Page 1 of 4 ER 100/200, Fall 2007 Topics Covered: Economic Analysis, LCA, Power Sector Regulation Problem Set #4 Total Points: 100 Due Thursday, 10/18 at 5pm. Solutions will be posted on Friday, 10/19. We will grade and return the homework by Monday morning 10/22. For this problem set only, NO LATE SUBMISSIONS WILL BE ACCEPTED FOR CREDIT!! 1. Life Cycle Analysis (LCA) - [55 points total] One of Horvath and Kammen’s former students (and a former ER100/200 GSI), Sergio Pacca, conducted a life cycle assessment of the climate change impacts from an upgrade of the Glen Canyon Dam (GCD). GCD is a 1,296 MW hydroelectric facility located near the Arizona-Utah border. He compared the impacts of GCD relative to a hypothetical set of renewable and non-renewable power stations in similar locations and delivering comparable amounts of electricity. Here we’ll conduct our own comparison based on a simplified version of his study.1 Although they don’t emit GHGs from electricity production, hydroelectric facilities emit pollutants during construction. Also, the gradual decay of biomass and the loss of net ecosystem productivity (NEP) caused by flooding of large land areas emits greenhouse gases.2 The analysis assumed that the flooded area was 65,300 ha. Including construction, biomass decay, and loss of NEP together, GCD will emit ~5 million tons of CO2 equivalent GHGs over its first 20 years of operation. Table 1 describes this in more detail (totals are rounded to one significant figure): Table 1: Emissions from construction and Land-Use Change for GCD Emissions in CO2 Equivalent (metric tons - MT) Quantity used in plant construction (MT or m3) Unit Cost (1997 $/MT) Total Cost (1997 $) CO2 CH4 N2O GWP b Concrete 9,906,809 30 297,652,257 400,792 751 7,898 409,441 Excavation (m3) 4,711,405 na 114,839,000 3,812 - - 3,812 Turbines and turbine generator sets na na 65,193,084 41,725 45 249 42,019 Power distribution and transformers na na 13,754,764 12,358 16 79 12,453 Steel 32,183 385 12,402,138 43,710 29 244 47,583 Copper 90 2,368 214,167 186 - 2 188 Aluminum 67 1,268 84,804 157 - 2 159 Total from construction a 500,000,000 500,000 1,000 9,000 500,000 Flooded Biomass – median estimate 4,000,000 Loss of NEP 400,000 Total (first 20 years) a 5,000,000 a Total emissions are rounded to one significant digit. b GWP is the sum of all GHGs in tons of CO2 equivalent (we’ll explain this concept later when we study climate change) 1 They published a paper on this study, but the solutions to this exercise won’t match the paper exactly because the model has changed and our assumptions are simplified relative to their analysis. Pacca and Horvath, GHG Emissions from Building & Operating Electric Power Plants in the Upper Colorado River Basin. ES&T, 2002. 36: p. 3194-3200. http://pubs3.acs.org/acs/journals/toc.page?incoden=esthag. 2 NEP is a change in the net carbon storage of an ecosystem, expressed as a rate of C loss or gain per area. Most ecosystems are steady-state (NEP ≈ 0). Only some ecosystems, such as regrowing forests, accumulate carbon and act as significant net carbon sinks. The landscape of GCD, before flooding, was accumulating carbon and therefore had an NEP > 0. In our analysis, we will count the loss of carbon uptake as being identical to carbon emissions.Page 2 of 4 a) Estimate the average GHG emissions in gCO2-equivalent per kWh for the dam over its 40-year life. In 1999, GCD produced 5.6 TWh of electricity, and you can assume that the dam will produce that amount of electricity every year. Also, assume that the rate of loss of NEP is constant throughout the 40 year period, and that this is the only source of carbon dioxide “emissions” after the first 20 years. [3 points] b) Now estimate the life-cycle emissions and emission factors resulting from the production of an identical quantity of electricity over a 40-year period based on 1) a large centralized photovoltaic (PV) facility and 2) a coal-fired power plant. To make this a bit less complicated, you should break it into the following steps. i. Calculate the capacity (in MW) of the coal and PV plants needed to produce 5.6 TWh/year. Assume that the capacity factor is 70% for the coal plant and 20% for the PV plant. [5 points] ii. Estimate emissions that will result from land-use change. For this, assume that the coal plant occupies a relatively small space so that we can ignore its land-use change impacts and only consider the land-use change impacts of PV, which we know requires much more space. Assume that the PV plant is made from 100W panels that are each 1.3m x 0.7m. The plant also requires space between PV panels to avoid shading and allow access roads and pathways (assume these needs add 50% to the total area of panels). Estimate the total land area occupied by PV arrays, including spacing, paths and roads. [3 points] Now, assume that that the PV plant is built on the same type of landscape as GCD, and causes the same loss of NEP per hectare. However, there is no decay of existing biomass. Estimate the loss of NEP resulting from shading from the arrays and paving on the access roads. Use data in Table 1 and assume the loss of NEP is directly proportional to the area used (for either shading or flooding). [2 points] Are we justified in ignoring decay? Are we justified in assuming that the loss of NEP per hectare is the same for the PV facility as for GCD? Explain why or why not. [5 points] iii. Now estimate the emissions resulting from plant construction – this is where we’ll use the EIOLCA model. First, estimate the total mass of each construction component and the electricity required for the production of the PV plant based on the information given in Table 2a and b and your answers to b(i). Enter the total cost of each component into the tables (you can paste them into Excel if you think it’s easier to manage calculations that way). Use these costs as inputs into the EIOLCA model (www.eiolca.net) and estimate the net emissions of the GHGs listed in Table 2a and b and complete the rest of each table (gray spaces shouldn’t be filled in). To keep things simple, only report total GHG emissions (“GWP” from the model’s output page). See hint below about which