Solar charging time calculator

How long your panels will take to charge a power station, month by month, using long-run UK sun figures. Not sure what size you need? Try what size power station do I need?

By the Ferncharge team · Figures last checked 18 October 2026

.calc{display:none}The interactive calculator needs JavaScript. You can still work it out by hand: the formulas and a fully worked example are below.

Fill in your power station and panels. Results update as you type.

Your power station

Battery capacity (Wh)On the spec sheet, in watt-hours

Max solar input (W)Optional, from the spec sheet

Charge now (%)Default 0%

Charge to (%)Default 100%

Your panels and place

Panel rating (W)Each panel's rated watts

Number of panelsDefault 1

Nearest placePVGIS 2014–2023 averages

Month

Panel angleFlat suits a van roof

Advanced settings (voltage check, solar factor, own sun hours)

Advanced settings

Solar input voltage, minimum (V)Optional, from the spec sheet

Solar input voltage, maximum (V)Optional, from the spec sheet

Panel array open-circuit voltage, Voc (V)Optional; on the panel label, add up panels in series

Solar factor (%)Default 70%: share of rated watts panels actually deliver

Your own peak sun hours a dayOptional; replaces the place and month

How the calculator works

energy to add Wh = capacity Wh × (target % − current %) ÷ 100
array W = panel W × number of panels
effective input W = min(array W, max solar input W) × solar factor
energy a day Wh = effective input W × peak sun hours a day
charging time in peak-sun hours = energy to add ÷ effective input W
charging time in calendar days = energy to add ÷ energy a day

Peak sun hours are the day's sunlight squeezed into hours of full-strength sun (1,000 W per m²), so a panel's daily output is roughly its effective watts × peak sun hours. We use the European Commission's PVGIS figures for London, Manchester and Edinburgh. The 70% solar factor allows for panels rarely reaching their rating (Jackery lists light, angle, temperature, cables and controller losses); it's our planning estimate, so change it if you know better.

If your panels are rated above the power station's maximum solar input, the station takes no more than its limit, so we use the lower figure and warn you. If you give the input voltage range and your array's open-circuit voltage (Voc), we check it fits: too high can damage the power station, too low may not charge.

Worked example: 1,000 Wh power station, two 100 W panels on a van roof, London in October

An imaginary power station, not a real product. Two 100 W panels wired in parallel, each with an open-circuit voltage of 24.4 V (an illustrative figure: check your panel's label).

Energy to add: capacity Wh × (target % − current %) ÷ 100
1,000 × (100 − 20) ÷ 100 = 800 Wh
Panel array rating: panel W × number of panels
100 × 2 = 200 W
Effective solar input: min(array W, max solar input W) × solar factor
200 × 0.7 = 140 W
Peak sun hours a day: PVGIS 2014–2023 monthly average
London, Oct, panel flat = 1.86 h
Expected energy a day: effective W × peak sun hours
140 × 1.86 = 260.4 Wh a day
Charging time in peak-sun hours: energy to add ÷ effective W
800 ÷ 140 = 5 h 43 min
Charging time in calendar days: energy to add ÷ energy a day
800 ÷ 260.4 = 3.1 days

Result: about 3.1 days (5 h 43 min of peak sun) to go from 20% to 100% in an average London October. The same charge takes about 1.1 days in Jun and 8.8 in Dec.

UK peak sun hours by month

UK winter output is much lower. A flat panel in London gets about 5.38 peak sun hours a day in June but 0.65 in December, and it's lower further north. These are long-run averages, not a forecast: a grey week can be far worse. Source: European Commission JRC, PVGIS monthly radiation (MRcalc), PVGIS-SARAH3, 2014–2023; daily values calculated by us from monthly totals.

Peak sun hours a day, panel flat (PVGIS 2014–2023 averages)
Place	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
London	0.85	1.5	2.58	4.15	4.95	5.38	5.13	4.35	3.21	1.86	1.03	0.65
Manchester	0.6	1.24	2.31	3.81	4.64	4.83	4.49	3.83	2.83	1.54	0.79	0.48
Edinburgh	0.53	1.19	2.25	3.68	4.55	4.73	4.56	3.83	2.66	1.43	0.69	0.38

Peak sun hours a day, panel tilted to face south (PVGIS 2014–2023 averages)
Place	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
London	1.7	2.45	3.39	4.73	4.99	5.18	5.02	4.64	3.99	2.73	1.91	1.39
Manchester	1.1	1.96	3.01	4.36	4.71	4.69	4.41	4.04	3.46	2.22	1.42	1.03
Edinburgh	1.21	2.16	3.13	4.29	4.63	4.61	4.5	4.12	3.37	2.22	1.44	0.95

Frequently asked questions

Why does it take so much longer in winter?

The sun is lower and the days are shorter, so the same panel collects far less energy. In our PVGIS figures, a flat panel gets 8 to 12 times as much in the best summer month as in December, depending on where you are.

Should I tilt my panel?

In winter, tilting a portable panel towards the south roughly doubles its output compared with lying flat in our figures (London, December: 0.65 flat, 1.39 tilted). In summer the difference is small.

Will more panels always charge faster?

Only up to the power station's maximum solar input. Beyond that the extra watts are clipped. Check the input voltage range too, especially when wiring panels in series, because their voltages add up.

Sources

Figures last checked: 18 October 2026.