Another Spectrum

Personal ramblings and rants of a somewhat twisted mind


Photovoltaic generation and more

PV generation

Since the 7th of May, our household has been generating some of its own electricity. Given that it’s only another three weeks until the shortest day of the year arrives, we’re achieving better savings than I expected. We have an all electric home (no gas, oil, coal, or wood), so we do consume quite a lot of electricity – 818.8 kW/h in 25 days of May to be precise. We generated 40% of that ourselves from 23 PV panels mounted on the roof.

In the highly deregulated electricity market of Aotearoa New Zealand, there is a considerable difference between the price supply companies sell electricity to consumers and the price they will buy back surplus home generation. Their sell price is typically around four times their buy price. The price differential made it tempting to install storage batteries so that we could call on surplus power when generation was low. But after discussing that option with several installers, we concluded the the return on investment was longer that the estimated life of the current generation of batteries.

Instead, we have installed an “intelligent” inverter that diverts any surplus electricity into the hot water storage system. Instead of maintaining a constant 55°C (131°F) the water is allowed to fluctuate between 40°C (104°F) and 78°C (172°F). Only after the water has reached its maximum temperature does the inverter allow electricity to be exported to the grid. Don’t worry, a regulator ensures that the maximum temperature at the tap (faucet) is no more than 55°C. In effect we’re using the hot water system as a sort of battery. We haven’t needed to use grid electricity to heat the water since the solar power was switched on. Even so that has been a few days where we have exported small quantities of electricity. I expect that in summer we’ll be exporting considerable amounts during the day, and as the heat pump will be switched off, our nighttime use should be minimal.

Covid alternatives to travel

For the most part we Kiwis have been largely unaffected by Covid-19 with the exception of international travel. In our case, it meant the cancellation of an extended holiday in Japan. We’ve concluded that at our age, it’s unlikely that we will feel the urge to undertake the journey once the dangers of the pandemic have passed. Instead we put the funds intended for travel towards solar power. Of course it’s not just a case of having the panels installed. The house, and especially the roof was in need of a repaint, so it made sense to paint the house before the solar panels were installed.

But if we’re going to paint the house, there’s a matter of some repairs that have been on the backburner for a while. The front door for example. Aging had caused fine cracks to develop in some of the wooden panels allowing daylight to be seen through them, not to mention a draft in windy weather. And if the door is to be replaced, why not replace the horrible single-glazed yellow sidelight with something that allows more light into the entrance lobby while reducing heat loss?

To cut a short story shorter, we had a new thermally isolated door and sidelight assembly custom made. The door has a digital lock so that’s one less key I have to worry about. The installers took only two hours to remove the old door and sidelight and install the new assembly. The transformation is quite amazing! Some of the recent changes can be seen in the images below.

The front door – before and after

The front (2 images) and rear (1 image) of the house before the repaint. The rear view clearly shows to state of the roof.

The final result with PV panels installed – 10 on the east facing front, and 13 on the rear facing west. The original paint scheme consisted of eight colours, the new has just four.