Solar lights need direct sunlight for optimal performance. However, they are designed in such a way that they can also use artificial light to generate power.
In some cases, they may have batteries to store power to be used later. As the sunset approaches, the sun rays weaken and cannot be efficiently absorbed by the solar cells.
Fortunately, the cells also contain photoreceptors that detect darkness and turn on the light.
Here’s a data table that illustrates the relationship between sunlight intensity and charging time for solar lights. Please note that these are small experimental values and can vary based on the specific model of the solar light and the capacity of its battery.
|Sunlight Intensity (%)||Approximate Charging Time (Hours)|
|100 (Direct Sunlight)||4-6|
|10 (Very Cloudy/Shaded)||12-14|
Above table suggests that the less intense the sunlight, the longer it will take for the solar light to fully charge.
For instance, in direct sunlight (100% intensity), a solar light may take around 4 to 6 hours to fully charge.
However, in very cloudy or shaded conditions (10% intensity), it could take up to 12 to 14 hours for the solar light to fully charge.
Further, if we move into the latest research, the relationship between solar lights and direct sunlight can be further explained by examining the efficiency of solar cells, particularly bifacial solar cells.
Bifacial solar cells, as the name suggests, are capable of absorbing sunlight from both sides, thereby increasing the generation of electrical energy per square meter of the photovoltaic (PV) module.
This is achieved through the utilization of light absorption from the albedo, which is the measure of the diffuse reflection of sunlight off the surface of the Earth.
In the research paper titled “A Review of Different Types of Solar Cell Materials Employed in Bifacial Solar Photovoltaic Panel,” published in the journal Energies, authors Muthu Vimala et al. conducted a study on the efficiency of various types of solar cells.
They found that screen-printed solar cells have produced a maximum efficiency of 22%. Furthermore, triode structure single-crystalline cells produced a maximum front side efficiency of 21.3% and rear side efficiency of 19.8%.
These findings demonstrate the potential of bifacial solar cells to harness sunlight more efficiently than their monofacial counterparts, which can only absorb sunlight from one side.
The efficiency of solar cells is crucial in the context of solar lights as it determines how much of the absorbed sunlight can be converted into electrical energy.
The higher the efficiency, the more sunlight is converted into usable energy, and the longer the solar lights can function.
Therefore, placing solar lights in direct sunlight can maximize their efficiency by providing them with the most amount of sunlight to absorb and convert into electricity.
Solar Lights in the Shade
Solar lights can work in the shade, but not as effectively as in direct sunlight. Shade means that less direct light is available in the area.
Consequently, the photon cells in the solar panel receive minimal light and do not charge normally, resulting in low amounts of energy being generated.
However, if the lights are in complete shade, for instance, behind a wall and almost no light is passing through, there will be no solar energy converted to electric energy.
Luckily, all solar lights have batteries that store power to use in such situations.
Charging Solar Lights in the Shade
Solar lights located in the shade have poor power generation.
So, you need to apply charging tips to improve their charging ability. Below are some tips you can use to increase the charging of solar lights in the shade:
- Clean the solar panels: Dirt on a solar panel reduces the absorption rate of the solar cells. Thus, if your solar lights panel is dirty, you need to clean the panel to increase the light absorption efficiency. However, you shouldn’t use detergents. Instead, use a wet cloth and clean water to scrub off the dirt.
- Redirect the light using mirrors: If the solar lights are in complete shade such that almost no light is passing, the use of mirrors will be quite handy. Get a mirror that is twice the size of the solar light and place it in the sun such that it reflects the sun’s rays to the lights.
- Use artificial lights: Solar lights can also use artificial light to generate lighting power. Thus, you can place the solar lights under an incandescent bulb to recharge and use them later where needed. Similarly, you can use LED flashlights, which will take 10 to 12 hours to fully recharge the solar lights.
Exposure Time and Solar Lights
The longer the solar lights are exposed to direct sunlight, the longer they will keep you away from darkness.
Most manufacturers recommend that they should be in direct sunlight for at least 4 to 10 hours.
- 8 hours of direct sunlight can give 12 to 15 hours of charge,
- while 4 hours of sunlight will give 6 to 8 hours of charge in normal weather.
Additionally, four pinnacle sun hours are essential because solar lights give maximum power generation. Actually, four pinnacle sun hours generate over 4000 watts.
Solar Lights and Artificial Light
Solar lights have solar cells which are responsible for lighting power generation. These cells are customized such that they can absorb both natural and artificial light.
Thus they absorb the natural light from the sun and convert it to direct current, which is later channeled to the inverter to be converted to alternating current, which is suitable.
Similarly, these cells can absorb artificial light, for instance, light from bulbs, and convert it to direct current. Consequently, solar lights do not necessarily need sunlight but can work on any form of light.
However, their operations are quite optimal in direct sunlight. Simply, less power is generated from artificial light in comparison to sunlight.
Shading Concerns for Solar Lights
Shading doesn’t look like a big deal, but it has adverse effects on solar lights in the long run.
For instance, these lights have cells that are likely to decrease efficiency if they are always placed in a shade.
Similarly, lack of direct sunlight will rarely have the batteries fully charged. As a result, their lifespan is shortened. The shade can be from various setups, such as trees, poles, and buildings.
- Trees: The effects of installing the solar lights may not be apparent, but they may become adverse as the tree grows. As the tree thickens and increases its branches, it will hinder the sunlight and may be worse, especially during cold seasons where the sun rays are not strong to penetrate through. Thus you may be needed to trim them if you want to see your solar lights serve you for many more years.
- Buildings: A tall building positioned on the east, west, or south of the solar light panel may cause a night in darkness despite investing heavily in solar lights. Ideally, you should ensure that the sun rays can efficiently reach the panel without destruction.
- Poles: Poles are not obvious obstacles, but looking out for them is quite important. Unlike big buildings, they do not cause big shades, making it easy to avoid and position the solar light away from them.
Frequently Asked Questions
Do solar flood lights need direct sunlight?
Solar flood lights, like other solar lights, perform optimally when exposed to direct sunlight. However, they can still function under artificial light or less intense natural light, albeit less efficiently.
Do solar lights need direct sunlight or just daylight?
Solar lights can operate under both natural and artificial light. They perform best when exposed to direct sunlight due to the higher intensity of the sun’s rays. However, they can still function with just daylight, though the charging time may be longer.
Do solar lights work in the shade?
Solar lights can function in shaded areas, but their efficiency decreases due to reduced light absorption. Long-term exposure to shade can also shorten the lifespan of the batteries.
Are there solar lights that don’t need direct sunlight?
Yes, solar lights can operate without direct sunlight. They can absorb both natural and artificial light. However, their performance is optimal in direct sunlight.
Will solar lights charge through a window?
Solar lights can charge through a window, but the charging efficiency might be reduced due to the window potentially blocking some of the sunlight.
Do solar lights work under trees?
Solar lights can work under trees, but their efficiency will be reduced due to the shade created by the tree. Over time, this could decrease the lifespan of the solar light’s batteries.
How much direct sunlight do solar lights need?
For optimal performance, solar lights should be exposed to direct sunlight for at least 4 to 10 hours a day. The longer the exposure to direct sunlight, the longer the lights will function.
Eng. Matthew Joseph Nandirio is the Founder of walkingsolar.
After graduating from the University of Houston in 2002, matt started working as a Solar Electrical Engineer for several multi-national solar energy companies.
He has a wide range of experiences including solar system requirement analysis, planning, maintaining, debugging and even solar device development through research.
He now shares his 20 years of expertise through his articles on the walkingsolar website.
Further, he is also the author of two books on Solar Technology, “Solar Power for Villages” and “DIY Solar System for Dummies”.