Keep the original estimate
After installation has been appropriately checked, keep a copy of the scenario you used when deciding. Record its weather reference, orientation, shade allowance, electricity price and usage profile. You need that baseline to understand later differences.
Save the date you started observing. Your first month might be bright summer or dark winter; it is a particular period, not a representative year.
Use a small, consistent log
| Record | Include |
|---|---|
| Generation | Daily energy shown by the system, units and measurement source |
| Grid data | Available import/export readings and the same time boundary |
| Battery | Reported charge/discharge data and where it is measured |
| Context | Shade, unusual weather, time away or a new appliance |
| Changes | Setting, date and reason for each change |
A blank is better than an invented value. Do not combine a device’s calendar-day total with a meter period that starts at a different time and expect them to reconcile exactly.
Generation is not the same as bill savings
One meter may show production; another may show grid imports. Production includes energy that might be exported, stored or lost before use. Multiplying all generated kWh by the retail price can therefore overstate the avoided bill.
For a clearly simplified example with no battery, suppose 20 kWh was generated over a period and 5 kWh was exported. Ignoring losses and assuming matching measurement boundaries, 15 kWh remains for on-site use. At $0.30/kWh, its retail-value illustration is $4.50, not $6. With storage, charge/discharge losses and the change in stored energy complicate the balance.
Explain a difference before changing everything
- Check that the compared periods, units and meter boundaries match.
- Look for changed shade, a weather difference or time away from home.
- Check whether the bill includes fixed charges or tariff effects absent from the model.
- Review system settings and documentation; leave electrical faults to qualified support.
Changing several assumptions at once makes it hard to learn which mattered. Revise one plausible input, label the scenario and compare again.
Make the next decision better
Thirty days can reveal questions and habits. It cannot establish a year’s savings, battery life or the outcome for every season. Continue observing across seasons before making a large upgrade decision.
If you plan to share a case study, use permission-based, anonymized records. Keep account numbers, addresses and identifiable bill images out of the public version. A useful case explains the period, equipment, measurement method and limitations alongside the result.
Sources & further reading
Worked examples use assumed values and are not product tests. A question or correction? Contact the publisher.
Make it personal
Turn a useful guide into your own comparison.
Put your notes into a comparison with and without storage. Change an assumption and see what it affects.
Compare solar & storageCheck the rules first