Solar Power Is Excellent, but Not Magical: Avoiding Unrealistic Expectations

20th Sep 18

Cameron Quin

Written by Cameron Quin

Photovoltaic technology can achieve a significant reduction of power bills, especially with the high electricity tariffs in Australia. However, before deploying a solar system, it is important to understand its technical capabilities and limitations.

There is no doubt that solar arrays can deliver low-cost electricity. However, you must have a clear picture of how solar panels operate before using them on your property:

  • Solar panels by themselves do not have built-in energy storage. This means they cannot deliver electricity at night unless equipped with batteries, and productivity is reduced drastically with cloudy weather.
  • Solar panels rarely operate at rated wattage, since the value is calculated based on special laboratory conditions. In actual projects, photovoltaic modules only operate close to peak output for a few hours around noon, and have partial output the rest of the day.

Going Off the Grid with Solar Power: Pros and Cons

Since electricity bills are very high in Australia, they often cause frustration. When property owners are considering solar power, a common idea that comes to mind is disconnecting completely from the grid. However, there are advantages of staying connected after going solar:

  • Even if your main electricity source is a solar system, the grid provides an excellent source of backup power. If you go completely off-grid, you must purchase an expensive diesel generator, to be used when you need more electricity than what your solar power system can produce.
  • A grid connection improves the stability of voltage and frequency, especially when using motor equipment. If you have an isolated system and use an air conditioner or pump, the inrush current can destabilise the power supply.

Remember that batteries become mandatory if you go off the grid with solar power. Their cost has been decreasing and they are now competitive against the kWh prices of Australia. However, do not underestimate the cost of an off-grid solar array; if you prefer this option, make sure you that batteries are included in the offer.

Using a Solar System of the Right Capacity

Assume you have a property that consumes 60 kilowatt-hours per day. Since there are 24 hours in a day, we can conclude that the average power consumption is 2.5 kilowatts. However, if you add a 2.5-kW solar power system to this property, the energy output will only meet a small fraction of total consumption, and the reason is simple:

  • The average power consumption is based on a 24-hour period.
  • A solar system does not provide its rated output all the time. You only get high production for a few hours around noon, reduced production in the early morning and late in the evening, and zero output at night.

Solar power designers can calculate a ratio that describes kilowatt-hours generated for every kilowatt of photovoltaic capacity. This depends on local sunshine and the orientation of your solar panels, but you can typically get more than 4 kWh/day, for every kW of capacity.

  • In this example, you need 60 kWh/day.
  • With the ratio of 4 kWh/day per kW of capacity, you need a 15-kW solar PV system.

This is still a very simplified example, but it illustrates the concept. To meet 100% of your electricity needs with solar power, the system capacity required is much higher than your average kilowatt consumption. This is because your average consumption is calculated based on a 24-hour period, while PV system output is based on the availability of sunshine.

To achieve satisfactory results with solar power, the best recommendation is getting assistance from qualified professionals. Rules of thumb and word of mouth are unreliable, and there is no substitute for getting a solar system designed according to your requirements and property conditions.

 

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