An electrical power network is all about power: at any moment, the network must deliver the power called upon by its customers. But wind turbines produce only variable power. Therefore the networks have to transform this variable power into a fixed guaranteed power in order to integrate it into their production plan.
This transformation requires backup generators, backdown generators, and, supposedly, various other exotic means like backup batteries or hydrogen storage. The costs of these tools are difficult to evaluate because they are hidden in the daily network’s operations. But we can have an idea of the type and magnitude of the problems encountered if we force the wind power plant to provide a fixed and guaranteed power and look at what has to be done to reach that goal.
The behavior of a wind power plant that has to provide a fixed and guaranteed power is illustrated in the following figure that shows, for each guaranteed power level, the average value of the various power flows in and out of the system.
The figure is drawn for a 1000 MW power plant, with a wind load factor of 28%, coupled with backup power generators and 4GWh batteries. The values are calculated for each guaranteed power value based on the day by day simulation of the system. The resulting daily values are then aggregated over the period to show the average power flows. Looking at the figure, one can see that:
- For all levels of guaranteed power, the wind turbines need some backup power to be able to provide the guaranteed power – except if this one is very low, which wouldn’t make much sense.
- A wind turbines power plant cannot even sell all the energy it produces if it must guarantee a power equal to its average power. In our example, about 25% of the wind energy produced by the wind turbines will need to be discarded and replaced by the production of some backup generators.
- Once the guaranteed power reaches the wind power average power, nearly all additional power will be provided by the backup generators, except for a few percent more of the wind power surplus that could finally be used to feed the load.
- The batteries can only be filled using a fraction of the wind power surplus: with or without batteries, the fraction of the wind power that can directly feed the load remains unchanged<./li>
- In our example, 4 GWh of batteries will allow for the saving of 9% of the wind power produced, thereby reducing the wind power surplus from 25% down to 16% of the wind power produced – probably at a huge price.
- The batteries are totally useless when they are full and there is too much wind, or when they are empty and there is not enough wind. This happens up to 50% of the time in our example. This is mainly due to the fact that the batteries are always too small with respect to the installed wind power (because of their cost).
- When the guaranteed power increases, the batteries become useless, because there is no enough wind power surplus to fill them. They remain empty most of the time.
- More surprisingly, the batteries become also useless when the guaranteed power decreases. This time it is because there is not enough wind power deficit to use the energy stored in the batteries. They remain full most of the time.
If you understand how a wind power plant forced to produce a guaranteed power works, you will also understand that any time someone promises you that wind turbines will provide some “magic things” that are not shown in the previous figure, what they really mean is that they intend to use the resources of the network to let you think that wind power is, well, “magic”.
You can try to add batteries in the customer houses, or use some hydrogen storage. But, because these things need to be filled with some power before being useful, they will behave as the main batteries of our example – very inefficiently.
That wind turbines are some kind of magic engines that could violate the laws of thermodynamics is one of the great illusions of our time. Only by pumping for free the resources of the network can wind turbines pretend to provide useful services.
There comes a time when people will realize that the laws of physics apply even if they don’t know them …
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