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You are here: Home > Knowledge Base > Renewable Energy Articles > MPPT vs PWM charge controllers by Blue Sky, Morningstar, OutBack and Xantrex

solar charge controller review

MPPT vs PWM charge controllers by Blue Sky, Morningstar, OutBack and Xantrex

Charge controllers are an important part of most alternate energy systems, be they solar or wind powered. This is because most renewable energy systems store energy locally in battery banks.

MPPT and PWM are the two dominant battery charge controller technologies on the market. The price, cost and benefits of MPPT and PWM charge controllers are different. The battery charge controller matches the alternate power source and the batteries. If you have a solar charge controller or a charge controller for wind, the issues are the same. Battery charge controllers must match the battery to the voltage of the power source. However, MPPT and PWM charge controllers have different objectives.

The alternate power source and storage batteries are the two principle cost items of an alternate energy system. The battery charge controller based on MPPT or PWM can do one of two things. The charge controller circuit of a MPPT controller (Maximum Power Point Tracking) unit is designed convert the voltage from your solar or wind power sources to the voltage optimum for maximum transfer of power to the battery or grid via a grid tie system. A PWM charge controller does not operate to optimize power transfer to the batteries; it is optimized to extend the life of the batteries. By applying higher voltage in short bursts a PWM controllers essentially clean off the lead plates that are a central part of the battery storage system. “How to charge controller” selection depends on if it makes sense to optimize power transfer, with an MPPT controller, or to optimize battery life, with the PWM charge controllers.

To make this tradeoff, we need to understand the relative cost difference between solar panels and batteries. Solar panels have long life- most manufacturers offer guarantees for output good for 20 years or more. Battery life, however, is rated by number of deep cycles and the number is typically rated in hundreds of deep cycles. Since a standalone solar or wind system might cycle once a day, life extension of batteries can be an important goal. To understand the balanced lifecycle cost of the generation + storage system we need to understand batteries will be replaced many times before the solar panels or wind turbine needs to be replaced. If we look at a very rough cut with solar panel life equal to 20 years and battery life equal to 1 year, we can estimate one dollar of battery is equal to twenty dollars of solar panel. How to select a charge controller is how we make this tradeoff.

First, consider solar battery charge controller systems that could be categorized as battery powered with solar charging. A good example might be a sailboat used for weekend trips or a country cabin. Such a boat might spend a week on a mooring or at the dock, and then used on a trip of a night or two, with deep discharge of the battery expected with every use. A cabin may sit in the sun for a week, and then deliver power to the limits of the battery capacity for when visited. For both of these, there is plenty of time to charge the battery, and in fact the boat might be able to use marina supplied grid power to do the charging. For both of these, deep discharge of the battery and consequential ‘wear and tear’ on the battery is to be expected. In a system like this, the critical variable is battery life, suggesting the use of a PWM charge controller. Efficiency of conversion of solar power to battery power is not the key variable since there is plenty of time to charge the battery, or charging from grid is possible and included in marine ship rental.

PWM Charge Controllers

PWM controllers are typically less expensive than MMPT systems and smaller too. To compare relative costs of PWM and MPPT technology, check the relative price of Xantrex MPPT and PWM charge controllers in multiple amperage and voltage ranges.

Xantrex PWM Charge Controllers

Xantrex PWM charge controllers include:

Morningstar PWM Charge Controllers

Low cost Morningstar PWM charge controllers offer a wide selection of PWM devices match any battery voltage and power range. The 12v charge controllers are very common for PWM systems on mobile homes, boats and cabins.

Not all systems face the same challenge as a sailboat or country cabin. The typical home solar power system has access to the gird for backup power, and can even sell excess power back to the grid using a grid tied inverter system. If there are batteries, they are used only for short term, emergency backup when both solar and grid power are unavailable. For this type of system, maximum power transfer from the solar panel or wind turbine to the battery or grid is the important issue. MPPT (Maximum Power Point Transfer) controllers meet this requirement.

MPPT Charge Controllers

MPPT circuit solar controllers are considerably more elaborate than PWM. The voltage of the solar panel changes with time of day and temperature. The optimum voltage for battery charging changes as the state of charge of the battery. The MPPT charge controller matches these voltages and can result in 30% more efficient transfer of power. This means good MPPT solar charge controllers can reduce the number of solar panels needed by up to 30%- a tremendous benefit. Even if the excess panels are purchased, benefits are realized in a Grid Tie system because more electricity can be sold back to the grid. While only a small part of system price, a MPPT solar panel charge controller can leverage the rest of the system to better performance.

Blue Sky MPPT Charge Controllers

Blue Sky Solar Boost MPPT controllers include many options for voltage and power.

Outback MPPT Charge Controllers

There is a line of Outback MPPT Charge controllers as well. The OutBack FLEXmax 80 and OutBack FLEXmax 60, MPPT Charge Controller provide options from 12 to 60 colts and 60 or 80 amps.

So, when selecting an alternate energy power system, consider the price and benefits of MPPT and PWM charge controllers. The amount of power they deliver, and the lifetime of your battery system, are important variables to consider.