What Solar Controller Do I Need

Solar Charge Controller Calculator

by Author Angela and Graham

This solar charge controller calculator will help you correctly size this important component in your camper solar setup.

Its simple and straightforward to use. Weve included a section below to answer some questions you may have.

And its just one of our electrical calculators for RVs and campervan conversions too.

Once youve sized your controller, head on over to our detailed step by step solar system installation guide and youll be living off-grid before you know it.

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Calculate The Power Output Rating And Voltage Of Solar Power System For Pwm

The simplest method is to know the peak output power of the solar power system and the battery voltage. Let say if the power output of a solar system is 500w and the battery of 12v, then 500 / 12 = 41.66A. So, you must buy a PWM solar charger of 45A rating or 50A as if your ampere rating is low, then it will damage.

Can I Use Multiple Charge Controllers At Once

Its perfectly fine to use more than one charge controller at the same time. However, we recommend that you get similar controller types to avoid complications. Also, know that having more charge controllers might be troublesome since you will manage more components in your system. Lastly, make sure all your controllers have the same battery setting input.

There are however reasons to add more charge controllers. These are:

• You require more solar panels
• Youre wanting to upgrade some of your solar panels
• You want to separate some of your solar panels to increase sunlight irradiance

So, dont worry about wanting/needing to add another charge controller to your system. Just remember each charge controller should have its own array of solar panels.

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What Size Mppt Charge Controller Do I Need

If youre wondering what size MPPT charge controller you need, the answer depends on a few factors. The first is the size of your solar array. The second is the voltage of your solar array. And the third is the maximum power output of the charge controller.

To figure out what size MPPT charge controller you need, youll need to know the size of your solar array and the voltage of your solar array. The size of your solar array is the number of solar panels you have, and the voltage of your solar array is the sum of the voltages of all the panels in your array.

Once you know the size and voltage of your solar array, you can use this formula to calculate the maximum power output of your charge controller:

Max Power Output = Solar Array Size * Solar Array Voltage

So, for example, if you have a 6 panel solar array with a voltage of 36 volts, your maximum power output would be 216 watts.

Now that you know the maximum power output of your charge controller, you can choose a controller that has a maximum power output that is equal to or greater than your calculated value.

There are a few things to keep in mind when choosing an MPPT charge controller. The first is that you want to choose a controller that has a higher maximum power output than your calculated value. This will give you some headroom in case your solar array produces more power than you expect.

How To Size Your Charge Controller

A properly-sized charge controller needs to factor in the following from your solar panel:

• Total wattage
• Open circuit voltage
• Current at maximum power

In addition, several solar panels have something called thermal characteristics. We need two pieces of information from here:

• Temperature coefficient of Voc
• Temperature coefficient of Pmax

The next area to look at is your batterys voltage, which is typically 12V or 24V. This is important because 24V batteries need a higher voltage and fewer amps from a charge controller compared to a 12V battery.

The final step is to find out the lowest temperature your solar panels will be exposed to. Obviously, this is not precise, but you can estimate it. This is needed because when the temperature gets colder, the voltage from solar panels increases.

Since an MPPT controller uses excess volts and translates them into amps to charge your battery as efficiently as possible, too small of a controller can be ineffective or malfunction in cold weather.

In order for the charge controller to work effectively for years, we need to factor in the increased voltage that the panel produces in cold conditions.

With all of this information, we can estimate the correct charge controller size for not only a single solar panel, but for an entire solar panel array.

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The West Marine Advisor Conundrum

The quote below was taken on 8/11/2012.

QUOTE = WEST MARINE ADVISOR:

Do you need a charge controller?

As a general rule panels that produce less than 1.5% of a batterys rated capacity in amp hours dont require regulation. This means that a 1.5A panel is the largest you should use without a regulator on a 100-amp-hour battery. Regulators should generally be used any time you have two or more large panels connected to your batteries.

If we translate the West Advisor advice into watts:

• The West Advisor is suggesting that approx 25% in watts/Ah capacity is safe
• The West Advisor is suggesting that unless you have two or more large panels connected to your batteries you will be safe without a controller

What are large panels?

Who defines large panels?

Unfortunately many boaters put a lot of trust in the West Marine Advisor articles. Generally speaking they are very good and fairly well researched. Sometimes they just miss the mark. Boat owners often blindly trust what the West Advisor articles say, and then do as they say..

I know this for sure because one of my customers did exactly this. Guess what? HE DESTROYED HIS BATTERIES! He is the 6V golf cart batteries on a sailboat from above. Thanks West Marine.. Not.

A 10W panel can produce, about 0.6A. This is actually a 637% increase in current from a float current of 0.08A that the batteries accept to maintain 13.6V.

PLEASE HEED ALL CONTROLLER-LESS SOLAR SUGGESTIONS WITH CAUTION

Sizing Your Charge Controller For A 12v Battery

My calculations below are based on the averages of three 50W solar panels and three 100W solar panels.

All data based on use with a 12V battery. Only 12V solar panels were used in this table. Data gathered from charge controller calculator from explorist.life with est. lowest temp. of -40 deg. F .

As you can see, both series and parallel connections work for the 150-400W examples above. But for a series connection with four 100W solar panels, the voltage is higher than 100V. Due to this, I recommend a larger 150V charge controller with 45A.

This MPPT compared to the others in the table is much more expensive. That being said, I recommend using a parallel connection if you decide to use 400W of solar.

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How Do I Work Out What Size Of Regulator I Need

To find the correct minimum size for your solar regulator, you can use the following basic guide below, depending on whether you want to use a Pulse Width Modulation or Maximum Power Point Tracking regulator. Please Note: this guide assumes you are using solar panels of the same type.

First, gather the following specifications from your solar panels and batteries:

1) Combined Wattage of solar systemeg. two 150W panels = 300W Combined Wattage of system

2) Nominal Voltage of solar systemIndividual solar panels will usually have a nominal voltage of 12V or 24V. If you are connecting them in parallel they’ll stay at the same nominal voltage, if they are connected in series the voltage will increase.

eg. two 150W 12V panels in parallel = 12V nominal voltage of systemeg. two 150W 12V panels in series = 24V nominal voltage of system

3) Max Power Voltage of solar systemThis is different to nominal voltage. Typically a 12V panel would have a max power voltage around 18V, while a 24V panel would be between 30V-36V. The same rules apply as above depending on whether your panels are in series or parallel.

eg. two 150W panels with 18V Max Power Voltage, in parallel = 18V Max Power Voltage of systemeg. two 150W panels with 18V Max Power Voltage, in series = 36V Max Power Voltage of system

4) Battery Charge VoltageThis is the voltage that your batteries will be charged at. Different battery types charge at different voltages, check your batteries for specifications if unsure.

Important Notes Before Choosing An Inverter For Solar Panel

Here are some important notes before buying an inverter

• Dont invest in above 80% efficient inverters they will be too much expensive.

• Always go for a pure sine wave inverter so your appliances will stay safe.

• dont use cheap wires or long distant wires which will cause an electricity loss

• Always go to more than what you need right now. Believe me, speaking from experience if its your first time buying an inverter I would suggest you go for a higher watt inverter instead of just only what you need right. because its soo much fun to increase the solar panels power but itll have just 700W of inverter itll limit your ways. and youll have to buy another inverter.

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How Many Batteries Can A 300

A properly installed 300W solar panel system can fully charge 1 x 200Ah batteries, 2 x 100 Ah batteries or 4 x 50Ah 12 volt batteries connected in parallel in about 4-6 hours each day.

The charging time of 4 6 hours of a 200Ah battery bank with a 300W solar panel system is based on:

• the battery bank is discharged to only 50% of its capacity. If it is discharged more , they will take longer to fill

• the solar panels are installed in a location that receives about 5 hours of sunshine. You will need more hours to charge the battery bank if it is installed in a location with fewer hours of sunshine.

The table below is an indicative guide of the number of batteries that you can connect to a 300W system for a location with 4-6 hours of sunshine.

Calculate The Power Output Rating And Voltage Of Solar Power System For Mppt

The simplest method is to know the peak output power in watts of your solar module and the storage battery voltage. Let say if you have a power output of the solar system in watts is 500 and storage battery voltage of 12v, then 500 / 12 = 41.66 ampere.

So, you can get an MPPT solar controller with a 40A rating as it is capable of regulating higher currents. The MPPT charge controller is a prominent choice for the solar power system as it limits the current and voltage input to the batteries.

They have compact circuitry capable of limiting high current values according to its size standard output. That protects the solar power system but at the same time reduces the efficiency when your MPPT solar charge controller is not of the required size.

My guide to best 2000 watt inverter here.

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How To Size Mppt Charge Controllers For 100w Solar Panels

An MPPT charge controller can restrict its output, so your solar array can be any size. Even so there are some factors you have to consider to get the best possible results.

Amp Reading. This information tells you how many amps the MPPT controller will use. If the reading says 50 amps, the controller will operate with 50 amps. If your panel produces 60 amps, the MPPT controller will reduce the output to 50 amps.

Unlike a PWM controller, the high amps will not cause damage. However, you are wasting your panels potential, so the MPPT controller must be a match to the panel output. Because an MPPT can make full use of the panel output, the controller amp size should be commensurate to the panel power.

Voltage Rating. The rating is going to be higher than the battery it is designed for, but that is because MPPT controllers can lower or increase the voltage accordingly. You may never have to use the high voltage capacity, but it is there in case you do need it.

Solar Input Voltage. On some MPPT controllers this can be as high as 100V. If you connect a 100W solar panel to it, the controller will reduce the voltage to match the module. The same adjustment happens when you charge a battery.

I Dont Know The Voc Or Isc Of My Panels What Should I Do

For accuracy, its best to enter the Voc and Isc of your chosen solar panels into the calculator.

If you havent already bought your solar panels but know the model youre getting, you can usually get the detailed specification from the manufacturers website.

Our solar charge controller calculator will work without them though, using an estimated Voc and Isc.

Just leave the fields set to zero in the calculator and well do the rest.

Its pretty accurate for panels upto 200w.

Most solar panel of the same wattage have more or less similar specifications, so the calculated result is a good indication of the size of the charge controller you need.

For more assurance though, try to get hold of the specification for your chosen panels.

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What Happens If I Over Size My Charge Controller

Solar charge controllers are sold with a maximum rating in current . If you choose to buy a larger charge controller than you need, you may spend a little extra money, but you should be safe in doing so. Be sure to read the safety documentation that comes with your controller to be sure that it will work in your particular case.

It can be beneficial to oversize your charge controller if you want to be certain to get the maximum power generation possible during bright sunny days. Clear days were the sun is high in the sky may cause solar panels to slightly over produce their rated wattage. So a 100W panel may end up producing 105W or more.

You can also oversize your controller, with the intention of upgrading the number or size of your solar panels in the future. This may save you money over buying a second or larger charge controller at the same time, since doubling the size of your charge controller doesnt necessarily double the cost.

My Solar Setup Produces Too High A Voltage When Wired In Series What Does This Mean

Solar arrays wired in series produce high voltages. The largest MPPT solar charge controller today can handle upto 250 volts.

If your setup is any larger than this, youll need to split your configuration into a mix of series and parallel.

If you received this message from the calculator, we have recommended a correctly sized solar charge controller to handle the mix of 2 even strings wired in parallel.

You can see our solar panel wiring diagrams for more detail about how to do that.

Also Check: How To Make Your Own Solar Cells From Scratch

How To Determine What Charge Controller You Will Need

Now that you have come to terms with what exactly charge controllers are, and what type you will need, Im sure you are still wondering what size charge controller do I need for a 100-watt solar panel?

It is important to have a correctly sized charge controller. If your charge controller is too small, then the amount that the batteries can be charged, as well as their power output, will be limited and will result in loss of energy and wont allow your solar system to work with peak performance.

For this reason, your charge controller either needs to be spot on with its size, or slightly bigger than what is required to get the maximum performance out of your system.

As much as the size is important, it is also crucial to make sure you dont go for the cheapest, poorest quality charge controller.

Although you may think it is something you can skimp on when you see the cheap ones that are available on the market, rather dont.

If you do, it can end up damaging the batteries of your solar array and can lead to failure of the batteries, as well as the entire system as a result, leaving you in the dark.

What Are The Types Of Solar Charge Controllers

The different types of solar controllers include the following:

MPPT Solar Charge Controllers. The Maximum Power Point Tracking solar charge controller is the latest innovation of solar systems today. This controller can determine the solar panel arrays optimum amperage and operating voltage and match it with the battery bank. This results in an additional fifteen to thirty percent more power out of your solar array.

PWM Solar Charge Controllers. Pulse Width Modulated solar charge controllers are the traditional style of controllers. They are common, widely used in many solar panel applications and very affordable. It is a passive controller technology that utilizes solid state gates and switches to generate a constant DC output from a varying DC input.

Lets compare the mppt charge controller and pwm charge controller one by one:

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