Solar panels in winter: yes, they still produce energy (complete guide)

Introduction: light, not heatA photovoltaic panel converts light into electricity, not heat. This distinction is essential to understanding why your solar modules continue to function in winter, even at sub-zero temperatures. In fact, cold weather significantly improves the efficiency of PV cells: the voltage of the cell (and therefore of the panel) increases much more than the drop in current caused by the drop in temperature, resulting in a net gain in power at equal irradiance.However, winter production remains lower than in summer. Why? Because winter brings other physical constraints: shorter days, the sun lower on the horizon, longer shadows, and sometimes snow or dirt that obscures the modules. This article separates fact from fiction and explains exactly what really changes between December and July.💡 Useful resource: Wattuneed toolboxFree sizing tools, calculators and technical guides for your photovoltaic installationMyths vs reality: debunking common misconceptionsThere are many beliefs circulating about the winter performance of photovoltaic systems. Here are the four most common myths, confronted with scientific facts.Myth 1: "If it's cold, it doesn't work"Reality: PV modules produce better when it's cold. The cell voltage increases significantly as the temperature drops, and this increase more than compensates for the slight decrease in current. The result: instantaneous power is higher at low temperatures (at equal irradiance). A cold, sunny day can produce 5 to 10% more than a hot day with the same amount of sunshine."Cold weather actually improves photovoltaic production: this is a physical fact, not a trade-off."Myth 2: "Without full sun, it's zero"Reality: Photovoltaic panels also react to diffuse light (light that passes through clouds or is reflected in the atmosphere). Admittedly, production drops on overcast days, but it never falls to zero as long as it is "daytime". A grey winter day can still provide 10 to 30% of the power of a sunny day, depending on the thickness of the cloud cover.Myth 3: "Snow destroys panels"Reality: Snow does not destroy modules (which are designed to withstand significant mechanical loads). However, it does block light if it remains on the surface of the cells. The real issue is therefore temporary masking, not material degradation. Bonus: as it slides off, snow can help to clean away dirt that has accumulated at the bottom of the modules.Myth 4: "It's useless in winter"Reality: Winter production is lower, but it often contributes to baseline consumption (internet box, refrigerator, CMV, lighting, etc.). And on a beautiful cold and sunny day, the instantaneous power can be excellent. In addition, winter accounts for about 30% of annual production in many regions: this is not insignificant.🔧 WATTUNEED SOLAR KITSComplete solutions for individuals, installers and businesses ⚡ DISCOVER SELF-CONSUMPTION KITS Why production drops in winter (even though the cold improves efficiency)This is THE section that avoids confusion between "efficiency" and "production". The efficiency of a module (its instantaneous efficiency) is better in winter thanks to the cold, but the total production (in kWh over the day) will be lower. Here are the three physical factors that explain this paradox.1) Less available irradiationWinter reduces solar resources for two reasons:Shorter days: In December, the sun rises late and sets early. In Belgium, we go from around 16 hours of daylight in June to less than 8 hours in December.Sun lower on the horizon: The angle of incidence is less favourable, as the light passes through a thicker layer of atmosphere, which reduces the irradiance received per square metre.More overcast skies: Depending on the region, winter brings more grey days, increasing the proportion of diffuse light (which is less energetic than direct radiation).Key phrase to remember: Winter reduces the "input" (the amount of light available), but the panel works better with this light thanks to the cold.2) The "shadow factor" explodesWith the sun low in the sky, shadows become much longer. A tree, a chimney, a skylight or a neighbouring house can cast shadows that did not exist in summer. Sometimes, in December, we discover that an obstacle that was marginal in June becomes critical in winter.On a conventional string (where the modules are connected in series), a single shaded panel can limit the current of the entire group, resulting in disproportionate losses. This is why winter shading analysis is essential when designing an installation.3) Snow, frost, dirt: losses due to maskingIn colder areas or at high altitudes, snow becomes a real operating parameter. But even in temperate regions, a film of dirt (dead leaves, dust, organic deposits) combined with winter humidity can reduce light transmission by 5 to 15%, depending on the condition of the modules.Sloping roofs encourage snow to run off and slide naturally... 🔗 See mounting systems Cold weather: a real ally (with one technical point to watch out for)Cold weather actually improves productionContrary to popular belief, cold weather is not simply "less detrimental": it actively improves production. Here's why:Cell voltage increases significantly when the temperature drops (approximately +0.3 to +0.4 V per panel for a 20°C drop).The current drops slightly (approximately -1 to -2%), but this decrease is minimal compared to the increase in voltage.Power (P = U × I) increases overall: a net gain of 5 to 10% at 5°C compared to 25°C (at equal irradiance).This is why cold, sunny winter days can produce excellent instantaneous power, sometimes exceeding that of a hot summer day with the same amount of sunshine.Critical technical point: DC voltage rises in winterThis increase in voltage has an important consequence for sizing:A panel with a nominal Voc of 45 V at 25°C can reach 50 to 52 V at -10°C.On a string of 20 modules, this can represent a total increase of 100 to 140 V.Critical consequence: If the sizing has not been done correctly, a PV field may exceed the maximum DC voltage allowed by the inverter (or protection equipment), which can lead to faults or even material damage. ⚠️ PRO TIP Mandatory check in winter✅ Always check the maximum string voltage at the minimum site temperature (according to DTU 61.2 or local standards) • ✅ Consult the module datasheet (Voc temperature coefficient) • ✅ Observe the maximum DC voltage of the inverter 📋 See inverters and max Vdc specifications Tilt and orientation: strategies for maximising winter productionGrid-connected: aiming for self-sufficiency from March to OctoberFor someone connected to the grid living in northern France, Belgium or similar latitudes, aiming for autonomy through photovoltaics in winter can be an unattainable challenge. The combination of short days, low sunlight and increased consumption (heating, lighting) makes this goal very difficult.Our Wattuneed recommendation: Don't aim for winter autonomy if you are connected to the grid. Instead, focus on achieving near-total autonomy from March/April to September/October, when solar resources are more than sufficient. The grid will naturally supplement your needs in winter, and you can even feed your summer surplus back into the grid, depending on your contract.Autonomous sites: multi-energy sizingFor our customers living in complete autonomy in our more northern latitudes, we recommend taking the drop in winter production into account in your sizing calculations. A few key principles:Avoid relying on solar energy for heating: winter production is too variable and insufficient to guarantee thermal comfort.Adopt a multi-energy approach: for example, use a gas, wood or oil-fired water heater for the most difficult months (December-January), while taking advantage of solar energy the rest of the year.Oversize the PV field: install more panels than necessary in summer to partially compensate for winter (but be mindful of costs and available space).Provide a large battery capacity: to store energy from the rare sunny days and smooth consumption over several grey days.Tilt and orientation strategies for winter autonomyWhen the goal is to maximise winter production (for autonomous sites or specific needs), here are the recommended strategies:Steeper tilt to the south: 50 to 60° (or even more) to better "target" the low December sun and encourage snow to slide off.East/west panels: Add a significant number of east- and west-facing panels to better distribute production throughout the day. This avoids unusable production peaks and improves self-consumption.Solar tracker: The ideal solution for significantly limiting winter production losses. 2-axis trackers follow the sun both on the east/west axis and on the tilt axis, maximising light capture at all times.🔄 2-AXIS SOLAR TRACKERMaximise your winter production with a photovoltaic tracker ⚡ DISCOVER THE 2-AXIS 16-PANEL TRACKER Helpful tip: PVGISThe best way to check the impact of tilt and orientation on monthly production is to use PVGIS (Photovoltaic Geographical Information System), a free tool developed by the European Commission's Joint Research Centre. It is based on historical weather data and hourly calculations over several years.You can simulate different inclinations and see precisely the expected production for each month. It is an excellent educational tool for calibrating expectations and avoiding winter disappointments.Shading: the real issue in winter (and how to limit it)Why it's more critical in DecemberWith the sun low on the horizon, shadows are much longer than in summer. A tree 10 metres tall can cast a shadow of 15 to 20 metres in December, compared to 5 to 8 metres in June. Even a small obstacle (skylight, chimney, antenna) can "bite" into key production hours (10 a.m. to 2 p.m.).How to explain it clearly (educational)On a conventional string (modules in series), the current is limited by the weakest module. If a panel is 50% shaded, the current of the entire string can drop by 30 to 70% (depending on the configuration and cell technology). This is known as the "weak link" effect.Typical solutionsDistribute the modules across several MPPTs if the inverter allows it (multi-string inverters): this way, one shaded string does not penalise the others.Use micro-inverters (one per module) or power optimisers: each panel operates independently, limiting the impact of localised shading.Review the layout (module arrangement): place unshaded areas on the main strings and isolate problematic areas on dedicated MPPTs or with optimisers.🔧 ANTI-SHADING SOLUTIONSMicro-inverters, optimisers and multi-MPPT inverters ⚡ DISCOVER INVERTERS Snow: "enemy" or "bonus"?1) Snow on the panel = rather negativeIf the cells are covered by snow, production drops (logical: no light = no conversion). A 5 cm layer of snow can block 90 to 100% of the light. The real issue is therefore the duration of coverage: the longer the snow remains, the more operating losses accumulate.Fortunately, solar panels are usually black or dark blue, which promotes heat absorption (even in cold weather). As soon as the sun reappears, the snow often melts quickly on the glass surface, especially if the angle of inclination is steep.2) Sliding snow can help cleanA positive side effect of snow: as it slides down the modules, it can carry away dirt that has accumulated on the lower part of the panel (see cleaning section below). This is a form of "natural cleaning" that can improve production once the snow has melted.3) Snow around the panel can help (albedo effect)Very light-coloured ground (fresh snow) can reflect up to 60-80% of sunlight, compared to 15-25% for dark ground. This reflected light can be captured by the modules, particularly by bifacial panels (which also produce energy from the rear).The albedo effect can increase production by 5 to 15% (or even more with well-designed bifacial panels and highly reflective ground). But beware: this effect does not compensate for losses due to snow on the modules."Simple message: snow on the module = loss; snow that slides off = free cleaning; snow on the ground = sometimes a gain (if the module remains clear)."💡 Bifacial panels: High-performance modules Production from the front AND the back to maximise albedo gainMaintenance & monitoring: what to do in winter (without risk)The critical point: dirt in the lower frameAn often overlooked aspect of winter maintenance concerns the frame at the bottom of the panel. This frame rises slightly above the glass sheet (usually 3 to 8 mm), creating a small "step" where dirt can accumulate:Dead leaves, dust and organic debris accumulate in this area and form a dark band.In winter, humidity promotes the formation of deposits that adhere to the glass.When the dirt reaches the first cell (which is usually between 5 and 15 mm higher than the edge of the frame), it can negatively affect production, especially on first-generation panels.The good news is that snow sliding down can help clean this dirt. But when this is not enough (or in regions with little snowfall), manual cleaning may be necessary.Even better: newer cells (Half-Cut, PERC, TOPCon), thanks to their multiple wires (busbars) that allow the current to find its way, are much less affected than first-generation cells (3 busbars). Partial shading on the bottom of the cell therefore has less of a negative impact on overall production."Useful" (and reasonable) maintenanceVisual inspection of the lower frame: Check for dark bands or trapped debris. Gentle cleaning (clean water, soft brush) can improve light transmission by 5 to 10% if this area is very dirty.Snow monitoring: In snowy areas, monitor periods of prolonged coverage (several days). If the snow does not slide off naturally, consider calling in a professional (never attempt this yourself on a roof).Checking connections: Freeze-thaw cycles can weaken certain electrical connections (MC4 connectors, cables). An annual visual inspection (before winter) is recommended.⚠️ Safety (important)NEVER attempt to clear snow or clean a roof yourself: risk of falling, slipping, or damage to the modules (scratches, microcracks). Instead:waiting for the snow to slide off naturally (aided by the slope and heat of the modules),monitoring production to quantify losses,calling in equipped professionals if necessary (rare in Belgium, more common in mountainous areas).Monitoring: current, a better indicator than powerA monitoring system (real-time production tracking) allows you to answer these essential questions:"Is it still producing?""Is a string at zero?" (possible sign of shading or defect)"Is winter shade affecting everything?""Is there still snow?" (production = 0 or close to zero)Important technical point: Beyond production in watts, it is the current (A) that is most representative of sunlight. Why? Because:Voltage varies with temperature (higher in winter, lower in summer).The current is directly proportional to the irradiance received (light).Two strings with different voltages (due to a different number of panels) must operate in the same current range under equivalent sunlight. If one string displays a significantly lower current, this is a sign of a problem (shading, dirt, defect).Intelligent monitoring (with current display per string) therefore allows anomalies to be detected quickly and action to be taken before losses accumulate.📊 MONITORING & PROTECTIONMonitor your production in real time and detect anomalies ⚡ DISCOVER MONITORING SOLUTIONS "What to expect": calibrating winter expectationsIt is essential to set expectations from the project design stage. Here is a realistic order of magnitude (variable depending on region, orientation, shading):PériodePart de la production annuelleCommentaireAvril à septembre~65-75 %Belle saison : jours longs, soleil haut, peu d'ombrageOctobre à mars~25-35 %Hiver : jours courts, soleil bas, ombrage marquéThis ratio is typical for Belgium and northern France. The further south you go (southern France), the more productive the winter is (up to 35-40% of annual production).Key takeaway: Yes, it produces in winter, but winter is not the "record" season. This is normal and is factored into profitability simulations. A well-sized installation remains profitable over the year, thanks to excellent summer performance that more than compensates.Summary table: cold weather vs solar resourcesFacteurEffet sur le rendement instantanéEffet sur la production totale (kWh/jour)Froid✅ Améliore (+5 à +10 %)✅ Améliore (si irradiance égale)Jours courts➡️ Neutre❌ Réduit (-40 à -60 %)Soleil bas➡️ Neutre❌ Réduit (-20 à -40 %)Ombrage marqué❌ Pénalise fortement❌ Réduit (-30 à -70 % selon config)Neige sur modules❌ Bloque totalement❌ Réduit (-90 à -100 % tant que présente)Neige qui glisse✅ Nettoie les salissures✅ Améliore après glissement (+5 à +10 %)Albédo neige au sol✅ Aide (bifacial)✅ Améliore (+5 à +15 % selon config)Salissures cadre inférieur❌ Pénalise (anciens modules)⚠️ Limité (modules récents multi-busbar)Conclusion: winter is a normal season, not a shutdownYes, a photovoltaic panel produces energy in winter: all it needs is light, even diffuse light. Cold weather actually improves production thanks to the increase in voltage, which more than compensates for the slight drop in current. The real causes of the drop are reduced solar resources (short days, low sun),more pronounced shading, and sometimes snow or dirt covering the modules.With a well-designed installation (analysis of winter shading, sizing adapted to your objectives, appropriate electronics, monitoring), winter becomes a "normal" season... and not a complete shutdown. The 25 to 35% of winter production contributes to your autonomy and the overall profitability of the system over 25 years.For grid-connected installations: Aim for autonomy from March to October, and let the grid naturally supplement your winter needs.For autonomous sites: Adopt a multi-energy strategy, favour east/west orientations and steep inclines, and seriously consider a solar tracker to maximise winter production."Photovoltaic winter is like a farmer's winter: the warm season provides most of the harvest, but the rest of the year also counts."Frequently asked questions (FAQ)Do solar panels produce energy when the temperature is 0°C?Yes, and even better than at 25°C. Cold weather actually improves production: the voltage increases significantly, more than compensating for the slight drop in current. It is light that is the limiting factor in winter, not temperature.Do they work when it's grey?Yes, but less so. The panels also use diffuse light (the light that passes through the clouds). A grey day can still produce 10 to 30% of the power of a sunny day, depending on the thickness of the cloud cover.Why does it produce less in winter?There are three main reasons: shorter days (fewer hours of production), the sun is lower on the horizon (reduced irradiance), and there is more shade (longer shadows). Sometimes snow or dirt can also obscure the modules.Should snow be cleared from the panels?Only if it is safe and professionally feasible. NEVER climb onto a snow-covered roof yourself (risk of serious fall). The real issue is how long the snow stays on the roof: if it slides off naturally within 1-2 days, losses are limited and the sliding even cleans off any dirt. Otherwise, consider hiring a professional.How can I effectively monitor my production in winter?Monitor the current (A) rather than just the power (W). The current is directly proportional to the amount of sunlight and allows you to compare strings even if they have different voltages. Two strings under the same sunlight should display similar currents.Should I aim for winter autonomy?It depends on your situation: If you are connected to the grid in Belgium/northern France, aim for autonomy from March to October. For autonomous sites, adopt a multi-energy strategy and consider a solar tracker or east/west orientation to maximise winter production.Is there a technical point to watch out for in winter?Yes: DC voltage rises in cold weather. Always check that the maximum string voltage (at the minimum site temperature) does not exceed the maximum DC voltage allowed by the inverter. This is a regulatory requirement and a safety imperative.Wattuneed SPRLRue Henripré 12, 4821 Andrimont, BelgiumTel: +32 87 45 00 34 – info@wattuneed.comwww.wattuneed.com | Technical support