How to Size a Solar Generator for a Shed

For lights, a laptop and cordless-tool charging, size a solar generator for a shed from daily watt-hours, starting demand and winter recharge. Our worked session needs about 550Wh of nominal battery capacity, and our starting pick is the EcoFlow DELTA 3 Plus with two NextGen 220W Bifacial panels, subject to the compatibility checks below. That kit offers useful recharge headroom over a single panel, but Seattle winter averages still leave little margin for shade and cloudy spells.

Quick picks and comparison

These are US station specifications from EcoFlow and Anker. Product cards and Amazon links cover the station alone; panels and cables are separate shopping checks.

Compare specifications and all conditions

Our pick for

EcoFlow DELTA 3 Plus

Battery expansion and separate panel inputs

Anker SOLIX C1000 Gen 2

Higher simultaneous running power; conditional panel alternative

Nominal storage

EcoFlow DELTA 3 Plus

1,024Wh

Anker SOLIX C1000 Gen 2

1,024Wh

Continuous / surge AC

EcoFlow DELTA 3 Plus

1,800W / 3,600W

Anker SOLIX C1000 Gen 2

2,000W / 3,000W

Solar ceiling

EcoFlow DELTA 3 Plus

1,000W total: two 500W inputs

Anker SOLIX C1000 Gen 2

600W

Input limits

EcoFlow DELTA 3 Plus

11–60V, 15A per input

Anker SOLIX C1000 Gen 2

11–28V at 8.2A; 29–60V at 14.5A

Proposed panels

EcoFlow DELTA 3 Plus

Two NextGen 220W Bifacial panels: 440W front rating total

Anker SOLIX C1000 Gen 2

One PS400 Bifacial: 400W; confirmation required

Expansion

EcoFlow DELTA 3 Plus

Supported extra battery

Anker SOLIX C1000 Gen 2

No capacity expansion

Full comparison table ↔

Swipe to compare. Row labels stay visible.

Decision	EcoFlow DELTA 3 Plus	Anker SOLIX C1000 Gen 2
Our pick for	Battery expansion and separate panel inputs	Higher simultaneous running power; conditional panel alternative
Nominal storage	1,024Wh	1,024Wh
Continuous / surge AC	1,800W / 3,600W	2,000W / 3,000W
Solar ceiling	1,000W total: two 500W inputs	600W
Input limits	11–60V, 15A per input	11–28V at 8.2A; 29–60V at 14.5A
Proposed panels	Two NextGen 220W Bifacial panels: 440W front rating total	One PS400 Bifacial: 400W; confirmation required
Expansion	Supported extra battery	No capacity expansion

Decision	EcoFlow DELTA 3 Plus	Anker SOLIX C1000 Gen 2
Our pick for	Battery expansion and separate panel inputs	Higher simultaneous running power; conditional panel alternative
Nominal storage	1,024Wh	1,024Wh
Continuous / surge AC	1,800W / 3,600W	2,000W / 3,000W
Solar ceiling	1,000W total: two 500W inputs	600W
Input limits	11–60V, 15A per input	11–28V at 8.2A; 29–60V at 14.5A
Proposed panels	Two NextGen 220W Bifacial panels: 440W front rating total	One PS400 Bifacial: 400W; confirmation required
Expansion	Supported extra battery	No capacity expansion

The EcoFlow current limit comes from its manual. Compare other sizes in our portable power station guide.

1. 1

   List energy

   Record watts and hours for an actual work session.

2. 2

   Screen power

   Check simultaneous loads and motor startup separately.

3. 3

   Choose reserve

   Allow for conversion, station draw and days without recharge.

4. 4

   Match recharge

   Use local winter sunshine, shade and an approved panel-and-cable combination.

Record loads before choosing a battery

Energy is watts × hours = watt-hours, as Anker explains. The following is an invented planning scenario, not measured appliance consumption; replace every input with your own readings.

Use charger input consumption, including its losses, rather than the cordless battery's capacity. For cycling appliances, record energy across a representative session instead of assuming maximum watts continuously. The P3 Kill A Watt P4400 displays watts and accumulates kWh; respect its 125 VAC, 15A and 1875 VA maximum ratings. Record readings before disconnecting your meter and consult its manual about counter retention.

All these example devices together draw 20 + 60 + 80 + 10 watts: less than 200W. That fits either inverter's continuous rating, but says nothing about a saw, compressor or vacuum added later. Obtain the tool's startup requirement or ask its maker: BLUETTI's manual warns that some motors and compressors start at multiples of running power. Do not treat ordinary meter readings or a headline boost mode as startup approval.

Add conversion losses, idle draw and reserve

For this worksheet we assume 90% AC conversion efficiency, 10W battery-side station draw while AC is on for four hours, and a 20% capacity reserve. These are planning allowances, not measured figures for either pick; BLUETTI's runtime equation illustrates why conversion and self-consumption belong in the calculation. The reserve is separate from conversion loss.

Battery energy per session = 360Wh ÷ 90% + 10W × 4 hours = 440Wh.

Nominal capacity required = 440Wh ÷ 80% = 550Wh for one session; 440Wh × 2 ÷ 80% = 1,100 watt-hours for two sessions without recharge.

Thus either 1,024Wh station covers the single-session estimate, but falls short of the two-session target with this reserve. If you need that autonomy, buy more storage or reduce consumption; a larger panel cannot replace missing overnight storage. Percentages in these equations are fractions: for example, 90% means 90 divided by 100.

• 550WhCalculated nominal capacity for one example session
• 1,100Calculated nominal watt-hours for two sessions without recharge

Keep AC enabled only when needed. Leaving our assumed 10W idle draw running for 24 hours would consume 240Wh, before appliance use. USB charging may change the losses, so recalculate for the ports actually used. Use the watt calculator to organize your figures.

How to calculate solar panel size for winter

Panel watts required = daily battery energy ÷ (winter peak-sun hours × collection factor × site-shade factor). Peak-sun hours describe energy equivalent to full-strength sunshine, rather than sunrise-to-sunset time; Anker's sizing explanation also warns that there is no universal loss percentage.

Assume the worked session repeats daily. For Seattle in December, the European Commission's PVGIS calculation gives 1.83kWh/m²/day of irradiation on a south-facing surface tilted 45°, equivalent to 1.83 peak-sun hours. This uses ERA5 data averaged over 2005–2023. We use its irradiation column, rather than its grid-connected electricity estimate, and apply our own portable-system losses below.

Assume 75% collection into the battery, allowing for panel conditions, cables and charging losses, with no credited bifacial bonus. Goal Zero's manual explains those sources of reduced output; this percentage remains our assumption. Start unshaded, then stress the plan with an assumed 20% additional daily-energy loss from local shade. That shade allowance is a sensitivity check: it does not mean shading part of a panel causes the same proportional loss. PVGIS's terrain horizon model excludes nearby houses and trees.

• Unshaded requirement: 440Wh ÷ (1.83 hours × 75%), rounded up to about 330 watts.
• With the shade allowance: 440Wh ÷ (1.83 hours × 75% × 80%), or just over 400W.

These are rounded estimates, conditional on compatible equipment. The 400W option leaves essentially no margin against the 440Wh daily requirement after shade; the 440W option has only modest surplus. Replacing a missed session and powering today's session needs twice 440Wh, beyond either modeled day's harvest. Monthly averages cannot guarantee recovery through successive cloudy days: retain wall charging, reduce use or commission a larger system. Occasional weekend visits allow recharge days between sessions, so one panel may suffice with the inverter off between visits. For another location, rerun the winter calculation with its actual orientation and shade.

Check the panel and the entire cable path

Check cold-weather open-circuit voltage (Voc), operating voltage, short-circuit current (Isc), input watts, connector and polarity. Cold can raise Voc; Anker's MPPT guidance says it must remain below the controller limit in the coldest expected weather.

• Yes: Match the exact panel generation and station region
• Yes: Use the maker-approved solar cable with its original polarity
• Yes: Check cold-weather Voc and total Isc for each receiving input
• Partly: A matching connector or operating-voltage figure is only part of compatibility
• No: Substitute car cables, improvised adapters or unapproved splitters

Keep the station dry and use the supplied cable reach as a purchasing constraint. If the sunny spot is farther away, obtain a maker-approved cable specification before ordering an extension. Our portable solar panel guide covers other panel sizes.

Best starting point: DELTA 3 Plus and two NextGen panels

Shopping list: one US DELTA 3 Plus, two NextGen 220W Bifacial panels, and two panel-supplied XT60i charging cables, specified as one panel per independent solar input. The panel page lists those cables in the box, along with protective bags; the station-only box does not include solar cables.

Each panel's published front-side values are Voc 21.5V, Vmp 18.4V, Isc 12.4A and Imp 11.9A, compared with the station's 11–60V, 15A and 500W per input. EcoFlow also explicitly recommends NextGen bifacial panels for this station in its compatibility FAQ. The panel separately lists rear-side current: do not add front and rear nameplate ratings into a promised harvest or assume unlimited current headroom. Confirm the exact bifacial combination for the planned reflective surface and minimum temperature with EcoFlow.

The approved replacement cable is named EcoFlow Solar to XT60i Charging Cable in the station manual. It is already supplied with these panels; a station-only purchase needs its solar cable checked separately. Preserve the factory connectors and polarity.

Variant trap: DELTA 3 and DELTA 3 Plus have different solar-input arrangements. Choose NextGen Bifacial, and check that a bundle actually contains both panels. EcoFlow advertises extra bifacial yield of up to 25% in the bullets versus 28% in the body; this worksheet credits none. Expansion is the reason to choose the Plus here, but extra storage still needs enough solar energy to refill it.

Check price on Amazon — station only

Higher-output alternative: C1000 Gen 2 and PS400 Bifacial

Conditional shopping list: one US C1000 Gen 2, one PS400 Bifacial, its supplied two 8.2ft solar charging leads, and 1.6ft XT60i charging cable. Anker offers a 400W bifacial option on the station page; the panel's own page supplies the cable inventory. Order the complete approved combination only after the checks below.

The appeal is 2,000W continuous output with one folding panel. However, the panel page publishes 48V / 8.33A as PV output, without identifying Voc or Isc. Those operating figures fit the station's upper input band on paper, but do not establish cold-weather compatibility. Obtain Anker's exact-panel Voc, Isc, cold limit and cable/polarity confirmation before purchase; this is not an unconditional winter-kit recommendation.

Anker's station selector describes its 400W bifacial option as IP67 and 23% efficient; the dedicated PS400 Bifacial page says IP68 and 25%+. Verify the exact model and supplied cables rather than treating every “400W” bundle as identical. C1000 Gen 2 cannot expand; do not buy an original-C1000 expansion battery for it. Its modeled winter harvest has virtually no shaded-day surplus in this example, even if the electrical checks pass.

Cold, moisture and the electrician decision

EcoFlow permits charging at 32–113°F; Anker specifies 32–104°F. A sunny panel outside does not make a frozen battery ready to charge. Plan a dry, ventilated station location within its permitted temperature range; do not cover ventilation or rely on the panel's water-resistance rating to protect the station. EcoFlow's advertised IP65 figure covers its battery pack, rather than the complete station.

A hypothetical 1,500W heater for one hour uses 1,500Wh before losses, already beyond either station's nominal capacity. For routine heating, compressors, sustained workshop machinery or permanent circuits, ask a licensed electrician to assess an installed supply and permits. Washington generally requires permits and inspections for electrical work, subject to exceptions and local jurisdiction. Keep this setup to appliances powered directly from the station; take building connections to the electrician.

How we choose

We researched official product pages, manuals and government solar data, checked the exact generations, and separated manufacturer specifications from editorial assumptions. We have not physically evaluated these products. Unpublished electrical values remain unresolved; the estimates are arithmetic, not runtime or recharge promises. Sources were checked on November 2, 2026.

Verdict

Choose the DELTA 3 Plus with two NextGen 220W Bifacial panels as the starting configuration for this light-duty shed, after the stated compatibility checks. Choose C1000 Gen 2 for its higher continuous output only when Anker confirms the exact PS400 Bifacial kit for your conditions. Increase storage for consecutive sessions without sun, and seek an installed supply assessment when winter recharge or heating drives the decision.