Promoting Green Power in Canada - Centre for Human Settlements

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Promoting Green Power in Canada Pollution Probethe current energy mix can be overcome byanother evaluation parameter, the EnergyPayback Time.2.2.2 Energy Payback Time (EPT) andEnergy Payback Ratio (EPR)The EPT is based on the number of yearsneeded for a given plant to make up for theenergy consumed during its manufactureand construction, as well as during its ownuse. The EPT is the amount of time it takesfor the plant to produce a positive net energyoutput beyond the amount needed for itsconstruction and operation.A similar ratio to the EPT, called the EPR, canbe calculated as a CO 2breakeven point,instead of one related to energy productionand consumption. EPT is generally used toavoid the controversy arising from trying todetermine the quantity of CO 2emissions analternative energy source can displace — assuch displacements are calculated based onthe existing energy mix, which can be shiftedtowards less greenhouse gas intensivesources through green power promotionpolicies. The energy breakeven point doesnot depend on the composition of thebackground mix and therefore helpsdetermine the most energy-efficienttechnology for a long-term energy strategy.Figure 2.3, with values calculated for NorthAmerica, shows that the energy paybackratios for hydro-based energy sources are farsuperior to those of all other options. Theother conventional and renewable powersources have similar ratios, with wind andforestry residues having a slight advantage.Intermittent sources are singled out asneeding back-up power for powermanagement purposes. Other sources, suchas large hydro or natural gas, need to be usedto fill in for these sources when they do notproduce enough electricity (e.g., due to lackof wind), so during those periods the EPRsof the back-up technology used would apply.Figure 2.3 — Comparison of Energy Payback Times of Different Technologies [HQ 2000]6
Promoting Green Power in Canada Pollution ProbeSolar PV is found to be one of the leastperforming options. The EPT for solar PVdepends on the technology used and whereit is used (i.e., local solar radiation intensityand duration). The EPT has been estimatedby one source at 10 years for monocrystalline,3–5 years for polycrystalline, and 0.5–2 yearsfor a-Si solar PV modules [GEF 1996, p. 37].A more recent study found EPTs of 4.1 yearsfor monocrystalline and 2.2 years for thinfilm modules, at an energy output of 1.7 MWhper m² per year, and the authors estimatethat a further 30% reduction is possiblethrough improved production techniques[KNAPP 2000]. As energy needed for themanufacture of transmission lines is notincluded in these calculations, gridintegratedsolar panels may enjoy a furtherEPT reduction in comparison to technologiesthat require new transmission lines to be builtto deliver their electricity to the power grid.2.2.3 Water and Land UseHydro power uses water to store energy,influencing the natural course of waterwaysand biological processes or ecosystems (e.g.,salmon runs, wetlands). Other energy sourcesneed water for cooling purposes, againinfluencing conditions in waterways or lakes.Land use varies depending on how diffuse aform of energy is. Solar energy, for example,requires a much larger surface than a gaspower plant in order to produce a givenamount of energy. Giving the typical surfaceused by a power generating plant in m² perkWh does not, however, reflect the kind ofuse. For example, a gas power plant does notleave any space for biodiversity on its premises;a wind power plant may use a lot more spaceper kWh, but will allow for secondary uses ofthe area around the wind turbines, such asTable 2.1 — Water and Land Use for Different Energy Generating SourcesPower SourceNuclearCoalNatural GasOilWaste-to-EnergyForest surface set aside forsustainable forestryEnergy cropsLarge HydroSmall HydroSolar PVSolar ThermalWindGeothermalLand Use [ha/1000GWh annual]4836325–20025–200445132,000–220,00060,00075,000Run-of-river: 282,00025011,666 total233 actual3,750Water Use[m 3 /GWh]3.6–5.7 (consumptive)995,000 (non-consumptive)2.8–4.3 (cons.)730,000 (non-cons.)1.1 (cons.)730,000 (non-cons.)1.3 (cons.) 1No data available 111.8>11.82,700,000–33,600,000;average: 16,100,00081,500,0000.14~4.2001Cooling water consumption for oil and waste-to-energy combustion are assumed to be in the same rangeas that of coal and natural gas.7
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