Solar Hybrid Hot Water Controller For Your Hot Water Heater

techlucktechluck Posts: 5Registered Users
I thought you guys would like to know about a new device that can save you money on your power bill by supplementing your hot water heater power usage with solar.

No pumps, pipes, re-plumbing or freezing to worry about, just two simple wires! No need to drain the tank.

Only minor modifications are needed for most standard water heaters, simple wiring modifications. NO HEATING ELEMENT CHANGES NEEDED. Simple wire up, only two wires (+/-) coming from the solar panels and two going to the water heater are needed.

This is a good way to reduce your power bill if you have a Smart Meter that doesn't "spin backwards".

It's really the easiest way to do solar hot water.

You can check it out at http://techluck.com
http://www.youtube.com/watch?v=YkPtPXfhiYk

Meter readings, amps and volts and more info:
http://www.youtube.com/watch?v=hPtVGMifewM

Comments

  • XRingerXRinger Posts: 588Solar Expert ✭✭✭
    Re: Solar Hybrid Hot Water Controller For Your Hot Water Heater

    Seems like a very easy way to use PV, maybe with a minimum of involvement with city inspectors.
    I've been heating hot water with PV for a while now and it's working okay for me. (on a small scale).
    Plus, I hear some Windpower guys use their hot water tank as a dump-load after their bank is charged up.
    Or, they just waste it on a big free air resistive load. :(

    It might be nice to get an extra 20 or 30 percent out of my HW PV array. :p
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Solar Hybrid Hot Water Controller For Your Hot Water Heater

    Heating water with PV us extridinarlly INNEFFICINT! It is generally much more cost effective to use direct soar hot water than to use PV,,, Exocet as a dump load. Even with PV at record low prices, it is still neither cost effective nor cost efficient to design a PV system from the ground up, instead of using direct hot water heating.

    Tony
  • XRingerXRinger Posts: 588Solar Expert ✭✭✭
    Re: Solar Hybrid Hot Water Controller For Your Hot Water Heater
    icarus wrote: »
    Heating water with PV us extridinarlly INNEFFICINT! It is generally much more cost effective to use direct soar hot water than to use PV,,, Exocet as a dump load. Even with PV at record low prices, it is still neither cost effective nor cost efficient to design a PV system from the ground up, instead of using direct hot water heating.

    Tony

    Luckily, I had 800 watts of PV sitting there doing nothing. So, heating hot water is better than letting all those photons go to waste.. :)
    It does work. I found this study a few years ago.. fire.nist.gov/bfrlpubs/build02/PDF/b02012.pdf
  • stephendvstephendv Posts: 1,571Solar Expert ✭✭
    Re: Solar Hybrid Hot Water Controller For Your Hot Water Heater
    icarus wrote: »
    Even with PV at record low prices, it is still neither cost effective nor cost efficient to design a PV system from the ground up, instead of using direct hot water heating.

    Yeah, agree that if you're starting from scratch using PV for heating is not economical, but if you're already using PV for something else, then it could be worthwhile using it for hot water heating too. I'm stuck with this question right now, should I spend 1000 euros on a new thermosiphon solar hot water system, or 100 euros on a water tank + 900 Euros on more PV. The latter solution would give me about 1800W more installed PV, which would mean less generator run time and solar hot water on most days between spring and autumn.

    PV energy is more versatile as I can choose where to spend it, while solar hot water just gives heat... which can only be used as heat.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Solar Hybrid Hot Water Controller For Your Hot Water Heater

    for most people a gt solar setup would be best as any excess produced by pv could go to the grid and you can get credit for later power use. in a gt system the power that electric water heater is using would still be supplied by solar provided you have enough in pv to cover the draw of the heater. you won't have to worry about reconnecting to the grid when solar production is low if it is already to the grid and you will have consistent heat all day and night.
  • solar_davesolar_dave Posts: 2,335Solar Expert ✭✭✭✭
    Re: Solar Hybrid Hot Water Controller For Your Hot Water Heater
    niel wrote: »
    for most people a gt solar setup would be best as any excess produced by pv could go to the grid and you can get credit for later power use. in a gt system the power that electric water heater is using would still be supplied by solar provided you have enough in pv to cover the draw of the heater. you won't have to worry about reconnecting to the grid when solar production is low if it is already to the grid and you will have consistent heat all day and night.

    And with TOU even the night time power is cheap enough to heat water if no excess is available then. Personally I like my solar thermal system with Nat Gas backup.
  • XRingerXRinger Posts: 588Solar Expert ✭✭✭
    Solar Hybrid Hot Water using PV & ASHP !!
    solar_dave wrote: »
    And with TOU even the night time power is cheap enough to heat water if no excess is available then. Personally I like my solar thermal system with Nat Gas backup.

    If you have a Nat Gas hotwater heater, that works during a grid failure, you're Golden..
    That's the problem with a standard GTI and a regular electric, or Heat Pump water heater.
    Without a backup system, if the grid fails and you don't even have luke-warm water.

    I'm using a heat pump (A7 AirTap) for hot water and I'm currently testing the tank
    (GE 40gal electric hotwater) with 800W of PV connected directly to the 230vac connections.
    If it wasn't so cloudy, I would be getting some results today..
    Yesterday it was partly sunny and the PV boosted the tank temp by 13 deg F in less than 45 minutes.
    And that was without MPPT.. :)

    Edit~~~
    Today is very overcast with no direct sun at all. The current flow into the 13 ohm element indicate 20 to 30 watts going in.
    Interestingly, it looks like the tank temperature is slowing drifting up.. I may not need a tank blanket!

    Note:~~~
    I wondered how well this GE 40 gal unit would work with 120VAC.. So, I checked it out.
    124.5Vac measured.
    9.4A measured. (1148.68 watts calculated into 13 ohms)
    1170W measured.
    13 ohms measured.
  • BB.BB. Posts: 28,079Super Moderators, Administrators admin
    Re: Solar Hybrid Hot Water using PV & ASHP !!

    Techluck,

    What is the the controller doing in this setup? It does not look like it has enough parts (i.e., good sized inductor, FETs may be on the rear of the heat sink where I cannot see them--but could have voltage isolation issues) for actual MPPT tracking? Is it a buck or boost mode controller? I could see using switched capacitors to double output voltage (and no inductors)--but that is not really MPPT as I would understand it.

    Also, what is the maximum input rating? You said 48 VDC (minimum?) and running a 240 VAC heating element on 48 volts will only run at about 4% of rated power (i.e., 2kW element will run at ~80 watts). You would need to run at ~333 watts for six hours to meet the 2kWH per day power generation you mentioned (or a 12 kW @ 240 VAC element and a 48 VDC Vmp-array).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_davesolar_dave Posts: 2,335Solar Expert ✭✭✭✭
    Re: Solar Hybrid Hot Water using PV & ASHP !!
    XRinger wrote: »
    If you have a Nat Gas hotwater heater, that works during a grid failure, you're Golden..
    That's the problem with a standard GTI and a regular electric, or Heat Pump water heater.
    Without a backup system, if the grid fails and you don't even have luke-warm water.
    Yep it works with no grid power.

    The solar thermal system today is producing 150F water and the storage tank is currently at about 135F. The 80 gallon electric hot water heater (not wired) storage tank supplies the gas heater and prevents it from starting, this is about the time of year I turn down the gas trigger temps. Thanks for the reminder! ;) LOL Looks like the mixing valve will be back working hard again today.
  • XRingerXRinger Posts: 588Solar Expert ✭✭✭
    Re: Solar Hybrid Hot Water using PV & ASHP !!
    solar_dave wrote: »
    Yep it works with no grid power.

    The solar thermal system today is producing 150F water and the storage tank is currently at about 135F. The 80 gallon electric hot water heater (not wired) storage tank supplies the gas heater and prevents it from starting, this is about the time of year I turn down the gas trigger temps. Thanks for the reminder! ;) LOL Looks like the mixing valve will be back working hard again today.

    Being able to burn gas without using any 120AC is nice. My kid has a gas hotwater heater and it has a small blower for the exhaust, and I think the nat gas controls use 120AC also.

    I have seen a gas space heater (outdoor venting duct) online at Home Depot that uses a battery.
    That would be great for grid failures in the winter.

    I had a solar thermal system hotwater system for years, but the water here is a bit to hard on copper.
    It worked great for years, but it didn't last. I hate being surprised by basement flooding!
    At least when it's raining, I expect it! ;)
  • Eric LEric L Posts: 262Solar Expert ✭✭✭✭✭✭
    Re: Solar Hybrid Hot Water using PV & ASHP !!
    Also, what is the maximum input rating? You said 48 VDC (minimum?) and running a 240 VAC heating element on 48 volts will only run at about 4% of rated power (i.e., 2kW element will run at ~80 watts). You would need to run at ~333 watts for six hours to meet the 2kWH per day power generation you mentioned (or a 12 kW @ 240 VAC element and a 48 VDC Vmp-array).

    I'm also having a hard time seeing how this could generate meaningful heating. 330 watts (which is the derated, expected output of the suggested 2 220 watt panels in full sun) is only delivering about 1100 btus. In an hour, or even five, that's barely going to make a dent in the temperature a 40 gallon tank, especially if cold line or well water is coming in. It's something, but not much. And that's on a sunny day.

    If possible, could the OP show a video with a multimeter displaying the input voltage at the heater element while the system is working?
  • XRingerXRinger Posts: 588Solar Expert ✭✭✭
    Re: Solar Hybrid Hot Water using PV & ASHP !!

    The way I'm looking at my 800w of PV assist, if the PV can provide us with hand-washing water
    and keep the heat-pump from starting up, while the sun is up..
    That's going to save use some money and maybe our heat pump will last a few years longer..

    These guys trying to profit off cheap panels?
    http://www.usa-eds.com/web/index.asp?page=main

    www.usa-eds.com/userfiles/file/Liberty_Box_Test_Results_final.pdf

    In this Test, the solar assist PV was about twice what I'm running (without MPPT).
    So, one tenant started living Green. He took his hotwater heater off-grid.
  • Eric LEric L Posts: 262Solar Expert ✭✭✭✭✭✭
    Re: Solar Hybrid Hot Water using PV & ASHP !!

    XRinger,

    I think the EDS unit you link to requires a low voltage DC element (this is what I remember, I couldn't find the info. just now). The OP in this thread says no element changes are necessary. He also says we could use a 12 volt panel. So if the incoming panel voltage is, say 17 v, and it's wired into a typical 240 volt, 4000 watt element, then it's producing almost no power (since each halving of the voltage reduces the power to 1/4th), unless the MPPT controller is boosting, and even then we need to know by how much.

    I have no problem with the idea in principle, and I think the Liberty Box you linked to is cool, but a bit expensive for what it does.
  • inetdoginetdog Posts: 3,123Solar Expert ✭✭✭✭
    Re: Solar Hybrid Hot Water using PV & ASHP !!
    Eric L wrote: »
    XRinger,

    I think the EDS unit you link to requires a low voltage DC element (this is what I remember, I couldn't find the info. just now).

    Calling the technical information on the EDS site minimal would be generous. But the linked description of the Tallahassee test shows this:
    ...in each apartment, the water heater was refitted with a 2500 watt lower element and the existing upper
    element of 4500 watts left in-service. The retrofit of the lower element to 2500 watt is required to
    match the impedance of the element and the output function of the Liberty Box.
    So it looks like a real MPPT controller coupled with a low voltage DC element, as you thought.
    That combination can actually make sense if the PV is there for other purposes and only the surplus energy goes to the water heater OR if the only alternative for water heating is electric.
    Solar thermal still has better efficiency in terms of power per panel area and probably a cost advantage unless the plumbing is too expensive. The nice thing about the Liberty Box is that it requires only some fairly small wiring to be run from the panels to the heater location. I have not found any information on actual cost of the box though.
    SMA SB 3000, old BP panels.
  • techlucktechluck Posts: 5Registered Users
    Re: Solar Hybrid Hot Water Controller For Your Hot Water Heater

    Thanks for all your comments and interest in the Solar Hybrid Hot Water Controller.

    I can see why there may be some confusion. A "48V" Panel set like mine, using "12V" panels, will generally MPPT at about 65V to 70V and is around 80V open circuit.

    The MPPT tries to get the most it can out of the panels, and it's pulsing so the voltage can go higher during the off period and then come down under load for that short period, so it all works out pretty well as the MPPT works it's magic.

    Of course the higher voltage you go the better, but dedicating a simple, cheap two 24V panel set to your water heater is good for most people and cost effective.

    The idea isn't perfection, it's how simple and hassle free can it be, and in the end does your upper element come on less for a total installed system cost around $700 ?

    That beats most of the other systems out there. All DIY, easy install with no plumbing nightmare, no soldering, no leaks and no worry of freezing. Almost anyone can wire up 2 wires.

    When I first started to want solar hot water I considered piping in a collector from outside. Then I watched videos and e-mailed a few guys that did that and found a few problems.

    First, if you don't put in some sort of system to drain back the water you are going to have freeze problems and possible panel damage and leaks. Setting that up is not fun, you have problems with air in the system. It needs to be designed to totally drain or it will still have problems. And it still costs a lot and gets complicated. More stuff to worry about in the winter.

    The other option is drain it every time the temp drops. Well, if you do that, there goes free winter hot water and what if you forget? I like simple and automatic stuff I don't have to mess with.

    And then there's the plumbing, all over the place, maybe a 2nd exchange / heat storage tank that will develop leaks later as any tank does. And a pump that wears out or gets clogged. It's a maintenance nightmare and still a costly install.

    So solar PV was the only way to go. I tried what XRinger is trying now, go direct to the element. But the mismatch in the morning and afternoon is brutal, the panels are nowhere near their MPP and you get little total daily heat that way unless you have the extra space and want to throw lots of panels at the problem and just say "oh well".

    Another choice would be to change the element. Have you ever seen the nut size on those things? What if I screw up the threads? Will it leak later? Do I really want to mess with a perfectly working expensive tank?

    And without MPPT, you still have a mismatch in the morning and afternoon anyway, doesn't really get that much better for all the hassle.

    So I built the MPPT Hybrid system and love it! It's simple and just sits there quietly and works every day saving me money with no worries and little up front cost.

    Installing wires instead of pipes is much easier, and it gives me other options, like if the grid goes down during a bad emergency I can say heck with hot water and simply re-configure the panels for 24V by switching a couple of connections and have more power for my emergency inverter and batteries.

    Simple is better.

    Thanks for your interest!
  • techlucktechluck Posts: 5Registered Users
    Re: Solar Hybrid Hot Water using PV & ASHP !!
    BB. wrote: »
    Also, what is the maximum input rating? You said 48 VDC (minimum?) and running a 240 VAC heating element on 48 volts will only run at about 4% of rated power (i.e., 2kW element will run at ~80 watts). You would need to run at ~333 watts for six hours to meet the 2kWH per day power generation you mentioned (or a 12 kW @ 240 VAC element and a 48 VDC Vmp-array).

    The unit can handle 250V max and higher voltage is better of course, but you have to look at the cost factors of buying more panels to get the voltage up. I think the best cost/space/install trade-off for most people is dedicating two "24V" panels to this, also taking into considering things like roof space and at some point your thermostat will start turning off with higher power input and that would throw away perfectly good solar power.

    I posted a video of meter readings and other info with a "48V" panel setup that may clear things up:
    http://www.youtube.com/watch?v=hPtVGMifewM
  • orlan7sorlan7s Posts: 9Registered Users
    Re: Solar Hybrid Hot Water using PV & ASHP !!

    im thinking of doing this with a homedepot GE 30-Gal 4500 Watt Double Element 240 Volts Mobile Home Electric Water Heater. i have 3.2 KW of solar and 2.5KW of wind, and there are many times when i have too much power and i would like to use some of the exsess power to a hot water heater. or use couple of pannel when there is little wind to preheat my main gas tank using the 30 gallon electric tank to reduce my heating bill.how do you suggest i would do this?
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