Centralized inverter is generally used in large power plants with uniform sunshine, desert power stations, ground power stations, and other large power generation systems. The total power of the system is large, generally above the megawatt level. Comparison of the main components of photovoltaic power station systems using centralized inverters: photovoltaic modules, DC cables, combiner boxes, DC cables, DC combiner distribution, DC cables, inverters, isolation transformers, AC power distribution, and power grids.
(1) The number of inverters is small, which is easy to manage;
(2) The number of inverter components is small and the reliability is high;
(3) Less harmonic content, less DC component, high power quality;
(4) The inverter has high integration, high power density, and low cost;
(5) The inverter has complete protection functions and high power station safety;
(6) It has a power factor adjustment function and low voltage ride-through function, and the grid regulation is good.
1. Safety issues. The DC combiner box is used in the centralized solution. Due to the built-in DC branch fuse, there is a risk of continuous fire, because the solar panel will be in working condition as long as there is light. Distributed rooftop workshops, it brings serious safety hazards. Not only the economic benefits of the power station itself will be affected, but also other equipment in the plant will be critically affected. A great loss to the owner.
2. For irregular roofs, a single 500KW inverter cannot make full use of the roof area. Inverters are often overloaded or lightly loaded, over-configured, or under-configured.
3. With multiple facing roofs, the solar panels are partially shaded, which leads to inconsistency of the strings. The single-channel MPPT leads to relatively low power generation; at the same time, the mismatch loss of each string will also lead to the loss of power generation.
4. The inverter needs to be maintained by professional engineers. The failure of a single inverter has a great impact on power generation and brings great challenges to the safety of maintenance personnel. At the same time, there are many types of spare parts, and the fault location and repair will take more than 3 days, which will seriously affect Customer power generation revenue. The failure rate of the DC combiner box is high, and it is impossible to monitor each string, which increases the fault location time. Due to the volatilization of the fuse, the failure rate and maintenance cost are high, and regular replacement and maintenance are required; the circuit is complex, and there are many joints processed on site, and the failure rate is high; After 1-2 years of operation of some projects, the effective power generation rate is lower than 90%.
5. The centralized scheme requires an inverter room and corresponding civil engineering and also needs to be equipped with corresponding fans, air ducts, smoke detectors, temperature detectors, and other equipment, and if a photovoltaic power station is installed on the roof of a traditional factory building, its power distribution room is not necessarily A large 500KW centralized inverter can be installed. At the same time, it not only increases the construction complexity but also increases the initial investment and operation and maintenance costs.
6. The centralized inverter needs forced air cooling, and the power consumption of the machine room is large, with an average of at least 300W or more. It needs regular dust removal, fan maintenance, and dust filter replacement.
7. The MPPT voltage range of the centralized inverter is narrow, generally 450-820V, and the component configuration is not flexible. On rainy days and in foggy areas, the power generation time is short.
8. There is no redundancy in the centralized grid-connected inverter system. If there is a failure and shutdown, the entire system will stop generating electricity.