2.1.2 Inverters

An excellent resource for UL listed modules and inverters is www.gosolarcalifornia.org.

2.1.2.a. Residential String Inverters                 

Best Practices: The Series - #7: Photovoltaic Labs - 2.1.2.a. Residential String Inverters


  • SUNNY BOY 3000US, or
  • 4000US w/ integral DC disconnect, or
  • Fronius IG Plus 3.0 or 3.8 with integral DC disconnect PV Powered PVP2000, PVP2500, or PVP3000 (optional)
  • Monitoring hardware and interfaces (essential)

Suggested Quantity:  At least one, preferably one of each.

Importance Rating: Essential.

Comments: Inverters connect to 208v or 240v.  Match the number of modules per string to the inverter voltage window. Many inverters are configurable to 208v, 240v or 277v. Remote monitoring is an important feature available with most modern string inverters. Several manufactures (such as Kaco, SMA, or PV Powered) have “dummy” inverter display units available for education. Integrated inverters have become mainstream with inverter, disconnects, and circuit combiner contained in one unit, which speeds up the typical installation.

2.1.2.b. Transformer-less Inverters

Specifications: Sunny Boy 4000TL-20 and 5000TL-20 transformer-less multi-string inverters with peak efficiency of 97% and a wide range of input voltages

Suggested Quantity: at least one demonstration unit.

Importance Rating: Desirable.

Comments:  Where traditional string inverters have iron core transformers, transformer-less (TL) inverters have computerized multi-step process with electronic components to convert DC to high frequency AC, back to DC, and ultimately to grid-compliant AC. The advantages include lower weight and increased efficiency. Transformer-less inverters are considered “ungrounded” in the traditional sense and use a resistive grounding method that can detect changes in ground current as low as 300mA. The National Electrical Code (NEC) requires the use of PV wire for systems using TL technology.

2.1.2.c. Micro Inverters         

Best Practices: The Series - #7: Photovoltaic Labs - 2.1.2.c. Micro Inverters

Specifications: Enphase M210 micro inverters, Direct Grid, Power One, Envoy communications system.

Suggested Quantity: 4 to 10, with one required per module – or approximately 20 for a 4 kW array (Micro inverters can be installed using the same array as string inverters.)

Importance Rating: Essential

Comments: Micro inverters have fewer restrictions than string inverters and are becoming more mainstream. Recognizing this trend, they should be included in up-to-date lab activities. Micro inverters offer a simplified design, overall system safety, and state-of-the-art monitoring. With micro inverter systems, remote monitoring is an integral part of the system and should be considered as essential during micro inverter lab activities.

2.1.2.d. Residential Battery-Based Inverters             

Best Practices: The Series - #7: Photovoltaic Labs - 2.1.2.d. Residential Battery-Based Inverters


  • Complete hybrid inverter/charger for off-grid, backup and grid-interactive solar energy systems, 2-4 kW minimum
  • Xantrex/Schneider Electric XW, Outback Power Systems, or Power One systems (Magnum offers a complete line of battery-based inverters and peripherals.

Suggested Quantity: One (or as appropriate for the situation).

Importance Rating: desirable

Comments: Residential battery-based inverters are necessary for NABCEP Entry Level Exam track instruction.

2.1.2.e. Small Commercial Grid-Tied Inverters

Best Practices: The Series - #7: Photovoltaic Labs - 2.1.2.e. Small Commercial Grid-Tied Inverters


  • PV Power One PVI-10 Delta or Trio 20 (1000VDC)
  • Fronius IG Plus 11.4-3 Delta or 12.0-3 WYE 277

Suggested Quantity: One

Importance Rating: Advanced.

CommentsThis is an optional purchase. Specify the unit for site voltage. Larger PV arrays and electrical services are required.

2.1.2.f. Medium Commercial Grid-Tied Inverter    

Best Practices: The Series - #7: Photovoltaic Labs - 2.1.2.f. Medium Commercial Grid-Tied Inverter

Specifications: Power One Trio-27.6 TL

Suggested Quantity: One.

Importance RatingAdvanced.

Comments: This is an optional purchase. The inverter connects to 208, 277, or 480V three-phase grids. Larger PV arrays and services are required.

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