Maximising your solar investment

Many people don't get the full potential out of their solar. Understanding how electricity in your home works and how that ties in with a solar system, gives you a much better chance of getting more out of it.

Power and Energy

Power is the rate of which electricity is used by a device. For example, a 1000W microwave, a 50W light globe or a 7 kW (7000W) air-conditioner (yep, they're a biggie). We don’t pay based on how powerful something is, we pay for energy. Energy is measured in watt hours (Wh) or kWh. It is power with time factored in. For example, your kettle likely uses 2400W when it’s running, so if it ran for an hour it's used 2.4 kWh. Let's say you binge watch your favourite soapie for 10 hours straight using your 400W 70” TV. In this example, you've used 4 kWh and maybe a pack of Hypo-Allergenic Kleenex 3 PLY.

Equating this to cost

Most people pay around 25c per kWh of energy. So going back to our soapie, this would cost us $1, which is probably cheaper than the tissues. If you leave the house and realise you left a light on, a 4 hour trip away is only going to cost you 5 cents - 0.05 kW x 4 hours x $0.25. What you're looking for in your home are powerful devices that run for a long time. A common example of this is an air-conditioner. Although mine can peak at 7 or 8 kW, it usually runs at 5 kW. It's not uncommon for me to run if for a few hours a day in summer though, so that costs me $3.75 per day.

How solar fits in

Solar systems work in a similar way, but instead of consuming, they produce. Your 5 kW system wouldn’t peak at 5 kW, but if it did and it sustained that for one hour, you’ve produced 5 kWh of energy. When you get a quote for a solar system, you should get an average daily kWh production figure, which is great for comparing your solar power system to your energy bill. It’s also what you should use to track performance.

If you get a quote for solar and it does not include a yield estimate, disclude it as you have no benchmark with your solar retailer for monitoring performance. This is poor practice on their behalf.

Solar power systems will produce around 4 kWh on average for every 1 kW of panels. The production will slowly come on in the morning, peak in the middle of the day before if falls away again in the evening. It looks like a bell curve, depending on panel orientation. Production peaks at around 85% of panel capacity on a nice day. If clouds come over, production drops sharply, but then returns again when the sunlight re-appears.

Getting the most out of solar

Your solar production is either used by your home or sold to the retailer, nothing is stored. When you consume your solar energy, you save by not purchasing from the retailer - around 25c per kWh. When you sell excess back to the retailer, you get a credit but it is smaller. So solar is worth more to you when you consume the power yourself.

Here's some tips to configure as many of your appliances as you can to run during the day.

  • Anything on a timer, move it to the middle of the day. This includes hot water boosters, heat pumps, pool pumps, solar pool heating etc.
  • Look to purchase smart devices which can be controlled remotely, or can be timed to come on during the day. For example, putting a load of washing in the machine in the morning, but having it come on later in the day.
  • Get creative! Someone suggested to me using a slow cooker the other day, which is a great idea. Not only do these devices use less energy than a typical oven, they can be left to run during the day off your solar.

Design Tricks

There's a few things you can do to your solar system to help you use the power that you produce. Installing panels on the west for example. Western panels produce a little less than the north, but they produce power later in the day, when most families are getting home from work and school. In summer particularly, it helps you between 3.30 to 6pm when you run your air-conditioner and cooking appliances.

Another useful item is to setup a monitoring portal with your inverter that also shows you your consumption. This will show you in real time how much power you're producing and whether you're using it or not. See my portal here. We've also done another blog post on this.

You could also install a battery, which would store your surplus energy for you to use at night. When you crunch the numbers though, you're still probably better off using your retailer as a battery, but that won't be the case for much longer.