Session 25

Case Study – Residential System, Part 2

Operation and Analysis

December 01, 2015

Session 25 - Value to class members

• Additional evaluation and analysis of a residential grid-tied PV systemso Operationo Life Cycle Costingo Payback Analysis

2

Grid-Tied PV Systems – The Design Process

Design Steps in a Residential Scale System

1. Examination of site and estimation of performance

2. Securing financing3. Carrying out PV system

engineering and design4. Securing relevant permits5. Construction6. Inspection7. Connection to the grid8. Performance monitoring

3

Grid-Tied PV Systems – The Design Process

Step 5 – Construction

Step 6 – Inspection

Step 7 – Connection to the grid

Step 8 – Performance monitoring

4

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: $13,450o $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)

5

Step 8 – Performance monitoring

6

on-peak - 14.4c/kWh; off-peak – 2.3c/kWh; average – 8c/kWhAll electricity costs – 12.3c/kWh

Step 8 – Performance monitoring

7

Economic Analysis

Current residential PV system example

• Assume that the installed cost of a 3.5kW PV system is $2.12/W after all incentives are accounted for. Assume that the system will produce an annual electrical amount of 6250 kWh (as measured). Assume the utility cost of electricity as $0.123/kWh.

• The plan here is to calculate the Life Cycle Cost (the numerator of the LCOE equation) on both an annualized and cumulative basis, and see when it crosses zero

Current residential PV system example• A spreadsheet was used to analyze this

situation; plotting the results yields (for annual return)

Current residential

• Plotting the cumulative return for 25 years

Payback – 8.5 years

Net Metering

11

• At the end of each month, a utility bill is calculated:

• Generation = N(kWh from utility) – N(kWh to utility) – N(some credits from previous month)

• This is all at the retail rate

Net Metering

12

• Once a year, the residual credits are cashed in

• This is all at the wholesale rate• For APS solar customers, the “settle-up” date is

12/31• For SRP solar customers, the date is 04/30• This is a critical difference

Step 8 – Performance monitoring

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APS Net Metering

Step 8 – Performance monitoring

14

APS Net Metering – Generation Bill

Avoided Electricity Cost = 0.123$/kWh * 5225kWh= $643

Step 8 – Performance monitoring

15

SRP Net Metering

Avoided Electricity Cost = $643 - $130 = $513

Revised Economic Analysis

Revised current residential PV system examples

• Assume that the installed cost of a 3.5kW PV system is $2.12/W after incentives, or $7415. Assume that the system will produce a net electricity reduction amount through net metering of 5225 kWh (APS calculation), or 4168 kWh (SRP calculation). Assume the utility cost of electricity is $0.123/kWh and does not increase over the lifespan of the PV system.

• The plan here is to calculate the Life Cycle Cost (the numerator of the LCOE equation) on both an annualized and cumulative basis, and see when it crosses zero

Revised current residential

Payback –> 10.5 – 13.5 years