Test Results From NREL Spur Change In Penetration Limits For Solar Power In Hawaii

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The test results from NREL’s recent inverter testing at the Energy Systems Integration Facility (ESIF), which was aimed at investigating means of quantifying transient Inverter Load Rejection Over-Voltage (LRO), are now in — bringing with them some progress. They will help address one of the primary technical barriers to large-scale integration of distributed generation into the grid.

Owing to the results of the tests, the utility company HECO recently announced — via a filing with the Hawaii Public Utilities Commission — its intention to increase its penetration limits for rooftop solar. The increase was pretty substantial, it’s worth noting — from the current limit of 120% of minimum daytime load (MDL) all the way up to 250%.

If these proposed changes are instituted, they will mark the highest threshold solar penetration on distribution circuits in the US.



A bit of background here — LRO conditions sometimes occur “when a local feeder or breaker opens and the power output from a distributed energy resource exceeds the local load.” It’s this that is theoretically responsible for the current limits on high penetration of distributed generation on the utility’s feeders in HECO’s territory.

Reportedly, the test results from NREL’s recent test program helped to “mitigate some of HECO’s LRO challenges generated from advanced photovoltaic inverters.”

“ESIF enables NREL and DOE to leverage strong partnerships with manufacturers and utilities to help integrate renewable energy into a smarter, more resilient energy system,” stated Bryan Hannegan, NREL’s Associate Laboratory Director for Energy Systems Integration. “NREL and its partners use state-of-the art capabilities to develop advanced PV inverter technology and successfully integrate that with plug-in electric vehicles, hybrid power systems, hydrogen fuel cells, microgrid controls and several other advanced energy technologies.”

Here’s a bit of background on NREL’s testing program via a recent press release:

NREL’s ESIF is a 182,500-square-foot user facility that is helping transform how the nation generates, delivers and uses energy by modernizing the interplay among energy sources, infrastructure, and data. ESIF offers partners access to some of the most advanced testing, research, and development capabilities in the country and was named 2014 Lab of the Year by R&D Magazine.

The collaboration among NREL, HECO and SolarCity continues, with testing on the ability of advanced inverters to mitigate ground fault overvoltage issues. Later this year, tests at ESIF will examine the capability of advanced inverters to support distribution voltage regulation, address challenges related to bi-directional power flow, and measure the effectiveness of multiple inverter islanding during faults.

The research has been supported by the Department of Energy’s Office of Energy Efficiency and Renewable Energy; SolarCity; and the SunShot Initiative.

Those interested can find the report here.

Image Credit: NREL

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James Ayre

James Ayre's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy.

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14 thoughts on “Test Results From NREL Spur Change In Penetration Limits For Solar Power In Hawaii

  • Rule out diesel generated electricity.
    Hawai will transit fast to Solar and Wind Power.
    too much Wind Power, too much Solar Power
    never run out of fuel.
    rule out diesel and gascars on the islands, EV cars only, for storage,
    there is no range anxiety, nowhere to go, but
    How much money is going out for diesel and gas bills on a year basis.
    Hawai can make this money on the islands itself.
    Solar is cheap, Wind is reliable, EV cars will take over anyhow.
    let Hawai be the first.

  • Nice to see progress, but couldn’t we just check in with the Germans on this one?

    Why all the hand-wringing and delays?

  • Has anybody heard of similar fusses in Germany over solar integration? They seem to take it as all in the day’s work.

    • I believe Germany’s current daytime record is under 70% of electricity from solar. An installed solar capacity of 120%, let alone 250%, of daytime demand could well lead to solar producing well over 100% of electricity demand on a sunny day in Hawaii’s climate.

      But more importantly, the German grid is not an island. It’s part of a much larger international grid on which the total share of solar power is generally in single digits. The Hawaiian islands are actual electricity islands that have nowhere to export excess solar to.

      As such, I don’t really think your comparison to Germany is fair.

      • first stop diesel generating excess electricity. its a stand in the way.
        and nice to see you agree on excess solar.

      • These are limits for “local load” not the whole grid, not even for a local village. Say you have 20 house in a group, feed by a transformer. That grid segment, can go to 250% of the minimum daytime load. Which is not to say to they maximum daytime load.

        • Correct, as I read it, this ia a local circuit limitations. It is effectively a distributed gen limit. You could also add utility scale solar/wind/hydro/geothermal to the grid beyond this point, the control circuits for utility scale can be more elaborate..

          • Right. HECO can improve their grid controls. They could also add more transmission wires to allow conduction of DG Solar PV power back to a central re-distribution point. You can do that for central generation plants. Why not for DG Solar PV? May not be the most elegant or economical approach, but they have a small grid and are throwing buckets of money away on diesel to generate electricity. It is one way to gitter done. It proves it can be done.

            Find a better way faster or get out of the business HECO.

            There is definitely a way to do this. I don’t see the Australians having a problem with this. People running HECO are fat lazy bureaucrats trying to block new tech that threatens their monopoly. Nothing less.

            Very low-cost storage will force a faster rate of change and put an end to this diddling. Thank goodness.

      • OK Australia then! 1 in 4 homes in SA have solar. The problem HECO is whining about is local over-voltage issues. Ever here about that being limiting in Australia? No!
        Your point on Germany being part of a larger grid is moot. Exporting excess power is not their problem in Hawaii. This can always be done with really big resistors. Seriously! More intelligent to do it with controls that can turn down power from your sources.
        HECO has no excuse. None!

        • So you suggest using resistor banks? Really? You’d pay a huge premium for electricity in the form of net metering only to dump it without making use of it? Building a billion dollar robot that digs ditches and then closes them would be a more productive use of one’s cash.

          More intelligent controls that ramp down production locally make sense, but would amount to curtailment. Try telling that to owners who would see their profit from net metering reduced.

          One option would be to impose a small grid access fee on solar PV owners that is used for local grid reinforcement and perhaps in the longer term for interconnections between the islands. That would solve the problem once and for all in a fair manner (only those who have solar and thus need the grid reinforcement would actually pay for it).

          • Agreed that excess solar can result in curtailment. The curtailment issues have to be separated from the issues of line voltage regulation. The voltage must be regulated regardless.

            Inverters can’t regulate load, at least not directly. To regulate load, best thing is for the inverter to communicate with smart nodes and appliances like Nest. Excess local generation in Hawaii can be used for local cooling like refrigeration or air conditioning like Ice Bear. It would be nice if this was done on a micro grid basis.

            In Australia, offgrid solar is now promoted on a subdivision basis.


            This could happen in Hawaii also.

            There must be transparent price mechanisms that reflect the costs of electricity. Then the right mix of storage, solar, transmission upgrades, grid practices, demand response, flexible generation, and other sources of generation can find its balance.

            In a sense, the local generation or micro grid must do all the functions of a power company. When you think about it, even demand and supply forecasts must be done.

          • My point is simple. There is more than one way to solve the Solar PV penetration problem HECO pretends to be vexed by. You yourself seem to agree. Yes, some are less preferable, but there are solutions! Net metering at full retail rates will not be economically workable going forward. There needs to be a change in that.

    • All PV inverters in Germany automatically reduce power output once a certain voltage or frequency is exceeded.
      All large PV inverters can be remotely controlled by the grid operators and provide reactive power even at night. link.
      Also, small PV-systems in Germany cannot generate more than 70% of their nameplate module capacity (in any case).

  • So much for myths about solar. Not only did Enphase upgrade their inverters operation in the field to improve voltage regulation, but NREL says the limits are high.
    This is engineering, not rocket science. The kink of breakthroughs needed here are rather mundane, not like the kind of research needed to improve solar cell efficiency by some novel technique.
    With modern semiconductor power devices and power management techniques coupled with grid communications and software, much can be achieved.

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