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Summary of Transpower’s peak forecast process Transpower, June 2013 Overview Our annual peak forecasting process can be divided into two inter-locking processes: top-down process – used to derive national and regional forecasts bottom-up process – used to derive grid exit point forecasts as well as inform our top-down process. We focus on finding a plausible range for future demand growth rather than on specific scenarios. Future demand is uncertain, particularly at the limits of the planning horizon and we feel it is important that our approach recognises this fact. Figure 1 shows the plausible range associated with our latest forecast for peak New Zealand demand. New Zealand Peak Demand Forecast 12000 10000 Would take major shift 8000 MW 6000 Plausible range 4000 Would take major shift 2000 Historical peaks 2013 provisional New expected New prudent Low bound High bound 2030 2029 2028 2027 2026 2025 2024 2023 2022 2021 2020 2019 2018 2017 2016 2015 2014 2013 2012 2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1998 1997 0 Figure 1, New Zealand Peak Demand Forecast Top-down forecast In 2011 we introduced an ensemble approach where a number of different models are used to derive forecasts. Each attempts to predict demand, excluding that of major industrial users but including demand serviced by embedded generation, in a slightly different way. Major industrials and embedded generation are tracked separately on a case-by-case basis so as to calculate “grid offtake” demand. Our ensemble approach uses four different approaches, each with uncertainty, and mixes these to generate overall national and regional forecasts. See Figure 2 for an overview. From the spread of the peak forecasts we take the 50th percentile as the mean peak forecast and a higher value as the prudent peak forecast. The prudent peak is set at the 90th percentile for the first seven years and grows at the mean rate thereafter. Ensemble of regional demand forecasts Populationand GDPbased forecast Trend forecast MET service temperature data Trend 20082012 forecast MBIE-based forecast Mix Modelled demand NZIER GDP forecast MBIE energy forecast Historical demand Embedded generation & industrials Stats NZ population forecast “Top-Down” regional peak forecast Forecast embedded generation & industrials Consolidate TP and lines’ companies’ local knowledge Lines’ Company Consultations Final GXP peak forecast “Bottom-Up” GXP peak forecast Figure 2 Peak demand forecasting process Trend forecast The trend forecast is based on straight-line regression of peak demand from 1997 to 2011 with savings campaign years (2001, 2003, 2008) excluded. The historical peak demand data is corrected to account for differences due to temperature effects before the model is fitted. Uncertainty comes from uncertainty in the regression parameters and uncertainty associated with temperature. Econometric forecast The econometric forecast regresses the logarithm of peak demand on the logarithms of population and GDP over 1974-2011 and then projects this forward using Statistics New Zealand population projections and New Zealand Institute of Economic Research GDP projections. As above, the historical peak demand data is also corrected to account for differences due to temperature effects before the model is fitted. Uncertainty comes from population and GDP variations, as well as that associated with regression and temperature. Ministry of Business Innovation and Employment (MBIE) forecast The MBIE forecast uses the 2011 Energy Outlook electricity energy forecasts. Uncertainty comes from the high and low versions of the MBIE forecast. Trend 2008-12 forecast The first three forecasts all predict similar growth rates but recent growth has been much lower. To account for the possibility that recent rates are the beginning of a new long-term trend, we have added a fourth member to the ensemble which is based on the recent trend since 2007, but otherwise identical to the standard trend model. The ensemble The four spreads of forecast values are mixed in equal proportions to form the ensemble. Bottom-up forecast To forecast each of the 200+ individual grid exit point (GXP) peak grid offtakes, we use: local knowledge from various sources including the relevant lines’ company, and local industry lines’ company intentions of (permanent or temporary) feeder changes forecasts of embedded generation and major industrial loads, and detailed history of the load. The individual GXP forecasts are derived with reference to the top down forecasts and passed to the relevant customer for comment before being finalised. The GXP forecasts are also used as a basis for calculating the contribution each GXP makes to regional and island peaks. Comparison with previous forecasts Figure 3 compares this national forecast with previous prudent forecasts. The effect of the lower growth rate from the short-term trend is visible in the difference between last year’s mean curve (orange dashes) and this year’s (red dashes). Figure 3, Historical comparison of prudent peak forecasts Regional Detail The figures below list the regional growth rates and how they have changed from last year. In the North Island, all regions are down except the Bay of Plenty. This is actually an artifact of redistricting – we have moved Kinleith from Waikato to Bay of Plenty in our planning region definitions. In the South Island, all regions show reduced growth, except South Canterbury where dairy and irrigation load growth continues. The West Coast has reduced the most as it has lost some Holcim cement load and Solid Energy developments off a low base. Figure 4, North Island Regional Forecasts, 2013 forecast vs. 2012 forecast Figure 5, South Island Regional Growth, 2013 forecast vs. 2012 forecast