The most important mistake people make when dimensioning a solar system

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If you are unsure of your electricity usage, sizing a solar system can be a small minefield.

Usually we first explain that the average power of a solar system in Sydney is about four times that of a system.

For example, a 5 kW system delivers 20 kWh per day, averaged over the year. So if you use around 30 kWh per day and you estimate that you could use around 60-70% of your power during the day, a 5 kW system would be a good solution.

The problem with this approach of using annual averages is that a solar system emits much more electricity in summer than in winter:

This can work very well when a household uses a lot of electricity in the summer. For example, the air conditioning and the pool pumps can be operated with solar energy throughout the summer without additional electricity having to be drawn from the grid. In winter, the reduced output goes hand in hand with a reduction in electricity consumption, especially if a house has gas heating.

But we have many customers who actually use more electricity in winter compared to summer because of the electric heating. If the solar system is not properly sized, it can result in a large and unexpected electricity bill in winter, especially if it is just a household assuming that the solar system will provide the extra energy needed to run the heating.

Here is an example from one of our customers showing a sharp increase in electricity consumption from May onwards due to heating:

You can see in the spring months that the solar system is pretty well sized.

There were some peaks in the summer with the air conditioning on all day, especially in January, but for the most part, all of the solar energy was being used in the home.

However, when the colder weather hits in May, the solar system's performance decreases while electricity consumption increases.

Because of this, using averages is not always the best way to maximize the benefits of your solar system.

In this example we would consider the system to be too small.

In reality, this installation was limited by the loft, so this family in the southern highlands does a great job of using as much solar energy in the house as it is being produced. However, we have many other customers who have no limitations and still end up installing too small a system.

Why you should install a larger solar system

You might be thinking, “But if I adapt the system to my winter usage, I'll generate way too much electricity in the summer.”

Yes. And that's good.

First, the feed-in tariffs for the solar power you export into the grid are much higher now than they used to be, to the point where many of our customers install as many solar panels as possible regardless of their energy consumption.

They are now getting a quarterly loan from their energy retailer. For more information on how this strategy works, check out our blog post here: How to Eliminate Your Electricity Bill Using Solar Power

Second, they now have the option to add battery storage when they're ready. A home battery like Tesla Powerwall captures excess solar power that can be used in the evening. If you have energy tariffs for the useful life, you can save a lot of money, since a tariff of over 50 cents per kWh often applies in the main billing period from 2:00 p.m. to 8:00 p.m. on weekdays.

We can help you assess a solar system in just a few minutes

For more personal information and advice, request a call back below. We'll help you find the right solar system for your home or business. With your utility bills on hand, it will take no more than a few minutes to go through your bills and figure out a solar system that works best:


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