I want to run my water heater on solar power (Newbie)

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  • mike95490mike95490 Solar Expert Posts: 7,307 ✭✭✭✭
    sisco said:
    why is it so hard to answer a question directly rather than go on about crap and just give a simple answer if you have solar power on the roof ,its making enough power to run the hot water system during the days ( depending on the size of the system and what other power is being used) but for the ones not in Australia and the warmer climate it could be a bit different 
    The direct answer is NO.
      and what do you learn from it ?  Solar electric water heating is maybe 10% efficient.  Solar Thermal water heating is about 40% efficient.
    If you want hot water, do you spend your $ on 4 PV panels and support gear, or 1 Thermal panel ?
    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 ,

  • softdownsoftdown Solar Expert Posts: 1,556 ✭✭✭✭
    In a tiny nutshell, solar electricity is generally a very expensive way to create heat 24/7. Propane may be up to double the costs of natural gas and is still far, far cheaper. Of course fuel prices vary from year to year, region to region, with seasonal variations. Was able to buy propane at $1/gallon in August, that may be somewhat competitive with natural gas. Propane has significantly more energy density than natural gas. 

    I don't know why sun rooms are not used more extensively. Mine starts pumping out a lot of heat around 8:30am or so. With a warm November, excessive heat has been a problem. The abundant sunshine also helps alleviate winter time blues.....now called SAD (seasonal adjustment disorder...of course). One large problem for developers is needing to face south.  

    I live in one of the coldest regions in the lower 48 and spend ~$100/year on heating fuel (propane). Due to a large sunroom and wearing extra clothes.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 150 watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • PhotowhitPhotowhit Solar Expert Posts: 4,276 ✭✭✭✭
    mike95490

    "...do you spend your $ on 4 PV panels and support gear, or 1 Thermal panel ?"
    Please understand that solar thermal is more than 1 thermal panel! It's a thermal panel, insulated piping, water pump, heat exchanger. Even a bread box water heater, where winter temps are above 20 degrees, requires a good bit of plumbing and equipment.

    Lots of good reasons to do solar electric water heating and might be less equipment than you think, panels a relay, for the thermostat, wiring, existing heating element, I would also add a shut off for DC at water heater. No reason to need an inverter, batteries or charge controller... This would be a slow recharge but doable.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • softdownsoftdown Solar Expert Posts: 1,556 ✭✭✭✭
    Photowhit said:
    mike95490

    "...do you spend your $ on 4 PV panels and support gear, or 1 Thermal panel ?"
    Please understand that solar thermal is more than 1 thermal panel! It's a thermal panel, insulated piping, water pump, heat exchanger. Even a bread box water heater, where winter temps are above 20 degrees, requires a good bit of plumbing and equipment.

    Lots of good reasons to do solar electric water heating and might be less equipment than you think, panels a relay, for the thermostat, wiring, existing heating element, I would also add a shut off for DC at water heater. No reason to need an inverter, batteries or charge controller... This would be a slow recharge but doable.
    Interesting....I was visualizing you with your crock pots and chiming in to disagree a bit. So I added the 24/7 caveat. That is the real issue with solar electric for heating purposes. It makes sense when the sun is shining. It makes no sense when batteries are being taxed. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 150 watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • PhotowhitPhotowhit Solar Expert Posts: 4,276 ✭✭✭✭
    softdown said;

    Interesting....I was visualizing you with your crock pots and chiming in to disagree a bit. So I added the 24/7 caveat. That is the real issue with solar electric for heating purposes. It makes sense when the sun is shining. It makes no sense when batteries are being taxed. 
    Solar thermal isn't going to work at night either!

    You can use a larger tank, which would be an addition to solar electric, or change use patterns. It would just be an added cost for a new install solar thermal.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • softdownsoftdown Solar Expert Posts: 1,556 ✭✭✭✭
    Photowhit said:
    softdown said;

    Interesting....I was visualizing you with your crock pots and chiming in to disagree a bit. So I added the 24/7 caveat. That is the real issue with solar electric for heating purposes. It makes sense when the sun is shining. It makes no sense when batteries are being taxed. 
    Solar thermal isn't going to work at night either!

    You can use a larger tank, which would be an addition to solar electric, or change use patterns. It would just be an added cost for a new install solar thermal.
    My late father tried it with very little success. 4" of foam insulation was used for a large storage container in the basement. I did find a 1984ish repair bill of ~$4500 for removing the panels and doing repairs. The whole thing was a tragic failure as he had the southern roof configured at 45 degrees which gives the whole house a peculiar look. 

    My cousin disconnected his solar hot water heating capabilities when an ~$700 valve needed replacing.

    Father was a medical electrician and very handy. Cousin has Masters from MIT in EE. These are not people without skills. 

    On the other hand, I do know of a Master Plumber who reportedly made his solar hot water heating work efficiently. His son is also a licensed plumber and will not try it due to excessive difficulties.

    I have a large stack of dads old panels sitting outside. I don't foresee trying my hand at it for quite awhile. There will be those who say it is easy. Well.....everything is easy once you know how to do it. We all have our skills....and our lack of skills. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 150 watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • jonrjonr Solar Expert Posts: 875 ✭✭✭✭
    edited November 30 #38
    This is well worth reading if you want to heat water with PV solar.  With some low cost panels and a DIY install, the economics look pretty good (depending on what other options you have).  http://techluck.com/


  • bill von novakbill von novak Solar Expert Posts: 711 ✭✭✭✭
    jonr said:
    This is well worth reading if you want to heat water with PV solar.  With some low cost panels and a DIY install, the economics look pretty good (depending on what other options you have).  http://techluck.com/


    I would also add that there are a few systems out there (Sun Bandit for example) that do the work for you - and give you emergency AC power if the grid goes out as well.
  • PhotowhitPhotowhit Solar Expert Posts: 4,276 ✭✭✭✭
    edited December 1 #40
    jonr said:
    This is well worth reading if you want to heat water with PV solar.  With some low cost panels and a DIY install, the economics look pretty good (depending on what other options you have).  http://techluck.com/



    So I went and looked at videos, it doesn't help the guy that he's using 'free' harbor freight multi meter, but heck I use them when I don't break out the Fluke(now that I have a Fluke!). It sure would be nice to have 'real' specs on output. He eludes to it being pulsed DC, and that makes sense since he feels free to run it by plugging it directly into a 240 outlet he has wired with the output of his unit which is roughly 70 volts/ 2 true 24 volt nominal solar panels. I guess the pulsed DC would help damaging the thermostat.

    I like the idea of it being one unit, as apposed to running a Dc in and having a relay to shut it down from the thermostat, running the relay with AC to shut off the DC's current.

    I don't buy that there is anything to 'track' calling this an MPPT unit, any DC power will run to the heating element, which is a pure resistance load.

    So how do you buy or create a bridge inverter that will handle up to 1000 watts? Do you think that would be enough to make safe use of the thermostat? I would imagine it would be within the specs. I would likely be running 740 watt array so 740 as a max wattage at 140 volts, a single string of 4 - 35VMP panels. I had initially planned on 2x2 configuration running about 10 amps at 70 volts DC(theoretically) ...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • NANOcontrolNANOcontrol Registered Users Posts: 6 ✭✭
    Everyone is right and wrong. Go on youtube and pretty much every one heating water with PV is a moron.  I heat water with PV and it is quite effective.  The old saying is that once PV got below $1.50 a watt that PV was better than tubes. Techluck is basically a sound idea but a poor execution, the unit heats up because it is IGBT based and the capacitors will likely go bad in a few years. So here is what I do. There are two tanks a 10 and a 20 gallon in series. It helps that the tanks were given to me.  Each tank has a 120V 2,000W element.  These aren't a bad match for a 36V, 48V or a pair of grid tie panels.  A controller made up of a capacitor bank, a couple FET and an Arduino.  That monitors the panel voltage and sets the PWM of each heater to maintain power point.  The capacitor bank stores the PV solar energy in the milliseconds that the FET is off.  Example: 50% duty cycle with an array that  can supply 5A. 5A goes into the capacitors while heating is off.  When it turns on, 10A goes into the heating element, 5A from the panel and 5A from the capacitors. Voltage isn't dropped, current is increased for a short period of time.  Basic power supply stuff.

    The controller knows the temperature of each tank and the primary is heated first. Any extra goes into the second make up water tank. At a certain temp tank #1 shuts off and all power is directed to #2.  Any little extra power goes to tank #1 again till a very upper temp limit is reached. The whole system costs about $30 to make.  Here is the real kicker, All my water needs are supplied from potential PV power that would be just wasted.  I have 1,100W in a 36V string powering my entire camp, refrigeration, lights and even a dishwasher. Since I only have a car battery, I am heavy on panels as everything operates in real time.  Typically I can divert 2.5KWH a day into water heating.  The system has paid for itself just from the elimination of monthly service charges.

    At home I have just installed two grid tie panels, $340 for 560W. Panels are cheap now. Compare that to the cost of buying a HPWH that may only last a dozen years. Electric savings are about the same.  For someone who doesn't want to go grid tie this is the most effective use of solar panels out there.  100% of the panels energy goes into heating water.  Nothing is wasted unlike the systems that almost all of you have.  The real trick is to keep it supplemental.  Depending on solar for 100% of your hot water needs is far too costly. Just think if about every household had just two solar panels. It is a simple cheap system to implement.  Evacuated tubes are very hardware intensive and installation can be a nightmare.  A wire is easy to run and doesn't have heat loss.

    It is my only source of hot water in the summer and it is quite reliable. Highly cost effective for a "hobby project" compared to powering a home office or garden shed. Can provide backup power in an emergency and keep your boat battery charged. In conclusion it is a great idea, the hardware is not available because the solar world is draconian, and it can't be implemented by muggles.
      

  • jonrjonr Solar Expert Posts: 875 ✭✭✭✭
    edited December 8 #42
    As NANOcontrol explains, with capacitance and fast PWM switching, you can control to hold ~Vmp to a resistive load without a DC-DC converter.  The panels will see a continuous load at about the right voltage.
  • PhotowhitPhotowhit Solar Expert Posts: 4,276 ✭✭✭✭
    I'm NOT particularly savy to what @NANOcontrol ; and you @jonr are saying. Curious if I could just use a 80V PWM DC Motor Speed Controller from my solar output to create a one sided wave (I know there's a name for that) to prevent problems with arcing fouling electrical contacts in a thermostat and run the DC current through the existing thermostat and heating element? 

    Please try to explain why this won't work. I have an incredibly dense skull so it might take a bit...lol.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • NANOcontrolNANOcontrol Registered Users Posts: 6 ✭✭
    I did want to say that the techluck unit does have an off time to it to quench the arc of mechanical thermostats.  Your idea is sound if you add a capacitor bank to store the energy during off periods.  If you buy an upper thermost switch with NC and NO contacts, adding a capacitor and resistor brings the switch DC working volts rating to nearly that of AC.  This is not a RC network and the resistor can be thousands of ohms.  A PWM speed control  will work fine as long as sit there and keep adjusting the "speed" as light conditions change. A fixed setting will give better results at lower levels but worse with more sun.  I have been searching ebay for some module that can be easily converted.  All that do require significant change.  This doesn't have to be done with a microprocessor.  There is a discrete chip board for inverters that looks  for under $4, but that is as much work as a micro. I will be in production of a small board that can be configured for multiple applications.   Everyone should download the FREE Arduino compiler and see if they can modify a stock program.  There is just so much you can do with these using very simple conversational English type statements.  I've given up building with parts these days.  Try it, no one has to know.  I'm just starting to work with grid tie inverters. I think there is a way to fake these stand alone units into powering a heater directly at power point.
  • jonrjonr Solar Expert Posts: 875 ✭✭✭✭
    edited December 8 #45
    It's pretty simple - a small microcontroller (with A/D), power supply, a mosfet/IGBT and capacitors.   I wonder it it wouldn't make sense to add a temperature sensor and not use the water heater's thermostat at all (ie, no more concerns about contact arcing).

    I'm in favor of seeing more of these controllers available - let me know if I can help.   Also note that by setting the controller's Vmp a little bit above the actual panel Vmp, the same controller can be used to control an opportunist resistance load.  Ie only send power to the water heater when the solar charge controller isn't using all of the available energy (ie, it's letting the voltage rise above panel Vmpp).

    Hacking the firmware on a low cost grid-tie inverter to turn it into a solar panel to hot water heater controller is an interesting idea.  Maybe just over $100 for "1000W".  But might need lots of reverse engineering.
  • PhotowhitPhotowhit Solar Expert Posts: 4,276 ✭✭✭✭
    Okay, sorta getting the idea that this isn't all I would need, these motor controller appear to have most of this covered. 

    Since they are variable voltage, can I assume they are regulated by the amount of amperage passing through?

    If I used something like this controller, and used it at 100% is it likely not to pulse the energy?

    https://www.newegg.com/Product/Product.aspx?Item=9SIABMK57W1761&ignorebbr=1&nm_mc=KNC-GoogleMKP-PC&cm_mmc=KNC-GoogleMKP-PC-_-pla-_-EC+-+Optoelectronics+&+Displays-_-9SIABMK57W1761&gclid=CjwKCAiAjanRBRByEiwAKGyjZVl8cY6AA-EZe7f25UhepTgcLb922RlKJd6sZDF-bzT5GdEntvcZPRoC0WQQAvD_BwE&gclsrc=aw.ds

    If it would become a straight pass through, could I set it at a 95% duty cycle and be okay?

    My reasoning, is I could use a transfer switch, with a DC and an AC breakers and use the same wiring to the Water heater.  I would wire the DC ahead of the transfer switch.

    I know some have recommended youtube videos, but unless you have a specific one, that you are comfortable with. I've found so much bad information I wouldn't send someone there.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • PhotowhitPhotowhit Solar Expert Posts: 4,276 ✭✭✭✭
    Curious if I can read the Hz of a DC current? I'll hunt around to figure that out, guess I could setup a couple pig tales and just do an experiment...lol.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • jonrjonr Solar Expert Posts: 875 ✭✭✭✭
    How long an off time is needed for an arc to extinguish and then not re-form is apparently a complicated question.  So is how far apart those off times can be without excessive contact damage.  
  • NANOcontrolNANOcontrol Registered Users Posts: 6 ✭✭
    Just as a guess 1ms might be enough, but in doing so you lose 15% of your power.  That can be significant since a lot of heating elements are higher resistance than you would like.  It also takes less time if the polarity reverses.    This is the trick the capacitor and resistor use in a NC/NO switch.  The capacitor charges up to the DC voltage through a high ohm resistor and the switch reverses the polarity extinguishing the arc.  There are designs out there that use a H bridge just like a MSW inverter.  Any tungsten contact is good for "one time" overheating events.  The advantage of going less than 100% is a three wire no brainer hook up. On youtube someone opening up a box gets 17K views. Something with technical content might get 100 views over a couple years.  I watched a guy plug in three solar panels and then asked you to come back for the next episode.

    If anyone wants to buy themselves a Christmas gift consider buying a USB scope.  The Hantek 6022BE is only $60 and attaches to the laptop.  It gives you time, voltage and frequency.  It also allows screen save so you can share with others.  It is great at my camp and if your computer is all plastic it is floating.  Not  the greatest scope in the world but more than sufficient. It comes with two 10X probes but I suggest you get a 100X.  The bad thing about it is that it is easy to overload.  If you get a perfectly straight line with no noise it is overloaded.  Wish they would turn the trace red when it is overloaded.

    Temp sensor is the way to go as long as the code recognizes a bad sensor.  Maybe I should get POWERJACK interested in a heater version.  It is still a very small market.  Techluck hasn't sold that many. Modifications are OK for me but just as much work as building something right.  The beauty is a micro can add other systems to the mix.  At my camp, I don't run the panels in real MPPT.  I use MPPC. Power point voltage only changes with temperature and within a season the slight loss of not tracking isn't that great compared to the other things it allows. There are a few chips that do this and call themselves MPPT, they have a set voltage and can vary that with a temp sensor.

    I use this set power point to set priorities of loads.  Just setting a devices power point 1/4 volt lower gives that device a priority.  This is how I share power with charging and water heating.  It works slick. It can then dump even just a few watts into the heater. This method also allows you to attach a heater control to an existing charge controller.

    That speed control is a little pricey and it still need a capacitor bank to work.  Why don't you wait and get a beta version if the board.
  • jonrjonr Solar Expert Posts: 875 ✭✭✭✭
    I agree, 1 or 1.5 msec of off time, perhaps every 10 msec seems like a good guess to protect contacts designed for AC.

    For a typical 4500W/240V heater element, three 36V panels in series is a good match.

    There would be a safety/approval advantage to using 36V panels in parallel (vs series) to power a water heater.   But, without DC-DC conversion, that would require installing a lower voltage/resistance element.


  • PhotowhitPhotowhit Solar Expert Posts: 4,276 ✭✭✭✭
    jonr said:
    I agree, 1 or 1.5 msec of off time, perhaps every 10 msec seems like a good guess to protect contacts designed for AC.

    For a typical 4500W/240V heater element, three 36V panels in series is a good match.

    I have a 3600 watt 240 v element I've been running on 120 V AC at @900 watts.

    I had intended to use 4 - 35 VMP panels in 2 x2 for @ 70 volts at 740 watts name plate. This should be just below the element's resistance wattage at 70 volts and what the panels will actually produce. 

    The panels are actually up, I have some 6 gauge wire for the 50-60 foot run, I have some 1" conduit... just need to figure out how I want to do it. Perhaps just a relay and another run from my Midnite Classic with some thin wires to run it. then just run it off the inverter. Slave in the array with my current array... I really wanted to try a stand alone system.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • jonrjonr Solar Expert Posts: 875 ✭✭✭✭
    edited December 9 #52
    As I see it, you have a 16 ohm element.  Connect it to 70V and no more than 306 watts will flow.    3 or 4 of your panels in series plus the techluck controller should work if you want a stand alone system (no AC).

    If you do the work yourself, get low cost panels and use 20+ gallons/day of  hot water, the payback of PV solar to DC electric water heater can be good.  Might be a good way for grid connected homes to use solar without net metering.
  • PhotowhitPhotowhit Solar Expert Posts: 4,276 ✭✭✭✭
    That sounds right, some where I was thinking it was around 520 watts at 70 volts, but at 60 it would be @225 so 306 sounds about right. I actually have 13 of these panels, could go to 95 volts pretty easy, the balance seems better.

    Again, just using the CC to run a relay and 120AC is likely simpler.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
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