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DC Appliances

  • Wed, Aug 13, 2014 - 05:08am

    #42
    TechGuy

    TechGuy

    Status Bronze Member (Offline)

    Joined: Oct 13 2008

    Posts: 300

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    DC Appliances

"directly to big loads such as hot water heater (via PWM board as I mentioned before) and DC based kitchen appliances, preferably with a simple PWM that targets the Vmax. I made pancakes this morning off of my PV panel output with NO inverter etc. inefficiency causing equipment (connected directly: no circuitry) and enjoy hot showers without that stuff. My panels and entire system cost is likely much less than just the gee whiz circuitry described."

The issue is that DC applicances are not readily available at local retail stores and usually designed for low voltage DC (ie 12V/24V/36V) which either needs excessive current or has limited power use (limited size). In a long term Grid-Down situation you will be hard pressed to find a replacement, on the other hand in a grid down, there will be an excessive number of AC applicances available for free. It would be far easier to stock replacement parts for the inverter than stock replacements for DC applicances.

DC to AC inverters can be up to 98% efficiency and since AC motors are typically a bit more efficient than DC motors (assuming no speed control), there isn't much to be gained by going with a pure DC system. To get good inverter efficiency its important to provide an input voltage that is close to the AC output voltage. Ideally a 96VDC to 144VDC will be about 98% efficient conversion to AC. The issue is that most Solar inverters are setup to use much lower input voltages, but there are inverters available that operate at higher DC voltages.

 Solar panels and batteries can be connected in series to increase the voltage. The higher voltages will also provide less transmission losses in the cabling (ie from the Panels to the inverter/voltage regulator and to the load). Pwr loss = I^2*R. the losses increases are squared for the current needed. It can be very expensive to run heavy gauge wire to all of your DC Applicances.

You will be hard pressed to find DC power tools (ie table saw, Skill saw, Jig saw, corded hand power tools) and other common devices such as vacuum cleaners, washing machines, window fans, etc. it would take a lot of effort to replace all of the motors and electronics in these devices to operate on DC.