Energy storage February 12, 2009 Outline Energy Storage • Review last week • Why do we store energy? Larry Caretto • What kind of energy is stored? Mechanical Engineering 496ALT • Fuels as energy storage Alternative Energy • Batteries • Thermal energy storage February 12, 2009 • Electrical energy storage • Mechanical energy storage 2 Air Pollution • Clean Air Act requirements – National ambient air quality standatds for criteria pollutanta • States must submit plans (state implementation plans or SIPs) to achieve standards by date – Toxic pollutants by separate process – Acid rain program by 1990 CAA amendment – Mobile vs stationary sources – Permitting requirements – Fossil fuel combustion biggest source 3 4 5 6 ME 496ALT – Alternative Energy 1 Energy storage February 12, 2009 Ozone Production Cap-and-Trade Programs • Emission requirements set for all sources in an area • Sources have three options – Comply with emission limits – Produce excess emissions and buy credits from others who generate credits – Reduce emissions beyond requirements to generate credits for sale • Alternative to “command and control” 7 8 Acid Deposition Results Ozone Layer and Greenhouse • Stratospheric ozone reduces UV radiation reaching planet’s surface • Chlorofluorocarbons (CFCs) reach stratosphere and destroy ozone • Natural balance between solar radiation reaching earth and IR radiation leaving • Balance upset by human activities producing “greenhouse gases”, espe- cially CO2 from fossil fuel combustion 9 10 IPCC 2007 reports Greenhouse Gases • Intergovernmental Panel on Climate •CO2 accounts for 86% of all GHG Change under United Nations •To reduce CO2 emisisons seek carbon – Regular assessment reports (latest 2007) free fuels, alternative energy sources • Reports have three separate reports and such as solar or wind synthesis report – Energy conservation also helps • Physical Science Basis, Impacts, Adaptation and Vulnerability, and Mitigationof Climate • Carbon capture and sequestration Change (CCS) removes CO2 from exhaust and – 2007 report has strongest conclusions stores underground about effects and human contribution – R&D required to reduce costs 11 12 ME 496ALT – Alternative Energy 2 Energy storage February 12, 2009 Why do we store energy? What kinds of energy stored? • To be able to respond to changes in • Fuel containers store fuel energy demand in a more efficient manner • Batteries and supercapacitors store – Electricity use fluctuates over seasons and electrical energy hours of the day – Natural gas use fluctuates over seasons • Flywheels and compressed air systems • Most transportation (land, sea, air) store mechanical energy needs to carry onboard energy supplies • Thermal energy storage as latent or • Solar and wind use energy storage to sensible heat used in heating and balance generation with use cooling systems 13 14 Energy Storage Measures Fuel Energy • Volumetric energy storage in Btu/gallon • Energy per unit mass (kJ/kg; Btu/lbm) – Gasoline: 109,000 to 125,000 • Energy per unit volume (kJ/m3; Btu/ft3) – Diesel fuel: 128,000 to 130,000 – Biodiesel: 117,000 to 120,000 • Rate of delivery of energy to and from – Natural gas: 33,000 to 38,000 at 3,000 psi, storage (kW/kg; Btu/hr⋅lbm) 38,000 to 44,000 at 3,600 psi, and ~73,500 • Efficiency (energy out/energy in) as liquefied natural gas (LNG) – 85% ethanol in gasoline: ~80,000 • Life cycles – how many times can the – 85% methanol in gasoline: 56,000 to 66,000 storage device be used – Hydrogen: ~6,500 at 3,000 psi, ~16,000 at – Particularly important for batteries 10,000 psi, and ~30,500 as liquid – Liquefied petroleum gas (LPG): ~84,000 15 16 http://www.eere.energy.gov/afdc/altfuel/fuel_comp.html Battery Basics Battery Terms • Zinc/copper cell Reduction at cathode: Oxidation at anode: • At cathode (left) positive pole, accepts negative pole, supplies ++ – –Cu + 2e → Cu circuit electrons circuit electrons –Cu++ ions from CuSO4 in solution Copper Zinc goes – electrons from circuit • At anode (right) deposits into solution on cathode at anode • Salt bridge transfers –Zn → Zn++ + 2e– = ++ Lower SO4 ions –Zn ions into Higher electrode ZnSO4 in solution electrode Salt bridge – electrons into potential completes circuit potential circuit 17 in solution 18 ME 496ALT – Alternative Energy 3 Energy storage February 12, 2009 Battery Terms II Nernst Equation • Cell voltage based on standard • Cell potentials are based on a standard reduction potentials (gain of electrons) concentration (1 gram mole per liter), • When two half-cells are joined the pressure (1 atm) and temperature (25oC) reaction with the smaller reduction • Call this potential ΔEo RT ΔE = ΔEo − lnQ potential is run in reverse • Actual potential ΔE nF –Cu++ + 2e– → Cu (0. 34 v) – R = 8.414 J/gmmol·K, T = temperature in K –Zn ++ + 2e– → Zn (–0.76 v) – F = 96485.3415 A·s/gmmol (Faraday const) – Zinc reaction is reversed – n = electrons in reaction – Potential difference is 1.10 v – Q depends on concentrations 19 20 Battery Types Solar System Batteries • Nickel Cadmium mature, relatively low • Optional – home systems can sell energy density, long life, lower cost, and high discharge rate excess power to utility • Nickel-Metal Hydride: higher energy • Can provide power during evening density than NiCd but lower cycle life hours for systems not linked to grid • Lead Acid: most economical where weight is not important • Also provide back-up power in cases of • Lithium Ion: high energy density and light blackout weight • Lead-acid batteries uses because of low • Lithium Ion Polymer: Li-ion in smaller cost packaging 21 22 Battery Properties Battery Voltages 23 http://www.mpoweruk.com/chemistries.htm Reference: http://www.intersil.com/data/an/an126.pdf ME 496ALT – Alternative Energy 4 Energy storage February 12, 2009 Discharge Battery Discharge Rates • Discharge • Manufacturer rates battery to have patterns: certain energy at specified discharge similar with rate known as the “C rate” different • Discharge at higher rates (e.g. 1.5C, batteries 2C, 10C, etc.) reduced capacity • Discharge at lower rates (e.g., C/1.5, C/2, C/10) increases capacity Reference: http://www. mpoweruk.com/ • Similar effect for charging battery performance.htm 25 26 Battery Discharge Rates Rate Effect • Higher discharge rates give lower energy • Reference: http://www.na p.edu/books/0 309087007/ht ml/64.html 27 28 Reference: http://www.intersil.com/data/an/an126.pdf Compare Ragone Plot • Batteries versus other motive power • http://www.n ap.edu/book s/03090926 12/html/40.h tml http://www.thewatt.com/ modules.php?name=Ne 29 ws&file=article&sid=92630 &mode=nested ME 496ALT – Alternative Energy 5 Energy storage February 12, 2009 Utility Storage Applications • Power Quality: applied for seconds or less, as needed, to assure continuity of quality power. • Bridging Power: seconds to minutes to assure continuity of service when switching from one source to another. • Energy Management: decouple the timing of generation and consumption of electric energy http://www.electricitystorage. 31 org/tech/technologies_comp 32 arisons_ratings.htm Flow Batteries • Charge and discharge electrolyte placed in storage tanks – Polysulfide Bromide battery (PSB) – Vanadium Redox battery (VRB) – Zinc bromide • Decouples energy capacity (due to storage tank size) and power (due to cell size) PSB • Sometimes described as fuel cells Schematic 33 http://www.electricitystorage.org/tech/technologies 34 _technologies_psb.htm PSB Battery Reactions • Charging reactions - + –Na2S4 + 2e + 2Na → 2Na2S2 - + –3NaBr → 2e + 2 Na + NaBr3 • Discharge reactions - + –2Na2S2 → Na2S4 + 2e + 2Na –NaBr + 2e- + 2 Na+ → 3NaBr VRB 3 Installation • External power charges electrolyte so (Reference next chart) that tanks contain Na2S2 and NaBr3 • Charged electrolytes power flow 35 36 ME 496ALT – Alternative Energy 6 Energy storage February 12, 2009 Energy Storage Costs • Flow battery increases transmission capacity http://www.leonardo- http://www.energy.ca.gov/pier/notices/2005-02- 37 38 24_workshop/07%20Kuntz-VRB%20PacifiCorp%20Flow%20Battery.pdf energy.org/drupal/files/2007/Briefing%20paper%20- %20Flow%20batteries.pdf?download Store Compressed Air •Symbols • CAES: Compressed air energy storage –fully capable • Gas turbine with compressed air stored –reasonable in caverns; later combustion/expansion –feasible, but • Electricity peak shaving not quite… – 290 MW, Hundorf, Germany, 1978 –not feasible – 110 MW, McIntosh, AL, 1991 • $591/kW; comes online in 14 mins – 2700 MW (planned) Norton, OH •http://www.electricit ystorage.org/tech/te • 1500 psi air pressure, 2200 ft underground chnologies_compari 39 http://www.electricitystorage.org/tech/tec 40 sons.htm hnologies_technologies_caes.htm Pumped Hydro • Used by power companies to provide peak energy • Pump water uphill during off-peak hours • Use potential energy to generate power during peak periods – Same equipment used for pumping and generation – Efficiency range is 70% to 85% – 1566 MW in Castaic http://www.electricitystorage.org/tech/technologies_technologies_caes.htm 41 42 ME 496ALT – Alternative Energy 7 Energy storage February 12, 2009 Flywheels Flywheels II • Store kinetic energy • Efficiency is about 80% for energy out – Exchanged with motor-generator set divided by energy in –E = Iω2/2 I = kmR2 • Can store energy for up to six months • k = ½ for solid disk uniform thickness • Demonstration systems for power • k = 1 for wheel loaded at rim (bicycle tire) quality by Beacon in NY and CA – Centrifugal force = mRω2 can tear flywheel apart so materials that