Peak Power Point Tracking (MPPT) Solar Charge Controllers you should know

What is a MPPT charge controller?

This section discusses the theory and operation of "maximum power point tracking" used in solar charge controllers.

A MPPT, or maximum power tracker, is a DC-DC electronic converter that optimizes the correspondence between the solar panel (photovoltaic panels) and the battery bank or the distribution network. Simply put, they convert a higher voltage DC output from solar panels (and some wind turbines) into a lower voltage needed to charge the batteries.

(They are sometimes called "power point trackers" - not to be confused with PANEL trackers, which are a solar panel fixture that follows, or follows, the sun).

Discover our MPPT charge controllers.

So what do you mean by "optimizing"?

Solar cells are neat things. Unfortunately, they are not very intelligent. The batteries either - in fact, the batteries are downright stupid. Most photovoltaic panels are designed to provide a nominal voltage of 12 volts. The plug is "nominal". In fact, almost all 12-volt solar panels are designed to operate between 16 and 18 volts. The problem is that a nominal 12 volt battery is close enough to an actual value of 12 volts - 10.5 to 12.7 volts, depending on the state of charge. Under load, most batteries will charge fully between 13.2 and 14.4 volts, which is quite different from what most panels are designed to be turned off.

OK, we now have this 150 watt solar panel. Catch # 1 is rated at 150 watts at a particular voltage and current. The Kyocera KC-130 is rated at 7.39 amperes at 17.6 volts. (7.39 amps times 17.6 volts = 130 watts).

What is the tracking of the maximum power point?

There is some confusion about the term "follow-up":

Panel Tracking - this is where the panels are on a mount that follows the sun. The most common are Zomeworks. These optimize the output by following the sun in the sky for maximum sunshine. These generally give you an increase of about 15% in winter and up to 35% in summer.

This is the opposite of the seasonal variation for MPPT controllers. As the panels have much lower temperatures in the winter, they produce more energy. And winter is usually when you need the energy from your solar panels the most because of shorter days.

Maximum Power Point Tracking is an electronic tracking, usually digital. The charge controller examines the panel output and compares it to the battery voltage. It then figures out what is the best power the panel can provide to charge the battery. It takes this and converts it to the best voltage to get the most AMPS in the battery. (Remember that it's the amps in the battery that matter). Most modern MPPTs have a conversion efficiency of about 93 to 97%. You generally get a power gain of 20 to 45% in winter and 10 to 15% in summer. The actual gain may vary considerably depending on weather, temperature, battery charge status and other factors.

Network junction systems are gaining popularity as the price of solar drops and electricity rates increase. There are several brands of inverters coupled to the network (that is, without batteries). All built in MPPT. The efficiency is about 94% to 97% for the MPPT conversion on these.

How does tracking maximum power points

This is where optimizing or tracking the maximum power point comes into play. Suppose your battery is low at 12 volts. A MPPT takes this voltage from 17.6 volts to 7.4 amps and converts it so that the battery now receives 10.8 amperes at 12 volts. Now you have almost 130 watts left and everyone is happy.

Ideally, for a 100% power conversion, you will get about 11.3 amps at 11.5 volts, but you will need to power the battery with higher voltage to force the amps. This is a simplified explanation - in fact, the MPPT charge output it is possible that the controller varies continuously in order to get the maximum amps in the battery.

MPPTs are the most effective under these conditions:

Winter and / or cloudy or foggy weather - when extra power is most needed.

Cold weather - Solar panels work best in cold weather, but without MPPT, you lose most of it. Cold weather is most likely in winter - when the sun is low and you need the energy to recharge the batteries to the fullest.

Low battery charge - the lower the charge level of your battery, the more power the MPPT receives - another time, when the need for extra power is greatest. You can have both conditions at the same time.

Long Cable Length - If you are charging a 12-volt battery and your panels are 100 feet away, the voltage drop and power loss can be significant unless you use a very large cable. This can be very expensive. But if you have four 12 volt panels wired in series for 48 volts, the power loss is much lower and the controller will convert this high voltage to 12 volts at the battery. It also means that if you have a high voltage panel configuration powering the controller, you can use a much smaller wire.

Ok, let's go back to the original question - What is a MPPT?

How does a Maximum Power Point Tracker work?

The Power Point Tracker is a high frequency DC / DC converter. They take the DC input of the solar panels, change it to high frequency AC and convert it to a different voltage and DC current to match the panels to the batteries. MPPTs operate at very high audio frequencies, typically between 20 and 80 kHz. The advantage of high frequency circuits is that they can be designed with very high efficiency transformers and small components. The design of high frequency circuits can be very tricky because of the problems posed by certain parts of the "broadcasting" circuit, just like a radio transmitter causing radio / television interference. Isolation and noise suppression become very important.

There are some non-digital (ie, linear) MPPT load controls. These are much easier and less expensive to build and design than digital solutions. They improve efficiency somewhat, but overall efficiency can vary considerably - and we have seen some lose their "point of tracking" and get worse. This can happen from time to time if a cloud is passed on the panel - the linear circuit looks for the next best point, then moves too far from the depth to find it when the sun rises. Fortunately, there are not many around.

The power point follower (and all DC to DC converters) operates by taking the DC input current, changing it to AC, passing through a transformer (usually a FGET transformer), and then straightening it to DC, followed by the output regulator. In most DC-DC converters, this is a strictly electronic process. No real intelligence is involved, except for some regulation of the output voltage. Charge controllers for solar panels need a lot more intelligence because the light and temperature conditions constantly change throughout the day, and the battery voltage changes.