What Size Charge Controller For 800w Solar Panel? (Beginner’s guide)

We majorly focus on solar panels and batteries and sometimes we neglect the importance of charge controllers. Choosing the right size charge controller is very important.

choosing the wrong size and type of charge controller for your solar panels can damage your batteries or can cause a huge loss in power.

for a 24v 800w solar power system you need a 24v 40A MPPT charge controller and for 48v 800w you need a 48v 20A MPPT charge controller, calculate the charge controller size by using this formula (watts/battery volts = amps + 25%)

How do I size my charge controller?

there are many different formulas and techniques to determine the size of the charge controller

but to make things simple and easy

Use this formula to calculate the size of your charge controller Watts/Battery volts = amps + 25%

the value of watts will be the solar panel’s wattage and the volts of the batteries. The extra 25% is for the safety margin which i’ll explain later on

so if you have an 800w solar panel system running in 24v, in peak sun hours it can produce 800 watts of power in an hour 37 volts, and 21 amps.

What does a charge controller do? having a charge controller will regulate the volts and amps according to the battery requirement. if you have a 24v connected battery a charge controller will reduce the voltage to 24v to charge the battery.

an MPPT and PWM charge controller will perform differently in this situation which I’m gonna share in a moment

so now put the values in the formula 800/24 = 33.3 + 25% = 41A to make it round about we’ll use a 40A charge controller

or you can buy a 50A charge controller if you’re thinking about enlarging the solar array in the future

Watch this video and you’ll see why I added the extra 25%. Just to make it quick and short, the solar panels will produce different volts according to the temperature (The ideal temperature is 25C)

The voltage will be increased at the lower temperature and will decrease at high temperatures so the number of amps will be changed.

so if it’s winter and it’s minus centigrade then the voltage of the solar panels and overall power can increase. this is why i recommend that extra 25 %

and is also recommended by many engineers to not use your electronics at their high capacity all the time it will decrease their lifespan

What Type of charge controller for 800w solar panel (MPPT or PWM)

there are two most popular types of charge controllers available in the market right now.

MPPT and PWM both charge controllers regulate the DC current from the solar panels to charge the batteries.

But a PWM charge controller can cause a huge power loss and here’s why

Sizing PWM charge controller

A PWM regulator stands for Pulse width Modulation

What does PWM charge controller do? it pulses power into the battery and can change the amount of time, length, or width of the charge this is what modulation called

If your solar panels are producing higher voltage and lower amps the PWM charge controller will decrease the volts to match the voltage of batteries and the amps will stay the same.

For Example, your 800w solar panels are producing 800 watts with 37 volts and 21 amps and you have connected a 24v battery so the PWM will decrease the voltage to 24 volts and amps will stay the same (21 amps)

Let’s calculate the power by using ohm’s law Volts x amps = watts (24*21 = 504 watts)

as you can see it will cause a 300w of power. as a general rule, PWM charge controllers are only 70% efficient means you’ll lose 30% of power in the whole day

PWM charge controller will be suitable for less than 300 watts o the solar array not ideal for larger solar setups

How Do I choose a PWM charge controller?

PWM charge controllers are not able to control the current output limit. So if you’re using a high amps solar panel system on a lower amps PWM charge controller it can damage the charge controller or batteries.

So it’s important to make sure that your PWM charge controller is matched, compatible with, and properly sized for your panels

Sizing MPPT charge controller

MPPT charge controller stands for maximum power point tracking

What does MPPT charge controller do? the MPPT charge controller has an internal device that regulates the volts according to the voltage of the battery and will increase the amps so you can get the maximum output power.

let’s use the last example if your solar panels are producing 800 watts with 37 volts and 21 amps so an MPPT charge controller will decrease the volts to 24v for 24v batteries and will increase the amps to 33 amps

33*24 = 800 watts

this is why an MPPT charge controller is recommended for larger solar arrays

Why MPPT is required? MPPT charge controllers are 30% more efficient than the PWM charge controllers because they adjust the volts and amps according to the battery which in result will not cause any power loss

How Do I choose an MPPT charge controller?

Unlike PWM regulators the MPPT charge controllers are able to limit the output power.

For Example, if you’re using a 40A charge controller then it will limit the amps up to 40. if you’re using a solar array that produces more current than 40A then an MPPT charge controller will only pass 40A to batteries.

Like amps, they also have an upper volts limit as well e.g if the upper limit of a charge controller is 100 volts then it’ll only accept the 100 volts.

so make sure to buy the right size MPPT charge controller for you according to the Current and Volts limit.

Watch this video for a better understanding

Video – Difference between MPPT & PWM Charge controller

How many watts can a 40 amp charge controller handle?

To calculate the watts we simply use this law watts = volts x amps

so to calculate the number we have the number of amps (40) but the number of volts is missing. So if you’re using a 24v the voltage will be 24 and for 48v the voltage will be 48.

40*12 = 480 watts

40 * 24 = 960 watts

40 * 48 = 1920 watts

40 Amps charge controller can handle 480 watts in 12v, 960 watts for 24v, and 1920 watts for 48v solar system

How much does a charge controller cost?

40A MPPT charge controller will cost you about $150

there are few factors that determine the price of any charge controller

  • Is it PWM or MPPT
  • the amps capacity

These are the two main factors, MPPT charge controllers are more expensive than the PWM charge controller

As the amps will increase the pricing of the charge controller will also increase.

the charge controller can cost between 50-800$ depending on the size (capacity) and type of charge controller

Video – How to the setup charge controller


charge controller plays a middleman role between solar panels and batteries, which regulates the DC power to charge the batteries or battery banks.

having the right size charge controller is important to get the maximum output from your solar panels and charge your batteries at their full capacity.

I hope this article was helpful if you have any queries do ask them at contact@dotwatts.com ThankYou!

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Chris Tsitouris is a renewable energy professional with 10+ years of experience as Director of Engineering at Solar Spectrum, previously working as Project Manager at SunPower and Energy Analyst at the National Renewable Energy Laboratory. As a thought leader, Chris has authored numerous articles and research papers.

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