The design of a PV plant involves a series of compromises aimed at achieving the lowest possible levelised cost of electricity. Choosing the correct technology (especially modules and inverters) is of central importance. Selecting a module requires assessment of a complex range of variables. At the very least, this assessment would include cost, power output, benefits / drawbacks of technology type, quality, spectral response, performance in low light, nominal power tolerance levels, degradation rate and warranty terms.
The factors to consider when selecting inverters include compatibility with module technology, compliance with grid code and other applicable regulations, inverter-based layout, reliability, system availability, serviceability, modularity, telemetry requirements, inverter locations, quality and cost.
In designing the site layout, the following aspects are important:
• Choosing row spacing to reduce inter-row shading and associated shading losses.
• Choosing the layout to minimise cable runs and associated electrical losses.
• Allowing sufficient distance between rows to allow access for maintenance purposes.
• Choosing a tilt angle that optimises the annual energy yield according to the latitude of the site and the annual distribution of solar resource.
• Orientating the modules to face a direction that yields the maximum annual revenue from power production. In the northern hemisphere, this will usually be true south.
The electrical design of a PV project can be split into the DC and AC systems.
The DC system comprises the following:
• Array(s) of PV modules.
• DC cabling (module, string and main cable).
• DC connectors (plugs and sockets).
• Junction boxes/combiners.
• Protection devices.
The AC system includes:
• AC cabling.
• Earthing and surge protection.
Every aspect of both the DC and AC electrical systems should be scrutinised and optimised.
The potential economic
gains from such an analysis are much larger than the cost of
carrying it out.
In order to achieve a high performance PV plant, the
incorporation of automatic data acquisition and monitoring
technology is essential. This allows the yield of the plant to be
monitored and compared with calculations made from solar
irradiation data to raise warnings on a daily basis if there is a
shortfall. Faults can then be detected and rectified before they
have an appreciable effect on production.