While the deployment of photovoltaic (PV) systems has grown exponentially over the past 10 years, solar energy still powers only a small percentage of the grid. What has kept solar power systems, a clean form of energy, from powering a larger percentage of the grid worldwide? Concerns over cost ($ per Watt) and efficiency have prevented adoption of PV systems on a larger scale. When developing new solar technology (solar inverters, power optimizers, etc.), a system designer must increase efficiency through intelligent system and subsystem topologies that also decrease the cost per Watt.
Figure 1. Photovoltaic array
The efficiency of PV systems is dependent on the power conversion subsystems and real-time monitoring of PV modules’ power. Traditionally, both functions occur within a solar inverter, allowing system architects to design highly efficient power conversion stages while enabling multi-string level power monitoring. As the number of PV strings increase in one PV array and its power capacity increases to 50 kW or greater, it is necessary to combine the PV strings into a high voltage Direct Current (DC) bus before the inverter. This system is known as a solar combiner box. The solar combiner box reduces the total system cost by decreasing the external cabling and copper DC buses. The solar combiner box also provides a location for a manual safety discount switch required by regional standards for PV system installations.
As the PV array size increases the efficiency becomes an even greater concern. As more panels and strings are monitored by one current sensor, a minor failure in one panel can remain undetected until the damage is unrepairable. While the failure is undetected, the solar panel cannot operate at full capacity, and the PV system is operating at a reduced efficiency. Once a failure is detected, technicians have to search within multiple strings for the damaged solar panel. Cost effective, string level current sensing lowers the cost per Watt by decreasing the system downtime and the equipment replacement costs.
In order to increase the granularity from multi-string level monitoring to string level monitoring, the solar combiner box became the smart combiner box when current and voltage sensing and monitoring technology was integrated. Beyond this “smart” technology, current and voltage sensing, a smart combiner box consists of one additional key feature: over-current protection. Each string is disconnectable from the entire solar power system if there are safety concerns or reason to believe that equipment could be further damaged, saving future equipment replacement costs. Figure 2 is a visual representation of a PV system with a smart combiner box.
Through accurate high-side current sensing, the smart combiner box decreases the system cost and increases the system efficiency. Texas Instruments offers a wide range of isolated and non-isolated solutions for current measurements, including Fluxgate sensors, Hall effect sensors 100A Closed-Loop Current Sensor Reference Design Using Bi-Polar Supplies (TIPD184) reference design, and current shunt monitors 40V to 400V Unidirectional Current/Voltage/Power Monitoring Reference Design (TIDA-00528). These solutions can best meet accuracy, cost, and current-range requirements for high-side current sensing in smart combiner boxes.
- Visit a recent blog post on "Enabling a more efficient, secure and resilient grid" by Kripa Venkat.
- View the new Systems Made Simple: Solar Inverters training videos about solar inverters.
- Download TI's Smart Grid & Energy Solutions Guide.
- Check out the following TI Designs reference designs related to photovoltaic and smart grid design:
- Isolated Current & Voltage Measurement Using Fully Differential Isolation Amplifier Reference Design (TIDA-00555)
- Shunt-Based AC/DC Current and Voltage Sensing for Smart Grid Applications with Reinforced Isolation (TIDA-00080)
- Multi-phase Energy Measurement with Isolated Shunt Sensors Reference Design (TIDA-00601)
- Extended Current and Voltage Measurement Using Shunts for Protection Relays Reference Design (TIDA-00738)
- Contactless AC-Current Sensing Using a Hall Effect Sensor (TIDA-00218)
- ±100A Bus Bar Current Sensor using Open-Loop Fluxgate Sensors Reference Design (TIPD205)