PROCEEDINGS, Thirty-Eighth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, February 11-13, 2013 SGP-TR-198 COMPARISON OF GEOTHERMAL WITH SOLAR AND WIND POWER GENERATION SYSTEMS Kewen Li China University of Geosciences, Beijing/Stanford University Stanford Geothermal Program Stanford, CA94305, USA e-mail: [email protected] estimated 208 gigawatts (GW) of electric capacity ABSTRACT added globally during 2011. Wind and solar photovoltaics (PV) accounted for almost 40% and Geothermal, solar and wind are all clean, renewable 30% of new renewable capacity, respectively, energies with a huge mount of resources and a great followed by hydro-power (nearly 25%). By the end potential of electricity generation. The unfortunate of 2011, total renewable power capacity worldwide fact is that the total capacity installed of geothermal exceeded 1,360 GW, up 8% over 2010; renewables electricity is left behind solar and wind. In this paper, comprised more than 25% of total global power- attempt has been made to find the essential reasons to generating capacity (estimated at 5,360 GW in 2011) cause the above problem and to look for the and supplied an estimated 20.3% of global electricity. solutions. Cost, payback time, size of power Non-hydropower renewables exceeded 390 GW, a generation, construction time, resource capacity, 24% capacity increase over 2010. Unfortunately, the characteristics of resource, and other factors were contribution of geothermal power is very small. used to compare geothermal, solar, and wind power generation systems. Furthermore, historical data from Not only do future energy technologies need to be geothermal, solar, and wind industries were collected clean and renewable, but they also need to be robust, and analyzed. Suggestions have been proposed for especially in some developing countries such as geothermal industry to catch up solar and wind China. Recently the heavy fog enveloped a large industries. swathe of East and Central China was an example. There was neither sunshine (no solar energy) nor INTRODUCTION wind (no wind turbine rotating). Beijing was hit 4 Renewable energy sources have grown to supply an times by heavy haze and fog within one month in estimated 16.7% of the total global energy January 2013. Hundreds of flights were cancelled and consumption in 2010. Of this total, modern highways were closed. Beijing meteorological renewable energy (wind, solar, geothermal, etc.) observatory issued a yellow alert (the highest level accounted for an estimated 8.2%, a share that has alert) for heavy fog on January 22, 2013. increased in recent years (Renewables 2012: Global Status Report). In this study, cost, payback time, capacity factor, size of power generation, construction time, resource It is known that geothermal energy has many capacity, characteristics of resource, social impact, advantages compared with solar and wind systems. and other factors were compared for geothermal, These advantages include weather proof, base load, solar, and wind power generation systems. Historical great stability, and high thermal efficiency. The total data from geothermal, solar, and wind industries were installed capacity of geothermal electricity, however, collected and analyzed. Possible directions have been is much less than solar and wind. The power of the proposed to speed up geothermal power growth. Note total solar PVs manufactured by China in the last five that only geothermal electricity generation was years were equal to the total geothermal power considered and direct use of geothermal energy was installed in the entire world in the last one hundred not included in this paper. years. As summarized in Renewables 2012: Global Status Report, renewables accounted for almost half of the COMPARISON OF RESOURCES, INSTALLED about 6500 TW and that over land in high-solar POWER AND CAPACITY INCREASE locations was about 340 TW, as reported by Jacobson (2009). The resources, installed capacity, and its increase in the last three years for PV, wind, hydro and geothermal energies are listed in Table 1. Note that the resources of the four energy types from different references are very different. According to GEA, the total geothermal power installed in world was about 11.2 GW until May 2012 (also see Clean Energy, v.6, p. 72, 2013). According to WEA (2000), geothermal has the largest resources among the four types of renewable energies. Figure 2: Modeled world Surface radiation (W/m2) Table 1: Comparison of Resources, installed power (global average: 193; land: 185) and increase in last three years (2009- 2011). Figure 3 shows the distribution of world average heat Energy Resource Resource Installed Increase (TW) (TW) (GW) (GW) flow rate (Figure 3a) and the location of world PV ① ⑥ ③ ③ geothermal power plants (Figure 3b). One can see 6500 49.9 70 47.0 that the two maps match very well, that is, the areas Wind 1700① 20.3 240③ 79.0③ with the highest heat flow rates have the most geothermal power plants. The geothermal resource Hydro ④ ③ ⑤ ③ 15955 1.6 970 (1010) 55.0 worldwide was about 67 TW (Stefansson, 2005). Geoth 67⑦ 158.5 11.2 0.30 ①Jacobson (2009) ②Chamorro, et al. (2012) ③REN21 Report (2012) ④Kenny, et al. (2010) ⑤Lucky (2012) ⑥WEA (2000) ⑦Stefansson (2005) Figure 1 shows the modeled world wind speeds at (a) Distribution of world heat flow rate 100 meter. The resource of all wind worldwide was (http://geophysics.ou.edu/geomechanics/notes/heatflo about 1700 TW and that over land in high-wind areas w/global_heat_flow.htm) average: 0.06 W/m2 outside Antarctica was about 70-170 TW reported by Jacobson (2009). Note that the predicted world power demand in 2030 would be 16.9 TW. (b) Location of world geothermal power plants (source: thinkgeoenergy.com) Figure 3: Distribution of world heat flow rate and Figure 1: Modeled world Wind speeds at 100 meter. geothermal power plants. The modeled solar downward radiation in the world The comparison of resources, installed capacity and is shown in Figure 2. The global average radiation the increase of power in the last three year is plotted was about 193 W/m2 and that over land was around 2 in Figure 4. 185 W/m . The resource of all PV worldwide was 100000 100 Resource (TW) 10000 Resource(TW)⑥ Installed(TW) 1000 10 100 10 Increase, GW Increase, 1 1 0.1 0.1 0.01 PV Wind Hydro Geoth PV Wind Hydro Geoth (e) power increase in last three years (a) Resource, installed power and increase Figure 4: Resources, installed capacity and the 100000 increase in the last three years. 10000 The change of the installed global power capacity with time for geothermal, PV, and wind is shown in 1000 Figure 5. One can see that PV’s power change rate was the maximum, followed by wind power. The 100 above trend can also be seen in Figure 6, which Resource , TW Resource demonstrates the average annual growth rates of 10 renewable energy capacity during the period of 2006–2011. 1 PV Wind Hydro Geoth 10000 Geothermal (b) Resource (Jacobson , 2009) 1000 Wind 100 PV 10000 10 1 0.1 1000 Global Capacity, GW Capacity, Global 0.01 0.001 1975 1981 1987 1993 1999 2005 2011 100 Resource, TW Resource, Year Figure 5: Comparison of installed global capacity for individual energy types. 10 PV Wind Hydro Geoth 100 (c) Resource (WEA) 2011 only(%) 1 80 74 58 0.8 60 0.6 40 26 20 0.4 20 Installed, TW Installed, 3 3 1 2 0.2 0 PV Wind Hydro Geoth Figure 6: Average annual growth rates of 0 renewable energy capacity, 2006–2011 PV Wind Hydro Geoth (d) installed power (REN 21, 2012). 8 Note that the average annual growth rate of geothermal power was about 2% while that of PV was about 58% during the same period and up to 74% 6 in 2011 only. 4 COMPARISON OF COST, EFFICIENCY, AND ENVIRONMENTAL IMPACTS year Payback, 2 The cost, payback time, and construction time for different energy types are listed in Table 2. The data are also plotted in Figure 7. The cost of geothermal 0 energy is very close to wind energy but much less PV Wind Hydro Geoth Coal Gas than PV. Compared with wind and PV, the main disadvantages of geothermal energy may be the long (c) payback time payback time and the construction period (Tc). 16 Table 2: Comparison of cost, payback time, and construction period (Kenny, et al., 2010) 12 Cost Payback Construction (US/kWh) (year) (year) 1-2.7 0.3~0.5 8 PV $0.24 year Tc, Wind $0.07 0.4-1.4 <1 11.8(small) 1 Hydro $0.05 4 0.5 (large) 10~20 Geoth $0.07 5.7 3~5 Coal $0.04 3.18 1~3 0 PV Wind Hydro Geoth Coal Gas Gas $0.05 7 2~3 (d) construction period 100.00 investment (US/kWh) Payback (year) Figure 7: Comparison of cost, initial investment, 10.00 Tc (year) payback time, and construction period. In addition to cost, parameters like capacity factor 1.00 (CF), efficiency, and environmental impacts for individual energy generation technology are also 0.10 important factors that affect the growth. These parameters are listed in Table 3 and plotted in Figure 8. 0.01 PV Wind Hydro Geoth Coal Gas Table 3: capacity factor, efficiency, and (a) All financial environmental impacts (Evan, 2009) 0.30 ① ② ③ CF(%) Efficiency(%) CO2 Water Land PV 8-20 4-22 90 10 28-64 Wind 20-30 24-54 25 1 72 0.20 Hydro 20-70 >90 41 36 750 Geoth 90+ 10-20 170 12-300 18-74 Cost, US/kWh Cost, Coal 32-45 1004 78 0.10 Gas 45-53 543 78 ① Average greenhouse gas emissions expressed as CO2 equivalent for individual energy generation 0.00 technologies: CO2 equivalent g/kWh PV Wind Hydro Geoth Coal Gas ② Water consumption in kg/kWh of electricity (b) cost generation 2 ③ Units: km /TWh 1000 200 Cf(%) 800 Efficiency(%) 160 CO2* 600 Water** 120 Land*** 400 Water 80 200 40 0 0 PV Wind Hydro Geoth Coal Gas PV Wind Hydro Geoth Coal Gas (a) All financial (e) Water: kg/kWh of electricity generation 100 1000 80 800 60 600 Land 40 400 Capacityfactor,% 20 200 0 0 PV Wind Hydro Geoth Coal Gas PV Wind Hydro Geoth Coal Gas 2 (b) Capacity factor (f) Land: in the units of km /TWh Figure 8: capacity factor, efficiency, and 100 environmental impacts 80 Geothermal power has the highest capacity factor, over 90% in many cases, as listed in Table 3.