How many watts does a solar panel produce per day?

How many watts does a solar panel produce per day? Yield, factors & practical values for Germany.

The energy transition has long been taking place on our own roofs and balconies. Anyone considering buying a photovoltaic system or a balcony power plant inevitably asks themselves: How many watts does a solar panel produce per day?

To clear up a technical misunderstanding right away: A solar panel does not produce "watts" over the course of a day (that is the pure power at a certain point in time), but watt-hours (Wh) or kilowatt-hours (kWh) – i.e., electrical energy.

In this guide, you will learn based on real practical data for Germany what solar yield you can really expect in summer, winter and on an annual average.

The most important influencing factors on daily PV yield

The yield of a solar panel is not a rigid constant. How much electricity ends up in your household appliances or in the electricity storage at the end of the day depends on a number of physical and geographical variables:

• Global radiation (solar irradiation): In Germany, the irradiation differs greatly between north and south. While the north averages around 950 to 1,000 kWh per square meter per year, the sunny south (Bavaria and Baden-Württemberg) often reaches over 1,150 kWh.

• The tilt angle and orientation: Optimal for year-round yield in Germany is a pure south orientation with a tilt angle between 30° and 45°. An east-west orientation provides less peak power at noon, but distributes the yield more evenly over the day (ideal for self-consumption in the morning and evening).

• The degree of shading: Even partial shading of a single module by a chimney, trees or power lines can drastically reduce the yield of the entire series (string), unless modern bypass diodes or module optimizers are installed.

• The temperature (the temperature coefficient): Solar panels like it bright, but cool. As temperatures rise, the efficiency of the solar cells decreases. A crisp, cold, sunny day in April can therefore generate more power per hour than a hot midsummer day in July.

What does a 400-watt solar panel produce per day?

A standard solar panel for residential buildings usually has a nominal output of around 400 watt-peak (Wp). This is the maximum output under standardized laboratory conditions (STC: 1,000 W/m² irradiation, 25 °C cell temperature).

In German practice, the reality is as follows:

• On an ideal summer day (May to August): An unshaded, optimally oriented 400 Wp module delivers 4 to 5 times its nominal output as daily yield. This corresponds to approx. 1,600 to 2,000 watt-hours (1.6 to 2.0 kWh) per day. This allows you to run a washing machine about twice at 60 °C.

• On a gloomy winter day (November to February): Here the factor drops drastically to 0.1 to 0.5 times. The module often produces only 40 to 200 watt-hours (0.04 to 0.2 kWh) per day.

• The annual average: Over the entire year (365 days including all bad weather days), a 400 Wp module in Germany generates approx. 1 kWh of electricity per day.

What does an 800-watt balcony power plant produce per day?

Balcony power plants (also called plug-in solar systems) are the trend in Germany. Since the legal adjustments, these systems are officially allowed to feed in with an inverter output of up to 800 watts. Usually, two solar modules with a total output of approx. 800 to 850 Wp are installed.

Since balcony power plants are often mounted vertically on the balcony railing (90° angle), the yields deviate slightly from the optimal roof pitch.

Typical daily yields of an 800W balcony power plant:

Weather condition / Season	Average daily yield (in kWh)	What you can operate with it (example)
Perfect summer day (south-facing, cloudless)	3.5 to 4.5 kWh	A modern refrigerator (24h) + home office workstation (8h) + several washing machine loads.
Cloudy spring day / Autumn day	1.5 to 2.5 kWh	Covering the continuous base load of the house (router, standby devices, refrigerator).
Gray, foggy winter day	0.2 to 0.6 kWh	Often only enough to cover the inverter's self-consumption and minimal standby consumption.

Practical tip: If you mount your balcony power plant steeply at a 90° angle on the balcony, the peak yield in summer will decrease, but you will capture the lower-lying sun much more effectively in winter and during the transitional months.

What is the maximum daily PV yield?

Can a photovoltaic system produce an infinite amount of electricity if the sun shines continuously? No, physical limits set a clear boundary here. The maximum daily PV yield is limited by the maximum daylight duration and the physical peak power.

In Germany, the absolute maximum on a perfect June day is about 6 to 7 kWh yield per installed kilowatt-peak (kWp) system capacity.

• If you have a small system with 4 kWp, the absolute maximum is approx. 24 to 28 kWh on one day.

• Higher values are hardly technically feasible in Central Europe due to the sun's position and the unavoidable heating of the modules during the day.

Solar radiation in annual comparison

The biggest dilemma of photovoltaics in Germany is the seasonal imbalance. The following graphic illustrates how extreme the monthly generation differences in Germany are over the years:

 

As can be clearly seen in the diagram of monthly solar generation, electricity production is almost entirely concentrated in the months of April to September. In late autumn and winter, yields plummet massively nationwide.

How much electricity does a 10 kWp photovoltaic system produce per day in winter?

A 10 kWp system (approx. 24 to 25 modern solar modules on a single-family house) is the classic homeowner size in Germany. While such a system easily generates 60 to 70 kWh on a single day in June, the situation in winter is completely different.

In winter (December and January), we have to contend with two main factors: extremely short days (often only 7 to 8 hours of daylight) and a very low sun angle, often combined with a thick cloud or fog cover.

The winter daily yield of a 10 kWp system in detail:

• On a sunny winter day (with clear sky): If the sky clears and the sun shines on the cold modules, a 10 kWp system can achieve 10 to 15 kWh per day even in January.

• On a typically gray, rainy or snowy winter day: Unfortunately, this is the standard in German winter. In diffuse light, the performance collapses. The system then often produces only 2 to 5 kWh per day.

• With snow-covered modules: If a thick layer of snow covers the modules, no light reaches the solar cells. The yield drops to 0 watts.

As a rule of thumb: a PV system generates only 10 to 15% of its total annual yield in the four months from November to February combined. Operating a heat pump or an electric car purely with solar power is impossible in these months without drawing from the grid.

Conclusion: Is the purchase worthwhile despite the fluctuations?

Yes, absolutely. Even if the daily yield drops sharply in winter, the summer more than compensates for these deficits. Anyone who consumes the electricity produced during the day themselves through clever consumption management (e.g., running the washing machine and dishwasher at noon) or by using a battery storage system will drastically reduce their electricity bill.

At current electricity prices in Germany, an optimally planned photovoltaic system usually pays for itself after 8 to 12 years – and then supplies free, clean electricity for at least two decades.

FAQ – Frequently asked questions about solar module yield

1. Does a solar module also produce electricity when it is cloudy?

Yes. Solar modules do not need direct, dazzling sunlight to generate electricity. They also use what is called diffuse light, which breaks through the cloud cover. However, the yield is significantly lower in heavy cloud cover – it often amounts to only 10% to 25% of the output that would be achieved in clear skies.

2. What is the difference between watts (W) and watt-hours (Wh)?

Watts (W) or kilowatts (kW) is the unit of measurement for instantaneous power – i.e., how much power the module generates at that exact second. Watt-hours (Wh) or kilowatt-hours (kWh) measure the energy/quantity that has been produced over a period of time. If a module constantly delivers 400 watts for one hour, it has generated 400 watt-hours (0.4 kWh) of electricity.

3. Does heat harm solar modules in summer?

Indeed, yes. Solar modules have a so-called temperature coefficient (usually approx. -0.35% per degree Celsius). As soon as the solar cells heat up above the standard test temperature of 25 °C – which quickly leads to cell temperatures of 60 °C on the roof on hot summer days – the maximum performance of the module decreases. The highest peak performances are therefore often measured on cool, windy, but sunny days in April or May.

4. Is an inverter with more watts than the solar modules worthwhile?

No, as a rule, not. In practice, it is even common and sensible to slightly "undersize" the inverter. This means that the solar modules collectively provide, for example, 900 watt-peak, but the inverter is limited to 800 watts. Since the modules rarely reach their theoretical peak performance in Germany anyway due to heat and weather conditions, the inverter operates in a more efficient operating range throughout the year due to the slight undersizing.

5. How much electricity does a PV system lose over the years?

Modern solar modules are subject to minimal aging, which is called degradation. Reputable manufacturers today guarantee that the modules will still deliver at least 80% to 85% of their original nominal output after 25 years of operation. The annual power loss averages only 0.3% to 0.5%, which is hardly noticeable in everyday life.