As the Berkeley Lab Environmental Energy Technologies Division notes:
In 2020, if all goes according to plan, the state of California will get 33 percent of its electricity from renewable power, including solar and wind, as required by the state’s Renewable Portfolio Standard.
But wind doesn’t blow all the time, and the sun doesn’t provide as much power on cloudy days—renewable power is intermittent.
This poses a problem for the electric grid’s operators, who need to be able to exactly match the generation of electrical power with the demand for it at any given moment.
The important things to note here are:
The power supply from renewable energy sources such as wind and solar is intermittent
The utilities must exactly match the generation of electrical power with the demand at any given moment
- And we are using more and more renewable energy sources to replace conventional sources such as coal, natural gas and nuclear.
Which logically lead us to our next section:
THE NEED TO BUILD ENERGY STORAGE FACILITIES
The conclusion from the above given quote is that the intermittent nature of solar and wind power generation makes energy storage a prerequisite for renewable energy generation.
Con Edison, the NYC utility and New York State Energy Research and Development Authority NYSERDA are offering incentives for energy improvements of up to $2600/kWh that provide summer on-peak demand reduction.
Forbes magazine put it very aptly when they said that
What society really wants and needs is energy on demand.
and that’s why “storage, not generation is the challenge to renewable energy”.
Let’s take an in-depth look at the challenges faced by the energy storage technology.
In our opinion this is by far the biggest challenge that the renewable energy integration to the grid is facing. Let’s have a brief look at the environmental impacts of three of the most well known energy storage systems.
PUMPED HYDRO STORAGE (PHS)
PHS consists of two water reservoirs at two different elevations. When we have excess electricity, that we want to store, we pump water from the lower reservoir to the higher reservoir using this electricity.
When we need to retrieve this energy we let the stored water flow back to the lower reservoir while at the same time using it to turn turbines and generate electricity.
Although this is the most developed and reliable storage technique, its drawbacks are glaringly obvious. First of all it is limited by the availability of a site suitable for building of two reservoirs with at least a 100 m elevation difference between them.
Secondly, the building of dams means undertaking huge construction projects which eventually end up displacing populations, destroying biodiversity and annihilating entire ecosystems.
And last but not the least is methane release. The forestation which is now underwater due to flooding, decays and releases methane which could eventually increase the carbon emissions annulling the effects of clean energy usage.
COMPRESSED AIR ENERGY STORAGE
This type of storage compresses air using excess energy and stores it in a cavern made up of hard rock or salt. The air is released when peak demand necessitates the retrieval of this energy.
Apart from the fact that this type of storage depends on availability of caverns, the bigger problem comes from overheating due to air compression which could eventually crack the rock compromising its structural stability.
So it has to cooled before it is stored and it has to be reheated when it is needed. This implies energy spending for storage and an increase in carbon emission.
While talking about storage devices and green energies, it is very easy to forget that the fundamental reason for the use of renewable energies like solar or wind was to protect the environment.
It does not therefore make any sense to fabricate storage devices which would eventually end up harming the environment by releasing toxic wastes at the end of their life cycles.
Unfortunately this might be the case with some storage device particularly the batteries which use metals like Cadmium, Nickel and Lithium.
ENERGY AND POWER DENSITY
Although in our opinion, negative impacts on the environment are the most important challenge to renewable energy storage, Power Density is by far the most talked about metric.
The Power density is rated output power divided by the device volume (W/kg or W/liter). Every designer out there is trying to pack a maximum amount of energy in as little space as possible. But doing so economically and efficiently is still a big challenge.
There is no point in storing energy in a device that would give a 70% loss on retrieval. The efficiency is a big challenge for today’s energy storage devices because it permits stocking of greater amounts of energy for longer periods of time.
Reducing charging time is such a big challenge that for the time being electric vehicle manufacturers are considering a battery swap instead of recharging a drained battery. All the efficiency and storage capacity that a storage device have become useless if it takes eight hours to fully charge a battery. This problem certainly needs to be overcome before renewable energies get fully integrated to the existing grids.
The discharge of a storage device is often incomplete which means that all the energy stored in the device can not be retrieved. Improvement of the storage capacity is a big issue because this could lead to low efficiency.
TOLERANCE TO FLUCTUATIONS IN INPUT
Most renewable energy sources have severe output power fluctuations during the day. These fluctuations can damage the device, the circuitry or even the measurement systems and probes attached to the device.
Designing a storage device that handles the changes in frequency and amplitude of the incoming power is a big challenge as well.
IMPROVEMENT IN DEVICE LIFETIME
Remember “renewable energy” is technically not renewable if the energy storage system has to be discarded after 15 years of operation and has to be replaced by a new one.
The improvement in device life times, specially for batteries and fuel cells, is still a big challenge and needs to be overcome before they are considered as candidates in grid level storage facilities.
Superconducting Magnetic Energy Storage devices store electrical energy directly and are very efficient but they are extremely expensive. A similar argument can be given about Hydrogen-based fuel cell which are quite efficient but expensive.
In so far as the nature of this problem goes, it is not different from any other product manufactured for public utilization. Good engineering sells only if it is affordable. But still cost-effectiveness remains a huge challenge for energy storage.
Renewable energy generation is already expensive, apart from being intermittent. Add storage costs (which are not needed for conventional energy generation) to the mix and the cost for consumers becomes very high. So much so that many consumers will find themselves unable to pay the utility bills while the utilities will have to turn to the remaining consumers to recoup their costs, driving the prices even higher.
The green energies as they are produced right now are not grid-ready. In order for them to meet the “energy on demand” criteria we need to find means to store energy. The main challenges are the subsequent damage to environment by these storage facilities and the increase in financial burden on the end-user. Our recommendation would be to perfect the means of energy storage before producing it using renewable resources.