Solar Power and Net Metering

Grid-tied solar power system (with net metering) diagram

Net metering, or also known as net energy metering (NEM), is another big reason why the solar panels are a good investment for your home or business.

Net metering is possible when your home maintains a connection to the grid even after you install solar panels, and of course, when the net metering is available in your area. The grid-connected (grid-tied) solar power system with net metering consists of solar panels, a grid-tied solar inverter that converts DC (direct current) to AC (alternating current), and net meter. DC generated from your solar panels is converted into AC, which is the type of current that is used by the electrical appliances in your home.

Let's explain simply what is net metering and how it works.

When your solar panels produce excess power, it goes to the grid. The utility company compensates you for the excess grid supply with credits added to your electric bill. For the time, when your solar panels produce less power than your household is needed, you can draw electricity from the grid. A net meter (bi-directional meter) is installed to register both the excess solar energy that you export to the grid and the energy that you consume from the grid. This ensures that consumers are only charged for their “net” energy use (energy consumed minus energy sent to the grid). 

Monthly net metering allows consumers to use solar power generated during the day at night. Similarly, during the spring and summer, when the sun is shining, and your solar panels are producing more electricity than you need, that extra energy goes to the grid. Then in the winter, when the days are shorter, you can draw on those energy credits to help offset some of your energy needs.

The grid acts as an energy storage system for your excess power and saves it for later use. The grid connection ensures that you still have power regardless of daily or seasonal variations in solar panels production levels.

So, with grid-tied solar power system and net metering billing mechanism, you save money besides that you help the environment and reduce your carbon footprints.

Net metering originated in the United States, where solar panels and small wind turbines were connected to the electrical grid, and consumers wanted to be able to use the electricity generated at a different time or date from when it was generated. In 1979 an apartment complex and a solar test house in Massachusetts were the first two projects to use net metering. Minnesota is commonly cited as passing the first net metering law, in 1983, and allowed anyone generating less than 40 kWh to either roll over any credit to the next month, or be paid for the excess. 

Keep in mind, however, that net metering policies can vary significantly by country and by state or province. It is not available everywhere in the U.S., which means that there is a need for other nighttime power supply options such as solar battery storage.

Net metering was slow to be adopted in Europe, especially in the United Kingdom, because of confusion over how to address the value-added tax (VAT). Only one utility company in Great Britain offers net metering. In Canada, some provinces have net metering programs.

How to Harvest Solar Energy on Cloudy Days

Image credit: SunModo

Talking about solar energy without sunlight, it is interesting to see how solar energy can be harvest on cloudy days. 

Even on cloudy days, there’s still solar energy send down to earth from the sun. And although solar panels don’t produce as much electricity as they do on sunny days, they have been shown to produce 25% of what they produce on a sunny day, or 10% when it’s very cloudy. The exact amount will vary depending on the density of the clouds, and may also vary by the type of solar panel - some kinds of panels are better at receiving diffuse light. SunPower solar cells, for example, have been designed to capture a broader range of the solar spectrum. By capturing more red and blue wavelengths, their solar panels can generate more electricity even when it’s overcast.

We may assume that solar panels thrive in hot, sunny weather, but too much heat can also reduce solar panel output 10-15%. The very hot climate isn't the best condition for them. Most solar panels' power outputs start to degrade if the temperature of the panel goes over about 25°C. 

Solar power can work well in areas known for cloudy, cold weather. For example, New York, San Francisco, Milwaukee, Boston, and Seattle. These cites often have bad weather, from blizzards to rain and fog. However, each of these cities tops the list of those that see major savings due to solar power installations. And rain helps to keep the panels operating efficiently by washing away any dust, pollen, and dirt. Clean panels turn out the most electricity.

San Francisco is well known for its foggy days with cool weather but rooftop solar power systems in San Francisco do function well. The amount of direct sunlight is reduced by fog and clouds, but as already was said, solar panels function better at cooler temperatures, so the electricity output in San Francisco is still significant. Using a home solar power system there can save approximately $1,500 per year on utility bills.

Germany is the fourth-largest PV market in the world that's famous for its lack of sunlight. Germany accounts for about 25 percent of the world's solar power output and achieved its strongest growth in half a decade during 2018, according to a recent Greentech Media article. 

Going solar is about saving on your energy costs as well as helping our planet and the weather can’t be an obstacle.

And if we choose to rely on solar panels for our home electricity use, we can also use a solar battery system to save money by storing free energy for use when it’s cloudy or for night use. Solar batteries have been around for a while, but up until recently, the costs were very high, the equipment was bulky and they were difficult to use. Except for people who lived off the grid, they weren’t so good investment. But that has changed in recent years. The price of solar batteries has dropped and in many cases, they are now an excellent investment for homeowners in cloudy regions who want to reduce their electricity bills.

Sources: Cleantechnika & Powerhome

                     

Indoor Light and Organic Solar Cells - Energy Without Sunlight

Image Credit: Thor Balkhed - Wuming Wang, PhD Student, and Jonas Bergqvist, Principal Research Engineer in the solar cell laboratory

The new organic solar cell, optimized to convert ambient indoor light to electricity, is being developed by scientists at Sweden's Linköping University, the Chinese Academy of Sciences, and the University of Science and Technology Beijing.

Although the power produced by it is low, the scientists believe it could be enough power to support the many products that the Internet of Things will bring online. 

Low energy consuming devices sensors that detect and measure moisture, particle concentrations, temperature, and other parameters will require small and cheap sources of renewable energy.

The researchers developed an active layer made up of donor and acceptor materials. The new combination - a non-fullerene acceptor blended with a polymer donor - supported the development of a photoactive layer allowing it to absorb the exact wavelengths of light that are typically found in most indoor environments. In a nutshell, donor materials absorb photons, while acceptors acquire electrons. Photovoltaic characterizations of the new solar cell revealed a low energy loss below 0.60 eV.

Two prototypes have been created so far, one measuring 1 square centimeter (0.2 sq in) and the other measuring 4 sq cm (0.6 sq in).

The optimized organic photovoltaic cell, with an area of 1 cm2, showed a power conversion efficiency of 26.1% with an open-circuit voltage of 1.10  V under an LED illumination of 1000 lux (2700 K).

“We are confident that the efficiency of organic solar cells will be further improved for ambient light applications in coming years, because there is still a large room for optimization of the materials used in this work,” said professor Jianhui Hou from the Chinese Academy of Sciences.

The technology is now being commercialized by a Linköping spin-off company. A paper on the research, which was led by the university's Assoc. Prof. Feng Gao, was recently published in the journal Nature Energy.

Sources: Linköping University & Newatlas

Organic Solar Cells Break New Efficiency Record: 17.3%

In recent years, scientists have been trying to find a way to improve the efficiency of organic photovoltaic cells. Some researchers have even thought that organic solar cells may never improve beyond 15 percent. Solar cells based on silicon, by comparison, are in the 18 to 22 percent range.

But in a new effort, the researchers in China have developed an organic photovoltaic cell that converts 17.3% of the energy in sunlight into electricity. 

“Organic solar cells have been studied for many years, but they’re still relatively young compared to silicon,” said Chen Yongsheng, a chemist at Nankai University in North China's Tianjin. “We still don’t understand their device performance very well.” 

Chen's group used tandem cells, which are put together by different layers of organic materials. Previous designs for tandem organic cells have failed to tap into the abundant solar energy of the near-infrared range, but Chen’s team addressed this issue. 

They used a non-fullerene acceptor molecule known as O6T-4F, which was able to work better at this wavelength. They then combined that with a layer containing a relatively new electron acceptor, called F-M for short, which the team had earlier developed. This material was shown to be an excellent match for its electrical properties and could absorb visible light.

"Different layers of the tandem cells can absorb different wavelengths of light. That means you can use sunlight in the wider wavelengths more efficiently and achieve a higher power conversion rate," Dr. Chen Yongsheng said.

"There’s no reason why an organic solar cell can’t have a similar or higher performance to silicon or perovskites,” according to Chen.

Sources:

https://physicsworld.com/a/organic-solar-cells-break-new-efficiency-record/

https://www.futuretimeline.net/blog/2018/08/15.htm

https://cen.acs.org/energy/solar-power/Organic-solar-cell-smashes-performance/96/web/2018/08

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The breakthrough is published in the journal Science

Organic Solar Cells (OSCs)

                      Organic Photovoltaic cell (Source: Fraunhofer ISE)

Organic solar cells (OSCs), also known as plastic solar cells are third-generation photovoltaic technology using organic materials (carbon-based in the form of small organic molecules, dendrimers, and polymers), to convert sunlight to electrical energy.

Organic photovoltaic devices are comprised of one or several layers including a photoactive layer between two electrode layers. These layers are printed using roll-to-roll manufacturing, similar to the way newspapers are printed, with thicknesses on the nanometer scale. Photoactive layers are typically printed on a thin plastic substrate followed by lamination with a protective and flexible foil.

In an OPV cell, sunlight is absorbed in the photoactive layers composed of donor and acceptor semiconducting organic materials (typically either polymers or small molecules), to generate photocurrents. The donor material (D) donates electrons and mainly transports holes and the acceptor material (A) withdraws electrons and mainly transports electrons.

For organic materials to become conducting or semiconducting, a high level of conjugation (alternating single and double bonds) is required.

Organic solar cells have several advantages over their traditional silicon counterparts. They are very environmentally friendly because they contain no toxic elements and can be processed at low temperature using roll-to-roll deposition, so can have an extremely low carbon footprint.

Conventional silicon solar cells are perfect for large scale electricity generation in solar farms and on the roofs of buildings, but they are not suitable for the electric vehicles and integration into windows on buildings. Organic solar cells can sit on curved surfaces, they are very lightweight, flexible and transparent.

Additionally, manufacturing cost can be reduced for organic solar cells due to their lower cost compared to silicon-based materials and the relative ease of chemical synthesis.

Disadvantages associated with organic photovoltaic cells include their low efficiency (currently ~15%) in comparison with inorganic photovoltaic devices.

Organic solar cells are new types of flexible solar cells and they will become a commercial reality very soon because it will give the designers more choice in the materials they can use.