Montag, 24. Oktober 2016

Global Demand for Energy Storage

Energy Storage Demand in a Sustainable World

The global transition to renewable energy production is in progress. Last year, 2015, more renewable power capacity, like solar and wind power, was installed as conventional capacity like coal and nuclear. Beside this nice development, there is a weak spot, the installed solar and wind capacity produce only when the sun is shining or the wind is blowing. For a full change to an emission free world, we need energy storage.

How big is the storage demand on a global scale, this is hard to guess, because it depends on a lot of assumptions. I will try to make a good guess within this post.

The Global "Energiewende" 

I will not describe the "Energiewende" (change of the energy system) in Germany, I will focus on the global change. This makes sense, because we have to change the energy system on the global scale to stopp the carbon problem and limit the exhaustion of the scare fossile fuels. 

The strong growth of PV installations, about 70 GW are expected for 2016, continues the long term trend of constant fast growing installations over the last decades. 

This trend will change the energy system as we know it today within two decades, to understand this lets look into the near history.

Growth of the energy consumption and the installed renewable energy production.
Consider the logarithmic axis of the installed power. Data source BP 
The first thing is, the electric power demand has a constant annual global growth of 3%. The installation of wind and solar power combined grows every year with 22%. The result will be, that somewhere around 2025, more fluctuating renewable energy is installed as conventional power plants. 

But be careful, the produced energy of wind and sun will still not match the demand, because they only produce energy when sunlight or wind is available. Resulting in the green line, which represents the mean renewable power generation. This line hits around 2030 the demand.

The result is, the next century will be dominated by the installation of storage to match the flucuating production at any time with the global demand.

Influence to the Storage Demand

The main impact for the storage demand has the electric grid infrastructure. The reason is, that the grid is the most efficient way to transport the electric power from the source to the customer. Is the sun shining in the southern part of a country, it is efficient to bring the energy to the cloudy northern part. And similar, if the northern part has a lot of wind during the night it makes sense to bring the energy with the same grid to the customers in the southern part.

This results in a competition between grid and storage.

To find the economic optimum between power grid size and storage is complex
Theoretical, it would be possible, to span a global grid around the globe and connect this grid with all solar power plants. This would result in a perfect 24 hour solar power supply without any energy storage at all because the sun shines always at some places on our earth.

The main problem seem the high price of such a grid and the energy loss in the power line. The other extreme case is a power storage at home with a seasonal capacity (only necessary in the northern region) of 1000 kWh for every person in the house. Then we can go off grid, sufficient PV on the rooftop assumed. The price for the batteries may reach a million dollars, not affordable.

If we dive into detailed computer simulations as done by J. Tambke und L. Bremen [1] we learn, that a country like Germany needs a storage capacity of seven days after a complete conversion to wind and solar has happend and there is a perfect power grid, often called a copper plate. 

Expanding the area of the perfect grid connection to an area like Europe only two days of storage is necessary. If we are optimistic and assume a perfect grid of this semi continental scale we need only a storage capacity of two days.

Further Chances to Optimize

Beside the grid, another chance to minimise the storage demand is the so called smart grid. Whenever possible, a energy consuming element in the grid goes offline if the power price is high or goes online if the price is low.

We dont know the exact possible amount of energy demand that can be shifted to other times but a optimistic guess might be, that 50% of the demand can be shifted in a way that the storage demand is halved.

Asuming this, we need only one day of storage if a smart grid and a comtinent size grid is available.

Adding up the Numbers

The energy consumption in the world in the year 2030 will be around 4,000 GW. To store this energy over one day, we need a 24h storage system with a capacity of 96,000 GWh. Keep in mind, the Gigafactory of Elon Musk may produce 100 GWh per year. If all the storage is used for the global Energiewende, the production for this demand needs about 1000 years.

But be careful, other solutions may be available.  The energy stored in the lakes of Norway contain an astonishing amount of 80,000 GWh, although there is no pump, the stored volume can only be used once in a year and has to be refilled by natural perception.
Pumped hydro technology may be a good solution, especially the Gravity Storage system, a typical site can store about 8 GWh. We still need 10,000 Sites, but tis seems to be more within practical reach, than a bure battery solution.  


References






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