Just a quick note for those looking at adding solar panels as a second power source to their genverters or anyone starting out in solar power. I looked into a new class of large solar panels that are rated at 200W or more per panel! Some of the prices of these units have come down in the last year to as little as $3.70 per Watt. Good news for those of us who rely on this charging source. Just a few years ago it was more common for 5-6$ per watt.
I began quickly digesting the data on these large solar panels. They are roughly 3 feet by 5 feet in size, the size of a refrigerator door! So watch shipping prices.
Strange Data?
On the data sheets I ran into one item, the max. panel current, that made me think some. I also noticed that the maximum power output happens at 23 Volts, and 10 Amps. Wow, that’s strange because the panel would never work if your battery bank was a common 24V system! If I purchased one of these solar panels and used it on my 12V system, I wouldn’t get 230W, instead I would have roughly 120W!
After some research, I realized that these solar panels are designed for grid-tie systems that use a special solar charging device. Instead of my passive 12V charge controller, I’d need a newer Maximum Point Power Transfer(MPPT) solar charger. These units can take DC voltages up to 150V and deliver battery charging to 12V to 60V battery banks.
Advantages of MPPT solar chargers
Since these chargers can take higher DC input voltages, that are not even related to the battery bank voltage, we can run lighter cables to our solar array! (I don’t even want to speak about how big or expensive the cables I have for a 12V system 75 feet from the panels!) The MPPT technology allows the controller to draw different amounts of current from the solar panel array, then measure the voltage at that current. The voltage times the current is the power in from the array, and the controller can continuously adjust the current to get the maximum power in possible.
Disadvantages
Cost.
Like anything else, thats cool, useful, and relatively new you will pay more. My old passive C40 from Xantrex runs about $120-150. The Xantrex XW solar charger runs about $550, but will handle 50% more charging current at 60Amp.
I would like to start over with one of these chargers. I could run multiple panels in series to get 50V dc and cut my power loss in the 75 foot cable by 75%. It would give me quite a bit of flexibility in how I add future solar arrays, once my current frame is full. Anyway, this is simply a cautionary tale about buying 230W panels and only having them run at 120W because you’re using the wrong solar controller!
Do you have experience with a MPPT charger in your system? Tell me about your experience with them below in the comments, before I get one next year!
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yes, you are quite right about MPPT being a must in your case. But does the MPPT controller realy cost $550?
I have designed one and I am in the process of building it for my 300w(max)PV. A small micro and an automatic boost-(buck,boost)-buck, DC-DC converter including battery charging algorithm. Parts about $120. The printed circuit board one-off was $60 + tooling cost cheers,
boris