How this calculator works
Battery decisions fail when people compare hardware quotes without testing assumptions around self-consumption and losses. This calculator bridges that gap with an operational estimate of delivered energy and annual savings.
You can use it to compare optimistic and conservative battery scenarios before committing capital. The key is to model realistic target self-use and round-trip loss, not brochure-perfect values.
How to use it well
- Use annualized solar generation assumptions, not summer peaks only.
- Set current and target self-use rates from real load patterns.
- Include battery loss and grid rate explicitly.
- Compare simple payback against your acceptable horizon.
Worked examples
Example: if 800 kWh/month is generated, current self-use is 40%, target is 70%, and losses are 10%, delivered additional self-use is 216 kWh/month.
At $0.30/kWh that yields about $777.60/year in modeled savings; with a $9,000 system, simple payback is around 11.6 years.
Interpretation guide
Use this as a screening model. If payback is borderline, run additional scenarios with lower target self-use or lower export penalties before purchase.
Common mistakes
- Ignoring round-trip losses.
- Using one-season generation data.
- Assuming flat tariffs forever.
Action checklist
- Run conservative and optimistic scenarios.
- Validate load profile assumptions.
- Compare at least two battery cost quotes.
- Recheck after tariff changes.
FAQ
How often should I update inputs? Monthly is a strong default; update sooner when conditions shift quickly.
Should I plan with optimistic values? Use conservative baseline values first, then compare upside and downside scenarios.
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