2011

Improving Microinverter Performance in Photovoltaic Systems

We have known for decades that the sun radiates enough energy to meet the world’s needs for power, both now and in the future. As in any energy conversion from original source to a “usable” form, however, the various stages of adaptation introduce efficiency losses. In the case of the photovoltaic system, this has limited what could be exponential growth. In fact, the best performance available from solar cells of any kind (excluding the concentrated approach) never rose above 15% efficiency. In cascade to the solar cell itself, a classical centralized inverter would add barely more than 90% efficiency to the chain. This “poor” performance and the obvious lack of large successes has also helped to keep the installation costs very high.

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Figure 1. The photovoltaic principle.
Only in the last ten years have multicrystalline cells gone beyond the limit, reaching the 20% efficiency dream. We also have seen the introduction of thin film panels, with efficiencies just above 10% at a cost less than one third of multicrystalline panels. Inverter technology, with the best use of new materials, has also gone above 95% efficiency and dramatically reduced system costs.

All of these advances, championed by a population leaning more and more toward green energy sources, and sponsored by national, corporate, and local incentives, has led to worldwide yearly installations in the 10GW range, from humble beginnings of way below 1GW just a few years back.

Regardless of the changes in technology, both in panels and inverters, the basic principles always remain the same: • Solar energy hits the solar cells (any technology) (Figure 1). • Due to the photovoltaic effect, the cells release a DC voltage and a certain amount of current. • Depending on how the cells are arranged, the resulting DC voltage and current will be converted into AC usable electrical energy by the inverter (performing other functions as well to maintain a safe and reliable grid connection) (Figure 2).

The Evolution of Solar SystemsTypical Microinverter Block SchematicMain Semiconductor Categories UsedBest in Class Semiconductor NeedsThe System Solution

Understandably, all these technologies must connect seamlessly in the microinverter system for performance and reliability. Obviously, much more semiconductor content per installed KW is needed in a microinverter as compared to a centralized inverter. In fact, the semiconductor content in a microinverter can account for 30% to 50% of its total cost, while in the case of a centralized inverter, the semiconductor content is below 20% of the system cost. However, the improved efficiency and higher energy gain of the microinverter, particularly within the concept of the smart grid, secures its importance.

This article was written by Luca DiFalco, Market Development Manager, STMicro - electronics (Geneva, Switzerland). For more information, contact Mr. DiFalco at This email address is being protected from spambots. You need JavaScript enabled to view it., or visit http://info. hotims.com/34458-201.

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