This is in a way continuation and almost repetition of the previous post where I have written about the "Sustenance Roof".

Last week I was invited to give a talk on my experiments with "Sustenance Roof" at the International Workshop cum Training on “Green Growth Strategies for Climate Resilience and DRR: Policies, Pathways, and Tools” Organized by the National Institute of Disaster Management (New Delhi) and the Institute for Social and Economic charge (Bangalore). The content of the talk is reproduced here with a few minor changes to suit the textual format.

INTRODUCTION :

As Population increase, demands on finite water resources and energy services threaten to push the limits of what our environment can sustain. Another compelling reason to give cognizance to the water-energy nexus is climate change, which will result in significant alterations to precipitation patterns, with all that implies altered water availability and the power derived from water.

United Nations Water asserts in the World Water Development Report 2014,” Water, Energy, and food are inextricably linked…. The global community is well aware of food, energy, and water challenges, but has so far addressed them in isolation,”.
There are many synergies and trade-offs between water and energy use and food production. Here are some examples from the report;

Using water to irrigate crops can promote food production but it also reduces river flows and hydropower potential.
Diverting more water for irrigation compromises water for domestic and industrial needs.
Growing bioenergy crops under irrigated agriculture can increase overall water withdrawals and jeopardize food security.
Converting surface irrigation into high-efficiency pressurized irrigation may save water but may result in higher energy use.

Recognizing these synergies and balancing these trade-offs is central to jointly ensuring water, energy and food security.

The world Business Council for Sustainable Development (WBCSD) notes on its portal,” There is an intrinsic link between the challenge we face to ensure water security and other global issues, most notably climate change and the need to sustainably manage the world’s rapidly growing demand for energy and food.

Humanity needs to feed more people with less water, in the context of Climate Change and growing energy demand, while maintaining healthy ecosystems. ”
The FAO outlines the global challenge posed by the nexus

The situation is expected to be exacerbated in the near future as 60% more food will need to be produced in order to feed the world population in 2050.
Global energy consumption is projected to grow by up to 50% by 2035
Total global water withdrawals for irrigation is projected to increase by 20 to 25% by 2050 (Maybe much more, emphasis added).

NEED TO BREAK THIS NEXUS:

Having acknowledged this nexus and almost linear inter-dependency, the need of the hour now is to cut this dependence as much as possible. We no longer can look at water or energy or nutrition in isolation. We need to innovate hybrid solutions that address this nexus and make each of them independent from the other to the extent possible. This hybrid model will be one of the ways to achieve sustainability in the long term.

EXPERIMENT WITH DECENTRALIZATION:

Keeping this nexus in mind and with the overall framework of sustainability, I have been experimenting with a decentralized model. This model, in my opinion, reduces the degree of this nexus to a large extent.

This experiment is limited to the basic needs of food, energy, and water. This is an ongoing experiment with many changes likely to take place depending on the results and observations made.

One of the ways of achieving this sustainability at a very local and decentralized level is to produce most of your essentials rather than buying them. This way you have more control over the quantity and quality of the inputs used and outputs produced and their respective environmental footprint.

Also, the energy and water footprint associated with logistics is reduced to a large extent.

I have been experimenting with the above over a course of time in my home.

I have been working on a model where my roof meets most of my water, food, and energy needs. In my opinion, this is as de-centralized as it can get. I call it the "Sustenance roof". Though I have not been entirely successful I have made some headway into this.

Below are my observations from the experiment so far.

WATER:

I have a roof area of about 105 SqM, considering Bangalore’s rainfall of 970 mm, I get about 970.00 x 0.85 (15% Loss) x 105.00 = 86,672 say 86,500 liters of water per year.
As a family of 3 plus a significant floating population and a decent rooftop garden (About 300 plants), our daily water consumption is about 430 liters.
With a rainfall of 86,500 liters, this translates to (86,500/430)= 201 say 200 days of water requirement or about 54%.
More importantly, we put a portion of this water collected into the aquifer through a recharge well. Through this recharge well, the soil around the well got saturated in one year and now the well is yielding water which can, in turn, be used for irrigating the rooftop garden. Over the course of the next two years, with the water level in the Recharge well raising, it will be possible to meet the total water demand by the recharge well itself (Which was fed by the rainwater).

Recharge Well:

Impact on the Nexus (Water):

1. The water which falls on the roof is directly used or recharged. Therefore the embodied energy is not converted to any form.

2. There is no energy used in the treatment of this water.

3. The water which fills the aquifer is withdrawn using solar power.

4. Energy footprint of this water is "0".

5. The water path, that is the distance the water has traveled from reception to consumption in this case is (7+3+3+7 = 20 M). This is perhaps the least distance the water can take before put into effective use.

6. With the underground aquifer getting recharged over a course of time, we may not need any water from the grid. This will complete the cycle. Thus, we replenish the quantity of water and increase its quality too.

7. Since the water run-off outside the building is almost 0, this serves as a good way to reduce urban flooding (And its cost and energy involved in flood mitigation).

8. When it comes to financial sustainability, Rainwater falling on one's roof or in one's aquifer is the cheapest source of water. Since there is no cost (and energy) involved in the treatment and supply of water, rainwater will be the cheapest source of water. The video below puts things in perspective.

ENERGY:

1. With a family of 3 plus a floating population, our daily requirement is about 5 units of energy (Electricity) including cooking.

2. We have the following to meet this demand

A 3KW Rooftop solar PV system. It is also an Agri-voltaic system using the space below the solar panel for growing vegetables.

A 150 Liter Rooftop solar water heater.
A 2 Liter Solar Cooker.

3. Our solar PV power system produces an average of 12 units per day that is more than double our requirement. So, we end up selling about 50% of the energy that we produce.

4. The Solar Cooker works well for good 220 to 250 days a year. Almost every day in summer we use our solar cooker for cooking our vegetables, rice, and dal.

5. Since the cost of energy from the solar PV system is much lesser than LPG, we have switched to electrical cooking or induction plate for cooking (When we do not use solar cooker). So, our LPG is mostly for emergency purposes.

5. Since the solar thermal line is also connected to the kitchen, water used for cooking is preheated to a certain extent. This reduces the heating load of the induction stove or LPG

6. We plan to install a biogas unit to completely eliminate LPG.

7. Heat seal white paint on the roof keeps the house cool. After adding few more plants on the roof directly above the bedroom, we have eliminated the need for AC in the bedrooms.

SOLAR ROOF.

PhotoVoltaic System

Solar Cooking

HEAT SEAL PAINT FOR COOL ROOF.

Impact on the Nexus (Energy):

1. Rooftop solar is the least polluting source of energy currently.
2. Research suggests that the EPBT or energy payback period for rooftop solar is about 1.4 years.
3. Since the energy generator sits on the rooftop, no agricultural land or real estate was used for energy production. The tranmission of generated energy is not more than 5.0 M.
4. The water footprint is recovered within 1.4 years or lesser.
5. There is hardly any thermal losses in the rooftop thermal system.
6. The T and D losses in rooftop PV system is nil or near negligible.
7. The Rooftop solar system generates energy to lift the harvested rainwater from the recharge well or the sump thus reducing the embodied energy in water.
8. Excess energy is pushed back into the utility grid which gets consumed in the neighborhood thus reducing losses in the grid as well as its related water, energy and carbon footprint.
9. The Space below the solar panels is used for growing vegetables thus reducing the space footprint for food production.
10. White roof keeps the roof cool as well as increases the rainwater run-off.
11. White roof reduces the energy footprint for cooling the home during summers.
12. White roof add albedo effect for the solar PV system
13. White roof give the extra light for the plants on the roof by increasing albedo. (This is beneficial for the plants for photosynthesis process) .
14. The energy generated here is almost independent of any water footprint since the electricity production process does not consume any water.

FOOD:
We are far from self-sufficiency in so far as nutrition is concerned. We have tried growing ragi and rice on the roof without much success. However, the following experiments have been fruitful.
1. The rooftop garden gives us enough leafy greens once in two days.

2. About 10 to 12 days of vegetable requirements like brinjal, ladies finger, tomato, beans, etc are currently harvested from the garden.

3. Papaya tree which is very easy to grow gives us an average of one large fruit every four days. Two papaya trees can theoretically feed a family.

4. An added advantage of a rooftop garden is that you have full control over the inputs to the plants and are absolutely sure what you are harvesting.

5. One is also consuming fresh and pesticide-free vegetables. This also eliminates the water and energy footprint of pesticides.

7. The leaf composters and kitchen composters complete the nutrition cycle and the so-called waste get back into the garden.
ROOFTOP FARM.
Impact on the Nexus (Food):

1. The Photo-voltaic system is combined with the vegetable garden. This is called the “Agro-PV” system.

2. No real-estate space is taken up for the vegetable garden.

3. Most of the inputs for the garden (Manure) are produced from the kitchen and garden waste.

4. The harvested rainwater and the shallow aquifer water are used for irrigating the garden.

5. There is no energy footprint embodied in the water that is used for irrigation.

6. The vegetables and fruits grown on the roof have no logistics involved. Therefore, no carbon and energy/water footprint in the logistics.

7. One is also consuming fresh and pesticide-free vegetables. This also eliminates the water and energy footprint of pesticides.

WASTE:
1. All the kitchen waste goes to our kitchen composter.

2. All the garden waste goes to our leaf composter.

Both the kitchen waste and garden waste is converted into beautiful rich compost which gets into our little garden. Thus the nutrient cycle is completed.

CONCLUSIONS:
This is an everlasting experiment with many things to learn, unlearn, re-learn and change. However, there are few key conclusions;

1. It is possible to decentralize for water, food and energy to the level of a roof for every household.

2. Most of the water, energy and food requirements can be met from one’s roof.

3. More the decentralization, lesser will be the degree of the nexus between Food-Water and Energy.

All of the above are baby steps. We as individuals, as a society and as a nation have a long way to go. As mentioned earlier, sustainability is now more relevant than any other time in the history of mankind. COVID pandemic has given us an opportunity to relook at our paradigm of living and developing. It will be prudent to introspect and mend our ways before it is too late.

From My Desk

Wednesday, December 2, 2020

Experiment to Break The WATER-ENERGY-FOOD Nexus