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PV Watts Calculator

Short on Time? Here’s The Article Summary

The article introduces the PV Watts calculator from the National Renewable Energy Laboratory (NREL), which analyzes photovoltaic systems' energy output. Users input their location, system size, panel type, orientation, and system losses. The calculator estimates energy costs and production, aiding in system design. Advanced settings include inverter efficiency and ground coverage ratio. Economic information, like electricity cost, helps calculate savings. Results include monthly solar radiation, AC energy, and annual output, aiding in system sizing.

The calculator is valuable for understanding system capabilities and ensuring proper sizing. It's particularly useful for grid-tied systems. Further, electrical calculations are essential for maintaining optimal solar panel system performance.


The PV watts calculator we’re going to be using in this article comes from the National Energy Renewable Energy Laboratory.

The calculator itself serves as a tool that’s used to do photovoltaic analysis on buildings or residential homes around the states.

The calculator is like an AC watts calculator, or any solar calculator for that matter, as you can use the values you obtain to determine if solar is feasible.

So, let’s dive in and see how this bad boy works. 

But first, what do people use this calculator for?

A Bit About the Calculator

The PV Watts calculator gives accurate estimates of the cost of energy as well as energy being produced on grid-tired photovoltaic systems.

pv watt calculator

In simpler terms, it allows users to size and determine how their system will perform before its built.

The calculator belongs to NREL, a company that has been at the forefront of transforming energy through research and deployment of solar technology.

Their calculator is easy to use and doesn’t require you to do any tedious mathematics.

How to Use the PV Watts Calculator

Let’s cover each step so that you can be on your way to building your dream solar system.

Enter Your Location and Select the Weather file

The first step to using a PV watts calculator is to enter your address so that the calculator can get an understanding of your location’s exposure to the sun.

You’re then greeted with a geographical representation of your house along with weather files surrounding the area.

If you choose the weather file, it will show up alongside your location, allowing you to proceed to the next screen.

System Information

The system information refers to the rating of your solar system, like how an appliance kWh calculator works.

You’ll first need to enter the DC system size in kilowatts followed by the module and array type.

The module refers to the type of panels your solar system uses. In other words, either polycrystalline, monocrystalline, or a thin film panel.

pv wattage calculator

Array type describes how your solar system is set up. You’d pick the fixed system if your solar panels are stuck to your roof, or a tracking system allowing the sun to come in from all angles.

The latter is used more in farming usage over residential but it's not uncommon.

The next two values needing to be inputted relate to the orientation of the solar panels. The first is the tilt angle, or the angle at which your solar panels are tilted, and the azimuth.

No, the latter isn’t a spell cast by wizards. It’s the arc between the North and the sun or moon.

How do we obtain this angle?

Well, 180 degrees is due South, 90 degrees is due east, and 270 degrees is due west.

Finally, we need to enter the system losses, or how much energy is lost within the system before converting the solar to electric energy.

NREL knows that certain elements affect this rating and it’s not the easiest variable to calculate manually.

Factors like soiling, shading, snow, and wiring can make the system perform less than optimal.

Luckily for you, NREL has a built-in calculator to help you get a more accurate reading while compensating for these factors.

This isn’t a completely new idea in the solar game as mah watts calculators have built-in calculators to assist in the conversion process of other non-related units of power.

More Advanced System Information

The NREL’s PV Watts solar calculator has a set of advanced settings that aren’t necessary to change. These include the dc to ac size ratio, the inverter efficiency, and the ground coverage ratio.

How to Use the PV Watts Calculator

This data isn’t as simple as looking at a voltage-to-watts chart and converting one unit of measurement to another.

Size ratios and efficiencies require calculators of their own or a real solar techy to know the mathematics.

Leaving these values at their default settings won’t hurt a fly.

Economic Information

This section lets the calculator know what kind of economic setup your solar system falls under. 

There’s a drop-down menu where you can either pick residential or commercial and chances you’re picking the former if you’re reading this.

However, if you’re a farmer with a far-stretching solar array, the latter is your best bet.

The next value that needs to be entered is the average cost of electricity purchased from the utility.

Depending on your location from the beginning, this data should automatically be entered and updated. If it’s incorrect or slightly off, you can edit it and use the value on your power bill.

If you’re a remote user and you plan on using a solar-powered generator or battery to store the incoming power, then this value won’t be relevant.


the use of PV Watts calculator


Results Page

Once all the variables have been entered correctly, the calculator gives you a monthly breakdown of the solar radiation, the AC energy, and the value of that energy.

It also gives you a yearly value of how many kilowatt hours the system can output each year.

These statistics can be downloaded, edited, and exported to an excel sheet, allowing you to organize the data with ease.

Knowing these values, along with your home solar needs, can help you size the perfect solar system.

It’s important to note to obtain the correct values that for your solar needs using a mA to watts conversion calculator, the variables are the correct unit of power.

the use of PV Wattage calculator

Why should you use a PV Watts Calculator?

The main reason that incoming solar users make use of this calculator is to get an understanding of the size and scale of their system.

Without this, you could be installing a solar system that’s underpowered.

Also, since you’re given annual kWh, you can compare this with your solar needs to see if it will match your daily kWh usage.


The NREL’s PV Watts calculator is a good way to ensure that your solar system can handle anything you throw at it.

Where this differs from the off-grid solar calculators is that the PV Watts is designed specifically for grid-tied solar systems.

It doesn’t stop there though. There are plenty more electrical calculations you need to familiarise yourself with to keep your solar panel system running optimally. Check out our VA to Watts converter.

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