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Entropy and your choice of energy: A distilled principle of choosing the type of energy for a given application

© Ajay Phatak, Think2Transform, Pune, India

Today’s society uses around 600,000 times the energy in absolute terms compared to late Palaeolithic foragers (IEA, 2019a).  At worst this number is alarming to the hilt and at best suggests that we must look at how we can choose the right form of energy for a given application to reduce the need for high density energy like fossil energy. 

We, as a society are almost addicted to convenience provided by technology driven by energy.  We are happy to use a clothes dryer run on electricity rather than using the sunlight and wind do their jobs for example.  We like to use cars for moving even a few 100 meters and the examples are plentiful.  These addictions have given rise to crisis in health by creating pandemics of obesity and so-called lifestyle diseases.  These very diseases then act as co-morbidities for the much-feared COVID-19 style pandemic diseases.

We might ask a question, what does energy use have to do with these pandemics and if so, what can we do something about this situation?

The principle goes as follows:

Based on fundamental laws of thermodynamics, additional reference to some work by Nicholas Georgescu Rogen and the way we use energy today, I have tried to distil a useful principle in term of how we should be using energy in our day to day lives.   We will need to know some fundamentals and need some knowledge about the basic laws, which I will try and provide as part of this article. 

For a given application and the given context, choose the energy at the highest level of entropy. 

My hypothesis is – it is quite possible that just using this principle all the time by all the population will help cut the use of energy by an order of magnitude.  Some changes in our temporal behaviour – or Notion of urgency and convenience with respect to time, will go a long way in energy reduction of this order. 

Let me now try to explain this principle.  But before I go ahead and explain this, we might need to understand a few concepts in thermodynamics, which I will try and explain with some simple examples. 

Even while entropy as a term in physics and thermodynamics can get quite complex, here are a couple of examples which will introduce you to this concept.

Let us first look at enthalpy or the total heat content.  Total heat content can be written in form a simple equation —  

Heat content = Cp x mass x temperature

(where Cp is the heat capacity or amount of heat a particular material can store in its unit mass)

Given this, we can have same amount of energy available in various forms.  An equivalent for Electricity is also available. 

As an example – the total energy content of 1KWh or 1 unit of electricity is same as 43Kg of water at 20 deg Celsius.  We can easily see that 1 Unit of electricity can do much more useful work such as run a 1.5 HP pump for 1 hour (as an example) than 43 Kg of water at 20 deg C, in spite of both cases carrying the same amount of total energy content.  In this example electricity is at a lower entropy level than the 43 Kg  water at 20 deg C and therefore can do more useful work.  Generally, sources of energy at lower levels of entropy can do more useful work owing to what availability of ‘FREE’ energy.

Consider an application where we need to maintain a temperature of a particular medicine (say) at around 20 deg C for say couple of hours, where outside temperature is day 18 deg C.  We have choice of both forms of energy – using Electricity of using this bank of water.   It is quite easy to see that choosing this bank of water, (I am using this example at a risk of over simplification) rather than using the electricity to achieve the same.  And if we do so, we will lose far less energy available to do useful work.  We can keep our 1 KWh of electricity in tact for doing more useful work and use the water bath at 20 deg C do our current work.  We have made a choice of high entropy energy in this case and ‘saved’ some energy, which could be used for application, which indeed needs that form of energy – for example running a computer for a duration time – for later. 

Let us quickly look at energy forms at higher and lower levels of entropy.  Here is a quick reference table in the order of decreasing entropy.  The last in the list can do most amount of direct useful work.

  1. Sunlight / Solar insolation in as-is form
  2. Wind in as-is form
  3. Energy production by flora like biomass
  4. Wood
  5. Coal
  6. Crude Oil
  7. Electricity
  8. (Information)

This means you should prefer 1 over 2 or 3 over 6 as a form of energy for a given application if it does satisfy our need – many times without compromising on the outcome. 

Let us take an example of heating the house.  If you live in a geography providing plenty of sunlight, your house should first use this sunlight / solar insolation directly to find a way to heat.  Also important of course is ensuring measures that allow retaining this heat once captured like excellent insulation. If we cannot use this measure, start exploring the option down this list and pick the one which can provide you best possible way to heat the house.   E.g. dry Biomass can be used to insulate your house to improve the efficiency of heating.  If you can use wood or coal without compromising on sustained availability of such a resource and negative impacts on human health due to pollution, those could be good options before we go further down the list.

Another example if moving short distances of say 1 km in a locality where ambient temperature is conducive to moving around.  Best option might be to walk (assuming you have those 20 min to go back and forth) and then could be to cycle if we are limited by time – rather than use a motorised vehicle of any kind. (by the time you pull the car out of your parking spot – you might reach the destination on a bicycle e.g.)   There are 2 aspects to consider here.  The energy that has gone into producing the vehicles (apportioned for this distance) and the energy that is used in the process of movement.  The added benefit of better health just due to such walking or cycling practices is not even considered here. 

Or take an example of heating water!  What can be better than keeping the water in a tank and let is heat by direct heat from the Sun.  If you need water around the clock, you may want to consider solar water heating system.  This of course has a downside of the panel manufacturing footprint!  However, it will always be better than using electricity from coal fired power plan to heat water.

Generally, if we accept sufficient elapsed time for an outcome (slower the process), we are more likely to accept the higher entropy energy source.  You have a few hours to heat the water, do not do anything but keep this water in the Sun.  Need hot water now, use the electric geyser – which uses a very low entropy electrical energy.

Another example, very easy to understand is drying clothes – give this a few hours on the clothesline and we would have dry clothes in a suitable climate.  If we want these same clothes dry now in a few minutes, we will have to go in for a low entropy energy option – like the electric dryer.

To elaborate the principle further: If you can identify applications which do not have stringent time constraint to get to the final result – like dry clothes – the source of energy can very well be high entropy – like the heat or light directly from the Sun.  Many things that we do daily, if planned well, can happen with a high entropy energy source, saving the precious fossil energy and also reducing the CO2 burden at the same time. 

As a next step in this process, we must plan to list all that we do during the day and put these in the buckets of urgent to those can be planned properly and are ok if these take more time.  Then we explore whether the urgent list can be further optimised to keep minimum number in.  Once done we start with available sources of energy and look at how various outcomes could be obtained with highest possible level of entropy.  To provide you a reference here is a list from highest to lowest levels of entropy once again.  We should go top down and choose the uppermost feasible form of energy. I have repeated the list for the sake of convenience below:

  • Sunlight in as is form – directly from the Sun
  • Wind in as is form
  • Produce from plants (Biomethane, Vegetable oil, Bio diesel) – This option is typically useful on a smaller scale.
  • Wood
  • Coal
  • Crude Oil
  • Electricity

This strategy is a potent way to manage transition to sustainable use of energy.  This will help us to substantially reduce our need for high density energy, which will continue to remain a scarce resource, even when we consider derived low entropy energy from solar electricity. This (solar electricity) requires high density energy to make the panels to convert the high entropy solar radiation to low entropy electricity for our use.

Another highly desirable side effect of this energy use strategy is substantially reduced pollution.  Any low entropy energy use is cause of accelerated increase in waste heat and associated pollution.  To sum this up, immediate steps we can pragmatically take to plan how we make use of available energy in various forms to achieve our end objectives in available time.  This means the application of my distilled principle of how form energy should be selected for a desired application and outcome.

Stick the form of energy with highest possible entropy level for every possible opportunity.

Ajay Phatak is a Trustee and Faculty at the Ecological Society. He advices early stage companies in the spaces of Healthcare, Environment on strategy and writes on subjects of energy, sustainability and circular economy.

5 Responses to “Entropy and your choice of energy: A distilled principle of choosing the type of energy for a given application”

  1. Very good article with lots of example in day today life which can use High Entropy energy sources !

  2. Good that you liked the article. Will keep posting more in coming time.

  3. Beautifully explained!

  4. Very nice article. It is showing easy way to make choice of type of energy source.

  5. Great article sir. It would be interesting to apply this methodology for the first case study we did on a day in the life of a regular modern urban family.


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