Electricity From Rainwater Harvesting

Rainwater harvesting is commonly known as source to give a very cheap water to household/industries as well as to replenish falling water table. However, have we thought that it be source of a non-conventional energy just like solar energy is? Can you start your venture out of it?

Rainwater Harvesting


As per Wikipedia, Rainwater harvesting is the accumulation and deposition of rainwater for reuse before it reaches the aquifer. In this technique, we channel the water falling on roof tops of buildings and homes, and open spaces to a storage tank through a filter. Excess water is directed to a well or pit through which water seeps in earth to increase water table.

Law and results

Many countries have a law to have ground water harvesting as one of the environmental clearance requirement. India too has its policies and laws for Rainwater harvesting

Rainwater harvesting has brought some very good results in conservation of environment such as ground water repletion, reduction in salinity of water, reduced demand of water by residents and industries, reduction of run-off water to dams etc.

How much water can be saved?

  • Let’s take example of Delhi city with an area of 1,484 sq km or 1,484,000,000 sq m.
  • Let’s consider that only 10% of area of Delhi can be occupied by buildings and houses that may have rainwater harvesting.
  • Let’s assume that only 10% of buildings are following norm to have rainwater harvesting implemented.
  • Area available for rainwater harvesting [A] = 1,484,000,000 * 10% * 10% = 14,840,000 sq m
  • Drainage Area for harvesting (average of 0.9 on a steep pitched roof and 0.4 on a flat roof with gravel) [DA]= 0.65
  • Filter efficiency [FE] = 0.9
  • Annual Rainfall [AR] = 617 mm (Reference Average annual rainfall of the states of India)
  • Amount of water collected in a year in L = A * DA * FE * AR = 14,840,000 * 0.65 * 0.9 * 617 = 5,356,423,800 L

Reference: Rain harvesting by yougen.co.uk

Generating Electricity

Many of the rainwater accumulation is done over the rooftops. In urban areas, a resident is allowed to develop one’s own structure upto a maximum height of 15 m and in apartments/commercial buildings the limit is much higher with sky scrapper going beyond 10 stories (40 m). If we consider that rainwater is accumulated at an average height of 10 m and then brought down to filter and accumulator then we may place a generator between an accumulator to a collector.Rainwater Harvesting Generating Electricity

Let’s make a calculation for Delhi.

  • Amount of water collected in a year = 5,356,423,800 L
  • Mass of water collected (m) = 5,356,423,800 kg
  • Value of g = 9.8 m/s2
  • Height of fall (h) = 10 m
  • Potential Energy of Water PE = m*g*h = 5,356,423,800 * 9.8 * 10 = 524,930,000,000 Joules = 145,813.8 kWh (Units of Energy)

If we consider an efficiency of 90% for the generator then 131,232 kWh (units) of electricity can be produced.

If we consider that an average household in Delhi consumes about 60 units per month then this energy can power approximately 200 homes for an year. It is to be noted that we have considered only 10% of potential buildings complying to rainwater harvesting and this number can potentially go up to 2000 homes per year in Delhi.

One of the Youtube video that shows such a System in action

[youtube http://www.youtube.com/watch?v=pp475yj7vvs]

Your Venture

  1. Create the complete Electricity Generation and Storage System that can fit between accumulator and storage tank/filter. This System can feed the electricity to grid or the energy can be consumed for the producer.
  2. The System has to be cost effective for consumers to buy that System.
  3. Convince Government to give subsidy to users of this System.


I see a fairly good potential of this System making a profitable venture. On top of it, one will be portrayed as a hero in energy conservation. Will you start this venture? If yes, go ahead and share your story. If no then keep tuned for next venture idea. Let the rain shower you with prosperity.


  1. Randym Jones December 19, 2013 7:20 am  Reply

    The amount of electricity generated could be *significantly* increased by passing the water through a *spiral* of multiple stators rather than attempting to capture water-force energy only a *single* time. This is because the *weight* of the water — rather than its moving force — is the important variable. Spiraling the water through a *series* of slightly-inclined-from-the-horizontal water-wheels — rather than a *single* vertical overshoot one — enables you to get multiple electricity-generating uses from a stream, rather than only one. Furthermore, a reservoir system that collects the water at the top into a container of known capacity so that the system waits until it has a sufficient amount to start the process enables you to collect energy from a rain-event of *any* size (because of a large collection area), rather than having to wait until a *minimum* amount of rainfall occurs to start the process.

  2. Himanshu Bansal December 22, 2013 9:14 am  Reply

    Dear Randym, this is a very nice idea. I did not think that we could utilize the force that a tsunami supposedly uses to cause destruction. Using weight of water can significantly improve the throughput. Furthermore, collecting the water until a known capacity threshold is reached is a good idea. Thank you for this wonderful comment. Can you share with our readers, if you have created any working model on this idea?

  3. Praveen July 3, 2016 4:28 pm  Reply

    Dear Himanshu, how to get in touch with you

  4. Cherryn Bijoy August 11, 2016 11:29 pm  Reply

    I was thinking of the as!e idea. If people and government work together for this then this could become a reality and India could save power.

  5. ARi June 29, 2017 7:56 pm  Reply

    It doesnt work out . If you calculate for one single 10 m bldg with 100 sqm area and 80 cm yearly rainfall… the electricity produced is less than 3 KWh yearly.

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