Photovoltaic Systems Engineering Session 19 SEC598F17 Photovoltaic Systems Engineering Session 19 Grid-Tied Systems – Residential, part 1 Standards and Codes Design Considerations October 26, 2017

Session 17 content Standards and Codes Design Considerations Purpose, value Examples Design Considerations Components

Learning Outcomes Introduction to the idea of standards and codes in engineering design Recognition of the importance of standards and codes to the safe operation of PV systems An examination of the design of a photovoltaic system leading to an understanding of the competing issues involved in solar power development and expansion

PV Systems - Applicable standards and codes Photovoltaic systems, like all engineered systems, must meet a variety of codes and standards, especially in the area of system safety Safety for homeowners (in residential PV systems) Safety for utility service workers Safety for firefighters and other first responders

PV Systems - Applicable standards and codes The codes and standards applicable to PV systems also ensure several other characteristics, including: Protection against the elements and tampering Durability and structural integrity Uniformity in construction and utilization

PV Systems - Applicable standards and codes The American Society of Mechanical Engineers (ASME) lists these definitions on their webpage: A Standard can be defined as a set of technical definitions and guidelines that function as instructions for designers, manufacturers, operators, or users of equipment. Standards are written by professionals who are members of a regulating organization They are generally voluntary and are not enforceable by law A standard becomes a Code when it has been adopted by one or more governmental bodies and is enforceable by law, or when it has been incorporated into a business contract

PV Systems - Applicable standards and codes Standards and Codes generally have these requirements. Suitable for repetitive use Enforceable – an auditor can easily see whether it is being followed Definite – it contains specific instructions Realistic – it is not excessively restrictive Authoritative – it is technically correct Complete Clear Consistent – it does not contradict other standards and codes Focused

PV Systems - Applicable standards and codes The technical issues related to connecting a PV system to the grid were essentially understood in 1999 The IEEE adopted Standard 929 in 2000 which listed performance criteria for grid-tied systems. If a PV system met the criteria of Standard 929 using inverters that were listed under UL 1741 and if it were installed in accordance with the current National Electrical Code (NEC), it automatically met all established performance criteria The IEEE adopted Standard 1547 in 2003. Among other things, it contains some revisions from Standard 929 related to PV power quality and PV disconnect issues. It is a functional standard, not a prescriptive one. That is, it specifies specific functions that must be performed, but does not tell how to satisfy the functional requirements

PV Systems - Applicable standards and codes Partial Listing of PV Standards and Codes

PV Systems - Applicable standards and codes Partial Listing of PV Standards and Codes

PV Systems - Applicable standards and codes The National Electrical Code is published by the National Fire Protection Association and is updated every three years. It was first published in 1897. The current NEC to be followed is the 2017 edition, available since November, 2016 The NEC is a collection of articles pertaining to wiring methods, grounding, switches and fuses, etc., relevant to the overall electrical safety of the system It is not US law, but is mandated by state or local jurisdictions

PV Systems - Applicable standards and codes NEC Article 690

PV Systems - Applicable standards and codes Regulating Organizations NEC – National Electrical Code IEEE – Institute of Electrical and Electronic Engineers IEC – International Electrotechnical Commission ISO – International Organization for Standardization UL – Underwriters Laboratories ANSI – American National Standards Institutes ASCE – American Society of Civil Engineers ASTM – American Society for Testing and Materials

Important Resources IEEE Standards: National Electrical Code: http://ieeexplore.ieee.org/xpl/standards.jsp National Electrical Code: http://en.wikipedia.org/wiki/National_Electrical_Code

Grid-Tied PV Systems – The Design Process Design Considerations for Residential Scale System 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 Design based on available space The objective is to produce as much solar electricity as possible The available space may refers to roof space or unshaded area for a ground mounted system

Grid-Tied PV Systems – The Design Process Design Goals in any Residential Scale System Meeting expected (or modeled) performance Reliable performance Safe operation Architectural aesthetics

Grid-Tied PV Systems – The Design Process Design Steps in any Residential Scale System Examination of site and estimation of performance Securing financing Carrying out PV system engineering and design Securing relevant permits Construction Inspection Connection to the grid Performance monitoring

Grid-Tied PV Systems – PV system engineering and design Steps in annual system performance design Evaluation of solar availability and electrical consumption PV array sizing Inverter selection Module selection Balance of system components

Grid-Tied PV Systems – PV system engineering and design Steps in space constrained design Evaluation of space availability and solar resource PV array selection Inverter selection Module selection Balance of system

Grid-Tied PV Systems – The Design Process Block diagram of two source circuit PV system

Steps 1 and 3 PV system engineering and design Part 1: Evaluation of solar availability and electrical consumption Suppose the average monthly electrical consumption is 440 kWh/mo at a residence in Phoenix, AZ Suppose design goal is to have PV system produce 100% of annual electrical need This means the PV system must produce, on average: Monthly production – 440 kWH/mo Annual production – 440 x 12 = 5300 kWh/yr

Steps 1 and 3 PV system engineering and design average Month #1 is April

Steps 1 and 3 PV system engineering and design Part 2: Estimation of PV System performance PVWatts can be used to calculate what the peak power production of the PV system should be to produce 5300 kWh/yr 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

Steps 1 and 3 PV system engineering and design Part 2: Estimation of PV System performance

Steps 1 and 3 PV system engineering and design Part 3: PV Array Sizing