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OwnerJuly 2015 to presentEl Cerrito

Finding best available technologies for meeting energy needs today and tomorrow: energy efficiency, demand response,, solar, wind, electric vehicles, biofuels and smart grid. It’s all the innovations that make the energy we use more secure, clean, and affordable. The energy world's best hopes lie in what's happening in the digital realm, especially in data analytics.

Thursday, September 26, 2013

Smart Inverters

Grids built to deliver power one way at constant voltages and frequencies have trouble accommodating two-way, intermittent flow. Achieving high penetrations of distribution connected PV will require the utilization of increasingly advanced inverters

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Back to Stimulus & Regulation Index
1. Background

2. Acronyms/Definitions
3. Business Case
4. Benefits
5. Risks/Issues
6. Case Studies
7. Companies
8. Next Steps
9. Links



1.Background
  • California Governor Brown has called for the implementation of 12,000 MW of “localized electricity generation”, namely DER, which can help the State reach its goal to acquire 33 percent of its energy from eligible renewable energy resources by 2020. However, high penetrations of these DER systems, located within distribution grids which were designed only for handling customer loads, could adversely affect utility operations.

  • Smart inverters could be a low-cost way to mitigate the voltage changes caused by the fluctuating solar generation, thus preventing potential power quality problems. Achieving high penetrations of distribution connected PV will require the utilization of increasingly advanced inverters

  • Voltage/VAR controls are a basic requirement for all electric distribution feeders to maintain acceptable voltage at all points along the feeder and to maintain a high power factor. In addition to increased PV on the grid, recent efforts by utilities to improve efficiency, reduce demand, and achieve better asset utilization, have indicated the importance of voltage/VAR control and optimization. Utilities continue to face system losses from increasing reactive load, such as air conditioners. By optimizing voltage/VAR control great efficiencies can be realized. EPRI estimates 55% of the 566,000 distribution feeders will include voltage/VAR control by 2030, at an average cost of $258,000/feeder. See my post Improved Volt/Var Control

SDG&E has about 1,000 distribution circuits.  Problems might start to pop up when penetration reaches 20% - 30%, forecast to be more than 20% of circuits by 2016  Source: CPUC Presentation Jun 13, 2013

2. Acronyms/Definitions
  1. AC Power – Produced by an Alternator (commonly referred to as a generator) that functions by rotating an energized magnetic field adjacent to a coil of wire. The energized field has a flux around it. When the magnetic field cuts across the coil of wire, electrons are induced to flow and AC electricity is produced. (Therefore the name, Induction Generator) Since AC power has a varying voltage, efficient power systems must therefore vary the current in synchrony with the voltage.
    • The polarity of the voltage across the wire coils reverses as the opposite poles of the rotating magnet pass by. When the direction of the AC voltage changes 60 times per second, it is called 60 Hertz (60 Hz) AC Power, the standard in North America
    • System operators can adjust the output of “real” and “reactive” power at short notice to meet changing conditions.
    • Numerically, the sine wave plot is:
      Angle Sine (angle) in degrees
      0 ............... 0.0000 -- zero
      45 ............... 0.7071
      90 ............... 1.0000 -- positive peak
      135 .............. 0.7071
      180 .............. 0.0000 -- zero
      225 .............. -0.7071
      270 .............. -1.0000 -- negative peak
      315 .............. -0.7071
      360 .............. 0.0000 -- zero
      The height of the plot (Y Axis) represents the voltage being produced. The peak of the plot does NOT measure the voltage output. Because the voltage varies through the entire cycle, and even goes negative for 1/2 the cycle, output voltage is actually a calculation of the RMS of the Phase Angle. The procedure consists of squaring all the positive and negative points on a waveform graph, averaging those squared values, then taking the square root of that average to obtain the final answer. A shorter equation is to take the sine of the voltage at 45 degrees. Sine 45 = 0.7071. Therefore, the RMS voltage is about 70% of the peak voltage plot.

  2. Active Power – see Real Power

  3. Amperage - Current is the rate of flow of electrons - A unit of measure for the rate of current flow. Symbol: I

  4. Apparent Power - The product of the current and voltage of the circuit. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power can be greater than the real power.

  5. Capacitor Banks- An array of capacitors connected into a circuit. Capacitors are used to control the voltage that is supplied to the customer by eliminating the voltage drop in the system caused by inductive reactive loads. Capacitors are considered to generate reactive power. This is the fundamental mechanism for controlling the power factor in electric power transmission; capacitors are inserted in a circuit to partially cancel reactive power of the load.
    • An automatic power factor correction unit is used to improve power factor. A power factor correction unit usually consists of a number of capacitors that are switched by means of contactors. These contactors are controlled by a regulator that measures power factor in an electrical network. To be able to measure power factor, the regulator uses a current transformer to measure the current in one phase.
    • Depending on the load and power factor of the network, the power factor controller will switch the necessary blocks of capacitors in steps to make sure the power factor stays above a selected value (usually demanded by the energy supplier), say 0.9.

  6. Capacitance - The ability of a body to hold an electrical charge.

  7. DNP3 - Distributed Network Protocol - A set of communications protocols used between components in process automation systems. It was developed for communications between various types of data acquisition and control equipment. It plays a crucial role in SCADA systems, where it is used by SCADA Master Stations (aka Control Centers), Remote Terminal Units (RTUs), and Intelligent Electronic Devices (IEDs)

    The IEEE adopted DNP3 as IEEE Std 1815-2010 on the Jul 23, 2010. In April of 2012, the IEEE approved Std 1815-2012 for publication. The 2012 version of the standard includes features for Secure Authentication Version 5.

  8. IEEE 1547 - Standards governing solar-grid connections in the United States. Under IEEE 1547 guidelines, the general practice for small PV inverters is that they will not attempt to directly regulate the voltage on the distribution system. IEEE 1547 requires that PV inverters disconnect any time the grid gets unstable for safety, to make sure solar power doesn't flow through a downed power line and shock a utility worker, for example.

    But that safety measure also prevents solar inverters from helping out in cases in which the instability isn’t caused by a downed line. Indeed, turning off lots of inverters all at once, can destabilize the grid even more.
    • 1547 prohibits DER systems from actively regulating the voltage at the Point of Common Coupling (the interconnection to the grid)),  limits the voltage “ride-through” range and limits the frequency “ride-through” range
    • 1547 is rapidly being “updated” to IEEE 1547a where these limitations are being revised to allow (but not mandate) more flexibility:  1547a may be published by the end of this year
    • 1547.1a (testing) also needs to be updated
    • UL 1741 safety requirements need to cover these new functions

  9. IEEE P1547.8 - Recommended Practice for Establishing Methods and Procedures that Provide Supplemental Support for Implementation Strategies for Expanded Use of IEEE Standard 1547

    Solar inverters in the United States are not allowed to perform certain functions, such as power ramping and volt/VAR control. It is hoped P1547.8 will allow inverter manufacturers to provide those smart grid features,

  10. Inverter - An electrical power converter that changes direct current (DC) to alternating current (AC). Photovoltaic systems generate DC power. Inverters convert this DC power to AC power so these systems can interconnect with the grid.

    An inverter can produce square wave, modified sine wave, pulsed sine wave, or sine wave depending on circuit design. The two dominant commercialized waveform types of inverters as of 2007 are modified sine wave and sine wave. Modern inverters use software-driven electronics to flip and smooth the output into standard 60 Hz waves. Since inverters are software driven, their output can be modified to benefit the grid.

    Grid-interactive inverters must produce AC power that matches the voltage, frequency and phase of the power line it connects to. There are numerous technical requirements to the accuracy of this tracking.

  11. Islanding - A distributed (DG) generator continues to power a location even though electrical grid power from the electric utility is no longer present. Islanding can be dangerous to utility workers, who may not realize that a circuit is still powered, and it may prevent automatic re-connection of devices. For that reason, distributed generators must detect islanding and immediately stop producing power; this is referred to as anti-islanding.

  12. LVRT - Low Voltage Ride Through - A capability of electrical devices, especially wind generators, to be able to operate through periods of lower grid voltage. Similar requirements for critical loads such as computer systems and industrial processes are often handled through the use of an uninterruptible power supply (UPS) to supply make-up power during these events.

    Many generator designs use electrical current flowing through windings to produce the magnetic field that the motor or generator operates on. Such devices may have a minimum working voltage, below which the device does not work correctly, or does so at greatly reduced efficiency. Some will cut themselves out of the circuit when these conditions apply.

    In a grid containing many distributed generators subject to low-voltage disconnect, it is possible to create a chain reaction that takes other generators offline as well. This can occur in the event of a voltage dip that causes one of the generators to disconnect from the grid. As voltage dips are often caused by too little generation for the load, removing generation can cause the voltage to drop further. This may bring the voltage low enough to cause another generator to trip out, lower it further, and causing a cascading failure.

    Modern large-scale wind turbines, typically 1 MW and larger, are normally required to include systems that allow them to operate through such an event, and thereby "ride through" the low voltage. Similar requirements are now becoming common on large solar power installations that likewise might cause instability in the event of a disconnect. Depending on the application the device may, during and after the dip, be required to:

    • Disconnect temporarily from the grid, but reconnect and continue operation after the dip
    • Stay operational and not disconnect from the grid
    • Stay connected and support the grid with reactive power

  13. Microinverter - an inverter integrated to each solar panel module. The output of each module can be paralleled to combine the capacity and interconnected to the grid.

    While more expensive than central inverters that use multiple modules connected in series, this arrangement provides easier installation, redundancy and more effective capture of energy when they're partially shaded.

    In 2009 panels were generally around $2.00 to $2.50/W, and inverters around 50 to 65 cents/W. By the end of 2012, panels were widely available in wholesale at 65 to 70 cents, and string inverters around 30 to 35 cents/W. In comparison, micro-inverters have proven relatively immune to these same sorts of price declines, moving from about 65 cents/W to 50 to 55 once cabling is factored in.

  14. OpenDSS - - A comprehensive electrical power system simulation tool created by EPRI primarly for electric utility power distribution systems. It supports nearly all frequency domain (sinusoidal steady‐state) analyses commonly performed on electric utility power distribution systems. In addition, it supports many new types of analyses that are designed to meet future needs related to smart grid, grid modernization, and renewable energy research. The OpenDSS tool has been used since 1997 in support of various research and consulting projects requiring distribution system analysis. Many of the features found in the program were originally intended to support the analysis of distributed generation interconnected to utility distribution systems and that continues to be a common use. Other features support analysis of such things as energy efficiency in power delivery and harmonic current flow. The OpenDSS is designed to be indefinitely expandable so that it can be easily modified to meet future needs.

  15. Phase Angle - In the context of periodic phenomena, such as a sine wave found in electricity, phase angle is synonymous with phase. The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0.

  16. Phase Shift - Current (amps) lags behind the voltage. When volts and amps no longer cycle together, it takes more of them to get the same effective power, that is, to do the same amount of work.

  17. Power – The rate of flow of energy past a given point. It is measured in watts. Electric power (watts) is transmitted by the simultaneous product of electric voltage and current in a wire. If large amounts of current are present when there is less voltage, the wires, transformers and other power equipment are heated, but less power is transmitted by the equipment. Since equipment is designed to remain cool up to a certain amount of current, vars waste some of the power unnecessarily as excess heat.

  18. PF - Power Factor - The ratio between real power and apparent power in a circuit. The equation for Power Factor is: PF = kVA / kVAR
    • Where the waveforms are purely sinusoidal, the power factor is the cosine of the phase angle (φ) between the current and voltage sinusoid waveforms. Equipment data sheets and nameplates often will abbreviate power factor as "cosφ" for this reason.
    • Power factor equals 1 when the voltage and current are in phase, and is zero when the current leads or lags the voltage by 90 degrees. Power factors are usually stated as "leading" or "lagging" to show the sign of the phase angle, where leading indicates a negative sign.
    • For two systems transmitting the same amount of real power, the system with the lower power factor will have higher circulating currents due to energy that returns to the source from energy storage in the load. These higher currents in a practical system will produce higher losses and reduce overall transmission efficiency. A lower power factor circuit will have a higher apparent power and higher losses for the same amount of real power transfer.

  19. PFC - Power Factor Correction - Achieved by switching in or out banks of inductors or capacitors. For example the inductive effect of motor loads may be offset by locally connected capacitors. When reactive elements supply or absorb reactive power near the load, the apparent power is reduced. Power factor correction may be applied by an electrical power transmission utility to improve the stability and efficiency of the transmission network. Correction equipment may be installed by individual electrical customers to reduce the costs charged to them by their electricity supplier. A high power factor is generally desirable in a transmission system to reduce transmission losses and improve voltage regulation at the load.

  20. Ramp-Up - If a slow enough ramp up is specified, there may not be a need for random reconnect timing. Most inverters can be designed to have soft start ramp up capability relatively easily.

  21. Ramp down capability - May be employed to coordinate with existing voltage regulation equipment and minimize adverse voltage impact. But ramp down may require some local storage.

  22. Reactive Power - The portion of power flow which returns to the source in each cycle. Reactive power flows backwards and forwards in an alternating current. Reactive power, measured in volt-amperes reactive (VAR), is the energy supplied to create or be stored in electric or magnetic fields in and around electrical equipment.
    • Reactive Power is measured in 'kVAR' pronounced as 'kaye-VARs'
    • Reactive power is particularly important for equipment that relies on magnetic fields for the production of induced electric currents (e.g., motors, transformers, pumps and air conditioning). It also must supply the reactive losses on transmission facilities.
    • Reactive power can be transmitted only over relatively short distances, and thus must be supplied as needed from nearby generators. If reactive power cannot be supplied promptly and in sufficient quantity, voltages decay and, in extreme cases, a “voltage collapse” may result. The power grid needs enough reactive power to maintain reliable service.
    • Reactive power is provided by generators, synchronous condensers or electrostatic equipment such as capacitors and directly influences electric system voltage. Examples of reactive loads include capacitors and inductors.
    • If the load is purely reactive, then the voltage and current are 90 degrees out of phase and there is no net power flow. A practical load will have resistive, inductive, and capacitive parts, and so both real and reactive power will flow to the load.

  23. Real Power - (aka active power) The portion of power flow that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction. Real Power flows one way, from generator to load. It is the rate at which work is performed or that energy is transferred and is usually expressed in kilowatts (kW) or megawatts (MW).

  24. Ride Thru Capability -

  25. Rule 21- Electric Rule 21 is a tariff that describes the interconnection, operating and metering requirements for generation facilities to be connected to a utility’s distribution system, over which the California Public Utilities Commission (CPUC) has jurisdiction. The Rule 21 tariff for each of California’s large investor owned utilities (IOUs) is available on each IOU’s website. The CPUC's open interconnection proceeding is R.11-09-011.

    Sep 13, 2012: Rule 21 Settlement Approved - In Decision 12-09-018 the Commission approved the full set of reforms to Rule 21 proposed via a multi-party settlement. The Commission anticipates that the significant reforms achieved in Rule 21 will advance the Commission's goals of ensuring a timely, non-discriminatory, cost-effective, and transparent interconnection process for distributed generation in California.

  26. Rule 21 Phase 2- Item #6 - The CEC initiated a joint effort with the CPUC to update Rule 21 to provide a consistent set of mandated and
    recommended DER functions
    – Initiated the “Smart Inverter” project in January 2013
    – Used experiences from the California utilities and the Europeans, as well as certain international standards
    – Discussed which DER functions should be mandated in bi-weekly meetings
    – Developed recommendations for a phased approach for Rule 21 mandates for DER functions

  27. Rule 21 Proceeding

  28. Var - Volt-Ampere Reactive power -  Measures h out-of-phase voltage and current  Unit used to measure reactive power in an AC electric power system. 1 var = 1 V•A. Vars measure unsynchronized "leading" or "lagging" currents. These currents are usually caused by the side effects of powering equipment that behaves like coils (e.g. motors) or capacitors (e.g. arc welders).


  29. VDE AR-N 4105 - German rules requiring its solar inverters to perform certain functions, such as power ramping and volt/VAR control, which lead to more stability that came into effect for medium-voltage connected solar in 2008 and for low-voltage solar as of January 2012.

  30. Voltage - Electromotive force - An electrical measurement of potential
    difference, electrical pressure, or electromotive force (EMF). Symbol: E

  31. VVO - Voltage and VAR Optimization - Improving on the traditional approach using uncoordinated local controls, VVO uses real-time information and online system modeling to provide optimized and coordinated control for unbalanced distribution networks with discrete controls.


3. Business Case
  • RPS target calls for increasing the amount of renewable electricity in California’s power mix to 33 percent by 2020.

  • To support this target, Governor Brown’s Clean Energy Jobs Plan called for adding 20,000 megawatts (MW) of new renewable capacity by 2020, including 8,000 MW of large-scale wind, solar, and geothermal resources and 12,000 MW of localized renewable generation close to consumer loads and transmission and distribution

  • Achieving high penetrations of distribution connected PV will require the utilization of increasingly advanced inverters.

  • Candidate Phase 1 Mandatory Autonomous DER Functions
    • Support anti-islanding to trip off under extended anomalous conditions
    • Provide ride-through of low/high voltage excursions beyond normal limits (L/HVRT)
    •  Provide ride-through of low/high frequency excursions beyond normal limits (L/HFRT)
    • Provide volt/var control by dynamic reactive power injection through autonomous responses to local voltage measurements (VV)
    • Counteract frequency excursions beyond normal limits by decreasing or increasing real power (FW)
    • Counteract voltage excursions beyond normal limits by providing dynamic current support
    •  Reconnect randomly within a preset time window after grid power is restored
    •  Limit maximum real power output at the PCC to a preset value
    •  Modify real power output autonomously in response to local voltage variations
    •  Provide reactive power by a fixed power factor
    • Set actual real power output at the PCC
    •  Schedule actual or maximum real power output at specific times


4. Benefits
  • Improve Existing Conditions - Smart Inverters could improve existing conditions:
    • Voltage drops on a power line as you move farther away from the substation. The end of a distribution power line can have very low voltage
      Voltage drops on a power line as you move farther away from the substation – The end of a distribution power line can have very low voltage

    • Lagging Voltage - Air conditioners and other motors cause lagging voltage. Increasing vars is wasted energy

  • Smart inverters can use their software-driven electronics to:
    • Ride-through wide ranges of voltage or frequency anomalies to improve resiliency and avoid unnecessary outages
    • Respond to emergency commands to improve reliability
    • Counteract excess vars by shifting the voltage-current phase
    • Counteract voltage spikes and sags to improve quality of service
    • Counteract frequency deviations to smooth frequency changes
    • Respond to demand response pricing signals to improve efficiency

    How much PV capacity a distribution feeder can handle depends on many factors.  Results of many simulations of PV penetration on one distribution feeder with  EPRI's Hosting Capacity Model.    In the Volt/var control scenarios, inverters react autonomously based on the interconnective voltage it sees.   Minimum hosting capacity was increased ~60%, maximum ~100%  Source:  EPRI CPUC Smart Inverter Presentation
  • Randomized Disconnect - Distributed generation resources are require them to disconnect at the first sign of trouble -- typically, when frequencies fall outside normal operating boundaries -- so they don’t feed dangerous and unexpected power back up downed or de-energized power lines.

    But that simple safety feature can actually backfire on the grid, by suddenly disconnecting whole neighborhoods of solar power during momentary grid power blips or faults, causing even more instability. In Germany, that problem was dealt with by randomizing the timing and specific frequency levels at which they tripped, as well as when they reconnected, to shift what would have been a concentrated impact to a more spread-out one.

  • Low Voltage Ride-Through - Prevents inverters from tripping during voltage drops caused by momentary grid disruptions.

5. Risks/Issues
  • Problems from High Penetration Problems of PV
    • Ride-through Problems -

    • Distribution Overvoltage - Too much solar power, and local grid voltage could rise, causing potential problems for motors, lights and other equipment.

    • Local secondary overvoltage - Too little solar power and voltage can sag. That may only flicker light bulbs at home, but it can lead to million-dollar work stoppages for customers like semiconductor manufacturers and server farms that need clean power at a near-to-constant voltage and frequency.

    • Variability and Excessive Cycling of Taps -

    • Plants Have Been Curtailed/Limited -

    • Unintentional Islands Have Formed -


  • Technological Uncertainty - It’s a bit hard to quantify the costs and benefits of making all new solar inverters smarter, versus taking other approaches based on adding new grid equipment, because for the most part, the problem of too much solar is a hypothetical one.

  • Manufacturing Cost - Smart Inverters could add about 10 percent to manufacturing costs to inverters, which make up roughly 5 percent to 10 percent of total solar system installation costs. However, adding a smart inverter at $150 per installation for each rooftop, for an inverter system with a typical cost of about $1,500 or more, is a smart investment.

  • Retrofit Cost - A 2011 study by German utilities and energy agencies estimated that retrofitting the country’s installed solar base will cost €175 million ($234 million), and adding administrative costs could ring that cost up to $300 million. That’s a price tag that could be avoided in the United States, if regulators and the industry can get ahead of it.

  • Reactive Power Costs - For example, a 150 kW solar facility with a 10 percent oversized inverter set at a 0.9 power factor can draw 15 kW of real power from the grid to convert to reactive power even when the solar facility is producing a full 150 kW of real power. While the costs of oversizing inverters are less than installing and maintaining capacitor banks, they are can still be significant for smaller generators. Therefore, generators should either be compensated for the costs of oversizing inverters or for the value of real power converted to reactive power, which can be easily accomplished by compensating based on KVA instead of KWh.

  • Maintenance - Inverters are only warranted for 10 years, so chances are at least two inverters are required over the course of a 25-30 year panel lifetime.

  • Compensation - If we want inverters to produce reactive instead of real power, capabilities for metering of ancilliary services must be developed.

  • Electro- Mechanical Voltage Control Equipment Can't Keep up with second to second changes

  • Communications -  How can utilities coordinate thousands or millions of DER systems,  located at customer sites and owned by non-utilities?
    • Most DER systems must operate autonomously most of the time.  Based on pre-established settings to meet utility requirements and taking into account the DER owner preferences
    •  Communications with utilities are required for::
      • Emergency situations
      • Market signals for demand response
      • Updating the DER settings used for autonomous operation

  • Field Experience with Smart Inverters is Lacking (And is Expensive)
    • What settings are optimal?
    • Whether or not one setting (for a given function) will benefit everywhere
    •  Response timing & control loop settings (typically not specified by standards) and associated stability among many devices 
    • How to manage smart inverter capabilities in coordination with other distribution controls
    • How will functions and multiple autonomous devices work together?
6. Case Studies
  • Germany

    The US is not entirely analogous to Germany. Most of the US is much hotter than Germany, which means that in summer, consumption and generation are much better matched than in Germany. In most German homes, in summer basically there is only the fridge running. In the US, hello non-stop air conditioning. In the US, oversupply of solar will come much later than 40GW solar for 82 Million inhabitants.

    European experience with high penetrations of DER has shown that the implementation of some DER functions can costeffectively improve the reliability and efficiency of the power grid.

    Waiting to implement these functions may lead to costly upgrades and replacements – which actually occurred in Germany
  • 3 phase, large capacity, large conductor primary voltage
    • •300-500 kVA service transformer
    •  Hundreds of customers per transformer
    • Large secondary network - 400 V, 3 phase much bigger than typical US Distribution network.
  • Obliged to provide an technically appropriate PCC for PV connection Obliged to provide an technically appropriate PCC for PV connection
    • 25% of cost on UDC
    • Control units 100 kWp and above
    • Still obligated to pay the FIT amount Still obligated to pay the FIT amount
    • Voltage tolerance +-10%
  • Voltage regulation issues on secondary network
  • Low load,, high PV output
  • Solution network upgrades
  • German Grid Code
    • Require PV systems to support the grid
    • Minimize network upgrade costs
  • California
    • Phase 1 -  Start with autonomous DER systems which provide volt/var management, low/high voltage ridethrough, responses to frequency anomalies, etc. Use interconnection agreements to ensure appropriate autonomous settings.
    • Phase 2 -   Expand to situational awareness with hierarchical communication networks, monitoring ggregated smaller DER and direct monitoring of larger DER. Issue broadcast requests (pricing signal and/or tariff-based) and/or direct commands
    • Phase 3-  Combine field and virtual modeling through power flow-based analysis, state estimation,  contingency analysis, and other analysis applications to assess economics and reliability.
    • Phase 4 -  Ultimately integrate DER management with distribution automation, load management, and demand response for optimal power system management.
  • PG & E - PG&E is seeing "some localized issues" with grid instability in neighborhoods where rooftop solar penetration has grown to around 5 percent, said Hal LaFlash, the utility's director of emerging clean technolog.

  • Current Rule 21 Installation Status
    2,407 PV inverters >30 kW, total of 514 MW
    85,264 inverters <= 30 kW, total of 443 MW Recommend to grandfather the existing units <= 30 kW due to the relatively low system impact and high retrofit costs. The existing units > 30 kW may need retrofitting to include the ride through capabilities and to avoid inadvertent tripping during major system disturbances.

  • SDG & E - has about 6,600 customers with solar rooftops. While that's growing by about 60 customers a month, it still only represents about 50 megawatts of generation, or about 1 percent of the utility's 5,000-megawatt total load. The utility can't monitor or control it, but there isn't enough of it to matter that much.

7. Companies/Organizations
  1. Advanced Energy - (NASDAQ: AEIS) Fort Collins, Colorado (Solar - San Jose, Calif)- AE(which recently acquired PV Powered) is working to address these challenges with partners Portland General Electric (PGE), Schweitzer Engineering Laboratories (SEL), and Northern Plains Power Technologies (NPPT) under the Solar Energy Grid Integration System (SEGIS) program

    Advanced Energy claims, "The SEGIS program advancements will help lay the foundation for an “intelligent” or smart inverter capable of integrating large-scale photovoltaic power generation into the smart grid with greater stability and protection,


  2. California Energy Commission - Rule 21 Phase 2 Inverter Settings Technical Working Group - For more information on these documents contact Rachel A. MacDonald
    Electricity Supply and Analysis Division
    California Energy Commission
    1516 Ninth Street
    Sacramento, CA 95814
    (916) 654-4862
    rachel.macdonald@energy.ca.gov



  3. Enphase - Petaluma, California - Leader in microinverters

  4. Fronius - German Inverter Manufacturer

  5. Petra Solar - South Plainfield, NJ - Pole-mounted, solar panel-connected microinverter arrays Their microinverter provides reactive voltage injection capability, allowing the modules to balance the sometimes grid-destabilizing character of solar power.

    In July 2009, Petra Solar signed a $200 million agreement with New Jersey utility Public Service Electric and Gas (PSE&G) to supply 200,000 utility pole-mounted units over three and a half years. Many of Petra’s pole-mounted systems utilize Suntech PV panels.

    Dr. Shihab Kuran, the CEO and founder of Petra is Jordanian as are some of the other senior staff at the firm, hence the name Petra. That connection to Jordan has also initiated Petra's next large project -- working with Jordan's utility to roll out more than 100 megawatts of solar on power poles and rooftops.

  6. Power One (Symbol was PWER) - Camarillo, California - Recently purchased by multinational power sector giant ABB, ranks as the second largest international inverter manufacturer.

    Purchased venture-backed Fat Spaniel Technologies in 2010.

  7. Satcon (OTCMKTS: SATCQ) - (Satcon, formerly a leader in the U.S. inverter space, filed for bankruptcy late in 2012 and was liquidated.)

  8. SMA - The inverter market's international leader, recently made a big investment in Zeversolar, a major Chinese supplier.

  9. SolarBridge - Austin, Texas

  10. SunSpec Alliance- A trade alliance of solar photovoltaic industry participants, together pursuing information standards for the renewable energy industry. SunSpec standards address operational aspects of PV power plants on the smart grid—including residential, commercial, and utility-scale systems—thus reducing cost, promoting technology innovation, and accelerating industry growth.

    SunSpec establishes open information standards that solar PV manufacturers use to achieve plug-and-play interoperability between solar PV power plant components and software applications. SunSpec publishes a series of specifications, each consisting of a data model and transport protocol map (Modbus®, SEP 2.0, XML ), for all components in the PV plant system hierarch

  11. Energy Recommence - Provide hardware and software for consumers to monitor their systems.
8. Next Steps
  1. Fill in Research Gaps
    • What settings are optimal

    • Whether or not one setting (for a given function) will benefit everywhere

    • Response timing & control loop settings (typically not specified by standards) and associated stability among many devices

    • How to manage smart inverter capabilities in coordination with other distribution controls

9. Links
  1. Smart Inverter Functionalities Workshop - CPUC (R.11-09-011) - June 21, 2013
    This workshop discussed the first phase of California's smart inverter implementation plan that recommends smart inverter capabilities that could be required to ensure the long-term safety, reliability, and efficiency of the power grid with high penetration distributed generation. Workshop discussions covered smart inverter functionality recommendations and a proposed testing and implementation plan for validating the recommended functions.

    Video Webcast


  2. CPUC Documents supporting Smart Inverters
    • 2012 Renewable Action Plan
    • 2012 California’s Transition to Local Renewable Energy: 12,000 Megawatts by 2020 (staff contribution).
    • 2011 Integrated Energy Policy Report, June 22, 2011-IEPR Workshop on Distribution connected DG
    • 2011 Energy Commission KEMA study of PV in Europe

  3. SunShot Initiative High Penetration Solar Portal - DOE EERE - High penetration solar research helps DOE understand, anticipate, and minimize grid operation impacts as more solar resources are added to the electric power system.

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