Recently, an owner of a photovoltaic power station in his home shared the situation of nighttime power generation of household photovoltaic power stations, which also aroused the curiosity of many people.

It is reported that on December 10, the owner's photovoltaic power station continued to generate electricity after 6 pm. From the power generation data chart, it can be seen that the power generation of the power station at night is only 26.4W. Judging from the power generation of the power station on that day and weather factors, the power station should be a photovoltaic power station of about 20 kilowatts, and the minimum power to maintain the operation of the power station should be about 20 watts.

However, since the light source is not 100% efficient, if the photovoltaic power station is to start normally, the power of the starting light source must reach at least 100 watts.

It is understood that the weather on that day was cloudy and there was no strong moonlight. At the same time, it can be seen from the power generation chart that after sunset, the photovoltaic power station did not stop generating electricity, but continued to generate electricity. If the power generation is caused by moonlight, then its image is a normally distributed curve, and this time the night power generation curve is completely horizontal, which also proves that there is a relatively stable light source.

The power station's nighttime generation of electricity was accidental, and such a situation was very rare before. It is reported that the power station generated 2.1 kWh of electricity at around 9 o'clock that night, and when it was checked the next day, its power level was still 2.1 kWh. This also shows that although this photovoltaic power station generated electricity at night, the amount of electricity generated was negligible and basically did not cause any changes to the overall power generation.

In what situations will photovoltaic power stations generate electricity at night?

First of all, we should make it clear that photovoltaic power stations generating electricity at night does not mean generating electricity without light.

As we all know, the reason why solar panels can generate electricity is mainly because they use the technology of solar photovoltaic effect to generate electricity, also known as photovoltaic effect. Its basic principle is to absorb light energy, generate photogenerated carriers, separate and collect carriers, and finally generate current.

Even if the photovoltaic power station generates electricity at night, it is also affected by the light source. For example, the situation that the photovoltaic power station continues to generate electricity at night is likely to be affected by strong light not far away, such as strong light sources at night in nearby construction sites or other relatively stable light sources.

So will the photovoltaic power station generate electricity at night? Usually, photovoltaics rely on sunlight to generate electricity. There is no direct sunlight at night, and photovoltaic panels cannot generate electricity in conventional ways. However, in some special cases, there may be a phenomenon that seems to be "generating electricity at night":

• Configuration of energy storage system: If the photovoltaic power station is equipped with an energy storage system (such as a battery), the electricity generated during the day can be stored for use at night. In this way, even if there is no sunlight at night, the photovoltaic power station can still output a certain amount of power.

• Radiative reflection and diffuse reflection: Even at night, there is still some ambient light on the ground, including reflected light from the moon (such as moonlight), attenuated light from surrounding buildings, etc. Although these lights are weak, they can still generate a certain amount of light energy on the surface of the solar panel, resulting in a certain degree of electrical energy output from the solar panel.

• Inverter backflow or meter error: In some cases, when the inverter enters standby mode at night, it may obtain a small amount of power from the grid to maintain its own operation, which may cause the meter to record reverse current, showing the phenomenon of "night power generation". In addition, meter measurement errors may also cause the input power of the grid to be misjudged as the output power of the photovoltaic system, and thus recorded as power generation.

• External power supply access: If other backup power sources (such as diesel generators, energy storage systems, etc.) are installed in the photovoltaic power station at the same time, during the power switching process, the meter may mistakenly record the output of the backup power source as photovoltaic power generation.

• Data acquisition system or inverter failure: If the data acquisition system or inverter in the photovoltaic system fails, it may also record incorrect power generation data, resulting in the illusion of night power generation.

In fact, compared with the power generation of photovoltaic power stations during the day, even if photovoltaic power stations generate electricity at night under some special circumstances, the amount of electricity is very small, even negligible. However, the power generation of photovoltaic power stations at night can also be well fed back to users to check whether there are any equipment problems in their own photovoltaic power stations.

Solar power stations that generate electricity both day and night

Since photovoltaic power stations can also generate electricity at night, can existing technology achieve power generation both during the day and at night? In terms of normal photovoltaic component products, it is actually impossible, but there are such power stations.

For example, in Gansu, my country, there is a tower-type solar thermal project currently under construction, the Gansu Aksai Huidong New Energy Solar Thermal Project.

The Aksai Huidong New Energy Project is one of the first batch of "solar thermal + photovoltaic" pilot projects in China, with a total investment of 5.06 billion yuan and a total installed capacity of 750MW. Combining 110MW solar thermal power generation and 640MW photovoltaic power generation, it is the largest "solar thermal + photovoltaic" project under construction in Gansu. After the project is completed, it is expected to generate 1.7 billion kWh of electricity annually, which will save 507,000 tons of standard coal and reduce carbon dioxide emissions by 1.47 million tons, which will have a positive role in promoting the development of local new energy and economic improvement.

Photothermal power generation, also known as solar thermal power generation, uses high-precision intelligent heliostats to track the sun in real time, reflect and focus sunlight on the absorber, and heat the molten salt in the absorber to a high temperature of more than 560 degrees Celsius.

Subsequently, these high-temperature molten salts are stored, and when power generation is needed, high-temperature and high-pressure steam is generated through heat exchange, which then drives the steam turbine generator set to generate electricity. The focused sunlight will generate high temperatures, melt the salt and store the energy in the melt. It is actually a thermal battery. At night, the stored heat is used to generate electricity. This allows for 24-hour continuous power generation.

In fact, this is similar to equipping your own photovoltaic power station with energy storage, collecting excess electricity during the day and using it at night, but currently, if you want to store it for your own use, it will greatly increase the cost for users, and it will be difficult to recover the cost in the short term.