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Home battery choices

The hills are alive with the sound of people talking about installing a home battery.  Batteries regularly pop up in the media with reports of Aussies taking to this technology like ducks to water.  Tesla and the South Australian government installed a whopping big battery. It’s busy smoothing out wrinkles in that state’s power supply.

We dipped our toes into this particular pond with a solar panel and battery system that powers our construction site.  Although the load increased when frame construction started, the system continues to meet their demand.

Advice for anyone considering a home battery.

Adding a home battery to a solar power system on the roof

Last year the NSW Government came to the rescue of enthusiastic amateurs, like me, who are interesting in a home battery.  They published the NSW Home Solar Battery Guide. The name says it all.

This is an easy-to-read booklet which covers the basics in digestible chunks.  I liked the step by step approach through what can be a technically challenging subject.  Key sections included:

  • Understanding energy use around the home.  Are there alternatives to installing a battery?
  • Battery basics and how to design a home power station (solar panels + battery)
  • Estimating potential return on the investment
  • Battery maintenance

I recommend anyone considering buying a home battery reads this booklet first.

Why are we installing a home battery?

Being asked why we want to install a battery does focus the mind on reasons for our decision.  “Just cos” is a bit glib.

Making the decision to purchase a home battery

We started out thinking that going “off-grid” in the suburbs was a way to be truly sustainable.  With enough solar panels and battery storage we’d never have to pay another power bill. However, attractive as that sounds, it’s a real stretch.  In the suburbs, going off-grid rarely makes economic sense. Also, cutting the wire means getting stressed about installing the correct amount of home battery storage. Too much capacity wastes money. Too little means running out of electricity after a run of cloudy days. Awkward!

So, we’re staying on the grid.  We now think of a home battery as a neat way of time-shifting solar power to save money.  Electricity generated during the middle of the day is used or stored, not exported to the grid. When the sun sets, the stored power runs our appliances.  There is an economic benefit because the tariff paid for exported solar power is less than the cost of buying electricity at the peak afternoon/evening rate.  Calculating the exact dollar benefit just got a whole lot more interesting with the Victorian Government announcing a time-varying feed-in tariff starting July 1.  Good news for anyone exporting during the late afternoon peak because the tariff jumps to 29c/kWh.

Chance to help the broader community.

Another justification for a home battery is the chance to become a “prosumer”.  Prosumers produce, store and consume electricity.

Prosumer usually has a home battery installed

Clever energy retailers like PowerShop recognise the advantages of engaging with prosumers to benefit the entire community.  Homes with batteries can be linked together into a virtual power plant that supports the grid during peak demand and reduces reliance on fossil fuel power plants.  If we have more electricity stored in our home battery than our predicted requirement, it’s better for the planet if we release that energy to the grid.  That sure beats the alternative of someone throwing more brown coal into a boiler at a power station.

What type of home battery for us?

In the good old days, only one battery chemistry was readily available – lead/acid (bigger versions of the ones found in cars).

At a recent ATA presentation on battery systems, a GridEdge representative outlined the advantages and disadvantages of the modern crop of batteries.

Two types, lithium-ion and sodium nickel chloride, seemed the best fit for us.

Lithium-ion getting all the attention.

Lithium ion is one type of home battery

Thanks to Elon Musk and Tesla, lithium-ion batteries are hogging the limelight.  Let’s not worry about exactly how they work but jump straight into the advantages and disadvantages.

The main advantages are lightweight construction and an 80% depth of discharge (DoD).  The DoD specifies how much of the storage capacity is actually available for use without damaging the battery.  In this case, a 10kW lithium-ion battery is good for 8kW of usable power. That’s better than the 50% DoD for a lead-acid battery.

Increasing global production of lithium-ion batteries means the prices are steadily falling, giving them a competitive cost.

But, there are a few things to think about:

  • Restricted temperature range of roughly 0 to 40 deg C.  They operate best in the mid-twenties so the location is important.  A lithium-ion battery isn’t going to enjoy working in a tin shed on the western side of the house during summer.
  • Degrading over time, dropping to 50 to 60% of rated capacity after 10 years.
  • Handle with care – bad things happen if the battery overheats.  Remember the problems Samsung had with the Note 7 batteries?  It’s also important to avoid damage by something hitting the battery. You wouldn’t want to drive the car a little too fast into the garage and bump into the battery on the back wall.
  • Recycling industry in its infancy – it is not yet clear how to recycle these batteries in commercial quantities. It would defeat the purpose if there wasn’t a sustainable cradle to grave process.

Molten salt battery is the second contender.

The GridEdge representative presented us with a less well known alternative to lithium-ion batteries.  The sodium nickel chloride battery is a molten salt battery. Wow! Inside an operating battery is a container filled with hot, molten salt.

Sodium nickel chloride batteries are another type of home battery

What are the advantages?  The following list looks like someone designed a product to address the concerns raised by lithium-ion batteries:

  • DoD up to 90%.
  • Wide temperature range from -20 to 60 deg C.  This battery is less worried about sitting in a hot tin shed.
  • Retains design capacity over 10 years.  There could be some debate about the lifespan.  The number of cycles (charge & discharge) the battery experiences might reduce the 10 years according to some articles I’ve seen.  Key point is the battery doesn’t lose capacity during this time.
  • Robust – not a fire risk.
  • Fully recyclable

So what’s the problem?  All these advantages come at a higher purchase price than a similar capacity lithium-ion home battery.  However, as GridEdge point out, the sodium nickel chloride battery becomes competitive if you look at the lifetime cost (purchase price and operating losses over a 10 year life).

And the decision is …

Still have time to make a final decision on the home battery type

The jury is still out on which home battery we’ll select for Unit 1.  Luckily, we don’t have to make the decision right now.

A little bit further down the track, we’ll get up to date quotes for both types of home battery. Perhaps the sodium nickel chloride battery costs will fall enough to fit within our budget figure which was based on 2017 lithium-ion battery costs.

1 Comment

  • Anne Thompson

    April 07, 04 2018 08:41:21

    Very informative guys! Thanks for your great research.

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