1. 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

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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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 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

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

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

11. 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 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

12. PV Systems - Applicable standards and codes NEC Article 690

13. 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

14. Important Resources IEEE Standards: National Electrical Code:
National Electrical Code:

15. 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

16. 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

17. 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

18. 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

19. 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

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

21. 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

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

23. 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

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

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