Step 2 - Determine the days of Autonomy for the system

The next decision to be made is the number of days of Autonomy desired by the PV System. The number of days of autonomy refers to the days you want to support your critical loads entirely by the battery system without being recharged by the PV system or another source. The more days of autonomy the larger the battery bank will need to be for a defined load to store enough energy to support the critical loads. The general range of autonomy is 2-3 days for non-essential uses or systems with a generator backup and 5-7 days for critical loads with no other power source

The most important factors in determining an appropriate autonomy for your system are the size and type of loads that need to be supported. Ensure that the critical loads you choose to support and indeed critical and need to operate at all times. As discussed before, choosing the appropriate loads and days of autonomy have a huge impact on the overall design and cost of your PV system.

Choose the number of days of Autonomy before you proceed to the next step.

• Step 0: Determine the Solar Hours of your location
• Step 1: Estimate the critical loads that need to be supported
• Step 2: Determine the days of Autonomy for the system
• Step 3: Select a "Nominal" DC side voltage that the design will be based on
• Step 4: Select the PV Panels to be used for the system
• Step 5: Select the Battery manufacturer and model to be used in System
• Step 6: Select an appropriate Charge controller
• Step 7: Select an appropriate Inverter
• Step 8: Calculate and select BOS components