Log into your account and go to:
- "View Billing History"
- "Billing History"
- "View Usage"
You should get a two year history of monthly usage.
Use this to determine your average annual usage.
Multiply your annual requirement / usage by 0.9 (90%) to determine the DC size of your system.
Example: If you use 10,000 kwh per year, you will need an 9,000 watt (9 kw DC) system to provide all your electrical needs.