A_AT1 Path_NN1 to_II Sustainable_JJ Energy_NN1 by_II 2030_MC Wind_NN1 ,_, water_NN1 and_CC solar_JJ technologies_NN2 can_VM provide_VVI 100_MC percent_NNU of_IO the_AT world_NN1 's_GE energy_NN1 ,_, elimiating_VVG all_DB fossil_NN1 fuels_NN2 ._. 
In_II December_NPM1 leaders_NN2 from_II around_II the_AT world_NN1 will_VM meet_VVI in_II Copenhagen_NP1 to_TO try_VVI to_TO agree_VVI on_II cutting_VVG back_RP greenhouse_NN1 gas_NN1 emissions_NN2 for_IF decades_NNT2 to_TO come_VVI ._. 
The_AT most_RGT effective_JJ step_NN1 to_TO implement_VVI that_DD1 goal_NN1 would_VM be_VBI a_AT1 massive_JJ shift_NN1 away_II21 from_II22 fossil_NN1 fuels_NN2 to_TO clean_VVI ,_, renewable_JJ energy_NN1 sources_NN2 ._. 
If_CS leaders_NN2 can_VM have_VHI confidence_NN1 that_CST such_DA a_AT1 transformation_NN1 is_VBZ possible_JJ ,_, they_PPHS2 might_VM commit_VVI to_II an_AT1 historic_JJ agreement_NN1 ._. 
We_PPIS2 think_VV0 they_PPHS2 can_VM ._. 
A_AT1 year_NNT1 ago_RA former_DA vice_JJ president_NN1 Al_NP1 Gore_NP1 threw_VVD down_RP a_AT1 gauntlet_NN1 :_: to_TO repower_VVI America_NP1 with_IW 100_MC percent_NNU carbon-free_JJ electricity_NN1 within_II 10_MC years_NNT2 ._. 
As_II the_AT two_MC of_IO us_PPIO2 started_VVD to_TO evaluate_VVI the_AT feasibility_NN1 of_IO such_DA a_AT1 change_NN1 ,_, we_PPIS2 took_VVD on_RP an_AT1 even_RR larger_JJR challenge_NN1 :_: to_TO determine_VVI how_RRQ 100_MC percent_NNU of_IO the_AT world_NN1 's_GE energy_NN1 ,_, for_IF all_DB purposes_NN2 ,_, could_VM be_VBI supplied_VVN by_II wind_NN1 ,_, water_NN1 and_CC solar_JJ resources_NN2 ,_, by_II as_RG early_RR as_CSA 2030_MC ._. 
Our_APPGE plan_NN1 is_VBZ presented_VVN here_RL ._. 
Scientists_NN2 have_VH0 been_VBN building_VVG to_II this_DD1 moment_NN1 for_IF least_DAT a_AT1 decade_NNT1 ,_, analyzing_VVG various_JJ pieces_NN2 of_IO the_AT challenge_NN1 ._. 
Most_RGT recently_RR ,_, a_AT1 2009_MC Stanford_NP1 University_NN1 study_NN1 ranked_VVN energy_NN1 systems_NN2 according_II21 to_II22 their_APPGE impacts_NN2 on_II global_JJ warming_NN1 ,_, pollution_NN1 ,_, water_NN1 supply_NN1 ,_, land_NN1 use_NN1 ,_, wildlife_NN1 and_CC other_JJ concerns_NN2 ._. 
The_AT very_RG best_JJT options_NN2 were_VBDR wind_NN1 ,_, solar_JJ ,_, geothermal_JJ ,_, tidal_JJ and_CC hydroelectric_JJ power_NN1 --_NN1 all_DB of_IO which_DDQ are_VBR driven_VVN by_II wind_NN1 ,_, water_NN1 or_CC sunlight_NN1 (_( referred_VVN to_II as_CSA WWS_NP1 )_) ._. 
Nuclear_JJ power_NN1 ,_, coal_NN1 with_IW carbon_NN1 capture_NN1 ,_, and_CC ethanol_NN1 were_VBDR all_DB poorer_JJR options_NN2 ,_, as_CSA were_VBDR oil_NN1 and_CC natural_JJ gas_NN1 ._. 
The_AT study_NN1 also_RR found_VVN that_CST battery-electric_JJ vehicles_NN2 and_CC hydrogen_NN1 fuel-cell_NN1 vehicles_NN2 recharged_VVD by_II WWS_NP1 options_NN2 would_VM largely_RR eliminate_VVI pollution_NN1 from_II the_AT transportation_NN1 sector_NN1 ._. 
Our_APPGE plan_NN1 calls_VVZ for_IF millions_NNO2 of_IO wind_NN1 turbines_NN2 ,_, water_NN1 machines_NN2 and_CC solar_JJ installations_NN2 ._. 
The_AT numbers_NN2 are_VBR large_JJ ,_, but_CCB the_AT scale_NN1 is_VBZ not_XX an_AT1 insurmountable_JJ hurdle_NN1 ;_; society_NN1 has_VHZ achieved_VVN massive_JJ transformations_NN2 before_RT ._. 
During_II World_NN1 War_NN1 II_MC ,_, the_AT U.S._NP1 retooled_VVD automobile_NN1 factories_NN2 to_TO produce_VVI 300,000_MC aircraft_NN ,_, and_CC other_JJ countries_NN2 produced_VVD 486,000_MC more_DAR ._. 
In_II 1956_MC the_AT U.S._NP1 began_VVD building_VVG the_AT Interstate_NN1 Highway_NN1 System_NN1 ,_, which_DDQ after_II 35_MC years_NNT2 extended_VVN for_IF 47,000_MC miles_NNU2 ,_, changing_VVG commerce_NN1 and_CC society_NN1 ._. 
Is_VBZ it_PPH1 feasible_JJ to_TO transform_VVI the_AT world_NN1 's_GE energy_NN1 system_NN1 ?_? 
Could_VM it_PPH1 be_VBI accomplished_VVN in_II two_MC decades_NNT2 ?_? 
The_AT answers_NN2 depend_VV0 on_II the_AT technologies_NN2 chosen_VVN ,_, the_AT availability_NN1 of_IO critical_JJ materials_NN2 ,_, and_CC economic_JJ and_CC political_JJ factors_NN2 ._. 
Clean_JJ Technologies_NN2 Only_RR Renewable_JJ energy_NN1 comes_VVZ from_II enticing_JJ sources_NN2 :_: wind_NN1 ,_, which_DDQ also_RR produces_VVZ waves_NN2 ;_; water_NN1 ,_, which_DDQ includes_VVZ hydroelectric_JJ ,_, tidal_JJ and_CC geothermal_JJ energy_NN1 (_( water_NN1 heated_VVN by_II hot_JJ underground_JJ rock_NN1 )_) ;_; and_CC sun_NN1 ,_, which_DDQ includes_VVZ photovoltaics_NN2 and_CC solar_JJ power_NN1 plants_NN2 that_CST focus_VV0 sunlight_NN1 to_TO heat_VVI a_AT1 fluid_NN1 that_CST drives_VVZ a_AT1 turbine_NN1 to_TO generate_VVI electricity_NN1 ._. 
Our_APPGE plan_NN1 includes_VVZ only_JJ technologies_NN2 that_CST work_VV0 or_CC are_VBR close_JJ to_II working_VVG today_RT on_II a_AT1 large_JJ scale_NN1 ,_, rather_II21 than_II22 those_DD2 that_CST may_VM exist_VVI 20_MC or_CC 30_MC years_NNT2 from_II now_RT ._. 
To_TO ensure_VVI that_CST our_APPGE system_NN1 remains_VVZ clean_JJ ,_, we_PPIS2 consider_VV0 only_JJ technologies_NN2 that_CST have_VH0 near-zero_JJ emissions_NN2 of_IO greenhouse_NN1 gases_NN2 and_CC air_NN1 pollutants_NN2 over_II their_APPGE entire_JJ life_NN1 cycle_NN1 ,_, including_II construction_NN1 ,_, operation_NN1 and_CC decommissioning_NN1 ._. 
For_REX21 example_REX22 ,_, when_CS burned_VVN in_II vehicles_NN2 ,_, even_RR the_AT most_RGT ecologically_RR acceptable_JJ sources_NN2 of_IO ethanol_NN1 create_VV0 air_NN1 pollution_NN1 that_CST will_VM cause_VVI the_AT same_DA mortality_NN1 level_NN1 as_CSA when_CS gasoline_NN1 is_VBZ burned_VVN ._. 
Nuclear_JJ power_NN1 results_NN2 in_II up_RG21 to_RG22 25_MC times_NNT2 more_RRR carbon_NN1 emissions_NN2 than_CSN wind_NN1 energy_NN1 ,_, when_CS reactor_NN1 construction_NN1 and_CC uranium_NN1 refining_VVG and_CC transport_NN1 are_VBR considered_VVN ._. 
Carbon_NN1 capture_NN1 and_CC sequestration_NN1 technology_NN1 can_VM reduce_VVI carbon_NN1 dioxide_NN1 emissions_NN2 from_II coal-fired_JJ power_NN1 plants_NN2 but_CCB will_VM increase_VVI air_NN1 pollutants_NN2 and_CC will_VM extend_VVI all_DB the_AT other_JJ deleterious_JJ effects_NN2 of_IO coal_NN1 mining_NN1 ,_, transport_NN1 and_CC processing_NN1 ,_, because_CS more_DAR coal_NN1 must_VM be_VBI burned_VVN to_II power_NN1 the_AT capture_NN1 and_CC storage_NN1 steps_NN2 ._. 
Similarly_RR ,_, we_PPIS2 consider_VV0 only_JJ technologies_NN2 that_CST do_VD0 not_XX present_VVI significant_JJ waste_NN1 disposal_NN1 or_CC terrorism_NN1 risks_NN2 ._. 
In_II our_APPGE plan_NN1 ,_, WWS_NP1 will_VM supply_VVI electric_JJ power_NN1 for_IF hearing_VVG and_CC transportation_NN1 --_NN1 industries_NN2 that_CST will_VM have_VHI to_TO revamp_VVI if_CSW the_AT world_NN1 has_VHZ any_DD hope_NN1 of_IO slowing_VVG climate_NN1 change_NN1 ._. 
We_PPIS2 have_VH0 assumed_VVN that_CST most_DAT fossil-fuel_JJ heating_NN1 (_( as_II31 well_II32 as_II33 ovens_NN2 and_CC stoves_NN2 )_) can_VM be_VBI replaced_VVN by_II electric_JJ systems_NN2 and_CC that_DD1 most_RGT fossil-fuel_JJ transportation_NN1 can_VM be_VBI replaced_VVN by_II battery_NN1 and_CC fuel-cell_JJ vehicles_NN2 ._. 
Hydrogen_NN1 ,_, produced_VVN by_II using_VVG WWS_NP1 electricity_NN1 to_TO split_VVI water_NN1 (_( electrolysis_NN1 )_) ,_, would_VM power_NN1 fuel_NN1 cells_NN2 and_CC be_VBI burned_VVN in_II airplanes_NN2 and_CC by_II industry_NN1 ._. 
Plenty_PN of_IO Supply_NN1 Today_RT the_AT maximum_JJ power_NN1 consumed_VVD world-wide_JJ at_II any_DD given_JJ moment_NN1 is_VBZ about_RG 12.5_MC trillion_NNO watts_NNU2 (_( terawatts_VVZ ,_, or_CC TW_NP1 )_) ,_, according_II21 to_II22 the_AT U.S._NP1 Energy_NN1 Information_NN1 Administration_NN1 ._. 
The_AT agency_NN1 projects_VVZ that_CST in_II 2030_MC the_AT world_NN1 will_VM require_VVI 16.9_MC TW_NP1 of_IO power_NN1 as_CSA global_JJ population_NN1 and_CC living_NN1 standards_NN2 rise_VV0 ,_, with_IW about_RG 2.8_MC TW_NP1 in_II the_AT U.S._NP1 The_AT mix_NN1 of_IO sources_NN2 is_VBZ similar_JJ to_II today_RT 's_GE ,_, heavily_RR dependent_JJ on_II fossil-fuels_NN2 ._. 
If_CS ,_, however_RR ,_, the_AT planet_NN1 were_VBDR powered_VVN entirely_RR by_II WWS_NP1 ,_, with_IW no_AT fossil-fuel_NN1 or_CC biomass_NN1 combustion_NN1 ,_, an_AT1 intriguing_JJ savings_NN2 would_VM occur_VVI ._. 
Global_JJ power_NN1 demand_NN1 would_VM be_VBI only_RR 11.5_MC TW_NP1 ,_, and_CC U.S._NP1 demand_NN1 would_VM be_VBI 1.8_MC TW_NP1 ._. 
That_DD1 decline_NN1 occurs_VVZ because_CS ,_, in_II most_DAT cases_NN2 ,_, electrification_NN1 is_VBZ a_AT1 more_RGR efficient_JJ way_NN1 to_TO use_VVI energy_NN1 ._. 
For_REX21 example_REX22 ,_, only_RR 17_MC to_II 20_MC percent_NNU of_IO the_AT energy_NN1 in_II gasoline_NN1 is_VBZ used_VVN to_TO move_VVI a_AT1 vehicle_NN1 (_( the_AT rest_NN1 is_VBZ wasted_VVN as_CSA heat_NN1 )_) ,_, whereas_CS 75_MC to_II 86_MC percent_NNU of_IO the_AT electricity_NN1 delivered_VVN to_II an_AT1 electric_JJ vehicle_NN1 goes_VVZ into_II motion_NN1 ._. 
Even_CS21 if_CS22 demand_NN1 did_VDD rise_VVI to_II 16.9_MC TW_NP1 ,_, WWS_NP1 sources_NN2 could_VM provide_VVI far_RG more_DAR power_NN1 ._. 
Declined_VVN studies_NN2 by_II us_PPIO2 and_CC others_NN2 indicate_VV0 that_DD1 energy_NN1 from_II the_AT wind_NN1 ,_, worldwide_RL ,_, is_VBZ about_RG 1,700_MC TW_NP1 ._. 
Solar_JJ ,_, alone_RR ,_, offers_NN2 6,500_MC TW_NP1 ._. 
Of_RR21 course_RR22 ,_, wind_NN1 and_CC sun_NN1 out_RP in_II the_AT open_JJ seas_NN2 ,_, over_II high_JJ mountains_NN2 and_CC across_II prospected_JJ regions_NN2 would_VM not_XX be_VBI available_JJ ._. 
If_CS we_PPIS2 subtract_VV0 these_DD2 and_CC low-wind_JJ areas_NN2 not_XX likely_JJ to_TO be_VBI developed_VVN ,_, we_PPIS2 are_VBR still_RR left_VVN with_IW 40_MC to_II 85_MC TW_NP1 for_IF wind_NN1 and_CC 580_MC TW_NP1 for_IF solar_JJ ,_, each_DD1 far_JJ beyond_II future_JJ human_JJ demand_NN1 ._. 
Yet_RR currently_RR we_PPIS2 generate_VV0 only_RR 0.02_MC TW_NP1 of_IO wind_NN1 power_NN1 and_CC 0.008_MC TW_NP1 of_IO solar_JJ ._. 
These_DD2 sources_NN2 hold_VV0 an_AT1 incredible_JJ amount_NN1 of_IO untapped_JJ potential_NN1 ._. 
The_AT other_JJ WWS_NP1 technologies_NN2 will_VM help_VVI create_VVI a_AT1 flexible_JJ range_NN1 of_IO options_NN2 ._. 
Although_CS all_DB the_AT sources_NN2 can_VM expand_VVI greatly_RR ,_, for_IF practical_JJ reasons_NN2 ,_, wave_NN1 power_NN1 can_VM be_VBI extracted_VVN only_RR near_II coastal_JJ areas_NN2 ._. 
Many_DA2 geothermal_JJ sources_NN2 are_VBR too_RG deep_JJ to_TO be_VBI tapped_VVN economically_RR ._. 
And_CC even_CS21 though_CS22 hydro_NN1 electic_JJ power_NN1 now_RT exceeds_VVZ all_DB other_JJ WWS_NP1 sources_NN2 ,_, most_DAT of_IO the_AT suitable_JJ large_JJ reservoirs_NN2 are_VBR already_RR in_II use_NN1 ._. 
The_AT Plan_NN1 :_: Power_NN1 Plants_NN2 Required_VVN Clearly_RR ,_, enough_DD renewable_JJ energy_NN1 exists_VVZ ._. 
How_RRQ ,_, then_RT ,_, would_VM we_PPIS2 transition_NN1 to_II a_AT1 new_JJ infrastructure_NN1 to_TO provide_VVI the_AT world_NN1 with_IW 11.5_MC TW_NP1 ?_? 
We_PPIS2 have_VH0 chosen_VVN a_AT1 mix_NN1 of_IO technologies_NN2 emphasizing_VVG wind_NN1 and_CC solar_JJ ,_, with_IW about_RG 9_MC percent_NNU of_IO demand_NN1 met_VVN by_II mature_JJ water-related_JJ methods_NN2 ._. 
(_( Other_JJ combinations_NN2 of_IO wind_NN1 and_CC solar_NN1 could_VM be_VBI as_RG successful_JJ ._. )_) 
Wind_NN1 supplies_VVZ 51_MC percent_NNU of_IO the_AT demand_NN1 ,_, provided_VVN by_II 3.8_MC million_NNO large_JJ wind_NN1 turbines_NN2 (_( each_DD1 rated_VVD at_II five_MC megawatts_NN2 )_) worldwide_RL ._. 
Although_CS that_DD1 quantity_NN1 may_VM sound_VVI enormous_JJ ,_, it_PPH1 is_VBZ interesting_JJ to_TO note_VVI that_CST the_AT world_NN1 manufactures_VVZ 73_MC million_NNO cars_NN2 and_CC light_JJ trucks_NN2 every_AT1 year_NNT1 ._. 
Another_DD1 40_MC percent_NNU of_IO the_AT power_NN1 comes_VVZ from_II photovoltaics_NN2 and_CC concentrated_JJ solar_JJ plants_NN2 ,_, with_IW about_RG 30_MC percent_NNU of_IO the_AT photovoltaic_JJ output_NN1 from_II rooftop_NN1 panels_NN2 on_II homes_NN2 and_CC commercial_JJ buildings_NN2 ._. 
About_RG 89,000_MC photovoltaic_JJ and_CC concentrated_JJ solar_JJ power_NN1 plants_NN2 ,_, averaging_VVG 300_MC megawatts_NN2 apiece_RA ,_, would_VM be_VBI needed_VVN ._. 
Our_APPGE mix_NN1 also_RR includes_VVZ 900_MC hydroelectric_JJ stations_NN2 worldwide_RL ,_, 70_MC percent_NNU of_IO which_DDQ are_VBR already_RR in_II place_NN1 ._. 
Only_RR about_RG 0.8_MC percent_NNU of_IO the_AT wind_NN1 base_NN1 is_VBZ installed_VVN today_RT ._. 
The_AT worldwide_JJ footprint_NN1 of_IO the_AT 3.8_MC million_NNO turbines_NN2 would_VM be_VBI less_DAR than_CSN 50_MC square_JJ kilometers_NNU2 (_( smaller_JJR than_CSN Manhattan_NP1 )_) ._. 
When_CS the_AT needed_VVN spacing_VVG between_II them_PPHO2 is_VBZ figured_VVN ,_, they_PPHS2 would_VM occupy_VVI about_II 1_MC1 percent_NNU of_IO the_AT earth_NN1 's_GE land_NN1 ,_, but_CCB the_AT empty_JJ space_NN1 among_II turbines_NN2 could_VM be_VBI used_VVN for_IF agriculture_NN1 or_CC ranching_NN1 or_CC as_RG open_JJ land_NN1 or_CC ocean_NN1 ._. 
The_AT nonrooftop_NN1 photovoltaics_NN2 and_CC concentrated_JJ solar_JJ plants_NN2 would_VM occupy_VVI about_RG 0.33_MC percent_NNU of_IO the_AT planet_NN1 's_GE land_NN1 ._. 
Building_VVG such_DA an_AT1 extensive_JJ infrastructure_NN1 will_VM take_VVI time_NNT1 ._. 
But_CCB so_RR did_VDD the_AT current_JJ power_NN1 plant_NN1 network_NN1 ._. 
And_CC remember_VV0 that_CST if_CS we_PPIS2 stick_VV0 with_IW fossil_NN1 fuels_NN2 ,_, demand_VV0 by_II 2030_MC will_VM rise_VVI to_II 16.9_MC TW_NP1 ,_, requiring_VVG about_RG 13,000_MC large_JJ new_JJ coal_NN1 plants_NN2 ,_, which_DDQ themselves_PPX2 would_VM occupy_VVI a_RR21 lot_RR22 more_DAR land_NN1 ,_, as_CSA would_VM the_AT mining_NN1 to_TO supply_VVI them_PPHO2 ._. 
The_AT Materials_NN2 Hurdle_VV0 The_AT scale_NN1 of_IO the_AT WWS_NP1 infrastructure_NN1 is_VBZ not_XX a_AT1 barrier_NN1 ._. 
But_CCB a_AT1 few_DA2 materials_NN2 needed_VVN to_TO build_VVI it_PPH1 could_VM be_VBI scarce_JJ or_CC subject_II21 to_II22 price_NN1 manipulation_NN1 ._. 
Enough_DD concrete_NN1 and_CC steel_NN1 exist_VV0 for_IF the_AT millions_NNO2 of_IO wind_NN1 turbines_NN2 ,_, and_CC both_DB2 those_DD2 commodities_NN2 are_VBR fully_RR recyclable_JJ ._. 
The_AT most_RGT problematic_JJ materials_NN2 may_VM be_VBI rare-earth_JJ metals_NN2 such_II21 as_II22 neodymium_NN1 used_VVN in_II turbine_NN1 gearboxes_NN2 ._. 
Although_CS the_AT metals_NN2 are_VBR not_XX in_II short_JJ supply_NN1 ,_, the_AT low-cost_JJ sources_NN2 are_VBR concentrate_VV0 in_II China_NP1 ,_, so_CS countries_NN2 such_II21 as_II22 the_AT U.S._NP1 could_VM be_VBI trading_VVG dependence_NN1 on_II Middle_JJ Eastern_JJ oil_NN1 for_IF dependent_JJ on_II Far_JJ Eastern_JJ metals_NN2 ._. 
Manufactures_VVZ are_VBR moving_VVG toward_II gearless_JJ turbines_NN2 ,_, however_RR ,_, so_RG thant_JJ limitation_NN1 may_VM become_VVI moot_JJ ._. 
Photovoltaic_JJ cells_NN2 rely_VV0 on_II amorphous_JJ or_CC crystalline_JJ silicon_NN1 ,_, cadmium_NN1 telluride_NN1 ,_, or_CC copper_NN1 indium_NN1 selenide_NN1 and_CC sulfide_NN1 ._. 
Limited_JJ supplies_NN2 of_IO tellurium_NN1 and_CC indium_NN1 could_VM reduce_VVI the_AT prospect_NN1 for_IF some_DD types_NN2 of_IO thin-film_JJ solar_JJ cells_NN2 ,_, though_CS not_XX for_IF all_DB ;_; the_AT other_JJ types_NN2 might_VM be_VBI able_JK to_TO take_VVI up_RP the_AT slack_NN1 ._. 
Large-scale_JJ production_NN1 could_VM be_VBI restricted_VVN by_II the_AT silver_NN1 that_CST cells_NN2 require_VV0 ,_, but_CCB finding_VVG ways_NN2 to_TO reduce_VVI the_AT silver_NN1 content_NN1 could_VM tackle_VVI that_DD1 hurdle_NN1 ._. 
More_RGR problematic_JJ is_VBZ the_AT claim_NN1 by_II Meridian_NN1 International_JJ Research_NN1 that_CST not_XX enough_RR economically_RR recoverable_JJ lithium_NN1 exists_VVZ to_TO build_VVI anywhere_RL near_II the_AT number_NN1 of_IO batteries_NN2 needed_VVN in_II a_AT1 global_JJ electric-vehicle_JJ economy_NN1 ._. 
Recycling_NN1 could_VM change_VVI the_AT equation_NN1 ,_, but_CCB the_AT economics_NN1 of_IO recycling_NN1 depend_VV0 in_RR21 part_RR22 on_II whether_CSW batteries_NN2 are_VBR made_VVN with_IW easy_JJ recyclability_NN1 in_II mind_NN1 ,_, an_AT1 issue_NN1 the_AT industry_NN1 is_VBZ aware_JJ of_IO ._. 
The_AT long-term_JJ use_NN1 of_IO platinum_NN1 also_RR depends_VVZ on_II recycling_NN1 ;_; current_JJ available_JJ reserves_NN2 would_VM sustain_VVI annual_JJ production_NN1 of_IO 20_MC million_NNO fuel-cell_JJ vehicles_NN2 ,_, along_II21 with_II22 existing_JJ industrial_JJ uses_NN2 ,_, for_IF fewer_DAR than_CSN 100_MC years_NNT2 ._. 
Smart_JJ Mix_NN1 for_IF Reliability_NN1 A_ZZ1 new_JJ infrastructure_NN1 must_VM provide_VVI energy_NN1 on_II demand_NN1 at_RR21 least_RR22 as_RG reliable_JJ as_CSA the_AT existing_JJ infrastructure_NN1 ._. 
WWS_NP1 technologies_NN2 generally_RR suffer_VV0 less_DAR downtime_NNT1 than_CSN traditional_JJ sources_NN2 ._. 
The_AT average_JJ U.S._NP1 coal_NN1 plant_NN1 is_VBZ offline_RR 12.5_MC percent_NNU of_IO the_AT year_NNT1 for_IF scheduled_JJ and_CC unscheduled_JJ maintenance_NN1 ._. 
Modern_JJ wind_NN1 turbines_NN2 have_VH0 a_AT1 down_JJ time_NNT1 of_IO less_DAR than_CSN 2_MC percent_NNU on_II land_NN1 less_DAR than_CSN 5_MC percent_NNU at_II sea_NN1 ._. 
photovoltaic_JJ systems_NN2 are_VBR also_RR at_II less_DAR than_CSN 2_MC percent_NNU ._. 
Moreover_RR ,_, when_CS an_AT1 individual_JJ wind_NN1 ,_, solar_JJ or_CC wave_NN1 device_NN1 is_VBZ down_RP ,_, only_RR a_AT1 small_JJ fraction_NN1 of_IO production_NN1 is_VBZ affected_VVN ;_; when_CS a_AT1 coal_NN1 ,_, nuclear_JJ or_CC natural_JJ gas_NN1 plant_NN1 goes_VVZ offline_RR ,_, a_AT1 large_JJ chunk_NN1 of_IO generation_NN1 is_VBZ lost_VVN ._. 
The_AT main_JJ WWS_NP1 challenge_NN1 is_VBZ that_CST the_AT wind_NN1 does_VDZ not_XX always_RR blow_VVI and_CC the_AT sun_NN1 does_VDZ not_XX always_RR shine_VVI in_II a_AT1 given_JJ location_NN1 ._. 
Intermittency_NN1 problems_NN2 can_VM be_VBI mitigated_VVN by_II a_AT1 smart_JJ balance_NN1 of_IO sources_NN2 ,_, such_II21 as_II22 generating_VVG a_AT1 base_NN1 supply_NN1 from_II steady_JJ geothermal_JJ or_CC tidal_JJ power_NN1 ,_, relying_VVG on_II wind_NN1 at_II night_NNT1 when_RRQ it_PPH1 is_VBZ often_RR plentiful_JJ ,_, using_VVG solar_JJ by_II day_NNT1 and_CC turning_VVG to_II a_AT1 reliable_JJ source_NN1 such_II21 as_II22 hydroelectric_JJ that_CST can_VM be_VBI turned_VVN on_RP and_CC off_RP quickly_RR to_TO smooth_VVI out_RP supply_NN1 or_CC meet_VV0 peak_NN1 demand_NN1 ._. 
For_REX21 example_REX22 ,_, interconnecting_JJ wind_NN1 farms_NN2 that_CST are_VBR only_RR 100_MC to_II 200_MC miles_NNU2 apart_RL can_VM compensate_VVI for_IF hours_NNT2 of_IO zero_NN1 power_NN1 at_II any_DD one_MC1 farm_NN1 should_VM the_AT wind_NN1 not_XX be_VBI blowing_VVG there_RL ._. 
Also_RR helpful_JJ is_VBZ interconnecting_JJ geographically_RR dispersed_JJ sources_NN2 so_CS they_PPHS2 can_VM back_VVI up_II one_PPX121 another_PPX122 ,_, installing_VVG smart_JJ electric_JJ meterd_NN1 in_II homes_NN2 that_CST automatically_RR recharge_VV0 electric_JJ vehicles_NN2 when_RRQ demand_NN1 is_VBZ low_JJ and_CC building_NN1 facilities_NN2 that_CST store_NN1 power_NN1 for_IF later_JJR use_NN1 ._. 
Because_CS the_AT wind_NN1 often_RR blows_VVZ during_II stormy_JJ conditions_NN2 when_RRQ the_AT sun_NN1 does_VDZ not_XX shine_VVI and_CC the_AT sun_NN1 often_RR shines_VVZ on_II calm_JJ days_NNT2 with_IW little_DA1 wind_NN1 ,_, combining_VVG wind_NN1 and_CC solar_NN1 can_VM go_VVI a_AT1 long_JJ way_NN1 toward_II meeting_VVG demand_NN1 ,_, especially_RR when_CS geothermal_JJ provide_VV0 a_AT1 steady_JJ base_NN1 and_CC hydroelectric_JJ can_VM be_VBI called_VVN on_II21 to_II22 fill_NN1 in_II the_AT gaps_NN2 ._. 
As_RG Cheap_JJ as_CSA Coal_NN1 The_AT mix_NN1 of_IO WWS_NP1 sources_NN2 in_II our_APPGE plan_NN1 can_VM reliably_RR supply_VVI the_AT residential_JJ ,_, commercial_JJ ,_, industrial_JJ and_CC transportation_NN1 sectors_NN2 ._. 
The_AT logical_JJ next_MD question_NN1 is_VBZ whether_CSW the_AT power_NN1 would_VM be_VBI affordable_JJ ._. 
For_IF each_DD1 technology_NN1 ,_, we_PPIS2 calculated_VVD how_RGQ much_RR it_PPH1 would_VM cost_VVI a_AT1 producer_NN1 to_TO generate_VVI power_NN1 and_CC transmit_VVI it_PPH1 across_II the_AT grid_NN1 ._. 
We_PPIS2 included_VVD the_AT annualized_JJ cost_NN1 of_IO capital_NN1 ,_, land_NN1 ,_, operations_NN2 ,_, maintenance_NN1 ,_, energy_NN1 storage_NN1 to_TO help_VVI offset_JJ intermittent_JJ supply_NN1 ,_, and_CC transmission_NN1 ._. 
Today_RT the_AT cost_NN1 of_IO wind_NN1 ,_, geothermal_JJ and_CC hydroelectric_JJ are_VBR all_RR less_DAR than_CSN seven_MC cents_NNU2 a_AT1 kilowatt-hour_NNT1 ;_; wave_NN1 and_CC solar_JJ are_VBR higher_JJR ._. 
But_CCB by_II 2020_MC and_CC beyond_II wind_NN1 ,_, wave_NN1 and_CC hydro_NN1 are_VBR expected_VVN to_TO be_VBI 4_MC kilowatt-hour_JJ or_CC less_RRR ._. 
