OffGrid_PV_Design_F19_part1.pptx Lecture from Humboldt State University

Off grid PV Design from Humboldt State University

1. Stand Alone Photovoltaic Systems: Design Principles and Components ENGR 475: Renewable Energy Power Systems Arne Jacobson and Liza Boyle Fall, 2019

2. Stand Alone PV Systems 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 PV Systems Photos by Arne Jacobson, Erika Rosenthal, Nina Stam, and Shannon Graham (clockwise from top left)

4. Solar Lanterns and LED 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. https:// realgoods.com /off-grid-solar Common Off-Grid PV System Components

7. Common PV System Components 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 System Components LED or CFL Battery & Circuitry Power Source (solar, AC, dynamo) Switches, Housing, Wires, Connectors, etc.

9. Residential Off-Grid Solar PV System (basic 12 volt DC configuration) Drawing my Mike Okendo for Energy for Sustainable Development Africa, Nairobi, Kenya

10. Residential Off-Grid Solar PV System (AC/DC system configuration) Source: SEI PV Design Manual, p. 102

11. Steps for PV System 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 Identify loads 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 Use by 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 for Load 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 for Load 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 Load AC DC hrs/day days/wk days AC DC Light Light TV Radio Fridge Total Daily Load: Maximum AC Load (Watts) Maximum DC Load (Watts)

18. Special Topics for Load 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 System Components 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

21. http://www.solcomhouse.com/images/diagram_solar_power.gif Common Off-Grid PV System Components Converting solar energy to electricity

22. What do you get 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 W p PV module Standard Conditions: 1000 W/m 2 25°C AM = 1.5

23. Photovoltaic IV Curve Basics

24. PV Array Sizing Calculations 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 Selection Issues 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 Including additional 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 System Components Storing energy for use when the solar input is less than energy use.

28. Battery Storage for PV 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. Batteries http://discoverpower.com/ http://www.germes-online.com/ http://fenggejohn.ec51.com/ http://www.mastervolt.com/ http://www.1st-optima-batteries.com/

30. Small Batteries for Off-Grid Lighting Systems Sealed Lead Acid Nickel Metal Hydride ( NiMH ) Nickel Cadmium ( NiCd ) Lithium Ion

31. Battery Types Lead Acid ( 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 (LiFePO 4 ), and others}

32. Battery Experience Curves Schmidt O., Hawkes A. & Staffell I. “The future cost of electrical energy storage based on experience rates” Nature July 2017.

33. Battery Cost Trend Range and Projections Björn Nykvist & Måns Nilsson, Nature Climate Change 5, 329–332 (2015) doi:10.1038/nclimate2564

34. Inside a Lead Acid 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 + PbO 2 + 2H 2 SO 4 <=> 2PbSO 4 + 2H 2 O Discharging  Anode (-): Pb (pure lead) Cathode (+): PbO 2 (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 Battery Capacity 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 for Pb-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 DOD on Cycle Life (data for gel cell type Pb-acid battery)

40. Impact of High Voltage Set Point and Depth of Discharge on Cycle Life

41. Pb-Acid Battery Capacity and Temperature • Lower temperatures decrease capacity • Higher temperatures increase capacity, but reduce cycle life

42. Comparison of Common Battery Technologies

43. Comparison of Small Battery 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 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:

47. Some Battery Installation Issues Well ventilated enclosure Vent H 2 and O 2 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