Understanding the Differences Between MPPT and PWM

If you are interested in using solar panels to charge a battery, then you may have come across the terms MPPT and PWM

MPPT actually stands for maximum power point tracker, and PWM pulse width modulation.

Both technologies can be used to protect your battery from any damages occurring during the charging process. 

In fact, using a MPPT or PWM charge controller is actually critical in your solar setup. 

In this article we will talk about the differences between a MPPT vs PWM charge controller and why you should choose one above the other.

What is the difference between MPPT and PWM?

Both maximum power point tracker (MPPT), and pulse width modulation (PWM) can be used to safely charge your solar battery.

The main major difference between the two technologies is the way in which they handle current and voltage.

Your solar system i.e. photovoltaic panels, generate their maximum power at a certain voltage when the current is optimal.

During this process resistance is created internally. This internal resistance is known as the panels Characteristic Resistance.

As stated by PV Education: "the characteristic resistance of a solar cell is the inverse of the slope of the line, shown in the figure above as VMP divided by IMP. For most cells, RCH can be approximated by VOC divided by ISC."

Why is this important to know? 

Well, It is uncommon for a batteries internal resistance to match the solar panels resistance. This equates to less than maximum power being generated. 

So what is the main difference between the two controllers? 

PWM technology actually pulls down the panels voltage to match whatever is required to charge the battery (safely that is). On the other hand, a MPPT charge controller matches the resistance of the battery to that of the panel. In doing so it can increase any extra voltage into current, which is very useful for optimum charging.

What are the pros and cons of using an MPPT device? 

  • Pros

1. The first pro and perhaps the most pronounced one, is the increased efficiency you get from your solar system as a whole while using a MPPT charge controller. In fact it can produce up to 30% more charging current. That is a lot. 

2. Another positive is that MPPT charge controllers are more efficient in overcast conditions. A feature that is very useful as solar panels already produce less electricity on a cloudy day, it stands to reason you wont want anything else hindering that efficiency even more.  

  • Cons 

1. It is quite expensive, much more so than its first cousin the PWM controller. 

2. MPPT charge controllers can be quite large in size, making installation slightly more tricky should your work space be limited. 

What are the pros and cons of using an PWM device? 

  • Pros

1. PWM controllers are often smaller in size when compared to MPPT charge controllers. If you limited area for installation (such as in a campervan) then PWM controllers will be quite beneficial.

2. They are cheaper, in fact PWM controllers can be up to 30% cheaper than MPPT charge controllers. 

3. PWM controllers generally offer longer lifespans as they have less electronic components inside and less thermal stress.

  • Cons

1. PWM is much less efficient than MPPT. If you are looking at a large solar build, perhaps a solar system that offsets your electricity consumption, then all that efficiency loss will definitely add up to be something quite substantial. 

2. It is not capable of generating the same output and thus supports less capacity in Amps. 

3. PWM controllers cannot be used in larger solar system setups where solar panel output is substantially greater than battery voltage.

Is MPPT really better than PWM? 

(Credit for the above diagram goes to Clean Energy Reviews)

The answer to this really all comes down to your application, budget and requirements. 

Let's put it this way, a PWM charge controller is a good option:

  • for smaller solar systems
  • for PV panels with a maximum power voltage (Vmp) of up to 18V for charging a 12V battery (36V for 24V battery, etc)
  • where effiency of your solar system is not incredibly important, for example trickle charging. 

 

On the other hand, the MPPT charge controller is best:
  • For bigger solar systems where an additional efficiency of up to 30% is worthwhile, such as in a residential rooftop setup.
  • when the solar arrays total voltage exceeds that of the battery voltage. A good example of this would be residential solar system charging 12V batteries. 

Final thoughts 

All in all, an MPPT charge controller will yield higher efficiencies/returns than that of a PWM controller, especially as the panel voltage increases. 

A great example we found from Solar 4 RVs highlights this point in more detail: "a 160W panel using 36 conventional monocrystalline cells with a maximum power amperage of 8.4A will provide around 8.6A at 12V; while the 180W panel having 4 more cells will provide the same amperage but 4 additional cells increases the panel voltage by 2V.  A PWM controller will not harvest any additional energy, but an MPPT controller will harvest an additional 11.1%  (4 / 36) from the 180W panel."

With this example you can see how MPPT controllers are capable of reducing your ROI period by offering increased efficiencies in your solar systems overall setup.

It should be mentioned that beginning with the AC50S all Bluetti solar generators are equipped with the latest MPPT charge controller technology. 

If you are interested in browsing our collection of solar generators, feel free to do so here: Bluetti Shop

What to Look for in a Portable Solar Generator for Emergency Support and Worksites

Written by Mike Jezek

Portable solar generators come in handy if you need high-capacity power for your next off-grid construction job. Not only do they pack a lot of ene...

Read more

How Much Does It Cost to Charge a Tesla in the US?

Written by Kyle Browning

How much does it cost to fill a Tesla's "tank," and will you save money doing it? 

Read more

Is a Portable Solar Generator a Good Alternative to Gas Generators?

Written by Mike Jezek

Just look at the upsides and downsides of both generators to see how effective they are and which of them is more viable to use for your ideal scen...

Read more

How Many Watts Does A Refrigerator Use?

Written by Kyle Browning

This article will break down a refrigerator's power consumption and how you might potentially reduce it by taking some actionable steps.

Read more