What Is Maximum Power Point Tracking (MPPT)?
Solar energy systems have become far more efficient, consistent and effective in generating electricity and charging batteries compared to the solar systems of yesteryear. One of the significant improvements is the efficiency of the solar cells themselves, which has gotten considerable attention in the industry. Another major advancement has been maximum power point tracking, which has enhanced both grid-tied arrays and solar systems with batteries.
Although solar PV panels and batteries are a winning combination, neither is particularly smart. When the solar photovoltaic panels don’t operate at the most efficient voltage for the batteries, they don’t receive as much current. Without maximum power point tracking (MPPT) capabilities, batteries often can’t use the maximum power available from the solar panels, resulting in waste.
Likewise, grid-tied systems can encounter the same issue but related to the power grid. Again, when there is a mismatch between the grid voltage and the solar output, production suffers.
Therefore, MPPT is critical for optimizing the relationship between the solar panels and the battery bank or utility grid. It maximizes energy extraction under various conditions by keeping the array operating in the ideal operating voltage range. For solar systems with batteries, installing MPPT solar charge controllers is the way to get this done because they regulate the voltage between the solar panels and batteries. In fact, MPPT charge controllers can even help protect the batteries and promote a longer lifespan. Likewise, MPPT tracking is a feature built into grid-tied inverters, but some have more advanced characteristics than others.
Understanding this critical topic can boost the productivity of a solar power system and result in more satisfied customers. Knowing when MPPT is beneficial to a PV array is essential because the equipment can be more expensive. Let’s explore this important topic so you can better serve your solar clients.
Understanding Maximum Power Point Tracking Charge Controllers
A charge controller, also known as a charge regulator, limits the electrical current rate added to or drawn from solar batteries. Their goal is to maintain the highest state of charge in the batteries without overcharging them. However, the solar system voltage and current can change suddenly due to variable irradiance, so the charge controller needs to respond quickly to adapt.
Maximum power point or peak power voltage is the voltage that PV panels produce maximum power. When charging batteries, maximum power varies by numerous factors, including solar radiation, the wire run length, the battery’s state of charge, and ambient and panel temperatures.
For example, solar panels are more efficient at low temperatures, but without MPPT methods, the photovoltaic array will lose out on the additional production. The idea behind MPPT is to extract the maximum voltage possible from the PV modules to most effectively charge the battery.
Solar charge controllers are rated by their maximum input voltage (V) and maximum charge current (A). The current amp (A) rating is the maximum charging current, and the voltage (V) rating is the maximum voltage of the solar panel(s). These ratings indicate how many solar panels can be connected to the unit and are critical for properly designing the solar energy system.
Sometimes, there is confusion about the word “tracking” because it doesn’t mean physically moving the array to optimize the orientation to the sun. In Maximum Power Point Tracking, it is electronic tracking, usually done digitally. The MPPT charge controllers use a tracking algorithm based on a power I-V curve for extracting the maximum available power from solar modules under certain conditions.
One line on the power curve is the voltage at maximum power, which occurs when the module is connected to a load and is operating at its peak performance output under standard test conditions (STC).
How A Maximum Power Point Tracker Works In Systems With Batteries
MPPT charge controllers are DC to DC converters that first take direct current (DC) input from solar modules and change it to alternating current (AC). Then, the charge controller converts the electricity back to a different DC voltage and current that matches the panels with the battery. Therefore, they convert a higher DC output voltage from solar modules down to the lower DC voltage needed to recharge the batteries.
Keep in mind that you can run more than one charge controller on an array.
Pulse Width Modulation Vs. MPPT Charge Controllers
Charge controllers are an essential element in off-grid solar systems and arrays with batteries. There are two types of charge controllers: MPPT and Pulse Width Modification (PWM). The two take different approaches to how they modify voltage. PWM modification doesn’t adjust the voltage of the solar system, so they are less efficient. These charge controllers pull the voltage down to what is required by the battery bank. Therefore, these units need to be used in PV systems where the array matches the battery voltage, therefore limiting the module options. The advantage is often a lower cost.
By contrast MPPT controllers take advantage of the sweet spot where voltage and current are maximum. Unfortunately, MPPT charge controllers cost more money but can expand the design options and capabilities of the project.
Panel Tracking Vs. Maximum Power Point Tracking In Grid-Tied Systems
Inverters commonly have MPPT capabilities, which mean they have a DC to DC converter that boosts energy harvest for the solar system. In solar inverters, there are two different options: single or dual MPPT tracking.
Single MPPT tracking offers monitoring at the array level. Data collection is for the overall array output and not specific strings or modules, even if the array contains multiple strings. In contrast, with dual MPPT channel tracking, the inverter monitors output at the channel level instead of the array level.
For solar systems with different azimuths, length of string, solar panels or pitch angles, dual MPPT tracking offers significant advantages. Therefore, dual MPPT offers greater design freedom, especially for complex rooflines or projects with different modules. Unfortunately, it often comes at a higher cost, but it can pay for itself in the greater energy production.
When Are MPPT Charge Controllers Necessary?
Having maximum power point tracking abilities can be priceless for some arrays and provide little benefit for others. Solar professionals need to learn in what situations MPPT abilities justify the additional equipment cost.
Maximum power is often most beneficial when the batteries are depleted or during the winter months, when the power is needed more because the days are shorter. Some solar experts report that for small solar arrays in warm climates, MPPT makes little impact. However, when solar panels are connected in series, raising the input voltage above the battery terminal voltage, MPPT is really helpful.
Therefore, MPPT charge controllers might not be advantageous in all situations. Understanding the project goals and your client’s needs can help in the design process. Often, customers want to use low-cost equipment. If it does seem beneficial, it is helpful to be able to explain to clients the advantages that MPPT provides to justify the additional expense. Educating clients can be critical to closing on projects.
Conclusion
Solar technology has advanced significantly in recent decades. This has allowed the technology to mature, be more reliable, and perform well in more complex conditions or properties. MPPT is a significant advancement in the solar energy industry because it boosts energy yield from PV cells and system reliability. MPPT algorithms are used in grid-tied inverters and batteries and adjust the current voltage.
Often, applying MPPT techniques results in higher equipment costs but they can provide system optimization. Therefore, solar designers and installers need to understand when this cost is justified. Unfortunately, many installers are challenged by the electrical engineering trials of working with solar energy sources.