Photovoltaic Systems – Residential ScalePart 1

March 17, 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

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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

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Residential Scale PV Systems

• Stand Alone PV Systems The objective is to produce electrical power for the

dwelling and for battery storage

• Battery-Backup Grid-Connected PV Systems The objective is to produce uninterrupted electrical

power for the dwelling

• Grid-Connected Utility-Interactive PV Systems The objective is to produce a specific percentage of

the electrical use of the dwelling

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Grid-Connected Utility-Interactive PV System

• Design Goals in any Residential Scale System

o Meeting expected (or modeled) performance Engineering professionalism

o Reliable performance Standards and Codes

o Safe operation Standards and Codes

o Architectural aesthetics Building and Zoning

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Grid-Connected Utility-Interactive PV System

• Design Considerations for Residential Scale System

o Design based on annual system performance The objective is to produce a specific percentage of the electrical use of

the dwelling One needs to know:

Annual solar resource amount Annual electricity consumption Utility regulations on residential generation percentage

o Design based on available space The objective is to produce as much solar electricity as possible The available space may refer to roof space or unshaded area for a ground

mounted system One needs to know:

Annual solar resource amount Utility regulations on residential generation percentage

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Design Steps in any Residential Scale System

1. Examination of site and estimation of performance2. Securing financing3. Carrying out PV system engineering and design4. Securing relevant permits5. Construction6. Inspection7. Connection to the grid8. Performance monitoring

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Grid-Connected Utility-Interactive PV System

Grid-Connected Utility-Interactive PV Systems

Step 1 - Examination of site and estimation of performance

oInspection of roof and yards

oEvaluation of obstacles, shading, and structures

oExamining the solar resource

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Step 1 - Examination of site and estimation of performance

Inspection of roof and yards

9South facing roof

Step 1 - Examination of site and estimation of performance

Four common roof types

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Step 1 - Examination of site and estimation of performance

Hip roof wind zones

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Step 1 - Examination of site and estimation of performance

Layout for low wind region

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Step 1 - Examination of site and estimation of performance

Inspection of roof and yards

13South facing roof and garage

Step 1 - Examination of site and estimation of performance

Inspection of roof and yards

14Backyard and garage west-facing roof

Step 1 - Examination of site and estimation of performance

South vs West

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Step 1 - Examination of site and estimation of performance

ASU Parking Structure

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Step 1 - Examination of site and estimation of performance

“Power Pergola”

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Motion of Sun Diagram – Phoenix

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North Pole

Summer Solstice

Equinox

WinterSolstice

23.5o

23.5o

zenith

latitudePhoenixLatitude = 33.5o

N S

Step 1 - Examination of site and estimation of performance

Estimation of performance

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PVWatts calculation – effect of module tilt

Grid-Connected Utility-Interactive PV Systems

Step 2 – Securing financing

oCash purchase• Customer pays cash (personal funds or loan from financial

institution), system provider installs system, ownership is transferred with payment, user responsible for O&M

oDealer credit• Customer pays system provider (down-payment plus

installments) on credit offered by system provider, system provider installs system, ownership transferred with contract conclusion, user responsible for O&M with system provider support

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Grid-Connected Utility-Interactive PV Systems

Step 2 – Securing financing, cont.

oThird Party Financing

• Power Purchase Agreement (PPA): System provider installs system, sells the power to the customer at a fixed rate (lower than utility rate, receives all tax credits and incentives, and is responsible for O&M with system provider support. At end of contract (10 to 25 years), customer may extend the PPA, buy the system, or have the system removed. Not allowed (or offered) in all states.

• Solar Lease: Similar to a PPA, but it does not involve the sale of electricity. Customer leases the system from system provider (like an automobile lease). Leases not always transferable during home sale.

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Grid-Connected Utility-Interactive PV Systems

Step 2 – Securing financing, cont.

oThird Party Financing in Arizona

• In general, when a third party installs a PV system, it can enter a Power

Purchase Agreement or a solar equipment lease arrangement with the

customer.  PPAs are a third party ownership arrangement, and an equipment

lease is not.  In Arizona, PPAs are not allowed, because that makes the third

party a virtual utility - so only solar equipment leases are permitted.  But there

is one exception – PPAs (called Solar Service Agreements in AZ) can be

established with not-for-profit governmental entities, such as schools and the

like – and that is due to a case in which the Arizona Corporation Commission

ruled that SolarCity would not be a utility under those circumstances.

 SolarCity hopes that the ACC will eventually change its mind and allow SSAs

to be granted with for-profit and residential customers too.

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