Using fields rather than roofs to place the solar modules on, it is possible to construct utility-scale power plants.
Free-standing modules can be mounted such that they face the best angle. Again, wind speeds need to be taken into account. With some mounting systems, the manufacturer advises to place the modules flat on the ground during wind storms.
The modules are usually configured in rows. In order to avoid one row causing a shadow on the following row, the rows have to be placed at a fair distance, which will largely depend on the latitude of the site. We have provided more details on this effect of self shading.
How much space is required? About one third of the space can be physically covered with modules. Consequently, for 1MW of name plate capacity a field of 2 hectares is required. Sites that are closer to the equator may need less space.
Ground-mounted solar installations can make use of tracking platforms that can tilt the surface along one or two axes with the help of a motor.
Automated tracking can be passive or active. Due to thermal inertia, passive systems tend to be slow in changing from the sunset position to the sunrise position. Active trackers either calculate the current position of the sun from first principles, or use light sensors that will point the modules to the brightest point in the sky, not necessarily the sun - especially when it is cloudy. In active systems, the motor itself is connected to a device that determines the angle of the sun.
The modules rotate around a horizontal axis, tracking the sun from south to north from winter to summer.
The modules are at a fixed tilt angle mounted on a platform rotating around a vertical axis following the sun from east to west.
The modules are mounted on a tilted bar that rotates. The modules are following the sun from east to west daily.
Dual-axes trackers allows tracking along both axis - east-west (daily) as well as north-south (seasonal tracking)
Energy Yield Gain thru Tracking
Tracking will always result in a higher energy yield. The amount of the boost however is very much dependant on the location. Generally, locations with a higher proportion of direct sunlight such as Spain or Finnland will benefit more from tracking than locations with a high proportion of diffuse light such as Germany.
However, the gain in the energy yields comes at a cost, as the tracking mechanics and associated operational costs are more expensive. The energy requirement for the motors on the other hand is negligible. Careful consideration is required.
Above diagram illustrates monthly output from a photovoltaic power plant in Zimbabwe for different tracking devices in comparison to a fixed tilt of 30°. In this location, there is very little difference between single axis tracking from east to west or from north to south. The annual performance gain achieved by single-axis tracking is over 20%. Another advantage of tracking is that monthly variations are less pronounced than with a fixed tilt. Whether tracking is the best solution for you location, please contact us for advice.