The risk of electrocution on photovoltaic systems
The incentives for photovoltaics in Italy and a method for choosing the lightning protection systems in order to protect photovoltaic systems by direct or nearby lightning strikes.
In recent years, governments of many countries in the world have tried to increase the share of electricity generated using photovoltaic systems through to various types of incentives.
In Italy, the construction of photovoltaic plants is promoted as defined by DM February 19, 2007 [1], through the adoption of the so-called "energy account", the Electricity Services Operator (ESO), pay to the owner of a fee (incentive fee) for all the energy that is produced from 'plant over twenty years. This incentive applies to today, around 0.40 € / kWh and can vary by ± 20%, depending on the plant size and its level of integration into the host structure. Preference is given to small installations and more integrated. The premium may be increased by 5% if special conditions exist (eg, replacement of asbestos roofs), or up to 30% if the PV is combined with the efficient management of electrical energy.
In addition to tariffs, an additional benefit can be obtained by using the energy produced. This energy can be used locally and / or fed into the grid and there are three alternatives on its value:
• Net metering - energy not used is fed to the network and will be a positive balance of energy to be subtracted from a negative balance due to consumption exceeding production over a billing period. The electricity bill will be calculated on the difference between these two values leading to savings proportional to the energy produced.
• Sale "indirect" - unused energy is sold to the GSE that pays a fixed price or a market price (depending on the volume of production) for production.
• Sale "direct" - unused energy is sold to the electricity market (which is not recommended for PV).
Generation systems (PVPGS photovoltaic power generating system) can be affected by direct lightning strikes and affected due to lightning neighbors. In the case of direct lightning strikes may cause physical damage or malfunction of the equipment of such systems. However, even the lightning neighbors, through electromagnetic pulse (LEMP English lightning electromagnetic pulse), can cause considerable damage.
In this context, it is clear that inadequate protection from damage caused by lightning may increase the time required for the return on investment (ROI English return on investment) and energy recovery (energy pay-back) [2] of the system photovoltaic (PV English acronym photovoltaic). In practice, the owner of the system that has made considerable investments, could see his aspirations thwarted if one or more components of its PVPGS were damaged by lightning.
The IEC 82-4:1998 (CEI EN 61173) [3] provides guidelines on measures for the protection of photovoltaic systems against the dangers caused by surge voltages, such as grounding, shielding, the interception of lightning and the installation of devices for lightning protection (English SPD surge protective devices). The adoption of such measures, to be useful, it must be based on a careful assessment of the possible risks made with engineering criteria.
Accordingly, the purpose of this paper is to describe the application of the procedure for evaluating the risk of electric shock proposed by CEI 81-10/2: 2006 (IEC 62305-2) [4], to validate the adoption of some of the protective measures suggested by the guidelines IEC 82-4:1998 (CEI EN 61173) [3] and, if possible, propose other measures that could be taken.
Conclusions
It was carried out a risk assessment of a lightning strike of a photovoltaic power generating system (PVPGS) connected to the distribution network, according to CEI 81-10/2: 2006 (IEC 62305-2). [4] Examples were given for a PVPGS site on a terrace and a PVPGS site on the ground of medium size (about 250 kWp). We evaluated the risk of loss of life and the risk of economic losses.
In the two examples considered the risk of loss of human lives is below the values considered tolerable, so the related PVPGS not require protection measures in this respect. Instead, the risk of economic loss, not at all negligible.
Looking at the values and the weight of each risk component has been highlighted as the greatest risks arise from the nearby flashes, by electromagnetic induction, and as the risk of failure is greater in the DC side of the system.
Considering the high value (about 20% of the cost of the system) of the expected annual economic losses, it becomes necessary to take in this case, some protective measures, otherwise the time required for the return on investment and energy recovery grow in excessive extent.
Therefore, in accordance with the IEC 82-4:1998 (CEI EN 61173) [3], have been proposed and evaluated certain protection measures in order to assess the effective change of the component of risk you are going to reduce.
As expected, the analysis showed that the best solution for extended PVPGS is to adopt shielded cables (the cables that come from the J-Box, located in the back of the PV modules, and the connection cables to the inverter) connected at both ends to the same equipotential bonding bar. Smaller PVPGSs can be protected by adopting SPD with the connection cables to the drive.
10/12/20100
----------------------------------------
Translated via software
----------------------------------------
Source:
Italian version of ReteArchitetti.it