Electrical properties

The practical energy savings in passive systems can now be calcu-lated using equation 5.2, in which the primary energy use values from table 5.1 are multiplied with the percentage gains available from each model. Using primary energy values has the effect of compounding the energy savings in the passive system back up through the entire energy conversion chain, and allows the reduc-tion in carbon emissions to be inferred.

Table 5.22 summarises the practical energy and carbon savings for the passive energy systems. It shows that the greatest absolute energy savings (column 4) are found in buildings, and in particular heated spaces and appliance systems. As with the ranking of con-version devices in the previous chapter (see table 4.6), aircraft are prioritised lowest, demonstrating that the aircraft engine (device) and the aircraft (system) are comparatively well optimised. In ad-dition, the low ranking for aircraft confirms that scale of energy flow through the system is a reasonable indicator of the absolute

Table 5.22 Practical energy and carbon savings

Passive Practical Energy Energy Carbon Carbon

System savings demand savings emissions savings

% EJ EJ Gt CO₂ Gt CO₂

Heated space 98 72 71 3.3 3.3

Appliance 67 88 59 4.1 2.8

Furnace 62 67 42 4.0 2.5

Car 91 40 37 2.8 2.6

Driven system 59 56 33 3.3 1.9

Truck 54 38 20 2.6 1.4

Steam system 66 31 20 2.0 1.3

Hot water system 80 23 18 1.1 0.9

Illuminated space 95 18 17 1.1 1.0

Cooled space 100 14 14 0.8 0.8

Ship 63 10 6 0.7 0.4

Train 74 8 6 0.5 0.4

Plane 46 11 5 0.8 0.3

Building 83 215 179 10.5 8.8

Factory 62 154 95 9.3 5.7

Vehicle 70 106 74 7.3 5.1

Total 73 475 348 27.1 19.6

energy savings available.

The analysis presented in this chapter demonstrates that an aver-age global energy saving of 73% is practically achievable in passive energy systems. It is the first time that the practical energy sav-ings in passive systems have been assessed separately from those in conversion devices. Representative global energy data was of-ten unavailable across the range of technology options, making the accurate assessment of current energy use in passive systems challenging. The allocation of energy use between the conversion device and the passive system also proved difficult in some cases.

Nevertheless, basing the practical limit on fundamental engi-neering principles has removed much of the uncertainty from the analysis. Current energy use is forever changing, but at least the

§5.5

practical target by definition will remain stable. Furthermore, technology options and efficiencies are surprisingly uniform across the world’s geographic and economic zones. There are clear ex-ceptions, such as wood fired stoves in the developing world, but in many cases economic status determines whether or not you own an energy consuming technology, not the efficiency of the technology.

Therefore, it is hoped that this research proves useful for under-standing the function and utilisation of energy in passive systems, and becomes a basis for setting future priorities for action in the field of energy efficiency.

Having determined the efficiency limits for all energy conversion devices (theoretical limit) and passive energy systems (practical limit), it is now possible to identify efficiency options from across the entire global energy network.

6.1 What new conclusions can now be made?

If all conversion devices and passive systems could be operated at their efficiency limit, then substantial reductions in primary energy use and carbon emissions would result. Today’s conversion devices are inefficient, converting on average only 11% of primary energy input into a useful energy output. Passive systems use only 27% of the useful energy input to deliver final services. The remaining energy is currently lost as low temperature heat to the environment. Multiplying these efficiency limits together gives an overall efficiency for the entire network of 3% suggesting more than a 30-fold improvement in efficiency is technically possible.

Table 6.1 shows the potential energy savings in conversion de-vices and passive systems. The largest potential saving across all devices and systems is found in the passive system of the heated space. This is due to both the scale of energy use for heating build-ing spaces and the possibility of thermally insulatbuild-ing the buildbuild-ings in most parts of the world, such that no artificial heat input is re-quired to keep the occupants comfortable.

Clearly, the potential savings in energy cannot be all achieved at the same time. Efficiency gains in the conversion devices cannot be simply added to the gains in the passive systems (as stressed

§6.1

Table6.1Efficiencylimits,energysavingsandcarbonsavings ConversionPrimaryPercentEnergyCarbonPassivePrimaryPercentEnergyCarbon deviceenergysavingssavingssavingssystemenergysavingssavingssavings EJ%EJGtCO2EJ%EJGtCO2 Electricheater5893543.1Heatedspace7298713.3 Dieselengine5880473.3Appliance8867592.8 Electricmotor5583462.6Furnace6762412.5 Biomassburner4994450.0Car4091372.6 Gasburner4788412.3Drivensystem5659331.9 Petrolengine4188362.5Truck3854201.4 Cooler3398331.9Steamsystem3166201.3 Coalburner3183262.2Hotwatersystem2380190.9 Oilburner2886241.7Illuminatedspace1895171.0 Heatexchanger2098201.2Cooledspace14100140.8 Lightdevice1896171.0Train87460.4 Electronic1698150.9Ship106360.4 Otherengine108280.6Plane104650.3 Aircraftengine117580.5 Heat2339021010.4Building215831798.8 Motion175831459.6Factory15462955.7 Other6798653.8Vehicle10670745.1 Total4758942023.8Total4757334819.6

several times in this thesis) without saving more energy than is consumed.

6.1.1 Where are efficiency gains most likely?

The analysis has shown that conversion devices on average operate at only 11% of their theoretical potential. Yet, given the sizeable effort already in progress to improve device efficiency, it is unlikely that this ideal—a factor 10 improvement—will be approached in the near future. Where should action and responses be focused?

Is it better to prioritise efforts on improving coal fired power sta-tions or diesel engines? This is difficult to answer because the theoretical saving in both energy and carbon emissions depends not only on the efficiency of the individual device, but also on the upstream efficiencies of all devices in the energy chain. A solution to this question can be found by performing a sensitivity anal-ysis to assess the energy savings that would be achieved from a small independent change in efficiency for each type of conversion device.

Applying an absolute efficiency change (for instance, increasing each value of by 1%) to each device might be misleading, as achieving an equivalent gain in an already efficient device is likely to be more difficult than for a less efficient device. Instead, the conversion loss (which equals the theoretical energy saving) for each device is reduced by 1%, and a modified device efficiency is calculated using:

⁰ =+ (1−)×1% = 0.99+ 0.01 (6.1)

The efficiency of each device in turn was changed to the modi-fied value (⁰) and the resulting total global energy input required to deliver the same useful energy was calculated. This leads to a sensitivity analysis of energy savings for the same relative level of improvement in each device, and provides a more equitable way

§6.1

to compare and rank individual conversion devices, irrespective of the location of the device in the energy network. This sensitivity analysis is performed for individual conversion devices, as opposed to energy chains, and the results are shown in figure 6.1. The chart shows the reduction in energy and carbon emissions resulting from a 1% reduction in the energy loss from each conversion device.

Efforts to improve the efficiency of coal-fired power stations will deliver the most savings in the upstream fuel conversion and electricity generation processes, because coal dominates electricity generation. However, greater energy savings are available from focusing individually on: biomass burners, coolers, gas burners and petrol engines. Collectively, prioritising efficiency measures for end-use conversion devices over fuel transformation and electricity generation delivers more than five times the potential gain (28 EJ versus 5 EJ). This is a surprising result, given the emphasis placed on improving the efficiency of electricity generation, for example in the International Energy Agency (IEA) report,Energy technology perspectives 2008.¹

Biomass burners emerge as the single most important conver-sion device and where the largest energy savings can be achieved from an incremental improvement in efficiency. These burners are predominantly open fires, which burn wood, dung, crop waste, coal and charcoal, to meet the energy needs of people living in the developing world. The reason biomass burners top the sensitivity list is due to the scale of use—used by half the world’s population and burning more than 10% of global energy supply—and the inefficiency of the burners, averaging only 7%. In this analysis, biomass burners do not contribute to carbon emissions, because it is assumed that the carbon dioxide (CO₂) released during combus-tion is equivalent to the CO2 absorbed when growing the biomass.

However, if the biomass is not replaced, for example in areas where deforestation is a problem, then net carbon emissions to the atmo-sphere result. Improving the efficiency of biomass burning stoves is technically very easy, and has the added benefit of reducing

res-Figure 6.1 Sensitivity ranking of individual conversion devices

piratory illness from the inhalation of smoke, which is ‘the single biggest killer of children under five years of age’.^190(p.24) However, wide-scale dissemination of improved stove technology is held back

§6.1

by insufficient international political backing, limited funding and the enormous number of open fires in use.

6.1.2 Application of this research

The results of this research demonstrate that significant energy savings are technically possible in conversion devices and passive systems. Yet such gains are not necessarily achievable, and his-tory has shown that technical efficiency potentials are typically under-realised. The use of theoretical and practical efficiency lim-its presents an ideal, an ideal which may not be realised because of economic or behavioural constraints. This work makes no at-tempt to assess the economic costs of developing and deploying advanced efficiency measures. Neither does it consider the many socio-economic barriers to the uptake of new technologies. There-fore, one must be careful to avoid claiming that the calculated efficiency targets will or even should be attained.

Economists tend to assume that change can be brought about by the choice of appropriately constructed policies. Such thinking can neglect questions of the fundamental physical and engineer-ing laws, which place limits on the energy that can be saved. By providing an overview of the entire energy network and assess-ing the potential impact of energy efficiency measures, this thesis contributes to the field of policy-making by demonstrating both the potential reach and the limits of energy efficiency. If techni-cal solutions can be found, and are supported by well designed policy measures, then large reductions in energy use and carbon emissions are possible.

Further research is required to evaluate the effect that efficiency gains have on the embodied energy in the device or system. It is possible that some of the potential energy savings may be eroded by the additional embodied energy required to manufacture the improved conversion devices and passive system. Thus, a fraction of the saved energy from transport or buildings may reappear as

an increase in factories for the production of materials and goods.

However, the common assumption that more efficient devices are always more energy intensive to build, does not always hold. Three practical examples are given to illustrate this point:

1. It is possible to design a super-insulated and air-tight building, which does not require artificial external heating or cooling, and therefore also dispenses with the need for energy intensive capital equipment such as boilers and air-conditioning units.

2. Light-weight streamlined cars deliver higher fuel efficiency as well as reductions in the size of the engine, drive train, braking system and structural components of the vehicle.

3. In many cases it is more cost effective for power utility compa-nies to give away efficient light-bulbs and appliances than increase generation capacity by building new power stations.

Such win/win options that reduce both operational energy useand the energy embodied in capital equipment, should be prioritised.

The scope of this thesis is wide-ranging, covering a large body of literature and drawing heavily on statistical energy data and previous efficiency studies. The intricacies of specific energy pro-cesses are only examined to the level of detail necessary to deter-mine the limits to efficiency. The accuracy of the analysis could, with more time, be improved. Despite best efforts to find repre-sentative global data for current device and system use, in many cases only regional or country specific data could be found. Allo-cating energy flows and losses between the conversion devices and passive systems proved difficult in some cases. It is hoped that other energy researchers will contribute understanding from their specific areas of expertise, to improve, correct and validate the re-search. Nevertheless, even in its current form, the results of this work are useful for directing future research priorities and setting energy policy in the field of efficieincy.

§6.2