Hi, Dear  Wolfram

I agree with Professor Amin Bennouna.

Kind regards.

the probleme in the renewable energie is the stocking, that this is the photovoltaique or thermal solar energy, losses are important and all researches converge on this probleme.

Wind energy can be stored as a potential energy in hydro pump storage plants.  When you have to much wind then you are pumping water in upper reservoir. 

You can stock renewable energy producing hydrogen, that could further be used in fuel cells, car engines, etc.

As Danijel Topic suggested, it is possible to store any stochastic renewable energy in the potential energy of water. The idea is simple. You need 2 basins of water, one higher than the second and you pump the water from the lowest to the highest using whatever renewable energy you have. When the renewable energy does not work, the water is sent back to the lower reservoir and some hydroelectricity is produced.

This concept is wellknown but rarely exploited. Importantly, it is not necessary to have a large difference in the altitude of the water reservoirs. If one needs to store more energy, the solution  is to add other pumps.

Interestingly, the conversion rate is very good.

From my view, this is going to be the solution for the future.

here's an example I read about just the other day.

http://www.npr.org/blogs/parallels/2014/09/17/349223674/tiny-spanish-island-nears-its-goal-100-percent-renewable-energy

Battery storage is improving, but is a few years away from what I'm told by researchers in the field. 

Also, consider adding flywheels to smooth out any momentary power losses to enhance battery life. We design backup power systems for hospitals and the batteries run 5 or 6 times per day due to millisecond interruptions from the grid. This can degrade the batteries life to 2 or 3 years. Adding a flywheel will increase the battery life to 8+ years.

Likely there will be a multi-technology solution to this problem of renewable storage for years to come.

The loss rate for these technologies will vary, but they all will have one.

Friction for flywheels, evaporation/leaks for pumped hydro, etc.

There is the same problematic in accumulator design as charge cycles efficiency. I think that solution could lie in a balanced combination of transformer (electric) facility and capacitors banks.  

Yes, you can store renewable energy. Can be a storage period of seconds to days and months. Losses related to several factors: the size of tank - insulation - time storage - Storage Temperature - ambient temperature - method placed the tank and others.

Electric vehicles

Definetly you can save renewable energy through an energy storage. Depend on what type of energy and budget you may pick/design energy storage. For exampel if you have extra electericity generated by renewable technologogy you may use electrical batteries, if you have surplus thermal energy you may use thermal energy storage. This is avery generic answer tp pick type of battery or thermal energy storage you need to consider your project circumestances.

Power to Chemicals (gaseous or liquid) could be a viable solution

http://ftp02.iass-potsdam.de/publications/epaper/epaper-Factsheet-E3/index.html#/0

Have you heard about Seasonal Storage? It is possible to accumulate energy for very long periods as summer to winter. Seasonal Thermal Energy Storage (STES) can accumulate the summer overproduction from large solar collector fields to cover the heating demands in winter. Thermal losses in these systems are "around 20%" of the energy accumulated even when the storage period is so long.

Conference Paper Analysis of Large Thermal Energy Storage for Solar District Heating

Conference Paper Geographic evaluation of Central Solar Heating Plants with S...

"Renewable energy" means that it comes from a renewable source. But renewable as it may be, the energy must be identified as belonging to one of the energy types:

- mechanical,

- thermal,

- electric,

- chemical (including electrochemical),

- radiant (from electromagnetic waves)

- nuclear (to my knowledge, there is still no "renewable" nuclear on the Earth).

Each one of these types can, at least  theoretically, be generated, but also stored, as kinetic or potential energy but the meaning of "kinetic" or "potential" is different from one of these types to another. The "losses" you mention above depend also on this, basically, the energy converter you are pointing to.

For this basic reason, your question, under its generic form, "Is it possible to save renewable energy, if so how and what is the loss rate (per time unit)?" sounds strange and I would like you to make it more specific because an answer to such a question would need books dealing with 6 different physics matters!

In most of today's problems, the energy storage is not as much a scientific or technical problem but cost. It is true that increasing energy storage efficiency (stored and returned) reduces the unit cost of the energy stored but in specific technologies existing today, even with 100% efficiency, the attractive cost would not be there. This justifies fully the research done to develop alternative storage technologies (by the way, I'm not working on storage).

Almost all renewables are intermittent and the day humanity will have solved the problem of the cost of storage, the problems of intermittence of renewables will resolve themselves.

All the best.

Hi, Dear  Wolfram

I agree with Professor Amin Bennouna.

Kind regards.

Question: "Is it possible to save renewable energy?"

Yes.

Question: "if so how ..."

By any energy storage you can even think of. It depends ...

Question: "... and what is the loss rate (per time unit)?"

It very much depends on the system you use. If you use batteries the loss is quite small, perhaps not more than 20%  ... but the cost of the batteries are quite high

Question: "The question is can this energy reasonably be stored, if so how and what is the rate of loss (because there is certainly some kind of loss)."

It again depends very much about the given situation ... if you have a situation where you have to store all energy for half a year ... or just leveling out the daily instability ...

... in any case you can also build up so much of renewable energy harvesting machines that you always have enough energy ... (and very likely ways too much of energy most of the time.)

Renewable energy is quite a challenge. I have use Solar in my house and I only good value when the batteries are of the right quality. The use of dc make losses minimum. The use of properly sized cables also makes a difference. All design of solar system Must be done with a cloud cover in mind. If the system works well in cloud, It will do wonders in sunny days. It can even be used to Iron clothes. there is also need to use efficient inverters for ac appliances.

How do you evaluate the effects of the performance of composite insulators in power system protection in tropical coastal and industrial areas?

Large scale storage a in power systems are pumped storage and compressed air energy storage system (caes)

And any answer depends very much from the scale of the system you are planning.

If you're talking about a "my home is my energy castle" solution, then you can forget "pumping water" as a solution, you will use batteries.

If you are talking about an energy system for a country ... you will very much talk about a reasonable grid for sharing the (locally) fluctuating different sources of renewable energy in a bigger scale where the netto generation and also the netto use is much more stable and much more predictable.

For example: Germany does not have a need for big storage solution for the next 10, 14 years with a ramp up of renewables share in electricity up to 40% to 2030. A better grid is sufficient ...