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Inverters

Inverters

What is an inverter?

An inverter is an electronic unit or device that changes/converts DC (direct current) into AC (alternating current). In most cases converting DC voltage from batteries to standard household AC voltage allowing the power to run standard household equipment.
DC Voltage is usually lower than AC Voltage which would be equal to the municipal/grid supply voltage of 120 volts, 240 volts or 400 volts(@3phase). – dependant on the country.
The specifications of the Inverter such as input/output voltages, frequency ranges and general power control are dependent on the design of the equipment by any given manufacturer and will vary on the application.

Why would I need an inverter?

Inverters are a great solution for an alternative power source.
In situations where constant power cuts and fluctuations are a problem or there is a need to be more self-sufficient/sustainable, moving in a ‘greener’ energy direction, there are different types systems that can be configured with inverters to accomplish that goal and provide a solution to the problem.
Inverters are not only for home or residential use, there are many companies and businesses that use inverters combined with batteries and solar panels to create a sustainable power solution or to simply have that back up power in a time of need.
Other applications can include but are not limited to:
Off grid power supply for isolated buildings, camping trailers, caravan power supply, back up power solutions, portable power solutions, Boats and many more.
Inverters are not only used as a back up solutions. Certain inverters can be used as UPS’s (uninterruptible power supply) – controlling or rectifying voltages and frequencies for sensitive equipment that may not have a high tolerance for voltage and frequency fluctuations.

How do I know what inverter I need?

There are many different types of inverters in the industry all having their own Pros and Cons.
unfortunately there is no real one size fits all. There are a few key points to consider when you are trying to figure out what is going to best suit your requirements:

• Power consumption

You need to consider your power consumption. There are a few different ways to check this such as looking at your average usage on your electricity bill, using a clamp meter(to read the drawn current in AMPS) or running a data logger on the suppling DB board which will monitor the voltages as well as the current being drawn through the DB board and will place it in a graph. This will allow you to see the peeks and lows and specific times through out the course of a specified time period.
Using a Data logger is often considered one of the best and most accurate methods of checking your usage, but not everyone has a datalogger laying around and some electricians may charge a fee to run the diagnosis.
If you are not able to get a data logger using a clamp meter on the DB board is still an option, it is best to run all the equipment that you would like to have powered by the inverter to assess the max current draw.

NB: it is important to keep in mind that the more energy efficient your household runs e.g. using LED lighting, Gas stoves/ovens, gas geysers or solar geysers and smarter appliances(many new appliances on the market run inverter technology and often draw less power) the more cost effective the system will be. The more power you needed to supply will determine the size of the inverter needed in turn raising the cost of the inverter and power storage solutions.

• Budget

There are so many different brands and designs of inverters. Considering your budget will allow you to determine the quality of the inverter and or system you would like to have powering your household. As they say you get what you pay for, it is important to remember that there are smaller companies building less expensive equipment that still has what it takes to get the job done. Bigger is not always better – that is why checking your power consumption is one of the most important key points – it will help you determine exactly what you need. Eliminating overspending on equipment that may be overqualified for the job.
Pay back period is also something that can be kept in mind and calculated to help decide the sort of costing out lay you would be willing to provide to get what you need – considering the fact that solar panels and batteries are going to be needed to run a back up or supply system – the bigger cost is often power storage – i.e. Batteries.
There are also financing solutions that can be considered – most part for companies and businesses however there are some financing solutions being offered for the residential market.

• End goal – Planning ahead

When making decisions on the correct inverter to purchase, it is very important to consider the future. Making provisions for what may lay ahead of you is always a good idea – prevention is better than cure!
Whether you are looking to have a small back up system to get you through those power outages, be self-sustainable or cutting down cost of electricity usage, there are various inverter designs that allow for expansion. e.g. you may start off small and want to grow to a point where you no longer need to have council/municipal power being supplied to your premises. Some inverters allow more than one unit to be connected to the system increasing the overall power output for instance you may purchase a 5kW/5kVA inverter and at a later stage purchase an additional 5kW/kVA inverter, some manufacturers allow for parallel operation and the equipment will communicate with each other running in a configuration of master and slave – the master inverter will supply the bulk of the power until such point that the demand exceeds the max output and will subsidise additional power for the demand from the slave unit.
Cost of inverter in turn will be dependant on capability and build quality. That is why planning ahead is important, should you purchase an inverter that is not able to be paralleled then you may end up spending more money for a much larger inverter to supply your needs and have smaller inverter that you may not be able to re-use or resell etc.
Not only do you need to consider the size of the inverter, you need to consider the capabilities of the inverter – the amount of input power from batteries, solar panels and other equipment will play a important roller in making a decision on your purchase.

Types of inverters

There are different types of inverters for different solutions.
The basic types of inverters are:

• Grid tied inverters

Grid tied inverters are usually connected to the incoming source of power from council or municipality. In certain countries, they allow feeding power back to the grid which in turn would credit units or points that you would be able to use without being charged as you would have them credited to you – in short you would be selling power back to the grid. Power would be supplied to the inverter via Solar panels generating power from the sun during the day. Feeding back to the grid is not currently an option in South Africa as feeding back to the grid through a prepaid meter for example would still deduct your units as the current meters do not measure the direction of flow and this would just be costing you money and does not make sense. There is talk about feeding back to the grid to assist the country’s power constraints becoming a possibility, however, has not been confirmed.

In grid tied solutions you do not have to supply power to the grid – in some cases the inverters will not allow it or may not have that capability.
The inverters accept grid power incoming and being coupled solar panels and batteries would allow you (case specific and inverter specific) to prioritise the power usage from the inputs to the inverter, one example: Solar first, batteries second and lastly supplement with grid power. During the day you would be generating power from the sun through the solar panels and using this to supply power to the loads being drawn from the inverter and as well as charging the batteries – granted that there are enough panels with the capacity to do so. If the solar is insufficient your batteries would then pick up the slack and lastly grid to supply, should it be required. These configurations can be changed to suit your specific need or setup.

In a nutshell a grid tied inverter is essentially connected to a grid power source and solar panels with batteries to provide storage.

• Stand-alone Inverters

Stand-alone inverters are typically used in remote locations where grid supply is not available – therefore would be coupled with solar panels, wind turbines, generators, hydroelectric turbines and/or batteries (again inverter specific) to generate power supply to the applications needed.
Stand-alone inverters would function similarly to grid tied inverters as stated only without the grid or council power supply.
Applications for these would typically be used for borehole pumps, remote housing, sewage treatment plants that are isolated, camping, caravans, and boats along with many others.

Sine Wave, Modified Sine Wave and Square Wave

Although we have grid tie and stand-alone inverters, inverters are also categorized by a definition of sine wave.

What is the difference between Sine Wave, Modified Sine Wave and Square Wave

Sine Wave (also known as “pure or true sinewave”)
Sine wave is what is provided from your utility company from a generator (power generators at power stations). Sine wave is generated from the Ac rotations of machinery such as alternators or power generators. A smooth S shaped waveform is generated. Almost all the equipment or appliances sold in the market are designed on the basis that they would run on Sine Wave. Using a Sine Wave inverter would allow the equipment being powered from it to run at its full specification/potential that it was designed to.

Modified Sine Wave

Modified Sine Wave inverters have a waveform that is not as smooth as a pure sine wave as it is slightly stepped. Most equipment will run off a modified sinewave inverter however may draw more power from the inverter due to lowered efficiency. This will affect some equipment negatively should they have less tolerances for frequency fluctuates e.g. clocks may run faster if connected to the power source, fluorescent lights may not operate as bright and variable speed control could be affected in such a way that they would only switch on and off with out any control on the variation on speed. The waveform is not as smooth as the Pure Sine Wave.

Square Wave

Square wave inverters are not common however they will be the cheapest.
Square Wave inverters would run simple tooling and equipment such as drills, universal electrical motors and pumps and not very much else. As the name suggests, the waveform is square.

Single Phase (230VAC) or Three Phase (400VAC)

The choice of single-phase or 3-phase will be decided by the equipment you are running and the power supply from your utility company.
Many residential properties run off single-phase power. 3-phase may be implemented should the current be too much off the single phase and be required to split the loads drawn between multiple phases such as 3 Phases. Majority of commercial and industrial properties run off 3-phase power.
There are 3-phase inverters available on the market although majority would be single phase.
various manufactures or brands allow the single-phase inverters to be joined in parallel.
3-phase could then be achieved by connecting 3 x single-phase inverters in parallel to provide 3-phase power. Essentially, 3-phase is split into 3 x single phases with 1 neutral and 1 earth.
The capability of paralleling of inverters would need to be confirmed upon designing of the backup system.

Moving Forward

Inverters along with solar panels and batteries will help drive a greener future with cleaner and more sustainable solutions to the generation and storage of power and electricity.
As technology advances more it will become more cost effective to get involved with these solutions. This will pave a clear way forward to a better and healthier living and assist in lowering the impact of fossil fuels on our environment.