Convert Panels from 30V to 60V

RDxRDx Registered Users Posts: 2
Hi there,
thanks in advance for all of your time and friendly advice.
With a limited amount of roof space and battery space, we would like to connect our off-grid 48V hybrid inverter to a 240V HWS immersion element at the far end of the house.
We have been advised by the inverter specialists to input ten to twelve panels, in order to keep the voltage over 300V.
With space for a maximum of six large panels, would it be possible to re-wire them internally to convert them from approx 30V to 60V?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,634 admin
    When you connect panels in series (+ of one panel to - of second panel, + of second panel to - of third panel, so forth), the voltage increases. 2x 30 volt panels in series will be 60 volts. 10x 30 volt panels in series will be 300 volts.

    Parallel is connecting all panels + to +, and all - to - leads... That will add current. your 30 volt panels will still be 30 volts... But the current available will be 2x, 3x, etc. Imp of panels.

    Of course, this is all maximum available power under noon time sun on a clear day.

    One big issue to be careful about... Your standard water heaters are designed for 120 or 240 VAC. The heating elements themselves, don't care. HOWEVER, the temperature switch and over temp shutdown do CARE, A LOT. DC current sustains arcs much better than AC power... Your AC switches will either arc and fail, or weld shut and fail. A least, ruining your switches, and at worse, not turn off the heating elements and cause your water heater to overheat. In the US, we are required to have TP valves (temperature and pressure relief valves). If the water temperature is >212F or 125 PSI (water heater limits), to prevent the water heater from overheating.

    If your off grid system (battery bank and AC inverter) is already large enough to support an electric water heater, you could simply power the water heater from your AC inverter. And some Solar Charge controllers have an auxiliary output signal (relay or similar) that can be programmed to turn on when the battery bank is full/in float. That would work well and safely.

    There are some Battery Monitor Systems that also have programmable outputs... You can set one to turn on when at 90-100% state of charge for similar results.

    Just be careful when doing something "different" with pressure tanks (like water heaters). Bad things can happen (Mythbusters exploding water heater video):

    https://www.youtube.com/watch?v=28ixJLtQBCc

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RDxRDx Registered Users Posts: 2
    Thanks Bill,
    We were intending to stick with standard 230V AC power and controls, integral with the HWS 3kW immersion elements.

    Our 5kW hybrid inverter specialist advised:
    "
    In order to operate a solar system without batteries it is strongly recommended to establish a high voltage DC link from solar Tpanels.
    Thatmeans anything between 8 to 12 panels.
    You need voltage over 300Vdc to be able to converter directly to 230Vac and feed substantial power from panels to domestic loads.
    "

    At this stage we have space for only six panels, providing approx 180V DC to the inverter. It sounds like the inverter would operate more efficiently of we could increase the DC input Voltage?

  • BB.BB. Super Moderators, Administrators Posts: 30,634 admin
    There are (at least in North America), we can get different voltage and different wattage heating elements.

    I am a little confused about the 300 VDC to 230 VAC conversion? What is planned to do this conversion (an inverter that can run directly from the solar panels?)?

    Or coupling a GT Inverter to your local Off Grid AC inverter? The OG inverter provides the 230 VAC @ 50 Hz, and the GT inverter connected to the 230 VAC house mains to help feed house loads, plus "back drive" energy through the OG inverter to charge the battery bank, etc. (includes some way of "modulating" the GT inverter when there is more GT Watts than need by house loads and battery bank charging).

    Is this planned to be a full Off Grid installation or a "Hybrid" solar (both GT inverter function and Batteries for backup power--Shifting power usage to off peak hours, etc.)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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