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

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

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

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

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

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

Stand-Alone PV Systems – Design Steps Solar powered fan

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

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

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

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

Stand-Alone PV Systems Example 1 – Solar Garden Light

Stand-Alone PV Systems Example 2 – Solar Fan

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

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:

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

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

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:

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:

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.