Water heating through SCC

[v_green57]

I have read that directly connected does not utilize all the power the panel can produce due to amp rise / voltage lost as it will pull all the amps the panel can produce lowering voltage so I was hoping that would be possible with just a controller and a panel. Looks like not.

The best way to "optimize" would be to have a resistive load that dissipates max. power at or near the voltage you are able to supply,

Batteries of any kind present a completely different type of load than a resistive heating element. I'm not sure how the MPPT algo that's designed to see a battery would treat a purely resistive load. That algo wants to see the voltage of the battery bank as a basis for optimizing the panel output. A resistive heating element does not source any voltage.

Perhaps somebody can try it and tell us what happens.

 

[sunsurfer]

I have read that directly connected does not utilize all the power the panel can produce due to amp rise / voltage lost as it will pull all the amps the panel can produce lowering voltage so I was hoping that would be possible with just a controller and a panel. Looks like not.

Panels are suppose to do better with "matched" loads to conditions. Thats one advantage of an MPPT controller, it can move the load on the panel around to keep at maximum panel output vs conditions. Heaters/resistive loads are more picky about voltage. Example, taking the voltage down by 50% reduces output(rating) down to 25%. So what is the best way to get a more of a current source matched to a voltage based load. In theory, I would think an MPPT would work fine as long as you can keep a small voltage source on the battery side.

Hope I got that right.

 

[v_green57]

Panels are suppose to do better with "matched" loads to conditions. Thats one advantage of an MPPT controller, it can move the load on the panel around to keep at maximum panel output vs conditions. Heaters/resistive loads are more picky about voltage. Example, taking the voltage down by 50% reduces output(rating) down to 25%. So what is the best way to get a more of a current source matched to a voltage based load. In theory, I would think an MPPT would work fine as long as you can keep a small voltage source on the battery side.

Hope I got that right.

Experimentation is indicated. Who has the requisite hardware and time to do it? Inquiring minds want to know...

 

[sunsurfer]

Experimentation is indicated. Who has the requisite hardware and time to do it? Inquiring minds want to know...

I actually have all the pieces to try this, just don't have time right now.

 

[Whats-n-Watts]

Although you can heat water with solar PV, and the above advice is excellent infiormation, it is far more efficient to do it with hot water solar panels.
Hot water panels vary in efficiency but on average only require about 1/4 or less of the surface area of PV panels to heat water.
If you, like most of us have limited space for panels, it is the best solution.

That's not practical if you need that hot water in the morning and panel space isn't an issue for me. Ground mount is the way I am going. I have 3 wide open acres and with a 500 sqft roof that doesn't allow for the power I need. Also my roof is east to west.

 

[Pierre]

I have read that directly connected does not utilize all the power the panel can produce due to amp rise / voltage lost as it will pull all the amps the panel can produce lowering voltage so I was hoping that would be possible with just a controller and a panel. Looks like not.

I do agree that it is not optimal without an mppt but it works and the energy is free!

 

[Whats-n-Watts]

I do agree that it is not optimal without an mppt but it works and the energy is free!

I can throw a small battery at it so no big deal. I have charge controllerers on the shelf and 4 panels to experiment with. I have a couple of flooded deep cycle marine also on a shelf doing nothing. Looks like a good day to order an element lol

 

[Steve777]

Saw this thread, and just ran a quick calculation. On a typical sunny winter day here (today) my thermal solar panels (4 - 3'x8' flat panels) my panels raised the water temp in the storage tank (85gal) from ~60F at dawn to ~150F at 4pm when the sun went down. It would do better in the summer, of course, but this is a good for comparison. Lets say that was 50 gallons that got heated (there is stratification in the tank), with a temp rise of 90F or 36,000 BTUs. 3412 BTU/KWH or 36,000/3412 = 10.55KWH of energy to heat that. My PV array (albeit a small older one of 2600w) made 13.4 KWH today. So those four thermal panels made as much heat as ~80% of the electric power from my PVs; and the area of the thermal panels is maybe 1/4 to 1/3 that of the PVs. [To be fair, there was also some energy used by the hot water system to pump water around, but that was minimal.]

I only bring this up to show that for making hot water, it is far more efficient to use thermal hot water panels. Of course if you have extra electric power from your PVs and no where else to use or store it, that is a different story; but for just gathering energy to heat water...

 

[McKravitts]

Saw this thread, and just ran a quick calculation. On a typical sunny winter day here (today) my thermal solar panels (4 - 3'x8' flat panels) my panels raised the water temp in the storage tank (85gal) from ~60F at dawn to ~150F at 4pm when the sun went down. It would do better in the summer, of course, but this is a good for comparison. Lets say that was 50 gallons that got heated (there is stratification in the tank), with a temp rise of 90F or 36,000 BTUs. 3412 BTU/KWH or 36,000/3412 = 10.55KWH of energy to heat that. My PV array (albeit a small older one of 2600w) made 13.4 KWH today. So those four thermal panels made as much heat as ~80% of the electric power from my PVs; and the area of the thermal panels is maybe 1/4 to 1/3 that of the PVs. [To be fair, there was also some energy used by the hot water system to pump water around, but that was minimal.]

I only bring this up to show that for making hot water, it is far more efficient to use thermal hot water panels. Of course if you have extra electric power from your PVs and no where else to use or store it, that is a different story; but for just gathering energy to heat water...

I get very similar result and I am using an older thermal panel and new pv panels.

 

[McKravitts]

You make a good point if you have the real estate to house these panels. Also they are single purpose i.e. only good for heating water. At least with solar pv you can use the power elsewhere when the water heater is on temp.

I am not proposing to replace PV with thermal panels. I have both.
The real estate to house the thermal panels is only about 1/4 of the real estate needed for equvalent PV panels.
If you don't use hot water, you could just stick entirely to pv panels.

 

[Starex]

I am not proposing to replace PV with thermal panels. I have both.
The real estate to house the thermal panels is only about 1/4 of the real estate needed for equvalent PV panels.
If you don't use hot water, you could just stick entirely to pv panels.

Actually you can do both on the same real estate.
https://hydrosolar.ca/collections/h...brid-photovoltaic-and-thermal-pvt-solar-panel

 

[Whats-n-Watts]

Saw this thread, and just ran a quick calculation. On a typical sunny winter day here (today) my thermal solar panels (4 - 3'x8' flat panels) my panels raised the water temp in the storage tank (85gal) from ~60F at dawn to ~150F at 4pm when the sun went down. It would do better in the summer, of course, but this is a good for comparison. Lets say that was 50 gallons that got heated (there is stratification in the tank), with a temp rise of 90F or 36,000 BTUs. 3412 BTU/KWH or 36,000/3412 = 10.55KWH of energy to heat that. My PV array (albeit a small older one of 2600w) made 13.4 KWH today. So those four thermal panels made as much heat as ~80% of the electric power from my PVs; and the area of the thermal panels is maybe 1/4 to 1/3 that of the PVs. [To be fair, there was also some energy used by the hot water system to pump water around, but that was minimal.]

I only bring this up to show that for making hot water, it is far more efficient to use thermal hot water panels. Of course if you have extra electric power from your PVs and no where else to use or store it, that is a different story; but for just gathering energy to heat water...

I won't be putting anything on my roof and 2 shower have to be taken in the mornings so over night the water will not be hot enough for the next morning. Also with no sun for one day and no hot water. I gave grid power on the property. 380 amps of it as well as a 8500w continuous generator so worse case scenario with the water heater on electric dc or ac I can power it I'd just rather not that way but am prepared.
I'm going to set up a 40 gallon buffer tank on pv and and dc elements and a 174 degree dc thermostat. It will have all day to heat as we do not use hot water during the day. The main water heater I am thinking of installing a 1500 watt dc element with a 140 degree dc thermostat in the bottom powered by a battery, pv with scc and a disconnect switch so I can stop the element from drawing power from the battery overnight. For the top element I plan to install a 300 w dc in powered by the dc load side of the scc. Im going to wire the dc load wires into the battery side of a second scc so it has power and then finally dc load side to top thermostat and element. Set the parameters so that when the voltage drops on the battery it will disconnect scc #2 automatically. It may not work or it may. I have no idea but seems good on paper lol
I'm also think about how I could just use a grid tie auto transfer switch for this purpose. In short I'm trying to eliminate current waste during the day and battery drain overnight. I figured if I can get it to 175 degrees by dark it will stay hot enough for one shower in the morning minimum having the buffer tank hot as well. Worse case scenario after shower 1 turn the battery loose to reheat the water for shower 2. Primary tank is 28 actual gallon capacity and the 40 is 38. The two showers combined are about 50 gallons through a 1.5 gpm shower head.
Thoughts? Im in Southeast Ga and the my well is 300 ft deep. The incoming water is never under 68 degrees.

 

[McKravitts]

I won't be putting anything on my roof and 2 shower have to be taken in the mornings so over night the water will not be hot enough for the next morning. Also with no sun for one day and no hot water. I gave grid power on the property. 380 amps of it as well as a 8500w continuous generator so worse case scenario with the water heater on electric dc or ac I can power it I'd just rather not that way but am prepared.
I'm going to set up a 40 gallon buffer tank on pv and and dc elements and a 174 degree dc thermostat. It will have all day to heat as we do not use hot water during the day. The main water heater I am thinking of installing a 1500 watt dc element with a 140 degree dc thermostat in the bottom powered by a battery, pv with scc and a disconnect switch so I can stop the element from drawing power from the battery overnight. For the top element I plan to install a 300 w dc in powered by the dc load side of the scc. Im going to wire the dc load wires into the battery side of a second scc so it has power and then finally dc load side to top thermostat and element. Set the parameters so that when the voltage drops on the battery it will disconnect scc #2 automatically. It may not work or it may. I have no idea but seems good on paper lol
I'm also think about how I could just use a grid tie auto transfer switch for this purpose. In short I'm trying to eliminate current waste during the day and battery drain overnight. I figured if I can get it to 175 degrees by dark it will stay hot enough for one shower in the morning minimum having the buffer tank hot as well. Worse case scenario after shower 1 turn the battery loose to reheat the water for shower 2. Primary tank is 28 actual gallon capacity and the 40 is 38. The two showers combined are about 50 gallons through a 1.5 gpm shower head.
Thoughts? Im in Southeast Ga and the my well is 300 ft deep. The incoming water is never under 68 degrees.

I totally understand your concerns. I had the same.
I ended up doing something siimilar. I left my existing propane hot water tank (40 gal) in place and fed the water into it from the solar storage tank (80 gal).
I used a differential controller and a circulator pump to circulate water from the solar tank through the propane tank and back when the solar tank is 6 degrees hoter than the propane tank. Even after 2 days without sun the solar tank maintains a temperature about 20 degrees above my ground water.

Worst case senerio; I get some preheating.
Best case senerio; I get 120 gals of ready to use hot water.
.

 

[Whats-n-Watts]

I totally understand your concerns. I had the same.
I ended up doing something siimilar. I left my existing propane hot water tank (40 gal) in place and fed the water into it from the solar storage tank (80 gal).
I used a differential controller and a circulator pump to circulate water from the solar tank through the propane tank and back when the solar tank is 6 degrees hoter than the propane tank. Even after 2 days without sun the solar tank maintains a temperature about 20 degrees above my ground water.

Worst case senerio; I get some preheating.
Best case senerio; I get 120 gals of ready to use hot water.
.

Heck yeah! If I had a decent number of hours hitting the solar water heater closer to the house I would jump on it. Right not during winter the only allowable spot only gets sun in the winter for just a couple of hours direct sunlight. Probably not enough gain to justify the expense sadly.