There has been a lot of discussion on the web on choosing between solar PV systems or trees in order to reduce one’s carbon emissions. Even beyond comparison to solar systems, quantifying the value of a tree has been coming up consistently nowadays. Very recently, the Supreme Court of India pulled authorization for some projects in West Bengal which involve trees being axed.
In this post I would like to share my thoughts on this with you. For simplicity, by emissions I am only referring to greenhouse gas emissions.
I hope this will simplify decision making and help you take action in case you are sitting on the fence or maybe advising someone else.
One clarification, before we get deeper. Rather than getting into an academic discussion on which one is better, this post is more about taking impactful action.
It is common knowledge that power generation will continue to be a leading source of greenhouse gas emissions. Add to this the fact that globally we are also aiming to electrify a large part of our transportation system in the medium to long run. As long as we continue to emit carbon dioxide and other greenhouse gases at the scale at which we are emitting them, solar panels do have a mathematical edge over trees.
This is in spite of the fact that in the overall scheme of things, solar panels ‘only’ help reduce carbon emissions in comparison to other fossil options for power generation. The trees, on the other hand, are a carbon sink and actually store the emissions during their lifetime, thereby removing it from the atmosphere.
Carbon Emissions Math
Let’s try some quick calculations to establish some reference for comparison.
In India, a small 1 kilowatt (kW) rooftop solar system would generate approximately 1200 units of electricity in a year. As per the CO2 Baseline Database for the Indian Power Sector (CEA), the emissions from grid electricity were about 820 g CO2 equivalent per kWh during 2016-17. The life cycle carbon emissions from solar panels were estimated to be less than 50 g CO2 eq. per kWh by the National Renewable Energy Laboratory in 2012.
Based on these estimates, our tiny 1 kW rooftop system would reduce carbon emissions by 1200*(820-50)/1000 = 924 kg CO2 eq. per year if it is used to replace grid electricity in India. A typical hardwood tree would capture about 22 kg of CO2 per year.
Thus by using a 1 kW capacity rooftop solar system to replace fossil power generation, one could offset carbon emissions equivalent to about 40 trees. Carrying out detailed calculations would definitely give more precise numbers, but for ballpark purposes this should be good enough.
But How Much Land Would This Require?
Now, let’s look at another set of numbers.
The annual CO2 emissions in tons per capita in India was about 1.6 back in 2014. For reference, the equivalent numbers are 16.5 in the US and 7.5 in China. Based on this, an average Indian would need to plant 340 trees in their lifetime to be carbon neutral. For a family of four, this would amount to 1360 trees.
Assuming 9 square meters for every tree, in terms of space this would require 1.2 hectares.
If, however, the same family chose to use a solar system to offset their emissions, they would need to install a (1360/40 =) 35 kW capacity solar plant. In India, this would require about (35 kW * 9 square meters per kW =) 315 square meters of space. Which is 0.03 hectares.
This monumental difference between the space requirement of the two alternatives is a sad quantification of the way we have been “progressing” as humanity.
Our comforting lifestyles have become so unsustainable that trees by themselves would find it difficult to bear the brunt of all our emissions. Interestingly, a paper published in Science estimated that in order to store an equivalent of 25% of the current atmospheric carbon pool, we would need to increase the forest cover across the planet by more than 25%.
Green Activism & The Mainstream Media
In this post I have only been talking about solar power and comparing its effect on carbon emissions with trees, but by no stretch of imagination is solar the only option.
If our goal is to reduce carbon emissions, energy efficiency and public transportation (among other options) would all have similar high level impacts.
Mostly when we read or hear about “green activists” in the mainstream media, we tend to assume that the opposing parties are the evil ones. But I would like to highlight a specific event in which so-called green activism or action has actually been a hindrance to climate goals. I am pretty sure you can find similar cases in other places.
Some time back, protests in Aarey Colony of Mumbai led to stalling of the work on Mumbai metro project. One of the project sites required the felling of 2100 to 2500 trees, and the mainstream media presented this as a battle between passionate green warriors and mindless profit oriented agencies.
The Mumbai Metro 3 project has been registered with UNFCCC under its MRTS Programme of Activities (PoA)- 9863. Based on the data available on its website, the metro project would help reduce 261,968 metric tonnes CO2 equivalent per annum. Based on our estimate for a grown tree we used earlier, even if we assume that 2500 trees had to be axed, they would have only avoided about 55 tonnes CO2 equivalent every year.
As far as emissions logic is concerned, the decision is simple. The metro project would reduce carbon emissions and local pollution by a quantum FAR more than the trees by themselves could.
There have been similar ironic reporting of important road projects getting delayed by “environmental” agencies on the pretext of reducing pollution even though completion of these projects would provide much more impact for that very goal.
Activism is important to highlight gross negligence, but only shouting will eventually (it already has to quite an extent) lead to common citizens turning a deaf ear to important environmental issues. Some meaningful action has to follow through.
With the cost effectiveness of rooftop solar systems improving rapidly over the last decade, it is even more important for developing economies to ensure that they get their foundations right and avoid the mistakes others have made. Since their power demand is still on the rise, it makes a lot of sense to integrate environmentally sound systems within their infrastructure.
What About Our Roofs?
Talking about meaningful action, thankfully we have enough space in our habitat that we don’t ACTUALLY need to choose between trees or solar panels. If one considers spaces like rooftops, it is quite plausible that they are more suitable for installing solar panels versus trees.
Also, based on the simple estimations we used above, installing and using even a small 1 kW rooftop solar system would create an impact equivalent to 40 trees.
We have to realize that the progress and the lifestyles which we have gotten accustomed to over the past 150 years can not simply be done away with by installing a single tree or maybe a few (per individual effort, that is).
If you are environmentally conscious, I hope this comparison would probably help you in creating awareness about solar panels or maybe installing some in your own campus.
Planting trees is noble and really important for an infinite number of reasons. Especially to ensure that our future generations do not lose their connection with nature. But please don’t stop there. Installing solar panels on rooftops is prudent.
Even a small 1 kW rooftop solar system will reduce your electricity bills, probably give you some tax rebates/subsidies and hey, you can count it as 40 trees! That is quite a deal.