, a conventional electric water heater can be used without water softener because elements can be replaced for $12, and tank cleaned out inexpensively.
The solar collector and solar heat exchanger are not as easy to clean as ordinary electric water heater.
Consider cost of water treatment.
Anode rod.
All metal tanks require anode rod to prevent tank from rusting. Includes solar tank.
Water softener causes anode to deteriorate faster.
Read about anode rods
Prices Price: Total price must include installation, anticipated maintenance, parts, repairs, expected life of unit, depreciation or appreciation on resale value of home
9) Ask for the total price up front.
Ask if glossy literature showing huge savings also includes cost of running circulating pump, cost of maintenance, cost of repairs, and cost of system replacement in 12-14 years.   (Hint: glossy brochures do NOT include these costs)
All costs are energy
Look at the parts sheet. What do replacement parts cost? Who carries the parts 5 years from now?
Who is going to climb roof and clean solar panels
Does insurance cover solar panels
Do you have lightning rod to prevent major damage caused by lighting coming down copper pipes on roof
Are you going to sell house?
Payback 25-35 years Payback 25-35 years? Do the math.
If the system costs $4000-6000 and saves year-round average $15-20 per month, then it will take 300-400 months to pay back, or 20-30 years.
Do not believe promotional claims that show savings more than $15-20 per month.
Your actual savings will be less than $15 per month, depending on how hot water is consumed.
Go full solar/ no back-up Payback 10 years if you go full solar and no water heater expense
10a) If you accept solar-only hot water, then you can save full cost of water heating... for example save $400-600 per year, then payback is quicker.
Do it yourself solutions are cheaper, and maybe best for you
Who covers warranty? 
Manufacturer, seller, installer? 
Probably You !!
You know the problem. Call for warranty never returned. Buck is passed
You paid for system and paid the installer before the system was tested at your home.

Make sure it works before you pay: Test drive the car first.
Get references, do not strike deal where seller and installer get paid before the system checks out 100% equal to promise.
Which means you better do the research and compare against similar installations IN YOUR AREA before buying expensive solar water heater.
Be a negotiator. If they want your business. And they are truthful about saving money at your home ... then they can wait to be paid.
Get it in writing.
High Temperature at high noon High Temperature at high noon
 11) Solar can reach temperatures of 180 midday summertime, assuming solar panels are clean
Ordinary water heater temperature is 120-135
Residential electric water heater thermostat range 90-150/ commercial thermostat 120-180
See residential and commercial thermostats
This high solar temperature is only available at peak solar heating, and not during hours when you usually consume hot water.
The very hot water from noontime continues to circulate through solar collector, and cools during this circulation unless temperature sensors stop the circulation pump.
All tanks lose heat to standby... just like cup of coffee cools.
Adding insulation will benefit all tank-type water heaters: residential, commercial, storage, indirect, tempering, gas, electric, oil, solar, geothermal
Water cools rapidly Water cools rapidly
12) Solar heat dissipates very quickly. Test this yourself with 1 gallon water left in sun.  Once fully heated, put gallon inside insulated picnic cooler located next to water heater and check temperature 1 hour later, then 5 hours later. Is the water still warm? Is it hot enough to use for shower? Probably not. Pour it on hand to gauge temperature.
Take showers early evening, and do not wait between showers Shower instead of bath extends solar heat
Shower uses 5-9 gallon hot water. Bath uses 12-15 gallon hot water.
Oversized bathtub, and spas are 'against the law' when considering energy-saving.
Shower is much more economical than bath in general terms... economic factors vary when two or more people bathe simultaneously by candlelight with lights and TV turned off.
When hot water is run from tank, then cold water immediately enters bottom of tank, causing tank to cool more rapidly, or causing electric element or gas burner to fire up.
To consume solar hot water, it is best to consume all the collected hot water at once with several showers in quick succession, before tank cools. This applies to off-grid applications that use only solar, and do not use fuel to heat water.
How much hot water does bath or shower use
Time and temperature Most hot water consumption at night or morning, after solar heat is gone
14) Consider: If you consume most hot water in late evening or early morning, the solar-heated water will be dissipated at those times, and water is being heated by conventional fuel. This means solar heating system is only saving standby cost during daytime hours. Standby cost is small, and does not warrant expensive solar heater.
When hot water is consumed during late evening or early morning shower, new cold water immediately enters tank and the new cold water must be warmed by conventional fuel. Heating incoming cold water is biggest factor in water heater cost, so if no hot water is being consumed at peak solar output, then water heating cost is minimally solved by using solar.
EXCEPTION: large 80-120 gallon solar water heater that was fully heated during day to temperatures in excess of 140-150. The tank is well-insulated, and located in naturally warm spot. The circulation pump stopped circulating when tank was fully heated at maximum temperature. The system is working right. The hot water was not consumed accidently by water leak. Mixing valve was added to top of tank to sip hot water and keep cold water from entering tank (described above), etc.
Honeywell mixing device Key thing for solar water heat is Make-when-it's-there and Sip-it-when-it's-not
Add mixing valve to save hot water. Important for solar. Also for regular tank.
Solar tank gets very hot during good solar day.
You do not want super-heated solar water for shower.
Mixing valve located at storage tank can be set to correct temperature for shower.
Mixing valve automatically adds cold water to the line so temperature of shower is correct.
How does mixing valve save hot water?
Remember, a mixing valve is exactly what you do during shower to keep temperature from being too hot... you add cold water to hot.
So each faucet; bath, kitchen, shower and tub faucet is a mixing valve... where you manually adjust water temperature by adding cold
Each time hot tap is turned on, cold water immediately enters bottom of water heater as hot water leaves top of tank going to shower..
When you use mixing valve located at water heater instead of mixing valve located at shower, then you save the amount of hot water that travels down the pipe going to shower.
How much hot water is saved? Every 10 feet of 1/2 pipe holds .12 gallons of water.
If bathroom is 20 feet away. 3 showers per day .72 gallons per day x 365 days = 262 gallons of cold water that does not enter tank.
The math is more complex than this 2-D example. But a mixing valve keeps more cold water out of tank, and water heater stays hotter
Buy from my affiliate links:
Mixing valve kit at Amazon
Water heater mixing valves at Amazon
How much hot water does bath or shower use
Special tank needed
Ordinary tank not rated for solar heat?
Solar tanks are made for high heat / solar temps can reach 180
Solar tanks are large: 80-120 gallons/ Let's you store hot water so it is available later
Residential water heater thermostat range is 90-150/ commercial thermostat range 120-180
See residential and commercial thermostats

Ordinary residential water heater tank cannot be repeatedly exposed to 180 temperatures without causing damage to tank. Residential tanks come with TP valve that releases water at 150. Exception Marathon heavy-duty with 5 year tank warranty is rated 175
Solar water heating tanks, and many commercial water heaters are rated for temperatures equal to 180
This mean solar requires special tank, and/or tempering valve that moderates temperature entering tank
Specialized parts are needed
Absolutely be aware that 180 temperatures can cause immediate life-threatening burn.
Full solar/ off grid/ 
Unpredictable hot water supply
Full solar without backup fuel
15) If home is using only solar to heat water, and no back-up fuel source is used, then solar system will save full cost of operating water heater.
But ordinary 120 hot water temperatures will not be available each day, or available all hours of day.

Off-grid full solar rations hot water to yourself
Basically the all-solar strategy saves money by reducing consumption, which you can do without buying expensive water heater.
Why install expensive water heater just to ration hot water to yourself, when a water heater timer, or DIY solar collector can do exact same thing for less cost?
Summer Summer is best for solar... but also best for ordinary tank
17) Solar works better in summer ... but so does ordinary water heater.
Ordinary water heating energy bill in summer months is much lower because incoming water temperatures are warmer.
This means water heater does not have to raise temperature as much to reach thermostat set point.
Summer months are best for solar water heater, but they are best months for conventional water heater too. 
See family charts
Add a tempering tank to preheat incoming cold water during winter
See passive tempering tank
Winter Winter without much solar heat
16) Solar water heaters will not generate much heat in winter in non-tropical regions.
How many months long is your winter?
How many cloudy days vrs sunny days? Southern Indiana winters are cloud covered.

Check weather almanac
Check weather archives for average temps, and understand that 'average high temperature' in winter might be 40, but the high temperature only lasts 1 hour of the day.
Winter preparations? Winter preparations? Requires planning and work
18) Ask if the system must run full-time in cold weather to prevent freezing.
Or if you have to drain system.
What are maximum low temperatures for equipment.
How sluggish is the glycol when very cold?
Will freezing temperatures affect wires and connections?
If the system has non-freezing glycol, what is low temperature limit, and what will happen if there is a leak on roof.
Ask if the system has automatic system to keep cold water from entering tank.
If system must circulate full-time to avoid freezing, then cold is circulating inside tank, and tank must use conventional fuel to warm the cold water.
If the system has a heater, ask how much power the anti-freeze heater uses.
Do you have to drain the system each winter?
If the solar heating pipes must be drained each winter, can you do the work?
Call others in same area with same installation Call other people in same area that have same equipment.
Ask if you can visit their location and see how their set-up would differ from yours.
For example if they are in sheltered valley and you are windswept hillside.

Wind will cause solar collector to average cooler temperatures
Parts Parts: Look at parts sheet, ask about replacement parts
19) Ask to see parts sheet to estimate general complexity of system.
Don't look at parts shown on glossy brochure, look at the replacement part list.
If there is no parts sheet available how are you going to get parts? Do you want to become a solar water heater expert.
Web search the parts before buying. There are all kinds of experts out there, each more knowledgeable than the next..
Maintenance and repairs are major factor in calculating costs. All costs are energy.
Ask about expected lifespan of each component part.
Ask which parts you should have on-hand in case of breakdown.
Part replacement Part replacement
20) Pumps, and other parts can become expensive to buy and repair.
Ask for price sheet for each replacement part, and ask who will carry the part when you expect part will fail.
Can you do the repairs yourself.
Who is available in your area to climb on roof and do repairs? In winter during snowy month.
Lifespan How long will the system last?
Do you really think it will last 13-20 years? Can you afford to buy another system a mere 13 years from now when prices are double or triple? Maybe prices will be the same? Maybe new local methods will be the answer?
Can your remaining spouse handle replacement installation, repair, maintenance, etc associated with rooftop solar collector over the expected lifespan of product

No particular reason why things happen ?
Cleaning solar panel/ maintenance
Can you make repairs and do the maintenance?
Trim tree limbs, wash panels, clean off leaves and debris, patch roof leak..

Do you want holes and pipes on roof?

Does insurance cover roof and solar panels injury?

Some day the solar heater will need to be replaced ... which is why most home resales require removal of solar system. There is no standard checklist for appraiser or inspector to check solar system.

While you're up there...
Tuck point the chimney
Coat the top with sealant
Crown saver chimney coating
Cleaning solar panel
Yes I've done this
Old ropes are NOT safe
Always use new ropes.
Passively preheat incoming cold water
Use old water heater as tempering tank.
Set tempering tank in naturally warm location

How to recycle water heater
Which is best gas water heater
How to install gas water heater
How to install electric heater

Increase amount of hot water

Add another thermostat to water heater
Tempering tank
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