With the recent string of cold and wintry weather, many people are thinking, “Oh great, more cold weather?! When is it going to be warm again?!” However, if you have an off grid system with batteries, you should be thinking, “Cold weather? Woohoo! Time to upgrade my charge controller!”
If you have a PWM charge controller, and you are using batteries in your system, wintertime is when you need to maximize the effectiveness of your system to counter the shorter days and less peak sun hours per day. The colder weather also means your battery bank has less storage, therefore the battery bank is working harder to supply your loads. An MPPT charge controller can increase the productivity of your system by up to 30% – that’s a huge difference in your system.
When solar panels are subjected to cold temperatures, the voltage on the panels will increase. If you look at these pictures of our altE 50 watt, 12 volt module (ALT50-12P), you can see on a cold day (25 degrees at the time of the picture) how much the VOC can be increased by the cold. Instead of a VOC of 22.3, we’re over 23V. This means the VMP would be more like 19V as opposed to 18V.
When you are calculating the output of the solar panel, you take the voltage of the battery bank, multiplied by the current, to find out how many watts are effectively being used. A PWM charge controller just connects the battery and the panel, so the panel is brought down to the level of the battery. If a battery bank is low, say at 11V, then 11V x 2.78A = 30.58W. If the bank is more fully charged, you would be using more of the panel: 13.8V x 2.78 = 38.4W. In neither of these instances is the panel being used to its full capacity. Let’s look at the same panel using an MPPT charge controller.
MPPT charge controllers have the advantage of taking all the power the panel can put out, and turn that higher voltage into additional current. So if you take the same situation, the MPPT controller will use all 18V that the panel is putting out, and increases the charging current. 18V ÷ 11V = 1.63 Current multiplier. So the 2.78A of charging current on the panel is increased by 1.63, giving it an effective charging current of 4.54 Amps. 11V x 4.54A = 49.94 Watts. 18 ÷ 14V = 1.28 Current multiplier, or an equivalent of 3.57 Amps of current, giving an effective wattage of 50W (14V x 3.57 Amps = 50.03W). For a 12V panel, the Genasun line of controllers are an excellent fit at a very reasonable price point.
For larger panels, there are a variety of MPPT Controllers out there to fit your needs, at varying price point levels. On the lower cost side we have the Blue Sky 2512ix-HV, which is great if you have a single larger 60 cell 230-270W panel and you’re looking to charge a 12V battery bank. Another great option is the Midnite Solar Kid 30A MPPT controller, or it’s big brother the Midnite Classic 150. These are very affordable and flexible controllers that can handle up to 30 Amps of current (96 Amps for the Classic 150). Other excellent options for larger systems are the Xantrex XW MPPT60-150, Morningstar MPPT-60, Outback Flexmax 60 or Flexmax 80 controllers – all are excellent choices. Call altE today to speak with a technical sales rep to help you find the right controller to make your system as efficient as possible!
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