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Solar Electricity

Solar Electricity. 14 April, 2009 Monterey Institute for International Studies Chris Greacen, Palang Thai. Palang Thai พลังไท. พลัง (palang): n 1. Power. 2. Empowerment. ไท (thai): adj. 1. Independence. 2. Self-reliance. Thailand NGO Objective:

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Solar Electricity

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  1. Solar Electricity 14 April, 2009 Monterey Institute for International Studies Chris Greacen, Palang Thai

  2. Palang Thaiพลังไท พลัง (palang): n 1. Power. 2. Empowerment. ไท (thai): adj. 1. Independence. 2. Self-reliance • Thailand NGO • Objective: • To ensure that the transformations that occur in the region's energy sector: augment, rather than undermine, social and environmental justice and sustainability. • Key approaches: • We teach hands-on energy technology • We help draft policies • We comment on projects and plans • We advocate reform in energy planning processes & regulatory regime

  3. Outline • Photovoltaics (PV) • Basic market trend • How PV works • Basic types of solar electric systems • Grid-connected systems • Components • Net metering • Calculating simple payback • (with detour on Peak Sun Hours, array tilt, shading) • Off-grid • Components • Lead acid batteries • Charge controllers • Inverters • System sizing overview

  4. Photovoltaics

  5. Not to be confused with Concentrating Solar Power (Solar Thermal Electric)

  6. How PV works

  7. Off-grid array-direct system Image source: Solar Energy International SEI

  8. Off-grid direct current (DC) system with batteries Image source: Solar Energy International SEI

  9. Off-grid system with AC & DC loads Image source: Solar Energy International SEI

  10. Grid connected (AC) Image source: Solar Energy International SEI

  11. Net metering Image source: Real Goods

  12. Image source: Solar Energy International SEI

  13. Image source: Solar Energy International SEI

  14. Net Metering in the USA www.dsireusa.org / April 2009 WA: 100 ME: 100 MT: 50* ND: 100* VT: 250 NH: 100 OR: 25/2,000* MN: 40 MI: 20* MA: 60/1,000/2,000* WY: 25* WI: 20* RI: 1,650/2,250/3,500* IA: 500* IN: 10* CT: 2,000* CO: 2,000co-ops & munis: 10/25 NV: 1,000* NY: 25/500/2,000* OH: no limit* IL: 40* PA: 50/3,000/5,000* UT: 25/2,000* WV: 25 MO: 100 NJ: 2,000* KY: 30* CA: 1,000* NC: 20/100* DE: 25/500/2,000* NM: 80,000* OK: 100* MD: 2,000 AZ: no limit* AR: 25/300 DC: 1,000 GA: 10/100 VA: 20/500* LA: 25/300 HI: 100KIUC: 50 FL: 2,000* 40 states & DChave adopted a net metering policy State policy Voluntary utility program(s) only * State policy applies to certain utility types only (e.g., investor-owned utilities) Note: Numbers indicate system capacity limit in kW. Some state limits vary by customer type, technology and/or system application. Other limits may also apply.

  15. Grid-connected Solar PV • System size: 3 kW

  16. Bangkok Solar 1 MW PV Grid-connected Solar PV • Bangkok • Project size: 1 MW

  17. How do you estimate how much electricity it will produce?How long does it takes to pay for itself?

  18. Solar panel produces more power when it faces the sun

  19. Seasonal array tilt 36.6 degrees in Monterey

  20. Peak Sun Hours San Francisco: 5.4 PSH annual average, tilt at latitude* 1200 1000 800 Watts/m² 600 Peak Sun Hours 400 200 10:00 14:00 16:00 18:00 6:00 8:00 *Source: http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/23234.txt

  21. annual average peak sun hours (PSH)

  22. Anacortes, WA = 3.7 PSH per day annual average San Francisco = 5.4 PSH

  23. Energy produced kWh per year = (PSH) x (peak kW of array) x (solar panel derating) x (inverter efficiency) x 365 Example: 5.4 hours x 2.5 kW x 85% x 95% x 365 = 4000 kWh

  24. Grid-tied solar simple payback period • Installed cost  $7K to $9K per kW 2.5 kW * $8,000 = $20,000 • Value of annual electricity offset: $0.25/kWh * 4000 kWh/year = $1000/yr • Simple Payback: $20,000 / $1000/yr = 20 years (assuming no subsidies)

  25. Financial sketch: MW-scale solar project in Thailand • Project size: 1 MW • Cost estimate: $4 million • Tariffs: • TOTAL: $0.33/kWh for 10 years • Simple Payback: 6.5 years • 10-year IRR: 14% Note: project is real. Financials are conjecture. 10% discount rate, 4% inflation

  26. Off-grid systems DC SYSTEMS SYSTEMS WITH AC LOADS

  27. Thai solar home systems

  28. Solar for computer training centers in seven Karen refugee campsThai-Burma border • 1 kW PV hybrid with diesel generator • Each powers 12 computers

  29. Off-grid system components Charge controller Solar panel Loads Battery

  30. Off-grid system components Charge controller Solar panel Loads Battery

  31. Lead Acid Batteries - + • Two electrodes • Negative electrode Lead (Pb). • Positive electrode Lead dioxide (PbO2). • Electrolyte • Sulphuric Acid (H2SO4). • Sulfation, equalizing PbO2 Pb Separator H2SO4

  32. Lead Acid Batteries

  33. Advantages: Water can be added. Cheapest. Most common. Disadvantages: Can spill. Hydrogen is vented during charging. More prone to vibration damage. Flooded Lead Acid

  34. Valve Regulated Lead Acid • Maintenance Free • Similar to Flooded Lead Acid. • Gel • Silica Gel contains the electrolyte • AGM (Absorbed Glass Mat) • Electrolyte is Absorbed in a Fiber Glass Mat

  35. Lead Acid Battery Types • Starting, Lighting and Ignition (car battery) • Shallow cycle: 10% DOD • Deep discharge drastically reduces battery life. • Thin plates maximize surface area and current. • Traction – golf cart and forklift • Deep cycle: 60% to 80% DOD • Thick plates or tubes withstand deep discharge.

  36. 4000 Deep cycle battery Cycles to 80% capacity 2000 Car battery 0% 50% 100% Depth of Discharge (DOD) Lead Acid Battery Cycle Life • Number of cycles to a particular DOD. • Cycle life decreases with increasing DOD. • Sulphation is the main cause of failure.

  37. Battery Capacity • Given in Amp hours [Ah] for a particular discharge rate at 25°C. • Empty is usually defined as 10.5 Volts. • Usable capacity depends on actual discharge rate and temperature.

  38. Charge and Discharge Rates • Written Ct or C/t Where t = Time = Capacity[Ah]/rate[A] • Examples: • A 200 Ah battery at 10 amps takes 20 hours and has a C/20 rate. • A 200 Ah battery at 2 amps takes 100 hours and has a C/100 rate.

  39. Capacity and Discharge Rate • Lead sulphate forms at both electrodes. • H2SO4 turns to water. • Discharge rate affects usable capacity. 12.0 C/100 Battery Voltage C/10 10.5 0% 50% 100% Depth of Discharge

  40. Charging Lead Acid Battery • Voltage is a function of state of charge and charge rate • Lead dioxide and lead form at electrodes. • H2SO4 increases. • Lower charge rates avoid gassing. 16.2 C/10 Battery Voltage 14.4 C/100 12.0 100% 0% 50% State of Charge

  41. Equalizing Charge • Only Applicable to Flooded Style Batteries • Provide a charged battery with a high terminal voltage, ~16V. • High voltage causes the battery to “boil”. • Lead sulfate is dislodged from plates. • Bubbling action mixes up the stratified layers • Equalize charge for a few hours at a time

  42. Off-grid system components Charge Controller Charge controller Solar panel Loads Battery

  43. Charge controller • Ensures that battery is not over-charged • For small DC systems, often features a Low Voltage Disconnect (LVD) to ensure that battery is not over-discharged • Fancy big ones sometimes have Maximum Power Point Tracking (MPPT) that squeezes more power out of solar panels

  44. Bulk Charge Absorption Float C/20 15 V Current Voltage C/100 Time Three Stage Charging • Reduces the charge rate as SOC increases.

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