Let's Dive into Solar Irradiance Technology and Maximizing PV Solar Energy Generation

Solar energy has become a cornerstone in the global transition towards renewable energy, and photovoltaic (PV) solar panels play a critical role in this shift.

One of the most important factors for optimizing energy production from PV systems is understanding Total Solar Irradiance (TSI) on the collecting surface of PV panels.

This post will explore TSI, including its components—reflected radiation, diffuse radiation, and direct beam radiation—and explain how each affects solar energy production. We will also examine strategies to maximize solar energy generation, including advanced sun-tracking systems, and touch on their effects on power quality, grid stability, and system innovations.

A. Components of Total Solar Irradiance on PV Collecting Surfaces

Total Solar Irradiance (TSI) refers to the solar power per unit area that reaches the surface of a PV panel. It is a combination of three components:

A1. Direct Beam Radiation (Gb):

The radiation that travels in a straight line from the sun to the Earth's surface. It constitutes about 84.7% of the total solar irradiance.

This is the most valuable component for PV systems, as it provides the most consistent and concentrated energy.        

A2. Diffuse Radiation (Gd):

The solar radiation scattered by molecules, particles, and clouds in the atmosphere before reaching the surface.

This contributes to about 10.7% of the total irradiance. Diffuse radiation is significant on cloudy days when direct sunlight is blocked.

A3. Reflected Radiation (Gr):

The sunlight that is reflected from surrounding surfaces (e.g., ground, water, or other objects) and then reaches the PV panel.

Reflected radiation accounts for only 4.6% of TSI and is often considered negligible due to its minimal impact on overall energy production.

Mathematically,

Total Solar Irradiance (GT) on the surface of a PV panel can be expressed as:

Total Solar Irradiance (GT)= Gb + Gd + Gr

Where:

Gb= Direct beam radiation

Gd = Diffuse radiation

Gr= Reflected radiation

Due to the low percentage of reflected radiation, it is often ignored in practical calculations, particularly in regions where the reflectivity (albedo) is low or the surface is non-reflective (e.g., concrete or soil).

This leads to the simplification of the equation as:

Total Solar Irradiance (GT) ≈ Direct beam radiation (Gb) + Diffuse radiation (Gd)

B. Maximizing Solar Energy Generation: Tracking Technologies

To optimize energy generation, we need to maximize the amount of solar irradiance hitting the PV surface.

This can be achieved through different tracking technologies:

B1. Fixed PV Solar Systems

PV panels are fixed in one orientation, typically south-facing in the northern hemisphere, to receive the maximum possible sunlight throughout the year.

These systems are cost-effective but have lower energy generation potential, especially during early mornings and late afternoons when the sun is at a low angle.        

B2. One-Axis Tracking Systems

The PV panels rotate along a single axis, typically east to west, to follow the sun’s movement across the sky throughout the day.

This method increases energy capture by 15% to 25% compared to fixed systems, as it ensures that the panels are exposed to direct sunlight for a longer period during the day.

Case Study: In regions like California’s Central Valley, large-scale solar farms utilizing single-axis trackers have shown a substantial increase in power output, contributing significantly to the grid.        

B3. Two-Axis Tracking Systems

These systems rotate along two axes, allowing the PV panels to not only track the sun’s daily east-west movement but also adjust for seasonal changes in the sun’s height.

This method can further boost energy capture by up to 35% compared to fixed installations, as it ensures that the panels are always perpendicular to the sun’s rays.

Case Study: A two-axis tracking system used in Spain’s La Muela Solar Plant has shown a 30% increase in energy generation, particularly during the summer solstice when the sun’s position is highest.        

C. Impacts on Power Quality and Grid Stability

Maximizing energy generation from solar systems affects not only the output but also the overall stability of the grid:

C1. Power Quality:

Increased solar penetration can enhance power quality by providing cleaner energy.

However, fluctuating irradiance (due to weather conditions) may introduce voltage variability, affecting grid voltage and waveform stability.

C2. Grid Voltage and Frequency:

With solar energy being intermittent, integrating PV systems, especially in large capacities, can cause fluctuations in grid voltage and frequency.

Power electronics like inverters are used to stabilize these parameters, ensuring that the grid remains balanced.

C3. Grid Impedance:

The addition of renewable energy sources like solar power affects the grid’s impedance. Lower impedance improves the grid's resilience to voltage drops and fluctuations.

Managing grid impedance involves the use of advanced controllers and energy storage systems, such as Battery Energy Storage Systems (BESS), to smooth out supply irregularities.

Case Study of Hornsdale Power Reserve, a large-scale battery system connected to a solar farm, demonstrates the synergy between solar PV and energy storage. The project has improved grid stability, reduced energy costs, and provided rapid frequency control, addressing the intermittency issue inherent to solar power.        

Effective planning for a solar project requires optimizing Total Solar Irradiance on PV collecting surfaces by factoring in direct beam, diffuse, and reflected radiation, along with implementing strategic tracking systems to maximize energy generation

Recent innovations in PV systems include the use of bifacial solar panels, which capture sunlight from both sides to increase energy efficiency, and the integration of Battery Energy Storage Systems (BESS) to store excess energy, enhance grid stability, and provide continuous power supply.

How do you think energy storage technologies can further enhance the integration of solar power into the grid? ??

This post reflects my personal knowledge and is for educational purposes only.

#RenewableEnergy #PowerCables #SolarEnergy #HVDCPowerCables #PowerQuality #BESS #GridCodeComplianceStudies

Source reference:

Boxwell, Michael. Solar Electricity Handbook : A Simple Practical Guide to Solar Energy : How to Design and Install Photovoltaic Solar Electric Systems. Coventry, Greenstream Publishing, 2015.

Staff, Energy. “Pumped Storage in Spain.” NS Energy, 11 July 2013, www.nsenergybusiness.com/analysis/featurepumped-storage-in-spain/#:~:text=La%20Muela%2C%20with%20an%20installed%20capacity%20of%20635-MW%2C. Accessed 25 Sept. 2024.

Electric Cables Handbook Third Edition; G.F. Moore, 1997

“Hornsdale Power Reserve.” Hornsdalepowerreserve.com.au, 2018, hornsdalepowerreserve.com.au/.