Off grid electric cooking and opportunity loads

mcgivor
mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
edited March 2017 in Energy Use & Conservation #1
Needed to find a way to use excess energy, my system is in float by 11:30 on a good day, the array still has a potential 45A+ with nothing to do but keep the battery on float and power the refrigerator running 6.5A at 24V nominal. Got a water cooler, very handy but not much of a load even with a hot water supply, can only use and drink so much water. As hot water for showers is not needed, hot climate, had to think of alternatives and cooking rice came to mind, we grow about 15 tons each year and is the staple for both humans and animals, 7 dogs consume a lot of rice. So went to buy a large rice cooker but ended up with something much more versatile, a rice cooker,steamer, slow cooker and oven, yes you can bake bread and cakes, see link. This is the most versatile appliances ever for utilizing excess power, the one I have is a 750W 230V, there are smaller 500W available, here's my findings electrically.

The demand is not a constant, initially it draws 750W until the cook temperature is reached, I'll use the slow cooker as an example as it needs more time, once the preheat is complete the unit cycles on for 7 seconds, off for 20 seconds, my observations were achieved using a clamp on ammeter and DVM on the battery side. Even when the sun was going down, the short on cycles, although greater than the array output, were short enough to not pull the controller out of float, sometimes dropping slightly below the 25v threshold but not long enough, 7sec, of the minute required to prompt an absorption-cycle. Over the last week I've attempted to see how much my 1.5KW array can supply, so far the highest is 5.5Kwh in a day, 3Kwh more than regular consumption/production, seems a lot to just throw away, would be significantly more with a constant load but passing clouds could be a problem. So if food is a priority this is a great way to utilize that otherwise wasted energy and although the price here is half of the US price, it would still be a worthwhile consideration.

http://shop.panasonic.com/microwave-and-kitchen/kitchen-appliances/rice-cookers/home-rice-cookers/SR-ZG185.html
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.

Comments

  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    In a hot climate, I'd consider an air to water heat pump (like Chiltrix) and using it to cool a very large tank of water (like 2000 gallons).  Then use it for space cooling.   But perhaps this is much more complexity than you want/need.

    I am available for custom hardware/firmware development

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    jonr said:
    In a hot climate, I'd consider an air to water heat pump (like Chiltrix) and using it to cool a very large tank of water (like 2000 gallons).  Then use it for space cooling.   But perhaps this is much more complexity than you want/need.


    One thought was to use a small refrigerator compressor to cool water in which the battery sits, a water bath, insulated with styrofoam, with a set-point around 25ºC, thereby not subjecting them extreme temperature and extending their life, always thinking of ways to improve upon the efficiency, thanks for the suggestion.
    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.
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    Opportunistic battery cooling makes sense to me (in a hot climate).   Would be interesting to know exactly how many btu batteries dissipate.  I suppose that even without a compressor, a large water bath might help cool batteries (more effective conduction and convection plus some evaporation).

    I am available for custom hardware/firmware development

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    10 to 20% off the charging current is dissipated as heat.

    Below 80% state of charge, only a few percent is lost as heat.

    Above 95% state of charge, something like 50% of charging current is lost as heat (equalization/gassing).

    During discharge, probably not much lost as heat (I^2R heating where R~0.005 to 0.010 ohms per 12 volt lead acid storage battery).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    You live in a hot climate, there is always a good old air conditioner!
    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.
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    In a hot climate with lead acids, would it improve battery life (by reducing heating) to only charge to 80% on most days and to 100% once every week or two?

    I am available for custom hardware/firmware development

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭

    Photowhit said:
    You live in a hot climate, there is always a good old air conditioner!
    Without getting into physics too deeply, water is about 1000 times more dense than air and for that reason the heat transfer between a heated body, the battery in this case, is around 4 times greater. Rational, a person can be comfortable in 24°C air, but can suffer hypothermia in water of the same temperature. Being more dense, water is also able to retain it's temperature for a longer period. Cooling the entire room would be less effective due to losses, in this case uninsulated concrete walls, lining the water bath with styrofoam and covering the  surface of the water as well, would be quite efficient in terms of losses.

    My battery temperature varies over a 24 hour period between 25 and 30°C, unless ambient air rises above 45°C for a week, it rises to 40°C, so keeping it stable at 25 would greatly increase the life expectancy. In a cold climates perhaps a warm water bath could be utilized to increase capacity otherwise lost to the cold, the tradeoff would be a lower life expectancy.
    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.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    I was more concerned with an opportunity load that would provide "you" with comfort.

    You may be more concerned with your batteries comfort than your own, but at about 85°F degrees, my comfort wins out! Actually my batteries remain reasonable the same temps during the day, just living in the shade of my array. There is pretty much no load on them running the A/C during the day, and during the night they will warm up a bit with the 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.
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Photowhit said:
    I was more concerned with an opportunity load that would provide "you" with comfort.

    You may be more concerned with your batteries comfort than your own, but at about 85°F degrees, my comfort wins out! Actually my batteries remain reasonable the same temps during the day, just living in the shade of my array. There is pretty much no load on them running the A/C during the day, and during the night they will warm up a bit with the load!
    Today was warm 104ºF / 40°C, battery temp 89°F / 32ºC, will in the near future build a system to provide a refuge room in the house with air conditioning,  for when it gets hot, the battery room is independent and shaded after 9 am. so stays cooler. My figuring is if I take care of the batteries, they will take care of me, for a little longer at least.
    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.
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited March 2017 #11

    jonr said:
    Opportunistic battery cooling makes sense to me (in a hot climate).   Would be interesting to know exactly how many btu batteries dissipate.  I suppose that even without a compressor, a large water bath might help cool batteries (more effective conduction and convection plus some evaporation).
    BB. said:
    10 to 20% off the charging current is dissipated as heat.


    Below 80% state of charge, only a few percent is lost as heat.

    Above 95% state of charge, something like 50% of charging current is lost as heat (equalization/gassing).

    During discharge, probably not much lost as heat (I^2R heating where R~0.005 to 0.010 ohms per 12 volt lead acid storage battery).

    -Bill
    My plan is to use the auxiliary output of the CC using the BTS to trigger the cooling , or an alarm, still in the thinking stage of things, personally I've  always been a manual type, automation can often lead to unwanted supprise, Bill has often mentioned this in reference to AGS. Used ground water 24°C last year but my pump is too large, and in storage the temperature rises so for less than $80 I could buy a water cooler, gut it and use that as a source for refrigeration, 90w compressor, but in the end I'm just entertaining myself and thinking outside the box. Ideas always welcome !
    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.
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited March 2017 #12
    A 90W compressor seems about right to opportunistically cool water surrounding a set of batteries in an insulated box.  Evidently reducing lead acid battery temp from 33C down to 25C can double life.  That's significant.

    I am available for custom hardware/firmware development

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    90w sounds a bit light to me. Say 2000w charging with 10% going to heat is 200w plus losses through box insulation. Current drops in absorb, but more lost to heat. Still better than nothing though.

    Maybe get multiple coolers and use in a hydronic loop for respite room as well?
    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
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    90 watt compressor with COP=3 is 270W of cooling.

    I am available for custom hardware/firmware development

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited March 2017 #15
    Estragon said:
    90w sounds a bit light to me. Say 2000w charging with 10% going to heat is 200w plus losses through box insulation. Current drops in absorb, but more lost to heat. Still better than nothing though.

    Maybe get multiple coolers and use in a hydronic loop for respite room as well?


     When the ambient outside is 35ºC, the battery room would be in the high 20's, a shaded concrete room, never in direct sunlight, cooled overnight. When temperatures are in the 45°C+ range, for a week then that's another story, but generally 35ºC is the normal high and 24°C the low. Currently it's normal, so morning battery temperature is 25°C , when transition to float occurs it's 29°C +/- a degree, so my thinking is, by using a 90w compressor setup,  starting after sunrise, should cool the water before the battery begins to warm. By 9 am. the array is producing around 750W, by noon it is 1150W (potential ) , from a 1500W array. So using a fraction of the power as sort of preemptive cooling would be benificial, as the array, on a good day, can actually produce 3.5Kwh excess if pushed to the limit. The system reference is to the system 1 in my signature, so battery is sized for the loads, 30% DOD, never need a generator as even on an overcast day the system reaches float, albeit a little later, 2 pm, winter or summer, there is very little difference.

    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.
  • 706jim
    706jim Solar Expert Posts: 514 ✭✭✭✭
    I never knew that dogs would eat rice.
    Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 30th year.
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited April 2017 #17
    706jim said:
    I never knew that dogs would eat rice.
    When you consider dog food is probably 90% grain, corn, wheat, rice whatever is cheaper, with a little fat and flavor that's much the same thing as feeding them rice, with chicken carcass, chicken  blood soup. Dog food is costly, I grow the rice and since selling it at low current prices is not an option, I use ti to feed the dogs. The uncooked rice is fed to the chickens converting it to protein, the chicken carcass and blood  is fed to the dogs, it's all a means to be as self sufficient as possible.
    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.
  • Shubham5421
    Shubham5421 Registered Users Posts: 2
    Well, renewable power generation provides low-cost solutions and maintenance to bring reliable electricity to rural households or island communities off the main grid which is a very good source. But while off-grid renewable energy systems are expanding rapidly on the ground, data that systematically tracks this progress remains limited.