Path-Q Solar
How many cloudy days should a battery backup plan account for?
Answer
There is no universal number. The plan should reflect the outage duration you want to cover, the local seasonal solar resource, the critical-load energy use, and the availability of another backup source. Model several consecutive low-solar days rather than relying on an average day.
Key points
- More cloudy-day coverage requires more stored energy, lower loads, more solar capacity, or another generator.
- Critical loads should be separated from discretionary loads.
- Seasonal outages and the worst likely solar conditions may matter more than annual averages.
What it depends on
- Desired resilience period
- Seasonal weather and solar production
- Essential-load consumption
- Battery capacity, reserve, and recharge power
Risks and trade-offs
- Sizing for rare extreme conditions can be expensive and leave capacity underused.
- Sizing only for typical conditions may fail during the outage scenario that matters most.
- Reducing loads can extend runtime but may affect heating, medical, food, or water needs.
Information you may need
- Target outage duration
- Essential-load daily kWh and peak power
- Seasonal solar production assumptions
- Generator or other contingency options
Your next step
What to do next
Define the outage scenario that matters most and have the system modeled for consecutive low-solar days under that scenario.
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