Sunlight coming through the northern windows and hitting the thermal mass.
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Winter sunshine benefits

What a difference the Sun makes on a cold wintry day!  Winter sunshine streaming through the north facing windows heats our home.  A clear sky means the solar panels pump out electricity to easily meet the home’s meagre energy needs.

In my last post, I talked about our experience of riding through a patch of cold, cloudy days.  Without the benefit of passive solar heating, we needed mechanical heating.  Thick cloud severely limited production from the solar panels.  To make up for the shortfall, I programmed the SolarEdge inverter to import off-peak electricity to run the reverse cycle air conditioner at minimum cost.

A week after the miserable, cold, cloudy days, Melbourne turned on a run of cold but sunny days.  The nighttime lows and daytime highs were similar, but there was hardly a cloud in the sky.  This provided an ideal opportunity to demonstrate the benefits of passive solar design when the Sun is shining.

Winter sunshine heats our home.

The first benefit from winter sunshine is free energy for home heating.

An angled eave on the north side of the house allows sunlight to hit the windows.  This is the complete opposite to Summer when the eave shades the same windows.

Sunlight enters the tall, narrow window in the kitchen, warming the thermal mass in the concrete floor.

Winter sunshine heating the slab in the kitchen

More light comes through the large sliding door to warm the family room slab and Timbercrete walls.

Winter sunshine entering the family room

My Wireless Tag temperature monitors tell the full story of what’s happening on a cold, sunny day.

Nighttime temperatures fell as low as 5 degC.  During the day, temperatures on the shaded, southern side of the house crept up to 15 degC.

Meanwhile, on the northern side, winter sunshine is beaming under the eave and directly onto the sensor mounted above the sliding door.  Temperatures here are peaking at a tropical 40 to 45 degC.  That’s an indication of the free energy available to heat the internal thermal mass.

Winter sunshine heats the north facing wall

The effect of all that sunlight is obvious.  Look at the trend on the kitchen temperature.  I use the reverse cycle air conditioner to hold a minimum indoor temperature of 16 degC overnight.  Once the Sun is up, the air con is switched off.  Winter sunshine pulls the temperature towards 23 degC all by itself.  As I often tell visitors, this is a house that “wants to warm up in Winter and stay cool in Summer.”

Winter sunshine solar power.

Numbers from May 17 are a good example of electricity demand during the five days of sunny weather.

Electricity production, consumption and demand using a solar power system and battery

Our fully electric home ran beautifully on less than 1kWh of purchased GreenPower while exporting over 10kWh of solar power to the grid.

Digging into the SolarEdge inverter data gives a clearer picture of electricity consumption and production.

Between 8am and 4pm, our 7.8kW system produced an almost perfectly smooth production curve peaking at 4kW.  I suspect the one dip is due to a high grid voltage issue plaguing the local network.

In the morning, solar power went to recharging the battery and running the hot water heat pump (10am to 12pm).

Graph of solar power production and consumption using winter sunshine

Throughout the day, we took advantage of the plentiful power supply to catch up on some chores like washing clothes and a bit of cooking.  With COVID19 restrictions in place, the Nissan LEAF hasn’t been going very far lately.  No electricity needed for the EV on May 17.

Cost-wise, the numbers are a bonus.  Let’s ignore the $1.35 per day grid connection cost.  It’s a fixed cost for the convenience of having grid back-up and the ability to export excess solar power.  Averaging three days of winter sunshine in the middle of this stretch, we paid $0.25 per day for GreenPower but earned $1.00 per day in exports.

Our experience agrees with RMIT study.

A recent article from One Step Off The Grid summarised the results of an RMIT study into the benefits of building new homes to a 7.5+ NatHERS Star standard instead of the minimum 6 Star requirement.

Although their study was based on sustainable homes built at The Cape, we clearly enjoy similar advantages.

The higher Star rating allowed us to purchase a smaller reverse cycle air conditioner than usual. Excellent insulation and passive solar design significantly reduced the heating and cooling load. Lower capital cost for heating/cooling devices was highlighted by RMIT.

From what we’ve heard in conversations with other homeowners, our energy bill for heating and cooling is significantly less than the norm.  RMIT reported a 40% reduction in annual heating/cooling energy costs for 7.5 Star compared to 6 Star.

Not relying on mechanical heating or cooling for comfort is a healthier, more natural lifestyle.  We take full advantage of sunshine for warmth and breezes for cooling.  RMIT noted this approach had the potential for improved health outcomes for residents of 7.5+ Star homes.

Hope for the future.

The One Step Off The Grid article points out that the advantages of 7.5+ Star homes aren’t well known amongst house buyers so large commercial builders aren’t pushed to exceed the 6 Star requirement.  However, that might be changing as word gets around about the economic and lifestyle benefits.  It’s not all about the upfront purchase price.  High operating costs for a home built to minimum standards are an ongoing drain on the bank balance.

Here’s hoping that sharing our experience with sustainable housing helps educate others. Informed consumers can ask for something better from their home designer/builder.

Informed consumer makes better decisions

1 Comment

  • GC

    June 09, 06 2020 02:22:06

    I’m not sure I understood every word but I did grasp that your systems are working well. You must be very pleased and great to have tested it all under real conditions.
    All looking terrific.

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