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Scan the Sun: new app predicts solar returns

Posted by Aldous Everard on 20 October 2014 at 12:12 pm

Anyone considering installing a PV or solar thermal system will want to know their likely returns. In the UK getting any kind of accurate idea of your returns is difficult to say the least. Predictions of generation are influenced by our famously changeable weather along with the physical constraints of the site. The main physical constraints of a system, for domestic customers at least, are the orientation of, and shading on, their panels.

Tools have been made to assess the impact of these influences, but they are often over-simplistic and lack accuracy and precision or highly technical and expensive. I have often dreamed of a day when I could position my phone where the solar panels would go (sad, I know), to get an instant assessment of the shading and solar path, so that I can accurately determine how much my system will generate in a year.

For us at Sheffield Solar, the availability of such a tool could enable us to better inform our members of system faults. Our Microgen Database collects data from thousands of PV systems across the UK. Members can view their systems' performance and that of their neighbours', allowing them to make real time, real world comparisons to assess whether their system has a fault. A mobile phone app which can instantly assess the shading scenario at a site could allow us to diagnose more subtle faults and so be of great use to our members.

The Scan the Sun app for Android smart phones could be just such a tool. This is a clever app which allows me to 'draw' the horizon as I rotate the phone with the camera on, then position the phone in the correct orientation and location for the panels and, hey presto, there is the pattern of solar energy which my panels will receive. A dream come true?

I took my phone with app installed up to the Sheffield Solar Farm roof to test it for myself. I was very impressed with the intuitive way it works and the graph outputs that it gives.


Figure 3. Slant your phone in the direction of your solar collector and see your generation patterns. Though in the UK you'd be lucky to see this level of generation, cloudy weather is not included. Also it doesn't show the orientation and tilt of the phone on the graph.

It is still very limited in its application, however, especially here in the UK where we get so much of our generation from diffuse light, as it only assesses direct sunlight. The part which assesses the shading pattern seemed to move about a lot, making it hard to 'draw' on the horizon with any accuracy (this may be due to my phone's poor compass, or too many metallic objects interfering). The app doesn't assess the type of shading, which is also important: close objects have a higher impact than distant; and trees have less impact in winter. The app also does not have a reporting section, so it couldn't be used as a professional tool.

This is an inspired app, with the potential to be an extremely powerful tool in the assessment of generation from solar collectors, and hopefully with the right development it can achieve that goal, but it has many limitations. I hope that its developers can get the investment they need to develop this tool, and I look forward to using it in the future, but for now don't make any decisions based purely upon its results.

Figure 1. Draw on the horizon with your finger on the touch screen. The lines wouldn't stay still!

Figure 2. Neat that it can show the solar location through the day, but again, not quite accurate.

Photo Credits: Aldous Everard

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About the author: As manager of the Sheffield Solar Farm. Aldous is passionate about breaking our addiction with fossil fuels, through renewable energy.

If you have a question about anything in the above blog, please ask it in the comments section below.

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2 comments - read them below or add one

Ernest Grodner

Ernest GrodnerComment left on: 10 July 2017 at 8:39 am

What's new in scanthesun version 2.6 ready for beta testing

NASA Surface meteorology and Solar Energy data implemented in the app.

Direct and diffuse solar radiation now calculated in the app. Direct solar radiation based on NASA data takes into account the atmospheric beam attenuation and weather conditions. Diffuse solar radiation based on NASA data. Technical documentation available at Short presentation video at Link to sign up for beta testing:

There is also significant update in the Google API used in the app. Now it operates the new camera2.api, which still may couse problems due to poor google documentation.

P.S. answer to John question: use any file browser on your phone and search for scan_the_sun folder. The files should be there. 

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MiroComment left on: 1 July 2016 at 11:33 pm

Hi, I have just been using this and it seems to answer most of my questions regarding panel positioning.  However, having saved the files for 4 seperate studies, I cannot now find the files!  Anyone know where they would be saved on my Android phone?




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