Photovoltaic Systems – Residential Scale Part 2 April 2, 2014

Learning Outcomes An understanding of the design process for residential scale PV projects A review of the permitting process and financing options for residential PV Case Study - A comparison of predicted and measured performance for residential PV 2

Value to participants A review of the design of a photovoltaic system leads to an understanding of the competing issues involved in solar power development and expansion An opportunity to examine residential PV systems in Arizona 3

Design Steps in any Residential Scale System 1. Examination of site and estimation of performance 2. Securing financing 3. Carrying out PV system engineering and design 4. Securing relevant permits 5. Construction 6. Inspection 7. Connection to the grid 8. Performance monitoring 4 Grid-Connected Utility-Interactive PV System

Grid-Connected Utility-Interactive PV Systems Step 3 - Carrying out PV system engineering and design o Evaluation of space availability, solar availability, and electrical consumption o PV array sizing o Module selection o Inverter selection o Balance of system 5

Step 3 - Carrying out PV system engineering and design Evaluation of electrical consumption 6 Average monthly baseline usage – 160kWh

Step 3 - Carrying out PV system engineering and design Comparison of electrical consumption to solar electricity production 7 4kW system, 18.5 o tilt

Step 3 - Carrying out PV system engineering and design Comparison of electrical consumption to solar electricity production Annual total electrical usage – 5290 kWH Annual total solar electricity production – 6324 kWh Ratio: 6324/5290 = 1.20; APS regulations, the ratio cannot exceed 1.25 However, 4kW system requires approximately 16 modules. Backyard has space for 14 modules. So, system size will be reduced to 3.5kW Expected total solar electricity production – 5534 kWh 8

Step 3 - Carrying out PV system engineering and design PV array sizing and module selection 9 14 modules: 7 x 2 array

Step 3 - Carrying out PV system engineering and design Solar availability 10 Consideration of shadowing on pergola arrays

Step 1 - Examination of site and estimation of performance Hip roof wind zones 11

Step 1 - Examination of site and estimation of performance Layout for low wind region 12

Step 3 - Carrying out PV system engineering and design Loss of solar availability from shading The shading of PV modules has a very large impact on the performance of PV systems There is a reduction in solar power production when the modules are shaded o Clouds can completely cover the modules from the solar radiation – but this often transient o Dust and other grime have a similar effect – and this grows with time o Partial shading (by falling leaves, other debris) can actually have a very deleterious effect 13

Step 3 - Carrying out PV system engineering and design Inverter Selection A new approach to combatting the effects of shading has emerged recently – the use of “microinverters ” A microinverter is a compact inverter installed directly on the back of a PV module o Therefore in a PV array, each module has its own inverter – the PV modules now have an AC output, not a DC output o Each module is separately operated at its own MPP – they are connected in parallel, so the current loss from shading is eliminated o The wiring and the connections are simplified, and high DC voltages are eliminated o A typical microinverter has a 25 year expected lifetime – a dramatic increase over the expected 10 – 12 year lifetime of a high power central inverter 14

Step 3 - Carrying out PV system engineering and design 15 Microinverters installed on back of modules

Step 3 - Carrying out PV system engineering and design Consider another case – a conventional pitched roof o Suppose the average monthly electrical consumption is 1500 kWh/month at a residence in Phoenix, AZ o Suppose design goal is to have PV system produce 33% of annual electrical need o This means the PV system must produce, on average:  Monthly production – 500 kWH/mo  Annual production – 500 x 12 – 6000 kWh/yr 16

Step 3 - Carrying out PV system engineering and design PVWatts can be used to calculate what the peak power production of the PV system should be to produce 6000 kWh/yr 17 PVWatts includes an estimate of these loss mechanisms in calculation of the conversion from DC power from the array to the AC power delivered to the grid

Step 3 - Carrying out PV system engineering and design 18 Sizing the array

Step 3 - Carrying out PV system engineering and design Inverter Selection o The PV system output is expected to be 4000W. This is the peak DC power output o If we use a PV system design that employs one inverter, it must be able to accept DC electricity with power of 4000W. 19 Inverter AC power Max array power Max DC V in V in MPPT Range Max DC I in V out I out W3800 W600 V200 – 500 V20 A 240 V 14.5 A W4400 W500 V200 – 400 V24 A 240 V 16 A Representative inverter characteristics

Step 3 - Carrying out PV system engineering and design Module Selection o The PV system output is a combination of all the separate modules’ power outputs o Both the open circuit voltage (V oc ) and the voltage at maximum power (V m ) vary with temperature; the ranges are shown in the following table 20 Module V oc (nominal) V oc (max) I sc V m (nominal) V m (min) ImIm P m (nominal) 133 V37 V8 A27 V20 V7 A189 W 244 V49 V5.5 A36 V27 V5 A180 W Representative module characteristics

Step 3 - Carrying out PV system engineering and design Inverter and Module Compatibility o Inverter #1 [V in (max) = 600V]  Module #1 [V oc (max) = 37V] : 600/37 =  16 modules  Module #2 [V oc (max) = 49V] : 600/49 =  12 modules o Inverter #2 [V in (max) = 500V]  Module #1 [V oc (max) = 37V] : 500/37 =  13 modules  Module #2 [V oc (max) = 49V] : 500/49 =  10 modules 21

Step 3 - Carrying out PV system engineering and design Inverter and Module Compatibility, cont. o Inverter #1 [V MPPT (min) = 200V]  Module #1 [V m (min) = 20 V] : 200/20 = 10  10 modules  Module #2 [V m (min) = 27 V] : 200/27 = 7.4  8 modules o Inverter #2 [V MPPT (min) = 200V]  Module #1 [V m (min) = 20 V] : 200/20 = 10  10 modules  Module #2 [V m (min) = 27 V] : 200/27 = 7.4  8 modules 22

Step 3 - Carrying out PV system engineering and design Inverter and Module Compatibility, cont. 23 CircuitNumber of modules Inverter #1, Module # Inverter #1, Module # Inverter #2, Module # Inverter #2, Module # Number of modules based on inverter requirements

Step 3 - Carrying out PV system engineering and design Required PV array power and modules o Module #1 [P m (nominal) = 189 W]  N Mod1 : 4000/189 =  22 modules o Module #2 [P m (nominal) = 180 W]  N Mod2 : 4000/180 =  23 modules 24

Step 3 - Carrying out PV system engineering and design Reconciling the module number calculations Consider the Module #2 + Inverter #1 combination:  To meet the array power requirements, 23 modules are required  But if the 23 modules are connected in series, forming one source circuit, their combined voltage would exceed the allowed inverter voltage input: 23 x 49V = 1127V >> 600V  Another approach is to split the modules into two source circuits, each containing 12 modules in series, and then combining the two source circuits in parallel to meet the power requirement. 12 x 49V = 588V < 600V  This does, however, double the total current, and it must be verified that it does not exceed the allowed inverter current input: 2 x 5.5A = 11A < 20A 25 Success!

Step 3 - Carrying out PV system engineering and design 26 Representative single source circuit Modules (15 in series)

Step 3 - Carrying out PV system engineering and design 27 Representative two source circuit Modules (2 parallel strings of 8 in series)

Grid-Connected Utility-Interactive PV Systems Step 4 – Securing relevant permits o Special overlay districts  Architectural considerations o Zoning ordinances  Setbacks, elevations, materials o Building permits  Construction practices; electrical enclosures, wiring, components o Engineering approvals  Mechanical considerations o Utility agreements  Connection arrangements; net metering rules; electrical signal quality 28

Step 4 – Securing relevant permits Current view, before PV installation 29 Perspective view of south facing roof and garage

Step 4 – Securing relevant permits Simulated view, after PV installation 30 Perspective view of south facing roof and garage

Grid-Connected Utility-Interactive PV Systems Step 4 – Securing relevant permits o Special overlay districts  Architectural considerations o Zoning ordinances  Setbacks, elevations, materials o Building permits  Construction practices; electrical enclosures, wiring, components o Engineering approvals  Mechanical considerations o Utility agreements  Connection arrangements; net metering rules; electrical signal quality 31

Step 3 - Carrying out PV system engineering and design PV array sizing and module selection modules: 7 x 2 array

Grid-Connected Utility-Interactive PV Systems Step 4 – Securing relevant permits o Special overlay districts  Architectural considerations o Zoning ordinances  Setbacks, elevations, materials o Building permits  Construction practices; electrical enclosures, wiring, components o Engineering approvals  Mechanical considerations o Utility agreements  Connection arrangements; net metering rules; electrical signal quality 33

Building Permits 34

Grid-Connected Utility-Interactive PV Systems Step 4 – Securing relevant permits o Special overlay districts  Architectural considerations o Zoning ordinances  Setbacks, elevations, materials o Building permits  Construction practices; electrical enclosures, wiring, components o Engineering approvals  Mechanical considerations o Utility agreements  Connection arrangements; net metering rules; electrical signal quality 35

Residential PV System Example 36 Block diagram of two source circuit PV system

Applicable codes and standards 37 Photovoltaic systems, like all engineered systems, must meet a variety of codes and standards, especially in the area of system safety o Safety for homeowners (in residential PV systems) o Safety for utility service workers o Safety for firefighters and other first responders The codes and standards applicable to PV systems also ensure several other characteristics, including o Protection against the elements and tampering o Durability and structural integrity o Uniformity in construction and utilization

Partial Listing of PV Codes and Standards 38

Partial Listing of PV Codes and Standards, cont. 39

Grid-Connected Utility-Interactive PV Systems Step 4 – Securing relevant permits o Special overlay districts  Architectural considerations o Zoning ordinances  Setbacks, elevations, materials o Building permits  Construction practices; electrical enclosures, wiring, components o Engineering approvals  Mechanical considerations o Utility agreements  Connection arrangements; net metering rules; electrical signal quality 40

Net Metering 41 At the end of each month, a utility bill is calculated: Bill = N(kWh from utility) – N(kWh to utility) – N(some credits from previous month) This is all at the retail rate At the end of the year, the residual credits are cashed in This is all at the wholesale rate

Comparison of Two Residential PV Systems 5kW system installed in 2010 Roof mounted 22 Siliken 225W poly modules Sunny Boy 4kW inverter No remote monitoring Installed cost: $28,979 $5.85/W (dc) Incentives: Utility co. rebate: $13,365 Federal ITC: $8,694 State Solar Incentive: $1,000 Total OOP Cost: $5,920 $1.20/W (dc) 3.5kW system to be installed in 2014 Elevated structure 14 Canadian 250W poly modules 14 Enphase micro-inverters o Enphase monitoring solution Installed cost: $13,450 o $3.84/W (dc) Incentives: Installer rebate: $1,000 Federal ITC: $4,035 State Solar Incentive: $1,000 Total OOP Cost: $7,415 $2.12/W (dc) 42