Solar panels on the roof - the first three weeks

 As Angela's said, we now have solar panels on our roof. So how's it going after three weeks or so?

Our motivation for solar was primarily to generate watts of power that didn't need to come from Indonesian coal, shipped across the Tasman to the Huntly power station. Secondary was to save money even if it took a long payback. 

We didn't do all the research we should have to fully understand all the nuances of what we were about to do - instead we put ourselves in the hands of Harrisons Solar who had a good reputation both from the internet and word of mouth. We don't regret it, they were extremely helpful, professional, and did a really good job. 

We (well, our bank) spent $13k all up on a 12 panel, 4.7kW system. This is for a smallish 3br house with a 250L electric hot water system, nice north facing sun on an appropriately sloping roof, and 2 of us living here (though we wanted to spec the panels for the next owners too). We turned down the $18k Tesla battery. 

We also changed power suppliers to Contact Energy who currently offer free electricity between 9pm and 12am - this works really nicely so we only really draw lots of power at dawn and dusk, the rest is mostly either free or helped along by solar. We've changed our behaviour to eg only run the washing machine and dishwasher at 9pm, or in the middle of the day if we need to. I'm going to put timers on the towel rails and suchlike.

Half our panels (the western ones)

So how's it gone then? This is what we've found.

There seems to be a lot to consider in the install. You don't just throw panels on the roof and hope for the best. They're interlinked in a way that means they only give you the power of the least performing panel in the bank; you need an even number of panels in a bank; and so on.  There are a bewildering selection of inverters at very different price, functionality and quality points too.  A DIY job would take a lot of research and discussion with experts, and the right sparky to work with you, although there are also a lot of websites that do much of this work for you.  We ended up with a bank of six north-facing panels, and a 2nd bank of six west-facing panels as the best solution.  

It's kinda obvious, but if your roof is dodgy you need to replace or fix your roof before you do the solar work. You don't want to put panels up then need to take them down again to sort your roof. We replaced our roof a few years back, from the original iron the house was built with.

Solar generates steady power, but you use power in short intensive peaks. That means that without a battery, it's hard to ensure that you're using the power you make - you're either spilling to the grid or sucking from the grid for most of the time. And you pay a lot more for power you use, than they pay you for power you export.

In the following pictures, 

• Yellow = solar power we use ourselves
• Grey = excess solar power we export to the grid
• Blue line = our actual consumption, when it spikes into the white area that's grid power we're using.

This is the best case - a sunny summer's day.

A more typical day with cloudy periods.

Our inverter is battery ready. I'm expecting batteries to come down in price a lot over the next few years, with increased demand, maturing tech and a heap of second life EV batteries hitting the market. Or we'll have a mobile battery with four wheels and a steering wheel in our garage in the next few years. Even a relatively small one to smooth out the peaks and troughs would be nice. Another thing is that when you sell your house you can take the battery with you no worries. Even if your next house didn't have solar you can charge it at night and use it during the day.

I was expecting to use the hot water cylinder as our battery. But, because its thermostat is either off (0W) or on (3000W) it peaks beyond what the panels can generally provide. After more research than I really wanted to do, I settled on a $26 timer fitted to the switchboard, that switches on the hot water cylinder just for three hours during the Contact Energy 'free power' evening. That's enough to provide hot water all day. I've since written a ridiculously detailed blog post about it.

I'm looking forward to my next electricity bill! I don't really know how our reduced grid usage, free night power and the (not much) money we get exporting power to the grid will all work out. I'm going to do a spreadsheet to see how our payback goes, including paying mortgage interest on the principal. I suspect not all that well. But, Indonesian coal.