Is it possible to harness solar energy during the night?

If you've ever purchased carbon offsets, you may have noticed that the majority of your investment goes towards wind energy rather than solar. In the realm of large-scale alternative energy, wind dominates, primarily due to its lower cost. However, a recent breakthrough in solar energy production might make solar power a more viable choice.

Typically, direct sunlight is converted into electricity in one of two ways: through photovoltaic cells that convert sunlight into electricity by utilizing a semiconductor material to absorb photons and release electrons; or by using solar-thermal turbines, which convert heat from the sun into steam that drives a turbine to generate electricity. The solar-thermal power plant is now on the verge of a significant transformation.

This article will explore whether solar panels function at night. We will also demonstrate how the power of sunlight can be effectively stored for use after sunset. Additionally, we'll examine the first commercial power plant utilizing this technology to understand its operation.

Do Solar Panels Function at Night?

Simply put, no – solar panels operate only when there’s sunlight to convert into energy. Even on nights with clear moonlight or starlight, these light sources are insufficient. Regardless of whether the panels are used for residential or commercial purposes, they only convert direct or indirect sunlight. So, what can be done to ensure solar panels store energy for use after dark?

One advantage of solar panel technology is that many models include battery storage, which captures sunlight in the photovoltaic cells and then releases that stored energy during the night. This feature not only provides power, but can also help reduce your electricity bills and lower your carbon footprint. However, the technology is still being refined by experts.

Are Solar Panels Too Restrictive?

The main issue with solar power is the obvious one: the sun doesn’t shine constantly. During the night or on overcast days, solar cells can't capture enough sunlight. This results in higher costs for solar power systems, as they can’t produce energy 24/7. If a cloud passes by, the plant goes into a temporary shutdown, generating no power. This limitation also means solar energy isn’t available at times when demand is at its peak, like at night.

The answer is simple: store the sun’s energy for use when the sun isn’t shining. However, making this idea a reality has been a challenge—until a recent breakthrough made solar battery storage a viable option for the energy sector. And the material behind this breakthrough? It's likely already in your kitchen.

The Struggle to Store and Convert Solar Energy

The concept of storing solar energy isn’t new. For as long as solar power has been considered a potential energy source, people have been trying to figure out how to temporarily hold onto the sun’s energy before converting it into electricity. Unfortunately, all previous efforts have encountered significant difficulties.

Some have attempted to capture the sun’s energy by using it to pump water uphill, storing the energy until the water flows back down and releases it. Another method involves compressing and then decompressing air. However, both techniques waste energy—only about 80 percent of the solar energy put in is recovered on the other side [source: Bielo].

Batteries are inefficient and too costly to be considered a feasible solution for large-scale energy storage. A laptop battery, which costs ten times more than a thermos, holds roughly the same amount of energy. However, the breakthrough lies in heat storage, which is far more practical.

Capturing Surplus Solar Energy

Think of a thermos that retains the heat of coffee. In the same way, a solar-thermal power plant generates electricity from heat. By storing heat, we can pause the process: Let the sun heat up an object, keep it hot when the sun sets, and later use that heat to create steam that drives a turbine.

Storing heat may be straightforward, but finding the right material for solar power applications is crucial. To capture the intense heat needed for solar-thermal plants, the material must remain stable at high temperatures of around 750°F (400°C) to avoid issues like vaporization and pressure fluctuations. Additionally, the substance must be affordable and easy to obtain.

Using Common Household Fuels in Solar Energy Systems

Think of the white, crystalline substance you likely use in your kitchen for seasoning scrambled eggs, rimming margarita glasses, or adding to edamame: salt. Salt melts only at extremely high temperatures, turns to vapor at even higher temperatures, and is available in vast, low-cost quantities. Additionally, it loses only about 7% of the energy put into it [source: Bielo].

In fact, the first solar power plant using salt for storage doesn't rely on common table salt. Instead, it uses a different salt mixture, often used as fertilizer – a combination of sodium and potassium nitrate. The Andasol 1 plant in Grenada, Spain, stores a massive 30,865 tons (28,000 metric tons) of this mixture [source: Bielo].

Andasol 1

The Andasol 1 plant, located in Spain, began operations in November 2008, and operates similarly to other solar-thermal power plants as long as the sun is shining. Sunlight hits solar collectors – in this case, a field of parabolic-trough mirrors that focus sunlight on tubes filled with oil – which heats up. The hot oil then boils water, producing steam that drives a turbine.

How Andasol 1 Operates

The solar power generation at Andasol 1 is only impacted by the storage system when the sun isn't shining. The solar panel field at Andasol 1 is vast enough to collect nearly twice the amount of sunlight needed to operate the plant during the daylight hours.

First, the excess heated oil is directed to a heat exchanger, which sits between large vats of molten salt. One vat contains relatively cool molten salt (around 500°F or 260°C). This salt is pumped into the heat exchanger, where it absorbs heat from the oil. The now hotter molten salt (752°F or 400°C) is transferred into the second vat, where it waits until the sun is obscured by clouds.

When the power plant requires stored heat, the hotter molten salt is pumped back through the heat exchanger. Here, it transfers its heat to the oil, which will then generate steam. The now warmer oil moves toward the power center, and the cooler molten salt flows back into the cooler vat. This process repeats itself.

Advantages of Cutting-Edge Solar Systems

By using salt to store the sun's heat, Andasol 1 can continue to operate even without sunlight, running nearly twice as long as other solar plants. This salt storage system allows Andasol 1 to produce 50% more energy than it would otherwise – generating 178,000 megawatt-hours of electricity [source: Fairly]. This added capacity reduces the overall cost of the plant’s electricity, making it competitive with natural gas power in the future.

Salt storage isn't the only method being explored to store solar energy. Some plants are experimenting with a more direct approach that bypasses oil altogether – they aim to both collect and store heat directly in salt. Another potential material for heat storage is sand.

A different group has developed a system that emulates the molecular process of photosynthesis to store solar energy: It uses sunlight to split water molecules into hydrogen and oxygen, which are then recombined in a fuel cell.

Does Installing Solar Panels Make Sense?

Absolutely! While the conversation often focuses on cutting-edge solar technologies, traditional solar panels still offer valuable benefits. Although they may have limitations, typical solar energy systems are capable of generating electricity and storing energy, making homes and businesses more self-sufficient when it comes to energy use.

Although the battery system still has room for improvement, solar panels generate enough solar energy to continue being a valuable investment. Ask any solar panel owner about the financial advantages, and they'll affirm: Solar panels generate more power and save homeowners more money with each passing year they are in use.