solar panels in the sun
PAT Roberts

How can optical filters make solar panels more efficient?

Solar panels use the photovoltaic effect to generate electricity from sunlight, starting from the very near infrared range and taking in much of the visible light spectrum, depending on the materials used and certain other characteristics of the solar panel itself.

The effect is similar to the photoelectric effect, when a photon hits a surface and excites an electron enough to break free; however, in the photovoltaic effect the electron remains within the conducting material, generating a current.

Photovoltaic solar panels are therefore an important contributor to sustainable renewable energy – at least until the end of the Sun’s life – and optical filters play a surprisingly complex role in maximising the efficiency of solar energy generation.

The physics of photovoltaics

There are several characteristics that go into a well-designed solar panel, for example:

  • Sensitivity to the correct wavelengths and frequencies of light
  • Sensitivity to photons above a minimum threshold energy level
  • Minimal reflectivity of light within the desired spectrum

This gives rise to the physical properties of solar panels on the mass market, which tend to be black (minimum reflectivity), thin (maximum sensitivity with minimal attenuation within the panel itself) and made of doped silicon to create the necessary conductive material.

But some of those properties can also be problematic. Thin panels may be more delicate, and any disruption to the conductive circuit can leave individual solar cells unable to carry an induced current. Black panels can also be more susceptible to excess heat in bright sunlight.

How are optical filters used in photovoltaics?

Einstein received the Nobel Prize for Physics in 1921 after he discovered that the energy of electrons ejected by the photoelectric effect depends on the frequency of the incident light, and not on its amplitude – in essence, dim light can work for solar panels.

This is why even on a cloudy day, photovoltaic panels can generate a current from the relatively dim, high-frequency ultraviolet light that is able to penetrate the cloud layer.

Optical filters are used to ensure that only the desired waveband of light impacts the solar panel, with minimal attenuation, so that the greatest possible current is generated without subjecting the panel to unnecessary stress.

A key element in this is reflecting or absorbing wavelengths associated with heating the panel, such as those at the infrared end of the spectrum, and optical filters can prolong the lifespan of solar panels significantly by doing this.

Beyond the photovoltaic effect

Optical filters for solar panels can improve efficiency beyond just protecting the panel itself, as the thermal energy they absorb can also be used in a variety of ways.

In this way, a solar panel can function similarly to an air source heat pump, heating water or transferring warmth into a property, or storing heat so that it can be used later when the solar cells are generating less current (for example overnight).

Because of the numerous roles played by optical filters – bandpass filters for the desirable incident light waveband, reflectors at unwanted wavelengths and absorption of thermal energy – it is important to use filters that are thin (to minimise attenuation) while still achieving this relatively complex overall effect.

Envin Scientific’s bespoke optical filters can be designed to deliver very specific bandpass, absorption and reflection properties, using advanced techniques in-house to achieve this on thin, low-attenuation substrates.

To find out more about this or bespoke optical filters for custom applications, please contact us today and a member of our team will be happy to discuss what you need.