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

AgroVenturesPeru

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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.
 
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Supervstech

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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.
First off, the battery is rated in KWh capacity.
At 24V that is around 500Ah. Wh/nominal battery voltage.
KWh usage depends on usage. As storage will be less than showering usage.
A daily 10 minute shower should use around 1.2KWh per week...
So, two, 15 minute showers likely would be around 3...
 

efficientPV

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There are calculators, quick rule of thumb is 6 gallon 60F rise takes 1KWH. I use a 6 gallon tank at my camp which has a 1500W 120V element. This works quite well on my 60VDC array using about 350WH a day to recover. It does have another small preheat tank. It does have a power point controller which only feeds excess energy when available. Even a relatively small PV system has enough free energy to provide camp hot water.

 

AgroVenturesPeru

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First off, the battery is rated in KWh capacity.
At 24V that is around 500Ah. Wh/nominal battery voltage.
KWh usage depends on usage. As storage will be less than showering usage.
A daily 10 minute shower should use around 1.2KWh per week...
So, two, 15 minute showers likely would be around 3...
yes. 12.8kwh. I forgot the "h"

It's a 48V battery.

The way I understand it, if no one takes a shower, the heater element will kick on once every 16hours to raise the temperature by 10C. This process will use 1200W, but I don't know for how much time it will be using those 1200W. Anyway that's my comprehension after reading the manual. I assume if one takes a long shower and uses all 50L of hotwater, than the thing will refill and use the 1200W for (probably) 2-3hours to bring the next batch of water up to 60C. The incoming cold water temperature will probably always be in the ballpark of 20-25C.

Sole50L.jpg
 
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AgroVenturesPeru

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There are calculators, quick rule of thumb is 6 gallon 60F rise takes 1KWH. I use a 6 gallon tank at my camp which has a 1500W 120V element. This works quite well on my 60VDC array using about 350WH a day to recover. It does have another small preheat tank. It does have a power point controller which only feeds excess energy when available. Even a relatively small PV system has enough free energy to provide camp hot water.


Thanks. That's a cool calculator. How accurate is it?
Sole50L calculation.PNG
So that's the electricity used to get the temperature up from the initial cold water temperature.

For maintenance heating (10C increase) once every 16 hours:

Sole50L2.PNG

FWIW, My off-grid inverter will produce 220V AC
 
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AgroVenturesPeru

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Thanks. That's a cool calculator. How accurate is it?
View attachment 45720
So that's the electricity used to get the temperature up from the initial cold water temperature.

For maintenance heating (10C increase) once every 16 hours:

View attachment 45723

FWIW, My off-grid inverter will produce 220V AC

I put this water-heater on its own circuit breaker. For my off-grid situation, I think I'm going to turn the circuit breaker on in the morning, so the water-heater can recover some energy from the sun as it heats the water, since the water can stay hot all day (or up to 16 hours according to the manual), at night I'll turn off the circuit breaker just before taking a shower.

That way, the water-heater won't draw 2.51kWh from the battery bank while it's dark outside.
 

12VoltInstalls

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I put this water-heater on its own circuit breaker. For my off-grid situation, I think I'm going to turn the circuit breaker on in the morning, so the water-heater can recover some energy from the sun as it heats the water, since the water can stay hot all day (or up to 16 hours according to the manual), at night I'll turn off the circuit breaker just before taking a shower.

That way, the water-heater won't draw 2.51kWh from the battery bank while it's dark outside.
Your scenario is where the ‘load’ feature many charge controllers have. You can set the load to switch when the PVs aren’t producing; use that as the signal for a high volt relay and just use that to turn off the element automatically every night, on every morning.
-just a thought

(I use a US$180 tankless propane water heater and never worry about capacity but threads like this have me thinking about experimenting w/ a small electric for fun)
 

wattmatters

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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).

You absolutely do NOT want to allow water in a hot water tank to sit below 60C for long periods.

The reason: Legionella disease is deadly.

Legionella bacteria love warm water and they will breed inside your tank if you only have it at 40-50C all the time. It requires a regular heating cycle of at least 30-min at 60C to ensure they are killed, and preferably longer. It's for this reason in many countries hot water tanks have a minimum heating cycle and temperature.

Ensure it heats to at least 60C once every day or two. I am being deadly serious.

If you want your hot water supply from the tank to be regulated to a lower temperature then fit a thermostatic mixer valve on the HW tank outlet which will mix in cold water supply to ensure the hot water supply at the outlet is at the desired max temp. Or of course you can always use the cold water mixer tap to adjust the outlet temperature as desired. Most places requires thermostatic mixer valves to be fitted to HW tanks so that hot water supply is below scalding temperature. Safer for children and the elderly or otherwise those unable to control taps easily.

By heating the water in the tank to a higher temperature, in effect you get more hot water supply from one tank, because you use less from the tank and supplement with cold water to deliver what you need at the tap. It's a useful way to store excess solar PV energy.

As to how much energy it will use, well that depends on how much hot water you use, plus the daily heat energy losses from the tank which itself depends very much on the environment the tank is situated in and how well it and the valves are insulated. e.g. is the tank outdoors, or in a cold environment, or is it indoors in a mild temperature location? The daily heat loss will vary accordingly.

Small tanks need to be reheated more frequently, while larger tanks act as energy storage systems and can be put on a once a day heating cycle, which suits solar PV nicely.
 

Diysolar123

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You absolutely do NOT want to allow water in a hot water tank to sit below 60C for long periods.

The reason: Legionella disease is deadly.

Legionella bacteria love warm water and they will breed inside your tank if you only have it at 40-50C all the time. It requires a regular heating cycle of at least 30-min at 60C to ensure they are killed, and preferably longer. It's for this reason in many countries hot water tanks have a minimum heating cycle and temperature.
that is quite interesting..
the EPA recommended hot water heater setting is just 120F so thats what I have mine at!!
It makes sense that you need "hot" water to kill nasty little critters. Hospitals typically use 165F water to wash.

Hmmm....I may have to crank up to at least 140F hehe
 

Supervstech

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Legionella requires stagnant water to propagate... if daily showers etc are being run in the tank, it isn’t an issue... and, not many people drink from the hot water tap.

I keep my home water heater at 145, but that is mostly for capacity. I have a mixing valve set to 110 feeding the house from it. My 30Gallon electric handles the needs of three women and me, never runs cold.
 

wattmatters

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Legionella requires stagnant water to propagate

That true. It can happen quite easily though, e.g. go away for a while. Or also depending on how the plumbing has been designed there's a chance of some stagnant water in the pipes.

IOW if a tank and pipes/outlets have been left not used for a while then it will need a flushing. But be careful...

not many people drink from the hot water tap.

Legionella is a respiratory disease and is inhaled in tiny water droplets released into the air as the water exits the water outlet. You can become infected while showering for instance.

That's why flushing the tank needs care because the water exiting the tap can cause bacteria to go airborne.

Just set the thermostat at 60C and be safe.
 

Supervstech

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Setting the tank to 60 wouldn’t protect the stagnant water in the plumbing scenario you bring up, would it?

I agree, legionella is a concern, but the vast majority of home water heaters are set to the recommended 120F, and I haven’t heard of an outbreak of legionella since the humidifier scare of 1990...

However, fire hydrants are regularly flushed to prevent legionella in that system. Perhaps the water treatment in cities are preventing it?
that wouldn’t protect well users of course.

What are the symptoms of the disease? Maybe more people have it and don’t know?
 

Supervstech

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Looks like 125F 51C is required to kill...
 

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wattmatters

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and I haven’t heard of an outbreak of legionella since the humidifier scare of 1990...
Home hot water systems don't cause "outbreaks". It just affects those in the home using that system.

There's in the order of 15,000-25,000 cases of legionnaires disease in the US each year. About 1 in 10 die.
 

wattmatters

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almost 100,000 people die in US every year from drinking alchohol; no need to panic
Not sure what this or frankly any of the rest of what you wrote has to do with the safe use of hot water tanks.

Legionella is politically agnostic, while legionnaire's disease is particularly deadly and entirely preventable.
 

AgroVenturesPeru

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Your

Your scenario is where the ‘load’ feature many charge controllers have. You can set the load to switch when the PVs aren’t producing; use that as the signal for a high volt relay and just use that to turn off the element automatically every night, on every morning.
-just a thought

(I use a US$180 tankless propane water heater and never worry about capacity but threads like this have me thinking about experimenting w/ a small electric for fun)
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?
 

AgroVenturesPeru

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You absolutely do NOT want to allow water in a hot water tank to sit below 60C for long periods.

The reason: Legionella disease is deadly.

Legionella bacteria love warm water and they will breed inside your tank if you only have it at 40-50C all the time. It requires a regular heating cycle of at least 30-min at 60C to ensure they are killed, and preferably longer. It's for this reason in many countries hot water tanks have a minimum heating cycle and temperature.

Ensure it heats to at least 60C once every day or two. I am being deadly serious.

If you want your hot water supply from the tank to be regulated to a lower temperature then fit a thermostatic mixer valve on the HW tank outlet which will mix in cold water supply to ensure the hot water supply at the outlet is at the desired max temp. Or of course you can always use the cold water mixer tap to adjust the outlet temperature as desired. Most places requires thermostatic mixer valves to be fitted to HW tanks so that hot water supply is below scalding temperature. Safer for children and the elderly or otherwise those unable to control taps easily.

By heating the water in the tank to a higher temperature, in effect you get more hot water supply from one tank, because you use less from the tank and supplement with cold water to deliver what you need at the tap. It's a useful way to store excess solar PV energy.

As to how much energy it will use, well that depends on how much hot water you use, plus the daily heat energy losses from the tank which itself depends very much on the environment the tank is situated in and how well it and the valves are insulated. e.g. is the tank outdoors, or in a cold environment, or is it indoors in a mild temperature location? The daily heat loss will vary accordingly.

Small tanks need to be reheated more frequently, while larger tanks act as energy storage systems and can be put on a once a day heating cycle, which suits solar PV nicely.

That's a good point to remember. It doesn't really use more energy than heating the water to 50C, because if the thermostat is set at 50C you will be heating more often, since you deplete the tank quicker to get the optimum shower temperature.
 
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