Anyone using a solar photovoltaic (PV) system is tasked with maximising its efficiency and extracting the highest possible energy charge at all times. This is particularly difficult given that weather conditions will vary, and in the UK especially, are very difficult to predict. A major element of the justification used when investing in solar PV panels is the expected electrical output and therefore how much this will save you in terms of reducing your reliance on the national grid. So it is important that you know what your system is capable of and can monitor the performance of the solar cells. The Maximum Power Point (MPP) is central to being able to do this.
What is the MPP in solar panels?
The maximum power point of a solar panel is the point at which the product of current and voltage is at its maximum. A more exact definition of MPP is the point on a power (I-V) curve with the highest value, when looking at the product of current and voltage. This in effect is the point at which the power output is at its highest. However, it is important to understand why we need to calculate this.
Why do we need to calculate the MPP?
A common problem with solar PV panels is the actual output achieved when matched against the manufacturers’ rated value. We want to maximise the output for the most efficient results, but the efficiency of the power transfer of a solar PV system is dependent on the amount of available sunlight and what shade is present from surrounding buildings etc. In other words, we might have a solar panel with a rated output of 130 watts, but when we measure the output of the panels and what charge is being sent to the battery, this might only be something like 90 watts. So where has the 40 watts gone? The truth is that it is not lost, it’s just not being produced.
The SP rating of a solar panel is under standard test conditions, which ordinarily will be at full sunlight with minimal shade, and your task in reality is to try and mimic those conditions as closely as possible. But that is very difficult, so you need to track the output from the solar cells – using test equipment such as the TIS IV-PRO advanced I-V curve tracer supplied by Test Instrument Solutions - to tell you what the power transfer is from the solar panels to the battery at any one time, and that is what MPPT is, maximum power point tracking.
Understanding MPPT in solar panels
The current and voltage produced by a solar panel generates a power curve which can be tracked to show where the highest values are produced. This is known as the load characteristic, and the solar PV system is optimised when the load characteristic changes to ensure the power transfer from solar cell to battery is at its highest efficiency, ie. when there is maximum exposure to the sun’s radiation. The optimal load characteristic is the MPP, and MPPT is the process of monitoring this.
You can physically mount the panels so that they follow the sun to continually catch and absorb the maximum sunlight as it moves across the sky. In this case, the charge controller would look at the real time output of the panels and compare it to the battery charge being received, to calculate the current MPP, and the system would be designed to move according to where the MPP is. The principle of MPP is also used when monitoring the performance of wind turbines and how their efficiency is dictated by weather conditions, except it is tracking the optimum wind speed, rather than exposure to the sun.
Please note that this section is for information purposes only. Anyone using equipment referred to in this section must be suitably qualified and/or experienced within the respective field. If in doubt before use, please consult a qualified electrician or engineer & thoroughly read all instruction booklets.