RV electric water heating on Solar—Lot of energy little return

[chrisski]

I ran my water heater today off solar, and as many know, takes a lot of energy.

Specifically took 1.28 kWh at 1602 watts at which is 48 minutes for my 6 gallon tank to get warm from a water temp of 60 degrees. This time seems in line with my 8800 BTU water tanks claim to heat 7.4 gallons an hour.

My water heater:


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Here’s some of the raw data. A bit hard to follow since there is solar power coming in and an electric fridge running. The power draw of the hot water is simply the total drain on the battery from the BMV-712 in the first pic below where the heater is on minus the BMV-712 in the second pic below where the heater is off.

From the battery, the fridge draw 1602 watts (61.2 amps X 26.15 volts). This is from the battery, so 12% less from the inverter perhaps 1409 watts from the inverter.

This shows the total power draw on the BMV-712 of 67.53 amps from the batteries, with 89 watts being fed from the solar panels. What’s not shown is the approximately 400 watts from the electric fridge.



After 48 minutes, the water is heated and the system draw is a 6.33 amps from the battery, with 224 watts being added by the solar panels.


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I make posts like this because when designing my system, exact data was a bit hard to come by. A lot of people, which I was one, when first getting wanting to go solar expect to put a couple of panels on top of their roof and then run both ACs, electric fridge, and electric hot water off that. Then they think they’ll just fill their RV roof with panels up, and finally the realization hits they can get a single AC, hot water, and electric fridge, if they fill their roof up with solar panels, put about as many on the ground, and then decide to only run AC for about 6 - 8 hours a day. No AC at night.

 

[time2roll]

I look forward to the day a compressor water heater and fridge combo is made. Cold into the food storage, heat into the water tank. This should be done for both homes and RVs. Excess thermal energy can be routed to the interior or exterior of the living space depending on the season.

 

[Rider]

I look forward to the day a compressor water heater and fridge combo is made. Cold into the food storage, heat into the water tank. This should be done for both homes and RVs. Excess thermal energy can be routed to the interior or exterior of the living space depending on the season.

I recently got a 40 gal hybrid hot water heater, and it's terrific at heating water. I leave it in heat-pump-only mode and it takes about 2 hours to replenish back to 125* after a 20 minute hot shower while drawing only 600 watts. However, the cold air discharge really isn't that cold, only about 52*. They'd have to do some magic to make a unit that could do simultaneous heat and chill in a package small enough for a camper.

But yes, that would be outstanding if they could.