Is it worth expanding your existing rooftop solar? Yes*

Twenty-one new LONGi LR4-60HPH-370M 370W solar panels have been added to the roof of my house, joining the existing twenty-four Axitech AC-250P/156-60S 250W panels I put there in 2015. All up there's a max generation of 13.7kW, a fair whack more than most homes get installed.

Why did I get more panels? Primarily because the cash spent on more panels will give me better returns reducing my electricity than sitting in the bank earning sweet fuck all interest.

The addition of an extra 7.77kw (3.7kw facing north, 4.07kw facing east) of panels cost me $6,700 and will generate roughly 8,659kw of power according to the NREL's estimator. If I don't use a single watt of that extra power, that'll give me $865.90/yr in feed in credit (10c/kwh come 1st July 2020) on my power bill.

That's a bare minimum saving though as realistically there's no way these new panels will be export only. I'll absolutely use some of the extra power I generate during the day instead of selling it to the grid. My heat pump hot water system and electric car love sucking up electricity when the sun is out! It's hard to estimate precisely how much of the new generation I'll use compared to sending it to the grid, but I'll try anyway. Napkin math is better than no math, right?!

Based on 18 months worth of stats I've collected from PVOutput and my power bill:

  • Generated 10,000.306kw via the 6kw of panels
  • Exported 4529.745kw of that power
  • Approx 55% of what I generate is consumed
  • With Amber Electric I pay on average 17c/kWh for power

If I consume a conservative 28% of the additional 8,659kw (estimated) new generation, that's 2,424.52kw I didn't use from the grid, saving $412.1684/yr. I'd still export 6,234.48kw, which at 10c/kw is $623.448/yr credit. All up a total saving of $1,035.62 a year.

By saving around $1,000/yr on my electricity bill, I effectively get around $1,000 a year in extra cash I wouldn't have otherwise. If I left the $6,700 in the bank, earning 1.5% interest, after 10 years I'd have earned a pissweak $521 - and that's with compounding interest. After 10 years of the new solar panels I'd have saved $10,000 off my power bill, achieving ROI after 6.7 years and "profit" of over $3,000 by the end of the 10th year.

Extra solar panels won't suit everyone however:

  • You'll get a better ROI playing the stockmarket via an index fund if you're happy to accept the risk, plus your investment is liquid, unlike the panels.
  • ROI on solar takes a few years, won't add value to your property and you can't take it with you. If you plan on moving house extra solar might not be worth it.
  • Three-phase power is required for more than 5kw of export and even in some distribution areas export capacity is capped quite low.
  • The FIT is dropping rapidly and will probably be scrapped entirely in 5 or so years, hopefully replaced with strong battery incentives.
  • Unless you have a high/constant power drain device (e.g: EV, heat pump, pool heater, etc) you probably won't use the extra power the panels produce.
  • You aren't eligible for a rebate on the second set of panels unless you installed the original set of panels prior to November 1st 2009 and you'd lose your sweet premium FIT, so it may not be worth upgrading.

That said, every home owner with a suitable roof should get at least some panels slapped on - in Victoria you can get 6.6kw for under $4,000 installed after rebates. If you don't already have panels on your roof, pull your finger out of your arse and hit up Solar Quotes now!

I know you nerds love stats and shit, so I'll do a quick write up of the solar monitoring stuff (Fronius Smart Meter, PVOutput & Solar Analytics) soon.