The combustion of fossil fuels provides the required energy for a variety of end-uses in all activity sectors. The emissions related to non-electric uses of energy are here determined for each sector. The CO2 emissions from non-electric uses of energy (CO2non-electric) will commonly be referred to as ‘non-electric emissions’ since they result
from uses of energy other than electricity. The determination of non-electric emissions depends on the electricity demand-flexibility scenario.
The residential sector is expected to strongly shift a significant part of its energy usage towards electricity. However, the use of natural gas will still be significant in the future to supply part of the domestic hot water, cooking, and heating needs. To ascertain the residential non-electric emissions, the natural gas consumption was determined for each end-use.
The non-electric emissions were determined similarly for the domestic hot water, cooking, and heating needs, considering the Portuguese average consumptions. The final natural gas consumption is calculated according to the useful energy required to satisfy the households that is not supplied by electricity for each end-use.
First, the final electricity consumption previously determined (see subsection 4.4.2.2) is split by the type of electric system, according to their distribution. The useful energy is determined using the efficiency of each type of system considered (𝜂𝑠𝑦𝑠𝑡𝑒𝑚,𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐). DHW and heating consider electric resistances and heat pumps as the systems used, while for cooking no specific equipment is used and only an overall efficiency is assumed. Using the electrification rate, the useful energy required for the natural gas appliances (e.g. boilers) is determined. Finally, the natural gas equipment efficiency (𝜂𝑠𝑦𝑠𝑡𝑒𝑚,𝑁𝐺) is applied to determine the primary consumption of natural gas. This process is repeated for each residential end-use (DHW, cooking, and heating) and each demand-flexibility scenario and each ensemble year.
A summarized scheme of the approach is presented in Figure 4.31 and the efficiency of the appliances is presented in Table 4.37.
Figure 4.31. Final energy needs for domestic hot water and cooking
Summary of the approach taken to determine the final energy needs for natural gas for domestic hot water and cooking needs.
Table 4.37. Efficiency of electric and natural gas systems
Efficiency of electric and natural gas equipment for domestic hot water and cooking appliances.
Efficiency of electric and natural gas systems
Domestic hot water Cookinga Space heating
𝜂𝑠𝑦𝑠𝑡𝑒𝑚,𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐
Heat pumps - COP of 3 [208]
Resistance - 93% [207]
77% [218], [219]
Heat pumps - COP of 2.5 [204]
Resistance - 100% [204] 𝜂𝑠𝑦𝑠𝑡𝑒𝑚,𝑁𝐺 92% [220] 38% [218], [219] 92% [220]
a It was considered a 7% improvement in technology efficiency, compared to present.
Having the total energy consumption of natural gas required to satisfy the residential sector ConsNG [TWh], the emission factor of natural gas (Table 4.36) is applied to
ascertain the non-electric CO2 emissions resulting from this sector, Equation (4.60).
𝐶𝑂2𝑛𝑜𝑛𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑟𝑒𝑠𝑖𝑑. = (𝐶𝑜𝑛𝑠𝑁𝐺,𝐷𝐻𝑊+ 𝐶𝑜𝑛𝑠𝑁𝐺,𝑐𝑜𝑜𝑘𝑖𝑛𝑔+ 𝐶𝑜𝑛𝑠𝑁𝐺,ℎ𝑒𝑎𝑡𝑖𝑛𝑔) × 𝑓𝑒𝑁𝐺 (4.60)
The non-electric emissions from the services, industry and agriculture sectors rely on the Portuguese RNC2050.
For industry and agriculture, a linear regression between electricity consumption and the non-electric emissions per capita is traced using the three scenarios considered in the
Efinal electricity
Electricity
Euseful electricity
𝜂 𝑠𝑦𝑠𝑡𝑒𝑚 #1
Natural gas
consumption Euseful natural gas
𝜂𝑠𝑦𝑠𝑡𝑒𝑚,𝑁𝐺 Natural gas
% electrification & % natural gas system
… %system #1 E final electricity system #1 Efinal electricity system #n %system #n 𝜂 𝑠𝑦𝑠𝑡𝑒𝑚 #𝑛
142
RNC2050 [109] (as shown in Figure 4.32). Using those regressions and the electricity consumption considered in this work for each electricity demand scenario, the non-electric emissions are determined.
a. b.
Figure 4.32. CO2 emissions and electricity demand for industry and agriculture
Linear regressions for electricity demand and CO2 emissions from RNC2050 for: a. industry; and b. agriculture. The
CO2 emissions assumed in this work for the electricity consumption are also shown: light red triangle – Low demand
scenario; red square – Central demand; and dark red diamond – High demand scenario. The grey circles represent the CO2 emissions for the three scenarios considered in RNC2050 [109].
In the case of services, the RNC2050 assumes that two of their scenarios have undergone complete electrification of the sector. For this reason, here, it is assumed that the scenarios with higher electricity demand (Central and High demand) are also completely dependent on electricity, thus they are free from non-electric emission originated in the services. The less electrified scenarios (i.e., Low demand) are considered to still rely on natural gas for other energy uses, e.g. for space heating. In RNC2050, the only scenario that is not completely electrified considers an electricity demand of 1.83 MWh/capita and 0.07 tCO2/capita. Since less electrification leads to the displacement of energy to natural gas, resulting in higher non-electric emissions, the non-electric emissions were considered to be inversely proportional to electricity demand. Thus, the non-electric CO2 emissions for the services is of 0.08 tCO2/capita for the Low demand scenarios.
For mobility, different approaches were taken. Non-electric light passenger vehicles were assumed to use gasoline (fegasoline of 73.7 kgCO2/GJ [217]) and to travel the same daily
distance as EVs. PHEV gasoline consumption was also considered since about 5% of its distance is travelled using conventional fuels. Equation (4.61) describes the calculation required to determine the CO2 emissions originated by light passengers.
𝐶𝑂2𝑛𝑜𝑛𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑙𝑖𝑔ℎ𝑡 𝑝𝑎𝑠𝑠.
= 𝑛𝑑𝑎𝑦𝑠× 𝑁𝑝𝑟.𝑣𝑒ℎ.× 𝑐𝑝𝑟.𝑣𝑒ℎ., 𝑔𝑎𝑠𝑜𝑙𝑖𝑛𝑒[(1 − 𝑆𝐸𝑉) × 𝐷𝑝𝑟.𝑣𝑒ℎ.,𝑔𝑎𝑠𝑜𝑙𝑖𝑛𝑒
+ 𝑆𝑃𝐻𝐸𝑉× 𝐷𝑃𝐻𝐸𝑉,𝑔𝑎𝑠𝑜𝑙𝑖𝑛𝑒] × 𝑓𝑒𝑔𝑎𝑠𝑜𝑙𝑖𝑛𝑒× 10−12
(4.61)
where ndays is the number of days in the year; Npr.veh. is the number of private light
passenger vehicles; cpr.veh., gasoline is the energy consumption of private light passenger
vehicles, assumed as 2.05 MJ/km 18; SEV and SPHEV is the share of electric vehicles and
light plug-in hybrid electric vehicles (PHEV) in the light passenger fleet, respectively [fraction]; Dpr.veh.,gasoline and DPHEV,gasoline are the daily distance travelled by the gasoline
private vehicles and the daily distance travelled by PHEV private vehicles in non-electric mode, respectively [km]; finally, the multiplying factor ‘10-12’ is used to adjust units. The Portuguese roadmap RNC2050 was used as a reference for the remaining fuel consumption, with some adaptations [175]. For freight vehicles, the vehicles propelled by hydrogen in the roadmap were shifted to biofuels, while the consumption from diesel-fueled vehicles is taken directly from the roadmap (fediesel of 74.1 kgCO2/GJ [217]).
To replace hydrogen consumption by biodiesel, a 48% [221] and 22.5% [222] efficiency of hydrogen and biodiesel were assumed, respectively. Heavy passenger vehicles were assumed to be completely fueled by diesel and biofuels. The roadmap includes a small fraction of electricity, that was converted to biofuel consumption (assuming also 22.5% efficiency for biofuel consumption).
18 A 20% improvement in efficiency was applied to the current energy consumption of 2.56 MJ/km [229],
144
Table 4.38. Fuel consumption from freight and heavy-duty passenger vehicles
Assumptions for the fuel consumption from freight and heavy-duty passenger vehicles, according to adapted results from the RNC2050 [175].
Freight and Heavy-duty passenger vehicles – Fuel consumption [GJ]
Low demand Central demand High demand
Freight Light-duty Diesel 6.6 - - Biofuels 2.9 - - Heavy-duty Diesel 25.2 - - Biofuels 28.4 17.9 35.8 Passenger Heavy-duty Diesel 2.68 0.02 0.05 Biofuels 3.78 5.64 11.3
CO2 emissions from railways, navigation and aviation were not considered in this work. The resulting non-electric emissions are shown in Table 4.39.
Table 4.39. Non-electric CO2 emissions
Summary of non-electric CO2 emissions for residential, services, industry, agriculture and mobility.
Non-electric CO2 emissions [Mton]
Low demand Central demand High demand
Residential 0.7-0.9 0.4-0.6 0.1-0.3 Services 0.8 - - Industry 12.3 7.3 2.3 Agriculture 0.9 1.2 1.4 Mobility Passenger Light-duty (private) 1.3 3.2 0.2 Heavy-dutya 0.2 ~0 ~0 Freight Light-duty 1.9 - - Heavy-duty 0.5 - -
Total non-electric CO2 emissions 18.6-18.8 12.1-12.3 4.0-4.2
a In Central and High demand scenarios, the heavy passenger vehicles are assumed to be mostly from