The Solar Duck Curve and the storage need CA

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The Solar Duck Curve and the storage need CA

As electricity travels almost as fast as light, the existing utility energy grid is designed so that every watt of power that is generated from a renewable or not renewable source, is used by a load connected anywhere into the grid, in the exact following moment that it was produced.

Solar Duck Curve: Average residential load profile
Figure 1. Average residential load profile. Source: Sciencedirect.

Graphs such as the one above display the daily energy demand profile of the load connected into the utility grid in a single day. This curve remains relatively steady all over the day, presenting the peak consumption at night.

This energy is supplied from several energy sources such as coal, fuel and gas plants, as well as from renewable sources such as hydroelectric, nuclear, solar or wind power plants.

Duck Curve. California average daily load
Figure 2. (a) Solar panels generation, throughout the day; (b) California average daily load. Source: Greenconvergence and RAPonline.gov

California’s solar duck-curve.

The increasing penetration of solar and wind energy generation on the grid has shaped the daily load demand curve of California in a unique way.

As solar meets the peak-generation during midday, this extra amount of energy offsets consumption from the grid. However, as the afternoon falls down, solar production drastically reduces and the demand needs to be rapidly compensated by the power grid.

Experts called this phenomenon, the solar duck curve, as the load reduction during midday and the peak consumption points at evening and noon assimilate the shape of a duck floating in the water.

The increase in solar energy throughout the years in the state intensifies the problem, generating certain issues for the power grid.

Problems faced by this phenomenon

The main problem with this behavior is that the utility system needs to support rapid increases in load demand as solar power goes down.

As it is evident in California’s demand curve, the load reduction product of the solar energy generation creates a ramp-up to 13.000MW of power in just a few hours. No renewable plant is designed to deliver such an amount of energy in such a short time.

The current facilities designed for peak demand are gas and fuel plants that can be put into service relatable quickly. The problem here is that such a service is really expensive and not sustainable in the long run.

Solutions

The most important solution for such a problem is the implementation of some kind of energy storage system.

Such systems will be able to store the energy produced at midday by solar and use it when it is required. Some worldwide solutions discussed, are water pump storage and battery storage.

Water pump systems operate by using the available abundant energy to move water in between an upper and lower reservoir. The energy is stored as potential energy in the mass of water and is released by letting the water flow downwards while collecting the kinetic energy to generate electricity.

The main problem with this energy storage is that it requires a vast majority of land and a height differential in-between reservoirs.

This is why the must discuss storage solution is battery storage. These systems implemented at large scale are a great way to store the excess energy from solar, but they are expensive. Large battery storage is developing throughout the country, but this technology is still in the developing throughout economics.

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