I recently made an effort to understand what happens when I pay to add some renewable generation capacity (like solar) to the grid — whether on my roof, or in a solar farm I buy energy from — so that one can charge an electric car. Most people charge electric cars at night, when the power is much cheaper than during the day.
The full analysis of that question, and efforts people make to green up their transportation will be the subject of an upcoming article. First, an examination of what happens when you succeed, and more renewable energy arrives, is needed.
The real electricity grid is a complex beast with very strange economics. This question of what happens is not an easy question to answer. The effect of any individual actions is almost impossible to trace, but one can ask questions like, “What if I am one of a thousand people who charge electric cars?” or “What happens after a few years if I am one of a thousand people who charge electric cars?”
To understand the grid, you need to know the properties of its main sources of power, and where they get their energy from, be it fuel or natural sources.
- Peakers — Can turn up and down quickly. Usually standard natural gas plants and hydro. An analogy is a gas stove that you can turn up and down quickly.
- Load following — Mainly a new generation of combined cycle gas turbines. Can be adjusted to load at moderate speed. The peakers can also do this, and hydro often does. Like an electric stove, these take more time to heat up and cool down.
- Baseload — Plants that take a long time to stop and start, which meet the well predicted and regular needs. Like a charcoal BBQ pit, which takes a long time to heat up and cool down.
- Coal — The nastiest of the fuels, and the one we want to get rid of.
- Nuclear — The safest and cleanest of the major types, though nuclear deniers fear it. This uses nuclear fuel, but that fuel is cheap compared to coal and gas.
- Peakers and load followers — you can use these for baseload, but it’s usually an expensive thing to do. If your area has tons of hydro, it will show up here.
- Variable — the renewables. They don’t have a fuel cost, but we don’t control, and may have trouble predicting, when it comes. If you don’t sell the power when it does come, you just throw it away.
- Solar — Clean, and now the cheapest new power plant in sunny places. Only runs during the day. Can vary quickly as clouds roll by, and by season.
- Wind — You get more the harder wind blows.
- Storage — They don’t generate energy but they store it to release later, up to their capacity.
- Hydro — It does everything. You can use spare power to pump water back up into reservoirs, until they are full
- Batteries — Minor today, but coming. Able to do instant peak supply, in a millisecond. Also found in cars.
Each fuel is pretty different, too. Coal pollutes horribly and estimates suggest it kills millions from pollution and outputs the most greenhouse gas. Natural gas has few unhealthy pollutants, but produces CO2 and leaks methane — and most of it comes from hydraulic fracking which has issues too. Nuclear has no emissions but produces nuclear waste and carries a small but real accident risk. Hydro’s “fuel” is clean but involves flooding valleys and over history, dam collapses have killed hundreds of thousands. Hydro dams do have a fuel budget — the capacity of the dam and the rainfall that year, but it’s more of an annual budget than a daily one and you can choose when to use it. Solar and wind don’t strictly use fuel, so are pretty good, but even they are not without downsides, mostly the consuming of land and killing large birds.
The fuel makes a difference because it affects how you sell your energy. As explained above, the renewable power comes when the weather allows it. If you don’t sell it, you throw it away. So what you don’t sell in advance at a decent price you price below anything else to be sure you make something off it. When a solar plant does that, the other plants that can dial back do so, because they would rather save fuel than sell at rock bottom prices. Nuclear plants can dial back (slowly) but the fuel savings from doing so are a small part of their total costs. Usually better to keep going.
When the renewables come
Renewables create an issue for the grid. They vary with the weather and must sell all their power. Unfortunately, this makes the grid more volatile. The baseload is always there, but now the variations due to changing demand, and the changing supply from renewables must be met. It used to only be the changing demand they had to worry about.
The problem is that the fast-changing “quick response” power plants, which are the only option, are less efficient — cause more emissions — than the slow-changing ones. The most common type of “peaker” plant is the simple cycle natural gas turbine. These are 30-40% efficient.
At the other end are Combined Cycle, plants, particularly those using natural gas. Most of them are very slow to adjust, but they can be up to 60% efficient. Aside from being cheaper, that means generating 2/3rds to 1/2 the emissions. No minor deal.
Before, if you needed 500MW all day long, you would fire up that combined cycle plant. But toss in 500MW of solar panels, and then when it’s sunny you need zero extra, but suddenly clouds can come and within minutes you need 400MW. This forces a strategy change: You have to get only the base 100MW from the efficient plant, and get the other 400MW from the less efficient one.
Same problem from wind. The wind stops blowing and suddenly you need a bunch more power, quick. When it starts blowing again, customers want to switch back to it, leaving the heat-based plant with a long and wasted cool-off.
If your grid has hydro, you’re lucky, because it’s clean and can turn up and down quickly. Batteries don’t generate energy but they can store it and provide it on a dime. But there is only so much hydro (depending on the region) and very little battery. People are eagerly trying to develop other forms of storage and better batteries.
The California grid operator graphed their “net” demand, which is to say, typical electrical demand minus the contribution from renewables. California has a lot of renewables and it’s growing, and so the curve has been named the “duck curve” for matching the profile of a duck.
A normal total energy demand curve is low at night, starts growing in the morning up to a peak in the late afternoon and early evening when the air conditioners work harder and people return to their homes. In the summer it peaks at 3pm, but in the winter it has two peaks, one at 8am and the other at 7pm when people use the most power in their homes.
The “duck” curve actually has a dip in the daylight on a sunny day rather than a rise. The dip is lowest at noon when the solar panels are doing the most. It’s a very deep dip on cool days when AC is not being used. Then, quite quickly between 5 and 8pm, the solar panels all fade out, the wind usually drops and the people turn on their lights and ovens. All at once, a whole lot of power is needed, from non-renewable sources, from power plants that can be turned on quickly.
Note this solar dip is almost all coming from utility solar farms, not rooftop panels. Rooftop panels are a small portion of the total grid, and don’t feed huge amounts back to it.
The sharp neck of this duck needs a fast response from the other power plants. Mostly, it’s less efficient plants that can provide this.
What solves this long term?
With no other factors, you could get a bad situation. Fortunately, there are things to fix this.
- When you have both wind and solar, they vary somewhat independently. Wind often blows at night, and in storms. Solar follows a well defined day and night path but clouds and rain cut it back.
- Thermal solar plants, unlike photovoltaic (PV) solar plants, are not variable in the power they generate. Due to the drop in the cost of PV, and the higher prices paid for daytime energy, people are favoring PV today.
- Solar panels can be steered (which adds cost) or pointed more westerly, to move their peak later in the day, at the cost of lowering total output. Though as sunset approaches, they will still fade.
- There are new generation combined cycle plants that can ramp up in 30 minutes. They can’t respond to a sudden load but they do let you put more of your load onto more efficient plants. However, the world mostly has older generation plants out there.
- Some hydro reservoirs are putting in pumps to move water back up into the reservoir to offer storage. There are limits on this, though, because it costs money to install such pumps, and you must maintain a certain flow level down river.
- There are aggressive plans for the future involve solar thermal, offshore wind and tons of onshore wind farms and other resources to even out the variability from PV. Stanford professor Mark Jacobson predicts all energy needs could eventually be met from wind, solar and water based resources, avoiding even nuclear.
- There’s tons of research into better forms of storage, including new batteries, compressed air and more. Right now it’s in the lab, not yet proven at scale.
- Smart energy use technologies can reduce demand peaks by moving loads by small or large amounts of time when that makes sense.
- Long distance grid interconnects with high voltage DC can allow more sharing between grids.
A more radical option is to beam the renewable energy up into space and reflect it off a lightweight structure in geosynchronous orbit, and back down to somewhere it’s not sunny. That’s not as crazy as it sounds, and requires lifting far less into space than putting entire solar power stations up there. (The latter is not practical from Earth but could make sense if the solar power stations are constructed from asteroids or the Moon.)
As I said, the grid is never that simple. One small blessing is that summer peak power demand is in the late afternoon, and that overlaps somewhat with where solar power arrives — more if it’s sunny — particularly if you tilt the panels slightly west instead of south. Solar is the most promising new form of energy, and today the cheapest form of new power plant in sunny places.
So what happens if you put your money into more solar and wind? Over the long term, you get more of it. In fact, if you get enough, power actually starts getting cheaper in the morning, when solar supply is high but air conditioning demand hasn’t yet arrived in force. This should switch many of the electric cars to charging then as well as at night, though for many that will mean charging at the office (or robotaxi charge centers) after rush hour. Cars want to charge when they are not needed for a bit, and energy is cheapest.
The problem of renewables is getting a way to store the energy — but not for electric cars, which come with their own storage. Their only concern is when they need to drive, and if they are at a place to charge when energy is cheap and they’re not driving. Right now, that’s the night, but it might change.
It also depends where you live. If there is hydro where you live, the only non-emitting solution is a bunch of nuclear (which, in spite of its reputation, is the cleanest and safest major energy source) to power the base load, and then as much wind and solar as you can take, with the hydro plants and some batteries filling in the gaps. You pump water back uphill at the hydro plant when load is lower, to give it enough for all your variable loads, and some of your baseload. This is the only non-emitting grid we know how to make until we find some other form of storage that can be built at the huge scale our power grid needs.
If you don’t have much hydro where you live, then natural gas plants (peaker and combined cycle turbine) will fill in for the hydro. You don’t really have much else for storage, except the electric cars. Unfortunately, the big spike is at dusk, when cars are either out driving, or just got home depleted for the day. The summer peak at 3pm is just before the cars want to be full for the commute.
The grid is complicated. Stay tuned for part 2, later this week.