01-23-2024, 10:29 AM
I started this post with thinking about fusing requirements for solar in our vans. As these systems have proliferated on camper vans, there has been some changes in NEC fusing requirements. My intent was to just update those requirements. Some of these fusing requirements are different for series versus parallel, so I thought it would be a good time to go over series versus parallel connections. Then I figured I might as well just start at the controller. Be aware that this post is tedious and has a lot of calculations that I was trying to show. I expect they are correct, but it could be possible I messed up, so don’t be shy, call it out.
What kind of controller, PWM or MPPT
A few years ago, it was evenly split on the use of PWM versus MPPT controllers. MPPT’s were more expensive than PWM’s and you really needed to have some voltage headroom to take advantage of what they offered. As the operating voltage of panels went up, MPPT’s pretty much made more sense. If we look at the same panel with the two different controllers, you can get an idea.
If we use a 100-watt panel that has an operating voltage (Isc) of 18.0V and an operating current (Imp) of 5.56A. This gives you 18 * 5.56 = 100.08 watts. If we take that panel with a PWM or Pulse Width Modulation controller, we get the output voltage or Bat voltage of 14.4V * the operating current of 5.56A = 80.064 watts. Simple put the PWM controller takes the incoming solar current and manages the output voltage or Bat Voltage by changing the duty cycle.
Taking an MPPT or Multi Point Power Tracking controller we the same 100.08 watts out of the panel, the difference now is that MPPT is a DC-to-DC converter that of uses all that power, so your 100.08 watts panel output is converted to 100 watts at the required bat voltage. We get 100 / 14.4V or 6.95A. You have some minor power loses doing the conversion. I like to look at it this way, we get the same 14.4V * 5.56 amps that the PWM controller puts out. The MPPT cam harvest the 18V (Isc) – 14.4 (Vbat) or 3.6 volts * 5.56 (Imp) = 20.016W. 20W/(Vbat)14.4V = 1.39A. Are MPPT controller can put out 14.4 at 5.56A +1.39A or 14.4 at 6.95A.
What kind of controller, PWM or MPPT
A few years ago, it was evenly split on the use of PWM versus MPPT controllers. MPPT’s were more expensive than PWM’s and you really needed to have some voltage headroom to take advantage of what they offered. As the operating voltage of panels went up, MPPT’s pretty much made more sense. If we look at the same panel with the two different controllers, you can get an idea.
If we use a 100-watt panel that has an operating voltage (Isc) of 18.0V and an operating current (Imp) of 5.56A. This gives you 18 * 5.56 = 100.08 watts. If we take that panel with a PWM or Pulse Width Modulation controller, we get the output voltage or Bat voltage of 14.4V * the operating current of 5.56A = 80.064 watts. Simple put the PWM controller takes the incoming solar current and manages the output voltage or Bat Voltage by changing the duty cycle.
Taking an MPPT or Multi Point Power Tracking controller we the same 100.08 watts out of the panel, the difference now is that MPPT is a DC-to-DC converter that of uses all that power, so your 100.08 watts panel output is converted to 100 watts at the required bat voltage. We get 100 / 14.4V or 6.95A. You have some minor power loses doing the conversion. I like to look at it this way, we get the same 14.4V * 5.56 amps that the PWM controller puts out. The MPPT cam harvest the 18V (Isc) – 14.4 (Vbat) or 3.6 volts * 5.56 (Imp) = 20.016W. 20W/(Vbat)14.4V = 1.39A. Are MPPT controller can put out 14.4 at 5.56A +1.39A or 14.4 at 6.95A.