Tracker with Ground Screw Installation
In the past, tracker systems have been installed with large concrete bases which essentially act as ballasts to hold down the tracker array in windstorms. A Deger 9000NT as we installed in this case, would normally have required a 3m diameter round base holdin 10cuyds (7.65cubic metres) of concrete weighing about 20 tons (19,000kg).
Working with Burnside Engineering, the same firm that certifies concrete bases for Deger and AllTask Property Improvements, we came up with a base that can be installed with ground screws. See a video of this installation.
Ground screws are much like very large lag screws in that they literally screw into the ground, compressing - not pulling up - the soil around them for a powerful connection to the ground. You never know what the condition of the soil may be under the surface unless you do extensive and expensive analysis, so the solution was to use oversize screws then specify and measure the torque required to turn them into the soil.
In the top left picture above, you will see that we positioned the screws such that they would align with the base. Each of these Krinner screws is about 2m long. The top centre picture shows the Krinner driver turning the screw into the ground. The Krinner driver is capable of 6000nm (4425lbft) of torque while the Burnside Engineering spec is that 2700nm must be achieved. In this installation, the lowest torque reading was 4200nm while the highest was 5600nm - well over spec.
Cost wise, a ground screw installation works out to about the same to slightly less than a concrete base system, especially in the cold months when expensive additives are required for "winter concrete". These installations are much cleaner than concrete; electrical equipment, controls and even the meter can be hung on the mast and easily accessed and the big advantage is this base installed in about 1-1/2hr from arrival to departure and the base can be immediately used with no cure time and of course does not depend on the temperature outdoors.