The post explains a cheap yet effective, less than $1 cheap yet effective solar charger circuit, which can be built even by a layman for harnessing efficient solar battery charging.
What is Maximum Power Point Solar Tracking?
For a layman this would be something too complex and sophisticated to grasp and a system involving extreme electronics.
In a way it may be true and surely MPPTs are sophisticated high end devices which are meant for optimizing the charging of the battery without altering the solar panel V/I curve.
In simple words an MPPT tracks the instantaneous maximum available voltage from the solar panel and adjusts the charging rate of the battery such that the panel voltage remains unaffected or away from loading.
Simply put, a solar panel would work most efficiently if its maximum circumstantial voltage is not dragged down to the connected battery voltage which is being charged.
For example, if the open circuit voltage of your solar panel is 20V and the battery to be charged is rated at 12V, and if you connect the two directly would cause the panel voltage to drop to the battery voltage, which would make things too inefficient.
Conversely if you could keep the panel voltage unaltered yet extract the best possible charging option from it, would make the system work with MPPT principle.
So it's all about charging the battery optimally without affecting or dropping the panel voltage.
There's one simple and zero cost method of implementing the above conditions.
Choose a solar panel whose open circuit voltage matches the battery charging voltage. Meaning for a 12V battery you may choose a panel with 15V and that would produce maximum optimization of both the parameters.
However practically the above conditions could be difficult to achieve because solar panels never produce constant outputs, and tend to generate deteriorating power levels in response to varying sun ray positions.
That's why always a much higher rated solar panel is recommended so that even under worse day time conditions it keeps the battery charging.
Having said that, by no means it is necessary to go for expensive MPpT systems, you can get similar results by spending a few bucks for it. The following discussion will make the procedures clear.
How to make a $1 MPPT Circuit
As discussed above, in order to avoid unnecessary loading of the panel we need to have conditions ideally matching the PV voltage with the battery voltage.
This can be done by using a few diodes, a cheap voltmeter or your existing multimeter and a rotary switch. Ofcourse at around $1 you cannot expect it to be automatic, you may have to work with the switch quite a few times each day.
We know that a rectifier diode's forward voltage drop is around 0.6 volts, so by adding many diodes in series it can be possible to isolate the panel from getting dragged to the connected battery voltage.
Referring to the circuit digaram given below, a cool little MPPT charger can be arranged using the shown cheap components.
Let's assume in the diagram, the panel open circuit voltage to be 20V and the battery to be rated at 12V.
Connecting them directly would drag the panel voltage to the battery level making things inappropriate.
By adding 9 diodes in series we effectively isolate the panel from getting loaded and dragged to the battery voltage and yet extract the Maximum charging current from it.
The total forward drop of the combined diodes would be around 5V, plus battery charging voltage 14.4V gives around 20V, meaning once connected with all the diodes in series during peak sunshine, the panel voltage would drop marginally to may be around 19V resulting an efficient charging of the battery.
Now suppose the sun begins dipping, causing the panel voltage to drop below the rated voltage, this can be monitored across the connected voltmeter, and a few diodes skipped until the battery is restored with receiving optimal power.
The arrow symbol shown connected with the panel voltage positive can be replaced with a rotary switched for the recommended selection of the diodes in series.
With the above situation implemented, a clear MPPT charging conditions can be simulated effectively without employing costly devices. You can do this for all types of panels and batteries just by including more number of diodes in series.
The explained circuit can be somehow made automatic, you may refer to the following post to learn the automatic version of the above explained design.