Short term (2020 is pretty short):

1) Energy conservation in HVAC (improved insulation, heating, air conditioning)

2) Improved fuel-efficient cars (Diesel, electro-hybrid systems)

3) Sustainable and simple biomass --> biogas systems with entry into urban gas supply nets.

4) Energy storage, particularly for wind energy (capacity: 1-2 weeks), but also for solar.

Mid term (beginning 2020):

5) Large scale marine power, including energy storage (for off shore wind parks)

6) Biofuels from algae or ligno-cellulosic biomas. Critical: lignin conversion.

7) Large scale solar: Main target is energy transport and economy of scale. Solar clearly is the electrical energy source of the longer range future.

Long term:

8) Salt tolerant biomass generation in desert regions along shores, watering by sea water.

I'm not sure if I will find 10 different technologies....

PV, Wind, Hydro, BioMass, Solar Thermal, CPV, BioFuels, Geothermal, Marine Power

Thanks for your contribution. We would like to sort them by priority and efficiency.

Short term (2020 is pretty short):

1) Energy conservation in HVAC (improved insulation, heating, air conditioning)

2) Improved fuel-efficient cars (Diesel, electro-hybrid systems)

3) Sustainable and simple biomass --> biogas systems with entry into urban gas supply nets.

4) Energy storage, particularly for wind energy (capacity: 1-2 weeks), but also for solar.

Mid term (beginning 2020):

5) Large scale marine power, including energy storage (for off shore wind parks)

6) Biofuels from algae or ligno-cellulosic biomas. Critical: lignin conversion.

7) Large scale solar: Main target is energy transport and economy of scale. Solar clearly is the electrical energy source of the longer range future.

Long term:

8) Salt tolerant biomass generation in desert regions along shores, watering by sea water.

I am not sure if it´s make sense to ask for the top ten renewable energy technologies. And to sort them by efficiency dito. E.g. the efficiency of PV varies between 8% for organic cells and over 40% for concentrated triple junction. But both “ends” of the PV technology spectrum have the potential to reach important energy markets. The marine technologies subsume very different technologies which will have also different future potentials.

The efficiency of a single conversation process or even a single installation plant may be an necessary indicator but says only little about the efficiency of the system.

The economic and technological success of renewables depends crucial from the local situation. From elementary conditions like the supply of natural resources over the structure of energy demand until the political framework, the social acceptance and the creation of local value. I guess so far as you not will find a single technology what fits all you can´t find two, three or ten. But it may be helpful to recognize that we will see plenty of different renewable technologies embedded in varies systems and well adapted to local and regional conditions. Follow this thoughts we can assume that centralized generation, storage, transport and consume will degrease. Decentralizing will be a (or maybe: the) key driver for the development of the future energy systems. Furthermore the previous strictly separation of energy generation and consumption will vanish more and more.

There’s is only one energy technology I am, very skeptical and this is nuclear fission. At least because it is a very centralized large scale technology.

Thanks for your valuable comments.

For me, I am very optimistic with the nuclear fusion for example in very near future.

I think you hear about the last news:

Apparent breakthrough in nuclear fusion silenced by shutdown

Scientists have come one step closer to harnessing the power of the sun. Researchers at the National Ignition Facility (NIF) have passed a milestone in achieving self-sustaining nuclear fusion -- but you won't hear about it from the researchers. The NIF team has been furloughed as a result of the U.S. government shutdown, which began on Oct. 1, and is not releasing updates to the press.

According to the BBC, a research experiment conducted in late September succeeded in releasing more energy through a fusion reaction than it absorbed by the fuel going in. NIF is the first research facility in the world to achieve this goal. A spokesperson for the NIF could not give CBSNews.com a comment on the results of the experiment.

Simplified diagram of the beam path of a NIF laser beam, one of 192 similar beam lines. On the left are the amplifiers and optical switch, and on the right is the final spatial filter, switch yard and optical frequency converter. / LAWRENCE LIVERMORE NATIONAL LABORATORY

NIF's method for achieving fusion involves sending 192 laser beams through a 1,500-meter journey that increases its energy output by a factor of more than a quadrillion. The laser beams' energy grows from one-billionth of a joule to 4 million joules in 5 millionths of a second.

http://www.cbsnews.com/8301-205_162-57606588/apparent-breakthrough-in-nuclear-fusion-silenced-by-shutdown/

For my nuclear energy is an energy that should be removed from use by the risks and wastes. Remember Chernobyl and recently Japan

I am 100% agree with you Dr.Rosa Compagnucci. So that, I am very optimistic with the nuclear fusion for example in very near future and hopping it will replace the nuclear fission.

Lets remain realistic. When I was a physics student, nearly 45 years ago, I visited a leading German fusion facility and was told that the necessary energy density was only 50% away from what was required - on a logarithmic scale. 45 years later: Are we there?

It seems that most technology developments take much longer than their proponents would expect or predict. But in terms of promise and its fulfillment, nuclear fusion , in spite of enormously heavy subsidies has about the worst record possible. I therefore stick to down to earth technologies that have their development path clearly outlined, carry moderate risk and demonstrate high short to mid term benefits.

Thanks Dr. Thomas Melin for your valuable comment. We just got high optimistic since the above mentioned new results.

http://www.cbsnews.com/8301-205_162-57606588/apparent-breakthrough-in-nuclear-fusion-silenced-by-shutdown/

The output efficiency is important these days since new achievements announced for some renewable energy technologies, for example PV increased from ~ 20% to 40% using focusing technique and so on.

Thanks for your detailed comment. I agree with you Dr. Holger Tuerk about the importance of efficiency and cost. Water have high out efficiency but limited by availability and geographical problems. About Biofuel, do you have recent data to help us understanding your opinion about it?

Thanks a lot,@Holger Tuerk, I will go through your files.

Triboelectric nanogenerator extracts energy from ocean waves...

http://onlinelibrary.wiley.com/doi/10.1002/anie.201307249/abstract;jsessionid=697843491CEB37C09FBE923D1CB687D8.f03t04

I think 2020 is not so far away and liquid fuels will still be important so the development of sustainable and carbon neutral liquid fuels will be a top 10 need. Biofuel is still a long way from reaching the needed scale. Although pioneering, natural gas conversion with CO2 uptake to create liquid fuels would be a chemistry of substantial interest for 2020.

Thanks for your valuable comment.

The various answers lead to a valuable brainstorming and sober balanced listing may result into a fine answer-orientation from 1-10. TWO from my side: 1) I wish to add strongly WAVE-POWER; I remember a statement that physically the wave-power along the German North-Sea-Coast would meet the total German energy-requirement. May be this is exaggerated, but the issue is very neglected. It seems that humans have not yet smartly managed to transform the simple vertical movement / force of marine waves into rotating energy-flows for generators. 2. Within a few years biogas-energy has been occupying some 20-30 % of the German arable land-area. My rating is, that biogas from crops / plant-produce will play a leading role in future. As agronomist I am quite proud. The ecological framing however is still sub-optimal.....maize-monoculture is just disgusting.

Thanks for your comment Dr. Bernhard Meier zu Biesen.

But during my last visit to Germany, Munich , I recognized that almost 30% of houses in Munich has PV panels on the roof !!

And, someone told me that they plan to increase this ratio soon !

I do not know the latest figures; 30% is possibly a bit too high; this achievement is very much due to subvention, but not due to "pure economics", anyhow: it will continue with our new government, but reducing subvention for wind-power. In my rural area state-/energy-actors are very busy constructing high-performance underground-cables for the many solar-power-sites in rural areas....but also hot-water-pipelines from the many bio-gas-units with dual-purpose (electricity and heat)

U need to do is to improve efficiency of ur technology and apply energy conservation.

Best renewable energy source vary from location to location some sites have good wind while some has solar radiation. Hydro is also best

These three are best growing .

Thanks Mahesh Lohano for your comment.

1))

Energy conservation in HVAC (improved insulation, heating, air conditioning)

2)

Improved fuel-efficient cars (Diesel, electro-hybrid systems)

3)

Sustainable and simple biomass --> biogas systems with entry into urban gas supply nets.

4)

Energy storage, particularly for wind energy (capacity: 1-2 weeks), but also for solar.

Mid term (beginning 2020):

5)

Large scale marine power, including energy storage (for off shore wind parks)

Dear researcher

Renewable energy technologies/sources (hydropower, wind power, solar power, marine-energy, geothermal energy, heat pumps, biomass and biofuels) are alternatives to fossil fuels contributing to the improvement of environment, enhancement of energy security and diversification of energy supply.

Thank you

Thanks Ahmed Al mayahi for your comment.

Thanks Hashem Azizi  for your comment.

I think high efficiency PV  panels, become more realistic these days among others.