How often a van battery runs flat in winter: five places, two panel sizes

Solar Camp, AI-assisted writing · 2026-10-31 · updated 2026-10-30

A van with a flat roof panel and a 100 Ah (1,280 Wh) lithium battery is a common winter off-grid setup. Our own PVGIS simulation, run on October 30, 2026, shows how often this system runs flat in five European locations, using real weather from 2005–2020 and the default hourly use profile [1]. The results below are our own calculation with the EU’s PVGIS off-grid calculator [2].

In Lisbon: 200 W is not enough for winter, even at moderate use

For a typical van in Lisbon drawing 500 Wh per day, a flat 200 W panel leaves the battery flat on 100% of December days and on 33.15% of all days in the year [1]. Even at a lower use of 300 Wh per day, the 200 W panel still runs flat on 25.2% of December days and 4.86% of the year [1].

Doubling the panel to 400 W sharply improves winter survival. At 500 Wh per day, the flat-day rate for December drops to 14.92%, and the yearly rate falls to 3.11% [1]. For 300 Wh per day, 400 W covers all of December: the battery never runs flat in that month and only on 0.1% of days across the year [1].

In Tarifa: Southern Spain, mild winters, much better odds

In Tarifa, Spain, winter is less of a problem. With a 200 W panel and 300 Wh per day use, the battery runs flat on just 6.85% of December days and 1.2% of the year [1]. This is the best outcome among the locations tested, showing how much southern latitude helps.

North of the Alps: Even 400 W cannot keep up with modest use

Moving north, the same setup struggles even with a doubled panel. In Munich, a 200 W panel and 300 Wh per day use means the battery is flat on 100% of December days and 31.9% of the year [1]. Upgrading to a 400 W panel halves the December flat-day rate to 49.4%, but this still means the lights go out every other day in December, and 8.73% of days overall [1].

Amsterdam and Edinburgh are even harsher. In Amsterdam, a 400 W panel and 300 Wh use lead to the battery running flat on 99.6% of December days and 21.49% of the year [1]. In Edinburgh, the same setup falls short every single December day and for over a quarter of the year (25.82%) [1].

What these numbers mean for your setup

Our PVGIS calculation (2026-10-30) shows what a flat roof panel and a 100 Ah lithium battery manage in winter [1]. In Lisbon, if you try to run 500 Wh a day from a 200 W panel, the battery runs flat on every December day—100% of them [1]. If you step up to 400 W, that drops to 14.92% of December days [1]. In southern Spain (Tarifa), at 300 Wh a day, a 200 W panel still leaves the battery flat on 6.85% of December days [1].

North of the Alps, even 400 W cannot keep up with 300 Wh a day in December. In Amsterdam, a 400 W flat panel runs flat on 99.6% of December days [1]. In Edinburgh, it is flat every December day at that use [1].

The daily output from a panel in December is much lower than most expect. In Edinburgh, a 200 W flat panel gives just 54 Wh per day in December, and a 400 W one manages 107 Wh [1].

These numbers are from our own test with PVGIS, not a field test [1]. They do not cover tilted panels, bigger batteries, shore power, driving, or cold batteries [1]. The results are for a flat panel on a static van.

A worked example

Suppose a van in Munich runs a 100 Ah lithium battery (1,280 Wh) with a 40% cut-off (1,280 x 60% = 768 Wh usable). With a flat 400 W roof panel and 300 Wh of use per day, our own PVGIS simulation (2026-10-30) shows the battery runs flat on 49.4% of December days—about every other night [1]. Drop to a 200 W panel, and it is flat every December day [1]. These results are from our own PVGIS off-grid calculation, not a physical field test [1].

Questions readers ask

Why does a flat panel perform so badly in winter?

Our own PVGIS calculation (2026-10-30) shows: in northern Europe, a flat roof panel collects much less sunlight in winter because the sun is lower and days are short [1, 3]. For example, a 200 W flat panel in Edinburgh delivers just 54 Wh per December day [1]. Tilting the panel toward the winter sun would help, but all results here are for a flat mount [1].

Would doubling the battery size help?

A bigger battery means you can go longer between charges, but our calculation confirms the limit is solar input, not storage [1]. In Munich, even with a 400 W flat panel and a 100 Ah lithium battery, the system still runs flat on 49.4% of December days at 300 Wh daily use [1]. The battery only lasts longer; it cannot solve winter shortages if the panel cannot refill it [1].

How much solar is enough for a winter van in the north?

In every case north of the Alps tested here, no flat panel up to 400 W kept a 100 Ah battery charged for 300 Wh daily use in December [1]. In Amsterdam, a 400 W flat panel left the battery flat on 99.6% of December days at that use [1]. Reliable winter running at that use means reducing demand, tilting the panel, or heading south [1].

Sources

*Corrected 2026-10-30: Author's self-audit before publication: the simulation specifies 300 Wh a day of use, not a 40-litre fridge; the usable capacity is shown as the arithmetic it is.*