Solar regulators or solar charge controllers are a very important part of a Solar solution. This is the link between Solar panels and the Deep Cycle Solar batteries.
In order to understand the importance of the regulator and the differences of same, it is firstly important to understand the characteristics of a Solar Panel.
A solar panel is sold on a rating. I.e 100 Watt panel. On the solar panel will be specifications as follows:
These are the ratings of the solar panels at what is referred to as STC-
The Solar Panel cannot deliver 22V and 9A at the same time (When 22V I=0 or When I=9A V=0) , if the Solar panel is connected to a battery which is for instance flat and at 11V, the Panels voltage will drop to 11V and it will try to put maximum current into the battery which is 9A. But this is not the optimum power ability of the panel.. and as the battery become fuller charged ..the less power the panel would deliver. There is an optimum point of loading at which the Panels voltage and current reach a point where the Panels actually deliver is maximum power…this is typically around the point of around 70% of the open circuit voltage and or 70% of the Short circuit current. See Graph below
In short you must understand there is a lot of variables which influence the working and performance of a Solar panel, Sun Intensity, Panel angle, Panel temperature, State of the deep cycle battery etc.
Fig 1 -
At first the” primitive” solar regulators were simple units with a relay control. One would for example have a 12V battery, connected to a 12V solar panel and basically a switch (relay) in between. The solar panel would charge the deep cycle battery to a certain preset voltage – ie 14.5V. When it reached this point, the solar regulator will disconnect the Solar Panel and no further be connected to the Solar Panel-
Figure 2 Old Type solar regulator-
The next “generation” of solar Regulators which came out was much more intelligent in the way they referred to as PWM solar regulators. PWM stands for PULSE WIDTH MODULATION. The concept is however the same as per discussion above, but instead of disconnecting the solar panel from the solar deep cycel battery, it will switch the solar panel very fast at a high frequency but with small pulses and as the battery get closer to the rated voltage, the pulses with narrow (PULSE WIDTH will reduce” ) to such level in order to maintain the solar deep cycle battery at the required voltage. From a normal multimeter it would seem as if the voltage are straight just DC, but is fact is fast switching pulses feeding the battery. The fats switching had various other advantages to the solar deep cycle battery, the PWM would also “move” the sulfate around a bit etc. This was a good improvement on solar regulators
Figure 3 PWM Controlled Switch solar regulator
A few years ago a few companies such a Outback, Morning Star and later Victron various others, started with the manufacture of a new generation of solar regulators called MPPT-
MPPT solar regulators allow us a variety of options. Let me explain the concept. A MPPT solar regulator – as the name says it tracks the maximum power point of the Solar Panel array. The unit is fitted like a regulator between the panels and the batteries; the MPPT will always LOAD the solar Panel and charge the deep cycle battery in such a way that the power drawn from the Solar Panel is optimum. It will always work at the Maximum power point of the Solar panel, independent of the actual Sun Intensity, or the Panel temperature or even the Angle or partial shading. MPPT solar regulator come with various methodology op working, but the more advanced units actually use a logarithm which actively always searches for the optimum power point in real time.
However in order to make use of a MPPT solar regulator, the Solar Panel voltages have to be higher than the battery voltage-
The MPPT solar regulators are usually designed to be able to go to a much higher input voltage, ie 75V 100V or 150V, for instance if you using 12V panels, you can now put 6 panels in series..etc. Unfortunately the technology also comes at a price as they are more expensive than normal PWM or Switch solar regulators, but if you compare the energy advantage and installation simplification which is bring, the advantages outweighs the cost – although I personally think they still too expensive.
MPPT also have limits and practical applications and the efficiency graph is not linear, as the transfer of power between the solar Panels and the solar battery is still done by an Electronic stepdown converter with limitations. I.e. as per Figure 4, if you do connect a system such as that 100V to 12V, the efficiency of the MPPT is only around 85-
Figure 4 MPPT Solar regulator , the way of connecting the Solar panels
Copyright : Dr Gawie van der Merwe ; PlanMyPower (PTY) Ltd