Residential Rooftop Solar Power – Part One

Posted on Sat 08/11/2012 by



We are told that the emissions of Carbon Dioxide (CO2) are the main cause of Climate Change, or Catastrophic Anthropogenic Global Warming (CAGW). While those man made emissions of CO2 come from a number of sources, by far the largest contributor is the electrical power generation sector which emits around 40% of all those CO2 emissions. While those CO2 emissions from that sector come from a few sources, the largest source is from coal fired power plants. Because of that, we are told we need to move away from generating power in this manner, and one of the ways this can be done is with the installation of rooftop solar power systems. With these systems in place, the thinking is that less electrical power will be required for that Residential sector. However, are these systems a feasible way to solve what we are told is a major problem?

In most Western World situations where a regular and constant supply of electrical power is always available, that Residential sector can consume up to 38% of all power being generated. Here in Australia, that situation differs a little. While constant and regular electrical power is readily available at every residence, Residential Energy as a whole comes from other sources as well. Natural gas is supplied to homes in some States for cooking and heating purposes, and wood fired heating and LPG also make up part of the total residential energy consumption as well. In fact, residential electricity consumption makes up only 53% of that total residential energy consumption.

The total for residential electricity consumption comes in at around 65TeraWattHours (TWH) and with the total electricity power consumption for all Australia of around 250TWH, then that residential sector consumes 26% of all Australian electrical power.

Keeping in mind that energy consumption in a residential setting covers a number of areas and that electricity consumption is just one part of that mix, then an average electrical consumption for a residential household can be somewhat misleading, and that would differ from State to State. That is because it is the Southern States where the largest supply of Town gas comes into play, so, while their overall energy consumption may be similar, the mix of electricity and gas is different to what it might be in Queensland where there is a lot less gas supply, and instead of gas being used for space heating as in the South, the main consumer of energy in the North would be for air conditioning in the hotter climate there, and all of that is supplied from electricity.

So, because of the many factors that are different from State to State, quoting an average electricity consumption can be somewhat misleading.

However, when averaging it out across the Country, that average electricity consumption comes in at around 20 KiloWattHours (KWH) per residence. Some States have a higher consumption and some have a little lower than that.

So, from this, we now we have a baseline of what size rooftop solar panel power system might be required, one that can actually supply all of that 20KWH on a daily basis.

This image shows just how much power can be generated by a rooftop solar power system. This chart covers numerous Australian areas, and excepting Cairns and Alice Springs, all the cities quoted here are the State Capitals. The chart also lists the differing sizes of systems from small four panel systems of 1KW up to a multi panel system of 4KW total power. The most Northerly cities on this list are Darwin and Cairns, and the most Southerly are Melbourne and Hobart.

As you can see from this chart, the largest of these systems is the 4.0KW system. The only place in Australia where a system of this size can actually generate that 20KWH is Alice Springs, a city in Central Northern Australia, where they do have a regular climate not subject to cloud cover of the other major centres, and Alice Springs is nowhere near the size of those other State Capitals mentioned in the chart, and in fact, Alice Springs is the smallest city on this chart. As is plain from this chart a system of this size cannot generate the requisite 20KWH supply for an average residence, unless you install it in one of the most isolated places in Australia.

This second image at the right shows an approximate total power generation for differing sizes of installations. So, from this chart we can now see that the system required to generate the required 20KWH per day that is the average consumption for an Australian residence is that system of 4950W (almost 5KW). It has 22 panels and each panel can generate 225Watts.

Differing Companies have different sized panels, and the technology that goes into making the panels is changing with their evolution, but we can only go by what we have available right now, and for the sake of the exercise, that is all we can do. If the technology does improve, no one will be removing their existing system to replace it with a newer one anyway.


So, with the average Australian residence consuming that 20KWH of power per day, we now need to work out how much that electricity would cost for the projected 25 year best case life span of any rooftop solar system. Again, we can only go on the electricity prices that are current right now for the sake of any comparison.

While there are numerous providers of electrical power here in Australia, the current cost for residential power is an average of 23.5 cents per KWH, so the cost of electricity by staying connected to the grid is a relatively simple calculation. For this costing, I have actually included the new post Carbon Price cost for electricity.

23.5 cents X 20KWH X 365.25 (This multiplier includes the leap year factor of 0.25) X 25 years

That comes in a tick under $43,000 for an average household residence’s electrical power consumption bill for those 25 years.


There are two scenarios we can observe here for costing purposes, the first being if the residence with the installed system remains connected to the grid, and the second being if the system is a stand alone system, not connected to the grid, and able to supply the full power requirements for the residence.

In the following Two Parts, I will do the exercise for both scenarios.