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Want to Learn Basic MLPE in 2020?

Module Level Power Electronics

Contents

  1. Background
  2. Basic Topology
  3. Micro-Inverters
  4. DC Optimizers
  5. Monitoring
  6. Benefits of MLPE
  7. Drawbacks of MLPE
  8. Conclusion

BACKGROUND

As of June 2020, according to the National Fire Protection Association (NFPA.org), the 2020 NEC is in effect in one state, the 2017 NEC is in effect in 34 states, the 2014 NEC is in effect in 9 states, and the 2008 NEC is still in effect in 3 states!

The 2014 NEC required an array level shutdown with no voltage outside of array upon shutdown.  The 2017 NEC instituted (among other requirements) that the rapid shutdown capability be brought to the module level. This mandates that voltage levels within an array boundary be 80V or less within 30 seconds upon shutdown.  The array boundary was amended to be anything within 1 foot of the array itself.  Voltage levels outside the array boundary were now mandated to be 30V or less within 30 seconds of the shutdown.

The 2020 NEC has somewhat tweaked that requirement and includes the UL 3741 product standard for a rapid shutdown within the code.

It should be noted that this rapid shutdown requirement is for rooftop installations with exposed conductors.  It does not affect ground-mounted installations.

BASIC TOPOLOGY

Module Level Power Electronics (MLPE) come as Power Optimizers such as Tigo (integrated into junction boxes or retrofitted onto modules upon installation) or as Micro-Inverters such as Enphase.

String, Optimizer and Micro-inverter diagram
Source: AuroraSolar.com

MLPE components improve energy production through the use of MPPT at the module level.  MPPT instructs the solar panel (or array) to operate at specific current and voltage combination that maximizes power output whereas string inverters ‘choose’ the operating point.  They do this by tracking and optimizing the powerpoint.

In the traditional string array, the production capability of the array is dependent on every module within the string.  Essentially the current is limited by the lowest current output device in series.  Voltage is additive but as two strings are connected in parallel, the resultant voltage becomes the average of the two inputs.

On rooftops, there is limited room for PV installation. There may be more than one tilt angle and perhaps roof areas facing in different directions.  Combined with the electrical limitations of the string-based arrangement, the result of string-based designs would be either wasted roof space or duplication of components.

MICRO-INVERTERS

Micro-inverters are a module-level replacement for a string inverter.  Each micro-inverter has the full functionality of a string inverter and cost control has been a continuous issue.  But each module can be monitored remotely, making operating and maintenance a much easier proposition.  By “Full functionality” I mean to include maximum power point tracking (MPPT) function, which is integral to the rapid shutdown capability now required by the electrical code.

Enphase Micro-Inverter

 

DC OPTIMIZERS

DC optimizers such as those made by Solaredge or Tigo are DC-DC converters that also integrate MPPT functions.  This allows for the module to optimize power independently from the performance of other modules.  Since the MPPT function is at the module level, a somewhat simplified inverter can be used.  The obvious implication is the possibility of cost reduction.

SolarEdge Optimizer
SolarEdge Optimizer

DC-DC Optimizers, built into junction boxes or retrofit (i.e. Tigo TS4-0 or TS4-R-0) increase solar production, reduce shade impacts, prevent burnt diodes and, add UL certified rapid shutdown. They also add module-level monitoring with sophisticated alerts. SMA (an inverter manufacturer) has a system that integrates Tigo optimizers (see diagram from SMA)

MONITORING

Cloud-based monitoring via computer or even a phone app makes PV system oversight a much simpler affair that can be crucial in maximizing your solar energy production.  Enphase, SolarEdge, and Tigo all have a proprietary monitoring software solution.

Tigo Monitoring and TS4 Platform

Benefits of MLPE

  1. Energy Production
    1. Shading mitigation
    2. A solution to the module mismatch problem
    3. A solution to the orientation mismatch problem
  2. Module Level Rapid Shutdown is a requirement on most rooftop systems
    1. Solar tiles (shingles) can be a notable exception
    2. A clearly superior safety arrangement for first responders
  3. Longer Warranties than traditional Inverters are possible
  4. Performance monitoring and diagnostic functioning provide O&M enhancements
    1. Pinpoints technical issues

Drawbacks of MLPE

  1. Higher upfront costs
  2. Higher installation labour

The current capabilities of MLPE are available through companies such as SolarEdge, Tigo, Enphase, and others.

CONCLUSION

As technologies such as blockchain, AI, and encryption collide with Power Electronics the benefits of these collisions will only increase.  This is most definitely a technology to keep on your reading list!

 

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