1. Photovoltaic Systems Engineering Session 15 Stand-Alone PV Systems
SEC598F17
Photovoltaic Systems Engineering
Session 15
Stand-Alone PV Systems
Design Considerations – Small Systems
October 12, 2017

2. Session 15 content Stand-Alone PV Systems Scale of stand-alone systems
Design basics
Inverter and battery selection
BOS components

3. Learning Outcomes
An examination of the original photovoltaic systems at small scale (solitary electrical components).

4. Stand-Alone PV Systems – Design Steps
Examples of stand-alone PV systems
Solar powered accent lights
Solar powered portable devices
Solar powered water pump
Solar powered fan
Solar powered lighting systems
Stand-alone refrigerator
Stand-alone residences
Stand-alone communication systems

5. Stand-Alone PV Systems – Design Steps
Solar powered portable devices

6. Stand-Alone PV Systems – Design Steps
Solar powered portable devices

7. Stand-Alone PV Systems – Design Steps
Solar powered fan

8. Stand-Alone PV Systems – Design Steps
Stand-alone (and remote) structure

9. Stand-Alone PV Systems – Design Steps
Stand-alone communication system

10. Stand-Alone PV Systems – Design Steps
Solar electric and solar thermal devices

11. Stand-Alone PV Systems – Design Steps
Steps in stand-alone component design
Evaluation of solar availability, electrical consumption, essential electrical loads
Battery selection
PV array sizing
Module selection
Charge controller selection
Inverter selection
Balance of system

12. Stand-Alone PV Systems
Example 1 – Solar Garden Light

13. Stand-Alone PV Systems
Example 2 – Solar Fan

14. Stand-Alone PV Systems
Example 3 – Solar Light Highway Advisory Sign

15. Example 3 – Solar Light Highway Advisory Sign
Step 1. Evaluation of solar availability, electrical consumption, essential electrical loads
Atlanta, GA
Solar availability (horizontal surface)
If modules of 18% efficiency are used, then the maximum solar availability is:

16. Example 3 – Solar Light Highway Advisory Sign
Step 1. Evaluation of solar availability, electrical consumption, essential electrical loads
Peak Solar Hours (per day) in Atlanta

17. Example 3 – Solar Light Highway Advisory Sign
Step 1. Evaluation of solar availability, electrical consumption, essential electrical loads
Suppose modules of 2ft by 5ft dimensions are to be used
Then each module has a maximum power output of:
Suppose 4 modules will be used to power the sign. And suppose the modules can only generate 80% of the max power due to dust. Then the maximum array power will be

18. Example 3 – Solar Light Highway Advisory Sign
Step 2. Battery selection
Suppose an MPPT charge controller is to be used and it has an efficiency of 96%, and suppose all wire losses are 2%. Then the maximum available power that can be delivered to the batteries is:
Suppose the battery bank operates at 12V. Then the maximum input current to the battery bank will be:

19. Example 3 – Solar Light Highway Advisory Sign
Step 2. Battery selection
During the month of lowest solar input (December), the average daily charge that will be available to recharge the batteries is:
If the charge/discharge efficiency is 90%, then only 90% of the above charge is available for use by the load:

20. Example 3 – Solar Light Highway Advisory Sign
Step 2. Battery selection
Suppose 5 days of storage is required (autonomy), to account for cloudy days. Then the batteries should be sized to meet that need, with an adjustment for depth of discharge kept to 80% (or a state of charge of at least 20%). Then the actual capacity should be:
So choose two 12 V batteries (to be connected in parallel) each rated at 315Ah with a C-rate of C/120. Such batteries, including AGM lead-acid, are available.