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Shiv Vembadi posted: How much of the world is currently powered by renewable energy? What would be the case in 2020? 2 years ago

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Narasimhan Santhanam . Thanks for the question, Shiv. And a pretty important one too at that,

Before I answer, I would like to spell out what I mean by Renewable energy. In addition to solar, wind, biomass, geothermal and ocean based (tidal/wave), hydropower is also renewable energy, though many do not consider it while discussing renewables, owing to a confusion between alternative and renewable sources (hydro is not alternative energy as it has been a conventional source for long, but IS renewable).

If we agree on the above definition, the total installed capacity of renewable energy sources end of 2016 was around 2.3 TW (2300 GW), with hydro contributing about 60% in terms of installed capacity (about 1300 GW), and the rest of renewables contributing about 1 TW (1000 GW). Of the non-hydro renewable sources, solar and wind will claim a large share (about 900 GW).

Given that the total global installed capacity of electricity is about 6.4 TW, the total % share of renewable power capacity is about 35%, quite a substantial share. However, when it comes to power generation (and not just capacity), the share of renewable will be a shade under 20% - my best estimate is somewhere almost 20%, with hydro contributing about 16.5, wind about 2%, solar and biomass giving about 1.5% together.

So, currently, in terms of installed capacity, renewable sources of power has about 35%, and in terms of generation, about 20%.

But as you can see, the elephant in the room is hydro power. If you take hydro power from the equation, the % share of renewable energy sources to the world's electricity consumption comes crashing down to just 3.5%.

Shiv Vembadi . Mr. Narasimhan, that's a lot of useful information. Thank you. So, if solar and wind are currently only about 3% to the total electricity demand, when do you think that could become 10% or 30%? Like

Narasimhan Santhanam . @Shiv - a difficult thing to predict. All I know in terms of formal estimate is that IEA thinks solar power will be the single largest generation source for electricity by 2050 - solar PV and CSP combined could contribute about 27% of total - Link />
Of course, 2050 is too far into the future to predict, or for that matter, bother about for the ordinary I and you.

If I were to take a guess, consider it a guess and no more, by 2020, renewables (excluding hydro) would be contributing about 4.5%-5%, and by 2025, possibly about 8%. A 10% contribution could take until close to 2030.

A 30% for solar and wind together would perhaps happen around 2040-2042, if we go with the above IEA estimates.

Prediction far into the future is a nice game isn't it? It's so far away, no one is gone to point fingers at you when I'm wrong - because it will take some 25 years to find out if if I am :-)

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Gayathri Kumar posted: Why has biomass gasification based power generation not worked well for Indian villages even though IISc implemented many projects? 2 years ago

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Narasimhan Santhanam . @Gayathri - excellent and timely question. Thousands of Indian villages have little or no power, and the chances of the power grid reaching them anytime soon are remote.

So what are the quicker options to electrify these villages?

It necessarily has to be based on distributed energy sources.

Surely, solar can be thought of, and it is indeed being implemented in many villages. At the same time, solar is not a complete solution unless you include a lot of costly batteries as part of the package.

This is where biomass gasification comes in. Biomass power is firm power. And biomass gasification can work on small scales, using waste agro residues or forest residues available in the village. Looks like a perfect fit, doesn't it?

It indeed is.

But how come many of these small biomass gasifier based power generation projects in hundreds of Indian villages have failed?

Well, don't blame it on the biomass, and nor on the gasifier.

The failure of these projects have to do mainly with the poor maintenance of the system.

You see, biomass gasification based power generation works as follows: The biomass is fed to a gasifier, which gasifies the biomass and produces what is called as the Producer Gas, a low calorific value, organic gas. This gas can be fed to gas engines, power generators similar to diesel engines or natural gas engines. The producer gas engine generates power.

Simple. Or is it?

The gasifier in itself is a sturdy piece of equipment which requires little maintenance. But that is not the case with the gas engine.

The Producer Gas contains significant amounts of biomass tar. This can clog the filters of the gas engine - remember, the gas engines were originally built for natural gas and biomass, neither of which have biomass tar in them.

Anyway, the higher the amount of tar in the producer gas, the higher is the frequency with which the filters in the gas engine get clogged.

All these essentially imply that there needs be a regular cleaning of the filter of the gas engine. Now, while this is not a complex operation, it still needs a bit of training.

Such training, and subsequent maintenance, were what were lacking in the case of villages in India that were running the small scale gasifiers. Owing to their small size, it was difficult or impossible for a professional industrial team to visit hundreds of villages regularly just to clean the filters. The only way would have been to train the villages and form a self help group within the village who had the capability to undertake this maintenance work themselves.

Such a local training and sustainable maintenance has been attempted in a few villages, and I understand in these villages the gasifier based power generation programs have been successful. However, there are many villages that still depend on external experts to maintain the gasifiers, and in most of these villages the gasifier no longer operates.

Not a great story to write home about, but there it is.

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Nikhil Vinay posted: What are the challenges in using biomass for industrial and commercial heating? 2 years ago

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Narasimhan Santhanam . Hi Nikhil, thanks for the question. While there are multiple challenges, the key challenge is the reliability (of lack of it) in the biomass supply chain. Lack of reliability in terms of quality of biomass supplied, consistency in biomass supply without disruption, and also sustainable/predictable prices for the biomass. Like

Vijay Wilfred . Biomass has a number of characteristics that makes it more difficult to handle and combust than fossil fuels.

1) The low energy density is the main problem in handling and transport of the biomass,
2) Some types of biomass used contain significant amounts of chlorine, sulfur and potassium. The salts, KCl and K2SO4, are quite volatile, and the release of these components may lead to heavy deposition on heat transfer surfaces, resulting in reduced heat transfer and enhanced corrosion rates. Severe deposits may interfere with operation and cause unscheduled shut downs.
3)The release of alkali metals, chlorine and sulfur to the gas-phase may also lead to generation of significant amounts of aerosols (sub-micron particles) along with relatively high emissions of HCl and SO2.

Vijay Wilfred . Also, the nature and severity of the operational problems related to biomass depend on the choice of combustion technique.

-> In grate-fired units deposition and corrosion problems are the major concern. In fluidized bed combustion the alkali metals in the biomass may facilitate agglomeration of the bed material, causing serious problems for using this technology for herbaceous based biofuels.

-> Fluidized bed combustors are frequently used for biomass (e.g. wood and waste material), circulating FBC are the preferred choice in larger units.

-> Application of biomass in existing boilers with suspension- firing is considered an attractive alternative to burning biomass in grate-fired boilers. However, also for this technology the considerable chlorine and potassium content in some types of biomass (e.g. straw) may cause problems due to deposit formation, corrosion, and deactivation of catalysts for NO removal (SCR).

Narasimhan Santhanam . @Vijay Wilfred - thanks for your responses. I agree that biomass presents operational problems as well. But in my opinion, those who have been handling coal fired boilers should not have too much trouble working with biomass - it is not as if coal did not present any problems! To the extent that the problem has to do with engineering, I am fairly confident that it will either be controlled or overcome soon.

On the other hand, the supply side/supply chain problem is not purely one of science or engineering, but more an intersection of agricultural practices, market demand and to a certain extent individual psychology! A far more difficult challenge to tackle, what do you say?

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