artificial light from lightbulb shining on solar panels

Can Solar Panels Work with Artificial Light?

Carlos

Written by qualified solar engineer Carlos on January 20, 2019

Solar panels can work with artificial light. However, their performance and energy outputs will never be as high as if they were exposed to sunlight. The energy output of the solar panel will also vary depending on the type of bulb, the type of light (warm or cold), intensity, and the wavelength of the artificial light.

Let’s analyze some of these facts in order to give you a good reference of the impact of artificial light on solar power performance. First, we must approach some technical factors.

Solar Radiation and Light Spectrum

Solar radiation is the main source of energy used by solar panels to generate electricity. We can describe it as the transference of energy from the Sun through a set of electromagnetic radiations that are distributed in a light spectrum that goes from ultraviolet to infrared radiation.

The solar radiation spectrum can be divided into several regions according to the wavelengths of the electromagnetic waves that reach the Earth, as you can see in the figure below:

Solar radiation spectrum chart to explain the solar energy distribution

Source: Geolycafe

From the figure above, we can notice that the highest irradiance values can be obtained in the region of visible light. This region contains all the colors of the rainbow and includes wavelengths that go from 400 to 700 nm.

Based on this approach, most solar panel manufacturers focus on maximizing the absorption of light within the visible region. However, solar panels can also be designed to absorb light in wider wavelengths. As we can see below, some of the most common solar panel technologies, like monocrystalline and polycrystalline modules, are able to cover a higher range of wavelengths including visible light. They can also include wavelengths in the near infrared region (up to 1200 nm). Other popular thin-film technologies such as CIGS and CdTe can also cover these regions, although with less efficiency. Amorphous (a-Si), Gallium Arsenide (GaAs), Dye-sensitized (DSSC) and Organic Solar Cells are mainly restricted to the visible region of light.

Line chart to show efficiency vs. wavelengths of different solar panel technologies

Source: A proposal for typical artificial light sources for the characterization of indoor photovoltaic applications, B.Minnaer and P.Veelaert, Ghent, University

As you can see, there are other wavelengths of light that can also be used by large, commercially available technologies like silicon modules to harness electricity. Therefore, we can ask ourselves, is it possible that solar panels can harness electricity from other sources of light, like incandescent or fluorescent bulbs?

Artificial Light

An incandescent lamp is composed of a balloon of glass in which a filament is heated to high temperatures (2,000 to 3,000 K) and is generally defined within a spectrum of 300 -830 nm wavelengths, having its peak on the infrared region of light. Therefore, if solar panels can extract power from wavelengths as low as 300 nm to 1,200 nm, then it is logical to think that solar panels could extract some energy from this source.

chart to explain the spectrum of incandescent light

Source: Comsol

On the other hand, fluorescent lights were defined and designed to be located inside the visible region of light. There are many types of fluorescent lamps (around 12) that are designed using different technologies. However, most of them use gases that are electrically charged, like mercury, to create a path for a current to flow. In turn, this will lead a phosphor to fluoresce and create visible light. This technology focuses on the lower band of the visible light spectrum which produces low ultraviolet light.

LED and metal halide technologies are also other common artificial sources of light. Metal halide lamps are high-pressure discharge lamps that use an electric arc in a gaseous mixture of vaporized mercury and metal halide to produce light in a broad spectrum. On the other hand, Light Emitting Diodes (LED) are solid-state lamps that use the electroluminescence of a bandgap (a barrier that limits electrons inside a material) to emit light. They can be divided into cool and warm technologies.

According to a research study done at the Ghent University in Belgium, we can visualize the typical wavelength ranges of all artificial light technologies scaled to 500 lux.

chart to explain the spectrum irradiance vs. wavelength ranges of light in different fluorescent lampsSpectrum irradiance vs. wavelength ranges of light in different fluorescent lamps. F2: Cool fluorescent lamp of a correlated color temperature (CCT) of 4230 K. F7: Broad-band fluorescent lamp (CCT=6500 K). F11: Narrow tri-band fluorescent lamp (CCT=4000 K)

Source: A proposal for typical artificial light sources for the characterization of indoor photovoltaic applications, B.Minnaer and P.Veelaert, Ghent, University

chart to explain spectrum irradiance vs. wavelength ranges of light in different led and metal halide lampsSpectrum irradiance vs. wavelength ranges of light in different LED and Metal Halide lamps

Source: A proposal for typical artificial light sources for the characterization of indoor photovoltaic applications, B.Minnaer and P.Veelaert, Ghent, University

Solar Panels Tested Under Artificial Light Conditions

Ben Minnaert and Peter Veelaert from the Ghent University asked themselves the same question that we wondered ourselves. So, to find the truth, they put all of the artificial lights into different categories: incandescent, fluorescent, LED, and metal halide lamps.

Then, they used different solar panel technologies like monocrystalline, polycrystalline, Cadmium Tellurium, CIGS, and others to quantify the power outputs of these modules under indoor conditions at 500 luxes (typical measure of the intensity of light in sq. meters inside offices) from the mentioned artificial sources of light. 

Amazingly, they found that it was indeed possible to harness electricity from artificial light through solar panels. However, efficiency values were nowhere close to what would be expected in outdoor daylight conditions.

They found that the monocrystalline technology and incandescent light were the best possible combination to obtain electricity from artificial light, followed by polycrystalline and CIGS technologies combined with incandescent light. Nevertheless, taking into account a 500 lux illumination, it was possible to obtain only 6 W/m2, too low for Standard Test Conditions.

Other sources of light like fluorescent, LED and metal halide were not as efficient with silicon cells, but instead with GaAs and CdTe solar panels. However, these technologies were not suitable at all since they were able to produce more than 1 W/m2.

Conclusion

There is a lot of speculation about how solar panels work in different scenarios. For example, whether solar panels work through glass or work when using artificial light are among the most speculated. Based on this research we can conclude that solar panels can work with artificial light, but the efficiency obtained from using this source of light is so negligible that is not worth it to be considered as electrical supply.

Moreover, if we compare the spectrum of irradiance from fluorescent sources of light with the solar radiation spectrum, we can notice great differences.

Solar radiation spectrum curve follows a smooth and continuous shape that maximizes the conversion of light into electricity. We can notice that by multiplying the wavelength in nm. with the spectral irradiance in W/m2, we can theoretically obtain values of 1000 W/m2.

However, when we compare it with the fluorescent, LED, or metal halide spectral irradiance, we can notice that many of them have irregular spikes that do not allow a smooth absorption of light. Besides, these values are in mW/m2 rated at 500 luxes. When we multiply them with the wavelengths in nm., we obtain values lower than 30 W/m2. The difference is just astronomic.

For applications inside commercial buildings related to BIPV, illuminance values can increase, however, they will not be as attractive as to consider installing solar panels to take advantage of artificial light. As a reference, a UEFA Champions League Stadium can have an average illuminance of 2,000 luxes, and if you multiply the estimated 30W/m2 at 500 luxes by four (to achieve approximately 2,000 luxes), then you would only be obtaining around 120W/m2 irradiance values, which is still very low.

References

  1. Uefa Stadium Lighting Guide 2016 – UEFA
  2. A Proposal for Typical Artificial Light Sources for the Characterization of Indoor Photovoltaic Applications – Energies
  3. Solar Energy Distribution – Ecotality
  4. Calculating the Emission Spectra from Common Light Sources – COMSOL

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12 Comments

    1. Carlos

      Hello Bob,

      The answer lies behind the figure titled ” Spectrum irradiance vs. wavelength ranges of light in different LED and Metal Halide lamps”. As you can see, cool LEDs have a higher spectrum irradiance, which means they are better for solar. For the wavelength close to 450 nm the corresponding color would be cool white. In other words, cool white is the best artificial light color for solar panels.

  1. Avatar

    Wow! that is quite an answer to a simple question. I think an ordinary mortal like me asked the question, will solar batteries be charged ONLY by sunlight, or will a functioning incandescent light bulb or a florescent tube light charge them not as much as the sun, but at least a little (like on a cloudy day when there is no sun to charge them)? That’s my question. I guess the answer is no on florescent tube lights and a tiny bit on incandescent lighting. I apologize for any errors in spelling and wonder if you’ll answer me. Thanks.

    1. Carlos

      Hello Jean,

      Thank you for your question,

      That is a good guess Jean. However, artificial light is nowhere close in terms of electricity generation for solar panels as sunlight, not even on a cloudy day. So the answer is no on both of them. Now, in terms of which source is better, in most cases, incandescent will generate more power as it has a higher spectrum irradiance in a wider wavelength range as you can see in this link .

      However, incandescent light power is more dependent on distance than fluorescent light, therefore it would need to be closer than a fluorescent light source to generate a decent amount of power for small gadgets.

      1. Avatar

        Good read very clear and understandable.
        What about laser light?
        Leaving the question broad as not to show too much ignorance

        1. Carlos

          Greetings Phil,

          Thank you for your question,

          Unfortunately, laser lights would not be suitable for this purpose. They have a very low amount of power that would be imperceptible for a solar panel.

  2. Avatar

    Carlos, I have a question I would like to ask you in private – could you e-mail me directly to open a discussion.
    Thanks, Pat

  3. Avatar

    Greetings Carlos,

    I am wondering whether we could have light source which generates light in same spectrum as that of Sunlight and wireless power transfer is possible. Correct me if I am wrong but do you think is it possible or it’s just not feasible because of low power density.

    1. Carlos

      Greetings Bipeen,

      That is a very interesting comment,

      So, the problem does not lie in finding a source of light that generates in the same spectrum as the Sunlight, that already exists. If you see the first picture of the article you will notice the visible region of light that the Sun uses. Now if you take a look at the pictures from fluorescent light and LED spectrum you can realize that they are within the same wavelengths.

      Therefore, the thing is not to find a source of light that generates light in the same spectrum as the Sun, but to find a renewable source of light that has the same intensity as the Sun, and that does not require power to be turned on. Unfortunately, that does not exists in our planet.

      About wireless power transfer, you can already find some devices that work with this technology and solar, such as power banks. That basically works with electromagnetic field interactions. In the electronics industry, that may be become more common, but I find it difficult to imagine would reach larger scales.

        1. Carlos

          Hello Adam,

          Thank you for reaching out,

          Unfortunately no Adam, solar powered garden lights emit very small amounts of lumens (which represents an even smaller amount of watts), this does not allow to power other solar devices using it as a source of light. And actually, for your application, a pond pump is believe or not a load that can demand large amounts of power during the surge period, therefore, you would need to couple it with a bigger grid-tied PV system or size a small PV system with batteries to power the pump at night.

          Hope this helps,

          Best
          Carlos

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