Inverters for PhotoVoltaic Systems © AH, ARJ 2002

Evolution & Applications of Inverters Square Wave: –mechanical switching –now extinct

Modified Square-Wave Modified Sine Wave (mid-70s): –low cost, high reliability, easy service. –Control Average Voltage. –not good for some TVs, ballasts, laser printers, energized coils/transformers.

Sine Wave Inverters Sine wave: Series I and II (early-90s): –higher cost, added features & complexity –handle surge currents, >2:1 –1st line tie capability, higher efficiency, less heat, increased size/weight

Added Features Battery Charging –full-bridge rectifier –3-stage advantages Power Management –Relays for generator starting, exercise, charge timing, selling power back to utility –voltage-driven, or clock-driven Temperature Management –Heat sinking, variable-speed fan control, high efficiency is your friend

High Frequency Switching Sine Wave Inverters Light-weight and with a very high quality sine-wave. Early units did not have the surge capability of the SW inverters.

Line-Tie Inverters Sine wave inverters dedicated or modifies to feed power back to the Utility Line. Stringent safety requirements to protect the inverter and utility. High efficiency, relatively low cost.

Inverter Classifications Uninterruptable Power/Stand-Alone: Battery powered; independent of electric utility; can often charge batteries with AC hybrid source. Utility-Interactive or Grid-Connected: Must detect the waveform and consume power (nighttime) from the electric utility to function; synchronizes voltage, frequency and phase with utility; controls the PV array directly. Stand-Alone with Utility-Interactive : Can operate in conjunction with utility but provide power independently if power fails.

Inverter Comparison Stand-alone Inverter creates voltage waveform. Load current may distort waveform or shift phase. –Motor current lags voltage –Computers demand current at voltage waveform peaks Utility-interactive Grid creates voltage waveform - inverter unlikely to distort. Inverter behaves like negative load, feeding current back into grid. Loads respond to grid voltage, not inverter current.

Inverter Comparison cont. Stand-alone Inverter has no control over battery charging via PV, wind, hydro, etc. Amount of energy extracted from PV array is a function of battery voltage. Utility-interactive Maximum Power Point Tracking (MPPT) eliminates separate controller & extracts max power from PV array at temperature.

Codes for Inverters UL 1741 and IEEE : Avoid islanding when utility-interactive: inverter powering loads on disconnected section of grid. Avoid dumping power into a short. Inverter to restart 5 min. after grid specifications restored (voltage and frequency).

Utility Defined Distributed Generation Separate, Emergency or Standby Generation- Non-parallel System No possibility of electrical connection. Break before make transfer switch required for main service box. Or move critical loads onto separate service box. Interconnected Generation - Parallel System Connected to electrical bus common with utility. Visible open disconnect switch required, protective relaying, metering, etc. Agreements with utility.

Selection Tree Power Requirement Less than 10kW (Residential / Small Commercial 120 / 240 VAC 80A max.) More than 10kW (Commercial 3 phase, 480 / 208 VAC)

Residential / Small Commercial Power /Use / Cost Requirement Sine WaveModified Sine Wave

Residential / Small Commercial Sine Wave Grid-TieStandalone

Residential / Small Commercial Grid-Tie PVHybrid Sunny Boy ST/XR SW

Sunny Boy High Voltage / high efficiency. Can be used in 3- phase circuits. Available as 1.8kW and 2.5kW.

Xantrex SunTie XR 48VDC Line Tie Inverter Built-in system display Optional Remote Display 1kW, 1.5kW, 2kW & 2.5kW Early ST inverters had problems which seem to have been solved in the XR series Components

SW Series Inverter Xantrex /Trace SW Inverter / Battery Charger. Can be used stand-alone or Grid-Tied (with interface) This is the workhorse inverter for many standalone systems. Available in 4kW and 5.5kW Inverters can be combined to provide 240VAC, or stacked in parallel to increase power.

Residential / Small Commercial Standalone ChargerNo Charger Exeltech Prosine AEI MM-5000 SW

Exeltech Innovative design that provides redundancy and upgrade capabilities by adding modules. No Battery charging capability. Very high quality sine wave.

ProSine Series Small, light inverters, often used in the RVs and boats.

Residential / Small Commercial Modified Sine Wave UX Heart DR Rail Mount etc.

DR Series Inverter Modified Square Wave. High Reliability. Relatively Cheap.

Commercial Power PVHybrid AES Advanced Energy Systems Australia Xantrex PV Series

PV Series Inverter High Voltage High Power PV only Inverter. Available from 10kW – 225kW. Requires additional transformer if not behind a Utility fence.

AES Hybrid Installation

Decision Tree