PV DHW

zozomikezozomike Solar Expert Posts: 125 ✭✭✭
So here's the deal, I finally got so pissed at my clever thermal DHW system I tore it out and converted to pv. My anger was not at Thermal, but at gravity. Evidently the interior pluming ( behind walls) had some dips, enough to cause just enough water to remain in the outside copper plumbing. SO tired of soldering split copper...
So I put 2 ( in plumbing series) 20 gallon 12volt electric heaters. Each on separate breakers, separate electrical. The reason was limited space. And temporarily we just turn the breakers on/off when the batts are full.  Works fine. But not a long term idea. I am running underground conduit now for low voltage from CC aux to probably a contactor or two to operate the heaters. Works fine unless I also turn on the table saw, and someone decides to shower, which kicks on the pump also. Then the 7000w of my stacked inverters overload and trip. So I guess a 3rd inverter might help. But surely there is a genius electronic way to supply power to  #1, and when it reaches temp, to send power on to #2? So that I was only running one heater at a time?
Thanks ahead 

Off grid, all solar, passive and active ( winter wood heat supplements) solar DHW, no backup.

Array 1-- 12 Sunpower 250, Outback FM 100

Array 2-- 12 Sunpower 250, Outback FM 100

Well array 780w, 6 Kyocera 130 w  with Grundfos sqflex 11 and cu200 to elevated  storage, ( 2- 330 g tanks,) no battery storage at well

8 24 volt Battle Born Lithiums

Outback FlexpowerTWO, VFX 3524a


Comments

  • Dave AngeliniDave Angelini Solar Expert Posts: 5,812 ✭✭✭✭✭
    I think you are defying the number one rule of offgrid design, the ability of shifting to propane/gas in winter.

    The gravity part is not a big deal you just have to learn from it. What did you do wrong? Forget to blow it out with compressed air? Wrong domestic hot water system design type?

    Many people offgrid shift to to electric, (hot water, cloths drying, baking, etc) offgrid. They also have the ability to shift to gas in winter. Keeping it simple in winter is basic to minimizing generator use, or avoiding it altogether in the right climate.

    Heck of a load you have for an inverter to deal with and even worse in summer when its ambient is high.

    You can still buy gas tank heaters that use zero electricity or a tankless that only powers a small fan when on. 

    I was hoping someone else would post first. Hate to always be on the bad cop side ;)

    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • mcgivormcgivor Solar Expert Posts: 3,736 ✭✭✭✭✭✭
    Heating water with  PV is, as explained above, not the best choice in an offgrid application particularly in cold climates where demand is high. Using gas with an instantaneous water heater is by far the best choice, perhaps using PV to temper the incoming water if excess power is available, as they tend to suffer from low  incoming water temperature..

    When using evacuated tube solar water heaters in cold environments it's best to use glycol in the outside loop with a heat exchanger to transfer heat to the usable waterr, otherwise split pipes may be the result, which is what I'm assuming is the reference to leaking pipes, just reading between the lines.

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • EstragonEstragon Registered Users Posts: 4,494 ✭✭✭✭✭
    What Dave and McGivor said.

    For the electric heaters, it seems to me you could in principle have heater #2 controlled by a thermostat on heater #1.  When #1 gets to the setpoint, the heater stops heating, and the stat should change state on its control output?  A relay on #2 could be triggered to change state from off to on based on #1 stat output.  Presumably #1 would be closer to the fixtures in the series, so that water gets used first.  If temp in #1 dropped, the stat would change state again, and #2 would stop heating.  Just a thought.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • jtdiesel65jtdiesel65 Solar Expert Posts: 195 ✭✭✭
    edited January 21 #5
    My bosch tankless propane unit uses 100w when running and it's real light on propane.  IIRC in the coldest month of the year in VT, it's been $300/mo for propane which is DHW, heat, dryer, kitchen stove, outdoor grill, generator, and a simple propane heater in the battery building.  I used to have a gas tank heater with a power vent and I'll never go back.

    I've been looking at running a tank pre-heater off an CC aux and have the lines already installed and the relays purchased. However, my expectation is that, without being over paneled, the heater wouldn't really come on much in a VT winter.

    Sounds like something like this device may be what you are looking for. You would put the temp sensor in/on tank1 and input to tank 2 connected to the cooling plug. Tank1 would never shutoff (except that it's essentially shut off when temp is reached). Cooling( and therefore Tank 2) comes on when the set the temp is reached. It wouldn't be perfect.


    Seems like it might be easier to rig up a recirculator pump between the two tanks and only let one have power.






  • zozomikezozomike Solar Expert Posts: 125 ✭✭✭
    Thank you folks,
     I actually own a different brand of the Inkbird, which has been controlling  my freezer to fridge conversion that has been running for 10 years. That would work, but inevitably the heater would come on in the middle of the night, and drain my batts to an unwelcome sunrise. I just need a device that will help me utilize solar, ( most days I am at parms by 11:00. So the light until 4:00 is just tanning my hide.
    As I mentioned in my post, manual works, gets us enough DHW, but is a POA. I am looking for the idea that reads battery levels, and says NO, Batts are below setpoint, you get no juice. And if some resident  just has to take a shower at 11 pm. BUCK UP buttercup, your last 5 minutes are going to be invigorating, or move back to town where other people take care of you. 
    I am confident there is an electronic way to take this switching burden off me. Or I will find another way.
    But guys, using propane? ( digging up million year old sunlight ) just to warm you at midnight? That is just too last century. I've been out here a dozen years making my own from current sunlight, ( I consider deadfalls to fit) I am not going back. 

    Off grid, all solar, passive and active ( winter wood heat supplements) solar DHW, no backup.

    Array 1-- 12 Sunpower 250, Outback FM 100

    Array 2-- 12 Sunpower 250, Outback FM 100

    Well array 780w, 6 Kyocera 130 w  with Grundfos sqflex 11 and cu200 to elevated  storage, ( 2- 330 g tanks,) no battery storage at well

    8 24 volt Battle Born Lithiums

    Outback FlexpowerTWO, VFX 3524a


  • mike95490mike95490 Solar Expert Posts: 9,251 ✭✭✭✭✭
    Just remember, most relays and thermal switches are only rated for AC.   Consider using a proper sized Mod Sine inverter for your resistive heating elements and just switch the AC.
    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 ,

  • Dave AngeliniDave Angelini Solar Expert Posts: 5,812 ✭✭✭✭✭
    edited January 22 #8
    I do not think anyone is saying to heat with propane ! Just a back-up that is reliable in winter when you can't heat the water directly with the sun. What you want to do can easily be done with wifi and appliances that can be controlled with it. Without a better plan the LFP batts that are not networked, will be the stress point in your system. Not many ladies would want to take a cold shower that I know! Maybe you are running a camp and normal home life is not required? Going to this "green" strategy sounds like it would increase your use of a genset so what is the difference, other than your decreasing the life of your power system with large surges?

    I am told firmware 1.10 (any day now) on Schneider Gateway will finally have the digital and analog wifi controlled apps going. This is how I plan to automate many of my client requests.  Wi-Fi is the way to go into the next 10 years and all of the wifi switching is slow start without using relays and switches. No extra wiring !

    Those switching surges always take their toll late at night and in winter during a rain/snow and windstorm. 
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • zozomikezozomike Solar Expert Posts: 125 ✭✭✭
    Thanks for your ideas gents, more to consider. Actually Mike I am running 2 VFX 3524s which claim to be able to deliver 7000 watts. If I can run one heater at a time, that's 2000w, and no impact on my daily use. Except as Dave mentions, those dark winter storms. And Dave is correct I have run the little generator all day a few days this winter. And no there is no difference I reckon, except to start another backup system.
    Actually I decided to try to learn to go all PV ( plus a bit of wood from my acreage) after I was working out of state for several months and my large propane tank leaked $350.00 and the company claimed it was not a leaker. So I had it pulled and just stubbornly decided to try to make it on PV. I'm no saint, just stubborn. 
    Wifi? I could go back to putting in a satellite, got stubborn about that also. Just use the phone. 
    The heaters are indoors, and they and the piping is highly insulated, And yes Dave, we do kind of live like it is a camp. But your comments about relays, ( and probably the PID I was considering) give me pause. Thanks again, I do not need more headaches.  

    Off grid, all solar, passive and active ( winter wood heat supplements) solar DHW, no backup.

    Array 1-- 12 Sunpower 250, Outback FM 100

    Array 2-- 12 Sunpower 250, Outback FM 100

    Well array 780w, 6 Kyocera 130 w  with Grundfos sqflex 11 and cu200 to elevated  storage, ( 2- 330 g tanks,) no battery storage at well

    8 24 volt Battle Born Lithiums

    Outback FlexpowerTWO, VFX 3524a


  • zozomikezozomike Solar Expert Posts: 125 ✭✭✭
    Estragon, thank you for the idea, being more of a carpenter than an electronics tech, I will be studying how to do that. 

    Off grid, all solar, passive and active ( winter wood heat supplements) solar DHW, no backup.

    Array 1-- 12 Sunpower 250, Outback FM 100

    Array 2-- 12 Sunpower 250, Outback FM 100

    Well array 780w, 6 Kyocera 130 w  with Grundfos sqflex 11 and cu200 to elevated  storage, ( 2- 330 g tanks,) no battery storage at well

    8 24 volt Battle Born Lithiums

    Outback FlexpowerTWO, VFX 3524a


  • Dave AngeliniDave Angelini Solar Expert Posts: 5,812 ✭✭✭✭✭
    Wifi can be local ! You do not need to have internet from the sky.  I would like to hear how you killed the solar domestic hot water. It actually is one of the things I do best for my clients. Some run it in Alaska and Canada. The design is everything !

    Keep it simple, the less you have,  the more you have in peace of mind ! Camp does not need to be offgrid squalor either!
     Good Luck!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • zozomikezozomike Solar Expert Posts: 125 ✭✭✭
    Thanks to many of your comments, my research led me to " Offgrid Steve", he uses the AUX to SSR to turn on his 220vac water heater, but he replaced the lower thermostat with an upper which is designed to send power to the lower element. This then sends to another use.  This is an idea similar to Estragon's above. 
    I will be figuring out the wiring and ordering parts, ( SSR, Upper Thermostat) my single element 120 VAC heaters only have a lower with ECO.
    Unless someone tells me i'm a dummy. ( which I would appreciate!) 

    Off grid, all solar, passive and active ( winter wood heat supplements) solar DHW, no backup.

    Array 1-- 12 Sunpower 250, Outback FM 100

    Array 2-- 12 Sunpower 250, Outback FM 100

    Well array 780w, 6 Kyocera 130 w  with Grundfos sqflex 11 and cu200 to elevated  storage, ( 2- 330 g tanks,) no battery storage at well

    8 24 volt Battle Born Lithiums

    Outback FlexpowerTWO, VFX 3524a


  • zozomikezozomike Solar Expert Posts: 125 ✭✭✭
    Oh god, I was afraid someone would ask me how I "killed" my thermal. So I fess up just to caution others.
     Let me preface by saying you cannot trick gravity. For 20 years I was a catastrophe adjuster, so I was often away from home for months at a time. Once I committed to this property, I wanted to have someone around during the days, and make progress on the construction while I was away. So I would try to keep 1 or 2 locals employed in my absence. Well running the piping of the drainback system ( ala Build it Solar) was done in my absence, with my diagrams and cautions via email, and the walls closed in, etc. So I have never seen those lines, but something was preventing full drain down, I can only believe the lines have dips or some such. I did not wish to tear out my kitchen to find out. Had I been more thoughtful I would have just run new lines on the exterior, but I was exasperated with it. At 73 climbing up 16 feet to pull 4x8 glass to repair split copper is not as much fun as it used to be. 
    The panels are still in place, so I may indeed later get busy on a way to use them as pre heaters, with the electrics as just a boost. I have not given up on that. 

    Off grid, all solar, passive and active ( winter wood heat supplements) solar DHW, no backup.

    Array 1-- 12 Sunpower 250, Outback FM 100

    Array 2-- 12 Sunpower 250, Outback FM 100

    Well array 780w, 6 Kyocera 130 w  with Grundfos sqflex 11 and cu200 to elevated  storage, ( 2- 330 g tanks,) no battery storage at well

    8 24 volt Battle Born Lithiums

    Outback FlexpowerTWO, VFX 3524a


  • EstragonEstragon Registered Users Posts: 4,494 ✭✭✭✭✭
    FWIW, I replaced all the copper piping with pex in my cabin.  The pipe itself is pretty freeze tolerant.  All the fittings and valves (which aren't) are where I can get at them if need be.  Heating loops are glycol filled.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • zozomikezozomike Solar Expert Posts: 125 ✭✭✭
    Understood, I love pex, almost all my pressure plumbing is in pex. The inside runs mentioned above are pex. But the panels and the first several feet are copper. FWIW again, I have had 3 different thermal DHW systems over the years. First was glycol,  I am no stranger to Taco pumps, or plumbing. All my panels are " rescues" of systems that had failed with professionals designs. I have learned that thermal DHW systems work long enough to allow them to be forgotten, and then they bite, with a dead pump, a plumbing surprise or some such. I love the one system I have that I use every day, but it requires frequent attention.  ( 3 4x8 panels inside a passive solar greenhouse with a 160 gal stock tank as reservoir) So when the new setup we had for the new house failed, I decided to try PV. We will see.
    I will post if the switching setup I'm planning works. 

    Off grid, all solar, passive and active ( winter wood heat supplements) solar DHW, no backup.

    Array 1-- 12 Sunpower 250, Outback FM 100

    Array 2-- 12 Sunpower 250, Outback FM 100

    Well array 780w, 6 Kyocera 130 w  with Grundfos sqflex 11 and cu200 to elevated  storage, ( 2- 330 g tanks,) no battery storage at well

    8 24 volt Battle Born Lithiums

    Outback FlexpowerTWO, VFX 3524a


  • Dave AngeliniDave Angelini Solar Expert Posts: 5,812 ✭✭✭✭✭
    Glycol is old school and prone to closed loop problems. The glycol itself losing it's freeze protection in a matter of months if certain problems exist in the maintenance/ design.

     In a well designed drainback, there is a site tube that shows the level when the pump is off. It is very easy to see that all of the water is out. The pipe has to be large enough to drain, and once it is working it should need very little other than pump maintenance. The drainback tank is mounted in conditioned space.

    Heating water with the sun is such an easy thing to do and since one needs a tank, you might as well have a propane back-up. It is built into the tank :)
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • zozomikezozomike Solar Expert Posts: 125 ✭✭✭
    A sight tube is a damn good idea. Assuming someone checks it. 

    Off grid, all solar, passive and active ( winter wood heat supplements) solar DHW, no backup.

    Array 1-- 12 Sunpower 250, Outback FM 100

    Array 2-- 12 Sunpower 250, Outback FM 100

    Well array 780w, 6 Kyocera 130 w  with Grundfos sqflex 11 and cu200 to elevated  storage, ( 2- 330 g tanks,) no battery storage at well

    8 24 volt Battle Born Lithiums

    Outback FlexpowerTWO, VFX 3524a


  • Dave AngeliniDave Angelini Solar Expert Posts: 5,812 ✭✭✭✭✭
    Most up north shut it down for winter or bad weather by just tuning off the pump/controller. People who live offgrid have to do their due diligence or they just keep paying for it. Good for the economy so not a bad thing!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • zozomikezozomike Solar Expert Posts: 125 ✭✭✭

    PV DHW UPDATE, 

    Thanks everyone for the comments. I learn so much here from my " betters" 

    Just in case anyone wishes to explore pv options vs propane or thermal dhw.  Here is what we did.

    A.      As my system is all 120 vac, we went with 2 each POU 20 gallon stainless heaters plumbed in series.

    B.      As each is 2kw, and my system is only 7kw, running both simultaneously, and the auto start of water pump or other induction devices proved too much. So I wanted to run the heaters sequentially.

    C.      We used the Auxiliary function of one of the two charge controllers to send a l2 volt dc signal to a SSR mounted near the heaters. This turns on heater#1.

    D.     We replaced the single element thermostat supplied with the heater, with a standard upper thermostat.        ( hats off to OFFGRID STEVE a helpful youtuber) The upper has a switching function, which sends power to the lower normally when the upper has reached setpoint. He uses this to send power on to other devices.

    E.      As it seems that use puts all devices downstream on the breaker for the first heater, we modified that idea by using that to close another SSR, which then sends individually protected power to heater#2.

    The setup has been working well for a few weeks. As we are not heavy users of dhw, it fills our needs. Heavy users would do better with a standard heater and dedicated PV, or better yet  with a larger total system and 220 vac inverters.


    Off grid, all solar, passive and active ( winter wood heat supplements) solar DHW, no backup.

    Array 1-- 12 Sunpower 250, Outback FM 100

    Array 2-- 12 Sunpower 250, Outback FM 100

    Well array 780w, 6 Kyocera 130 w  with Grundfos sqflex 11 and cu200 to elevated  storage, ( 2- 330 g tanks,) no battery storage at well

    8 24 volt Battle Born Lithiums

    Outback FlexpowerTWO, VFX 3524a


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