All support structures should be anodised aluminium, galvanised steel or stainless steel and need to be designed to withstand the maximum possible wind loading for the particular location (Ibid ). Lock washers or equivalent should be used on all bolts to remove risk of them coming loose during the subsequent 20 years. The structures should be located as close as possible to the water source to minimise wire lengths, and where necessary fencing may be used to protect from animals, theft, vandals etc. (Ibid.).
Tracking support structures can be useful to enable the solar panels to point more directly at the sun throughout most of the day. Motorised or passive tracking mechanisms in Madrid, for example, have been calculated to boost annual water flow by 40% or more. However, trackers operating outside for extended periods can introduce considerable expense, maintenance and reliability problems (Illanes et al., 2003). Vilela et al. (2003) calculate that tracking could increase the pumped water volume by up to 53%, partly by allowing the pump to start earlier each morning. A more affordable alternative is to use a manual tracking system, whereby a simple adjustment by an operator can take advantage of the changing sun position. One such regime is where a seasonal adjustment of the tilt angle is made a few times each year, to compensate for the variations in the sun’s angle of declination. Another form of adjustment allows for redirection of the solar panels twice a day to take greater advantage of both the morning and afternoon sun. Yet another mechanism for adjustment is a continuously-variable one, where it becomes the responsibility of the operators to redirect the panels whenever they wish. The mechanical structures for the latter tend to be more complicated, less robust and more prone to failure. Of course, the option of manually redirecting the solar panels depends on the availability of an operator, which for some remote or inaccessible locations may not be feasible nor practical. However, to give an appreciation of the potential benefits, in 1981 the World Bank, using one of the most efficient photovoltaic water pumping systems then available (Arco Solar System), added a simple manual tracking system requiring two adjustments per day. The result was that a 30% relative improvement in the daily efficiency of the system was achieved (Halcrow & Partners, 1981 b).
