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Micro inverters from Enecsys have a life expectancy of over 25 years
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Four key factors determine the return-on-investment for solar PV systems: total capital costs, the power harvested from the system over its lifetime, maintenance costs and the Feed-in Tariff (FIT) rate.
In conventional PV solar installations solar modules are wired in series then connected to a string inverter that converts high voltage DC from an array of PV modules to AC for connection to the grid. For residential and commercial installations, the inverter will typically be rated between 2 and 5kWp. More than one may be used in larger systems.
Today, a different solar PV system architecture based on micro inverters is fast gaining popularity. A small inverter is attached to the rack behind each solar module to convert DC to grid-compatible AC. Alternatively, a duo version accepts DC input from two solar modules, delivering a single AC output. Micro inverter outputs are wired in parallel and a 7kWp system might use 29 single micro inverters each rated at 240Wp. No string inverter is needed.
The growing popularity of micro inverters is due to fact they provide up to 20% improvement in price/performance over the life of the solar PV system compared to existing inverters. With micro inverters, shading of one module does not degrade the performance of others and more power can be extracted from each module through maximum power point tracking (MPPT). The output of each module varies with the incident light level. MPPT ensures that the micro inverter presents the optimum load to the module under these varying conditions in order to extract maximum energy from it at all times. This technique cannot be applied so effectively in systems with series DC strings, where shading from any source can dramatically reduce the total energy output.
On a cost-per-watt basis, systems using single micro inverters costs a little more than those with string inverters. Where duo versions are used, the capital costs are comparable to string inverter systems. However, any cost premium is more than offset by increased energy harvest and other benefits, including greatly simplified installation. There are no risks from lethally high DC voltages, making the systems safer for installers to fit. Fire risk from high voltage DC arcing is eliminated, as is the electrocution risk to firefighters in the event of a fire.
Sulaiman M. Ahmad is from Enecsys Limited. Visit www.enecsys.com for further details.
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