Detecting anomalies in solar power generation

Solar panels lose efficiency when they’re covered with dust, dirt or snow, or are shaded. Although cleaning them is not a huge issue, keeping an eye on them to determine when they need cleaning is physically demanding, because solar panels are usually installed in inaccessible locations like rooftops. So as part of our study, we explored some automated methods to detect soiling.

In our first study, we used solar power traces to detect soiling using an algorithm we developed. We were able to detect ten types of anomalies, including temporary shading, permanent shading, fallen leaves, accumulating snow, and melting snow [1].

While working with solar panels, we noticed that shading affects power output in a different way than soiling. In our second study, we used solar power traces along with solar intensity information to detect obstructions of both types. Our detection algorithm achieved an 85% accuracy when tested on two real PV installations in Ontario, Canada [2].

[1] B. Hu. Solar Panel Anomaly detection and classification, MMath thesis, University of Waterloo, May 2012.
[2] X. Gao, L. Golab, S. Keshav, What’s wrong with my solar panels: a data-driven approach, Proc. Workshop on Energy Data Management, March 2015, pp. 86-93.

Allowing solar farms to enter into firm contracts with electric grid utilities (TSOs)

A large barrier to integrating solar power into the electric grid is the variability of sunlight. Because solar power generation depends on the intensity of sunlight in the moment, it’s tough to control solar energy generators to match fluctuations in demand from the electric grid. This means solar farms cannot confidently participate in the day-ahead electricity market, unless they add generous safety margins when committing to a certain level of power generation for the next day.

To allow solar farms to participate more confidently in the day-ahead electricity market, we developed a technique that considers the variability of solar intensity to predict how much electricity can be generated in the upcoming day. We also show how the same technique can be used to determine the best storage size for a solar farm to help meet fluctuating demands in energy. We tested our technique using a 10-year dataset, and found that it attains 93% of the maximum revenue that would have been achieved in the daily market if the entire schedule of the sun’s intensity was known ahead of time.

For energy storage specifically, our model determines the optimal size by taking into account the following three factors that affect solar power generation:

1. The position of the sun in the sky
2. Long-term cloudiness at time scales ranging from 10-minutes to a few hours
3. Short-term cloudiness that last less than 10-minutes

Given a target output power and an allowable loss of power threshold, our technique computes a near-optimal storage size.

[1] Y. Ghiassi-Farrokhfal, S. Keshav, and C. Rosenberg. Firming Solar Power, Extended Abstract/Poster, Proc. ACM SIGMETRICS, June 2013.
[2] Y. Ghiassi-Farrokhfal, S. Keshav, C. Rosenberg, and F. Ciucu. Solar Power Shaping: An Analytical Approach, IEEE Transactions on Sustainable Energy, Vol 6, No. 1, Jan. 2015.

Optimal budget allocation

Suppose you had a million dollars to spend, some on solar panels and some on a storage system. While adding more solar panels increases the amount of power your solar farm can generate, adding more storage means you can source excess power on days with less sun so that the overall power supply is less varied. With this in mind, what would be the best way to split your budget if you’d like to maximize revenue by selling electricity in the day-ahead market? We provide an algorithm to determine this, taking into account factors such as:

• the power level committed by a solar farm owner
• the capacity of the transmission link between the solar farm and the power grid
• the need to curtail excess solar generation
• the degree in fluctuation in the purchase price of energy
• the inherent variation in solar generation due to fluctuations in sunlight

Ghiassi-Farrokhfal, F. Kazhamiaka, C. Rosenberg, and S. Keshav, Optimal Design of Solar PV Farms with Storage,  IEEE Transactions on Sustainable Energy, October 2015.