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Plan your system
Plan for several cloudy days off grid
The difficult day is often the second or third cloudy day. Plan the sequence while the battery is healthy and the household has time to make choices.
Begin with usable energy and a reserve
Write down the energy you are willing to use above the agreed reserve, not the entire nameplate capacity. Record how that estimate was derived and whether it includes conversion losses. Battery age, temperature, operating limits and uncertain charge estimates can all affect what is actually available.
A reserve is an operating choice for your circumstances. It does not replace the manufacturer’s protection limits or an installer’s system design. Keep those technical settings separate from a household decision to defer optional loads.
Work through three days on paper
An illustrative sequence
Suppose the planning estimate is 8 kWh available above reserve. Essential use is estimated at 4 kWh per day, and poor-weather generation at 1.5 kWh per day. The daily deficit is 2.5 kWh. After two days, the simple balance leaves 3 kWh; after three, only 0.5 kWh.
This arithmetic ignores changing efficiency and uncertainty. It is a warning that the plan has little margin, not a reliable battery runtime prediction.
Try a worse-generation scenario and a higher-load scenario separately. If either removes the margin, decide what action starts earlier rather than waiting for the optimistic estimate to fail.
Give each trigger an action
A trigger should be observable: available energy approaching the planned reserve, a second day of unexpectedly low production or an essential load using more than expected. Pair it with a specific, feasible action from your load inventory.
Possible household choices include postponing optional tasks or moving them to a better generation window. Any backup-power arrangement needs its own manufacturer-approved operation and suitable installation. Do not improvise electrical connections when the weather deteriorates.
Check actual results each day
At a consistent time, record solar energy, household consumption, battery charge trend and missing data. Compare the observed deficit with the worksheet. A cloudy forecast does not quantify your array’s actual daily production.
DOE’s storage explanation establishes why energy collected at one time can support demand later. It does not supply a site-specific cloudy-day forecast. Sunstead’s available measurements can inform the daily review, but this worksheet remains a planning estimate.
Leave a short operating card
- Where to view current readings and their timestamps.
- The household reserve trigger and who decides.
- Essential services that remain priorities.
- Tasks that can be deferred, with realistic alternatives.
- The separate backup-system instructions and contact.
- A time for the next review.
Keep the card accessible without internet. If another person is staying at the property, walk through the decisions before a poor-weather period.
Afterward, compare planned and actual daily deficits. Improve the inputs that were wrong. A useful plan gets more specific with evidence; it does not become more confident merely because the arithmetic has more decimal places.
Sources & further reading
Documentation checked October 10, 2026.
Your next step
Estimate runtime with explicit assumptions