We have heard much about renewable energy sources, mainly wind and solar; they appear to be long term solutions to our energy problems and reduce greenhouse gas (GHG) emissions. True, but we live in the present, and right now, and probably for decades to come, renewables are simply not economically sustainable. Were it not for major government subsidies, investment in large scale renewable energy is not economically viable. Why is this so when after all, wind and solar are free, and the technology appears to be available?

The answer lies in the unreliable, intermittent nature of renewable sources. Wind blows seemingly when it wants, night or day, whether its energy is needed or not. Sometimes it does not blow at all, and sometimes it blows too strongly for wind turbines to be operated safely. Solar is a little better – at least the sun shines during the day when electrical energy is most needed. But energy is still required at night. And then at times the sky is overcast. And in winter when generally the most energy is needed, solar radiation is reduced. Because of this almost fatal drawback, renewables are difficult and expensive to apply, and unless some inexpensive way of storing energy is developed, they are destined to remain small players.

Because of the enormous variability of wind energy, the Australian Energy Market Operator (AEMO), has determined that only 8% of installed wind generating capacity can be considered as reliable system supply in Victoria. In NSW, the figure is 5%, and in South Australia it is just 3%! This means that in Victoria, for every 100 units of installed capacity, only 8 units are reliably usable to the network. The other 92 units must be backed up with fossil fuel plants. And with the unit capital cost of wind plant more than double that of good, efficient gas fired plant, it is obvious that wind plant is completely commercially unviable. In addition, because wind force can reduce suddenly, fossil plants must pick up the dropped load rapidly, and if they can’t, system overloads and instability problems can result, with widespread blackouts. Transmission lines to wind farms must be sized to meet the maximum capacity of the generators, yet, for most of the time, they will be carrying only a small percentage of that capacity, thus reducing economic viability even further. For these reasons, the provision of large scale wind energy is problematical, and must be carefully considered. Jumping on to the wind energy bandwagon may be more a salve for our environmental conscience than a practical long term solution.

At this stage, large scale solar is even more problematical than wind, with the only readily available technology being rooftop Photo Voltaics (PV). AEMO figures indicate that it is unlikely that solar electricity will exceed 14% of all renewable electricity by 2021. The retreat of government subsidies on domestic PV installations, and the reduction of feed-in tariffs gives credence to this, with governments realising that domestic PV electricity is expensive, and not a potentially significant contributor of electricity. Unless huge investments are made in central solar thermal (CST) systems with salt storage, in hot remote parts of Australia, requiring long transmission lines, solar will not be a significant contributor. Geothermal energy does not suffer from variable availability, but its development is still embryonic, and beset with technical problems. It is unlikely to be a significant energy source in the foreseeable future.

Presently, the main argument supporting renewables is that they don’t emit GHG. But what if we could significantly reduce emissions while still using fossil fuels, which we have in abundance? The key to this is to increase their efficiency of utilization. The largest GHG emitter in the US in 2011 was electricity generation, with 33% of total emissions. Commercial, industrial and residential heating accounted for 31%, transportation for 28% and agriculture for 8%. Figures for Australia would be in the same order. When electricity is generated, only about one third of the energy in fossil fuels is converted to electricity. The other two thirds are lost to the atmosphere, mainly through cooling towers. But suppose that half of that lost heat could be saved and used to meet the commercial, industrial and residential needs. Then suddenly, the fuel that had been burned for this need not be burned, with a massive reduction in the rate of GHG emissions of 31%.

But how could this be done? Does it require new, advanced or undiscovered technology? No, the method is simple and has already been used for decades, though on a fairly small scale, in district heating schemes in Europe and the US. With these schemes, often called co-generation systems, the heat that is normally lost in cooling towers is transferred to hot water which is pumped throughout an area in insulated pipes to heat buildings. The concept can be extended to include industrial process heating, most of which can be supplied at a temperature compatible with co-generation. In winter buildings can be heated, and in summer they can be cooled using absorption refrigeration.

So why don’t we use large scale co-generation? In Australia urbanisation is typically ‘urban sprawl’ – low density development which would require hot water distribution pipework to be extensive and expensive. But if development were to be compact and planned so that large industrial energy users were close to a central energy plant, the concept would not only be feasible but highly economical.

The idea of energy efficiency in the context of planned compact cities, can be extended to transport efficiency and water use efficiency using techniques such as storm water harvesting. The concept also ties in well with the need for containing urban sprawl in our cities, which is escalating costs of infrastructure and housing, and increasing road congestion to unacceptable levels. If urban boundaries were set about capital cities, and population increase directed to planned satellite cities, all of these ills could be addressed economically in an environmentally friendly way. This ‘managed urbanisation’ not only enables efficient energy utilization, but prepares the way for widespread use of renewables. Electrical power in the satellite cities would be generated using combined cycle gas turbine (CCGT) technology which is very efficient and flexible, thus able to pick up and drop loads quickly in response to rapid variations in availability of renewable energy.

The establishment of satellite cities requires that jobs be generated so that people can live where they work. The inherent efficiency of such cities would ensure this because development moves with efficiency and low costs, just as water moves with gravity.

Frank Reale is a mechanical and electrical engineer and environmental scientist with a special interest in energy efficiency, urbanisation and sustainable growth. For more information on the content of this article visit www.managedurbanisation.com