The PV panel system converts solar energy into direct current, so it is necessary to have direct current converters from PV panels into alternating current to connect to the system. Inverter is the device used to perform this role. The principle of the inveter operation is the DC inverter and the grid frequency as a sample.
Hình 1. Sstring inverter
The reasons for choosing Inverter are as follows:
– Connection diagram of the factory
– Maximum capacity of the PV string
– Inverter performance
– Reasonable price
– The rated power used is suitable for minimal installation, highest efficiency with the lowest investment costs
– Reliability and prestige of the manufacturers, suppliers.
For solar power systems, especially those with large to very large capacity, the use of centralized solar power solutions brings back better and more efficient operation than the use of distributed soalr power solutions.
Using centralized solar power solutions allows:
– Minimizing connection, reduce the equipment layout area by reducing the number of inverters used for the system;
– Reducing DC and AC losses;
– Allowing the centralization of management, operation and maintenance;
– Reducing the cost of system construction investment;
With the current technology, manufactured inverters can be paired synchronously with step-up transformers to reduce AC losses. Some well-known brands are trusted to supply to solar power plants such as: SMA, ABB, TMEIC, Schneider, ….
Hình 2. Central inverter
Inverter technology according to the design voltage level
Using this inverter type allows max DC voltage input of 1000V, which corresponds to PV panels with insulation voltage of 1000VDC.
General comments for 1000VDC technology:
+ Using PV panels with 1000VDC insulation then the price of PV panels is reasonable, common and easy to choose;
+ The maximum capacity of inverter is no more than 2500KVA, except for the case of integrating a working model in the house with multiple inverters (such as ingeteam). In which 1000kVA is relatively common;
+ Cheap, popular inveter, suitable for small to medium capacity plants (100MWp and below);
Using this inverter type allows max DC voltage input of 1500V, which corresponds to PV panel with 1500VDC insulation voltage.
General comments for 1500VDC technology:
+ New manufacturing technology, introduced in early 2016;
+ Saving wiring costs and losses when using high voltage;
+ Saving installation space;
+ High performance;
+ Allowing working even ordinary panels (1000VDC technology).
+ Using PV panels with 1500VDC insulation, the price of PV panels is high (higher than conventional ones from 3cent-5cent / Wp), difficult to choose panels due to the unpopularity;
+ Inverter and transformer substation up to 5,500KVA, saving connection costs and transmission lines, easy for operation and maintenance;
+ Currently, 1500VDC technology is strongly supported by manufacturers with competitive prices and when 1500VDC PV panels become popular, the selection of 1500VDC inverter will be come general trend.