Solar Micro Inverters

Micro inverters in Solar Energy is a recent phenomenon which has started replacing solar string inverters in residential small solar installations in a small way in USA.Enphase Energy has been instrumental in making this niche technology popular which increases solar panel efficiency by 5-25% and has a number of other advantages over central inverter as well.This has made the major solar inverter companies sit up and even introduce microinverters even on their own.Though the Costs of the Solar System are increased as microinverters cost more per watt,however the reduce the lifecycle costs in small installations through increased reliability,life and productivity.As the Solar Industry has matured,focus has shifted more towards the Levelized Cost of Energy (LCOE) from Solar Panels Electricity generation rather than just on the Solar Capital Investment costs.

How Solar Micro Inverter Works

A solar micro-inverter just like a Solar Inverter has the primary purpose of  converting the Direct Current (DC) which is generated by Solar Panels to Alternating Current (AC) which is used by appliances at home .Note each microinverter works with a single Solar Panel in contrast to  a string inverter which works with 10-5000 Solar Panels depending on the Size of the String Inverters (which can be as large as 1 MW).Microinverters on the other hand are only 200 W in size.

Microinverters eliminate the need for string sizing exercises that require fitting equal lengths of module strings on a roof. Each PV module is connected directly to its own microinverter and mounted on the racking underneath. The microinverter’s AC wire harnesses are connected to form a continuous AC branch circuit that leads ultimately to the AC utility distribution center.

System safety is enhanced since all of the output wiring from the PV array is AC, and therefore doesn’t contain hazardous DC voltages once the AC power is shut down for service or emergency. If the AC to the array is shut off, only the DC voltage of a single module (typically under 50VDC) is present in the array creating a much safer situation for maintenance personnel or firefighters.

Reasons for Higher Reliability of Microinverters

Microinverters are much more reliable than Solar Inverters with Mean Time to Failure more than 300 years.Micro inverter companies give warranty of 15-25 years which is much more than the 5-10 years given by String Inverters.The Design and Components used in Microinverters determine the Life of a Micro inverter which is generally more than String Inverters.

1. Heat – String Inverters operate at much higher temperature which leads to much more stress and shorter life times for these inverters
2. Voltage – Since each microinverter works with a single solar panel,it operates at a much lower input voltage .Lower power allows lower number of components which also decreases chance of integration problems.
3. Better Packaging – Solar microinverters are generally well packaged and sealed compared to most string inverters (though there are brands with almost as good packaging).This also improves reliability

Monitoring by Microinverter fitted with Communication Chips

Microinverter communicates with the Internet through a Communication device which can monitor the microinverter through a power line connection. Data is monitored 24/7 and the system can notify if any solar module does not perform to its potential.Communications protocols like Wi-Fi,Zigbee etc are used in communication in addition to physical communications.

Pros of Solar Micro-inverter compared to Normal Solar  Inverters.

1. Reliability and Longer Life  – Micoinverters are more Reliable as the failure of a single piece affects only that solar panel and not the whole solar array of solar panels in case of Solar Inverters.Also the Mean Life of Solar Inverters are much more than the life of the Solar Panels compared to the 5-10 year life of String Inverters which have to be replaced.
2. Productivity – Microinverters claim to have 5-25% more power production from solar panels as they manage to maximize the power production from each solar panel (MPTT) compared to string inverters which MPTT the whole solar array.Microinverters give more accuracy  If a single panel is operating at a different point, a string inverter can only see the overall change, and will move the MPPT point to match. Shading of as little as 9% of the entire surface array of a PV system can, in some circumstances, lead to a system-wide power loss of as much as 54%
3. Ease of Installation – Installing Solar Panels with Microinverters is easier and faster and leads to lower costs compared to Solar Inverters though there is still some dispute on this.
4. Flexibility – Another benefit of the distributed microinverter design is the potential for installations to be expanded over time. An initial set of solar modules can be installed and additional modules added as needs and budgets grow without requiring the replacement of a large centralized inverter.
5. Reduction in Lifecycle Costs – Installers are no longer limited by string design, marginal designs, co-planarity, and matched modules. Microinverters reduce wiring time, and remove the need for DC switching points.
6. Space and Heat of String Inverters – String Inverters occupy more space (though not a big problem) and generate a lot of heat which has to be cooled by used fans.
7. Higher Power Inverters have to be used – Because of the limited range of power rated inverters available,solar panels have to generally use power inverters of greater size for eg. 800 W of Solar Panels will have to use 1 KW solar inverters wasting the 200 W