The star at the center of our solar system, the sun, is humanity’s most plentiful energy source. It functions as a giant fusion reactor and will continue burning for billions of years.
Solar power operates by transforming energy from the sun into usable power. It produces two types of energy: electricity and heat.
To utilize solar energy effectively for powering everyday devices, humanity has developed photovoltaic cells, also called solar panels.
But what is the mechanism behind the functioning of solar panels?
How Solar Panels Produce Electricity
The sunlight shining onto a solar panel gets absorbed by the PV cells within it. This absorption generates electrical charges in the cells, prompting the flow of electricity due to an internal electrical field.
Photovoltaic Solar Panels: Converting Photons to Electrons
Semiconductors like silicon, commonly used in photovoltaic cells, are the materials responsible for converting light into electricity.
When light hits the panel, the semiconductor material absorbs a portion of it, transferring the light’s energy to the semiconductor. This energy release dislodges electrons, enabling them to move freely.
PV solar panels employ electric fields to direct the liberated electrons in a specific direction. This movement of electrons forms an electric current, which can be extracted for external usage by placing metal contacts on the top and bottom of the PV cell.
The combination of this current and the cell’s voltage, generated by its internal electric field, determines the power output (in wattage) of the solar cell.
Silicon in Solar Panels: A Detailed Look
Silicon, particularly in its crystalline form, possesses unique chemical characteristics. A silicon atom consists of 14 electrons distributed across three shells, with the outer shell having only four electrons.
To complete its outer shell, a silicon atom shares electrons with four neighboring atoms, forming a crystalline structure crucial for photovoltaic cells.
However, pure crystalline silicon isn’t a good conductor of electricity because its electrons lack mobility compared to materials like copper.
To enhance conductivity, impurities are intentionally added to the silicon in solar cells.
Doping Agents in PV
The intentional addition of impurities is known as doping. When silicon is doped with phosphorus, it becomes N-type silicon, denoted by “n” for negative due to the abundance of free electrons. N-type silicon demonstrates superior conductivity compared to pure silicon.
The other component of a standard solar cell is doped with boron, which possesses three electrons in its outer shell. This doping transforms the silicon into P-type silicon, indicated by “p” for positive. Unlike free electrons, P-type silicon contains free openings and carries a positive charge.
Energy Loss in a Solar Panel
The electromagnetic spectrum includes more than just visible light. It consists of a variety of wavelengths and energy levels.
Because light hitting the cell contains photons with a range of energies, some may lack sufficient energy to affect an electron-hole pair. These photons will pass through the cell without causing any changes, behaving as if the cell were transparent.
The Energy Gap
Some photons possess excessive energy. For an electron to be dislodged, it requires a specific amount of energy, typically around 1.1 electron volts (eV) for crystalline silicon, known as the band gap energy.
If a photon carries more energy than this threshold, the surplus energy is dissipated. These phenomena alone can explain the loss of approximately 70% of the radiation energy reaching the cell.
Fixing the Energy Gap
Selecting a material with an extremely low band gap seems like a solution to utilize more photons. However, the band gap also influences the strength of the electric field, which determines the voltage.
If the band gap is too low, although we gain extra current by absorbing more photons, we lose voltage. Recall that power equals voltage multiplied by current.
Hence, the ideal band gap, considering these factors, is approximately 1.4 electron volts (eV) for a cell crafted from a single material.
How Solar Panels Generate Electricity in a House
To power your house with solar energy, several steps are involved. While it’s not as straightforward as merely installing modules on your roof, it’s also not excessively complex.
Initially, not every roof possesses the suitable orientation or angle to maximize solar energy utilization. In the Northern Hemisphere, non-tracking PV systems should ideally face true south.
However, orientations toward more easterly or westerly directions are viable options as well, although they may result in differing degrees of efficiency loss.
Optimal Solar Panel Installation
Solar panels should ideally be inclined at an angle close to the area’s latitude to capture the maximum energy throughout the year.
If you aim to optimize energy production for specific times or seasons, you can adjust the orientation and/or inclination accordingly. It’s crucial to ensure that nearby trees or buildings never shade the modules, regardless of the time or season, as even partial shading can significantly diminish power output.
In a PV module, shading on just one panel can drastically reduce power production.
For a house with an unshaded, south-facing roof, determining the appropriate system size is necessary. However, this decision is complicated by unpredictable weather patterns affecting electricity production and varying energy demands.
Professional solar installation services are essential to navigate these complexities.
Fortunately, overcoming these challenges is relatively straightforward, with meteorological data providing average monthly sunlight levels for different regions.
Can Solar Power be Generated on a Cloudy Day?
Yes, solar panels continue to produce electricity even on cloudy days, albeit with reduced efficiency compared to sunny days. They can capture both direct sunlight and indirect light that penetrates through clouds. However, their performance decreases to approximately 10-25% of their normal efficiency during cloudy conditions.
Despite the lower efficiency, cloudy days have advantages. Rainfall cleans the panels, enhancing their overall efficiency.
Do Solar Panels Work at Night?
No, solar panels rely on sunlight to produce electricity and are inactive during the night.
Nevertheless, home solar systems often generate surplus electricity during daylight hours. This excess energy can be stored in batteries or fed back into the local grid, earning the solar owner net metering credits. This arrangement ensures continuous power supply even when sunlight is unavailable.
PV Panels Vs Solar Thermal Panels
Solar PV panels produce electricity through the photovoltaic effect, where photons from sunlight strike a semiconductor surface like silicon, causing the release of electrons. Conversely, solar thermal panels generate heat directly by heating water or other fluids with sunlight.
In domestic settings, solar thermal panels are installed on sun-facing roofs to heat water stored in a hot water cylinder, supplying hot water and heating.
Solar thermal technology can also be implemented on a larger scale in power stations.
Concentrating Solar-Thermal Power Basics
Concentrating solar-thermal power (CSP) systems employ mirrors to reflect and focus sunlight onto receivers.
These receivers collect solar energy and convert it into heat, which can be utilized to generate electricity or stored for future use. CSP technology is predominantly utilized in large-scale power plants.
Solar Power Trends in the US and UK
The US and UK governments have set targets to decarbonize their electricity systems by 2035, with a significant reliance on renewable energy sources such as solar power.
Solar energy in the US
The Solar Futures Study, released by the U.S. Department of Energy (DoE) in 2021, outlines their strategy for achieving a zero-carbon grid and underscores the significant role of solar energy in decarbonizing the nation’s power grid. As per the study, there is potential for solar energy to contribute to 40% of the country’s electricity by 2035.
In April 2023, the Biden-Harris administration announced an $82 million investment aimed at advancing technologies to integrate solar energy into the grid. This investment will bolster domestic solar manufacturing and recycling efforts, ultimately enhancing the resilience of the clean energy grid in the US.
Solar energy in the UK
In May 2023, the UK’s inaugural transmission-connected solar farm was activated. This solar array marks the first instance of a PV solar facility directly supplying electricity to the UK’s transmission network, facilitating its transport over longer distances. Previously, UK solar farms were linked to the country’s distribution networks, which are lower-voltage regional grids responsible for delivering power from the high-voltage transmission network to residences and businesses.
Situated near Bristol, this solar plant is projected to produce more than 73,000 megawatt hours (MWh) annually, sufficient to power over 17,300 homes. Additionally, it will mitigate 20,500 tons of CO2 emissions annually compared to traditional energy production methods.
The UK government’s Powering up Britain report has restated its goal for a five-fold increase in solar generation deployment by 2035, with up to 70 gigawatts (GW) installed capacity, capable of powering around 20 million homes.
Solar Power In a Nutshell
Solar energy technologies are continuously advancing, and the declining prices of solar make it increasingly accessible for U.S. homeowners.
These trends are expected to persist in the foreseeable future.
The Biden Administration’s focus on climate change resilience and clean infrastructure, aiming for a carbon-free grid by 2035, suggests that more solar incentives may be introduced to achieve these objectives.
Already, the federal tax credit has been extended for a decade due to the Inflation Reduction Act, indicating the potential for further incentives in the future.
However, it’s essential to acknowledge a significant challenge facing the solar industry: utilities nationwide are advocating for the elimination of net metering, a key factor in the attractiveness of solar investment.
To maximize solar savings, it’s advisable to transition to solar sooner rather than later.
