Do Energy Saving Light Bulbs Really Save Energy?

Some considerations about the usefulness of energy saving light bulbs.

Conventional light bulbs which are now banned in the EU since 1st September 2012 are very inefficient when it comes to turning electrical energy into visible light. More than 90 % of the energy input are emitted in the form of heat. Thus with a less than 10 % efficiency in terms of light production the classical light bulb may indeed look a rather hopeless case and energy saving lamps appear to be the preferable choice.

However, a closer inspection shows that the odds are not at all so bad for the conventional lighting medium. During the cold season, i.e. whenever people feel the need of switching on their heating, the classical light bulb contributes to the heating effort. Thus whenever we count heading degree days the old fashioned light bulb lowers the need to switch on the heating. From a physical point of view during the heating period the energy saving light bulb does not save energy. That is a simple deduction from the law of energy conservation. On the contrary, if we turn to energy saving lamps, the work load of our heating systems gets higher.

On the other hand, it is true that during the warmer period energy saving light bulbs are the better choice because then we really do not need any extra heating. So in order to understand the energy balance of both lighting systems we developed a model which is based on the following assumptions:

Get-up time: 6:00

Leaving home in the morning: 8:00

Returning home in the evening: 17:00

Sleepy time:  24:00

In addition to that we assume an average performance of 200 W(el). Our model is then applied to two European cities, one in the northern (Stockholm) and the other in the southern part (Rome). From this model it follows that the maximum number of lighting hours per day is 9 which is reached during the dark winter months. On the other hand, during the long daylight hours in summer, it may be necessary to switch on the light for no more than 2 hours per day. Electricity consumption for light sources is thus fluctuating between those two extremes. Fig. 1 shows the distribution of lighting hours in both cities.

Fig. 1 Lighting hours in Rome and Stockholm.

How much artificial light we actually need is largely determined by the length of the daylight period which in turn is governed by sunrise and sunset.  The data for those astronomical observables are easily accessible, clearly highlighting the differences between northern and southern locations. Although these differences may be very large during certain periods of the year, their overall impact on our model is far less dramatic than expected. On an annual basis the number of lighting hours in Stockholm is not very much different from the one in Rome, 2160 vs. 2110, respectively, i.e. less than 3 percent difference. These lighting hours correspond to an average electricity consumption of 432 kWh and 423 kWh, respectively.

Lighting and heating

What is, however, different is the number of heating degree days between the two cities. Correspondingly, the number of lighting hours during the heating period is much larger in northern Europe than in the southern part. Our analysis shows that more than 80 % of lighting hours are consumed during the heating period in the case of Stockholm. This, in turn, means that during that period there is no gain from using energy saving light bulbs. The respective number for Rome is 62 %. Thus also in southern Europe a substantial amount of lighting is used when people are likely to put on their heating. The rest of Europe lies, in its vast majority, somewhere between these two extreme values. There are exceptions, but these are statistically insignificant.

From a physical point of view, energy saving lamps are only useful when it is warm outside, because then there is no need for excessive heat. During winter those lamps do not lead to an overall reduction of energy consumption. Let us look at the situation from the point of view of a classical light bulb. It wastes energy in summer, but not in winter. According to our model, the waste energy produced by a classical lighting system amounts to about 78 kWh (Stockholm) and 145 kWh (Rome), respectively, over the whole year. We may also ask how much heating energy we can save by using normal light bulbs. The figures are 311 kWh (S) and 235 kWh (R), respectively. Thus we may conclude that, physically speaking, the energy balance of classical light bulbs is clearly better than the one of their energy saving competitors. Their contribution to heating in winter outweighs their waste of energy in summer. Of course, the effect is much more pronounced in northern Europe than in the southern countries. But even in the latter ones, the result is undoubtedly in favour of normal light bulbs. Figs. 2 and 3 demonstrate the contribution to heating and the waste energy of conventional light bulbs for the two cities.

Fig. 2 Heating potential vs waste energy of conventional light bulbs in Stockholm.

Fig. 3 Heating potential vs. waste energy of conventional light bulbs in Rome.

It is, of course, conceivable that under certain circumstances energy saving light bulbs live up to their expectations. Our model indicates that this may be the case in tropical areas where heating is hardly ever needed.

In any case, energy-saving lighting systems are not reducing energy consumption at the level of private consumption which we have considered inour model. This is even less so at a more general level, when taking into account the energy effort for producing and disposing of light bulbs. The recycling of energy saving systems is putting an extra burden on their overall energy balance, therby seriously questioning their high expectations.

How Much Energy Do We Actually Need?

This posting is rather philosophical than technical. Whenever we talk about energy, we tend to think in terms of oil, gas, nuclear, electricity, and the like. But throughout the longest part of its history mankind has been living without any of these “modern” energy types. And yet, throughout its entire history humanity has been dependent on energy, even without knowing it to the degree we are aware of it.

Why is that so? Every living being needs energy, just to stay alive. From a very basic point of view, what you essentially need to keep yourself alive is food, the nutritional value of which is measured in kcal which, in turn, is a measure for energy.  So we have to supply our body with energy if we want to stay on this planet.

The basic energy need of a human being is about 2000 kcal per day. This is an average value which may vary according to age, sex, physical activity etc. Our basic value is meant to be valid for no or little physical activity. Thus, for people who are physically active it may be significantly higher (30 – 50 % or more). Since in the energy business it is rather uncommon to use kcal as a unit we may remark here that the above-mentioned 2000 kcal are equivalent to 2.33 kWh. From this we may calculate that the annual energy needs of a human being are about 1 MWh, taking into account a slight level of physical activity.

However, even for a society where technology has not yet developed to the level we are used to, the energy requirement per capita may well exceed 1 MWh per year. For the sake of simplicity let us consider a human being living in the Middle Ages. This means that the technological standard of that society is still much lower than nowadays, whereas at the same time its living standard is much more sophisticated than the one of, say, a society of Stone Age people.

In the Middle Ages, the vast majority of people were living an agricultural life. Thus, their energy needs reflected their living conditions. The technology of that time made extensive use of animals which was essential in order to produce a sufficient amount of food. Needless to say that the animals themselves had to be fed, too, and were thus energy consumers. The most important labour animals in such a society are horses and cows (oxen). Since they are, in general, bigger and doing much more labour than the humans, they also require more energy. Let us assume that, on average, we have one cow or horse per human being. A horse requires about 12000 kcal (14 kWh) per day, and the same is true for a cow (ox). This corresponds to about six times the energy requirements of a human. A largely inactive horse will need some 5 MWh per year. In case the animal is used for labour purposes this value will increase dramatically.

In our simple model, the minimum energy needs of a human being (plus his/her labour animal) may be estimated to about 6 MWh per year. In practice, this value might be considerably higher (30 % or more). Life was not easy then and certainly more physically demanding than in our times.

What we have considered so far was a very basic life mostly devoted to producing food and satisfying the elementary needs only. In some parts of the world, however, an additional factor comes into play: heating. Especially during the winter and the colder seasons, people need to keep a certain temperature for survival. In order to get an idea how much energy we need for heating purposes we may take the corresponding value from Switzerland which is about 6.5 MWh per person and year. This is a modern value. Linking it to a society several centuries back we have to take into consideration that on the one hand people living centuries ago might have been happy at a lower average temperature than today. On the other hand, however, we may also consider that then heating was not as efficient as it is in our times. Thus, taking the present day values may be a justified approach as the correcting factors go into opposite directions and may cancel each other.

Putting everything together leaves us with an energy need of about 13 MWh per person and year in an environment with present day climatic conditions in central Europe. One should not forget that all those basic energy needs (with the notable exception of heating) may be coverd by solar energy. In our model society it´s the sun which makes the crops grow which, in turn, serve as essential food for both humans and animals.

It goes without saying that the average energy requirements per person will increase with technological progress. Not only do we produce a number of goods nowadays which simply were not existing in the distant past, but we also enjoy a higher level of mobility. Thus both the production of goods other than the ones needed for satisfying elementary surviving conditions and mobility lead to additional energy requirements.

The above considerations are far from being simply of an academic nature. We may compare our estimates with present day statistical data. Let us look at some countries with different economic development. Taking the UN figures for energy per capita from 2008 reveals the following (GDI = gross domestic income per person):

Zambia    6.9 MWh   (GDI: 950 USD)

Zimbabwe 8.9 MWh   (360 USD)

Paraguay   8.1 MWh   (2110 USD)

Mongolia   13.7 MWh  (1670  USD)

Romania   21.3 MWh   (8280 USD)

Uzbekistan   21.5 MWh   (910 USD)

UK     39.5  MWh  (46040 USD)

US   87.3 MWh   (47930  USD)

There is a clear correlation between the level of industrialization and energy consumption. In addition, there is a climatic factor which must not be neglected. As we climb up the economic ladder we require more and more extra energy.

However, by using energy in a smart and efficient way we may limit the extra requirements. The average energy consumption per capita in the UK corresponds roughly to the EU value (40.8 MWh). Whereas the GDI of a US citizen is only slightly higher than the one of a UK citizen, his/her energy consumption exceeds the one of a person living in UK more than twofold. Thus, energy efficiency in the US is only half as good as it is in the UK.

Where are the limits? On the one hand we have to live with the fact that getting wealthier comes at a price in terms of energy consumption, on the other hand we want to squeeze as much wealth as we can from every MWh. As I have discussed in some of my previous posts (here, here and here) there is a clear tendency to become more energy efficient. Extrapolating those tendencies may give us a clue where we are heading to.

Household Energy Use – The Case of Switzerland

Modern societies need a considerable amount of energy, which is almost entirely used the three sectors industry (including services), mobility and household, at roughly equal parts. Thus, the energy consumed at home forms a substantial part of the entire final energy use.

In this posting we study the situation in Switzerland which is one of the most competitive and industrialized countries of Europe, though not being a member of the EU. All raw data for the subsequent investigation stem from Swiss Statistics which provides excellent information on all areas of consumption. In particular, we will focus on the period 2000-2010. The above-mentioned sectors had the following shares in the total final energy consumption in 2010: industry and services 35 %, mobility 34 % and household 30 %.

Total household energy use went up by 14.1% during the first decade of this century. However, this obvious increase does not take into account that the number of people living in Switzerland has also risen during that period. Thus, the relevant figure to look at is the consumption per capita, and here the situation looks quite different as can be seen in Fig. 1.

The trend line makes clear that the specific energy use per person has gone down over the years. The steep increase since 2007 is well in line with the number of heating degree days (HDD) following a similar pattern as can be seen in Fig. 2. Apparently, it has become colder between 2007 and 2010.

Fig. 2 Heating degree days (HDD) and heating effort in Swiss households.

The similarity between the red curves in Figs. 1 and 2 is not accidental, as more than 72 % of total household energy are used for heating purposes (in 2010). Thus, changes in the number of heating degree days should be reflected in the heating effort. Warm water makes up for another 12 % of household use while the remaining 16 % are shared among various sectors such as lighting, cooking, washing, drying, etc.

A closer look at the figures for warm water reveals that consumption has remained relatively stable (Fig. 3).  Taking into account the growing number of households (+ 11 %) during the period in question naturally leads to the conclusion that each household uses less and less warm water.

Fig. 3 Total energy used for warm water and consumption per household (/HH).

Fig. 4 shows the contribution of other sources of household energy use. Their aggregated consumption volume is relatively moderate as stated above. Nevertheless, as a whole they are not to be neglected although their individual shares are not as important as the ones for heating and warm water.

Fig. 4 Household energy use (except heating and warm water).

Whereas lighting, cooking and refrigerating (including freezing) have remained virtually unchanged over the years, washing (including drying) and miscellaneous have increased dramatically by 52 % and 32 %, respectively. This is well in line with a growing population as more people require more clothing to be washed. So there are some areas of energy consumption being more sensitive to the number of persons involved while others like lighting tend to be rather independent of population figures.

Thus, as stated in my previous posting, growing energy consumption figures (in absolute terms) should not be obscured by ignoring the simultaneous changes in the number of consumers. On an individual basis, we gradually tend to use less energy. This is the good news. But, of course, the crucial question is how much further we can get in becoming more energy efficient. Or, to put it differently, is there a limit and, if yes, where is it?

How Do Heating Degree Days Vary With Temperature?

Once again heating degree days (HDD). In two of our previous postings we investigated the correlation between HDDs and energy consumption. The first posting aimed at highlighting the influence of the number of HDDS on gross energy consumption, while the second focused on more specific data, namely the amount of energy devoted to heating purposes. The results were not very encouraging, since no strong correlation between the two parameters could be found. In fact, we might have expected otherwise.

In this posting we aim at a more fundamental approach. Is is clear from the definition of HDD that changes in temperature are reflected in the number of days where the heating needs to be switched on. This argument is straightforward on a daily basis. But does it also hold if we take monthly averages instead? Intuitively, the answer would be yes. But what we want to know is to what extent a montly average temperature may be considered a reliable measure for determining the value of HDDs.

In order to find the solution to this riddle we analysed the data from Sweden during the period 2003 – 2011. The baseline heating temperature for our investigation was taken to be 20°C, but HDDs for other baseline temperatures may easily be calculated. Our analysis lead to the conclusion that there is a very strong and reliable (negative) correlation between the average outside temperature and the number of HDDs over the years. As the annual data show consistently the same pattern we are not surprised to find that the same relationship holds for the multi-annual averages taken over a 30-year period as is shown in Fi.g 1.

Fig. 1 Average temperature and HDD in Sweden over a 30-year period

After these enouraging findings we might wonder if we could go one step further and look at the correlation between the annual data. Thus, we take the annual average temperature and relate it to the number of HDDs per year. As the resolution gets coarser we might expect a weakening of the relationship. However, the results are once again quite stimulating since at annual level the relationship between the two sets of parameters does not seem to loosen.  This is demonstrated in Fig. 2.

Fig. 2 Annual average temperature and HDD, 2003-2011

There is a nice negative correlation between the mean outside temperature and the number of HDDs, similar to the one we have seen for the monthly data.

A numerical analysis of our findings leads to the conclusion that, on a monthly basis, one degree of temperature difference (T,in – T,out) in centigrade corresponds to 30.5 HDD. Thus, if the monthly average temperature drops by 1 °C the number of HDD increases by 30.5. As a consequence, the number of HDDs may be directly calculated from the mean temperatures. Needless to say, that this is in perfect agreement with our own expectations.

Energy Consumption and Productivity

In a recent study we analyzed the relationship between two basic parameters which are crucial for every economy: its final energy consumption (FEC) and its productivity level. Conventional wisdom has it that, in order to stay competitive, a modern economy has to become more productive over the years. There are clear differences between various countries as far as their productivity growth is concerned. The overall picture is such that between 1995 and the beginning of the financial crisis in 2008 economic output per working hour increased significantly in most EU Member States. Then, with very few exceptions, a general downturn set in yielding lower output figures than before the crisis. One  notable exception was Spain where productivity rose even during that difficult period.

If, on the one hand, economies are supposed to increase their production per working hour they are, on the other hand, also keen on using as little energy as possible. The aim is to produce more with the same amount of energy or, in other words, to improve energy intensity.

In order to make the two things comparable, we have indexed them, setting 2005=100, and followed them during the period 1995 – 2009. All the raw data of our investigation have been taken from Eurostat.

Let us look at the EU-27 data first (Fig. 1).

Fig. 1 Productivity and final energy consumption (FEC) in the EU. 2005=100.

We see that productivity has increased siginificantly stronger than final energy consumption (21.8% vs. 4.0%). Remarkably, just before the economic crisis, the EU managed to go up in productivity while at the same time consumption figures climbed only moderately. The crisis of 2008 led to a slight downturn in output per hour and and to a substantial lowering of energy needs.

The overall EU picture is nicely reflected by Germany showing a similar pattern (Fig. 2).

Fig. 2 Productivity and final energy consumption in Germany, 2005=100

Germany´s final energy consumption index has been fairly stable over the years, mostly oscillating between 95 and 100 and reaching its lowest value in 2009  (-3.5%). Her economic performance, on the other hand, was outstanding (+20.1%). Similar conclusions may be drawn for France and the Netherlands which are not shown here.

The situation is strikingly different in the case of Spain (Fig. 3).

Fig. 3 Productivity and final enrgy consumption in Spain, 2005=100.

First we note that Spain´s productivity gain has not at all been outstanding over the 14-year period. Compared to other countries like Germany, the increase was rather moderate (9.6%). Second, energy consumption has gone up at a much higher pace than output per hour (39.6%). As a consequence of economic crisis the consumption index went down for the first time in more than 10 years. A rather similar conclusion can be drawn for Italy (not shown), whereh a moderate rise in productivity was met by a soaring energy consumption. After 2005 consumption figures came down here, too, and the productivity index followed shortly after.

The situation looks entirely different in Sweden (Fig. 4).

Fig. 4 Productivity and final energy consumption in Sweden, 2005=100.

In terms of energy consumption Sweden has steadily gone down (-9.5%) whereas productivity gains were quite impressive (30.3%), the latter, not surprisingly, being shaken by the global economic situation from 2007 onward. This picture clearly reveals that Sweden not only managed to produce considerably more per working hour but also with less energy.  The situation is a bit similar in the UK (Fig. 5) with substantial improvements on the productivity side (30.5%). Consumption figures, on the other hand, show a slight downward trend though less pronounced than in the case of Sweden (-3.2%).

Fig. 5 Productivity and final energy consumption in the UK, 2005=100.

Thus, it is possible to see productivity rising and at the same time consume less energy. If, however, energy consumption is growing faster than productivity, this clearly indicates that there is a gap in energy efficiency which needs to be closed. Some countries set nice examples of how this can be achieved.

Does Saving Energy Push Renewables?

Yes it does. Let us look at a concrete example in order to get the point. The EU plans to improve its energy efficiency by 20% by 2020. In other words, 20% less energy will be used by then, according to plans. The baseline is the primary energy consumption for 2010 which was 1770 Mtoe. Thus, if all measures are in place, by 2020 this figure should be down to 1416 Mtoe.

In all likelihood, the savings will concern almost exclusively the use of conventional energies (coal, nuclear, oil) whereas renewable energies will not be touched by this development. Therefore, we may safely assume that on the consumption side renewables will be equally well off  as they are now. In fact, this is a very conservative estimate. On the contrary, renewable energy use may well be expected to rise over the next decade. But let us stick to our conservative approach for the time being. In 2010, the consumption of renewables amounted to some 172 Mtoe corresponding to 9.7% of total consumption.

Fig. 1 EU Gross inland consumption in 2010

Given our  2020 scenario from above and keeping renewable consumption at 172 Mtoe, we may conclude that by then renewables account for about 12.2% of total consumption. Bear in mind that this is true even if energy production from renewable sources does not increase.

The projection for 2020 would consequently look like this.

Fig. 2 EU Gross inland consumption in 2020

Thus, by saving energy the relative weight of renewables in the energy mix is automatically increased. The bigger the savings on the one hand the bigger the extra share of renewable energies on the other.



Europe´s Energy Production and Consumption

Europe´s energy production is declining. Taking the year 1990 as a baseline, total energy production was down by more than 13 % in 2009. Although the years 1995 and 2000 show a slightly higher output compared to the baseline scanario, the overall trend is pretty obvious. In absolute figures, the loss amounts to some 125.6 Mtoe. The source data for the following figures have been taken from Eurostat.

Fig. 1: Total EU Energy Production 1990-2009, Mtoe

However, this observation based on the entirety of all primary energy sources deserves a closer inspection. Let us therefore have a look at the various sectors of energy production. These are as follows: solid fuels, oil, gas, nuclear, renewables and others. Examining these sectors in more detail reveals some important facts.

The first striking observation is that the production of solid fuels went down by more then 50 % during the period in question (1990-2009). Simultaneously, the production from renewables more than doubled. Nevertheless, the increase of the the latter (76 Mtoe) is by far insufficient in order to compensate for the decline in solid fuel production (201 Mtoe). Compared to those two factors the variation of the other components such as gas, nuclear etc. has been of minor importance.

Fig. 2: EU Energy Production by Sector, 1990-2009, Mtoe

At the same time, Europe´s energy hunger is increasing as can be seen from the figure below. Yet, this is not the only remarkable piece of evidence. Whereas production output is ranging slightly over 800 Mtoe in 2009, the consumption figures are about twice as high. This creates a significant import dependency which gets even more pronounced as the data clearly indicate that indigenous production is decreasing while simultaneously consumption is growing (with the exception of 2009 due to obvious economic problems).

Fig. 3: EU Gross Inland Consumption, 1990-2009, Mtoe

It is worthwhile to combine the data for production and consumption in one figure. This clarifies the dimension of the gap between these two basic parameters. This gap needs to be filled with imports from third countries. The slump in consumption in 2008/2009 is caused by the financial crisis which severely affected the European economy. Once the economic activity recovers, an increase to pre-crisis levels may be anticipated.

Fig. 4: Gap between EU Energy Production and Consumption 1990-2009, Mtoe

As a matter of fact, Europe is highly dependent on energy imports. This is not the place to discuss the strategic, political and economic consequences of that clearcut observation. Moreover, it remains to be seen to what extent this apparent import dependency may be compensated by the increasing use of renewable energies. At first glance, it appears that the huge gap may never be filled completely by renewables. So the question is to what extent they may contribute to diminishing Europe´s import dependency on primary energy sources.