How MOSFET technology will boost the effectiveness solar energy installations

How MOSFET technology will boost the effectiveness solar energy installations

According to market analysis conducted by IHS, by the end of this year the world’s total installed photovoltaic capacity with be over 310GWatts - that is 8 times what it was at the start of the decade. GlobalData predicts by 2025 this capacity will have more than doubled again, reaching 652GWatts.

With demand for solar technology continuing to grow, and the conversion efficiencies of photovoltaics still relatively low (though gradually increasing), there is an ongoing need to minimise the power losses of the supporting electronics (and thereby make full use of the converted energy). Simultaneously there are increasing pressures to reduce inverter form factors and also secure greater system reliability (as once installed this photovoltaic equipment should operate for 15 to 20 years).

Photovoltaic inverters convert the DC current produced by photovoltaic arrays into an AC current with the appropriate line voltage and frequency that it can subsequently be fed into the grid (or alternatively used to power an off-grid network). Because they are straightforward to drive, power MOSFETs will normally form the basis of inverter switching functionality in solar energy installations. There are a series of important attributes that need to be considered when specifying MOSFET devices for this kind of application.

  • Firstly devices should be rated at 600V or 650V, as this will generally provide more than adequate protection against the threat of high voltage transients.
  • So that switching losses can be mitigated as much as possible and system efficiencies elevated, the inclusion of fast recovery diodes (FRDs) may be called for. The tuning of the body diode of the MOSFET as FRD can reduce the switching losses considerably.
  • Thought must be given to how the balancing of MOSFET conduction and switching losses can affect system performance.
  • Also the influence that the MOSFET’s gate charge (QG) has on its switching capabilities must be taken into account - with lower QG allowing high frequencies to be supported, but how this will conversely lead to higher RDS(ON) (on-resistance) values and thus increase power losses.

Toshiba has produced a white paper on the optimising of power design through better informed MOSFET selection (and awareness of the latest semiconductor process technologies). To download this material click here:

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