I have a 17 liter hot
water tank on my Dragonfly which can be heated from the engine's
cooling system.
I also have rebuilt my
refrigerator with Aerogel
insulation and installed a
keel cooled Vitrifrigio
compressor.
As I have only one bank of
batteries (200 ah worth of LiFePo4) but 320 watts worth of
solar panels, I have LOTS of spare electricity, and don't need to run the
engine for
power.
Hot
water is the only thing left wanting, so I decided to do an
experiment with my 1500 watt sine wave
inverter.
This time of year the
weather around the
PNW is nasty and cloudy most of the time, but I decided to go ahead with the
experiment anyway.
The water tank started out at 47 degrees fahrenheit, and the
lithium phosphate 200 amp/hour
battery bank was 100%.
(See the thread on
LiFePo4 for house bank)
The
battery temp
sensor indicated 48 degrees at the start.
I hooked up the 1.5 kw sine wave
inverter to the 1 kw hot water tank and took measurements every 5 minutes.
As soon as I turned on the inverter, the floating
batteries (13.8v) immediately went to 12.6 volts.
The discharge
current from the batteries averaged about 105 amps.
Solar input was minimal as we had heavy overcast during the whole test.
Slowly over the space of one hour, the battery voltage dropped in a linear fashion from 12.6 to 12.3 volts while the discharge
current stayed constant at 105 amps.
The inverter supplied 117 VAC @ 9.5 amps AC as measured with my trusty Fluke 97 at the input to the tank through a cheesy six foot extension cord from the inverter to the tank.
At one hour and one minute, the thermostat on the tank shut off the
heating element.
The battery
monitor indicated 105 amp hours used, my 200 ah battery bank was at 45% and the battery temp was at 65 f.
(LiFePo4 batteries can go to 20% before any damage takes place)
The inverter never missed a beat, the fan only ran at low speed the whole time, and the water temp (measured at the
galley faucet) was 157 f !
The battery voltage immediately jumped back to 12.6 when the tank thermostat turned off the load.
I figured doing this experiment with COLD water this time of year and no sun would be the absolute worst case scenario, so if it was doable now, it ought to be a piece of cake in the summer with longer days.
Kicking the hot water tank around noon, and then topping up the batteries during the rest of the day ought to keep the
MPPT in bulk mode most of the day instead of floating half the time. Make the sun
work for its living!!
Hot showers, here we come. WOO HOO !!