Capacitors in Renewable Energy: Solar Inverters & Wind Turbine Applications

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The boom in renewable energy generation expected during the next 10 years will drive demand for capacitors used for a number of critical purposes, including power conversion functions in the fast-growing solar and wind segments. Global installed capacity for renewable energy sources is expected to expand by more than 100 percent during the next decade, according to market research firm Frost & Sullivan. Total capacity will increase to 3,203 GW in 2025, up from 1,566 GW in 2015.

Solar photovoltaic (PV) will lead the growth, accounting for 33.4 percent of new capacity during the period. Wind is following close behind, representing 32.7 percent of the additional capacity. Growth will be somewhat slower in other areas, including hydropower.

Frost & Sullivan cited several factors driving the renewable surge, including plunging prices spurred by technological advances and increased economies of scale. For instance, the cost of solar panels dropped by 70 percent from 2008 through 2013. Such declines have made renewable energy more cost-competitive with fossil fuel generation.

Capacitors in Solar Systems: Solar PV Inverters

Capacitors play a critical role in the solar market. Among other uses, they are employed in PV inverters, which are devices that convert the DC power produced by solar cells into AC power that can be used in the electricity grid. Inverters typically make extensive use of large-sized capacitors that store electricity.

The overall global PV inverter market amounted to $6.6 billion in 2014, according to IHS. The business is currently undergoing intense competition as Chinese suppliers enter the market to fulfill burgeoning domestic demand.

Reliability is critical for these inverters. Solar systems must remain in operation for extremely long periods of time, with some installers offering 25-year warranties for their systems. PV panels can retain the vast majority of their output for 40 years or more. And because these systems are located outdoors in a variety of climates, they must operate reliably over a wide temperature range.

Because of their essential role in solar systems, PV inverters also must be able to withstand weather extremes and remain in operation over long lifetimes.  Inverters in the past often lasted for much shorter periods of time, sometimes as briefly as five years. However, most new products are rated to last much longer, with SolarEdge Technologies offering a 12-year warranty on its inverters, for example.

Capacitor Failure: Solutions for Longer Capacitor Life Spans

Capacitor failure is a significant cause of malfunctions in PV inverters. These components are subjected to a variety of strains, including vibrations, mechanical stress and continuous operation at maximum voltages. Experts also note that electrolytic capacitors based on non-solid electrolytes age more quickly than those using solid electrolytes. This can lead to a shorter lifetime for these capacitors and the PV inverters that employ them. In light of this issue, some inverter designers are turning to other capacitors, including thin-film capacitors and ceramic capacitors, which have longer life spans.

EPCOS is offering the power capacitor (PCC), which is suited for such applications. This compact power capacitor features extremely low ESR and ESL values and can be mounted directly onto the IGBT module. The ruggedness and small form factor of the PCC makes it suitable for space-constrained inverters in photovoltaic installations.

Microinverters in Solar Panels: New Generation of Products

The opportunities—and problems—for capacitors in PV inverters only increase in a new generation of products known as microinverters. PV inverters traditionally have operated in string configurations, combining the output of multiple solar modules. In contrast, each microinverter is paired with a single solar module. This means that a reduction in output from a single module does not disproportionately reduce the output of the entire array.

Microinverters can be integrated directly into solar panels to produce AC solar modules. This simplifies the installation process and cuts down on materials costs. It also can more than compensate for the increased cost of the microinverters compared to string inverters. The microinverter segment is expected to expand at a rapid pace, with global market revenue set to rise to $1.1 billion in 2018, more than triple the $329 million total in 2013, according to the market research firm IHS. However, with microinverters sometimes attached directly to PV modules, it’s imperative for these devices to have warranty lifetimes equivalent to the solar panels themselves—again at about 25 years.

Microinverters & Plastics

Some microinverter designs now are able to employ polyester film capacitors. One design includes a bulk capacitor from EPCOS based on polyester film, a type of plastic. The use of this device avoids the lifetime problems associated with electrolytic capacitors.

Wind Turbine Capacitors

Capacitors also are playing an increasing role in wind energy. The wind market in recent years has seen the arrival of a new generation of turbines that eschew gearboxes. These gearless wind turbines use a direct connection between the rotor and the generator. Proponents of gearless technology say this approach makes wind turbines less complex, reducing the need for maintenance. This is a particularly important attribute for offshore turbines, whose remote location means costly repair.

The generators in gearless wind turbines require capacitors that can deliver high levels of capacitance, reliability and ruggedness. To serve this market, EPCOS is offering a line of screw-terminal aluminum electrolytic capacitors suited for gearless wind turbines. Along with high capacitance, these EPCOS capacitors are designed to meet requirements for reliability, long life, and temperature. The capacitors have high energy density, which suits the confined spaces inside wind turbines. They are connected in series and parallel to suit applications in wind power installations.

Capacity for Change

With renewable energy investment and production on the rise, capacitor makers are viewing the market as an increasingly attractive opportunity. Manufacturers are offering parts specifically designed to suit the needs for solar and wind systems. With these efforts, capacitor makers are enabling the faster deployment, lower-maintenance costs and greater efficiency of renewable energy.

 

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