Solar Trees
While renewable energy is beneficial to the environment, it comes with its own problems. You need large tracts of land to generate significant power, and these areas can be far from places that would use the energy. Storing energy for long periods of time can be hazardous, while transporting it long distances can get expensive and cause more pollution. Using solar trees, a combination of synthetic trees (which absorb CO2 from the atmosphere) and solar panels, may help solve these problems. Similar to artificial tree cell towers, they would blend in with normal trees in places like parks or near roads. The trunk would be the synthetic tree portion, supporting the “branches” which will be coated in photovoltaic paint to generate solar power. These aesthetically pleasing alternatives to large solar grids can have outlets to let anyone charge their devices with clean free energy, or be used to provide energy to nearby buildings. You can ideally plant solar trees wherever there are trees, so they could be used in most of the world. The ability to place these power sources close to buildings and people would lessen the need for long distance travel by trucks or ships. Acting as synthetic trees, they would also absorb CO2 from the atmosphere wherever they are planted, cleaning the air slightly. These solar trees can get renewable energy to companies and people in many places. Providing many people with clean energy is a good first step to mitigating carbon dioxide in the atmosphere.
Arturo Gutierrez
Postdoctoral Appointee
This is a great idea for removing CO2 emissions from the air! A couple of questions for you.
1. Seems like the amount of CO2 capture would be dependent on the amount of wind being produced. Any thoughts on how you might overcome inefficiencies dependent on this?
2. Directed at the photovoltaics: At 10 % efficient, do you have a sense of how much energy would be converted per day by one tree? Would it be enough to charge a phone, car, etc.?
Kashif Rahman
1) The best way to make sure that there are no diminishing returns is to build our solar trees in areas with a lot of wind. The US has its highest average wind speeds in the Plains and Midwest, as well as in large cities throughout the country such as New York City, Chicago, or Cambridge, MA. These areas have average wind speeds of over 10 mph, and often get constant winds almost throughout the entire year. It will be in places like these that the trees will be the most useful. There is very little that can be done about places that have little to no wind. We could have a fan or device to draw in air, but that will add to the already hefty cost. Also, a fan might make obnoxious noises that go against our aesthetic design and image. Trees don’t make much noise, so we want to keep the amount of moving parts to an absolute minimum, or have none at all. One other possible alternative is to make the grills bigger to get more air through it over time, but that may not make a difference in places that simply are not windy.
2) This is also a case of location. Some places have better weather, or longer and brighter days. Generally speaking, our tree will have paint all over the multiple branches, to make sure there is always sunlight hitting it and to maximize our surface area. There is very little on the exact amount of power this paint can produce and there is no set size on our tree. Erring on the side of caution, each tree would be able to provide at least a consistent 80 to 150 watts of power over the course of a day. This number is taken by dividing what a typical small household roof covered in paint would make at 5% efficiency by two to get what seems appropriate for the amount of surface area our tree would take up. Now this is enough to charge your devices, and power small appliances or lights. To put it into perspective, one tree would need several weeks to generate enough power to take an electric car 100 miles. That seems negligible right now, but there are groups working to make paint that could be up to 30% efficient. Furthermore, it is hard to tell exactly how much surface area that the paint would use due to the shape of the branches, so an accurate number would be hard to find without a full design plan for one of these trees.
In conclusion, while they will definitely work anywhere to an extent, location is everything for getting the maximum value out of these solar trees. In time, as the parts of our tree get more advanced, it may get more feasible to have them everywhere. If you have any more questions or need clarification, please let us know.
Nathan Tompkins
Assistant Director of Research and Education
I really like your idea to have “art” installations in the park that clean the air and generate electricity while simultaneously appearing natural and aesthetically pleasing. I have two questions:
1) Have you considered how the CO2 is extracted from the tree? You mentioned a gentle stream of water, but is this some sort of automatic system or does a work crew come in to extract the CO2 manually?
2) Do you have an idea how often the CO2 would need to be extracted from the tree? You mentioned that each tree extract one ton of CO2 per day, but how much CO2 can each tree store before it becomes saturated and stops collecting?
Kashif Rahman
Currently, the grill has a filter inside of it that holds the carbon dioxide, which will need to be replaced once it has reached capacity. The old filter would need to be taken into some sort of processing facility to remove the carbon dioxide, which can be transported elsewhere for commercial use or stored away safely. Each filter can be reused after drying. This job should be able to be done by a work crew, although there would have to also be a place to store and process the CO2.
We could not find anything on the maximum capacity of these artificial trees, only that they could remove several thousand times the CO2 a normal tree can. Hopefully this will not be an issue, but it is not something we can address at this point. The ones currently in consideration are very large, and our trees would be at least 2 times smaller, so capacity could be an issue in the long run. One possible solution is that these trees would be in very accessible places in towns and cities, as we want to place these in communities and near people. The close proximity to roads and buildings will make replacement much easier as it would take little time to reach these trees with any equipment that is needed.
While we could not answer your question about capacity, if you need clarification for any other part of our answer or have any other questions, feel free to ask.
Daniel Jones
Teacher (retired)
This is a very interesting idea, and I think a lot of people would find it inspirational to visit a cluster of your “solar trees” on the south edge of some busy urban park where they can sit down and charge up a device…maybe even a car. But, we live in a world where we don’t always stay on top of things after they get built. You mention a regular maintenance crew, and I’d like to know more about what they would have to do and what ideas you might have for minimizing constant upkeep requirements.
Kashif Rahman
The regular maintenance crew would have two jobs. The first job is replacing the filter in the grill.
The filter is what holds the sodium carbonate and traps the carbon dioxide. The second job is processing the filter. It needs to be rinsed in water to release the CO2 as a bicarbonate(baking soda). This baking soda will need to be packaged and then sent out to either be stored safely or used commercially.
We don’t have any developed ideas on a specific size or design on a tree, plus we couldn’t find a specific capacity of the CO2 component. Without these, we can’t estimate how often maintenance occurs or how much it may cost. Despite this, we do have a few ideas on how to minimize cost and effort:
1) We want these to be in cities and towns. Because of this, the equipment and facilities needed can be a short drive away in the city, cutting travel time to get filters around or to get to the tree itself. This convenience will make it easier to do maintenance, and lower the cost of transportation.
2) The filters are reusable once the CO2 is washed off and the filter is dry, so a lot of money does not have to be spent on new filters.
3) Since water is the primary agent for cleaning these filters, we don’t anticipate the cleaning process to be very intensive or expensive.
Sorry for the lack of specific numbers on how often maintenance occurs or how much effort it needs. If you have any more questions, please ask.
Stephanie Luff
Graduate Research Assistant
I love how your solution addresses multiple concerns—capturing CO2 emissions, generating green energy, and improving the aesthetics of current technologies.
You say currently photovoltaic paint gets 10% efficiency, but you hope for 20-30% in the future. How does this compare to our best solar panels currently. If other solar panels are better, how can you incorporate their technologies into the PV paint?
Kashif Rahman
When it comes to solar panels, the main issue is efficiency vs. cost. Most commercial products now are about 15% efficient. The PV paint with a similar efficiency is less costly. The more efficient versions can be up to 44% efficient or more, but are not cost effective compared to the lesser versions. The same goes for PV paint, but the paint is much cheaper to make than solar panels. Hopefully, the paint will be cheaper than solar panels at the same efficiency.
One major technique that is used is multijunctioning solar panels, or having layers to absorb different wavelengths of light to maximize the amount of light a panel can get. This addition is already under development and will push the paint to an estimated 40% efficiency. Like in solar panels, there is a chance that this will cause the paint to be really expensive, so the change may not be worth it. The output of the paint may pay for itself, but we don’t really know if that would happen.
Thank you for viewing our project and giving us your feedback.