A solar string inverter is a device used in photovoltaic (PV) systems to convert the direct current (DC) electricity generated by solar panels into alternating current (AC) that can be fed into the commercial electrical grid or used onsite.
Introduction
String inverters are connected to a string – or series – of solar panels in an array. They convert the DC output from each panel string into grid-compliant AC power.
String inverters offer efficiency ratings of up to 98% and advanced safety features. However, they can only handle a limited number of PV panels in each string. Multiple parallel strings are required for large solar arrays.
String inverters emerge as a balanced compromise between lower-cost central inverters and higher-efficiency microinverters for commercial and utility-scale solar projects in the UK.
Key Features and Benefits
Efficiency
String inverters achieve high conversion efficiency, with the best commercial units rated between 97-98%. This minimizes power losses during DC to AC inversion.
High efficiency means maximum solar energy harvest and revenue generation from a PV system over its lifetime.
Reliability
Proven solid-state designs ensure string inverters operate reliably for decades in outdoor environments. Manufacturers typically provide 10 year warranties.
Built-in surge protection and weatherproof casings offer robust operation in harsh conditions. Top brands undergo rigorous testing.
Monitoring and Control
String inverters come equipped with smart interfaces, data logging and remote monitoring capabilities. This enables optimized system performance and timely fault detection.
Advanced units feature power curtailment when needed and integration with smart grids. Remote firmware upgrades are also possible.
Safety
Certified string inverters have anti-islanding protection to prevent hazardous back-feeding into the grid when power is down. They also minimize DC leakage risks.
Fused string connections, isolation transformers, and earth fault interrupts provide multiple levels of shock hazard protection.
Cost
While more expensive than central inverters, string inverters cost 60-70% less per watt than microinverters. They offer a cost-effective balance for mid-range PV systems.
Easier installation and higher generation offset potentially higher upfront costs.
Limitations and Challenges
- String inverters can only handle a limited number of panels in each string, based on the DC voltage and current rating. Typically up to 30 x 330W panels in each 3-phase string.
- Multiple parallel strings are required for large solar arrays, increasing complexity. Central inverters are better suited for very large utility-scale systems.
- Shading or failure of one panel impacts the output of the entire string. Module-level electronics offer better optimization and redundancy.
- String inverters are not compatible with all panel technologies. Manufacturer and model selection is important.
For mid-scale commercial and industrial solar projects in the UK, string inverters provide an optimal balance of high performance, safety, and cost-effectiveness. They maximize solar energy yield while minimizing project costs. With smart capabilities, string inverters form a flexible platform for grid integration. When properly designed and installed, string inverter systems deliver outstanding lifetime value to British solar power plant owners.
