Four hours. One winter morning. A 9.1kW array going onto one of the better looking roofs in Raglan, and by lunchtime the job was done and the owner had his driveway back.
Here is the part we enjoyed. The owner is a builder. He designed this house, he built this house, and he knows exactly what sits under every sheet of steel on that roof. Anyone who has installed anything for a builder knows that is either the smoothest job of your year or the longest one. This was the smooth kind, because he knew what he wanted before we turned up.
The whole install is in the video above. It is oddly satisfying to watch.
What he actually wanted
Two things, and they pulled in slightly different directions.
He wanted it to generate properly. Not a token array, an honest system sized to what the house actually uses.
He also wanted it to vanish. This is an architecturally designed home on the Waikato coast with a dark steel roof, and he had not spent that long getting the lines of it right to have someone bolt a silver grid across the front of it.
Generate properly, and disappear. That is a design brief, not a problem.
What we put on the roof, and why
9.1kW of all black panels. All black modules on a dark roof read as a single surface. Same tone, same finish, no bright frames catching the light from the road. Stand at the letterbox and your eye slides straight over them. On a plain roof that is a nice-to-have. On this house it was most of the reason the layout got signed off.
A 10kW Sigenergy hybrid inverter. Two decisions are hiding in that sentence, and the second one is the interesting one.
First, the inverter is rated a little above the array rather than matched to it. That leaves room to add panels later without the inverter becoming the thing in the way.
Second, it is a hybrid, which means it is battery ready from day one. There is no battery on this house right now. The household did not need one, and we are not in the business of selling hardware for the sake of it. But if that changes, whether because a battery starts to stack up financially or because the power goes out one time too many, adding one is a job rather than a rebuild. Fit a standard string inverter today and a battery in three years, and you are usually buying a second box or replacing the first.
That is the whole argument for spending slightly more on the inverter than the array strictly needs. You are buying options, not output.
Install day
About four hours, start to finish, in the middle of winter.
Coloured steel is one of the nicer roofs to work on. The fixing points are predictable, the set out can be accurate, and a crew that has done a few hundred of these moves quickly.
Winter is worth a word too. A system commissioned in June switches on at the quietest point of the solar year, so the first couple of power bills are not the ones to judge it by. Install between roughly May and August and you should expect output to climb steadily through to December. That is the season doing its thing, not the system underperforming.
What it should generate
Raglan averages around 3.9 hours of usable sun a day across a year. Against 9.1kW of panels, that comes out at roughly 35kWh on an average day, or close to 12,900kWh over twelve months.
Two things to hold alongside that. It is the figure the system was designed to hit rather than a measurement, so read it as a target and not a promise. And 3.9 hours is an annual average that the seasons pull around considerably. Expect well over 35kWh on a clear day in January and well under it in July.
For scale, the average New Zealand household gets through a bit over 7,000kWh a year. So across twelve months, this system is designed to make more than a house that size uses.
Which sounds like the happy ending, and it isn’t quite. Generating more than you use does not mean a zero power bill, because the thing that actually decides the saving is how much of that generation gets used inside the house while the sun is up, rather than exported for a few cents. That is true of every solar system in the country. It is also the single most useful thing to understand before you sign anything, so our system size guide walks through how to work it out for your own place, and the battery guide covers where a battery fits into it.
We do not have post-install bills from this house yet. When there is a full year of metered data we will put it here, including if the numbers land under the estimate.
Thinking about solar on a Raglan or Waikato home? Send us a recent power bill and we will model what your roof can realistically do, including telling you if the answer is not much. Call 0800 428 557 or request a free assessment.
Sources
- MBIE via Figure.NZ: Average electricity consumption per household in New Zealand
- Generation estimate: the system design figures supplied to the homeowner in their contract