Monitoring a solar array output

After years of hoping and wishing [Dave] finally took the plunge and installed solar panels on the roof of his house. He’s got twelve panels that are each rated at 240 Watts! But just having them sitting there and pumping power back to the grid isn’t enough. Understandably, he decided to add his own solar array monitor so that he could see just what those babies are bringing to the party.

The solar array has an inverter which takes the DC from the cells and converts it to mains voltage AC for use on the grid. The system includes a panel meter which you’d normally find on the supply to the house. All he needed to do is find a way to grab the data from that device. It’s an Elster meter, and offers two types of feedback: a blinking LED that corresponds to each Watt-hour passing through the meter, and an IrDA port which provides a more error-proof method of reading data. Monitoring the 1 Wh pulse is quite a popular method for keeping track of your electric meter, but if your hardware misses a pulse the data will be off. [Dave] chose to use a light sensor to monitor the IrDA output, which is encoded data. As long as you can read the protocol, which has been published by Elster, a transmission can be missed now and again without disturbing the overall power consumption data.


  1. DrivenMad says:

    Would a cheap automotive amp meter with a counter work? Was just working on the truck and thought of it :)

  2. Andrew says:

    If your hardware misses a pulse it will be off by one unit. To get around this problem you should periodically read the meter and check it against your logged data. Correct as necessary.

  3. kidcrash says:

    I’m planning an off-grid setup on vacant acreage. The one thing that has me stumped is the pure sine inverter compatibility with a modern 80+ pfc computer psu. Just cant find any info on an off gridder running a quad core.

    • adcurtin says:

      If you get a high quality computer power supply, it shouldn’t have any problems with a pure sine inverter (even cheaper ones shouldn’t have problems). Computer power supplies are generally very good and taking whatever crap (so long as it’s around 120v or 240v, and close to 50 or 60 Hz) it gets on the input and putting out solid voltages on the output.

      You could also measure voltages on the output of the psu before you hook up the mainboard and make sure they’re within spec, then use software once the computer is hooked up to make sure it’s still in spec under load.

    • Louis says:

      Check out mini-box – they have DC based power supplies for PCs. I run my entire server rack on them – including a dual opteron raid box and my quad core server boards. Everything is powered from an 8D RV battery – which is charged (at the moment) with an RV park converter – and I hope to take it all off grid.

  4. urlax says:

    Pure sine wave shouldn’t be a problem. modified sine wave is not good for any switching PSU.

    because most PSU designs contain a rectifier directly after the AC input, you can feed them 325 VDC as well..

    325 VDC = 230VAC*sqrt(2)^-1

    if that voltage is hard to reach, try looking for car pc supplies. the operate from 6..30 VDC and up to 300 watt (look up M4-ATX)
    there are other versions with higher capacity.

  5. Fallen says:

    Agreed with urlax.

    You should be able to feed them an appropriate amount of DC. So you could wire the solar panels in series to get an appropriate voltage. Obviously some form of regulation would be needed to prevent it from going too high or too low for the PSU.

    With the PSU set to 120V, you should be able to use about 170VDC to supply it. Since 120*1.414=170VDC

    Although you might want to test it out on a cheap PSU, just incase I didn’t take something into account.

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