How To Choose The Right Photovoltaic Inverter

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For most of us out there Solar Power seems like a complicated concept to grasp. The notion that we can produce electrical power from sunlight is quite a cool thing but to understand how it works and the different components that make up a solar power system are something else. The inverter is probably the most important component of a solar power system.

 

The inverter is really the brains behind the whole solar power system acting as the central hub and it serves different functions. Here we look at what an inverter does and the different types of inverters available.

 

What Does an Inverter Actually Do?

At its most simplest form an inverter converts DC power to AC power and here we thought AC/DC was only the name of a rock band. DC otherwise known as direct current is an electric charge that flows only in one direction. AC or Alternating Current, on the other hand, is an electric charge that periodically changes its direction. The voltage in AC circuits also periodically reverses because the current changes direction.

 

Most homes are wired for AC yet many of our appliances actually use DC such as our flat screen TV sets, Cell Phones, Ceiling Fans, Alarm Systems, Telephones etc. AC Power can be produced by means of an alternator. AC also comes in different wave-forms such as Sine Wave, Square Wave and less frequently the triangle wave. The AC power we find in our homes though is the Sine Wave.

 

Most buildings including our homes are wired for AC, this is because AC is used to transmit electricity over vast distances from power stations.  Generating and transporting AC across long distances is relatively easy. At high voltages (over 110kV), less energy is lost in electrical power transmission. Higher voltages mean lower currents, and lower currents mean less heat generated in the power line due to resistance. AC can be converted to and from high voltages easily using transformers.

 

AC power is also used in powering of electric motors. An electric motor and AC generator are effectively the same thing. Just that the electric motor converts the electrical energy to mechanical energy.

 

What about DC though?

 

DC is current that flows in one direction only.

 

Energy stored in batteries uses DC as well as electric vehicles.

 

Renewable Energy generators such as the Solar Power system on your roof also generates power in DC.

Why do I Need an Inverter for My Solar Panels?

A Solar PV inverter is the gateway “between the photovoltaic (PV) system and the energy off-taker”

At its most basic function, an inverter converts DC power to AC power. Whether the Solar PV system is a 5kW system or a 5MW utility installation, the same applies. Solar PV inverters have advanced technologically over the years. They no longer just convert the DC power to AC power but also provide other functions such as ensuring the system operates at the optimal performance level. This is done by providing services such as data monitoring, advanced utility controls, applications, and system design engineering.

 

In case something goes wrong with your solar power system, through the inverter monitoring system one should be able to pick up that is something has gone faulty.

 

Inverter manufacturers also provide post-installation services that are integral to maintaining energy production and a high level of performance for the project, including preventative maintenance, O&M services and a quick mean time to repair (MTTR).

 

How Do You Connect Solar Panels to the Grid?

Solar Panels that are installed on the roof are connected to a Solar PV inverter and this in turn is wired to the AC mains of the building.

 

The grid-connected Solar PV inverter then converts the DC power produced by the Solar Panels into 240V AC power. This power is used internally in the building for appliances etc and the excess power is then either used to charge an energy storage system if available or the Solar PV inverter feeds this excess power into the grid.

 

Most utility’s have set standards for grid tied Solar PV systems. Inverter manufacturers have to abide by these standards when developing Solar PV inverters. Some of these standards include minimum quality power requirements and frequency bands.

 

What’s the Difference Between a PV Inverter and a Hybrid Inverter?

Solar PV inverters are the most common and cheapest of Solar PV inverters. Whereas hybrid inverters combine both a solar PV inverter and battery inverter. This could be for an Off-Grid application or for a grid tied Solar PV system with an energy storage solution to provide increased self-consumption.

 

In the past one would require a Solar PV inverter and a battery inverter. The purpose of the battery inverter is to convert the AC power from the Solar PV inverter to DC and charge the batteries effectively ensuring the batteries are sufficiently charged and not over or undercharged.

 

These battery inverters would also manage the distribution of the Solar PV energy and energy stored in the battery system. Ensuring the electricity generated by the Solar PV system is used efficiently as possible within the facility. Whether it be providing power to internal loads or charging of batteries or even feeding excess power into the grid.

 

With advances in technology in recent years though, both Solar PV inverters and Battery inverters have been combined into a single unit in what is known as a Hybrid inverter. Hybrid inverters are more cost effective than purchasing a Solar PV and a seperate battery inverter.

 

How to Choose an Inverter

Now choosing an inverter needn’t be a complicated affair, even though there are literally hundreds of Solar PV inverter suppliers out there. There are a few basic pointers to be aware of before making that all important decision. If you are opting for a purely grid-tied Solar PV inverter then choosing the right inverter is even simpler.

 

The inverters AC output power should be matched to the Solar PV array. A Solar PV arrays Standard Test Conditions (STC) power rating will provide a good idea of the minimum size of the needed inverter. A typical example of this is the standard size Solar PV system for an average sized home of 5 kW. A 5 kW Solar PV array will require a grid tied inverter with about a 5 kW power output.

 

It is possible to undersize an inverter by 10 to 20% should local climatic conditions prevent the STC from being reached. In colder elevated locations that are sunnier though it might be necessary to oversize the inverter slightly. An oversized inverter will also allow for future expansion.

 

Another thing to look out for is the DC Voltage Input Window. This is the voltage range that the inverter will accept from the PV array. Local climate data and temperature coefficients will determine the maximum and minimum expected voltages. Exceeding the inverters voltage range can be exceptionally dangerous. As it may damage the inverter or worse cause an electrical fire.

 

Grid tied Solar PV inverters also use MPPT or Maximum Power Point Tracking. This feature enhances the power output of the Solar PV array. Some grid tied Solar PV inverters have multiple MPPT’s. This allows one to configure multiple Solar PV arrays in different orientations and maximise solar energy harvesting.

 

It’s also important to consider a quality Solar PV inverter with a good track record in terms of quality and after sales service. Spend a little time doing your homework researching different Solar PV inverter suppliers.

 

Conclusion

An inverter is a vital component of any Solar PV system. It’s the brains behind the Solar PV system that manages the power generated from the Solar Panels. It’s primary function is to convert DC power to AC power. Solar PV inverter technology has advanced in recent years to also include such functionality such as power performance monitoring, advanced utility controls, applications and system design engineering.

 

Hybrid inverters combine both Solar PV inverter technology and battery inverter technology. Not only converting DC to AC power but also manage the charging and discharging of energy storage systems. Hybrid inverters are also more cost effective than having a seperate Solar PV inverter and battery inverter.

 

When selecting a Solar PV inverter one needs to take into account the size of the Solar PV array or arrays, the DC voltage window and how many MPPT’s does the Solar PV inverter support. It’s always better to select a high quality inverter that will bring years of hassle free service.

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