Capturing solar power is a lot harder than you may think. You would think that all you have to do is put the power leads from a HQRP 50Watt Solar Panel onto a car battery and the work is done. Yet, as with anything involving electricity or mechanical operations, “Anything that can go wrong, will go wrong.” or just Murphy’s Law is going to stop you in your tracks eventually.
Last week, I realized that I was overcharging my Deka Dominator Group 24 Gel-Cel Model 8G24M battery by leaving the new 50 Watt solar panel connected to it. The solar panel outputs as much as 18.5 VDC and was causing the battery to go above 14.2 VDC which can permanently damage it by overheating the electrolyte inside. The solution was to find a charge controller. I was quickly surprised as a new term kept surfacing during my research, MPPT.
Reading the instruction manual for the WellSee MPPT15 controller and conveying my own electrical engineering course work, I am phrasing this discussion at what MPPT technology means to us in the solar panel community. For off the grid systems specifically, we are concerned about the long term viability of our batteries.
What Is MPPT?
MPPT stands for maximum power point tracker. Inside these controllers is a high efficiency, DC to DC voltage converter that pulls the maximum load from a solar panel and then, using a preprogrammed algorithm that accounts for temperature, charge state along with power draw, pushes the power into the battery array.
MPPT units also incorporate temperature sensing. The WS-MPPT15 reduces its primary charging voltage by -3mvdc per 1 degree Celsius. The function protects your battery from receiving too much voltage during the summer months and ramps up the voltage during the winter to heat up the electrolyte so that it can charge faster. In Southwest Louisiana, we see regular plug in battery chargers on boats dry out flooded, lead acid marine batteries in less than a year. With temperature sensing, the charger has the ability to throttle back the voltage in an effort to predict an overheating situation before the battery array is damaged.
All of these functions are controlled by a central processor which is powered by the battery itself. The processing functions require less than 10ma of power.
While my summary may be basic in concept, I encourage you to do your own research as well. I understand that no single article on this technology can keep your attention so I choose to summarize its benefits to increase your own curiosity!
Caution: You Can Spend A Lot Of Money On BAD Solar Controllers!
In a strange twist of fate, MPPT controllers are rather bland in appearance compared to other solar charge controllers. The Sunforce 60032 30 Amp Digital Charge Controller features a big back light voltmeter and six LEDs to tell you the current status of the solar array. Numerous switches dot the surface of this product as well so you can feel like you are in total control. The WellSee WS-MPPT15 only has three LEDs and with a single RESET button managing this true MPPT is very hard.
Many solar charge controllers on the market today are also cheaper than a MPPT based unit so you may be wondering whether that additional cost is worth it.
First, a MPPT based unit is at least 30% more efficient.
Second and most importantly for my needs, the MPPT can auto detect the storage battery type and accommodate charging rates. Gel-Cel batteries cannot be charged above 14.2 VDC for long without bursting.
Finally, the ability to make the most of the sun on cloudy days with the solid state, DC-DC converter gives you an edge over those traditional charge controllers.
I have been using my WS-MPPT15 Solar Charge Controller for a week now without any problems. I was able to remove all those pesky blocking diodes since the charge controller will automatically prevent draining of the battery at night. As a result, I saw an instant spike in voltage output from my solar panels. My adventure in solar energy continues, but I hope you save yourself some money and create more power than I ever did by purchasing an MPPT charge controller first!
Here are the links to the previous articles in this series:
How to Generate Your Own Electricity with Cheap Solar Panels – Part 1
How to Install a 50 Watt Solar Panel – Solar Power Project Part 2