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Solar Regulators

MPPT - Technology for Technology's Sake?

There's always debate about solar regulators and what type and what technology performs best.

PWM (Pulse Width Modulation) is the technology used by most of Morningstar solar regulators. PWM is tried and tested technology which works well and operates efficiently and without fuss or problems.

MPPT (Maximum Power Point Tracking) is a comparatively newer technology and some companies have done it much better than others, investing the necessary time in product testing and development.  

MPPT is a more efficient means of harvesting solar energy in low light, poor weather, cold conditions and early and late in the day when the sun is low. The jury is still out on exactly how much extra solar can be collected using MPPT technology on motorhomes but NZ tests and our own tests indicate that the 30% claimed by some companies is not realistic for small scale systems as we have in motorhomes.  MPPT essentially works best in Winter when our tests show it can increase solar input by as much as 20%, in Summer it's likely nearer 7%.  

Its worth taking the next step and considering what this means in practical terms:

Description of Solar array Avg Daily Input
 Avg Daily input
anticipated benefit of MPPT over PWM7%20%
SMALL ARRAY: 1 x 140W (8Amps input) Solar array with PWM
48 Amp hrs16 Amp hrs
                             1 x 140W (8Amps input) Solar array with MPPT 51.5 Amp hrs19.2 Amp hrs
                                                extra solar collected with MPPT3.5 A/hrs daily3.2 A/hrs daily
LARGE ARRAY: 3 x 140W (24Amps input) solar array with PWM144 Amp hrs48 Amp hrs
                              3 x 140W (24Amps input) solar array with MPPT154 Amp hrs57.6Amp hrs
                                               extra solar collected with MPPT10 A/hrs daily9.6 A/hrs daily

All MPPT controllers are NOT created equal, remember you get what you pay for. A quality MPPT controller (as opposed to a cheap one which could offer questionable performance) will cost approximately $200 more than a good PWM controller of the same size yet in a small solar array you'll get less benefit than you would by replacing a single halogen bulb with a $25 LED bulb. For $200 you could upgrade all your lights to LEDS and gain significantly more benefit.

MPPT comes into its own with high voltage systems and large solar arrays (i.e. households)  however there can still be benefits in certain situations for motorhoming and some of these include:

  • solar arrays of at least 400watts and over
  • a system using a GOOD quality MPPT controller which has been well field tested and with proven performance
  • 24V panel being used in a 12V battery system
  • when panels are being run the panels in 'series' to reduce cable size