5.3% Diffuse Booster

Soltec Power Holdings

1. INTRODUCTION

Solar tracking systems can turn Photovoltaic Modules (PV) to positions in which received irradiance is enhanced. Single Axis Tracking Systems (SAT) are traditionally designed to “follow” the sun throughout the day, generating up to 25-30% more energy than fixed structures [1].

However, there are tracking strategies which orient trackers to not sun-oriented angles (other than the “typical“ one) with the aim to maximize available power. This performance is normally associated to specific irradiance conditions in which captured irradiance in a position other than solar tracking is more beneficial.

2. ASTRONOMICAL TRACKING

Solar trackers are traditionally oriented to the sun, regardless of whether direct irradiance exists or not. Such type of tracking is called “astronomical tracking”. The sun position for a site (latitude and longitude) at a specific time is known thanks to astronomical Earth movement models and can be easily known using Solar Position Algorithms (SPA) [2, 3]. Based on this information and using geometric relations, astronomical algorithms determine the tracker rotation angle which optimizes PV module orientation [4].

3. SOLTEC TEAMTRACK®

To best use this energy, tracking systems have to include diffuse energy optimization functionalities. Figure 3 shows the performance of this function compared to standard astronomical tracking throughout a representative day in which the sky gets cloudy. Early in the day, the sun shines and therefore trackers maintain their orientation. As clouds appear, irradiance on the oriented plane decreases considerably, fluctuating as the sky gets overcast and horizontal plane irradiance exceeds steadily oriented irradiance. The lower graph shows how, throughout this period, the angle of the tracker in astronomical tracking remains oriented to the sun position (as shown in Figure 2.a), whereas the tracker with Diffuse Booster active remains horizontal to optimize energy and capture all celestial sphere irradiance (as shown in Figure 2.b). Energy collected by the tracker in optimization mode exceeds in 94 Wh/m2 the astronomical mode one, achieving a daily generation improvement of 1.4%.

Figure 4 shows this comparison for an example of fully cloudy day. Tracking with active Diffuse Booster increases captured irradiance by 54 Wh/m2, improving full-day power generation in 12.4 %, offering instantaneous improvement peaks of up to 29%.

To achieve production improvements associated to diffuse irradiance optimization, tracking systems require local weather data which can be obtained via forecasts and sensors. Furthermore, determining the exact return-to-tracking time is one of the main challenges for these systems.

Figure 5 shows Soltec Diffuse Booster system performance when the day clears, and the sun comes out. As can be seen, energy levels during periods when the sun shines are five-fold those of fully cloudy event. Such energy gain needs to be utilized. Systems which position trackers based solely on sensor data will return to tracking position when sensors detect increased direct irradiance. Since these systems cannot predict conditions, energy (direct irradiance) is partly wasted while returning to the sun-oriented tracking position. To ensure efficiency of this functionality, it is necessary for systems to predict the return-to-tracking mode, orienting trackers before the first sun’s rays appear. Similarly, a reliable system should ensure trackers are not moved to a diffuse irradiance optimization position in case of one-off fluctuations, which are not sustained in time and are therefore irrelevant in terms of production maximization, thus preventing unnecessary tracker movements.

This anticipation criterion is based on the same concept that fruit ripening schedule: the later they are picked from the tree, the tastier they’ll be, but waiting too many results on fruit falling to the ground. A failed movement of the trackers attempting to improve means lost everything. Systems based solely on the use of sensors wait for fruit to fall to the ground. On the contrary, within the weather forecast inclusion, Soltec Diffuse Booster is activated by double-check information, just the accurate shot.

To achieve production improvements associated to diffuse irradiance optimization, tracking systems require local weather data which can be obtained via forecasts and sensors. Furthermore, determining the exact return-to-tracking time is one of the main challenges for these systems.

Figure 5 shows Soltec Diffuse Booster system performance when the day clears, and the sun comes out. As can be seen, energy levels during periods when the sun shines are five-fold those of fully cloudy event. Such energy gain needs to be utilized. Systems which position trackers based solely on sensor data will return to tracking position when sensors detect increased direct irradiance. Since these systems cannot predict conditions, energy (direct irradiance) is partly wasted while returning to the sun-oriented tracking position. To ensure efficiency of this functionality, it is necessary for systems to predict the return-to-tracking mode, orienting trackers before the first sun’s rays appear. Similarly, a reliable system should ensure trackers are not moved to a diffuse irradiance optimization position in case of one-off fluctuations, which are not sustained in time and are therefore irrelevant in terms of production maximization, thus preventing unnecessary tracker movements.

This anticipation criterion is based on the same concept that fruit ripening schedule: the later they are picked from the tree, the tastier they’ll be, but waiting too many results on fruit falling to the ground. A failed movement of the trackers attempting to improve means lost everything. Systems based solely on the use of sensors wait for fruit to fall to the ground. On the contrary, within the weather forecast inclusion, Soltec Diffuse Booster is activated by double-check information, just the accurate shot.