System to heat water from PV panels

gactrx
gactrx Solar Expert Posts: 72 ✭✭
Hi, first, please don't tell me the reasons why not to use PV panels to heat water. I have the panels, I'm doing it.
Ta

Hi, I am planning to get a Morningstar MPPT 45 controller for my 6 x 320w (1920watts) panels and also use another PWM Morningstar 45 set in diversion mode to divert power to a 24vdc water heating element. I will have two batteries set up for 24 volts connected to the MPPT controller. The how water cylinder thermostat will operate a SSR to disconnect the diverter controller therefore the cylinder element and another SSR will connect the main 24volt battery bank This setup is mainly to heat water and secondary to change the main battery bank. As the two batteries directly connected to the MPPT controller will have a small capacity compared with the PV output, they will nearly always be charged therefore the majority of power will heat the water which is my goal. Can anyone tell me what the voltage will be at the element and what current would I expect? Would it be 24 volts the majority of the time the sun is shining?
Also can the Morningstar controllers be turned off via a signal? eg can the thermostat turn off the divertor controller rather than open circuiting the input with an SSR?
Thanks,

Comments

  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    Re: System to heat water from PV panels

    It looks like you have decided to do it but the approach is unusual, most folks use a heat pump hot water heater to heat water with solar. The HPHWH has a COP of around 3 so every watt in equals 3 watts of heating.

    Good luck with your project
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: System to heat water from PV panels
    gactrx wrote: »
    Hi, I am planning to get a Morningstar MPPT 45 controller for my 6 x 320w (1920watts) panels and also use another PWM Morningstar 45 set in diversion mode to divert power to a 24vdc water heating element. I will have two batteries set up for 24 volts connected to the MPPT controller. The how water cylinder thermostat will operate a SSR to disconnect the diverter controller therefore the cylinder element and another SSR will connect the main 24volt battery bank

    I don't understand your setup, can you post a diagram or schematic? Also, at 24 volts your MPPT controller is way undersized for a 1920 watt array.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: System to heat water from PV panels

    As vtMaps said ... 1920 Watts on 24 Volts is around 80 Amps; 45 Amp controller is not going to handle that.
    Heat water with 24 Volts? How many Watt heating element? Watts / Volts = Amps.

    Most tank type electric water heaters have 3500 Watt elements. Very small ones have 1500 Watt elements. Don't expect much hot water too soon.

    There's a good reason why people don't do this.

    The Voltage output from a diversion controller is slightly under V set point for diversion. So with Absorb around 28.8 the output will be around 28 Volts - close enough for government work anyway. It will also be pulsed to regulating the battery Voltage, not steady-state. When it drops to Float level the same thing will occur, but at a lower Voltage.

    Many people do use water heating to make use of 'surplus' power from PV that would otherwise be wasted. Usually they just have the AUX port on the controller (if equipped) turn on a standard AC heater powered from the inverter. Even so it takes some figuring to get it balanced, hence the reason for MidNite's "Waste Not" function.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: System to heat water from PV panels

    I'm looking into doing something similar, I only will heat water. I intend on a system with out batteries or charge controller! an array about 2000 watts direct DC into the thermostat and water heating element. This makes several things easier/cheaper.

    I will use the existing 3900watt 240 volt heating element, I'm currently running 120volts into it so it is effectively 1/4 the wattage, drawing about 920watts at 120 volts. I intend on running the panels 2 strings of 5 - 185watt 35v vmp panels, or about 175 volts at @10 amps max. The thermostat should act much as a charge controller and the element should be fine, it's a pure resistance load so AC or DC doesn't matter to it. I should be near the optimum balance voltage to amps at the peak, I also could do a setup with 3 strings of 4 of the same panels, though I think that they wattage might exceed the elements resistance(?) at that voltage? Only real concern I see, is will the contacts of the thermostat have a problem with the DC. And will I have enough time to set this up before the shorter days of winter.

    Though leery of it I have also thought about running the DC into a switch to change the source back to AC, with a toggle much as an Epanel has so the sources would never meet, wonder if the switch part of the breakers are designed in such a way that all Din rail breakers have the same specs, AC or DC?

    I think 24 Volt DC elements only go up to 600watts? even at 920 watts it takes an awfully long time to heat a 30 gallon tank of water!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Re: System to heat water from PV panels

    I too was going to do 24v waste not via ssr. But couldnt find a decent 24v element. I did find 1250W ones,

    http://www.altestore.com/store/Charge-Controllers/Dump-Loads-Dump-Load-Controllers/Diversion-LoadsDump-Loads/Water-Heating-Element-for-12V-or-24V-DC-1-NPT-Male/p2326/

    but they have a different thread size, and cost over 100 bucks. Now i have two inverters i guess ill just go ac waste not diversion. I HATE plumbing.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • gactrx
    gactrx Solar Expert Posts: 72 ✭✭
    Re: System to heat water from PV panels

    Hi, thanks for your replies which I shall read in depth today.
    I have attached a diagram from Morningstar so I know it will work. I wouldn't have the load control TriStar or wind generator so all the right hand section can be cut off. Also I attached the specs for my solar panel array which shows the current. I would prefer to use the Midnite controller rather than two Morningstar's if possible. The last diagram is my main battery bank and SSR. I hope they attach correctly.
    Thanks,Attachment not found.Attachment not found.Attachment not found.
  • ZoNiE
    ZoNiE Solar Expert Posts: 100 ✭✭
    Re: System to heat water from PV panels

    I want to use PV to heat water... In my Keurig. Damn that thing draws a lot of current...:roll:

    X2 on the heatpump. More efficient use of the energy, and you can use the output from the evaporator to help cool a living space or battery compartment if ducted properly...
  • gactrx
    gactrx Solar Expert Posts: 72 ✭✭
    Re: System to heat water from PV panels

    Thanks for your answer Photowhit. I'll have a think about that. I don't want to use a heat pump so I can keep the system as low tech as possible. If I was feeding directly from the panels I would have the thermostat operate a solid state relay as DC will weld the thermostat contacts together in a short time. I should have mentioned I will connect the panels up to supply around 48 volts to the MPPT controller then charge a 24 volt battery system. Higher the better for the panels and at 24 volt, there isn't a problem getting inverters, lamps, etc. Seems I can get what ever size element i want made up for reasonable cost and with the correct thread. The only problem with feeding direct is I think an MMPT controller will supply more usable power to the element at lower light levels. Is this correct?
    Cheers,
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: System to heat water from PV panels

    So I spent some time today looking around at relays that would allow for 120v AC control and 200v DC load, not cheap or readily available, unless I'm blind found 1 at $105 that will handle 10 amps, my peak should be around 10.5 on a perfect day.

    So I ran across a DC thermostat claimed to be made by Missouri Wind and Solar(yes I'm already fearing this). It is a replacement for the current water heater thermosat with a single temperature shut down, I'd choose 140 degrees f, They sell this to use with their 12,24 and 48v heating elements, I intend to use what I got, heating elements are pure resistance loads, their specs say it will handle 50 amps at 12 volts and AC or DC up to 220 volts! They say it uses a "•Uses a simple and typical "loop" circuit to interrupt power to wiring harness on overheat (Use 10 gauge wire for loop circuit)." This is not my end of the world, should this be like a breaker, if it will handle 50 amps at 12 v it should handle it at any voltage?

    Here's what specs they give;

    The thermostat remains on until the temperature reaches the rated number. For example, our 140 degree Fahrenheit thermostat will remain on until the temperature reaches 140 degrees Fahrenheit.

    All of our thermostats can handle 50 amps at 12 volts! No relay needed! (Can handle all voltages from 12 to 220 volts, AC or DC)

    Opens circuit on overheat, effectively cutting power to the heater (normally closed connects).

    Heating Element Features:
    •Simple in-line wiring system
    •Connections are 1/4" spade terminals
    •The heat sensor (reverse side) must be firmly mounted on the side of tank with screws or silicone caulking
    •Uses a simple and typical "loop" circuit to interrupt power to wiring harness on overheat (Use 10 gauge wire for loop circuit).

    Heat ratings are averages (+ or - 3%)

    Non. Pos. / Neg. polarity
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: System to heat water from PV panels

    What about using a cheap inverter, with a "shutdown control wire" to power up a 120VAC heater element. Just switching the inverter control wire, no heavy amps. ??
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: System to heat water from PV panels
    mike95490 wrote: »
    What about using a cheap inverter, with a "shutdown control wire" to power up a 120VAC heater element. Just switching the inverter control wire, no heavy amps. ??
    That would require a battery and charge controller to stabilize the voltage for the inverter. Otherwise it would be the only sensible way to go.
    Photowhit wrote: »
    I only will heat water. I intend on a system with out batteries or charge controller! an array about 2000 watts direct DC into the thermostat and water heating element.
    I can see this being very difficult, as PV output under such a load will be all over the place as light conditions change from moment to moment. But hey, I haven't actually tried it.
    gactrx wrote: »
    If I was feeding directly from the panels I would have the thermostat operate a solid state relay as DC will weld the thermostat contacts together in a short time.
    Rather than welding the contacts together, DC voltages above the DC handling capacity of the mechanical thermostat will cause an arc when the contacts open, This arc will almost certainly cause the thermostat to ignite in flames.
    gactrx wrote: »
    Hi, first, please don't tell me the reasons why not to use PV panels to heat water. I have the panels, I'm doing it.
    Can anyone tell me what the voltage will be at the element and what current would I expect? Would it be 24 volts the majority of the time the sun is shining?
    The voltage and current available at the element, if directly connected to the PV, will be all over the place depending on how much light is hitting the panels, and the angle of the light source in relation to the panels.
    I wish you luck sir.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: System to heat water from PV panels
    The voltage and current available at the element, if directly connected to the PV, will be all over the place depending on how much light is hitting the panels, and the angle of the light source in relation to the panels.

    The use of a pure resistance load is common as a diversion load for wind, I'm sure this will bounce around much more than solar. I don't think the heating will be a problem, and while it will bounce around a bit the voltage from an array tends to remain in a reasonable consistent ballpark. I just worry about stopping the load, the thermostatic switch under a DC load.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: System to heat water from PV panels
    Photowhit wrote: »
    The use of a pure resistance load is common as a diversion load for wind, I'm sure this will bounce around much more than solar. I don't think the heating will be a problem, and while it will bounce around a bit the voltage from an array tends to remain in a reasonable consistent ballpark. I just worry about stopping the load, the thermostatic switch under a DC load.

    When used as a diversion load that would be with a battery bank and diversion controller; more stable Voltage than PV output alone, even though it is pulsed by the controller to maintain battery Voltage level.

    And yes there is a big danger from using the standard thermostat with DC instead of AC, even at lower Voltage.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: System to heat water from PV panels

    Any ideas on a relay that would work for my needs? 120v AC control and a 200v DC Load?

    I found this; http://www.alliedelec.com/search/productdetail.aspx?SKU=70131279

    I could leave the 120v AC to run the relay from the current thermostat, and use the solar at 170V DC, but it has the potential to run 10.5 Amps, not likely in any real world but above the rated amperage.

    ...or of course the cheapy Missouri Wind and Solar(scares me every time I post that, I've heard to much poor advice given by them on the forum) Thermostat that claims to work to 220 v DC. their specs say it will handle 50 amps at 12 volts and AC or DC up to 220 volts! They say it uses a "•Uses a simple and typical "loop" circuit to interrupt power to wiring harness on overheat (Use 10 gauge wire for loop circuit)." This is not my end of the world, should this be like a breaker, if it will handle 50 amps at 12 v it should handle it at any voltage?

    No mention of UL rating, no insurance to worry about, I'll just be out in the cold(or heat) if it burns my place down.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • gactrx
    gactrx Solar Expert Posts: 72 ✭✭
    Re: System to heat water from PV panels

    Hi, thanks for the info. As mention there are SSR relays about so switching isn't a problem. The one below would do:
    Crydom D1D40 Relay; SSR; Gen Purp; Cur-Rtg 40A; Ctrl-V 3.5-32DC; Vol-Rtg 0-100DC; Pnl-Mnt; 4 Pin
    I might read up on the Midnite aux option because I think an MPPT controller may help to keep the voltage at a higher level to the element.
    Cheers,
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: System to heat water from PV panels
    gactrx wrote: »
    Hi, thanks for the info. As mention there are SSR relays about so switching isn't a problem. The one below would do:
    Crydom D1D40 Relay; SSR; Gen Purp; Cur-Rtg 40A; Ctrl-V 3.5-32DC; Vol-Rtg 0-100DC; Pnl-Mnt; 4 Pin
    I might read up on the Midnite aux option because I think an MPPT controller may help to keep the voltage at a higher level to the element.
    Cheers,

    Sorry, I didn't intend to hijack the thread. That should work for you with a DC thermostat, I think some regular water heater thermostats will have a DC rating for some reason, I think I read that over on Midnite's forums. I need to eyeball my Thermostat since I've decided to pick a project today, (it was scheduled to rain... but not a drop) Do you have a DC, or DC rated thermostat?

    That relay would also work well off Midnite's waste not feature. I had originally planned on doing that with my Classics, I just like the idea of having a stand alone system with out a battery. I would like to see how well it would work. I'm over paneled now and have pretty much every thing to hook it up that way, 3 classics, space in power center, another 2.5Kw of panels, even have the 'extra' combiner box now... What I don't have is a large inverter, I could only run it at 120V AC, which as I said is awfully slow at 920 watts!

    A voltage in a battery system, will be limited to the batteries' state of charge unless you completely switch to only heating from DC and take the battery out of the system. Though perhaps I don't understand what your saying.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: System to heat water from PV panels

    If you are thinking of doing this with out a battery, keep in mind most charge controllers need to boot up from a battery, before the solar PV is applied. Some PWM may not need battery, but ALL MPPT controllers will.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: System to heat water from PV panels

    If your addressing me, I don't intend to have a charge controller, nothing to charge. In essence the water will be the battery, energy heat and the charge controller the thermostat, since solar just needs to be shut off this should work... I think, all theory so far.

    His diagrams show a battery.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • gactrx
    gactrx Solar Expert Posts: 72 ✭✭
    Re: System to heat water from PV panels

    I received a very good reply to the same question and diagram in an email so thought I should add it here in case it's uesful to someone. I think it makes alot of sense:

    Interesting diagram from Morningstar. Bit frightening, I think:

    1) When the thermostat turns the SSR on it'll connect the two
    batteries. If the heating battery is full but the main battery
    is less so then a lot of current will flow likely blowing
    fuses or the SSR.

    If, on the other hand, the main battery is full so the current
    is small enough and everything survives then the main battery
    could be discharged by the diversion-mode controller resulting
    in the tank continuing to heat despite the thermostat opening.

    I think this is all fixable with diodes in the right places.

    2) Thermostatic protection of the tank relies on the SSR, etc.
    It would very desirable to have a second thermostat which cuts
    off the cylinder element no matter what for safety. Tricky as
    it might have to break a heavy DC current.

    I assume the main battery is normally charged by a generator,
    wind turbine, hydro or other PV array?

    Wouldn't it all be a lot simpler, more robust and flexible to
    have the water-heating PV array and whichever MPPT controller
    you choose feed the main battery directly then have a separate
    circuit run the water heater from there.

    You could then choose your strategy for controlling the heating
    of the water. Your current scheme is:

    - match the output of the PV array until the thermostat trips

    but others are possible giving relative priority to charging
    the main battery and heating the water depending on their state
    of charge and temperature respectively.

    This is the scheme I plan to use. There's more to it with
    multiple thermal stores and solar thermal input as well but
    for electricity the PV array will charge the battery bank
    then there will be diversion of electricity to the hot water
    tanks.

    I'm planning to use LiFePO₄ batteries so there's much less
    need to keep them full than there is for lead-acid batteries.
    The strategy will be based on a list of priorities:

    1) Make sure there's a few kWh in the batteries so there's no
    risk of them over-discharging.

    2) Make sure there's a bit of hot water in the top of at least
    one of the DHW cylinders.

    3) Split available PV power between the battery and the DHW
    taking into account input from solar thermal and leaving room
    in the batteries to store further charge expected for the
    rest of the day.

    4) Try to avoid taking more out of the batteries (for general
    domestic loads and water heating) than is going in from the
    PV to avoid “micro-cycling” the battery. E.g, if there's 3 kW
    coming in from the PV and general loads around the house are
    at 500 W then limit the power to the DHW cylinder to 2500 W.
    If another 1 kW load is turned on (in the kitchen probably)
    then drop the power to the DHW cylinder to 1500 W to keep the
    battery from charging or discharging.

    Basically, control of the immersions will be done in software
    looking at a much wider range of parameters than just battery
    state-of-charge and thermostat state.

    Back to your system: if you had the PV/MPPT connected directly
    to your main battery what you'd probably want is a PWM output
    from the MPPT to control an SSR to the immersion heater. I
    think that PWM should be proportional to the PV input unless
    the main battery is dangerously low or the thermostat has
    triggered. Maybe the Midnite controllers can do that - might
    be worth asking them.
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Re: System to heat water from PV panels

    Yes its kinda tricky to do right. Say your array is 2kW. So you (try to) size your element at say 1.5kW, to aloow for average losses. Sunny, few loads, works at 100%. More loads, less sun: requires throttling the element down some. Midnites aux2 waste not hi feature does this with a approx 1kHz PWM. The pulse width is propoartional to the amount fo spare power the controller thinks there is.

    With a DC element you then use a DC (MOSFET based) SSR. You need obviously a high current, and lowest possible Rds on resistance, typically 100A, 0.004 ohms. These do run around the 100 dollar mark. You want one that is name brand, QUALITY. Omron, Crydom, Not ebay junk.

    If you use a diversion controller in place of the mosfet, then you lose the waste not hi functionality, relying instead on the coordiation of float voltages. Thats going to be less effective through high end bulk, and absorb, becasue the nescessary coordination is not possible.

    Lastly if you do AC waste not (after the inverter), then the PWM that comes from the controller, then gets kind of messed with by the AC (triac based) SSR. They can only switch on AC zero crossing. So you get this weird harmonic clash between the 50Hz and the 1000Hz. People do say it works if slightly eratically.

    Some people also manage to do a pre controller diversion. Midnite have said they dont recomend it, because it confuses the Mppt algo, however if you dont use all the power and a decent sized diode to protect the controller it can work, and means you can run 120V array into 120V elements.

    For the thermostat you can wire it with a 12v signal that ANDs with the waste not aux signal and bobs your uncle. Or use a $5 temp cut out unit such as you find in heaters. They come in a wide range of temps and you just glue it on to the side fo the cylinder.

    Using every last drop, turns out to be difficult to do, but good enough is where youre aiming. Ive heard noone being able to say what the effect of the "micro cycling" (from the PWM) on the bank is. Most report that the waste not PWM makes teh tanks buzz kind of loudly. Both phenomons could be mitigated using a high value capacitance on the element. But it would need to BIG to make any difference.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: System to heat water from PV panels
    zoneblue wrote: »
    ...For the thermostat you can wire it with a 12v signal that ANDs with the waste not aux signal and bobs your uncle. Or use a $5 temp cut out unit such as you find in heaters. They come in a wide range of temps and you just glue it on to the side fo the cylinder...

    Is this what They describe as "•Uses a simple and typical "loop" circuit to interrupt power to wiring harness on overheat (Use 10 gauge wire for loop circuit)." ?

    Their description says it can handle 220V and that it will handle 50amps at 12 volts, would this be like a breaker, where it should handle 50 amps (10.5 amps in my case) up to 220v?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • gactrx
    gactrx Solar Expert Posts: 72 ✭✭
    Re: System to heat water from PV panels

    Thanks for the info. I think I'll look into using a Midnite Classic and then running a 24v element from a 24v battery bank via an SSR. I see an element on http://www.survivalunlimited.com/diversionloads.htm the HE2448 which would do and give some flexibility.
    Cheers,
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Re: System to heat water from PV panels

    The thing im thinkin of looks a bit like (but arent) a TO3 transistor. Its some kind of thermal bimetal or similar at a guess. Youll find one in your average heater but you can buy them to any temp spec you want.

    Photowhit wrote: »
    Is this what They describe as "•Uses a simple and typical "loop" circuit to interrupt power to wiring harness on overheat (Use 10 gauge wire for loop circuit)." ?

    Their description says it can handle 220V and that it will handle 50amps at 12 volts, would this be like a breaker, where it should handle 50 amps (10.5 amps in my case) up to 220v?
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar