Research shows that a combination of wind, solar and energy storage can provide the seven fundamental services needed to run the power grid at levels ranging from “Good” through “Excellent”.
The old trope is that you can’t replace the inertia of the rotating mass of metal that makes up a generator – because that’s what keeps the grid running at a consistent frequency. This is no longer true – with Sunrun showing us a big step just last week for residential solar+storage.
In a paper developed by Michael Milligan, formerly of the US Department of Energy’s National Renewable Energy Lab (NREL), titled Source of Grid Reliability Services, we are shown that of the seven required services to keep power grids running smoothly – a combination of wind, solar and energy storage can meet all them all with a rating of at least “Good”, through “Excellent”.
The research concludes that not all resources will perform equally, and therefore grid service definitions should be constructed in such a way that resources can be distinguished, making it possible for grid experts to assess whether there is a sufficient level of reliability services to avoid problems.
The paper does also look at demand response, in addition to wind+solar+storage, and as can be seen by the table above it does offer a great many values to the grid as well.
The paper covers each of the services that need be provided, giving a description of how they help the grid, and which resources can provide the service. For instance, when considering “contingency events” – which is often when a large generating unit or transmission line disconnects unexpectedly and results in a mechanical or electrical failure. The cry through this event, historically, the large spinning masses held their inertia simply because they were so large.
Modern variable energy resources (wind+solar – VERs) and batteries have sufficient controls to offer these services, as long as they are run in a partially curtailed state (as First Solar showed us can economically occur in Tampa).
When considering a second service, frequency response, the author noted,
In many cases this primary frequency response is much faster than that provided by thermal generation and can have a beneficial impact on the initial rate of frequency decline immediately after a disturbance. In ERCOT, distributed resources provides up to one half of the contingency response obligation for the market, and thus distributed resources can contribute to arresting the frequency.
As noted in the above image, reaction times are measured in full seconds for standard “spinning inertia”. Last summer in Australia, a coal plant crashed the the Tesla 100 MW /129 MWh battery reacted by injecting 7 MW of power within milliseconds. Noted in the below image, it is seen that at the point where frequency is projected to drop below 49.8 Hz, the battery reacts seemingly instantly – and before the frequency falls further to 49.75 Hz.
Not all services are best supported by wind+solar+storage though, even though these systems can meet the system demands. Some of the reasons though aren’t fundamental to the hardware – but instead economics at current pricing. For instance, wind and solar plants can both provide very fast and accurate dispatch/ramping response. However, this may be costly to the system because these plants typically have the lowest marginal cost for producing energy and therefore incur the largest lost opportunity cost if they are backed down to retain headroom for ramping, so may not be utilized often. Most, but not all, natural gas generators have the potential to ramp and are often the resource of choice to do this because they have reasonably good flexibility and are often marginal units in the dispatch stack.
However, as we’re clearly seen – the economics of wind+solar+storage are evolving (getting much cheaper) – and a far back as 2015, we’ve been hearing that natural gas peakers are an endangered species. Expect our evolution to continue, and that the lumbering inertia of the dinosaurs will be consumed by modern electronics.