Late April sunshine warming the concrete slab in the main bedroom
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April comfort and cost report

The downhill run into Winter continued during April.  By the end of the month, the house was ready to move into a blend of passive solar and active heating modes.  We’re almost ready to turn the air conditioner on for the first time in a while.

Our energy bill for the month flipped from a $4 credit in March to a net cost of $18.  Average daily electricity consumption hovered around the 11kWh mark.

Solar power production dropped again, down to 525kWh.  Even though production is about half what the panels produce in Summer, production still exceeded household demand.  We exported 230kWh to the grid.

April weather

Despite a run of warmish days in mid-April, the monthly average maximum and minimum temperatures are definitely on their way down.

The average daily maximum dropped from 25.4oC in March to 21oC.  The overnight minimum average also had a reasonable fall, going from 13.6oC to 11oC.

We also saw another reduction in the BOM solar exposure measurement.  The April average of 10 MJ/m2 is well short of March’s 15 MJ/m2

I’m monitoring solar exposure because it’s a good indicator of solar power production.  High numbers correlate with good production and vice versa.  It’s also a useful indicator of how much solar energy is available for passive solar heating.  Short, cloudy Winter days limit the solar exposure and, hence, the amount of energy available for passive heating.

Staying comfortable in April

This temperature chart compares conditions in our living area (kitchen) with ambient temperatures on the north and south sides of the house.

Indoor and outdoor temperature measurements for April
Blue – kitchen; green – outside (north wall); black – outside (south wall)

Once again, there are a couple of kitchen temperature spikes, caused by the reasons discussed in the March report.  With the Sun lower in the sky, it’s warming a larger area of the thermal mass (concrete slab).  However, late Summer temperatures are lingering longer so we don’t yet need the extra passive heating.

Fortunately, Melbourne provides cool nights so we used natural air circulation to vent warm air.  We didn’t have to resort to the air conditioner.  Switching on the ceiling fans was enough to boost the air circulation after the warmest days.

During the colder, sunny days, we use sunlight coming through the large north facing windows to heat indoors.  Here you can see sunshine warming the concrete slab in our main bedroom.

Late April sunshine warming the concrete slab in the main bedroom

The temperature graph shows we stayed below the recommended indoor summer temperature maximum of 27oC.

Major electricity users

I didn’t see significant changes to the major electricity users.  Most of our energy goes to hot water, kitchen appliances and EV charging.

EV charging could be the one to watch for a cost impact in the next couple of months.  During Summer, there is plenty of excess solar power for charging.  We charged the car like you might charge a mobile phone.  Plug it in whenever we have the chance to top up the battery.

That’s not so easy to do in the Winter months when solar power production is much lower.  The 8kW array can’t meet household demand and charge an EV.  The back-up plan will be importing off-peak GreenPower from the grid at night.

Solar power production observations

The two solar panel production charts highlight a downward trend.

Average daily production dropped below 20kWh.  The system struggled to get above 25kWh on a sunny day.

Daily solar power production for April

Weekly production is down to the 120kWh mark, the lowest since August 2021.

Weekly solar power production since July 1 2021

April electricity cost

GreenPower imports edged up slightly from a total of 11kWh in March to 24kWh in April.  The jump happened because I topped up the battery twice in the month.

Topping up the battery means importing off-peak GreenPower before a cloudy day when the solar power + battery isn’t likely to get us through the late afternoon or evening.  In preparation, I program the inverter to import off-peak GreenPower and top up the battery.  Adding the imported electricity to the next day’s solar production avoids the battery running out just when grid power prices are at their highest.

Less production meant less excess power so exports fell to 230kWh.  That’s not surprising and it won’t get better for a while.

The feed-in tariff helped but didn’t cover the $33 grid connection cost and our small amount of importing.  The April bill came to $18, up from a $4 credit in March.

Energy cost since July 1

Let’s review the energy balance and costs since official records began on July 1, 2021.

  • Electricity imported = 556 kWh or 1.8 kWh per day (and flatlining)
  • Electricity exported = 4 143 kWh or 13.6 kWh per day (and falling)
  • Energy cost = $139 or $0.45 per day (and flatlining)

Moving beyond the peak solar power production season is starting to affect these averages.

Both the electricity imported and energy cost daily averages have plateaued.  With the impending production shortfall, they are likely to start rising.

The electricity export average is falling.  Given we are heading towards the June/July production minimum, this figure will drop again next month.

Looking ahead to May

Given the cold start to May, we’re already using active heating during periods of cloudy days and cold nights.

Comfort-wise, that’s not an issue.  The air conditioner does a great job of moderating indoor temperature fluctuations when passive heating isn’t enough.

Cost-wise, I forecast another energy bill due to lower solar production and increased electricity consumption due to active heating..

However, the house will continue doing what it does best – keeping us comfortable at a low energy cost.

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