STRING INVERTERS

What is an Inverter?

An inverter can be defined as it is a compact and rectangular shaped electrical equipment used to convert direct current (DC) voltage to alternating current (AC) voltage in common appliances. The applications of DC involves several small types of equipment like solar power systems. Direct current is used in many of the small electrical equipment such as solar power systems, power batteries, power-sources, fuel cells because these are simply produced direct current.

The basic role of an inverter is to change DC power into AC power. The AC power can be supplied to homes, and industries using the public utility otherwise power grid, the alternating-power systems of the batteries can store only DC power. In addition, almost all the household appliances, as well as other electrical equipment can be functioned by depending on AC power.

In some cases, generally, the input voltage is lesser whenever the output voltage is equivalent to the grid supply voltage of either 120 V otherwise 240 V based on the country. These devices are standalone devices for some applications like solar power. There are different types of inverters available in the market based on the switching waveform shape. An inverter uses DC power sources to provide an AC voltage to giving the supply to the electronic as well as electrical equipment.

Solar Inverters

A solar inverter helps in converting the direct current into alternate current with the help of solar power. Direct power is that power which runs in one direction inside the circuit and helps in supplying current when there is no electricity. … Solar inverters are also called as photovoltaic solar inverters.

Working Principle of a Solar Inverter

The inverters work by taking in power from a Direct Current (DC) Source, i.e., the solar panel. The power is generated in the range of 250 Volts to 600 Volts. DC power is converted into AC power by the inversion process taking place in the inverter. This process of DC to AC Conversion is achieved by using a set of solid state devices like Insulated Gate Bipolar Transistors (IGBT’s.). These devices when connected in a typical H-Bridge arrangement oscillate the DC power thereby creating AC power.

A step up transformer is used in between the devices. At this stage, the AC power output is obtained, which is either consumed by the local loads or can be fed to the grid. A few manufacturers have started manufacturing transformer-less inverters which have higher efficiencies as compared to inverters having transformers.

In any solar power inverter a micro-controller chip is present which is programmed to execute various complex algorithms in a precise manner. The controller maximizes the power output from the photovoltaic panels through the Maximum Power Point Tracking (MPPT) algorithm.

Components of a Solar Inverter

Capacitors – are used to filter ripple contents (undesirable phenomenon due to semi-conductor switching) on dc lines. It is also be used to keep the dc bus voltage stable and minimize losses between the PV array and the inverter.

Software and monitoring – the software designed to run on the inverter’s digital signal processor or microcontroller. Data monitoring is important since it lets owners and installers know its status and provides quick alerts if there are any faults.

Solid state switches – they are basically a combination of power semiconductors – IGBTs, Metal Oxide Semiconductor Field Effect Transistor (MOSFETs) or both in some cases – to invert dc to ac power.

Magnetic components – these include the inductor and the transformer to filter the wave shapes and smoothening them, and bring ac voltages to the correct levels for grid interconnection. They also provide isolation between the dc circuits and the ac grid.

Solar Inverter Advantages:

After knowing in detail what a solar inverter is and how different useful it is to make appliances work at residential and industrial levels we must discuss about the many advantages of the device.

• Solar energy has always helped in reducing global warming and green house effect.

• Also use of solar energy helps in saving money many people have started using solar based devices

• A solar inverter helps in converting the Direct current into batteries or alternative current. This helps people who use limited amount of electricity.

• There is this synchronous solar inverter that helps small homeowners and power companies as they are large in size

• Then there is this multifunction solar inverter which is the best among all and works efficiently. It converts the DC power to AC very carefully which is perfect for commercial establishments

• This inverter is cost effective i.e. less expensive than generators

• Apart from solar inverters there are other devices too that make use of solar energy namely, solar cooker, heater.

• Solar inverters are the best way and they are better than the normal electric ones. Also their maintenance does not cost much money

Solar Inverter Disadvantages:

• Initially you need to shell out a lot of money for buying a solar inverter

• It will work effectively and produce direct current only when the Sunlight is strong.

• The solar panels that are used to attract Sunlight requires lots of space

• The device can work efficiently only if the presence of the Sun is strong.

• Solar Inverters can work when there is no Sunlight but provided their battery is charged fully with the help of Sunlight.

Types of Solar Inverters –

1. String Inverters

These are the most common type of inverter used for residential purposes. All the solar inverters above are basically a string inverters. It is called a string inverter because there is a large number of strings are connected on them.

String inverters

A string inverter is the type most commonly used in home and commercial solar power systems. It is a large-ish box that is often situated some distance away from the solar array. Depending on the size of the installation, there may be more than one string inverter present.

Leading string solar inverter brands are Sungrow and SMA.

String inverter advantages

 Allows for high design flexibility
 High efficiency
 Robust
 3 phase variations available
 Low cost
 Well supported (if buying trusted brands)
 Remote system monitoring capabilities

1. Smaller in size when compared to central inverters
2. Better MPPT capability per string
3. Scalability for future expansion by adding parallel strings
4. Short DC wires
5. Monitoring at string level