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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