Photovoltaic SystemsVirginia Solar Pathways

June 11, 2015Shirshak Dhali

Old Dominion University

TOPICS

Grid-connected PV systemsMicro-gridsPV Inverters

ODU InstallationsODU Solar Partnership

System Sizing for a residential unitPanel and Inverter Selection

Grid-connected PV Systems EconomicsComparison to other renewable sources

Grid Connected PV SystemInverter has circuitry for Maximum Power Point Tracking (MPPT) and also it has circuitry to sense and disconnect if there is power loss

http://www.egr.unlv.edu/~eebag/Photovoltaic%20Systems%20II.pdf

Micro Grid

Distribution Transformer

Utility SystemPrimary (13.2 kV)

Isolating Device

Master System Controller

(Synchronization, Fault Protection, Islanding

Detection etc.)

Gen

Charge RegulatorFuel Cell

DC Bus

Building Electric

Load

AC Bus

DC to AC

DC to DC

EnergyStorage

Grid connected/Islanding micro grid

Heat Storage

Heat Load

Today’s inverters do a lot!

Synchronize and Inject current in phase with Voltage

Monitor the PV array, track the

maximum power and operate at that

point

Monitors the grid and disconnects in case of

trouble

Dominion Solar Partnership Program/Old Dominion University

Old Dominion University Solar Partnership

REC Solar (REC250PE)15.1% efficiencyNominal Power voltage 30.5VNominal Power Current 6.56AArea 1.65 m2Weight 18

Inverters: Advanced Energy Industries:DC in 412V AC = 480 V 1. AE 75TX-480 V (75 kW) 2. AE 50TX-480 V (50 kW)

AC capacity 125 kWDC Capacity 151 kWNumber of panels 602

Old Dominion University Solar Partnership

Energy year to date 52,431 kWhCO2 Avoided 69.995 Ibs

SO2 avoided 252 lbsNOx Avoided 100 lbs

Daily power variation over a seven day periodODU –Dominion Solar Partnership

-20

0

20

40

60

80

100

120

140

-1.00 4.00 9.00 14.00 19.00 24.00

AC p

ower

gen

erat

ed (k

W)

Time of the day

ODU Rec Center (Daily Power)

25-Mar

26-Mar

27-Mar

28-Mar

29-Mar

30-Mar

31-Mar

Residential System SizingGoal: Rooftop PV to annually displace 7500 kWh/yearSolar Resources: 5.2 kWh/m2 or 5.2 h/day of 1-sun or 5.2 peak sun hours (PSH)

Pac=7500/(5.2x365)= 4 kWPdc=4/.75 = 5.3 kW (de-rating =0.75)Number of Panels=5.3/.16= 33 panelsNumber of panels per string• 2 panels gives 46.4V X• 3 panels give 69.6 V Number of || strings = 33/3=11Total panel area = 33x1.3 = 44 m2

PV ModuleRated Power: 160WVoltage at max power 23.2 VSize 1.3x1 m2

Efficiency: 12.4%

Inverter characteristicsAC power 6000 WAC voltage: 220VPV voltage for MPPT: 44-85 V

Capacity Factor (CF) = (hours/day of peak sun)/(24 h/day) = 5.2/24 = 0.22

Dominion’s Interconnection Requirements

• Electrician Certification—we require a licensed electrician to sign-off to ensure the entire system is up to code.

• Inverter—the inverter manufacturer/model must be approved by System Protection to ensure safe operation. Most inverters used for small solar installations have been reviewed and approved before, so this process is usually fairly quick.

• Vendor Certification—this ensures that the inverter and all interconnection system equipment is in compliance with UL 1741.

Residential Hourly Energy Consumption http://en.openei.org/datasets/files/961/pub/

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

0 4 8 12 16 20 24

kWh

(Hou

rly)

Time of Day

Hourly Energy Consumtion

Winter Summer PV

How does monthly PV energy generation compare to residential use?

In 2013Average of 910 kWh/month

LA had the highest 1273 kWh/monthHawaii had the lowest 515 kWh/month

0

200

400

600

800

1000

1200

1400

1600

1800

0 2 4 6 8 10 12M

onth

ly E

nerg

y (k

Wh)

Month of the year

PV Energy Vs. Residential Usage

Single Family Unit

4 kW PV

System Tradeoffs

0

100

200

300

400

500

600

700

800

0 2 4 6 8 10 12

Mon

thly

Ene

gy (k

Wh)

Month of the year

Mounting Options

Fixed

1-axis

2-axis

Fixed (ODU Rec Center)

Single axis (ODU Rec Kaufman Hall)

Two axis

Economics of PV Systems

• Reported pricing for PV system installation in 2013• Residential and small commercial (<10 kW) was $4.69/Wdc• Large commercial (>100kW) was $3.98/Wdc• Utility-scale (>MW, ground mounted) was $3.00/Wdc

• Price breakdown• Panel cost about the same for all scale ($0.9/Wdc)• Inverter cost decreases with size ($0.3-$.1/Wdc)• Balance of System decreases with size ($2.5/Wdc -$1.0/Wdc)

SunShot USDoE:http://www.nrel.gov/docs/fy14osti/62558.pdf

How does PV stack up with other renewables?

PhotovoltaicsSignificant decrease in price of modulesSince 2012, the cost of PV has fallen by an average of 15%.System Useful Life 25 to 40 yrCapacity factor (CF) =24%-27%

http://www.nrel.gov/analysis/tech_lcoe_re_cost_est.html

Installed Costs for Electric Generating Technologies

WindSteep declining unit cost ($/kw) as size of wind turbine and projects increases.Newer units have lower lifetime O&MSystem useful lifetime 20 yrCapacity Factor (CF) =32-34%

Biomass combined heat and power (CHP)Economically competitive technologyNot yet experienced wide-scale deployment

Electric Power Monthly-http://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_6_07_b

Solar Resource BaseWind Energy: CL Archer and MZ Jacobson, J. Geophys. Res. 110, D12110 (2005)

Solar Energy Resource Base 1.5x1018kWh/year

1.7x105 TWave

Solar Resource onEarth’s Surface

5.5x1017kWh/year3.6x104 TWave

Wind Energy Resource Base

6x1014kWh/year 72 TWave

Human Energy Use(mid to late century)

4x1014kWh/year 50 TWave