Power Generation from Renewable Energy Sources Fall 2013 Instructor: Xiaodong Chu Email：chuxd@sdu.edu.cn Office Tel.: 81696127

Electrochemically Stored Energy Batteries: Invented in 1800 by Alexandro Volta "... In this manner I continue coupling a plate of silver (Ag) with one of zinc (Zn), and always in the same order, that is to say, the silver below and the zinc above it, or vice versa, according as I have begun, and interpose between each of those couples a moistened disk. I continue to form, of several of this stories, a column as high as possible without any danger of its falling". Cathode (-) Zn Paper with Electrolyte, H20 V Ag Anode (+) Vbatt = V1 + V2 + V3 +...+ Vn

Electrochemically Stored Energy I. Types of Batteries Non Rechargeable: - Carbon Zinc - Cadmium Zinc - Zinc Chloride - Manganese Dioxide (Alkaline) - Magnesium – Air Fuel Cell - Zinc Air - Zinc-Bromine - Lithium Manganese - Silver Oxide - Mercuric Oxide Rechargeable: Nickel-Cadmium Nickel-Metal Hydride Nickel-Zinc Lead Acid - Lithium Ion

Electrochemically Stored Energy Rechargeable Batteries Comparison 1000+ 1000 End ENEL 669 Lec. # 17 (9Nov2009) ; End ENEL 581 Lec. # 19 (10Nov2009) 1.75 - 5.25 Which type of battery would be the most suitable for a low power lighting installation?

Chemistry of Lead Acid Batteries When the battery is discharged: Lead (-) combines with the sulfuric acid to create lead sulfate (PbSO4), Pb + SO4  PbSO4 + 2e- Lead oxide (+) combines with hydrogen and sulfuric acid to create lead sulfate and water (H2O). PbO2 + SO4 + 4H + 2e-  PbSO4 + 2H2O lead sulfate builds up on the electrodes, and the water builds up in the sulfuric acid solution. When the battery is charged: The process reverses; lead sulfate combining with water to build up lead and lead oxide on the electrodes. Lead Acid Batteries Consist of: Lead (Pb) electrode (-) Lead oxide (PbO2) electrode (+) Water and sulfuric acid (H2SO4) electrolyte. PbSO4 + 2e-  Pb + H2SO4 PbSO4 + 2H2O  PbO2 + H2SO4 + 2e-

Sealed Lead Acid (SLA) Batteries Instead of water and sulfuric acid the SLAs have the acid in form of a gel The battery is valve regulated to prevent the build up of gases which are produced during charging. Maintenance free Safer against leakage

Using SLA batteries in a Solid State Lighting System Deep discharging will shorten the battery life time Safe limit - do not discharge the battery more than 20% of its full capacity Keep the battery charged all the time Never short circuit the battery terminals Let the users be aware about the proper handling of the battery Operating Temperature Limits (-30º C to 65º C) Heat can kill the battery Cold slows down chemical reactions inside in the battery End ENEL 519.39 Lecture # 30 (Wed22Nov2006)

Discharge Pattern of SLA batteries in a Solid State Lighting System Example: A 12V 7.2 Ah battery can store *E = Voltage (13.2v) x Capacity (7.2 Ah) E = 95 Wh or 342 KJ A luxeon lamp takes 110 mA when battery voltage is at 13.2 V Then Pconsum = 13.2 V x 110 mA = 1.4 W Assuming 75 % power transfer efficiency from battery to lamp) Tdisch = Capacity / consumed current x 0.75 = [7.2 Ah / 110 mA] x 0.75 = 49.09 h or Tdisch = Energy / Power consumption = [95 Wh /1.4W] x 0.75 = 50.89 h End ENEL 581 Lec. # 17 (Tues. 4Nov2008 “President Obama Day”) Capacity of a battery (C) is measured in Ampere-hours (Ah)

Discharge Pattern of SLA batteries in a Solid State Lighting System

Electrochemically Stored Energy II. Fuel Cells: Convert chemical energy into electric energy Chemistry of a Fuel Cell Chemical Process: 1.- Platinum Catalyst (electrode) Separates Hydrogen gas into electrons- and Ions+. 2.- Hydrogen Ions+ pass through membrane only. 3.- With help of the Platinum catalyst Hydrogen Ions- combine with electrons and oxygen to form water. Proton Exchange Membrane Net reaction: 2H2 + O2  2H2O + Electricity + Heat

Electrochemically Stored Energy Reversible Fuel Cells / Electrolizer: Chemical Process: 1.- Platinum Catalyst Separates Water into Oxygen and Hydrogen electrons and Ions+. 2.- Hydrogen Ions+ pass through membrane only. 3.- With help of the Platinum catalyst, Hydrogen molecules are formed when hydrogen Ions- and electrons are combined. Electrolizer Proton Exchange Membrane Net reaction: 2H2O + 4H+ + 4e-  2H2 + O2

Fuel Cells Usually named according to their electrolyte and categorized according to their operation temperature. Low temperature fuel cells (< 200°C): Polymer Electrolyte Membrane Fuel Cell (PEMFC) Direct Methanol Fuel Cell (DMFC) Phosphoric Acid Fuel Cell (PAFC) Alkaline Fuel Cell (AFC) High temperature fuel cells(600° to 1000° C): Solid Oxide Fuel Cell (SOFC) Molten Carbonate Fuel Cell (MCFC)

Fuel Cells Advantages: Environmentally Friendly (When Hydrogen obtained using RE) High energy density Quiet operation compact size scalable Disadvantages: Requires Refill of Hydrogen Low Efficiency (55% - 25%) Cost ($3/W - $4/W) End ENEL 581 Lecture # 16 (Thur. 1Nov2007)

Magnesium - Air Fuel Cell Powering Three LUTW WLED (1 W) Lamps (Feb2006)

Electric Energy Storage I. Capacitor: is an electrical device which serves to store up electricity or electrical energy. C = 0.0885 x10-12 K · A / d C = Capacity (farads) K = dielectric constant A = area of one plate (square centimeters) d = distance between plates (centimeters) A Q = CV d Q = charge (Coulombs) V = voltage (Volts) Stored energy: E = ½ C · V2 e.g. 1000μF at 35 volts will store 0.6125 Joules (enough to power 1 W WLED lamp for ~ 0.5 seconds, assuming 90% power transfer efficiency and 1.2 W of lamp consumption)

Electric Energy Storage II. Ultracapacitors or Supercapacitors: Similar to a normal capacitor, a supercapacitor or ultracapacitor stores energy electrostatically by polarizing an electrolytic solution. Highly porous carbon-based electrodes increases the area to be charged as compared to flat plates. Negative electrode Capacitance: 2500 - 5000 Farads Voltage: 2.5 V Charging/Discharging Efficiency: 90% Charging/Discharging Cycles: 500 000 Stored Energy: E = ½ C · V2 E = 7.81KJ to 15.62 KJ Enough to power a 1W WLED lamp for ~ 1.6 to 3.2 Hours (assuming 90% energy transfer efficiency and 1.2 W lamp consumption) Ion-donor electrolyte Positive electrode Ultracapacitor cross section view when is being charged

Lead Acid Batteries vs Ultracapacitors Lead Acid Batteries Ultracapacitors 1000 Charging Cycles 100K – 500K Charging Cycles (Years?) Lifetime 10 years Deteriorates 80% in 10 years *Require discharge controllers *Not require charge controllers *Toxic compounds (H2SO4, Pb) *No toxic compounds Slow charge and discharge Safe fast charge and discharge High energy density Low energy density Low power density High power density *Cost – US $0.11/ Wh (Initial) *Cost US$ 12.8 / Wh (Initial) Efficiency 75% to 80% Efficiency 95%

Electrochemical Storage Devices Comparison

Superconductive Magnetic Energy Storage (SMES) In SMES, Energy is stored in the magnetic field produced by a current passing through a superconductive coil immersed in liquid helium vessel. L = Coil Inductance (H) I = Current (A) Superconductive  no resistive losses 0.1% of stored energy is used for the cooling system, needed to mantain superconductivity in the coil (~ -200°C). Rapid response for either charge/discharge It is claimed that SMES are 97-98% efficient. Commercial SMES systems are able to store up to about 6 MJ.

Superconductive Magnetic Energy Storage (SMES) Advantages: SMES systems are environmentally friendly Capable of releasing megawatts of power within a small period of time Recharges within minutes Can repeat the charge and discharge sequence thousands of times Disadvantages: Complex  expensive parts & maintenance Big size Cost