1. What is a photovoltaic inverter?
As an important part of the solar energy system, the inverter is gradually attracting people’s attention. It is a device that converts direct current into alternating current. In solar energy system, it can convert the DC power generated by solar panels into AC power, which can then be used by household appliances. Inverters are also used in a wide range of other applications such as: electronic equipment, industrial applications, radio communication, ships, etc.
2. Some basics and technical parameters of PV inverters
2.1 Power of PV inverter
The unit of power of an inverter is watt, which is the product of current and voltage. For example, consuming 20A of current at 5V and 10A at 10V are the same meaning, they consume the same power. When selecting an inverter you need to choose an inverter power rating slightly greater than or equal to this value according to the total power demand of the load equipment.
2.3 Current of PV inverter
Rated current
The rated current is the current required for long-term operation of the inverter. There are mainly the maximum current delivered by the battery to the inverter, the maximum current output from the battery from the inverter, the maximum current delivered by the PV panel to the inverter, and the maximum current output from the PV panel from the inverter.
Above all, the maximum current flowing into and out of the inverter varies from form to form, and for different types of inverters, it has different ratings for these currents. No matter for which type of inverter and which form of current, the rated current must not be exceeded, otherwise the inverter will be damaged.
Instantaneous current
The transient current of an inverter refers to the instantaneous current surge that occurs during the operation of the inverter. It lasts about 3 seconds over the rated current to return to a smooth current.
2.4 Output voltage and frequency of PV inverter
The inverter can output single-phase and three-phase power.
The voltage of single-phase electricity is 110V 60Hz or 220V,230V,240V, 50Hz, which consists of a fire wire and a zero wire, and is commonly used for household appliances and small commercial equipment. Three-phase electricity has a voltage rating of 380V, 400V, 440V, and a frequency of 50Hz or 60Hz, and it usually consists of three fire wires and one zero wire in a three-phase, four-wire system. It is suitable for large industrial and commercial equipment.
There is also split-phase power, which has a voltage of 240v, 60Hz and is mainly used in regions such as the Americas.
2.5 Load power factor of PV inverter
It is the ability of the inverter to carry inductive or capacitive loads. When the power equipment is purely resistive load or power factor is more than 0.9, the rated capacity of the selected inverter should be 1.2~1.6 times of the power equipment.
2.6 PV inverter fuse
Its role is to cut off the power supply in time when the inverter is faulty and overloaded to avoid the danger caused by circuit overloading.
2.7 Surge protector of PV inverter
Surge protector is to prevent the system from being damaged by lightning or some inductive loads (e.g. refrigerator, air conditioner, washing machine, etc.) generated during startup of the high voltage or high power to the inverter, so when selecting the inverter, the rated capacity of the inverter should be left with sufficient power.
3. PV inverters with different output waveforms
3.1 Sine wave inverter
Sine wave inverters output a better waveform, which is very similar to the AC waveform output by grid companies. All devices sold on the market are designed for sine wave and there are some appliances (microwave ovens, medical devices, computers, etc.), which can produce maximum output only with sine wave power. Sine wave inverters use high-performance control chips and maintenance techniques, and typically provide better quality AC power than the grid. As a result, it is more expensive.
3.2 Modified sine wave inverter
The Modified Sine Wave waveform is more similar to a square waveform; it has one more step than a square waveform. Modified sine wave can be used with most devices (TVs, cell phones, game consoles, etc.), but may reduce the efficiency or power of some devices (high power appliances such as microwave ovens, home air conditioners, etc.).
3.3 Square wave inverter
The quality of AC power output from a square wave inverter is poor and may cause damage to the load and the inverter itself. It has a weak load capacity and is only suitable for use with simple equipment such as tools with universal motors, not for inductive equipment. It is the cheapest.
4. Solar Inverters for different grid connection types
4.1 Grid-tied PV inverters
Grid-tied inverters are used for grid-connected systems in solar energy systems, which are not connected to the batteries first. It can convert the DC power generated by the solar panels into AC power for household appliances and when the load is reached, the remaining power is delivered to the grid company. Therefore, in the event of a power outage, homes with grid-tied solar systems will also lose power unless you have other means of generating electricity.
4.2 Off-grid PV inverters
Power can be supplied to the load in an off-grid system through a solar charging and discharging system, and after the load is fully charged, the remaining power recharges the battery. On cloudy days and at night, the off-grid inverter converts the DC power from the batteries into AC power for home use. It’s surplus power is not delivered to the grid company by the off-grid inverter. So in the event of a power outage, it has little effect on homes with off-grid solar systems.
4.3 Hybrid PV inverter
Hybrid inverter is a collection of grid-connected inverter and off-grid inverter, the electricity generated by solar energy and can charge the battery, but also can send the remaining electricity to the grid company.
5. How to choose the right PV inverter for you?
5.1 Refer to the inverter’s parameters. The inverter will be labelled with its efficiency, power, etc. Refer to the inverter basics listed above to help you find a better inverter.
5.2 Confirm the demand
5.21 Power Requirements. Calculate the total power consumption of household appliances, the amount of power required by the selected inverter should be greater than or equal to the total power consumption of household appliances. Also need to consider whether some appliances will be added in the future, need to reserve a certain amount of power capacity.
5.22 Efficiency. Inverters with high efficiency ratings can be selected to minimize energy loss during the conversion process.
5.23 Size requirements. If you are considering adding solar panels to your solar system in the future, you can upsize the solar inverter for future needs.
5.24 Usage Scenarios and Systems
Determine the scenario in which your inverter will be used and consider whether to choose a grid-tied, off-grid, or hybrid system.
5.25 Cost . When choosing an inverter, you also need to consider the price of the device. Inverters of different brands, powers, and waveforms have different prices. A balance needs to be found between cost and performance. Although the quality inverter is more expensive, but in the long run, it brings good convenience and benefits, but can save the cost.
5.3 Brand after-sales
For some famous brands like Growatt, Huawei, Deye, Solis, etc., their technology is more mature and they have reliable after-sales service.
6. Conclusion:
The performance of the inverter plays a great role in the operation of the solar system. If you are planning to install a solar system, you must carefully understand the types of inverters and their technical parameters, and then consider your needs comprehensively, so as to choose a highly efficient inverter, which can make your solar system operate efficiently and stably.
