Any Idea How Many kWh this 50L Water Heater Uses?

Simi 60

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The 180 litre 240v HWS on our boat cuts on @ 52c and off at around 60c
But I do a manual turn on when amps are smashing in and turn breaker off when done or else it comes on again around 3am and destroys the 24v batteries pulling around 70amps.
Ours has an 1800w element
 
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12VoltInstalls

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I'm not familiar with that. Would you please link to some good info for beginners? Would the device still work, even if there are other high-draw appliances that run at night?
Many charge controllers have a programmable switching 10A output. Often these are setable to shut off sundown and on at sunup, off at sunup and on at sundown, on for a time period, or off at some voltage set point. So you use the settings to trigger a continuous-duty relay that controls water heater input; the trigger side would be low voltage, while the switched leads would be 120V. Then it only uses power under the conditions you desire.

No links unfortunately.
But there’s various relays for the HVAC industry available for this.

Another alternative is to use a DC element which ALSO can be controlled by a properly rated DC relay.

I didn’t look it up to confirm but I believe I recall the 40A epever I use has one parameter where you can enter a voltage (like 12.8V or 12.3V) which will cut the ‘load’ output at the set voltage only being “on” if above. That’s one way of selecting usage only when there is surplus power available. So it would be automatic if sun is out or a decent generator was providing power at 13.8 or whatever.
(A downside with the voltage cutoff scenario is if you use lead acid batteries that method could potentially stop proper equalize function unless the water heater was satisfied FYI)
 

MattiFin

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This is for an off-grid system.

I'm trying to figure out if this small, 50L (about 13 gallons) hot water heater makes sense for my solar system, or if I should just chuck it and instead plumb one of those passive solar water-heater units.

The energy-efficiency sticker just says 1200W, and doesn't give a kWh/year rating.

The manual says it's controlled by a thermostat which keeps the temperature between 50-60 degrees celsius (a little too high for my preference).
It also says the unit can maintain the water in this range for 16 hours when located at room temperature.

I'm going to be installing 6.4kW of panels, with a 12.8kw (useable capacity) LFP battery bank. I'm trying to calculate my consumption, and this is the one appliance that I haven't been able to figure out.

Edited to add: I want to calculate for two, 10-15minute showers per day.
50 L cylinder insulated with 30mm layer of PU-foam (assuming thermal conductivity Lambda 0.035w/m*K) consumes 1.4watts per degree.
20 degree ambient, 60 degree inside = 1.4*40= 56W to keep the water warm. Or 56*24 =1.3kWh per day.
Insulation might be even 2x better than that but at least we have some ballpark numbers.

Two 15 minute showers per day use hell lot more:
Typical shower setup here uses 10-15L/min.
Lets assume 12L/min, total 30 minutes, input water temp 20C and shower temp 40C (delta T 20cel)
12*30=360L
4.2kJ/kg/Cel = 360*4,2*20 = 30240kJ == 8.4 kWh

Biggest savings can be had from shower usage: I have been experimenting on RV and clocking shower usage and Instead of 15 minute shower using 180L water you can shower yourself with as little as 3 liters! (if you have short hair)
 

12VoltInstalls

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Instead of 15 minute shower using 180L water you can shower yourself with as little as 3 liters!
Possible I suppose.
A low-flow shower head will let you shower fairly nicely with 3-5 gallons, and turning off water while you shave/shampoo/do your nails/brush your teeth/whatever so it doesn’t just run much for no reason can cut that further- maybe 2-3 gallons if you’re quick.
I’m clueless as to how a15-minute shower is necessary LOL
(I have been using a 250gal tank for four years now)
 

efficientPV

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I use a 50L (13 gallon) at my camp and it serves my needs. Prior to that I had a 10 and 6 gallon in series. I replaced the 10 gallon with this when it started leaking.. Decided to see if the 50L was enough alone to serve my needs. I have a dishwasher and no problem with two showers after that. This 1500W 110V element is sufficient giving me about 450W, typically about 2KWH a day. It runs from 60V of the array using only excess power. The 6 gallon ECOsmart next to it had much less heat loss but is twice the price. I had to add extra insulation to prevent it cooling down overnight. The digital temperature display is nice to have, works on 12V.
 

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efficientPV

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The dishwasher does draw from the hot water tank. Tank is set to 62C and the dishwasher does turn on the heating element if the water is below 120F. The control for the hot water tank switches to the dishwasher when heating is called for pulling element power from the PV array. The dishwasher itself needs less than 100W to run.
 

wattmatters

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Tank is set to 62C and the dishwasher does turn on the heating element if the water is below 120F.
I found this statement confusing.

When you say the dishwasher turns on the heating element if the water is below 120F, do you mean the dishwasher heats its own water if the water supply is not hot enough or do you mean the dishwasher has drawn so much hot water from the HW tank that the tank's thermostat will switch on the HW tank's heating element?

The control for the hot water tank switches to the dishwasher when heating is called for pulling element power from the PV array.
I am struggling to follow what you mean here as well.

Is not the HW tank thermostat what controls whether/when the HW tank heating element switches on? Not sure what the dishwasher has to do with it other than being a HW "load".

How does the dishwasher clean properly if the HW tank does not have enough hot water?

Not sure about your local codes but here a HW tank outlet must have a tempering valve fitted to mix in some cold water supply to reduce the outlet water to no more than 50C for safety reasons. That would be inadequate temperature for sanitary cleaning of dishes. In some cases separate supply lines can be installed which bypass the tempering valve but they are not meant to supply general HW outlets.
 

efficientPV

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Dishwashers have a pretty high heat loss due to large surface area and almost no insulation. I added extra insulation to mine. The water heater thermostat is set to 62C. From what literature I read the dishwasher will add additional heat to bring the water up to 120F. I don't think the dishwasher is designed to bring cold tap water up to that temperature though I'm not sure. The water heater controller keeps the solar array at a fixed power point for higher power transfer. When the dishwasher heater calls for the element to turn on on, it switches from the hot water heater element to the dishwasher. Additionally, in the dry cycle the dishwashers duty cycle is about 50%. I extend this time to 100% because of the lower voltage I supply to the heater element. The dishwasher will throw a fault if it is unable to reach 120F before end of cycle. So far it has never indicated a temperature fault. Next year I will probably give the dishwasher its own controller so I can continue powering the water heater.
 

wattmatters

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The water heater thermostat is set to 62C. From what literature I read the dishwasher will add additional heat to bring the water up to 120F. I don't think the dishwasher is designed to bring cold tap water up to that temperature though I'm not sure.
I must admit I'm not really following the description of your system, but it's working for you, so great!

Simple question:

How many water inlets does your dishwasher have?
 
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