One of my favorite pastimes is following the development of game strategies. Especially in the realm of video games, slight tweaks or counterplay to the gameplay results in new discoveries without changing the underlying game. In other words, a finalized version of a release may evolve over time as the same physical product.
Solar panels occupy a similar space; even without considering changes to the underlying material, there exist some notable technology considerations for performance and safety. Solar might already seem well-established in the decades since its initial inception, but there is still significant room to grow. System design has greatly improved the efficiency of PCB solar panels, and additional advancements, like the sun itself, are on the horizon.
How to Maximize the Potential of Your PCB Solar Panel
A board is only as good as its source, which takes on an interesting wrinkle for solar panel design. The sun is going to travel throughout the sky on orbits of varying lengths and arcs throughout the year, yet the board needs to ensure it can best capture insolation by forming a perpendicular surface to the incoming rays. The solution is maximum
power point tracking (MPPT). MPPT provides guidance for tracking systems by quantifying the intensity of the sunlight hitting the panel through secondary measurements. There are multiple approaches for maximizing this particular performance aspect:
- Hill climbing. The most popular method adjusts the angle of the panel, measures the resultant power, and compares the change in power (if any). If this adjustment resulted in an increase, the process is repeated until there is zero change in the power, indicating an arrival at the maxima. Though it may sound crude and poor implementations of the strategy can result in
oscillations in the power, a well-devised system is extremely efficient.
- Temperature. As voltage directly correlates to irradiance in a solar panel, one solution to maximizing performance is to measure the temperature of the panel and compare it against a reference. Summing the MPPT voltage at a given temperature with the product of the temperature coefficient and the difference between the temperature and reference temperature produces an equation. It is simple to solve and avoids oscillations due to the relative time invariance of the measurement. An optimization in this style is incredibly cost-effective and well-geared for low power consumption control circuits.
- Power-conductance relationship. A more computationally intensive design with less oscillation on output, power-conductance allows for much greater responsiveness to stimuli. The controller analyzes for the point where differential (or incremental) conductance is equal to average conductance, based on the relationship between power and voltage. This is accomplished by differentiating
P = IV
with respect to voltage, with current as a function of voltage. By setting the differential power with respect to the voltage equal to zero for maximization conditions, the stipulation between the two conductances is met.
MPPT is sometimes combined with additional control methods, such as the open circuit voltage ratio, to provide additional stability. Here, the power is interrupted on a schedule to measure the open circuit voltage, which provides a performance goal for the circuit to strive for. This open circuit voltage represents a static maximum power point (as opposed to the active trackers outlined above), in effect, a hard-coded answer to MPPT.
Preventing Islanding, Protecting People
Islanding may sound like a fantastic vacation idea, but it’s a potentially deadly phenomenon for electrical workers. For generators that are connected to a greater grid, those operating on downed or malfunctioning power lines are at great risk if solar panels do not automatically disconnect from the greater network. This does not account for the cases where a solar panel array is designed to operate absent any grid activity such as a power outage where islanding would be beneficial.
Islanding arises from the DC-to-AC inversion that normally allows for the generated current at the source to be transferred to the grid on a buyback program. The problem occurs when the grid is disabled, intentional or otherwise, and the inverter unknowingly continues to provide a live wire. The inverter attempts to match the phase and voltage of the grid for best metrics, and in most cases, this results in the inverter turning off during a grid shutdown. However, this check is not instantaneous, and a load at the inverter may see a match on the grid at the final moment before it goes offline, ensuring the inverter continues to act as a supplier to the grid. Moreover, transients arising from the interruption in service may also match those generated at the inverter, further perpetuating the danger posed.
Detection systems that can accurately diagnose when a system has ceased service are necessary to prevent this situation. The range of parameters by which the system determines when a system has gone down has some built-in blind spots, known as the nondetection region, which creates false negatives that fail to account for a downed grid. While it is impossible to completely eliminate the entirety of false negatives, minimizing the range of nondetection and testing helps save lives.
Your Contract Manufacturer Can Shine Some Light on Solar Design
PCB solar panels represent an enticing technology for various economic and environmental factors. With their overall adoption set to increase within the coming years, customers will seek optimal performance for installations that can last up to twenty years. Designers need to be well-versed in the best schematic and layout practices to improve efficiency if they want to maximize the technology. Whether you’re looking to revise or design a whole new board, VSE has you covered. Our team of engineers and manufacturing partners is committed to building electronics for our customers, and we aim to deliver an excellent board for solar or many other applications.