If you have started researching charge controllers (aka battery regulators), you will inevitably come across the question of whether you should buy a Pulse-Width Modulator controller (PWM for short) or a Maximum Power-Point Tracking controller (MPPT). Here at Voltanic we promote the use of MPPT controllers in our solar kits. Read on to find out why. TLDR: PWM controllers can only harness 70% of the available watts from your panels whilst MPPT controllers can harness 99.9%. What is Maximum Power Point Tracking? Non-Technical Explanation Imagine that you have a simple hosepipe. You have a steady stream of water gently pouring out and you want to maximize the power of that water so you can hit your spouse sunbathing at the other end of the garden. How would you do it? Simple – you put your finger over the end of the hosepipe to reduce the size of the hole. If you put too much finger over the end of the hosepipe you just get a fine mist of water – i.e. very little power. If you don’t put enough finger over the end of the hosepipe, the water won’t go far enough. There is a “maximum” power point where you can get the water to spray a great distance without misting. The MPPT controller’s job is to find that point. Now imagine someone were to open up the tap, you may find that you have to adjust the finger to keep your jet of water from becoming a mist, and vice-versa. In the same way, the MPPT in your controller has to constantly adjust itself as the strength of the sun varies, or a cloud passes. Technical Explanation Let’s begin with some basic electronic theory. The power of any electrical device is the current flow multiplied by the voltage. Note that current flow is written as ‘I’ but measured as ‘amps’ – confusing we know). In our case, the electrical device is a solar panel and the power it produces is measured in watts. But due to changing weather fluctuations, the power or watts that a panel produces is not fixed. As weather changes – for example, when shade hits the panel – the voltage generated by the panel will decrease. Because ‘V’ multiplied by ‘I’ = Power, this means that as the voltage reduces, so too will the current flow or amps. The amount of amps that can be produced by any given voltage is determined by a graph called an IV curve. These will be found on any solar panel’s specification sheet and typically looks like this: This graph shows you what the amps or current flow through a solar panel will be for any given voltage (V). In the graph below, the blue line shows a voltage of 30V which corresponds to a current of about 6.2 amps. This produces power of 186 watts (30v x 6.2a = 186w). The green line shows a Voltage of 35V which corresponds to a current of 5A. This produces power of only 175 watts (35v x 5a = 175w). As you may have noticed, as you move along the red curve you will find one point where the Voltage multiplied by its corresponding current is higher than anywhere else on the curve. This is called the solar panel’s Maximum Power Point (MPP) & is the place where we will find the most power. Finding the Maximum Power Point In the example above the point of maximum power (MPP) is somewhere between where the blue line touches the red line and where the green line touches it which would be about 33V and 6A. It is the job of an MPPT controller to always operate on that MPP. To do that, the MPPT forces the controller to work at 33V through electronic wizardry that varies the resistance at the controllers input terminals. Due to Ohms law, when resistance increases, voltage must correspondingly increase. Staying on the Maximum Power Point But the MPPTs job is a lot harder than finding an MPP and forcing the solar panel to stay there. Remember that the voltage that the solar panel would like to work at is moving all the time as weather changes. So the MPPT has to constantly adjust its settings to keep the solar panel at its MPP. In essence, it is chasing a constantly moving target.But wait, won’t 33v flowing into a 12v battery damage the battery? This is where the true magic arises. Whilst PWMs work by simply reducing the voltage of the panel to the voltage of the battery resulting in significant power losses, MPPT controllers ‘convert’ those volts into amps which can then safely flow into your battery. This allows them to harness 99% of the solar energy coming in versus 70% with PWM controllers. This is the true brilliance of MPPT technology and why Voltanic prefers MPPT controllers.