Designing Solar PV Systems

When starting any solar PV system installation it is important to define expectations, the level of energy the solar system is expected to generate and how that energy is to be used (exported) or stored. Will it be connected to the National Grid via a utility company and export unused energy under the UK’s FITs (Feed-in-Tariff) scheme? Is the primary objective cheaper energy bills or to reduce the owner’s environmental impact? Will the solar power system be the only source of electricity? Will it be connected to some form of energy storage (batteries, for example) and a back-up generator and UPS (uninterruptible power supply)? All of these questions need to be asked (and answered) before a system is designed and specified.

Alongside the solar PV (photovoltaic) array (the solar panels, basically), other equipment factored into system design include mountings for the panels to be connected to the roof, wall or other permanent structure, wiring, disconnects (for the dc and ac sides of the inverter, ground-fault protection, surge protection for solar modules, fuses, the inverter itself, a meter and utility switch.

The best and most common place to mount solar panels is on a South-facing roof, angled at 30-50degree (from horizontal). But there are other options too. Most PV systems produce 15-30 Watts per square meter of array area. A typical 2kW PV solar system will require 70-150 square meters of unobstructed and none-shaded area to site the system. Consideration should also be give for access, which can add another 20% required area. Solar power panels can be roof mounted, attached to a shade structure such as patio cover or shade trellis, or building integrated (although these system are not commonly available and tend to be expensive), such as in the materials used to construct a roof (roof tiles).

The key factor about solar PV system design is to choose the right system for the job, taking into account the property owner’s needs and what they want it to do (reduce energy bills, provide back-up power) and environmental issues. It is crucial to ensure the installation site (whether a roof, wall or other permanent structure) is capable of handling the desired system size without reinforcement. Materials that are sunlight and weather resistant should be specified for all outdoor equipment. The impact of shading on the effectiveness of the solar array should be taken into account at the design stage so as to be minimised. Even a tiny bit of shading from a vent pipe could detrimentally affect system performance.

In the UK, it is unlikely planning permission will be required for solar PV installations but your local authority planning office should be consulted. Your system should also comply with building and electrical regulations. Electrical losses should also be considered at the design stage. Every electrical system will suffer from loss to some degree. It can be minimised at the planning stages if the system is properly designed.

The system’s battery energy storage system (if there is one) should be properly housed and managed. If the intention is to connect to a utility supply to take advantage of the FITs (Feed-in Tariff) scheme, your renewable power systems installer should contact your utility company on your behalf and obtain all the necessary permissions, technical data and information.