What Is The Best Inverter For A Solar Panel System?

Categories: Solar PV Panels.

Where does the best inverter get inserted into a solar powered system? A typical solar power system comprises of solar panels, wiring and the inverter; then add on batteries and regulator/ charge controller. The power generated by the solar panels and batteries is in the form of direct current or DC power. Standard home appliances are run using alternating current, or AC power. In order for the home appliances to run on the solar power, DC power needs to be converted to AC. This is the job for an inverter, which is connected to the house side of the solar panels and batteries.

Best inverter

DC power flows in the circuit in one direction, providing current to power electrical items. It can be used to power up small appliances and small gadgets which store power in their battery, like iPods, and MP3 players. AC power, is supplied back and forth inside the circuit. It is mostly used for running  most household appliances like TV, Refrigerator and Microwave.

A power inverter does the same job as a solar inverter. A solar inverter changes DC to AC so appliances and  gadgets can run on AC power that is sourced from the solar system. You can either use a normal powered inverter in this process or a solar inverter which uses the solar energy itself to convert DC to AC power. A solar inverter is the best inverter for a solar system since the idea behind installing a solar system is to use sun’s energy to the maximum. Inverters today come with several enhanced built-in features like advanced utility controls, data monitoring, systems and applications design engineering.

best inverter

Fig 1.1 Inverter set up in a standard solar system

Types of Solar Inverters

Before making a choice based on knowing your requirements you probably want to know and understand the various types of inverters available in the market. A solar PV system can have one or multiple inverters depending on the size of the photovoltaic system.

There are three main types of inverters used in solar PV power plants:

Central Inverters

These inverters convert DC to AC. They also handle power management from one device that is centrally located. There can be several central inverters in a solar farm but the size of each central inverter will have to be 1 MW and above.

String Inverters

The load of a central inverter is divided amongst multiple inverters using a string inverter. String inverters are small in size as compared to a central inverter. Around 40 of these, 25 kW each, can be used in a 1 MW solar power system.

Micro Inverters

Micro-inverters as the name suggests, are quite small in size. They are attached to individual solar panels. Since they support smaller size solar panels, their capacity can be as low as 240 W each. 

Central inverters are the preferred choice for solar farms due to their capacity. The drawback to these inverters is the high-level maintenance that they require because of their size. String and micro inverters, on the other hand, require negligible maintenance. However, string and micro inverters are expensive when compared to a central inverter on their cost per W.  The central inverter is the best inverter when it comes to large-scale solar installations. For smaller rooftop solar systems, any of the three types can be used.

best inverter

Fig 1.2 String and Central Inverter

Off Grid Inverters

An off-grid solar system, which as the name inplies, is not connected to the national electricity grid.  The inverter gets its DC power from a battery which is charged by solar panels.  In an off-grid solar system, the need for an inverter might not arise if only DC loads are to be powered. Off-grid systems are not required to match the requirements and regulations of the national electricity grid since they are not connected to it. These inverters can be categorised in two variants.

Off-Grid Modified Sine Wave Inverters

The Modified Sine Wave Inverter is the best inverter for simple solar systems and are relatively cheaper. These inverters can be used for old appliances, motors with brushes, and incandescent lights. However, the modified sine wave inverter is not suitable for electronics, induction motors, rechargeable batteries, and gadgets like digital clocks.

If your power needs include appliances like an HDTV or any other appliance that requires a high energy load, then this inverter is not for you. They might the right choice if you have a DIY solar system such as a simple PV system that is used to power the needs of a small rural cabin.

Off-Grid Pure Sine Wave Inverters

The pure sine wave inverter is the preferred choice for large solar system setup although it is on a higher price point. These inverters are the ideal selection for powering electronics, dimmers, and fluorescent lights. Pure sine wave inverters work efficiently with almost all type of off-grid solar systems. The pure sine wave inverters are preferred for larger off-grid solar systems, and they can be used for the smaller systems too.

When deciding on the type of off-grid inverter, you need to take into account the power load your inverter will be handling. For appliances like an HDTV for instance, a pure sine wave inverter is the best inverter. Pure sine wave inverters are available in all sizes from 100W to over 7000W.  They can even take on larger loads in the range of 12V, 24V or 48V systems. Constant technological advancements have led to pure sine wave inverters evolving to come in more versatile versions that are lightweight and easily programmed.
best inverter

Fig 1.3 Sine wave Inverter Functionality

Grid Tied Inverters

Grid-tied Inverters form part of the solar system connected to the grid and work to the utility grid’s requirements and regulations. These inverters transfer your solar generated power to the electricity grid. A grid-tied inverter must generate AC voltage of a strictly sinusoidal form. They are programmed to automatically shut down in case they detect supply loss from the utility. This protects the technicians repairing the utility network from getting an electric shock.

A Grid-tied PV system is made up of solar panels attached to a grid-tied inverter, and can be configured with or without batteries. The inverter converts the DC voltage coming from the solar panels directly into AC power for matching the grid. If batteries are attached to a grid-tied system, then, the power is transferred to the grid after the batteries are charged. Then the power from the batteries can be used at night.

Battery backup Inverters

These inverters draw energy from a battery of the solar system. The battery charge is preserved through a charger. Any excess energy is transferred to the grid. Battery backup inverters can provide AC power during power outages.

Hybrid Inverters

A hybrid inverter operates bidirectionally, converting DC power to AC and then converting AC power for storing in the batteries that power loads at the time of requirement. Hybrid inverters are available in various sizes, features and price levels. These inverters can be grid-tied and use renewable as well as mains energy sources for charging batteries and load-offsetting. Hybrid inverters can be used in urban residential applications as well as remote off-grid home applications.

 In areas where the access to a reliable power grid is difficult, like in some developing countries, hybrid inverters are the best inverter. In the US, hybrid inverters are used for solar systems but they can be used for simply storing energy from the grid into a bank of batteries for self-consumption. The batteries can provide electricity during peak demand/ high cost periods or as a backup power source during emergencies.
best inverter

Fig 1.4  Hybrid off-grid inverter

Tips For The Solar System Inverter Buyer

As a solar buyer, you might consider some of these things when you choose and buy your best inverter:
  • What kind of maintenance will the inverter of your choice require and what will that cost?
  • An inverter should not cost more than 20% of the total cost of the solar PV system. But don’t simply get a cheaper inverter without comparing the features of each type.
  • What is the ‘AC power rating’ of the best inverter?
  • check
    Does the best inverter have MPPT and what is the warranty offered by the manufacturer? Standard lifespan of a good inverter ranges between 10 to 20 years. Most manufacturers provide a warranty cover for at least 8 years. A warranty less than 8 years should be taken off your purchase list.
  • check
    Do you need a single inverter or multiple inverters?
  • check
    Do you plan to expand the solar system in the near future? The best inverter that you select to buy would need to accommodate that future extra load.

The inverter forms an integral part of a solar PV system. Any electrical component in a competitive market will have its advantages as well as disadvantages. These could also be considered before choosing a solar inverter. You can watch the video below to see how an inverter works.

Inverter Summary

A solar inverter can be used for converting DC into AC or topping up your bank of solar batteries. This is the best inverter and will be useful for people who need only a small amount of electricity.

A synchronous solar inverter can be used as effectively by a small home as a large one. Because solar inverters can be manufactured to any size from small to large size those are the best inverters to be used by power companies in solar farms.

A multi function solar inverter is the best inverter for many commercial establishments because it converts DC to AC efficiently and is the most cost effective.

The Future Technology In Inverters

There is a pressing need to have both centralized and decentralized inverter designs. This refers to using multiple inverters throughout a project to achieve higher efficiency while simultneously lowering the cost across the same timeframe. This is happening in the micro inverter set-up in some places. Using three-phase string inverters for a decentralized PV system off grid solution is gaining popularity.

Inverters are the spine of a solar PV system and smart inverters with MPPT are moving to take a larger share of the inverter market.  Soon smart inverters will be matched with the smart grids and smart home technology.

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