Improving Microinverter Performance in Photovoltaic Systems
- Created: Thursday, 01 September 2011
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.
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)
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.