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Understanding Solar PV System Availability

Updated: 3 days ago

Solar photovoltaic (PV) systems have emerged as a promising solution to meet the ever-increasing energy demands while mitigating environmental impacts. Notably, the performance of solar PV systems hinges not only on their design and technology but also on their maintenance. Availability is a critical metric that measures the ability of an energy system to deliver its intended function when required. In the context of solar PV systems, availability is typically categorized into technical availability and operational availability, and each metric can be calculated for reports as a time-weighted value or an energy-weighted value.

Rooftop solar photovoltaic system in Southern Israel (2018).
Fig 1. Rooftop solar photovoltaic system in Sharon region (2018).

Technical Availability refers to the readiness of the system to generate electricity based on its design specifications. It encompasses factors such as equipment reliability, maintenance downtime, and system failures. Technical availability is calculated as the ratio of the actual operating time to the total planned operating time, expressed as a percentage. It provides insights into the system's reliability and its ability to function under normal operating conditions.

Operational Availability, on the other hand, considers external factors such as scheduled maintenance events and grid connectivity, which affect the system's ability to generate power. It reflects the percentage of time the system is available to produce electricity when accounting for both planned and unplanned downtime, including maintenance activities and grid outages. Operational availability provides a more holistic view of the system's performance in real-world conditions.

Availability of a single-inverter rooftop PV system.
Fig 2. Availability of a single-inverter rooftop PV system, indicating an acute 25% production drop during the period.

When assessing solar PV system availability for reporting purposes, two common methodologies are employed: time-weighted availability and energy-weighted availability. The energy-weighted availability is basically the only choice for daily reports, since it must weigh-in the hours of daytime and darkness in a relative matter. However, for longer time frames (week, month, year), one can choose which metric fits operations best.

Time-Weighted Availability calculates availability based on equal weighting for each day within the reporting period, whether it be monthly or annually. This approach assumes that each day holds equal importance in assessing the system's performance. Time-weighted availability is relatively straightforward to calculate and interpret, making it suitable for general assessments of system reliability over time. Energy-Weighted Availability, on the other hand, assigns different weights to each day based on the amount of energy generated during that period. Days with higher energy production are given more significance in the calculation, reflecting the impact of variations in solar irradiance and weather conditions on system performance. Energy-weighted availability provides a more nuanced understanding of the system's efficiency in converting sunlight into electricity, offering insights into its economic viability and potential revenue generation. In conclusion, solar PV system availability indicator plays a crucial role in ensuring reliable and sustainable energy generation. By distinguishing between technical and operational availability and employing appropriate methodologies such as time-weighted and energy-weighted availability, stakeholders can accurately assess the performance of solar PV systems and make informed decisions regarding their deployment and management. Soltell's solutions include automatic operational availability assessment for distributed solar PV systems, enabling to assess both time-weighted and energy-weighted availability metrics.

Solar solution providers - interested in automatic solar PV availability assessment and measuring PV system performance without the need to install weather sensors at the site? Fill details to receive a demo or contact us.

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