That calculation also doesn't take into account the depressingly regular increases in the price of electricity.
That same system will continue to produce power for a minimum of 25 years, and probably 30. With all this in mind, it makes sense to lower your home's energy requirements first, before calculating what sized solar array you need. Here's how you do it.
Lighting
LED lighting is a revolution in energy efficiency. With lighting making up, on average, eight per cent of a home's energy use, this energy cost can be cut by at least 80 per cent.
On a power bill of $250, $22 will be spent on lighting with traditional incandescent bulbs. Replace them all with LEDs, and you're looking at more like $4.50.
Of course, it has limited impact during the day when lights aren't needed so much, but it pays dividends at the power bill.
Hot water heating
The efficiencies gained from the coupling of a solar array and a heat pump water heater (HPWH), which transfers the warmth in the air to your water, can only be described as a match made in heaven. With hot water making up at least one third of an electricity bill, a HPWH (pictured right) alone will slash that cost by two thirds, and adding solar power to the mix should effectively halve it again.
An 'all-in-one' HPWH can be installed as a retrofit for between $3000 and $4000, and for between $2500 and $3500 in a new build. Some HPWH models can also be set to heat water during sunlight hours and keep hot water ready to use during evening or early morning - ideal for solar generation or cheap daytime grid electricity.
Insulation and heating
On a frosty but clear day in winter the thought that your solar panels are running your efficient heat pump will certainly warm the cockles. But consider that a well-insulated home, with draft proofing measures throughout, double glazing and thermal curtains, will decrease the amount of heat needed to bring the room to a comfortable temperature. Heating throughout winter generally makes up one third of a power bill, so any inroads which can be made can make a very pleasant difference.
Electronics
Electronics take up around 18 per cent of power usage. When your solar system is installed, it obviously makes sense to charge all your mobile devices during the day. Turn off appliances at night, as left on standby they are just money down the drain. It also makes sense to choose those appliances with the Blue Energy Star mark, which are among the top ten per cent for efficiency. For example, refrigeration takes around 11% of the electricity used in your home. Over the 15-year life of a fridge, an efficient model will more than pay for itself.
Heated towel rails
These innocuous little appliances are a 24-hour draw on your power and the best thing you can do is to have an electrician install a timer switch. With a solar system installed, it makes sense to have them come on when the sun is high in the sky, but that will only work to dry towels after your morning shower, and not your evening bath. A damp towel will dry on a heated towel rail in less than four hours, after which your timer can switch it off for the night.
Now that your home is as energy efficient as possible, it's time to figure out your energy usage during the sunlight hours, so that you can choose the correct-sized solar array. Your solar installer will be able to help here. Other considerations include whether you plan to purchase an electric vehicle in the next decade or two. For this reason you may like to have spare capacity in your inverter (the unit which converts DC solar power in AC power suitable for your appliances) for more panels in future, or whether you opt for micro inverters (which can fit under the panels and be scaled modularly).
This editorial series is made possible with funding from Energy Alternatives. To find out more about energy efficient products visit energyalternatives.co.nz
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