Working principle

Solar panels are usually made of silicon, a semiconductor material, installed in a metal frame with a glass casing. They are responsible for converting solar energy received from the sun into electric energy that can be used to power various appliances. 

Panels are made up of smaller individual units called solar cells which are made up of semiconductor elements, commonly silicon. The silicon inside each cell is arranged into 2 separate layers, n-type silicon and p-type silicon layers. The n-type silicon layer has an excess of electrons, making it negatively charged. The p-type silicon layer has holes, which are extra spaces or ‘holes’ for electrons, making it positively charged. Where the two layers meet, called the p/n junction, the electrons are free to travel between the layers. Solar cells can be strung together to create large solar panels.

Energy received from the sun, light energy, is mainly composed of “tiny packets of light” called photons. When a photon strikes a silicon cell, it knocks out an electron from the n-type layer due to its high energy, leaving a hole. The electron and hole created are free to move around both layers. However, due to the electric field created in the p/n junction, they can only move in one direction. Thus, the hole is drawn towards the positively charged p-type and the electron to the negatively charged n-type. The mobile electrons are then collected from the n-type layer and the conductive metal plates around the cell which help move them from the cell to an electrical circuit, thus generating electricity.  

Choosing the most appropriate solar panel 

Different solar panels were researched upon, factoring primarily cost and efficiency before choosing an appropriate option.

The main types of solar panels: 

• Mono-crystalline Solar Panels (mono-SI): 15-20% efficiency. Not affected much by high temperature. Expensive.

• Poly-crystalline Solar Panels (poly-SI):14-16%. Comparatively less expensive than Mono-crystalline panels. Less efficient in higher temperatures.

• Thin-film solar panels: 10-12% efficiency. Compensated by installation taking place in a large area (thus a larger space is required). Not useful in a situation where there is limited space for the solar panel. (different types of TFSP not discussed, such as CdTe and CIGS, due to the same prevalent disadvantages). Cheap. 

• Concentrated PV cells: 40% efficient. Very expensive. Extra tracking systems and sometimes cooling systems required, causing  an increase in price. Moreover, in the context of a solar lamp, such high-efficiency rates do not have much-added benefit due to comparatively lesser electric load.

Other types of solar panels, such as Building Integrated Photovoltaic (BIPV) (integrated into buildings, roofs, windows, etc) and Bifocal solar panels (can capture solar energy from both sides) are not discussed because they can in no way be used in solar panels. The most suitable options to choose from were from mono-SI and ploy SI solar panels. Mono-SI panels offer slightly higher space efficiency at a higher price but compared to Poly-SI, power outputs are very similar. Mono-crystalline panels are expensive due to their energy-intensive and inefficient manufacturing process (with only a 50% yield for every silicon crystal). Poly-crystalline modules are cheaper because they make use of the crystal fragments leftover from mono-crystalline production, which results in a simpler manufacturing process and lower production costs.4 Furthermore, the expected load for LED light bulbs being used in the lamp is around 10-15 watts. This power could easily be provided using poly-SI panels. Thus it was chosen, to keep costs low.