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Which element for solar water heater:

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Example Renogy mono-crystalline panel

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One 100 watt solar panel at Amazon $149

One 250 watt panel at Amazon $350

Two 150 watt panels at Amazon $300

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Branch wires

Mounting brackets

Specifications of the 250 Watt RENOGY panels

Maximum Power: 250W

Optimum Operating Voltage (Vmp): 30.1V

Optimum Operating Current (Imp): 8.32A

Panel Ideal resistance at 1000W/m^2 solar isolation = Vmp / 1mp 30.1V / 8.32A = 3.617 Ohms (per panel)

Which element for solar water heater:

the math shows it:

volts x amps = watts

Example: 91 volts x 16 amps = 1456 watts

If your 91 volts drops to 60, then the wattage drops and element produces less heat

If you connect 1456 watt output to an element rated for 120 volt 900 watts, then element will probably burn up.

If you connect 1456 watt output to an element rated for 120 volt 2500 watts, then element will still produce 1456 watts heat

If your solar panels generate 145 volts x 15 amp = ?

240 volt x 15 amps = ?

What happens when you connect 240 volt 15 amp electricity to 120 1500 watt element?

The element burns up.

The math shows it:

volts x amps = watts

Example: If your panels produce 91 volts x 16 amps = 1456 watts (the 91 volts 16 amps will probably burn up the thermostat when direct connected to water heater so use high voltage design).

If your 91 volts drops to 60 volts in the afternoon, then the wattage drops and element produces less heat

If you connect 1456 watt output to an element rated for 120 volt 900 watts, then element will probably burn up.

If you connect 1456 watt output to an element rated for 120 volt 2500 watts, then element will still produce 1456 watts heat.

If you connect 1456 watt output to an element rated for 24 volt 600 watts, then element will burn up.

If your solar panels generate 145 volts x 15 amp = ?

240 volt x 15 amps = ?

What happens when you connect 240 volt 15 amp electricity to 120 1500 watt element?

The element burns up.

Choose element rated for your output:

Volts and watts are printed on end of each element.

Ordinary elements work fine for AC or DC.

You can connect 100-250 volt 30 amp solar installation directly to residential water heater... except alterations are needed, otherwise the thermostat will melt. Read about converting to high voltage DC

In 2017, most local hardware stores do not carry elements rated for low volt and watt ratings, so you need DC element for those applications.

Single U and double U DC elements, 24 volt 500-900 watts.

The single U has ordinary element style with 2 screws for connecting the wires. So your solar panels are connected directly to the element.

The double U element has 4 screws for 4 wires and can accommodate two separate connections.... meaning you can have two separate sets of solar panels, and each set of solar panels can supply power to one of the U

3U elements are usually made for 3-phase boiler installations, have larger thread, and will not fit a residential tank.

Buy:

DC elements

Single U 24 volt 600 watt element

Double U element

Resources

Solar PV safety

How to set up array

How to replace water heater elements

Figure volts amps watts

All solar links

Convert AC water heater to DC water heater/ high voltage

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E-mail: geno03245w@gmail.com

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