The sunMAX Microinverter (SM-MI-*) converts DC Power (from sunMAX Panels) to AC Power that returns to the customer mains AC electrical system. Whether or not the MI is compatible with the customer's mains AC system depends primarily on the AC output voltage and frequency of the MI as well as the voltage and frequency on the customer's AC system.
Due to variations across parts of the world, there are two categories of MI models available. The two models cover the two common frequencies that are encountered: 50 or 60 Hz. The nominal AC output of each sunMAX MI is listed below:
- SM-MI-250: 240V (ranging 211-264V); 60Hz (ranging 59.3-60.5Hz)
- SM-MI-250-EU: 230V (ranging 184-264V); 50Hz (ranging 47.5-51.5Hz)
Note that the wide voltage range on the EU-version MI accommodates many different regulatory regions; actual operating voltages may be limited by your region.
Ubiquiti recommends only using equipment rated to the system in which you are installing your components.
The mains electricity specifications vary for each country. For example:
- United States = 120/240V at 60Hz
- Virgin Islands = 110V/220V at 60Hz
- Uruguay = 230V at 50Hz
The SM-MI-250 model, whose nominal voltage is 240V and nominal frequency is 60Hz, should be used with the US & Virgin Islands, whereas for Uruguay, the SM-MI-250-EU version should be used.
1-, Single-, & 3Ø
Despite using a compatible voltage and frequency to the mains electricity system, the MI(s) must also be compatible with phase of the electrical system.
In 1-, Single-, or Split-Ø systems, the voltage differs across conductors simultaneously. This system is most common at residential customers' sites.
In the United States, Split-Ø, 3-Wire systems run at 120V-0V-120V (the 240V is split across two 'hot' (voltage carrying) conductors, and a neutral conductor. In many other countries, 220 or 240V is used directly.
For comparison and nomenclature (L1 = Line 1, N = Neutral, etc.) purposes:
- United States (3-Wire) = L1 (120V), L2 (120V), N (~0V)
- China (2-Wire) = L1 (220V), N (~0V)
Being more common to commercial sites or customer with high power requirements, 3Ø systems vary voltage across conductors sequentially. For example, 3Ø is described accordingly (where LX = Line 1-3, etc.):
- United States (4-Wire Wye) = 120V (LX to Neutral), 208V (LX to LX)
- United States (3-Wire Delta) = 480V (LX to LX)
Because of the different voltages, sunMAX equipment (MI, AC Trunk Cabling, etc.) could be damaged if connected to these systems.
There, it is recommended to only connect equipment rated to the system in which you are installing your components. Use sunMAX MI (SM-MI-250) with Single-Ø systems (most common in residential systems).
Interconnection Compatibility: Three-Phase Systems
The current model of sunMAX MI and AC Trunk Cabling are designed for Single-Ø. This does not prevent the interconnection of sunMAX MI's to 3Ø systems, but the following guidelines MUST be adhered to to avoid damage to the sunMAX equipment, and to ensure acceptance by the utility to which the MI is being connected. Most importantly, the voltage and frequency of the source to which the MI is connecting MUST match the voltage and frequency of the sunMAX MI being installed.
United States MI
- A sunMAX MI cannot be directly connected to a 208V or 277V source in the United States. A 3Ø, 4-Wire 240V source must be created from either an existing 120V/208V premises wiring system, or from an existing 277V/480V premises wiring system. The created 240V source must include a direct neutral connection from the premises supply. This new 240V source, with neutral, is achieved by the use of a 3Ø autotransformer (usually composed of three single-phase autotransformers wired together). The resulting new source will then provide three 240V LL single phase sources (if derived from a 120V/208V premises), or three 240V LN single phase sources (if derived from a 277V/480V premises). Each sunMAX MI branch circuit can now connect to one of the single phase (AB, BC, CA if derived from a 120V/208V premises, or AN, BN, CN if derived from 277V/480V premises) supplies in the new three-phase 240V source.
- The installed sunMAX system output must be balanced across the three phases of the new source. This will require designing the sunMAX system to comprise a quantity of MI branch circuits divisible by three, and for the difference in MI quantity between any two branch circuits to not exceed one microinverter. In this way current imbalance on the new three phase system (and on the existing premises wiring system) will not exceed 1.05A on any phase.
- The EU-version sunMAX MI is designed for connection to a 230V single phase source. In those regions where a 230V single phase source is common, the predominant three-phase system is 230V/400V. Each sunMAX MI branch circuit is connected to one of the 230V LN sources in the 230V/400V three phase system.
- The installed sunMAX system output must be balanced across the three phases of the new source. This will require designing the sunMAX system to comprise a quantity of microinverter branch circuits divisible by three, and for the difference in microinverter quantity between any two branch circuits to not exceed one microinverter. In this way current imbalance on the new three phase system (and on the existing premises wiring system) will not exceed 1.1A on any phase.
To take advantage of Net Metering (credit for excess energy), the customer site must have a Bidirectional Meter installed & accounted for by the Utility. For this reason it is very important that you complete the Interconnection Agreement / Contract with the customer & utility in order to complete installation & commission the system.
Despite most new meters today counting both directions (production/consumption), older meters typically only read forward. In this case, sunMAX will still offset consumption, provided it is producing energy at the customer premise—but excess energy will go to the grid, and the customer will not be credited.
Pure vs. Modified Sine Wave
Intended for use in grid-tied applications, sunMAX MI's produce pure-sine waves (not modified-sine waves).