Free PV system performance estimate

08 February 2019

Is my rooftop solar PV system working correctly?

Select your location with the map. Adjust the sliders at left to match your solar PV system's characteristics, and mouse over the bar chart at right to see how many kWH you should have generated.

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Use the above PV yield estimation tool to compare your actual generation to expected generation based on Solcast cloud cover data (Instructions are included below, if you need them)

If you like the above tool, you can sign-up for a free Solcast API Toolkit account to get forecasts of the power output from your home PV system. Simply register for your account and select 'Home User' as your account type. No hidden fees. No 'gotchas'. Your data and information are confidential, and Solcast generates no revenue from your usage of our data. We simply want to enable you to become part of the solar powered future!

Read on to learn more about our PV system performance checking tool

All around the world, solar owners are wondering the same thing: Are my solar panels performing as expected? How can I monitor my PV system's performance? Are my solar panels working?

There is plenty of reason to ask this question. Solar PV installations can be quite complex. Mistakes are often made during the installation. Trees grow to shade part of the solar array. The accumulation of dirt and dust is common. Solar isolators or inverters often wear out over time. So how can you check if your solar panels are working? And how could you do that for FREE?

Solcast's FREE PV system performance check tool

To make this easier for the many people who are wondering how to answer this question, we've launched a new tool, which will provide you with estimates of the total daily energy generation from your rooftop solar system from today + the last 6 days. We provide an energy generation estimate in 'kWh' which stands for kilowatt-hours. The tool is meant to be very user friendly, so give it a try! For those of you wanting more information on how it works or how to use it, scroll down the page for more information (and don't forget to read our blog)

How to use the free solar panels performance tool

To proceed, you’re going to need to know your PV array capacity (kW). The capacity of your PV system is the total Wattage of solar panels installed, or its DC rating. If you have a 3.4 kW PV system, this value would be 3400W (1kW = 1000 Watts). You can use your inverter rating as well, to make things easy, but the actual installed capacity of the solar panels is best.

You'll also need to take note of the direction your solar array points (its azimuth) and an estimate of its tilt (most PV systems are mounted between 15-25º from horizontal). You can adjust these two variables with the slider on the performance check tool.

Finally, drop the pin on the map where your PV system is located, so that we can match up the characteristics of your PV system with the recent cloud cover conditions at your location.

Checking the performance of your rooftop solar system

On the right side of the tool are several columns in a bar chart format. If you hover over these values with your mouse (or touch them on a mobile device), a value of the exact # of kilowatt hours will appear. You can also of course 'eyeball' the values on the bar chart with those displayed on the vertical axis.

From there, you can adjust the efficiency factor slider until the values produced by the performance checker tool match those reported by your local monitoring solution. You can gather these data from online tools (e.g the Enphase Enlighten portal, SMA Sunny Portal, Fronius Solar.web, etc), or you can simply read the display on your home inverter system to compare! If you observed a very low efficiency factor (0.85 is the average) you likely have an underperforming solar PV system!

The efficiency factor is a representation of the performance of your PV system, as compared to how it should perform under ideal conditions. A value of 1.0 is perfect, or 100%. A value of 0.8 is 80% efficient. A value of 0.5 is 50% efficient, and so on.

It is important to note that we already take into consideration the standard losses of your solar inverter and the impacts of temperature.

How does the solar PV performance check tool work?

Solcast owns and operates a proprietary PV model which is based on the performance of thousands of solar arrays which we monitor as a part of our commercial services. The primary input to this model, and the main driver of the performance of all solar PV systems is cloud cover and the impacts of that cloud on the available solar radiation.

One of the reasons it is so hard to determine whether a solar installation is performing as expected, is that many factors can impact its performance. But one factor stands out from all of the rest - and that is the local cloud cover. Luckily for you, that's our area of expertise!

Global cloud tracking and solar PV power modelling

Solcast has deployed a global network of cloud monitoring and forecasting systems for the purposes of enabling the hard-working folks in the solar energy and electricity industry to build the solar-powered future. We operate commercial services which detect, monitor and predict the locations and thickness of cloud cover to solar radiation, for the purposes of producing estimates for utilities, solar farm operators and energy traders/analysts.

We utilise 5x weather satellites to provide rapid-update solar forecasting services, as well as to produce a large library of historical data in order to make it easier for our customers to accomplish their solar mission. To do this, we produce forecasts like this one, all around the world, updating them every 5-15 minutes:


We use our extensive knowledge, experience and datasets to deliver the tool you find here. And we're making it free in hopes that it will help maximise the amount of solar energy making it into our electricity networks and to help folks like you make the best decisions on your solar investment.

How can I learn more about Solcast?

The best place to keep up with us is by reading our blog, following us on Facebook, Twitter or LinkedIn.

Hey this tool is great, how can I thank you?

We're glad you like it! The best way to repay us is to share this tool with your friends and family via your own blog, a relevant website or your favourite social media account. We've even embedded some social networking sharing tools in this blog post to make that easier, which you can find near the 'Blog Author' section of this webpage. Thanks in advance!

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Dr. Nick Engerer

Dr. Nick Engerer

Solcast Co-founder • Author

Nick is an expert in the field of solar radiation and distributed solar PV modelling, and has co-founded Solcast out of a sincere desire to enable others to build the solar-powered future.

Read more about Dr. Engerer's scientific papers

Solar Power Forecasting