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![Battery Sizing Calculations
AC Average Inverter + DC Average DC System = Average Amp-
Daily Load efficiency Daily Load voltage hours/Day
[( ) + ] =
Average X Days of Discharge Battery Ahr = Batteries in
Amp-hours/day Autonomy Limit Capacity Parallel
X =
DC System Battery = Batteries X Batteries = Total
Voltage Voltage in Series in Parallel Batteries
= X =
Battery Specification: Make: Model:](https://image.slidesharecdn.com/offgridpvdesignf19part1-240610190017-73474113/75/OffGrid_PV_Design_F19_part1-pptx-Lecture-from-Humboldt-State-University-46-2048.jpg)
OffGrid_PV_Design_F19_part1.pptx Lecture from Humboldt State University
- 1. Stand Alone PhotovoltaicSystems: Design Principles and Components ENGR 475: Renewable Energy Power Systems Arne Jacobson and Liza Boyle Fall, 2019
- 2. Stand Alone PVSystems PV Powered Radio Transmitter in Northern Canada http://www.canren.gc.ca/ Off-Grid PV Powered Home in Colorado http://www.renewableenergyaccess.com PV Powered Road Sign http://www.safetysupplyandsign.com/ PV and Wind Powered Gas Platform in North Sea http://www.ecofriend.org/
- 3. Stand Alone PVSystems Photos by Arne Jacobson, Erika Rosenthal, Nina Stam, and Shannon Graham (clockwise from top left)
- 4. Solar Lanterns andLED Lights
- 5. Basic (sometimes competing)Design Goals • Technical functionality and durability • component selection and integration • Ease of Installation • User Interface • Ease of Maintenance • Flexibility for change / future growth • Safety • human and environmental • Low Cost
- 6.
- 7. Common PV SystemComponents • PV array • Auxiliary power sources • Battery storage • Charge controller • Inverter • AC and DC power handling equipment • Switches and disconnect • Fuses and circuit breakers • Conductors (wires) • Mounting structures
- 8. Off-Grid Lighting SystemComponents LED or CFL Battery & Circuitry Power Source (solar, AC, dynamo) Switches, Housing, Wires, Connectors, etc.
- 9. Residential Off-Grid SolarPV System (basic 12 volt DC configuration) Drawing my Mike Okendo for Energy for Sustainable Development Africa, Nairobi, Kenya
- 10. Residential Off-Grid SolarPV System (AC/DC system configuration) Source: SEI PV Design Manual, p. 102
- 11. Steps for PVSystem Design • Load evaluation (total energy req’d for loads, peak loads, AC vs. DC, choosing a system voltage,) • Solar resource (number and size of PV modules) • Auxiliary Power (generator, wind, hydro, others) • Sizing storage (# and type of batteries) • Charge control strategy • Siting Issues (solar access, distances) • Wiring sizing (also disconnects & over-current protection)
- 12. Load Evaluation Equations •Basic Equations for DC Systems: • Power = Current * Voltage (P = I*V, W) • Energy = Power * Time (E = P*∆t, Whr) • Amp-hour consumption = Current * Time (Ahr) • AC power a bit more complicated • Power factor must be considered for some appliances & inverter combinations
- 13. Load Evaluation • Identifyloads and power requirements • average daily loads and peak loads • Determine load usage profile over time • often this is a very crude process • Hard to estimate actual usage patterns • Especially true when system does not yet exist • sometimes iterative approach is req’d • Get initial load profile, design system, see how much it costs, then adjust design
- 14. Estimating Power Useby Appliances • Appliance power consumption data sources (in order of preference) • 1) measure power use for appliance • 2) manufacturer’s data on power use • (often over-estimates power use) • 3) “typical” data for appliance type http://www.codinghorror.com/blog/archives/000353.html
- 15. Critical Issues forLoad Evaluation • AC vs. DC power to end use • AC allows for use of more electrical devices, but requires purchase of an inverter • inverter con’s = cost + efficiency (70% - 95%) • DC common for small systems, AC for large
- 16. Critical Issues forLoad Evaluation (cont) • System voltage (12V, 24V, 48V, etc.) • AC systems allow for high DC voltage (reduced wire loss) • DC systems often have 12 VDC (appliance availability) • Choosing appliances: efficiency usually worth the extra cost for PV applications
- 17. Load Analysis Worksheet Electric LoadAC DC hrs/day days/wk days AC DC Light Light TV Radio Fridge Hrs Watt 7 Use * Use * Watts Amps * Volts Qty Total Daily Load: Maximum AC Load (Watts) Maximum DC Load (Watts)
- 18. Special Topics forLoad Evaluation • Cycling loads • i.e. appliances that automatically turn themselves on and off (e.g. refrigerator) • “Phantom” loads • loads that draw power even when they are “off” • Estimating surge requirements • some appliances require considerably more power when starting than during continuous operation • e.g. motor loads often require 3-5 times their continuous operating power for a brief time when starting
- 19. http://www.solcomhouse.com/images/diagram_solar_power.gif Common Off-Grid PV SystemComponents Solar Resource Evaluation
- 20. Solar Resource Evaluation •What is the solar resource at the site? • annual average daily; monthly average daily • choosing orientation and tilt for PV array • impact of shading • How does resource match demand? • seasonal distribution of loads? “Full Sun Hours” from Solar radiation data 0 200 400 600 800 1000 1200 6:00:00 9:00:00 12:00:00 15:00:00 18:00:00 Solar Radiation (W/m 2 ) Time of Day 6.8 kWh/m 2 /day
- 21. http://www.solcomhouse.com/images/diagram_solar_power.gif Common Off-Grid PV SystemComponents Converting solar energy to electricity
- 22. What do youget out of a PV module? • PV module output is affected by insolation and module temperature • IV curve is best indicator of module performance IV Curve for 20 Wp PV module Standard Conditions: 1000 W/m2 25°C AM = 1.5 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 5 10 15 20 25 Current (amperes) Voltage (volts) Maximum Power Point
- 23. Photovoltaic IV CurveBasics 0 0.4 0.8 1.2 1.6 0 5 10 15 20 0 5 10 15 20 25 IV Curve Power Voltage Curve Current (amperes) Power (watts) Voltage (volts) Maximum Power Point Range of Battery Voltages
- 24. PV Array SizingCalculations Avg. Load Battery Peak Sun = Array Peak Ahr/Day Efficiency Hrs/Day Amps = Array Peak = Modules Module Short Peak Amps Amps/Module in Parallel Circuit Current = DC System Nominal = Modules in X Modules in = Total Voltage Module Voltage Series Parallel Modules = X = PV Panel Specification: Make: Model:
- 25. Photovoltaic Module SelectionIssues • Module watt rating • Efficiency • high efficiency important when space is limited • IV curve performance • Environment • temperature (special modules for extreme temps.) • specific environmental conditions (e.g marine env.) • Reputation and Warranty • Cost
- 26. Auxiliary Power • Includingadditional power sources can increase system reliability and may reduce life cycle cost • But it increases system complexity • Battery capacity often smaller with backup power • Common additional power sources: • Generator (gas, diesel, propane) • Available whenever fuel is provided • Wind turbine, hydro-electric turbine • Availability depends on wind and hydro resources • Electrical grid • Grid intertie system
- 27. http://www.solcomhouse.com/images/diagram_solar_power.gif Common Off-Grid PV SystemComponents Storing energy for use when the solar input is less than energy use.
- 28. Battery Storage forPV Systems • Batteries provide storage for PV and other RE systems • Batteries store day time energy for night use • Systems often have storage capacity for 2 to 10 cloudy days • Batteries cannot store energy for more than a few weeks due to “self-discharge” effect
- 29.
- 30. Small Batteries forOff-Grid Lighting Systems Sealed Lead Acid Nickel Metal Hydride (NiMH) Nickel Cadmium (NiCd) Lithium Ion
- 31. Battery Types • LeadAcid (Pb-acid) Battery • Flooded cells (a.k.a. open wet cells) • Starting and lighting battery (SLI) • Deep cycle battery (many types) • Sealed wet cells • Gel cells • Nickel Cadmium (NiCd) • Nickel Iron (NiFe) • “New” battery technologies {nickel metal hydride (NiMH), lithium ion (Li-Ion), lithium iron phosphate (LiFePO4), and others}
- 32. Battery Experience Curves SchmidtO., Hawkes A. & Staffell I. “The future cost of electrical energy storage based on experience rates” Nature July 2017.
- 33. Battery Cost TrendRange and Projections Björn Nykvist & Måns Nilsson, Nature Climate Change 5, 329–332 (2015) doi:10.1038/nclimate2564
- 34. Inside a LeadAcid Battery Images Developed by Kevin R. Sullivan of Skyline College in San Bruno, CA see http://www.autoshop101.com/trainmodules/batteries/101.html
- 35. Pb-Acid Battery Chemistry Charging Pb + PbO2 + 2H2SO4 <=> 2PbSO4 + 2H2O Discharging Anode (-): Pb (pure lead) Cathode (+): PbO2 (lead oxide) Electrolyte: sulfuric acid/water solution • Specific gravity of electrolyte changes with state of charge (ratio of water and sulfuric acid changes)
- 36. Battery Vocabulary • BatteryCapacity • Ahr of storage @ C-xx (or @ 0.xC) • Whr of storage • Days of autonomy = # days batteries can meet load without being charged • Rate of discharge or charge • C-xx charge rate = Current at which the battery will be completely discharged in “xx” hours • e.g. for 50 Ahr battery, C-10 is 5 amps • Alternatively, 0.1C is 5 amps
- 37. More Battery Vocabulary •State of Charge (SOC) • % of battery capacity (in Ahr) remaining • Depth of Discharge (DOD) • % of battery capacity (in Ahr) removed e.g. 40% SOC = 60% DOD • Usable Storage Capacity = Ahr Capacity * Max recommended DOD • Cycle life = # of discharge - charge cycles a battery can provide before its useful life is over
- 38. Good Practices forPb-Acid Battery Use • Respect limits of each battery type • Avoid deep discharges • “deep” is different for different technologies • deep discharges cause “sulfation” of lead plates • Charge battery to full regularly • Use moderate charge rates (C-5 is max) • Equalize batteries every few months • overcharging helps remove sulfate from plates • Electrolysis during overcharging stirs up electrolyte
- 39. Impact of DODon Cycle Life (data for gel cell type Pb-acid battery)
- 40. Impact of HighVoltage Set Point and Depth of Discharge on Cycle Life
- 41. Pb-Acid Battery Capacityand Temperature • Lower temperatures decrease capacity • Higher temperatures increase capacity, but reduce cycle life
- 42. Comparison of CommonBattery Technologies Pb-Acid wet cell deep cyc Pb-Acid sealed shallow cyc Pb-Acid Gel Cell NiCd wet cell rec. DOD 40-80% 15-25% 15-25% 100% Self- discharge (per mo.) 5% 1-4% 2-3% 3-6% Typ. Cap. (Ahr/ft3 ) 1000 700 250 500 Range (Ahr/ft3 ) 200- 1425 160- 1400 100- 460 100- 1000 Typ. Cap. (Ahr/lb) 5.5 4.6 2.2 5.0
- 43. Comparison of SmallBattery Types Source: Lighting Global Technical Note No. 10 “Lithium-ion Battery Overview” (May, 2012), http://www.lightingafrica.org/resources/technical-notes.html
- 44. Battery Selection Issues •Battery storage capacity • Maximum charge and discharge currents • avoid currents that exceed the C-5 rate • Match battery voltage to system voltage • Pb-Acid batteries come in 2 V, 6 V, and 12 V configurations • Add batteries in series to increase voltage • Add batteries in parallel to increase storage capacity
- 45. Battery Selection Issues(cont) • Cycle depth characteristics • shallow vs. deep cycle, etc. • Maintenance requirements • e.g. low maintenance battery good for remote apps • Environment and Special use requirements • e.g. temperature performance varies by battery type • e.g. sealed batteries do not have to be installed upright • Cost
- 46. Battery Sizing Calculations ACAverage Inverter + DC Average DC System = Average Amp- Daily Load efficiency Daily Load voltage hours/Day [( ) + ] = Average X Days of Discharge Battery Ahr = Batteries in Amp-hours/day Autonomy Limit Capacity Parallel X = DC System Battery = Batteries X Batteries = Total Voltage Voltage in Series in Parallel Batteries = X = Battery Specification: Make: Model:
- 47. Some Battery InstallationIssues • Well ventilated enclosure • Vent H2 and O2 gases from electrolysis • Vent corrosive sulfur compounds • Keep batteries away from ignition sources • Clean, dry area with moderate temperatures • Use over-current protection (fuses, circuit breakers, and disconnect switches) • Protect against acid spills (wet cell Pb-acid) • Have water and baking soda available if spill occurs • Maintenance issues • Configure batteries for easy access
Editor's Notes
- #2 6
- #34 - 100mAh to 10Ah – pico PV sized batteries - 10Ah to 100Ah – SHS and larger sized batteries - From 2008 to 2012, lithium-ion battery prices decreased by 42% (Dalberg 2013) - Historical pricing is mostly based on real pricing data recorded over the last few years. Where real pricing data was not available, estimations were made. Forward pricing is not set on a financial model, but on Navigant Research’s expectations for where the industry is headed based on manufacturing scale, materials prices and demand. Prices do not take into account transportation costs. 2009 figures are modelled numbers as pricing data was not available before 2010. - Price ranges have not been adjusted for inflation. - Source: Navigant Research custom research