Simulation only – this house has a LOT of panels for a domestic dwelling !

A Powerful Story by Emmjay

So we’ve had our solar power installation for about six months now – in Sydney, on a  fairly flat second storey roof with no shading – until late afternoon.  It’s a 5 KW rated system with 20 panels, but it’s got to be a super sunny day to get much over 4 KW… AND if its a stinking hot day, the panels become less efficient and so there are limits in how much juice we can expect even on a good day.

Wet and rainy ?  Lucky to be making 1 KW.  That’s not completely tragic, but it’s not a massive win.

I’ve seen the power production fluctuate significantly with even a single cloud passing – dropping the power from 3.5KW down to 1.5KW.  But the rises and falls happen pretty quickly.

How do the economics look ?  Twenty panels is a fairly meaty system for a domestic dwelling – many houses you will see in the inner west of Sydney have seven panels ~ making about 1.5KW. This isn’t going to roll back climate change, but provides a good feeling, if not much actual juice.

The cost for FM and I off the bat was just under ten grand.  But there was a rebate that brought the cost down to about $6,500 – that went straight onto the mortgage.  For most Sydney mortgages, an increase of this size results in an almost undetectable increase in the monthly payout.

Here’s a table that tells our solar story.

When we’re out, and the house is using very little power, on a bright sunny day, we sell power back into the grid (no cash, just a reduction in our bills).  We make about 20c per hour.  So no Ferrari coming before I die, but over the summer quarter we reduced our power bill by about 40% – and remember this was a pretty wet, rainy time – not a great solar opportunity.  Power we put back into the grid reduced the bill by about 10% – so the rest of the savings came from displacing purchased power.  If we can maintain these savings the system will pay for itself in three years or less.  Maybe two years if the coming El Nino is a bad one.

You can guess that the best strategy is to try to balance our consumption with either our production and shift usage into the lower cost shoulder – or best – off-peak if we can.   If we’re making say 3 KW /hr , that covers a many of our appliances, but it would be foolish to imagine that it would be OK to run the dishwasher, washing machine and drier all at once. Pick one – and there’s a good chance we will not need to buy power.  Note, we have gas hot water – if you have electric hot water, the whole game changes.

Of course the elephant in the room is that the peak rate is still in force when we get home from work and the solar system has put on its jamies and gone to bed.  Solution – battery storage !

Not, not yet, friends.  Had we gone to a system with lead acetate batteries, the whole show would have cost around $30,000.  Not ever going to be economical.

But there is a glimmer of hope. Last week Elon Musk – the billionaire boss of Tesla (those wonderful fully electric cars that can get down the standing quarter as fast as a Ferrari – and when driven reasonably can go for up to 400km on a charge.  They aren’t cheap $90-110,ooo AND the charge takes hours – and costs about $25 at home – but they ARE beautifully engineered and look the part.  Sorry, where was I – oh yes batteries – and Tesla. Tesla is building a massive fully self-powered lithium battery plant – and they will start selling the domestic Tesla PowerWall later this year.

These are brilliant !  Most families will need one or two domestic models – there are also industrial models.  There is a lot of speculation about actual pricing in Australia, but the suggestion that seems to be sticking is that the lithium storage will cost about one third of the cost of lead acetate batteries.  And be smaller, easier to maintain and a lot more environmentally friendly.

And this will give consumers the choice of whether they go off-grid (maybe not on day one, I suggest) – or whether they use the PowerWall to store solar power for use when it’s dark – or even to charge itself up at off-peak rates.

The nay sayers (heaven forbid to suggest they are apologists for big coal) are going ballistic about the thought that this will cause a massive hit on the coal-fired generators – who have engineered their businesses for peak loads that (if the domestic and commercial storage economics work out) will leave the generators high and dry with a disappearing peak rate market.  They are bagging Tesla out because they say that Tesla is not yet profitable – but one suspects that Elon Musk does have pretty deep pockets – and big ideas that will continue to be game changers.

I have this sincere hope that the days of big coal – even peak coal – are coming to an end-  an end that is in sight – hoping again that it’s in time to slow climate change.  And of course, I hope the declining power bills will keep on keeping on.

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