It was in 1950s that the Bell labs had produced solar cells for space activities. Since then, the solar Photo Voltaic (PV) technology around the world has seen a continuous improvement in module efficiency, development of new and smart modules, varying configurations of solar cell, etc. Out of all such improvements, the introduction of Alternating Current (AC) modules has been exhilarating. The AC module(also known as “plug and play” module) as the name suggest directly produces grid compatible AC output. This is possible due to an extra device known as micro-inverter (Figure 1) which is now mostly integrated with the junction boxes (present in the primitive PV modules).

Figure 1: A typical micro inverter (Source: Enphase Energy) Solar power

This micro inverter is connected individually to each module performing two important functions namely:

Figure 2: Conversion of DC power to AC power Solar energy

Figure 3: I-V curve depicting the MPP of solar module (Source: Waaree Energies) Solar panel

The individual AC module are connected to each other to form an AC branch circuit which is further connected to the load/main supply panel or the generated energy is directly exported to the grid. The primary advantages of using AC modules are mentioned as below:

Conversion of the Direct Current (DC) power to AC power: The prime and the most important function of micro converter is to convert the DC power to grid compatible AC power. Here the micro inverter (similar to central or string inverter) takes the reference from the grid and produces the grid compatible power accordingly.
Maximum Power Point Tracking (MPPT) of the solar module: As an integrated device with the solar module, it is important that the micro inverter continuously extracts the maximum out of available power from solar panel. The electronics present in the device enables it to track the operational I-V curve. Out of all the points available on this I-V curve, the device ensures that the module is operated in such a way that it delivers maximum power (MPP has been shown in Figure 3 i.e. 325.1 Wp, 259.9 Wp, 193.8 Wp, 127.5 Wp & 61.6 Wp at varying irradiance respectively).

Improved string level performance: As mentioned above, these micro inverters have in built MPPT tracker. This enables them to extract the maximum power from the solar panel. Such feature helps when there is a partial shading (say due to cloud cover) in the power-plant. This partial shading in usual case would drag down the power output of entire string. In case of AC modules, the partial shading would affect only a single module thus leading to improved string level performance. Additionally any mismatch effect between the solar module say due to their orientation, tilt, azimuth, etc. may be eliminated as the micro-inverter optimizes the power output of each solar module independently.
Easy monitoring and failure detection: The latest micro inverters come with in-built communication system. Such devices are perfect match to monitor module level power output and failure detection. Any defect in the plant can be traced down to module level and can be rectified within short span of time giving ease to operation and maintenance of power plant.
Ease of increasing the plant size: The size of power plant which uses DC modules is (mostly) fixed due to inverter capacity. This means that expansion of such power plant may not always be possible. However, the plant using AC modules could initially have only a limited number of modules which can always be increased as and when required. As the AC modules produce grid compatible power, the customer does not need to worry about module mismatch.
Reduced installation time: An AC module forgoes the DC side cabling (and combining output via combiner box) until the inverter. This reduces the time required to set up the entire plant. Additionally the output from the AC modules can be directly (with added protection device) fed into the AC panel of the customer. This significantly reduces the number of components and amount of time required to install such components.

Such modules are of important while deployed on field primarily for the rooftop owners. For rooftop plants (while comparing to a utility scale plant) size and shadow free area availability is always constrain. This may (sometimes) lead to mismatch between the module and the inverter. Additionally future erections of property around the rooftop plant may lead to shadows being casted on the existing power plant. AC modules may offer simple yet tailor made solutions to all such plants where any future expansion or contraction in size of power plants is required. Adding or removing the modules (where required/not required) would not have any effect on the plant performance or its output characteristics.

While AC modules and micro inverters were present in the market for quite a long time, their market penetration is poised to increase in years to come. One of the reasons which may be attributed to such increase is the increased awareness of rooftop and utilizing AC modules at the rooftop. Additionally, there has been huge advancement in micro inverter in terms of both its efficiency and power output. This has given a much needed push to AC modules while enabling the top module manufacturers to add it to their product basket.

Waaree Energies had recently announced its partnership with one of the leading micro inverter manufacturer Enphase Energy to bring AC powered modules to Indian market while maintaining its top notch quality. We had recently launched our AC modules at Intersolar Mumbai, where it had got excellent response from the attendees. We would continue this innovative drive to deliver the best of class products and service to our consumers.

Figure 4: AC solar module by Waaree Energies go solar

Let us all pledge to make solar energy the primary source of energy in the near future.

RAHE ROSHAN HAMARA NATION