My 1.8kw off grid set up, what to do with excess power?

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  • jimmyazjimmyaz Registered Users Posts: 114 ✭✭
    I have installed the 600watts 24V DC element, using 8AWG wire.  I prefer to use DC in this situation, to be as effecient as possible.  If I use AC, need to invert the power and would loose 10-15%....vs if I use DC directly, only loose about 3% to wire distance which is about 20ft away.

    It has been working much better than I expected, I keep reading online that using electric to heat water is INEFFICIENT.... yes maybe so, but for my case it's perfect to use the excess power.  I was able to heat my 22gal from 80F to 120F in about 2-3 hours (since the ambient is averaging 90-110F in my garage, it help quite a bit to heat the water... haha.  Been doing this for the past 4 days and my gas heater is on Vacation mode.  It seem the 22gal is enough for the 3 of us no problem.

    I will upload some video soon... thanks all.




  • Wheelman55Wheelman55 Registered Users Posts: 139 ✭✭✭
    With the extremely low humidity here in the Chihuahuan Desert, evaporation alone keeps the water cool. If memory serves, I've set up seven battery banks this way. A couple are in waterproofed concrete enclosures and others are in plastic tubs or wooden boxes with pond liners. No water circulation or forced air is needed. Two of the banks are set below grade level, and this is good for a few more degrees of cooling. All but one are outdoors and covered. The lids/covers are not airtight; they are loose enough to allow evaporation.
    Mr. Desert Rat...how often are you finding that you need to add water throughout the high heat season?
    Building Off-Grid in Terlingua, TX
    14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048, Mini PDP, MPPT 80-600, SCP. 1 Discover AES 48 volt LiFePO4 battery 130 ah
  • JohannJohann Solar Expert Posts: 245 ✭✭✭
    edited August 2016 #34
    jimmyaz said:
    I have installed the 600watts 24V DC element, using 8AWG wire.  I prefer to use DC in this situation, to be as effecient as possible.  If I use AC, need to invert the power and would loose 10-15%....vs if I use DC directly, only loose about 3% to wire distance which is about 20ft away.

    It has been working much better than I expected, I keep reading online that using electric to heat water is INEFFICIENT.... yes maybe so, but for my case it's perfect to use the excess power.  I was able to heat my 22gal from 80F to 120F in about 2-3 hours (since the ambient is averaging 90-110F in my garage, it help quite a bit to heat the water... haha.  Been doing this for the past 4 days and my gas heater is on Vacation mode.  It seem the 22gal is enough for the 3 of us no problem.

    I will upload some video soon... thanks all.




    I am glad that it worked out and you are able to use that left-over power.
    It does not matter on what you use your left-over power or sun generated power.
    I consider a water heater to be a storage device, instead storing electrical power, you store heat/thermal power, it is almost like a battery. At least, that water heater should last about 10 years or longer, comparable to a pricey battery.
    A heat element turns almost all the  power into heat, nothing inefficient here.  
  • Desert RatDesert Rat Solar Expert Posts: 122 ✭✭✭
    Mr. Desert Rat...how often are you finding that you need to add water throughout the high heat season?
    I check the batteries monthly for electrolyte levels and tightness of the connections. During the summer I can usually add a bit to top off the water bath. It doesn't lose as much water as you might think.
  • jimmyazjimmyaz Registered Users Posts: 114 ✭✭
    In case anyone wondering how my Pre-Heat electric solar water heater is working.  It has been working so good... that I had turn my Gas water heater to Pilot.  Only electric preheat tank are running around 2-3 hours daily now and keeping up just fine.  Water is actually hotter than what I set my gas tank at.  If it work out as good as now in winter time, I may be able to cancel my Gas completely and save another 15.00 a month just for the service fees and another 20-30.00 on gas.






  • JohannJohann Solar Expert Posts: 245 ✭✭✭
    edited August 2016 #37
    jimmyaz said:
    In case anyone wondering how my Pre-Heat electric solar water heater is working.  It has been working so good... that I had turn my Gas water heater to Pilot.  Only electric preheat tank are running around 2-3 hours daily now and keeping up just fine.  Water is actually hotter than what I set my gas tank at.  If it work out as good as now in winter time, I may be able to cancel my Gas completely and save another 15.00 a month just for the service fees and another 20-30.00 on gas.






    I do not know if I would cancel the service. Yes it would save even more money, but keeping the service will give you another backup system just in case.
    On the other hand, you could turn your natural gas heater into a propane system and hook up your own propane bottle to it and this way you still have a gas heater as back-up and you do not have to pay a monthly fee on gas if you do not use any gas. If you have to use gas just get your container filled up again.

    Very nice video update.
    it takes 1 btu to raise 1 pound of water 1 degree.
    1 btu =0.29307107
    1 gallon of water is about 8.5 pounds = so you need 8.5 lb times 0.29307107 watts = 2.49 watts to heat 1 gallon of water 1 degree.

    You could use the build-in thermostat to turn a relay on and off which would switch your heat element on and off. Those relays can be bought with different amps and use very little amps to power the coils.  No more worry to burn the thermostat up.

    Put more insulation on the fridge itself, sides, tops and bottom if you have an external coil for that fridge, you may have to loosen the coil on the fridge and move it away from the chassis to make room for the insulation. Put more insulation on the battery box also.

    The airflow on your fans for the mini-fridge battery cooler needs to be reversed. In the fridge, the cooler air would be on the bottom without a fan, so the air that is coming into the battery box from the fridge should be coming from the lower hole/fan. The return air that goes back into the fridge should be the upper fan cut-out since the air should be warmer. On the other hand, since you have a fan it may not matter.  Right now, I guesstimate that your battery box got about an R value of about 7 maybe a pinch more.

    I  like  your set-up, it is nice and practical.

  • jimmyazjimmyaz Registered Users Posts: 114 ✭✭
    Johann said:
    jimmyaz said:
    In case anyone wondering how my Pre-Heat electric solar water heater is working.  It has been working so good... that I had turn my Gas water heater to Pilot.  Only electric preheat tank are running around 2-3 hours daily now and keeping up just fine.  Water is actually hotter than what I set my gas tank at.  If it work out as good as now in winter time, I may be able to cancel my Gas completely and save another 15.00 a month just for the service fees and another 20-30.00 on gas.






    I do not know if I would cancel the service. Yes it would save even more money, but keeping the service will give you another backup system just in case.
    On the other hand, you could turn your natural gas heater into a propane system and hook up your own propane bottle to it and this way you still have a gas heater as back-up and you do not have to pay a monthly fee on gas if you do not use any gas. If you have to use gas just get your container filled up again.
    Natural Gas water heater can be use with Propane?  no need to modify anything?  Is it safe? 


  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    edited August 2016 #39
    jimmyaz said:
    Natural Gas water heater can be use with Propane?  no need to modify anything?  Is it safe? 
    There is definitely a need to modify something... propane needs a smaller orifice than natural gas.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mike95490mike95490 Solar Expert Posts: 9,261 ✭✭✭✭✭
    It's a $5 part (new orifice) and $40 shipping charge.   Maybe, if you have a good propane shop in town, they have the proper orifice on hand.
    I'll bet 95% of gas appliances have interchangeable orifices between natural gas and propane


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  • jimmyazjimmyaz Registered Users Posts: 114 ✭✭
    Nah, in that case I don't want to mess with it... I never like messing with gases.  I don't even know what a orifices is.  :)

    Wait to see how it would do in the winter if the pre-heat tank would be enough in winter.


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