How Much Plug-In Solar Do You Need? Read Your Daytime Interval Data Before You Buy

By PlugInSolarUS Editorial Team · Published 2026-10-30 · Updated October 30, 2026 · 8 min read

Use seven days of utility interval data to understand your daytime demand before choosing a small solar kit. Includes a practical sizing worksheet.

A panel’s watt label is not a measure of how much of its electricity your home will use while it is being made. Before comparing a small plug-in solar kit, look at when your home draws electricity during the day. A week of your own interval data can reveal whether a modest daytime system is a plausible match, whether you would need to investigate flexible loads, or whether it is wiser to wait.

This is a measurement worksheet, not an annual-production or bill-savings forecast. For annual bill-offset illustrations, see our California examples. Here the question is narrower: during representative daylight intervals, how much demand do you actually have available to meet?

Start with the right data

Look in your utility portal for usage data, interval data, Download My Data, or Green Button. Green Button is a standard through which customers can download detailed energy-use data; utilities may provide it in 15-minute, hourly, daily, or monthly intervals. For this worksheet, 15-minute, 30-minute, or hourly readings are useful. A monthly total cannot show whether your home uses electricity at 11 a.m. or 8 p.m. [1]

Download at least seven days that represent your life, rather than choosing one unusually sunny or unusually busy day. Include ordinary weekdays and a weekend day. If you work at home only on certain days, include them. If your cooling, heating, or pool equipment changes with the weather, note that alongside the date. Seven days are a starting sample, not a forecast of a year.

Before calculating anything, open the CSV in a spreadsheet and inspect its column headings. You need an interval timestamp, an energy-use value in kWh, and either an interval-duration field or enough information to derive the duration from adjacent timestamps. Preserve the original file. Export formats vary, and a number labeled kWh is energy over an interval—not a power reading.

Write down the time zone shown by the export. A timestamp may be local time, standard time, daylight time, or UTC. Do not silently compare a UTC load timestamp with a local solar-monitoring timestamp. On the spring daylight-saving change, local clock intervals may skip an hour; on the fall change, an hour may occur twice. Keep the date, time zone, and offset or DST label if the export supplies one. If the file gives two identical local times, treat them as separate readings only when the offset or source ordering distinguishes them; otherwise ask the utility what its timestamp convention means.

Convert interval kWh into average load

Average power is the interval’s energy divided by its duration:

average load in kW = interval kWh ÷ interval hours

For example, 0.15 kWh ÷ 0.25 hours = 0.60 kW. That means the home averaged 600 watts during that 15-minute interval. It does not mean every appliance drew exactly 600 watts continuously.

For a 30-minute row, divide kWh by 0.5. For an hourly row, divide by 1. If a CSV reports 15-minute kWh but you divide by one hour, you will understate the average load by four times. If the duration column is in minutes, convert it first: 15 minutes is 0.25 hours; 30 minutes is 0.5 hours; 60 minutes is 1 hour.

Use the utility’s consumption or delivered-energy field when it is clearly identified. Do not combine columns, subtract an unexplained register, or assume an export field is household consumption. If you already have solar, distinguish grid import, export, and whole-home load before using the data; a net reading is not automatically the home’s underlying demand.

Fillable worksheet: seven representative days

Account or meter reviewed: ____
CSV download date: ___
Time zone exactly as shown in file: __
Timestamp meaning, if documented (start/end of interval): __
Interval duration: minutes = hours
Energy-use column used and units: __
Any missing, duplicated, estimated, or DST-transition rows: _____

Choose seven dates. Include at least one weekend and note why each day belongs in the sample.

• Day 1 / date: _ | weekday or weekend: _ | typicality note: ____
• Day 2 / date: _ | weekday or weekend: _ | typicality note: ____
• Day 3 / date: _ | weekday or weekend: _ | typicality note: ____
• Day 4 / date: _ | weekday or weekend: _ | typicality note: ____
• Day 5 / date: _ | weekday or weekend: _ | typicality note: ____
• Day 6 / date: _ | weekday or weekend: _ | typicality note: ____
• Day 7 / date: _ | weekday or weekend: _ | typicality note: ____

For each date, copy the rows that overlap the part of the day when a proposed array could receive useful sun at your actual location. A 9 a.m.–4 p.m. review window is a practical starting view, not a claim that every site generates throughout those hours. Note your unobstructed-sun window and any shade, orientation, or weather observations beside the data.

For each selected interval, fill this short line:

Date/time: _ | duration: _ h | use: _ kWh | average load: _ kW | notes: ____

Then identify three readings from the seven-day sample:

• Lowest ordinary daytime load: __ kW at __. Exclude an obvious outage, vacancy, or bad-data row and explain any exclusion: ____.
• Typical daytime load: __ kW at __. This is a descriptive middle observation, not a forecast: ____.
• High but recurring daytime load: __ kW at __. Likely cause: ____.

Those three values make the decision easier to see than a single monthly total. A consistently low midday floor means a larger solar output may have less opportunity for immediate on-site use. A recurring daytime load can indicate a better match. Neither observation predicts production, exports, billing treatment, or savings.

Compare a proposed kit with actual solar, not a constant watt label

Use equipment labels to screen the size you are considering, but do not turn a panel’s DC nameplate into constant AC generation. As qualified examples, Rowkin’s Solo is listed with 420 W of panel DC nameplate and 420 W maximum AC output. The Rowkin Dual is listed with 840 W of panel DC nameplate and a 900 W-rated AC microinverter. Keep DC panel rating and AC inverter rating separate. [2] [3]

Those numbers are ceilings or ratings, not a promise that either system will produce that output in an interval. Actual solar AC output changes with sun, shade, orientation, temperature, equipment behavior, and configuration. For a direct-use check, pair each interval of actual solar AC output from a monitoring source with the matching interval of actual household load. The interval durations and time bases must match, or you must aggregate the finer series to the coarser one first.

The basic ceiling is:

direct on-site power in an interval = the lower of actual household load and actual solar AC output

Suppose the utility row is 0.15 kWh for 15 minutes. Its average household load is 0.60 kW. If a matching solar-monitoring record shows 0.38 kW of actual AC output for the same 15 minutes, direct on-site power cannot exceed the lower value: 0.38 kW. For that interval, that is 0.38 kW × 0.25 hours = 0.095 kWh. This is an illustrative arithmetic check, not a production or billing estimate.

If actual solar output is unavailable because you do not yet own a system, stop at the load measurement. Compare the observed load shape against the proposed system’s documented AC rating only as a preliminary fit screen. Do not substitute a flat 420 W, 900 W, or panel-nameplate output for solar data and call the result direct use.

Turn the observations into a buying decision

A home with steady daytime equipment—such as regular work-from-home equipment, refrigeration, or other recurring demand—may show a useful baseline to investigate further. A mostly empty home may show very low midday demand, especially on workdays. That is a reason to slow down, not a reason to assume output will earn a particular credit. A home with flexible loads may find that running a dishwasher, laundry, or other suitable task during daylight changes the load curve, provided the appliance’s instructions, household routine, and electrical setup support it.

Complete these decision fields before shopping:

Lowest ordinary daytime load: __ kW
Typical daytime load: _ kW
Proposed kit’s documented AC rating: kW
Could actual output and load be time-matched after purchase? yes / no / not sure
Flexible daytime loads I can safely schedule: __
What would make this sample unrepresentative? _____
Provisional result: suitable to investigate / investigate smaller output or scheduling / wait and reduce load or consider another option

If your sample suggests a potential fit, use the PlugInSolarUS calculator for a separate estimate with its stated assumptions, then complete the Readiness Checker. The Product Finder can help compare product types, beginning with Rowkin where its foldable solar-only format fits the space and goal. The data worksheet does not replace checks on state rules, utility requirements, property permission, the exact equipment documents, or the electrical conditions at your home.

A good outcome is not necessarily “buy the biggest kit.” It is a defensible next step based on when your home uses electricity: investigate a modest daytime system, adjust a flexible routine and measure again, or decide that this particular use pattern is not a good match today.

References

[1]: https://www.energy.gov/data/green-button "Department of Energy Green Button"

[2]: https://rowkin.com/shop/rowkin-solo-420w-plug-in-solar-kit "Rowkin Solo 420W Plug-In Solar Kit"

[3]: https://rowkin.com/shop/rowkin-dual-840w-plug-in-solar-kit "Rowkin Dual 840W Plug-In Solar Kit"

Sources

• Department of Energy Green Button
• Rowkin Solo 420W Plug-In Solar Kit
• Rowkin Dual 840W Plug-In Solar Kit