Category Archives: Solar Panels

Cleaning Solar Panels without Water

Most installations of solar panels are in desert areas that provide plentiful amounts of sunshine. While the desert property is cheap, winds are also common. When the wind blows, it carries a huge amount of dust, which forms a layer on the solar panels. Dust on the solar panel reduces their performance, and the electrical output from the panel can reduce by about 30% with only a month of exposure to the elements.

For a 150 MW solar panel installation, even a 1% drop in the output could translate to a loss in yearly revenue to the tune of US$200,000. According to researchers, a reduction of 3 to 4% power output from solar plants all over the world could lead to an annual loss of nearly US$3.3 billion to US$5.5 billion. Therefore, it is essential to keep solar panels clean, and the most common technique presently is by using water.

However, keeping solar panels clean presently requires an annual supply of nearly 10 billion gallons of water. This is enough water necessary for a million people in developing countries. Cleaning solar panels without water is a labor-intensive task, and carries with it the high risk of scratching and damaging the surface of the panels, which also leads to a reduction in the efficiency of the cells.

MIT researchers have come up with an innovative method of cleaning the surface of solar panels. The method does not require the use of water, is contactless, and is automatic.

This innovative new method from MIT uses electrostatic repulsion. This makes the dust particles jump off the panels and does not require water or brushes. When activated, the system runs an electrode just above the surface of the panel. This results in the dust particles acquiring an electrical charge. The solar panels have a transparent conductive layer on top of their glass covering, and this is only a few nanometers thick. The system applies the same electric charge to this transparent conductive layer.

The same charge on the conductive layer and the dust particles makes them repel each other. As the conductive layer cannot move, the dust particles fall off the panel because of the repulsion. The researchers had to change the voltage until they found a range that overcame the adhesion forces and the pull of gravity and allowed the dust to lift away. They then automated the system using guide rails on the sides of the panel and an electric motor.

This is not the first time that engineers have tried to use an electrostatics-based approach to keeping solar panels clean. However, most approaches used electrodynamic screens and interdigitated electrodes. The problem with such screens is they allow ingress of moisture that can damage the electronics. If the atmosphere is dry, and moisture is not an issue, such as on the surface of Mars, the arrangement could be useful. However, on Earth, this can be a serious problem, because even the desert has ample amounts of moisture.

The researchers have found that as long as the humidity is more than 30%, dust removal was easy. However, the process of dust removal got increasingly more difficult with a decrease in humidity. 

Wash Your Solar Cells

To augment the energy supply, many are installing solar energy systems or residential solar panels. In general, these are flat units, placed at an angle on the rooftop. That naturally leads to the question of keeping them clean, which people equate to cleaning the roof itself. As this cleaning is usually left to the rainwaters, the next question comes as whether we should depend on the rains for cleaning the surface of the installed solar cells as well. Moreover, some also worry about whether water is good for the cells and will not damage them.

For these skeptics, scientists have a new type of waterproof solar cell that generates electricity even when compressed, stretched, or soaked in water. This is good news for those in the wearable solar cell industry. Wearable solar cells provide power to devices for monitoring health, usually as sensors incorporated into clothing, recording heartbeats, body temperature, and other parameters, for providing early warning of medical problems.

These extremely thin and flexible organic solar cells, or photovoltaic cells as scientists call them, are a result of research in the University of Tokyo. A material, by name PNTz4T, coats both sides of the cells with a stretchable and waterproof film. The researchers then deposit the cells within an inverse architecture of a one-micrometer-thick parylene film. After this process, the researchers applied an acrylic-based elastomer coating to both sides of the cell, which prevents water infiltration.

The elastomer is transparent and allows light to enter the cell, but does not allow air and water from leaking into it. This makes the solar cells longer lasting compared to conventional photovoltaic cells. The researchers decided to test the effectiveness of the coating by immersing the coated cells in water for two hours. They found the cells’ resistance to water to be high, as its efficiency to convert from light to electricity dropped by only 5.4 percent.

Next, the researchers tested the durability of the coated cell by subjecting it to compression. They compressed the cell by half for twenty cycles while placing drops of water on it. Even after surviving this brutal test, the researchers found the cell still had more than 80% of its original efficiency still intact. The above tests confirmed the cells’ mechanical robustness, high efficiency, and great environmental stability.

Not only as wearable sensors, these new washable, stretchable, and lightweight organic photovoltaic cells will also be suitable as long-term power sources as rooftop solar panels. Most experts do not recommend washing solar cells regularly for keeping the dust and debris from collecting on the surface. Since these new solar panels have the additional feature of being waterproof, there is no danger from giving them a frequent wash.

Experts feel it is best to let the rain take care of washing the solar panel. By monitoring the system functionality such as checking the energy bills and usage on monthly basis, the user can detect changes in the electricity bill. Another check can be made by visually inspecting the surface of the panels. If cleaning is necessary, washing it with a hose of water will do the job.

Five New Advancements in Solar Cells

The earth receives a huge amount of sunlight every hour. Converted to electricity, this would amount to 52 PW/hr. This is more than ten times the entire amount of electricity produced per hour by China in 2013. In the same year, top countries of the world together produced only 16 PW/hr. of electricity. As this is much less than the actual potential of generation of electricity from the solar energy falling on the planet earth, several countries are actively engaged on research and development on photovoltaic cells.

There have been several breakthroughs in photovoltaic cell technology. For instance, early cells were very expensive and inefficient—almost $1800/watt and 4% respectively. Costs have now come down to $0.75/watt, while the efficiency has increased to 40%. Since, then, there have been several other breakthroughs in the solar cell domain.

Printable Solar Cells

At the New Jersey Institute of Technology (NJIT), researchers have developed a printable solar cell, and they can print or paint this on a surface. According to the lead researcher Dr. Mitra, they are aiming for printable sheets of solar cells that any home-based inkjet printer will be able to print and place on the wall, roof, or billboard to generate power. The printable cells are made of carbon nanotubes 50,000 times smaller than a human hair.

All-Carbon Flexible Solar Cells

Scientists at the Stanford University have made these flexible solar cells from a special form of carbon called graphene. According to Zhenan Bao, one of the team and a professor of chemical engineering at Stanford, the flexible carbon solar cells can be coated on to the surface of cars, windows, or buildings for generating electricity.
By replacing expensive materials when manufacturing conventional solar cells, the all-carbon solar cell is expected to make the cells much cheaper.

Transparent Solar Cells

At the Michigan State University, a team of researchers has made solar cells that appear transparent to the visible spectrum of sunlight. Rather, these non-intrusive solar cells convert light beyond the visible spectrum to electricity. Therefore, these can be used on smartphones, on windowpanes of buildings, or in windshields of vehicles without impeding their performance.

According to MSU assistant professor Richard Lunt, their aim is to produce solar harvesting surfaces that are invisible. However, the present efficiency of these cells is a mere 1%, as they are in their initial stages.

Wearable Ultra-Thin Solar Cells

In South Korea, at the Gwangju Institute of Science and Technology, scientists have used gallium arsenide to develop solar cells with a thickness of just one micrometer, more than 100 times thinner than human hair. According to Jongho Lee, an engineer at the institute, such thin cells can be integrated into fabric or glass frames to power the next wave of wearable electronics.

To create such thin cells, the scientists removed extra adhesives from the traditional cells, and cold-welded them on flexible substrates at 170°C.

Solar Cells with 100% Efficiency

By extracting all the energy from excitons, researchers at the University of Cambridge have found methods of making solar cells that are more efficient. Such a hybrid cell combines organic material and inorganic material into high conversion efficiency.

Powering the Pacemaker from Solar Energy

Those suffering from certain ailments of the heart, have to have a pacemaker installed. Surgeons place this tiny medical device in the chest or abdomen of the patient and it helps to control abnormal heart rhythms. The device generates electrical pulses and prompts the heart to beat at a normal rate. Power comes from implanted Lithium-iodide or Lithium anode cells, with Titanium as the encasing metal. The downside to this arrangement is the cells need replacement once they are discharged, and that means periodic surgeries.

To avoid repeated surgeries, scientists prefer using solar cells placed under the skin for continuously recharging the implanted electronic medical devices. According to Swiss researchers, a 3.6 square centimeter solar cell generates enough power necessary to keep a typical pacemaker running through the year.

Lukas Bereuter of Bern University Hospital and his team from the University of Bern in Switzerland have presented a study that provides real-life data on the potential of using solar cells to power implanted devices such as deep brain stimulators and pacemakers. Lukas is confident it will become commonplace to wear power generating solar cells under the skin. This will save patients the discomfort of undergoing repeated surgeries to change batteries of such life-saving devices. Lukas has reported the findings in Springer’s journal Annals of Biomedical Engineering.

Electronic implants are invariably battery powered, with their size depending on the volume of the battery necessary for an extended lifespan. When the battery exhausts is power, it must either be charged or changed. This necessitates expensive and stressful medical procedures involving implant replacements, along with the risk of medical complications for the patient. The implantable solar cell is attractive as it converts the light from the sun penetrating the skin surface to generate enough energy for recharging the medical devices.

Lukas and his colleagues have developed devices specially designed for solar measurement to investigate the feasibility of rechargeable energy generators in real-life situations. The devices measure the output power generated. According to the team, 3.6 square centimeter cells generated enough power and were small enough for the intended implantation.

The team tested ten cells by covering them with optical filters for simulating the properties of human skin. This influenced the amount of sunlight penetrating the skin. A test group of 32 volunteers wore the cells on their arm for one week during summer, autumn, and winter months.

According to the team, the tiny cells were able to generate power more than the 5-10 microwatts required by a regular cardiac pacemaker, irrespective of the season. The lowest power output the team recorded on average was 12 microwatts. The overall mean power obtained from the cells was enough to power a pacemaker completely, or at least extend the lifespan of an active implant. Furthermore, the use of solar cells or energy-harvesting devices for powering an implant dramatically reduces the size of the device, while at the same time, helps to avoid device replacements.

According to Lukas, the results of the study may be suitably scaled up and applied to other mobile applications, especially solar powered applications on the human body. The only aspect that requires attention is the efficiency and catchment area of the solar cell, and the thickness of the skin covering it.

Waspmote Plug & Sense! : Solar-Powered Wireless Sensor Platforms

Today, we use sensors for a myriad of activities such as intrusion detection, fall detection, patient surveillance, art and goods preservation, offspring care, animal tracking, selective irrigation, and many more. Where the sensor network has to operate outdoors, what can be a better way of powering them other than through solar means?

Using an external or internal solar panel, one can safely recharge batteries for the system. For external solar panels, the panel is usually mounted on a holder tilted at a suitable angle ensuring the maximum performance of the outdoor installation. When space is a major challenge, such as indoors, the solar panel can be embedded on the front of the enclosure. Typical rechargeable batteries used for powering loads are rated 6600mAh, and this ensures the sensors do not stop working even when the sun is not providing adequate light.

Such platforms of wireless sensor networks provide solutions for Smart Cities. Waspmote Plug & Sense! from Libelium is a system of encapsulated wireless sensor devices that allow system integrators to implement modular wireless sensor networks in a scalable manner. The Libelium system reduces the installation from days to just hours.

Each node of a Waspmote Plug & Sense! comes with six connectors. You can connect sensor probes to these connectors directly and the system is ready to install and easy to deploy. Using connectors ensures that the services remain scalable and sustainable. The possibility of powering the platform through solar power allows energy harvesting and years of autonomy.

Once the sensors have been installed, the nodes on the Waspmote Plug & Sense! can be programmed wirelessly. This is possible because of the special feature, OTAP or Over The Air Programming, incorporated into the platform. Thanks to OTAP, users can replace or add sensors without having to uninstall any of the nodes. This helps to keep the maintenance levels within reasonable limits. For example, to extend the service, you can easily add a noise sensor to a network consisting of CO2 probes, simply by attaching it.

The applications are endless for the Waspmote Plug & Sense! platforms. Apart from Smart Cities, the models are preconfigured for creating other widely applicable services out of the box, such as radiation control, ambient control, smart security, air quality, smart agriculture, smart parking and so many more.

You can use these sensor platforms anywhere in the world, as they use the generally available radio frequencies 2.4GHz and 868/900MHz, besides complying with certification standards such as CE, FCC, and IC. Usually, these sensor platforms send information to a sensor gateway that in turn, uploads the data to a cloud service. Therefore, the data is accessible from anywhere in the world and users can integrate it easily into third-party applications.

Use of solar-powered wireless sensor networks makes it so easy for adding a new sensor that municipalities find they do not have to reinstall the network for Smart Cities. The solution reduces the complexity of the installation and its maintenance, while providing it with a high degree of scalability. Available with IP65 enclosures for outdoor deployment and no software license fees, these platforms offer remarkable opportunities.

Rectannas : Will They Make Solar Cells Obsolete?

Professor Baratunda Cola and colleagues at the Georgia Institute of Technology, Atlanta, claims to have improved on the solar cells available. They have reported their findings in Nature Nanotechnology. The new type of solar cell is actually a rectenna – half antenna and half rectifier that can be tuned to any frequency as a detector, while generating electricity from solar and infrared light falling on it.

The team claims they can achieve a broad-spectrum efficiency of 40 percent with their new cell, although the efficiency they have achieved so far is only one percent. Comparatively, conventional solar cells such as the silicon and multi-junction gallium arsenide types have a maximum efficiency of 20 percent. The team also claims their rectenna can achieve an upper limit of 90 percent efficiency for single wavelength conversion at only a one-tenth the cost of conventional solar cells.

The theory of rectennas is not new, but was discovered more than 50 years ago. However, so far, technology was not advanced enough to fabricate them. According to Professor Baratunda Cola, with currently available technology, it is now possible to make cheap solar-to-electricity converters from carbon nanotubes with ends turned into a special tunnel diode. Cola says the concept is well suited for mass production.

Rectennas are made by growing fields of vertical carbon nanotubes. Their length roughly matches the wavelength of the energy source – for solar radiation, it is one micron. An insulating dielectric such as aluminum oxide caps the carbon nanotubes on the tethered end of the bundles. On the dielectric grows a low-work function of metal – calcium/aluminum. This arrangement makes each nanotube a rectenna with a two electron-volt potential when collecting sunlight and converting it to direct current.

According to Cola, the process uses three steps. In the first step, they grow a large array of vertical nanotube bundles. Then one end of the tubes is coated with a dielectric, while a layer of metal is deposited. One end of the nanotubes changes to a super-fast metal-insulator-metal type of tunnel diode by this process. This method is eminently suitable for mass production, and up to ten times cheaper than making crystalline silicon cells.

With its metal-insulator-metal form, the structure resembles a capacitor with a rating of a few attofarads (1aF = 10-18F). Each nanotube bundle is only 10-20 microns in diameter and consequently, the area of the capacitor plates is so small that the electrical field concentration at the end of the nanotube is very high. With the low work function of the metal, the device behaves just as a tunnel diode does in the peta-hertz (1015 Hertz) region when excited by solar energy and emits electrons in bursts of femtoseconds (10-15 seconds).

Commercialization will require several trillions of nanotube bundles growing side-by-side. Once optimized for higher efficiency, this bunch of nanotube bundles could ramp the power output well into the megawatt range. According to Cola, increasing the efficiency can be achieved by lowering the contact resistance between the antenna and diode. The team expects to improve the efficiency up to 40 percent in only a few years.

Monitor Your Solar System with a Raspberry Pi

Most photovoltaic systems contain parts such as the solar modules (panels) to provide the electrical power, a battery charger for converting the panel output to the battery voltage, a battery pack to store energy during the day and provide it during the night time, an inverter to transform the battery voltage to the proper line voltage for operating home appliances and an line source selector to switch between the solar and grid power.

When the sun is shining during the daytime, the solar photovoltaic cells convert the sunlight falling on them into electricity. Although the efficiency of the conversion may be only about 17%, solar power can easily reach 1KW/m2 and suitable panels can produce 5000 Watts in these conditions.

Solar panels typically produce a high voltage, 120V DC being a common figure. The battery charger has to convert this to match the battery voltage, generally 48V DC. Solar light power charges the batteries continuously during the daytime; therefore, the charger has to keep tracking the maximum power point to optimize the yield of the system. As the charger has to charge the battery also, this device forms the most elaborate part of the system.

With the above arrangement, the solar panels charge the battery during the daytime and the battery discharges during the night. The size of the battery depends on one day of consumption plus some extra to tide over an overcast day. That also decides the size of the solar panel. Batteries are essentially heavy and the lead-acid types generally have a lifespan of about 7 years.

The batteries feed the inverter, which converts the 48V DC into the line voltage – usually 230V AC or 110V AC. With a 5KW continuous rating, inverters can essentially run almost all household appliances such as the clothes dryer, the washing machine, the dishwasher and the electric kitchen oven. When the inverter is supplying a large load, the battery current may climb up to 200A.

Multiple sensors measure the solar field power from and temperature of the solar modules divided into arrays. The information comes to a PV panel via a CAN bus, which unites all the sensors. The PV panel also acts like a gateway between the CAN bus and a single board computer.

The tiny, versatile single board computer, the Raspberry Pi or RBPi is suitable for gathering data from the PV panel and storing them in a database. On the RBPi is a web server connected to the home Ethernet network.

Another set of sensors monitor the battery voltage, current and temperature. These are also on CAN bus and the information collects on a PV battery monitor board. A Wi-Fi module on the board acts as a gateway between the CAN bus and the Ethernet.

The boards and modules of the monitoring subsystem do not provide any interface with the user, except for a few activity modules. The system is meant for being supervised and controlled remotely. This is possible with a Web User Interface or an Android application.

Long Lasting Solar Aqueous Flow Battery

Yiying Wu, Professor of chemistry and biochemistry at the Ohio State University, Ohio State, and his team has combined a solar cell and a battery to form a single device. A novel solar panel on top of the battery captures energy from sunlight. The battery is able to source 20% of its energy from sunlight. Although the design is pending a patent, the researchers have published their findings in the Journal of the American Chemical Society.

Tests conducted by the researchers show that their solar flow battery produces the same output as a lithium-iodine battery does, even when the solar flow battery had a lower charge. They charged and discharged both batteries 25 times. Each time, they discharged the batteries until the terminal voltage fell to 3.3 volts. Conventional lithium-iodine batteries have high energy densities, approximately twice that of lithium-ion batteries. Hence, lithium-iodine batteries have the potential to fulfill the needs of long-driving-ranged electric vehicles.

In the experiments, lithium-iodine batteries had to be charged up to 3.6 volts, before they could be discharged down to 3.3 volts. Comparatively, solar flow batteries produced the same energy output with a charge of only up to 2.9 volts, as the solar panel made up the difference in their terminal voltage. That represents an energy saving of nearly 20 percent.

The team has made two changes to their earlier design from 2014. The solar panel, which was a mesh earlier, is now a solid sheet. Additionally, they now use a water-based electrolyte within their battery. With water circulating within the battery, the team has assigned the new design to an emerging class called the aqueous flow batteries. Yiying Wu claims their solar battery with aqueous flow is the first of its kind.

The water-based solar battery is compatible with the current battery technology and is easy to maintain. The environmentally friendly technology can be very easily integrated with existing technology.

According to Wu, the design of the solar flow battery is adaptable and can be applied to grid-scale solar energy conversion and storage. In the future, electric vehicles might also benefit from the electrolytic fuels used in the solar flow batteries.

In the earlier design, Wu and his team had designed the solar panel with a titanium mesh, which passed air to the battery. The new design using water based electrolyte does not require air to function, and hence, the solar panel is now a solid sheet.

The solar panel has a red dye so that it can tune in to a specific range of wavelengths of solar light to capture and convert to electrons. The team calls their solar panel dye-sensitized and the electrons it produces serve to supplement the energy stored within the lithium-iodine battery.

The electrolyte within the battery helps to absorb the electrons produced by the solar panel. A typical electrolyte is actually part solvent and part salt. Earlier, the researchers had used the organic solvent dimethyl sulphoxide to dissolve the salt lithium perchlorate. They have now changed over to lithium iodide salt dissolved in water, as this is more eco-friendly and offers higher energy storage capacity at lower cost.

Solar Powered Drone Beams Internet

Certain regions of the Earth are presently out of the ambit of the Internet. Nearly 10% of the population or more than 4 billion people live so far from fiber optic cables or cell towers that they are unable to reach the Internet. Facebook is set to end this isolation by having a drone fly overhead while beaming Internet down to such areas.

At their Connectivity Lab, which is a division of Facebook’s, researchers confirm the completion of such a drone. This is the first step Facebook is taking before it builds a larger fleet. They have not yet flown the craft, but Facebook has already been testing their concept over the UK with versions one-tenth the size. They intend to conduct flight tests of the full-size drone before the end of this year.

Facebook will be using the solar-powered V-shaped carbon fiber craft, named Aquila or Eagle (in Latin), for beaming down wireless Internet connectivity to expand Internet access. About a year ago, Facebook launched Although their intentions were to provide Internet access to those in the world who do not have a reliable connection, the project has received a lot of dissension for not adhering to net neutrality – especially in India.

Facebook has designed and built Aquila in 14 months. The drone will fly in the air for 90 days without touchdown. To launch it up into the air initially, technicians will be attaching Helium balloons to the plane.

With a wingspan of 46 yards or 42 meters, Aquila has to move constantly to stay aloft. Therefore, it will circle a three-km or two-mile radius. During the day, when the craft can generate energy from the sun, it will float up to 90-thousand feet or 30 Km. However, the craft drifts down to 60-thousand feet or 20 Km at night for conserving energy. While not planning to sell the drones at present, Facebook intends to use them for expanding Internet access.

The research team has been able to increase the data capacity of the lasers involved in the project. This is one of the biggest breakthroughs as the new system can communicate at speeds of 10 GB per second using a ground-based laser to talk to the dome on the underbelly of the plane. This is about 10 times faster than the current capabilities allow.

Facebook is not alone in their endeavors to bring wireless Internet to rural regions. Rivals Google also have a program up their sleeve – Project Loon. They plan to put up high-altitude Helium balloons with transmitters attached. Although Google has not launched their project yet, they claim it is in a more advanced stage compared to where Aquila is at present.

Therefore, very soon, you may see a huge 900 lb. drone nearly the size of a Boeing 737, slowly circling 11 miles up in the sky. Currently, Facebook’s mission is mired in controversy. All over the world, critics are questioning several practices of Facebook’s on security, fairness and privacy grounds. There is a danger countries may spy on and repress their citizens. In addition, first-time users of the Internet might be limited to what Facebook provides them as news and information.

Butterfly Technology Boosts Solar Panel Output

We normally do not relate butterflies to solar panels. After all, bees and butterflies are good for pollinating flowers and transforming them to fruits so that nature can propagate. On the other hand, solar panels are human creations that collect energy from the sun for the use of humankind. The link between the two seems rather distant, apart from the fact that the sun is the basic force that drives all life on our planet. However, science finds the humble butterfly could be holding the key to unlock new techniques for making solar energy cheaper and more efficient.

Cabbage White butterflies need to heat up their flight muscles before they can take off. Researchers at the University of Exeter have observed that the butterflies adopt a specific posture to maximize solar heat capture. The butterflies position their wings in a V-shape, which, when the researchers adapted for their solar panels, increased the power-to-weight ratio of the panels by about 17 times, making them more efficient.

Scientific Reports, a leading scientific journal has published the research. The research team contained members from both the Centre for Ecology and Conservation and the Environment and Sustainability Institute, based at the University of Exeter in the Penryn Campus in Cornwall. According to Tapas Mallick, the lead author of the research, although bio mimicry is popular in engineering, such unparalleled multidisciplinary research is opening pathways for developing low cost solar panels.

Butterflies usually depend on the sun to heat up their flight muscles before they can take off. However, researchers found the Cabbage White butterflies taking flight before other butterflies did, even on cloudy days. The energy from the sun is limited on cloudy days, forcing insects to make maximum use of the available energy to heat up their flight muscles.

Researchers observed that Cabbage White butterflies adopted a v-shaped posture, known as reflectance basking. That allows the butterflies to maximize the concentration of solar energy onto their thorax, so necessary for fast heating up the flight muscles. The wings of the butterflies have a specific sub-structure that allows maximum light from the sun to be most efficiently reflected onto their muscles, which warm up to the optimal temperature as quickly as possible.

The scientists then investigated the process of replication of the butterfly wings for developing a new, lightweight reflective material solar energy products could use. They found that by replicating the simple monolayer of scale cells on the butterfly wings, they could optimize the power-to weight ration of solar concentrators. That made the solar cells lighter and more efficient.

The team also found the optimal angle at which the butterfly held its wings. When the butterflies tilted their wings by about 17 degrees to the body, they were able to increase the temperature of their bodies by 7.3°C more than when they held their wings flat. By positioning the reflectors at 17 degrees within the solar cells, researchers found the output from the solar cells increased by 50 times.

Therefore, by studying the manner in which the lowly butterfly maximized its use of solar energy, scientists could not only double the output of their solar cells. They were also able to improve its power-to-weight ratio significantly.