Solar water heater

[willem wikkel spies]

Hello world, lol.
Had a hick-up with a kidney stone, so was out of action for a while.
but let me give you some more info.

i choose a 2000 watt heating element for a reason.
the panels maximum/ peak current is 13 amps, so working rather on a average instead of peak power.
a 2000 watt heating element current draw is a mere 8,7 amps.

this does leave one soem space to work with, but the down side to it all is, that even if one had 13 amps available, the heating element would only consume 8,7 amps current.
one cannot force current down the tube................................

so, i ended up with 6x 550 watt Canadian solar panels. we have tiled roofs, so around 30 degrees.
all connected in series and facing east words. i have been thinking of placing 3x panels facing east and 3x panels facing west.
this could assist with cloudy mornings or something.
my worries were that, even though, the panels are not shaded, what effect will it have, when the 3x panels facing east has no current through them "afternoon", but the 3x panels facing west "afternoon", might have real good current through them. moving them can easily be done, but one needs double rails. ahh lets just leave it.
the 6x panels in series configuration gave me 240 volts dc.
so i had the volts and amps to run a heating element to its capacity.

i then sourced a plastic drum which i filled with 200 liters of water.
the heating element was placed at the bottom of the plastic drum with no insulation.

i used a temp probe to monitor the water.
night temperature the water went down to 30 degrees Celsius "evening temps currently is around 22 degrees and day time is around teh 30 deegree mark.

so i ran the system and found that the 2000watt heating element would heat up the water in the drum to around 59 degrees.
it was clear that the path was good and level.
even on some cloudy days, the water temp went up to around 58 to 60 degrees.

my whole family has been following this project, so it has been fun.
the system was run for about two weeks up until i was happy to move it all over.

on Saturday, i completed the change over after sun set, the only difference is that the existing heating element is a 3000 watt.
so panel series voltage has dropped down to 210 volts dc, the current draw on a 3000watt heating element is 13 amps, which means peak current is needed to run it good. will do some calculations later on.
by 10:30 the water is already 75 degrees and the system switches off until it reaches 60 degrees whereby it switches on again.
i have had some hot water for sunday night, as well as monday night "`tonight".
im still doing some tests, so i will give you guys another update is a week or so.
for now, im happy.
all is good and now we will see how nature will heat our water.
stay safe.

 

[willem wikkel spies]

Math doesn't lie.

Why don't you take an array / heater element and calculate the the power going from 10A down every couple amps.

People hook up a couple panels to a charge controller and battery and think it is easy. The way to really understand solar is by heating water.

im too far beyond it.
what i can do now, is to check the 3000 watt heating element and see how it performs, and then decide if i need to revert back to the 2000watt heating element.

 

[willem wikkel spies]

You are not dealing with independent variables.

If the resistance is fixed (and with the exception of some variance with temperature it largely is when inside a tank of water), and you apply (and can sustain) a given voltage across the resistor, then current (and power) will be what it is,
i.e.
I = V/R
P = V²/R

So if you have a 26.7 Ω resistor and apply and can sustain 240 V across it, then:
I = 240 V / 26.7 Ω = 8.99 A
P = (240 V)² / 26.7 Ω = 2,157 W

You can't just magic 10 A in the circuit.

To increase the current and/or power you either have to increase the voltage, reduce the resistance, or both.

Note the use of the phrase "and can sustain" with respect to voltage. If a supply cannot sustain the voltage, then you are dealing with different issues.

The reason for the 2000 watt heating element was to be in the middle, rather then peak, which one could only get for a very short period of time.
the panels can give a maximum of 13 amps when the stars align. but i was rather looking at a midpoint on teh panels.
average as advised earlier in this tread.

 

[wattmatters]

by 10:30 the water is already 75 degrees and the system switches off until it reaches 60 degrees whereby it switches on again.

Is the thermostat controller rated for switching DC?

 

[Daddy Tanuki]

what are everyone's thoughts on using a heat pump water heater? here in Japan there are plenty of used heat pump water heaters on the market.
a friend who is a licensed A/C & R tech here explained to me that the Japanese units have a heat exchanger built into the compressor/fan side (the box that sits out side with the compressor etc. in it), and that theoretically any tank could be used.
If they used standard freon based refrigerants they were limited due to the gas itself of about +50 to+60°c where as if i got one that used CO2 as the refrigerant they were good up to about +80°C they also come with a programable timer that allows them to run only when you want (TOU setup)

so take a look at this tank in the photo, i just won it on yahoo auction. It is a 1700 liter insulated tank used to chill milk down. it has 1" of the blue type foam cast between the interior stainless wall and the exterior stainless wall. my thought was to pour a pad, and then build an enclosure around this adding more insulation to the exterior. originally I wanted a bigger tank (12,000 liter) but could not afford one and it would not be insulated so i think this size is perfect for my experiment.

run it for 2-4 hours per day starting at a time when my batteries are at about 80% charged and let it run till the sun starts to drop or my batteries discharge to say 70% i would need to play with it a bit to find the sweet spot between production and battery SOC against what my panels can produce.

and lastly no resistance heater, the heat pump would always be working at its peak efficiency and would just be skimming off the top bit of power which is not an issue for lithium cells as they do not need to be charged to 100%

that or i could go the resistance heater route. thoughts?

 

[Daddy Tanuki]

so tank is bought and paid for. Next is the waste oil burner for emergency heat when solar is not enough. I have a CO2 cylinder which will make up the core of the burner. I have a kerosene forced air burner that will be the light off assistant. after that it is up to the waste oil to provide the needed heat.

I will provide photos as this project advances. solar will be (at this point) two heat pump water heaters, that run from 1100 to 1500 when solar is at max with a limiter of 53 volts on the pack.

So when batteries are at 53 volts the two heat pumps will run off of a Sigineer 5kw HF inverter at 230 volts on a timer that is built into the two heat pumps.

If voltage is below the target of 53 volts a relay will interrupt the heat pumps and not allow them to turn on.

If its above 53 the heat pumps will run until there timer shuts them off or until the voltage on the pack drops below 53 volts. So figure about 3-4 hours a day.

This will take some observation to get the cut off points correct, but the longer I think about this the more I am sure that analog controls will be better than iffy digital controls. This is very location dependent as WF and BT are not available at the location.

 

[Daddy Tanuki]

so no thoughts on this at all? disappointing. I just received two of the grundfos pumps I need to ensure circulation... used of course.. I am all about recycling. third (spare) is on its way as well. next is to procure the two heat pump water heaters and move on.

 

[Zwy]

so no thoughts on this at all? disappointing. I just received two of the grundfos pumps I need to ensure circulation... used of course.. I am all about recycling. third (spare) is on its way as well. next is to procure the two heat pump water heaters and move on.

I installed a 50 gallon heat pump hybrid water heater ahead of the 50 gallon propane in series and turned the temp setting on the propane lower than the heat pump water heater. I don't need a circulation pump.

I'm seeing less than 2 Kwh of power drawn by the heat pump water heater. It took 6.2 Kwh to heat the whole 50 gallon tank from about 60°F to 140°F on the initial run. I've since turned water temp down to 130°F. Water temp out of the faucet is about perfect.

The heat pump water heater draws such a minimal amount of power in a day that I can't see spending much time trying to dump load it. Just heat the water and forget it. Wife has done laundry everyday since the install plus normal usage such as showers and hand washing pots/pans too large for the dishwasher.

If it was winter and I had excess with cloudy days ahead, I might run the electric element and crank the tank temp up to 140°F using the app to gain a little extra hot water to power thru. With 100 gallons of hot water and we don't do laundry when it is cloudy for extended days, I doubt it would be needed.

As for heat pump water heater efficiency, the efficiency goes down as tank water temp increases due to Delta T is narrower. One thing I don't like about your bulk milk tank is it is not completely sealed. That creates a problem of evaporation and the heat loss in that water vapor. Second is Legionella, you will need to ensure your water temps remain high enough to prevent Legionella growth.

 

[willem wikkel spies]

Is the thermostat controller rated for switching DC?

So we have loadshedding in south africa, which means is that there is a green drive to install solar systems.
and some political reasons behind it.
so i cannot rely on our electrical supply from council as we might have a power outage when the sun is shinning at its best.
so, in any case,
i have 2x w1209 controllers which is use to check tank temperature.
1x is fitted inside the thermostat which is close to the heating element.
the other is fixed to the outlet copper pipe.
so temp difference is around 6 degrees between the two.

i have a separate 24volt solar system, which is brought down further to 12 volts.
so i run all my security equipment from the system as well as wifi, and some 12 volt led lights.
so currently im not concerned about our load shedding.

the w1209 are used to activate a 12 volt coil contactor.
its a old contactor i have, which is working perfectly fine.
will the contacts fail, yes they might fail. or eventually will.
so even if we have loadshedding present, the contactor is still in operation, which means, i have heated water.

tank maximum temp is set to 75 degrees Celsius.
in future i will connect both w1209 in series, to make sure i have a fail safe system
its still very easy to understand and operate.

since 3 march 2024 the system has been running, without any troubles.
every night we have very hot water.
even on some cloudy days water is too hot.
sun rise now is around 06:00 in the mornings and by 10:30 the contactor is switched off as tank temperature is 75 degrees.

maybe some waiste with electricity produced, but what the heck, i will get it to work somewhere else in future, i believe.

regards

 

[wattmatters]

I guess if the external DC rated controllers are doing the load switching at water temperatures which are somewhat less than the tank's thermostat set point, then presumably the thermostat switch is always closed which would help minimise chance of failure.

I still think a DC rated thermostat switch would be prudent.

 

[efficientPV]

All your requirements and can use existing inline mechanical thermostats without arcing issues.

 

[NIFE]

what are everyone's thoughts on using a heat pump water heater? here in Japan there are plenty of used heat pump water heaters on the market.
a friend who is a licensed A/C & R tech here explained to me that the Japanese units have a heat exchanger built into the compressor/fan side (the box that sits out side with the compressor etc. in it), and that theoretically any tank could be used.
If they used standard freon based refrigerants they were limited due to the gas itself of about +50 to+60°c where as if i got one that used CO2 as the refrigerant they were good up to about +80°C they also come with a programable timer that allows them to run only when you want (TOU setup)

so take a look at this tank in the photo, i just won it on yahoo auction. It is a 1700 liter insulated tank used to chill milk down. it has 1" of the blue type foam cast between the interior stainless wall and the exterior stainless wall. my thought was to pour a pad, and then build an enclosure around this adding more insulation to the exterior. originally I wanted a bigger tank (12,000 liter) but could not afford one and it would not be insulated so i think this size is perfect for my experiment.

run it for 2-4 hours per day starting at a time when my batteries are at about 80% charged and let it run till the sun starts to drop or my batteries discharge to say 70% i would need to play with it a bit to find the sweet spot between production and battery SOC against what my panels can produce.

and lastly no resistance heater, the heat pump would always be working at its peak efficiency and would just be skimming off the top bit of power which is not an issue for lithium cells as they do not need to be charged to 100%

that or i could go the resistance heater route. thoughts?

View attachment 200130

Are you trying to heat the water in the tank? If so, some refrigerant system re-plumbing would be required. As purchased, I think the way this works is the refrigerant extracts heat from the milk and gets rid of it through the heat exchanger built into the compressor. They must use domestic water to carry the heat away from the heat exchanger, perhaps to drain. . The tank also is not sealed nor designed for pressurization. That looks like a milk stirring motor on top.

 

[Daddy Tanuki]

Are you trying to heat the water in the tank? If so, some refrigerant system re-plumbing would be required. As purchased, I think the way this works is the refrigerant extracts heat from the milk and gets rid of it through the heat exchanger built into the compressor. They must use domestic water to carry the heat away from the heat exchanger, perhaps to drain. . The tank also is not sealed nor designed for pressurization. That looks like a milk stirring motor on top.

yes that's exactly what it is and how it "worked" as milk tank.

The Japanese heat pump hot water heaters use a heat exchanger built into the heat pump and pump water from the tank, through the heat exchanger, so any tank will work.

This "milk" tank is insulated with 1.25"+ of xps foam between the stainless steel inner and outer shell. so two of the heat pumps with their built in heat exchangers heat the "demineralized water WITH ANTIFREEZE" in the 1700 liter tank. (this is important as most of these heat pump water heaters die due to scale buildup from hard water. (heat exchanger gets plugged, stuff burns up)

You then you create your own heat exchanger in the 1700 liter tank (stainless coils inside the tank with bulkhead fittings) one loop goes directly into your house hot water heater (mine is an on demand propane type. if the water is hot enough, the burners will not come on. If its cold in any fashion the unit will adapt its water flow as well as gas flow to bring the water temp to the desired setting. so pump 40°c water in and if you unit is set at 40 the heater will not come on. pump it in at a lower temp and it will come on as much as is needed.

flip side take a second heat exchanging coil and run it into either radiators or pex pipe and heat the house.

Questions, thoughts, concerns?

I am asking you all to critique the thought process and concepts. so I will attempt to shoot down your objections. this is part of the scientific process that so much of the US ignores these days. ask for criticism and see if your answer eliminates the problems.... think tank style.

 

[NIFE]

yes that's exactly what it is and how it "worked" as milk tank.

The Japanese heat pump hot water heaters use a heat exchanger built into the heat pump and pump water from the tank, through the heat exchanger, so any tank will work.

This "milk" tank is insulated with 1.25"+ of xps foam between the stainless steel inner and outer shell. so two of the heat pumps with their built in heat exchangers heat the "demineralized water WITH ANTIFREEZE" in the 1700 liter tank. (this is important as most of these heat pump water heaters die due to scale buildup from hard water. (heat exchanger gets plugged, stuff burns up)

You then you create your own heat exchanger in the 1700 liter tank (stainless coils inside the tank with bulkhead fittings) one loop goes directly into your house hot water heater (mine is an on demand propane type. if the water is hot enough, the burners will not come on. If its cold in any fashion the unit will adapt its water flow as well as gas flow to bring the water temp to the desired setting. so pump 40°c water in and if you unit is set at 40 the heater will not come on. pump it in at a lower temp and it will come on as much as is needed.

flip side take a second heat exchanging coil and run it into either radiators or pex pipe and heat the house.

Questions, thoughts, concerns?

I am asking you all to critique the thought process and concepts. so I will attempt to shoot down your objections. this is part of the scientific process that so much of the US ignores these days. ask for criticism and see if your answer eliminates the problems.... think tank style.

What is the heat source for your heat pump?

 

[Daddy Tanuki]

What is the heat source for your heat pump?

ambient temps, hence the waste oil burner as a back up for Jan~early April. I can get free used engine oil from 10 different locations... they have to pay for disposal. I will be using a drip with forced air system, so no filtering needed, just drip down into the center of a hot enough fire and it will flash into combustible vapors and repeat the process.

 

[NIFE]

ambient temps, hence the waste oil burner as a back up for Jan~early April. I can get free used engine oil from 10 different locations... they have to pay for disposal. I will be using a drip with forced air system, so no filtering needed, just drip down into the center of a hot enough fire and it will flash into combustible vapors and repeat the process.

A line diagram or more photos would help. I am assuming the compressor is part of the tank assembly and just not shown in your photo, or does the tank have a remote compressor? Are those 4 or 5 tubes in the Post # 80 photo electrical conduit, refrigeration lines, water pipes?
Below is a tank with a built in refrigerant system.

 

[Daddy Tanuki]

A line diagram or more photos would help. I am assuming the compressor is part of the tank assembly and just not shown in your photo, or does the tank have a remote compressor? Are those 4 or 5 tubes in the Post # 80 photo electrical conduit, refrigeration lines, water pipes?
Below is a tank with a built in refrigerant system.

the tank is now a bare tank with no cooling lines attached. the plan is to replace the original cooling system with two heat pumps and plumb them separately as earlier stated. it is a tank nothing more. the heating will come from separately plumbed hot water heat pumps.

 

[Zwy]

Is this for domestic hot water or heating purposes?

 

[Daddy Tanuki]

Is this for domestic hot water or heating purposes?

both. initially hot water, then a test run to see how much heat can be produced under the house for pipe freezing issues. then later mini radiators for heat. on step at a time. originally I wanted a 12,000 liter tank. as this was not in my price range, I decided to try a much smaller tank as a test run.

 

[Zwy]

both. initially hot water, then a test run to see how much heat can be produced under the house for pipe freezing issues. then later mini radiators for heat. on step at a time. originally I wanted a 12,000 liter tank. as this was not in my price range, I decided to try a much smaller tank as a test run.

With a high temp emitter such as a radiator, you might need 140°F or higher water temp. There are some lower temp emitters out there like fan coils. The trouble with using a heat pump with high temp emitters is the heat pump may need to be 2 stage in order to get the temp high enough. Something like infloor radiant is well suited for use with a heat pump/buffer tank as water temp can be 100 to 120°F.

120°F domestic hot water could lead to Legionella growth, even though you see that temp commonly used with heat pump water heaters. It depends on whether any stagnant water is present or if temps exceed 130°F on occasion. Open to atmosphere might present a problem with 120°F water. You can overcome this by running higher water temps with thermostatic mixing valves to the loops. My biggest concern is running water thru a heat emitter and return water is mixed into your domestic hot water. I wouldn't do it myself, I'd use coil or plate heat exchanger so the 2 systems are separate.

 

[Daddy Tanuki]

basic plan was for a heat exchanger loop of stainless piping inside the tank for potable water. under house and in house heating would be direct from the tank, with a 80/20 coolant mixture to avoid freezing/corrosion/bacteria if conditions went that far. the plan is to hold the tank in the 80-90°c range so legionella is not a concern.

heat pump when extra solar is available (all summer long) then waste oil burner in the coldest of the winter months when the HPWH would not be feasible/keep up. I am also considering two 2400 watt hot water elements for the winter. depending upon heat pump style some of them have these already installed.

The system i am looking at use's CO2 as refrigerant so they run the temps up to 90 centigrade and you use a tempering valve to lower it to safe temps. As such the under house heating would be whatever the max the system can output and the hot water for household consumption would be run through a tempering valve to regulate it down to the level wanted.

 

[Brett V]

@Daddy Tanuki … interesting topic. I get the concept but much of it is over my head. Some of it reminds me of a oil fired system in a house I once lived in. The oil burner heated a low pressure water tank that circulated with a pump through a series of baseboard radiators. Potable hot water was pulled from a separate coil inside the tank using the homes water pressure in an on demand basis. Very efficient and reliable system.

 

[Daddy Tanuki]

@Daddy Tanuki … interesting topic. I get the concept but much of it is over my head. Some of it reminds me of a oil fired system in a house I once lived in. The oil burner heated a low pressure water tank that circulated with a pump through a series of baseboard radiators. Potable hot water was pulled from a separate coil inside the tank using the homes water pressure in an on demand basis. Very efficient and reliable system.

basically the same idea but using a waste oil burner vice heating oil. I can go collect waste oil for free from many locations so the fuel itself is free. its just designing the system with controls that make it as autonomous as possible to eliminate me needing to tend it.

 

[willem wikkel spies]

So its still running. had to use all the hot water the other day at 12:00 o clock, by 17:30 the water was at 68 degrees.
i have only used 30 units on my electrical bill this month.
so a big middle finger for our eskom from my side!!

 

[The Terrible Triplett]

I’m wanting to put a couple of solar panels on to outbuilding roof and use output to heat immersion heater for domestic hot water ( I have boiler backup)
I don’t want a grid tied system - completely standalone
I want to keep the existing 3kW element as I don’t think it will come out of the cylinder!
Don’t want batteries- just want to feed the output via inverter direct to immersion
Is there an inverter that will do this?
Anyone done it?

What I realized, if you put up solar panels to heat a geyser, that geyser will be heated in a couple of hours.

So what then happens with the panels?

So a penny dropped ... get a Solis grid-tied inverter, slap the panels on it, connect it to the main DB, put in a timer for when to switch the geyser on, like a Shelly relay that gets one very far ito what time/s to come on and with a temp sensor, for when to switch on/off if the geyser temp is too low/high, and one can automate it all.

Can even use Home Assistant/NodeRED if that is ones flavor.

Then when the geyser is heated, when the solar panels are sitting idly on the roof, use that free power for other loads in the house.

My 2 cents.