Off grid electric cooking and opportunity loads
mcgivor
Solar Expert Posts: 3,543 ✭✭✭✭✭✭
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
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 bank
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal 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
I am available for custom hardware/firmware development
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.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
I am available for custom hardware/firmware development
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
I am available for custom hardware/firmware development
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.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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!
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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 !
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
I am available for custom hardware/firmware development
Maybe get multiple coolers and use in a hydronic loop for respite room as well?
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
I am available for custom hardware/firmware development
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.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.