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.

Author: Barry

A post war baby boomer from Aotearoa New Zealand who has lived with migraines for as long as I can remember and was diagnosed as being autistic aged sixty. I blog because in real life I'm somewhat backwards about coming forward with my opinions.

11 thoughts on “Photovoltaic generation and more

  1. That’s some beautiful work you managed to have done. You use a lot of electricity. I think the most we have used is ~300kWh. But we use gas to cook so maybe that’s where we have a difference n no heating.

    • Our heat pump runs 24/7 from early May through to mid september, so that consumes quite a lot of electric power.

      We also use a slow cooker every other day during winter for soups, stews and casseroles whereas in summer meals tend to be lightly and quickly cooked. Our Winter electricity bills are around $100 – $150 per month higher in winter than in in summer.

      When we had the kitchen renovated around 10 years ago, we considered gas for cooking, but the daily connection fee made it uneconomic unless we used gas for heating and hot water as well, but we didn’t have the financial resources at the time to make such a major change.

  2. Wow… awesome updates, esp the door!

    I grew up with solar water heating in the 70s. I can’t afford solar on my current place. Plus, with living alone, I wouldn’t see ROI until I sold.

    • There was a time when solar water heating was “the thing” but it seems to have fallen by the wayside. I suppose modern PV arrays are more energy effective than heating water directly? Besides, it can also be used for other uses and any excess sold to the electricity grid.

      • Yeah. The breakeven point I always heard was energy bills of $350/mo. Mine averages less than $50.

        • Wow! I wish our energy bills was somewhere near yours. In winter ours is over $400 per month, in summer around $250.

          • I’m annoyed it’s up from $27/mo and my energy usage almost equals efficient neighbors. I think it’s because I was keeping the work computer plugged in.

            My water heater, dryer, wall heater, and stove are all natural gas. No a/c. You?

            • We’re electric only – no gas, coal, oil or wood. We used to have a wood burner but it cost a fortune to run. Even though we used it only in the late afternoon and evening over the 4 coldest months of the year, the firewood cost around $600 and there’d be another $200 to clean the flue each year. We now have a heat pump which runs continuously from early May to late September for about half the cost of the wood burner running 8 hours per day, and heats the whole house instead of just the living area.

              We have server, 2 desktop computers, 2 printers and a laptop or two and other miscellaneous equipment in our home office that run most of the day and they definitely use a lot of electricity!

              The heat pump is optimised for heating but works almost as efficiently for cooling as well. However daytime temperatures seldom get above 25°C (77°F), so there’s little need to run it in summer.

  3. Phenomenal new look Barry.

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