December 29, 2016

Home Power Generation: The Inverter.

According to the Australian Bureau of Statistics (ABS) year book for 2009-10, most of Australia’s carbon dioxide emissions occurred due to the burning of fuels. In 2007 this figure sat just over 81% with energy industries contributing 60% of these CO2 molecules.
At the core of these numbers sit coal-fired power stations. Road transport, in comparison, contributed just 18%. The heartening thing is that there are alternatives, and as technology advances we’re seeing the home as an important part of change. In this series we’ll take a peek at what components are available to the home owner to make yourself a little less dependent on the grid.

So today we’re going to begin with the core of all alternative energy setups – the inverter – the magic box that makes the harvested energy ready to come out of your power points. Nice.

To begin with  it’s worth taking a quick peak at the two basic flavours of electricity. The first being direct current or DC. Batteries pump this version of the sparky stuff out into all manner of gadgets. As a happy coincidence, solar panels supply the same thing. In the proverbial nutshell, DC electricity sends power in one direction, say at 12 volts. One wire will be the ground, or zero volts, and the other end will be at a “constant” voltage – just like a hill has a high point and a low point.

The other form of electricity is the alternating current or AC.

You’re probably reading this courtesy of the wonders of the national grid and the AC electricity that it supplies. With AC power, instead of the one way traffic of DC power, you get a two-way flow or an alternating positive and negative. This alternating happens many times per second – in Australia we run at 50 times per second – otherwise noted as 50 Hertz (Hz). So how do we change the electricity coming from our solar panels on our roof – remember this is a DC voltage and our Playstation runs on 240 volt AC?

Enter the inverter.

But what fundamental bits of information do you need when shopping for the ideal inverter?

What is it?

Australian general manager for Conergy, David McCallum, explains. “Solar PV (photovoltaic) panels produce low voltage DC electricity. The inverter converts this into AC electricity needed to supply power for standard appliances and to be fed into the grid”.

 

How does the homeowner calculate the right size for their inverter?

Chelsea Sneyd from Beyond Building Energy reckons the inverter buyer should consider a couple of things first:

  1. Is their power usage likely to change in the future?
  2. Do they want to allow for future expansion (of their PV system)?

Chelsea elaborates by warning that while an inverter may work for a family today it may not in the future. Power price hikes, that new spa with its big pump, a new air-conditioner, or even a new baby all add to your home’s power requirements. In a nutshell, do you spend more to future proof or make do with a smaller system?

A great starting point to find out the size of inverter (and the system as a whole) needed is to take a look at your electricity bill. You can then adjust the energy requirements up and down from here – remember that as your solar setup increases in capacity so too does the initial cost. On the other hand if you under-size the system you’ll have to rely more on the electricity companies to keep the lights on.

Do inverters have to be matched to the solar panels on the roof?

This can be a complicated question to answer. The simple answer is yes. Chelsea tells us that “a solar power system must allow for the right combination of panels and inverter. While installing less than the inverter capacity will still create a functional system, installing over the capacity will make the extra panels redundant”.

David from Conergy ventures into more daunting territory by explaining that “every (PV) module has an off-load voltage (e.g 36.8 volts). If you put ten of these modules in a string you will get a total off-load voltage of 368.7 volts for this string. The string voltage must not exceed the maximum DC voltage (rating of the inverter) but should be not much less than this value”.

David warns that an underrated pairing (string voltage too low) could mean lower efficiency in your system or a system that may not want to turn on at all. On the other hand an overrated pairing could see your inverter damaged or destroyed due to too high a voltage when the sun really gets shining.

What do we recommend?

Speak to the experts. Don’t be shy. The dollars involved in your investment more than warrant a visit to a guru. They’ll talk to you about MPPT or Maximum Power Point Tracking and other such features that allow your inverter to get the most out of the solar cells attached to the system.

What pitfalls should I look out for when I buy my inverter?

Both Chelsea and David list a great warranty as their number one feature. Chelsea continues, saying that “since the inverter has a life span of 25-30 years you want to make sure you are protected”.

David from Conergy recommends the use of a highly efficient (>=97%) inverters to reduce unnecessary losses and to maximise the power output. In other words, a lousy inverter can waste a lot of the harvested energy. Buy something more efficient and you’ll keep more of the electricity rather than burning it up as heat.

Chelsea, from Beyond Building Energy, list other features to look for:

  • Anti-islanding technology for inverters feeding power back to the grid – this is a super important feature. Simply put, the inverter shuts down in the event of a black-out to stop it feeding power back into the grid. This stops your system from frying the local power company workers as they try and restore the power.
  • Look for a good IP rating – All this means is that the higher the IP or Ingress Protection rating the better your expensive inverter is at surviving rain, hail or dust-storm.
  • Look for a trusted brand. Chelsea recommends that you “research what solar retailers use”.

Should the homeowner grab one of those deals they see in the newspaper?

David reasons that the buyer should “always consider the reliability, the financial backing, the warranty, and the overall quality if both system and service”.

David also cautions that buyer beware when buying from a retailer that imports products without direct connection or ownership of the manufacturing of the product?

Chelsea agrees and recommends the buyer:

  • Choose a company registered with the Clean Energy Council.
  • Be wary of fly-by-nighters – “companies that set up to make a quick buck” and leave behind “shonky installations and customers left out of pocket”.
  • Be aware the deal may not include installation and have other hidden costs.
  • Find out if the installation itself is warrantied, not just the components.
  • Make sure the installer is licenced and accredited.
  • Ask if the components are approved for Australian use.
  • Be aware of all payment terms.

What’s on the horizon for inverter technology?

Like any technology, the solar industry is evolving and advancing, but most of the media attention is focused on new solar panel technologies. See through, spray-on, solar roof tiles, and higher efficiencies all garner the word counts in the broadsheets. What about the inverter?

Just like Watson was to Sherlock, the inverter is there to make the solar panels look good. To do this we’re seeing amazing advances like:

  • Greater input voltage ranges.
  • Remote tracking of your solar power system – yes, there’s an app for that.
  • Higher efficiencies (>98%).
  • Transformerless.
  • Bluetooth communication.
  • Advances in MPPT (Maximum Power Point Tracking) including multiple trackers to track multiple strings of solar panels.

Can I use my inverter to convert power from my solar cells as well as my wind generator?

Unfortunately no is the answer from David. He says “it is not possible to use one inverter on both a wind turbine and a PV array. Additional equipment is required to control the inverters for each input technology and the overall system. Either multiple grid connections or a system controller are required”.

Final words from the experts?

David from Conergy says “quality is important for longevity, confidence, and output of any system.

Chelsea from Beyond Building Energy reinforces research, “talk to your neighbours and friends who have solar and listen to their experience”.

So, anything else?

Of course. There’s always more. The key is to talk to the experts. Gather your questions, and don’t sign on any dotted line until you’ve covered everything.

If your budget says yes, stick with brands that have been around for some time and have service backup in the region you’re living in. You’ll regret installing a system bought from eBay that’s shipped from Hong Kong and your closest technician is 3000 kilometres away.

Remember that a solar system is an investment over 20 plus years. Make sure your inverter is up to the task and it’ll look after you.

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