The basic renewable energy source is the sun, which radiation can be used directly or indirectly through hydro power, wind turbine or biomass. According to the World energy Coucil, the total amount of solar energy falling annually on the earth surface is 1,059 E15 MWh, while, according to OCDE,  the annual primary energy use of the mankind is 15 E10 MWh. The total solar energy potential is then about 7'000 times the human actual use. Of course, we cannot use the total potential, buit there is a good margin. In addition, the geothermal energy, i.e the heat generated in the earth core by natural radioactivity, could also be used. Its potential is about 30 TW or, annually, 2.63 E 11 MWh. This also cannot be exploited totally, and estimates of the electricity generating potential of geothermal energy vary from 35 to 2000 GW depending on the scale of investments or, annually, between 3 E8 and 178 E8 MWh.

There are many potential pitfalls in calling something sustainable and even renewable, which in effect can cause harm to environment.

By strict definition, the most (or  ‘truly’) renewable energy is that that comes from sun and wind.

While the European Union, for example, has announced that it will strive to use 20% more renewable energy by 2020, its main source of these renewables seems to be biofuel. The organic matter that makes up that makes up plants is known as biomass. Biomass is derived from organic material such as trees, plants, and agricultural and urban waste. It can be used for heating, electricity generation, and transport fuels, and is currently widely used in the EU (http://ec.europa.eu/energy/en/topics/renewable-energy/biomass). Biomass is used to generate bioenergy or biofuels and produce electricity, transportation fuels, or chemicals.

However, there are severe side-effects.

All types of bio-generated energy involve burning of plant or algae matter and often times actually destruction of pristine habitats for planting ‘fuel forests’, as well as competing with agricultural land for production of food. Agricultural crops or plantations used for biofuel production that have taken increasingly larger proportion of originally biologically diverse land. Another source of biomass energy, mixed waste incineration, often referred to as “Waste to Energy,” “energy recovery,” “thermal treatment” or simply burning of garbage, is presently widely used within the European Union.

Burning garbage to generate energy, may seem ‘green’, but it is only one step removed from the cradle–to- grave model in which valuable materials are lost (see the authors of Cradle to Cradle, McDonough and Braungart 2002). In reality, “Waste to Energy” contributes to environmental degradation and climate change at levels far beyond the short-term benefits gained from producing secondary fuel. “Waste to Energy” is literally wasting valuable resources by exacerbating raw material shortages and intensifying the loss of CO2-capturing topsoil. It also prevents effective recycling solutions due to competition for high-caloric recyclable content (Braungart 2013).

@Thanks Helen

I largely agree with your comments.

Hence I am interested in an estimate of real renewable energy. With the eception of geothermal energy, I believe every other [today available] renewable source of energy comes [directly or indirectly] from the sun. 

So it would seem that the amount of solar energy received by the earth, minus some efficiency conversion coeficient would be the maximum value. To this we should discount at least land preserved for other forms of biodiversity [30%...].

Can we get anywhere with this calculation? Has anybody make an estimate like this arriving to any figure total MWh/year [or TOE/year]?

http://en.wikipedia.org/wiki/Solar_energy

I think the estimate there is quite good 

There were estimates published some years go that if an area the size (and location) of the Sahara were covered in solar panels it would provide enough energy to power the world's energy demand. See http://cleantechnica.com/2011/12/14/solar-energy-from-the-sahara-desert-could-power-the-world-but-will-it/

Pretty interesting article [@Johannes] and quite interesting proposal [@John].

It seems clear than the Earth receives from the sun much more energy that humanity uses, but .. how much of such energy is required by the Earth to perform as it currently does? If we cover the Sahara with panels... will not Sahara climate change? will it not later affect Global Climate?.

Sun energy is used in many ways for maintaining the earth in its current state [by evaporating water, by creating winds, by allowing plants and forests to grow, by creating local climate and allowing surface temperatures that enable life,...] , so .. how much can we appropiate without causing more damage than we avoid? [i.e., how much of such energy use can we consider to be sustainable?]

Buenos días Ricardo

nosotros estamos trabajando en el desarrollo de la economía de la energía renovable, y centramos parte de nuestra atención en el consumo relativo a las economías domésticas. Es eso lo que precisas?

Gracias

Ricardo, Moriarity & Honnery's work is very relevant to your question and well worth considering. I'd recommend these two articles as a starting point: http://dx.doi.org/10.1016/j.enpol.2011.02.044 and http://dx.doi.org/10.1016/j.rser.2011.07.151.

Miller, Gans & Kleidon have made important methodological contributions to this area, specifically in relation to wind, by clarifying how this is ultimately limited by the proportion of overall insolation that goes to driving atmospheric circulation. See: http://dx.doi.org/10.5194/esd-2-201-2011; http://dx.doi.org/10.5194/esd-2-1-2011 and http://dx.doi.org/10.5194/esd-3-79-2012.

Work from Adams & Keith is also relevant here, in terms of looking at how extraction of wind energy at large scales affects atmospheric circulation, as a constraint on practically realisable conversion: http://dx.doi.org/10.1088/1748-9326/8/1/015021.

De Castro and colleagues have taken an approach to estimating conversion potential for solar, wind and biofuels based on top-down methodology, along lines similar to that advocated for wind by Miller, Gans & Kleidon. On this basis, they arrive at estimates very much smaller than those from other analyses. I think the methodological arguments they make, and the implications of this, are worth considering. Their work is available here: http://dx.doi.org/10.1016/j.energy.2013.10.049;  http://dx.doi.org/10.1016/j.enpol.2011.06.027 and http://dx.doi.org/10.1016/j.rser.2013.08.040.

Depending on methodological assumptions, you'll find a very wide (orders of magnitude) range of perspectives on global renewable energy potential. It's a contentious area. The more prominent work tends to be at the very optimistic end of the scale e.g. from Jacobson & Delucchi (http://dx.doi.org/10.1016/j.enpol.2010.11.040). Consider, though, that the estimate for wind potential that that study is based on (from Jacobson & Archer) has recently been revised downward very significantly -- see http://dx.doi.org/10.1073/pnas.1208993109.

So no straightforward and simple answers here, but hopefully this helps you on the way to making better sense of the very important question you've raised.

@ Rosa. Ahora mismo estoy trabajando mas en la escala del consumo total asociado a una economía. Muchas gracias por el ofrecimiento.

@Joshua

Well, that's is a pretty large list of information !!!

Allow me some time before providing feedback, though a first overall view allow me to think that indeed there are some answers to my question in the information you send. Thanks.

 The basic renewable energy source is the sun, which radiation can be used directly or indirectly through hydro power, wind turbine or biomass. According to the World energy Coucil, the total amount of solar energy falling annually on the earth surface is 1,059 E15 MWh, while, according to OCDE,  the annual primary energy use of the mankind is 15 E10 MWh. The total solar energy potential is then about 7'000 times the human actual use. Of course, we cannot use the total potential, buit there is a good margin. In addition, the geothermal energy, i.e the heat generated in the earth core by natural radioactivity, could also be used. Its potential is about 30 TW or, annually, 2.63 E 11 MWh. This also cannot be exploited totally, and estimates of the electricity generating potential of geothermal energy vary from 35 to 2000 GW depending on the scale of investments or, annually, between 3 E8 and 178 E8 MWh.

@ Claude

Interesting comments. Your figures suggest that there is a limit. So, do you think there is possible to suggest any specific figure as a limit?

On the other hand, limits are always never 'crisp' values, so let us just speak in 'fuzzy terms'. Is it possible to suggest a value below consumption of energy is optimum, and a value above which energy consumption increase constitues a problem?

Dear Ricardo

For the geothermal energy, we are in fact using the heat stored in the globe, since  heat naturally flows to the surface by conduction at a rate of 44.2 TW and is replenished by radioactive decay at a rate of 30 TW (seen on Wikipedia). So the Earth core is cooling down  at a rate of 14.2 TW, but its content is about 10E31 Joules (same source). The cooling time constant is hence 7E18 s or 226 billion years, much more than the Sun's remaining lifetime. We could therefore extract in addition the total energy use of mankind (17 TW on average) without significantly cooling down the Globe.

We should remember that any use of energy ends in heat, which increases the Globe temperature. Therefore, we cannot use the solar energy in an unlimited way. Of course, the conversion of solar energy into useful energy (electricity, hot water) emits much less greenhousae gases than the same conversion from fossil fuels, and replacing fossil fuels by solar power plants would contribute to reduce the global warming (see attached paper). But, if mankind converts a siginificantly large part (say more than 0.1%, but this should be checked by the GIEC experts) of the solar energy received by Earth, this will have an impact on the climate.

Basically, we live on the outer shell of a space vehicle that is nearly spherical, and hence has limited ressources. Therefore, there are limits!!

@ Claude. Interesting commments and article.

You raise the issue of local temperature increase caused by converting solar energy, which is a largely interesting issue.

Some authors have pointed out that too much surface of PV in cities would produce temperature increases at which also their efficiency lowers [this effect being possible to be removed if PV efficiency raises to 28% or above levels].

And that even it could have impacts at regional level [temperature increase and wind modifications] as Millsten and Menon [2011] Regional climate consequences of large-scale cool roof and photovoltaic array deployment

This raises some uncertainty when discussing projects as the one intended for Sahara Dessert. A large surface of black panels may get to have impacts on local weather [temperature and wind], and a very large surface will probably be able to have impact even at a regional level.

Besides those probable effects, we have problems as storage and transmision,etc...  [Moriarty and Honnerly, 2012-2012], water suply, etc....

But also, many of our actions translate into energy consumption, and knowing that there are limits is a good start, but it is not enough to set the appropriate goals.

We really need to set some kind of figures that let us know whther we are performing good or bad.

But... is there anyone who can propose such figures building on some consistent basis ?

Maybe an interesting book for you to read would be "Sustainable Energy - without the hot air", by David MacKay, which is an interesting and pragmatic look at the potential renewable energy available for the UK (available for free as a pdf online).

You can also find some information in the works of Trenberth, although they do not specifically answer your question as it is a quite complex problem they give some estimates of the energy flows between atmosphere, oceans, weather events...:

http://journals.ametsoc.org/doi/abs/10.1175/2008BAMS2634.1

Dear All

Thank you so much for your suggestions, which I have found very useful

I already uploaded a preliminary version of the indicator. It can be found at:

https://www.researchgate.net/publication/274696519_20150408_Revision_Metabolismo

• Pages 1-4 explain the common approach for designing 6 metabolism indicators [Water consumption, water pollution, Bioproductive Land, Solid Waste, Energy and GEI emissions]
• Pages 5-10 explain the proposed indicator for assessing the sustainability degree of Energy consumption
• Pages 11-14 explain why linear modeling seem to be the best choice, even if it does not fully comply with the Mathematical Theory of Sustainability

Unluckily, currently it is only available in Spanish [I will upload a copy in english at some point, but it still will take me some time]

Ricardo

Dear All

Let me apologize. A further review of application of last proposal for the indicator has shown some inconsistencies.

It seems that the right solution will require not only to assess both NRE [Non-Renewable Energy] and RE separatelly, but also each type of NRE independently.

I am currently testing a new design for the indicator on a wide range of 20 possible urban transformations [covering mobility, rooftop use and Waste management], and the results it is providing so far have been largely consistent.  

If no inconsistent result is obtained, I will be able to upload the corrected version in about a week, along with a summary of the results of application to urban transfomations.

Best Regards

Ricardo

Hi All

I already udated and uploaded the document. Unfortunately, currently I can only upload a spanish copy. You can find it at:

https://www.researchgate.net/publication/271511706_4.2__INDICADORES_QUE_MIDEN_LA_PRESIN_SOBRE_EL_ENTORNO__ECOSISTEMA_GLOBAL?ev=prf_pub

To understand it you have to read:

• Overall explanation of metabolism assessment [pg 3-8]
• Energy consumption [pg 38-48]
• Annex VI: Procedures when relevant variables [consumption] surpass unsustainability thresholds pg 54-59.

For non spanish readers, I can at least provide the most consisten answer to my initial question that I can state from received information. Total amount of RE by 2050 around 470 EJ.

Any comments on the text shall be welcome

Best Regards

Technical Report 4.2_ INDICADORES QUE MIDEN EL GRADO DE SOSTENIBILIDAD DEL ME...

Dear AllI

I uploaded an updated version, including some comments on the energy consumption indicator received from Iñigo Capellan, who found a mistake in table for EJ projections made by him and his team [Castro, Mediavilla, Carpintero and Capellan]

https://www.researchgate.net/publication/271511706_4.2__INDICADORES_QUE_MIDEN_EL_GRADO_DE_SOSTENIBILIDAD_DEL_METABOLISMO_URBANO?ev=prf_pub

The structure of fthe text is the same than explained above

Since it still will take some time till I am able to uplodad a translated document, I have uploaded a word file, so anyone very interested can open it and use an automatic translator [there are some available in the web, including the one provided with Ms-Word itself].

Regards to all, and as always, any comment shall be welcome !

Ricardo

Technical Report 4.2_ INDICADORES QUE MIDEN EL GRADO DE SOSTENIBILIDAD DEL ME...

Currently, there is a renewable energy techology gap so steep that if we were to stop using non-renewbal energy now or suddenly there would be local and global economy black outs...currently the ratio seems to still be 4 to 1/non-renewable to renewable....You may find my paper interesting:

Understanding the Road Towards the Current Dominant Non-Renewable Energy Use Based Economy: Using An Inversegram to Point Out a Step by Step Strategy Towards an Efficient Dominant Renewable Energy Use Based Economy

https://www.researchgate.net/publication/281230333_Understanding_the_Road_Towards_the_Current_Dominant_Non-Renewable_Energy_Use_Based_Economy_Using_An_Inversegram_to_Point_Out_a_Step_by_Step_Strategy_Towards_an_Efficient_Dominant_Renewable_Energy_Use_Based_Economy

Article Understanding the Road Towards the Current Dominant Non-Rene...