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Solar panel directly connected to immersion heater?

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  • #16
    I currently do this at my camp and an able to put about 3KWH into making hot water consistently. That is from 900W of panels connected as a 36V string and about a 52V power point. Keep in mind that this is only the excess power after everything else is powered. There are two tanks, 10gal with 2000W 125V element and 20gal with 1500W 125V element. These are connected in series with the 10 gallon as the final. That allows fast heating in the morning and can usually get to 45C by 10am. Either heater or both can be on. A couple FET control each heating element by PWM from a UNO. FET are driven at low frequency via a simple opto isolator driver. It operates from a simple program that monitors the fixed power point voltage of the panels. Really no need to track. If voltage is over the setpoint, the PWM counts up. And down if lower. You could do the same with a TL495 switching regulator chip. Controls are powered by wall warts. A good percentage of them work easily at 50V. The whole secret is a large capacitor bank that stores panel power between on pulses. I use an old TURNIGY 130A to record power. Variants of these sell for only $10. This picture is my power shed that holds the two tanks and all my electronics.

    I also tried a variant of this at home using cheap ebay boost converters. Boost converter runs at full bore and the input voltage is monitored with uno driving a FET. Even just a 250W panel is quite effective since normal water heater losses are about 150W.
    Attached Files

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    • #17
      Originally posted by PNPmacnab View Post
      I currently do this at my camp and an able to put about 3KWH into making hot water consistently. That is from 900W of panels connected as a 36V string and about a 52V power point. Keep in mind that this is only the excess power after everything else is powered. There are two tanks, 10gal with 2000W 125V element and 20gal with 1500W 125V element. These are connected in series with the 10 gallon as the final. That allows fast heating in the morning and can usually get to 45C by 10am. Either heater or both can be on. A couple FET control each heating element by PWM from a UNO. FET are driven at low frequency via a simple opto isolator driver. It operates from a simple program that monitors the fixed power point voltage of the panels. Really no need to track. If voltage is over the setpoint, the PWM counts up. And down if lower. You could do the same with a TL495 switching regulator chip. Controls are powered by wall warts. A good percentage of them work easily at 50V. The whole secret is a large capacitor bank that stores panel power between on pulses. I use an old TURNIGY 130A to record power. Variants of these sell for only $10. This picture is my power shed that holds the two tanks and all my electronics.

      I also tried a variant of this at home using cheap ebay boost converters. Boost converter runs at full bore and the input voltage is monitored with uno driving a FET. Even just a 250W panel is quite effective since normal water heater losses are about 150W.
      Man. That breadboard system with all the loose wires looks scary to me. I hope that area is dry and bug free or you will find it can get real messy after a while.

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      • #18
        Not scary at all. I solder in converter FETs with the power on. That is an old picture just after the electronics was moved from the basement stairs. That was scary, only three steps were left and those were cracked. Micro board was above the fridge. Software updates were always interrupted by my wife wanting to get in the fridge. All that stuff ran everything, fridge, two solar converters, two hot water tanks and a pump. It had to be up and running in less than an hour or the fridge would overheat. It looks better now, but I have tried to keep that look to show people that electronics can be done by anyone. The shed is really nice with a sun roof, Anderson windows and Hardie plank for siding. I am new to this host software and see the saved icon pop up all the time. However, I have lost posts at least four times as I have been writing them and found no way to recover them.
        Attached Files
        Last edited by PNPmacnab; 11-07-2016, 09:55 AM.

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        • #19
          Originally posted by PNPmacnab View Post
          Not scary at all. I solder in converter FETs with the power on. That is an old picture just after the electronics was moved from the basement stairs. That was scary, only three steps were left and those were cracked. Micro board was above the fridge. Software updates were always interrupted by my wife wanting to get in the fridge. All that stuff ran everything, fridge, two solar converters, two hot water tanks and a pump. It had to be up and running in less than an hour or the fridge would overheat. It looks better now, but I have tried to keep that look to show people that electronics can be done by anyone. The shed is really nice with a sun roof, Anderson windows and Hardie plank for siding. I am new to this host software and see the saved icon pop up all the time. However, I have lost posts at least four times as I have been writing them and found no way to recover them.
          If your posts had any weblinks attached then they went to an Unapproved area first. One of the Mods would have to review it first before it would show up as a view able post.

          What I was trying to covey about it being scary was that open circuitry and wiring is not necessarily a safe way to have a system due to someone being able to touch live contacts or insects getting into the works which may add paths for shorts.

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