Sun and shadows

In a cloudy day we can see each other, but we can’t see our shadows.

This is because solar radiation is made of two components: direct and diffused. In a sunny day, the direct component is the stronger one. It moves according to the laws of geometrical optics and it is responsible for generating our shadows. Diffuse radiation, on the other side, is less strong. It doesn’t follow geometrical optics because it is generated by the impact between the solar radiation and the air molecules and is therefore more homogeneously distributed across the sky and does not generate shadows.

In a cloudy or hazy day, the only solar radiation available is the diffused one: this is why in a cloudy day we can’t see our shadows, but we can still see each other!

Fig.1: Direct and diffuse solar radiation

Catching more sun in a cloudy day

Depending on on the percentage of cloudy days of the considered location, diffuse radiation can reach up to one third of the solar radiation hitting the ground annually , and it is an important input for the performance of solar power plants – particularly when powered by solar trackers.

Standard solar tracking algorithms orient the PV modules to the sun, in order to maximise the capture of direct solar radiation according to the rules of optical geometry.

However, during cloudy or hazy times, solar radiation is dominated by the diffused component.

In such times, Soltigua’s new MaxRad tracking algorithm adapts and makes trackers rotate to an alternative, less inclined tracking position which maximises the collection of diffuse radiation and – as a consequence – the yield of the plant. MaxRad continuously calculates the potential benefit of the alternative tracking position, and regularly transmits the results to the tracker controllers, which adapt the position of each table.

As shown in Fig.2 below, in locations such as Central Europe (where cloudy days are not an exception) the additional annual power output can be more than 1%, boosting the solar income for the plant owner.

Fig.2: Annual production showing MaxRad monthly gains and the cumulative extra output in MWh/MWp

As shown in Fig.3 below, the extra daily gain can easily reach 7% or more.

Fig.3: Daily production showing MaxRad hourly gains (in orange) and the cumulative yield increase in %

Innovation of a time-tested system

MaxRad can be easily implemented in the standard weather stations of SolControl –  Soltigua’s proprietary SCADA developed specifically for Soltigua’s tracking system.

The first version of SolControl was released 13 years ago.

Since then it was continuously improved and expanded to become one of the more versatile products on the market, having been tested not only in the PV industry, but also in the most demanding industry of concentrated solar power, in which tracking accuracy of less than 0.1° is required to enable solar concentration.

SolControl comes as a standard with Soltigua’s tracking systems and enables the users to monitor and operate the trackers at field level as well as at single tracker level.

With SolControl it is easy to check the status of the trackers, visualizing messages and alarms, or to put a subarray into maintenance position.

SolControl can be operated directly at the plant or remotely, thanks to the integrated router which creates a dedicated VPN. The VPN can be used from a desktop, or on mobile devices, thanks to SolControl WebApp, empowering operators to have a constant access to the plant also while travelling.

Thanks to its Modbus TCP/IP communication, it can also easily be integrated into any external plant SCADA.

Optional features include a local HMI or a SMS messenger.

Fig.4: Example of SolControl interface

Shadow minimisation with 3D tracking

SolControl includes advanced AI technologies, which enable it to optimise wind management, as well as to maximize the plant yield. For example, SolControl integrates a very advanced backtracking algorithm, which includes a 3D topographic evaluation of the trackers relative position. The software adapts backtracking angles to the ground undulations, avoiding mutual shadows which would drop the plant output. In hilly or undulating sites, this feature produces up to 3% more power output compared to traditional backtracking algorithms.

A sunnier, brighter future

As solar input in the energy system is increasing, the energy spot price is becoming lower at midday and in sunny days.

On the other side, energy is winning a higher price when there is less sun available, i.e. in the early morning/late afternoon (backtracking time) and in cloudy days.

This corresponds to a higher unit price for the energy gains from SolControl’s time-tested 3D tracking and from its recent MaxRad improvement.