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11520Re: Hybrid Generator and Solar

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  • Jay Ring
    Jan 25, 2013
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      I'm interested in the question also.

      I'd say your solution is probably the best solution in a lot of cases.

      Realistically, if the generator is large enough to handle the load alone (as you have said you require), I would just take the PV offline in grid-down situation and let the generator handle it alone.

      This completely eliminates any worries about damaging either the inverter or the generator though back-feeding.

      The grid is only down 1% of the time; it's okay to lose the PV generation during that time. There is no good reason to incur a lot of extra cost (via batteries) or risk (of backfeeding) for a 1% improvement.

      For lighting and motors (pumps, compressors, air conditioners, elevators, etc) this is probably the way to go.

      For sensitive loads (datacenter, industrial control, medical systems), you want fast switch over and high quality power instead of dirty generator power. In those cases, this probably isn't going to cut it, in which case I would consider feeding the generator through the DC side of the inverter and letting the inverter clean it up into high grade power. You'd still need a battery, but it could be much smaller.




      --- In hreg@yahoogroups.com, "Chris Boyer" wrote:
      >
      > People always ask about grid-tied solar systems running with a generator.
      > Most people (I've talked with most of the inverter manufacturers) will tell
      > you it can't happen and give a long list of reasons why. However, the world
      > needs this solution because there are so many places that need solar, but a
      > huge battery bank is not practical. So I tried it myself and I have proof
      > that you can run solar grid-tie with a generator. Here's what I've seen
      > work and how to make it work.
      >
      >
      >
      > Here's the general conditions:
      >
      > 1) The generator should be able to cover the loads independently of the
      > solar (big gen, small solar).
      >
      > 2) The load power draw must never be greater than the solar power input
      > plus a minimum output from the generator.
      >
      > 3) The inverter must be able to match the inverter frequency and
      > voltage through a wider range than what would be seen from the Grid.
      >
      > 4) There are some fine voltage/frequency/reactive power controller
      > points in #3 that require a longer explanation, but I'm not going to put
      > that in this e-mail
      >
      >
      >
      > Example #1: 100kW Genset with 36kW PV inverters. The Genset was an
      > expensive, high quality machine that could hold a very steady frequency and
      > voltage. Even still, the voltage and frequency of the generator would drift
      > outside of the limits imposed by UL1471/IEEE1547. The Inverters were SMA
      > Sunny Boys which actually let you adjust the voltage and frequency limits,
      > so we went in and widened the limits. Also, a load management system made
      > sure there was always at least 30 kW of load on the system. Worked great
      > even through load changes!
      >
      >
      >
      > Example #2: 350kW Genset with 100kW PV inverter. This Genset was an
      > expensive, high quality machine that could hold a very steady frequency and
      > voltage. The PVPowered inverter was not changed, however, the output was
      > limited to 10kW when the grid was down and the generator was running. The
      > system was not well automated and tested with a steady load of greater than
      > 30 kW, so the frequency and voltage didn't move around and stayed in the
      > IEEE1547 window. It worked.
      >
      >
      >
      > Example #2: 5kW Genset with 600W PV inverter. The Genset was the cheapest
      > thing on the market. The inverter was a Chinese non-UL1741 grid-tie
      > inverter with a very wide voltage and frequency window. These ran together
      > just fine in short term testing. I could tell that switching loads on and
      > off caused the generator frequency to change and the inverter was a little
      > slow (about a second, 60 cycles) to resynchronize with the generator. I had
      > motor and lights running as loads and could see no flicker to motor sounds
      > during load switches. However, the power meter would blib an unusual power
      > factor reading indicating that the sine waves between the inverter and
      > generator were not lined up perfectly for a second during those load
      > changes. Didn't hurt anything short term, but still investigating long term
      > effects.
      >
      >
      >
      > Anyone out there that has found another solution? Is anyone else out there
      > interested in these solutions?
      >
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