Australia has the highest average solar radiation per square metre of any continent in the world. More than two million Australian households have a rooftop solar system. When is it time to go solar? We get the lowdown from an unbiased expert.
When is it time to go solar? “Well anytime is good because solar is a no-brainer for many households, but there are some exceptions,” says Dom Gelonese from Emberpulse and part of GadgetGuy’s campaign to #Stop the energy rip-off.
We spoke at length to Dom about when is it time to go solar. We paraphrase the interview to avoid extensive use of ‘he said’.
It turns out that while solar is always a good idea (as daily showering is a good idea) it has some not very well publicised issues ranging from shonky installers to unrealistic expectations of payback times. We also discuss hooking up a battery and why that is not always economical due including what 3rd party companies are trying to do with your battery.
What is electricity?
You measure electricity use in kilowatts (1kW=1000 watts) and the total power usage over time in kWh (kilowatts per hour). Hence you see a tariff of X cents per kWh on your energy bill.
For example, let’s say that a small home uses 5kWh (500W x 10 hours) during the day (at a low and shoulder tariff of 10-25 cents an hour or $1.25). That covers the fridge, TV, computer with occasional spikes for boiling the kettle or making toast.
And at night it uses 5kW for lighting, cooking and cooling/heating (at a peak 50 cents per kWh tariff or $2.50 plus $1 a day supply charge).
On-grid you would spend around $5.00 per day or $1000 per year. We will use those figures through this discussion as they are typical of a 2-3 person, standard family home.
What is solar power
The sun is up for 8-12 hours a day. Solar panels and a box called an inverter converts sunshine into 240V power. Unless it is raining or cloudy.
The sun sets every day, and the solar system goes to sleep. It cannot produce power, so you are back on-grid unless you have a battery (more later).
When is it time to go solar? (rounded prices used for this example)
First, and most importantly, the solar system kW rating is not the power it can produce per day.
A 10kW solar system costing about $10,000 (for a good quality system), produces around 10,000kWh per year. This averages 30kWh per day but can range from as low as 9kWh in winter months or cloudy days to nearly 50kWh in summer months. See the table below for Sydney.
Source: https://pvwatts.nrel.gov/pvwatts.php (Value $ calculated at an average of 25 cents per kWh).
Back to our 10kW system example
Remember we are using a theoretical example. In this case, the
household energy usage is low to average, but the 10kW solar system size is oversized
for the home.
If you use 5kW in the day or ($1.25 a day or about $500 per year) the solar system repayment time is about 20 years (which is almost the operational life of the panels). That can be longer if you have a lot of cloudy days or the system is not as efficient as it should be.
Most solar salesman will quote you a return on investment of about 2.5 – 3.5 years (based on 25 years use) – if you sell power back to the grid at $2000 per year. That assumption is often very flawed.