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

Solar Electricity14 April, 2009

Monterey Institute for International Studies

Chris Greacen, Palang Thai

Palang Thai พลั�งไท

• 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

พลั�ง (palang): n 1. Power. 2. Empowerment. ไท (thai): adj. 1. Independence. 2. Self-reliance

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

Photovoltaics

Not to be confused with

Concentrating Solar Power (Solar Thermal

Electric)

How PV works

Off-grid array-direct system

Image source: Solar Energy International SEI

Off-grid direct current (DC) system with batteries


Off-grid system with AC & DC loads


Grid connected (AC)


Net metering

Image source: Real Goods



Net Metering in the USA

State policy

Voluntary utility program(s) only

www.dsireusa.org / April 2009

*State policy applies to certain utility types only (e.g., investor-owned utilities)

WA: 100

OR: 25/2,000*

CA: 1,000*

MT: 50*

NV: 1,000*

UT: 25/2,000*

AZ: no limit*

ND: 100*

NM: 80,000*

WY: 25*

HI: 100KIUC: 50

CO: 2,000co-ops & munis:

10/25

OK: 100*

MN: 40

LA: 25/300

AR: 25/300

MI: 20*

WI: 20*

MO: 100

IA: 500* IN: 10*

IL: 40*

FL: 2,000*

KY: 30*

OH: no limit*

GA: 10/100

WV: 25

NC: 20/100*

ME: 100

VT: 250

VA: 20/500*

NH: 100

MA: 60/1,000/2,000*

RI: 1,650/2,250/3,500*

CT: 2,000*

NY: 25/500/2,000*

PA: 50/3,000/5,000*

NJ: 2,000*

DE: 25/500/2,000*

MD: 2,000

DC: 1,000

40 states &

DC have adopted a

net metering policyNote: Numbers indicate system capacity limit in kW. Some state limits vary by customer type, technology and/or system application. Other limits may also apply.

http://www.dsireusa.org/

• System size: 3 kW

Grid-connected Solar PV

Bangkok Solar 1 MW PV

• Bangkok• Project size: 1 MW

Grid-connected Solar PV

How do you estimate how much electricity it will produce?

How long does it takes to pay for itself?

Solar panel produces more power when it faces the sun

Seasonal array tilt

36.6 degrees in Monterey

1200

1000

800

600

400

200

Wat

ts/m

²

8:00 10:00 14:00 16:006:00 18:00

Peak Sun Hours

Peak Sun HoursSan Francisco: 5.4 PSH annual average, tilt at latitude*

*Source: http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/23234.txt

http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/23234.txt

annual average peak sun hours (PSH)

Anacortes, WA = 3.7 PSH per day annual averageSan Francisco = 5.4 PSH

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

Grid-tied solar simple payback period

• Installed cost $7K to $9K per kW2.5 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)

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%

Discounted accumulated cashflow

(120,000,000)

(100,000,000)

(80,000,000)

(60,000,000)

(40,000,000)

(20,000,000)

-

20,000,000

40,000,000

0 2 4 6 8 10

bah

t

Note: project is real. Financials are conjecture. 10% discount rate, 4% inflation

Off-grid systemsDC SYSTEMS

SYSTEMS WITH AC LOADS

Thai solar home systems

Solar for computer training centers in seven Karen refugee camps

Thai-Burma border

•1 kW PV hybrid with diesel generator•Each powers 12 computers

Solar panelCharge controller

Battery

Loads

Off-grid system components


Battery

Loads


PbO2

PbSep

arat

or

+ -

H2SO4

Lead Acid Batteries• Two electrodes

– Negative electrode Lead (Pb).

– Positive electrode Lead dioxide (PbO2).

• Electrolyte – Sulphuric Acid

(H2SO4).

• Sulfation, equalizing

Lead Acid Batteries

Flooded Lead Acid

• Advantages:– Water can be

added. – Cheapest.– Most common.

• Disadvantages:– Can spill.– Hydrogen is vented

during charging.– More prone to

vibration damage.

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

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.

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.

0% 50% 100%

Depth of Discharge (DOD)

Car battery

Deep cycle battery

2000

4000

Cyc

les

to 8

0%

cap

aci

ty

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.

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.

Capacity and Discharge Rate

• Lead sulphate forms at both electrodes.• H2SO4 turns to water.• Discharge rate affects usable capacity.

12.0

10.50% 50% 100%

C/100

C/10

Ba

ttery

Vo

ltag

e

Depth of Discharge

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.

12.0

14.4

0%

Ba

ttery

Vo

ltag

e

16.2

50% 100%

C/100

C/10

State of Charge

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


Battery

Loads

Off-grid system componentsCharge Controller

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

Three Stage Charging

• Reduces the charge rate as SOC increases.

Bulk Charge Absorption Float

Cu

rre

nt Vo

ltage

Time

15 V

C/20

C/100


Inverter• Converts Direct Current (DC) to

Alternating Current (AC) to power ‘regular’ loads

• Sometimes includes battery charger

• Typically can surge to 3X rated power

Inverter Waveforms

• Square Wave

• Modified Square Wave

• Sine Wave

Back-of-the-envelope steps for designing an off-grid solar

electric system1. Load analysis

2. Specify capacity of solar panel, battery, charge controller, and inverter (if necessary)

3. Wire sizing

ITEM LOAD(Watts)Ceiling Fan 10-50Clock Radio 5Clothes Washer 1450Electric Clock 4Iron 1500Sewing Machine 100Table Fan 10-25Refrigerator/Freezer (19 Cu Ft) 1000 Wh/dayRefrigerator/Freezer (12 Cu Ft) 470 Wh/dayRefrigerator/Freezer (4 Cu Ft) 210 Wh/dayBlender 350Coffee Pot 1200Microwave (.5 Cu Ft) 750Electric Range 2100Incandescent (100W) 100Incandescent (60W) 60Compact Fluorescent (60W equivalent) 16Incandescent (40W) 40Compact Fluorescent (40W equivalent) 11CB Radio 10CD Player 35Cellular Phone 24Computer Printer 100Computer (Desktop) 80-150Computer (Laptop) 20-50Stereo (average volume) 15Stereo (Large Full volume) 150TV (12 inch black and white) 15TV (19 inch color) 60VCR 40Band Saw (14”) 1100Circular Saw (7.25”) 900Disc Sander (9”) 1200Drill (1/4”) 250

Load analysis

Qty LoadWatts each

Watts total

Hours per day

Watt hours

per day

2 light 13 26 4 104

1laptop

computer 50 50 5 250

1tv (19 inch

color) 60 60 1 60

1 DVD player 30 30 1 30

1 circular saw 900 900 0.25 225

1 blender 350 350 0.25 87

Totals 1416 756

Load analysis

Qty LoadWatts each

Watts total

Hours per day

Watt hours

per day

2 light 13 26 4 104

1laptop


1tv (19 inch

color) 60 60 1 60

1 DVD player 30 30 1 30

1 circular saw 900 900 0.25 225

1 blender 350 350 0.25 87

Totals 1416 756

Inverter

Load analysis

Qty LoadWatts each

Watts total

Hours per day

Watt hours

per day

2 light 13 26 4 104

1laptop


1tv (19 inch

color) 60 60 1 60

1 DVD player 30 30 1 30

1 circular saw 900 900 0.25 225

1 blender 350 350 0.25 87

Totals 1416 756

Solar panels,

batteries

Solar panel derating: 15%

Loss from Wiring: 3%

Loss from Battery: 15%

How many solar panels?What size controller?

Battery size?

Qty Load Watts each Watts total Hours per day Watt hours2 light 13 26 4 1041 laptop computer 50 50 5 2501tv (19 inch color) 60 60 1 601DVD player 30 30 1 301circular saw 900 900 0.25 2251blender 350 350 0.25 87.5

Totals 1416 756.5

Solar panel derating 85%Battery efficiency 85%Wiring efficiency 97%Inverter efficiency 90%Total efficiency 63%Total adjusted watt hours per day (= watt hours / total efficiency) 1,199 Nominal system voltage 12Adjusted amp-hours per day (= adjusted watthours / system voltage) 99.95 Peak Sun Hours (average) 5.4Amps of solar power required (=Adjusted amp-hours / PSH) 18.51 Imp (amps) per solar panel (Astopower PV120. 120 watt. Imp = 7.1, Isc = 7.7) 7.10 Number of solar panels (= amps solar required / amps per panel) 2.61 Rounded up… 3 Isc per panel 7.7Minimum controller current (amps) = 1.25 x Isc 29 Maximum number of days of autonomy 3Max allowable depth of discharge 0.5Battery ampere-hours (= adjusted amphours x days of autonomy / allowable depth of discharge) 600

Wire sizing

• Voltage drop – how much power is lost to heat

V = I R

• Ampacity – how much current the wire can safely conduct

12 Volt 2% Wire Loss ChartMaximum distance one-way in feet

Multiply distances by 2 for 24 volts and by 4 for 48 volts.

http://www.affordable-solar.com/wire.charts.htm

http://www.affordable-solar.com/wire.charts.htm

Wire sizing

http://www.csgnetwork.com/voltagedropcalc.html

Typically aim for 3% or less loss

http://www.csgnetwork.com/voltagedropcalc.html

Ampacity table

PV system errors

User error: bypassed controller battery

overcharge1. Villager bypasses broken

controller and charges battery directly from PV

2. Battery over-charged. Electrolyte level drops and plates are exposed to air. Battery fails.

1

2

User error: Controller bypass leads to burned diode

1

2

1. Villager bypasses broken controller and charges battery directly from PV

2. One mistake of reverse battery polarity blows up bypass diode in PV junction box, melting junction box.

User error: Villager u sed inefficient 60 W l ight bulb

Problems found during training surveys

Installation error: Battery failure caused by solar panel installation in shady location

14:00 Saw Kre Ka village, Tha Song Yang District

Installation error: Bad panel locations

“The Service & Support Department is like the guy in the parade who walks behind the elephant with a broom and a big bucket”

Ministry of Interior

PEA

Installation company

End users

$

$

SHS

Existing linkages

warranty

Tax payers

$


PEA


End users

$

$

SHS

Missing linkages

warranty

What happens when systems fail? There is no feedback loop from the end users to

installation company, PEA, government or taxpayers

Tax payers

$

Warranty awareness Self-help: local technicians

+ user training


PEA


End users

$

$

SHS

Missing linkages

warranty

Tax payers

$

Feedback on status of systems, failure

modes, successful interventions

SHS Warranty• Postcards with warranty

and maintenance information could be distributed by Tambons

• Idea presented at meeting with DLA (Department of Local Administration)

BGET SHS trainings in Tak province

Documents

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