Renewable energy from solar PV plants has steadily increased in recent years. The current estimate is over 4.16 million PV installations in Australia, from rooftop solar to large scale solar, with a combined generating capacity of over 41 GW. Currently there is over 7 GW of large-scale solar farm generating capacity across 59 projects, with a further 27 projects in the planning stage, according to the Clean Energy Council.
A cornerstone of any electricity generation plant is to ensure reliability and system uptime, as well as stable grid operation, and this is especially so for large scale solar farms. Production downtimes are closely monitored, and any losses can have a negative impact on the annual performance volume measured across the minimum service life requirement of 30 years.
Science has identified the connection between solar radiation, air humidity and the frequency of lightning discharges. A region with high solar radiation is ideal for PV energy production, however these regions often experience higher air humidity and can be susceptible to lightning strikes.
When we assess the risk of lightning strikes according to AS 1768, consideration must be given to the regional lightning frequency (lightning strikes per square kilometre/year) and the location and size of the area to be protected. A large-scale PV power plant will most likely be positioned in an area of high solar radiation and cover a large area, typically about 1.5 to 2 hectares per megawatt.
As an example, a 300MW solar farm in south central NSW would cover approximately 600 hectares in an area designated with a lightning frequency of 2, according to Bureau of Meteorology data. The risk assessment of AS 1768 calculates that the solar PV plant of this size and location could be subjected to a direct strike 5 times per year and be subjected to the influence of indirect strikes 7 times per year. In the service lifetime of the solar farm, it could be anticipated it will have up to 150 direct lightning strikes.
Direct lightning strike damage to PV systems can be destructive to the PV panels and other infrastructure. The consequential damage caused by the electromagnetic effects of a strike can damage inverters, charge controllers, monitoring and communications systems. The resultant economic damage can be extensive with repair and replacement costs together with the cost of lost production.
Due to the high exposure area, the value of the infrastructure, and the need to fulfill network operator supply obligations, it is essential to review lightning and surge protection requirements for any solar PV plant.
To ensure effective protection, a lightning protection system must incorporate elements including a well-designed air terminal system, earth termination system, lightning equipotential bonding and surge protective devices for the power network and data systems. Surge protection should include an SPD on the DC side from the solar panels and on the AC side of the inverter. If the distance from the inverter to the main switchboard is less than 10m, an SPD at the main switchboard will provide protection. If the distance is greater than 10m, SPD protection should be provided, in both the main switchboard and near the inverter AC output. Additional protection should be provided in combiner boxes also, if they exist.
The theory of lightning and surge protection applies to rooftop solar PV as much as it does to large-scale solar farms. In domestic applications often lightning air terminals may not exist, but equipotential bonding of solar panel mounting frames and the provision of surge protective devices is still equally important.
IPD can assist with the design and application of lightning protection systems and surge protection devices for any application in accordance with AS 1768 and IEC 62305.