Efficiency vs. Effectiveness – towards sustainable cities

An important concept in this discussion is exergy, or the quality of energy. This follows from the ‘laws of thermodynamics’. The first law states that energy can never be lost, that it will remain. The second law introduces the notion of quality: although energy cannot be lost it loses quality and entropy is created when used (google for exergy and ‘laws of thermodynamics’ to learn more).

Using resources – energy, water, materials, etc. – in an efficient way means using these resources while trying to limit waste, trying to do things in the right manner. The concept of ‘Trias Energetica’ will be used to explain and some examples will be given. Trias Energetica was developed by Lysen and Duijvestein (1997). It consists of three, consecutive steps:

  1. Limit energy demand and energy use;
  2. Use renewable energy sources;
  3. Use fossil fuels as efficiently and cleanly as possible to fulfill remaining demand.

The first step is the most important, because each amount of energy that is saved does not have to be produced. An example of this first step is to insulate dwellings properly so less energy is needed to heat the dwellings. Remaining demand should be fulfilled by applying renewable energy sources, like solar or wind. The third step talks about the efficient use of fossil fuels. For example, the introduction of fuel-efficient cars or even hybrid cars. These cars still need fossil resources, but they use these resources more efficiently, see graph 1.

Graph 1: Fuel-efficiency of some car types, gasoline use

It is important when looking at efficiency and energy-saving measures that they do not result in a rebound effect. So, e.g., changing non-efficient light bulbs with efficient ones (LED, fluorescent light bulbs) is a good measure. The pitfall though is that people leave the lights on, because they know it is more efficient, so they think that it does not matter. This results in the end in more energy use anyway.

For a true sustainable system, the Trias Energetica should be adapted. Measures to save energy may not result in loss of comfort or health problems. A system can only be sustainable if it uses renewable resources. The rate in which we use fossil fuels, is not renewable. The resources of oil, coal and gas are not regrowing. Another point to consider: is it nowadays cheaper to invest in more insulation or to invest in renewable energy production systems? The importance of re-use, re-cycle and manufacturing, keeping the end of products in mind, is also growing. Therefore, a new concept has been developed ‘the New Stepped Strategy’ (Dobbelsteen and Tillie, 2009). In this strategy, the last step is replaced:

1.   Reduce consumption without loss of comfort and health;

2a.  Exchange and re-use waste energy systems;

2b.  Use renewable energy sources and ensure waste is re-used as food.

Applying those steps to a city or region towards sustainability can be seen as a sign of effectiveness. This means trying to use resources in the right way, trying to reach the result, to do the right things. Think with the result or purpose in mind and do not start from the means. For example, do you need your laundry cleaned or do we need the best, most energy-efficient laundry machine to clean our clothes? The question is ‘what is the most resource effective way to clean our clothes’ (we can come back to that another time)?

Reduce consumption still is the most important step. The New Stepped Strategy introduces also the importance of different scales, from dwelling level to neighborhood to city level. Before a decision is made, it has to be studied what is the most effective step to take at which level. Some things can be arranged very effectively at dwelling scale, like insulation, but others will be more effective at a larger scale, like cascading remaining qualities. An example is the remaining heat of a power plant or industry. Nowadays, it will be the remains after fossil fuel burning, but in the future it may well be the remains of renewable fuel burning or use. The idea is that the remaining heat of this industry is not a waste product, but can still be useful for another purpose. For example as processing heat for an industrial facility that needs only heat of lower temperatures. After use in this industry, it still has some heat quality remaining that can be used in, e.g. green houses. A last step can be heating of houses that needs only  a low energy (in the form of heat) quality, see graph 2.

Graph 2: Example of a heat cascade in an urban system

So, in order to reach sustainable cities, it is important to reduce energy consumption and to apply the local available renewable and residual resources in an effective way. The urban metabolism has to evolve to a circular metabolism in which any waste product is seen as a remaining quality that can be used by another function within the city. This will decrease dependency on foreign resources. It will increase the search for local potentials and characteristics. Cities are multi-functional entities. The different functions should and need to be connected and in close proximity to effectively use the local potentials towards sustainable cities.

Wouter Leduc

References:

Dobbelsteen, A., van den, Tillie, N., 2009. Towards CO2-neutral Urban Planning: Presenting the Rotterdam Energy Approach and Planning (REAP). Journal of Green Building, 4.

Duijvestein, C.A.J., 1997. Drie Stappen Strategie. In editors D.W., Dicke, E.M., Haas, Praktijkhandboek Duurzaam Bouwen. WEKA, Amsterdam, pp. (20) 1-10.

Energy Efficiency – A Sectorial Approach

Becoming more energy-efficient is one of the major challenges of our time. Modern societies are highly energy-dependent and thus all efforts to save this valuable resource are more than welcome. For many years, or rather decades, the responsible people, politicians and experts, have urged the importance of using less energy.

We may ask ourselves what has been achieved so far. We may equally ponder about future developments. How much more can we save?

In this posting we investigate the achievements of getting more energy-efficient in the UK from a sectorial point of view. The country can serve as a typical example of a European state trying to do both, using less energy for the same economic outcome and reinforcing its potential of renewable energies. The raw data for our analysis have been taken from UK National Statistics.

We consider the following sectors: Industry, domestic, services, passenger transport and freight transport. The energy consumption of the various sectors is measured as follows: industry (Mtoe/unit of output), domestic (Mtoe/household), services (Mtoe/unit of value added), passenger transport (Mtoe/person-km), freight transport (Mtoe/tonne-km). The transport sectors cover road transport only. In order to see how well each sector is doing compared to the others, we have indexed the quantities as 1980=100.  The results is given in the figure below.

Energy efficiency in the UK for various sectors.

This picture reveals immediately who the good and the bad guys are. Let´s start with the good ones. Both industry and services managed to reduced their energy use per unit of output considerably. In fact, in 2010 British industry was able to produce more than twice as many goods per unit of energy as in 1980. Within 30 years the index went down to less than 48. The services sector was even more successful. During the same period its specific consumption plummeted to an index value of 43 only.

The situation looks quite a bit different for the other sectors with passenger transport being the most successful among those. Since 1980 the use of energy per passenger-km has decreased by almost 20 % (index 81.9). Unfortunately, freight transport cannot compete with that value. Instead its energy consumption per tonne-km went up by almost 12 % during the reference period. This finding is both, surprising and disappointing at the same time. Surprising, because car producers make us believe that modern vehicles need less gasoline than older ones. Disappointing, because freight transport is the only sector showing a clear increase in its energy hunger.

When looking at the figures for household consumption we may equally feel disappointed. There is a slight tendency to use less energy per household, with the index being at 93 in 2010. This is a rather weak performance when compared to the other sectors with the notable exception of freight transport. Countless public campagnes have been run with the clear goal of getting more energy efficient. It is hard to imagine that millions of households have not got the message. However, the results are meagre. Why is that so? Is there too little incentive for households to save energy?

Renewable Energies in the UK

As in many other countries, the share of renewable energies in the UK is growing dramatically. During the past two decades renewables have surged at an impressive pace. In fact, supply from renewable energy sources has more than quadrupled since 1990 whereas overall consumption has remained fairly constant. The raw data of this analysis stem from Eurostat and UK National Statistics.

The huge gap in the respective trends between the overall energy demand and the contribution of renewables can be seen in Fig. 1 where the data for final energy consumption and the supply figures from renewable energies are shown. To make comparison easier we present the figures in an indexed form with 1990=100.

Fig. 1 Final energy consumption (FEC) and energy supply from renewable sources in the UK. 1990=100.

Whereas final energy consumption has increased only slightly (index value 105 in 2010) with a decreasing tendency since 2001, supply from renewables has more than quadrupled over the same period. Accordingly, the weight of  hydro, wind, biomass etc. in the energy mix has risen sharply. Nevertheless, this picture should not obscure the fact that in 2010 renewables contributed only 7 % to the entire energy production.

One interesting aspect of looking at the UK figures is to check the specific output of the various renewable energy sources, i.e. MWh produced per MW of installed capacity. Here we find significant differences between hydro, wind and other renewables as shown in Fig. 2. The latter comprise landfill gas, biofuels, waste combustion etc.

Fig. 2 Specific output of renewable energy sources in MWh per MW installed.

All of them show annual fluctuations which is normal since not the entire capacity is available all the time. Wind and hydro are particularly vulnerable to external factors. However, there is a significant difference between the two as regards short-term availability. Electricity generated from water is much more stable for the grid than wind which is by definition more erratic in its availability.

Apart from that we can see clearly in Fig.2 that the specific output of the various sources differs enormously. The least efficient way to produce electricity from renewables is wind as becomes apparent from Fig. 2. This conclusion is fairly independent of the fluctuating nature of all the sources taken into consideration. The average output of wind farms is 2140 MWh per MW installed. The values for hydro and others are 3060 MWh/MW and 5200 MWh/MW, respectively. Thus we may safely conclude that using hydroelectric plants is on average 43 % more efficient than using wind turbines. The difference is even more striking for the other renewables which tend to be more than 140 % more efficient than wind.

Given this state of affairs it might be worthwhile to put more emphasis on other green power sources rather than wind. However, wind farms have already become a significant factor in several countries as we have shown in some of our previous posts, e.g. here, here and here. Bearing in mind the inherent weaknesses of wind power, it appears that other renewables such as hydro and biomass are not only more reliable, but also more efficient. They, too, deserve their chance.