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Solar pv for hot water service ?

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  • Solar pv for hot water service ?

    i have 20 , 250w solar panels and want to connect them to a hot water service with a 3.6kw , maybe even a 2.4kw element. i will then connect the hws via pipe work only , to our solar hws ( NOT PV )....i`ll either direct connect to element or via a SSR...what would be the best configuration , series / parallel etc to connect the pv panels up ? I want it this way as during winter the non pv doesnt work that great. not interested in evacuated tubes or anything else.

  • #2
    There is a thermostat in the water heater that was designed to work with AC so you l will need to disconnect that and find an alternate way to trigger the SSRs when the water get to the desired temperature. The output of those panels will vary over the seasons and during the day as the sun or clouds move across the sky. In order to answer the question about series or parallel the voltage and amperage specs of the panels must be known to make a preliminary calculation. You would probably want to start with 240 volts as the target voltage and let that be the driver for how many Amps you will get. If the non pv isn't working that great you may have the same issues with the PV panels.

    What latitude are you in?
    Are there trees that shade the non pv in winter?

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    • #3
      You must be in Australia where everyone has 7KW of panels that they can't find a use for and every trash day there are panels at the curb for free. I heat with PV and it has become my specialty simply because no one seems to know how to do it. With a lot of panels and plenty of sun, you can heat water with a dead chicken as a control system. With clouds it takes a smarter control. It is all about making the best of limited options. Lower light levels may mean parallel is a better option to increase current. Just as an example, many battery voltage elements are dual heaters in parallel. At just 70% of ideal current, you get more heat from just one element instead of two in parallel. By 50% you get twice as much. Power is a square function and small changes make a big difference. Designing for the less ideal condition will be a better choice. Halving the voltage to the heating element will produce 1/4 of the rated elements power. But on bad days, this is when you need the heating. If you have the ability to have multiple heating elements a pseudo MPPT can be created and is within the scope of most people. I match power electronically to the element for always the best transfer of power. Always use the the emergency thermal cut out in series with the heating element. It may not last multiple switches, but it will always work once.

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      • #4
        yep, i`m in australia , and everyone doesnt have 7 kw solar panels, maybe 6kw, and the solar panels arent on the curb for free , who told you that utter crap ? you be surprized how QUICK the pv panels sell here..

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