Quora Renewable Energy Question of the Week
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Quora Renewable Energy Question of the Week
Quora is a social platform based on a simple premise: ask a question, and people will answer it. Upvotes and downvotes test the quality of a response, and any member can vote an answer up or down. In practice, however, politics lie behind some of the participants on Quora, especially in the renewable energy space. Therefore, I’ve started answering questions on Quora—an often frustrating endeavor.
Here’s my latest response. I added images and edited slightly for this more receptive audience.
Why does the calculation for solar and wind power not take into account that buffering (by battery or conversion to hydrogen and reconversion) must still be organized for continuous availability? Isn't that unfair?
This question implies some reporting of electric power that is unjust. I don’t see this anywhere inside the industry, only outside, where people make incorrect assumptions about the grid or its energy sources.
I’ll get to the calculations I think you mean, but first, look at the grid and its energy. That energy is a massively delicate balance between supply and demand. The grid operator must know what resources to deliver electricity are at their disposal and need extraordinary predictions for electricity demand. Failure means too much energy on the grid that gets ‘curtailed’ (not purchased) or too little power, which means that current user demand must be reduced (rolling blackouts).
Now let’s talk about solar and wind power and ignore batteries for a moment. My experience is specifically in California, where solar and wind power combine to provide about 70% of the energy on our grid most days during daylight hours. The solar component disappears at night, which is a considerable loss. Your assumption that these sources are buffered by hydrogen or batteries is incorrect—at the moment.
Solar and wind power, as tracked by California’s grid operator CA ISO, are reported the same as every other source of energy on the grid: in MW or GW at any moment in time. That is broken down by source type: large hydro, nuclear, batteries, natural gas, coal (California has one coal plant today), imports (and exports) from outside the CA grid, and all renewables.
Renewables are further broken down by source: biomass, biogas, wind, solar, small hydro, and geothermal. They are all reported on a level playing field because they are measured similarly; reporting has no exceptions.
Wind and solar energy present challenges to electric utilities and the grid operator. They are produced when the sun shines, and the wind blows; the grid either accepts them or curtails them. Nonetheless, the operators have gotten quite good at dealing with these energies but sometimes curtail them. They also have natural gas power plants across the state that stand ready to dispatch energy when needed to meet unmet demand.
In your question, I think you mean the calculation where people like me try to explain the amount of energy produced by wind and solar power, which are not dispatchable. We talk about capacity factors, the fraction of the time the energy source produces its rated energy. For solar, that’s 25–33% of the time. For the wind in our area (it’s very windy), our capacity factor is about 42%. This leads to estimating the number of homes one or a collection of sources can power over a year. It’s our way of explaining a complex situation, but it is not what is monitored or purchased by the grid. Without these calculations, the reported solar and wind production would be unfairly HIGH. 100 MW of wind capacity is different than 100 MW of solar panels, and both are very different from 100 MW from a conventional power plant.
The conventional power plant produces 100 MW whenever needed on a given day, so its capacity factor is 100%. In CA, our average home uses about 9000 kWh a year, and basic math suggests that a 100 MW conventional electricity plant will power approximately 100,000 of them, day or night. The 100 MW of solar also powers 100,000 homes at its peak but falls to 0 at night, so the capacity factor of 33% adjusts this downward to 33,000 homes when averaged over a day or a year. 100 MW of wind provides power for 100,000 homes when the wind is blowing 25 MPH or greater, but a capacity factor of 42% lowers this to 42,000 homes averaged over time. I don’t think that’s unfair; it’s our way of being fair.
To your point about buffering in batteries (let’s ignore hydrogen for another discussion), this is how you turn a non-dispatchable resource into a dispatchable one, and virtually all new solar projects in California will likely include batteries. Our grid is otherwise saturated with solar energy and would have no market. These power plants will not be treated the same as a naked solar farm without batteries because the power will be “on-tap” for grid operators to use after the sun sets. These so-called hybrid plants will be a new category of reported renewable energy. Each hybrid solar plant will be rated by its capacity (like all other sources) and how long it can provide power at that level. So a 200 MW solar array might generate 1,600 MWh of electricity that all goes into batteries, and the battery array is rated at 400 MW, fully discharging 1,600 MWh in four hours.
Our grid also sports batteries, which are reported along with other sources. The key to grid-connected batteries is they are not tied to a production source. They charge when there is excess energy on the grid, purchasing or banking electricity for later sale or release. Dedicated grid storage in batteries is growing significantly in California, in several cases to replace natural gas power plants designed to meet peak energy demand. This is all made possible by the extensive installation of grid-solar farms in the state, which inexpensively produce electricity when the sun is shining.
Note that rooftop solar panels are not reported to the grid operator. They effectively reduce the home’s demand for grid electricity, a solar offset. Surplus energy ends up in someone else’s house and is accounted for by the utility. The grid operator only sees reduced demand.
Thanks for reading.