What Would a Harris Presidency Mean for the Climate?

[progree]

5. Efficiency and waste

Last edited Tue Jul 23, 2024, 09:08 AM - Edit history (1)

Thanks much for the Lawrence Livermore flow diagrams and EIA info on efficiency. I haven't seen the LL flow diagrams posted here for a long time (years).

I see the footnote:

"EIA reports consumption of renewable resources (i.e., hydro, wind, geothermal and solar) for electricity in BTU-equivalent values by assuming a typical fossil fuel plant rate. The efficiency of electricity production is calculated as the total retail electricity delivered divided by the primary energy input into electricity generation."

I don't know what the "typical fossil fuel plant rate" is that they use (I'm sure I can find that if I dig down enough), but I see in the graphic in https://www.eia.gov/energyexplained/us-energy-facts/ that 41% is used and 59% is lost (the black and gray box at the bottom center of the "U.S. energy consumption by source and sector, 2023" ),

then my example in post#1 using 40% is quite close. Using 41%, 1 TWH of electricity is equivalent to 1 TWH * 1.00/0.41 = 2.439 TWH of primary energy = 8.32 trillion BTUS (or 0.00832 quadrillion BTUs) of equivalent primary energy. Using the theoretical 100% 3.412 BTU per watt hour to convert the 2.439 TWH of primary energy into 8.32 trillion BTUs of primary energy.

The footnote goes on to say, for those reading the rest of the right half of the diagram,

"End use efficiency is estimated as 65% for the residential sector, 65% for the commercial sector, 49% for the industrial sector, and 21% for the transportation sector..."

=========================================

Energy from renewables can also be “rejected." What if solar panels or wind turbines are producing more electricity than is required at the moment? That excess electricity is lost, unless it is stored somehow — perhaps in a battery of some sort.

One clarification from my years as superintendant of operational planning at Northern States Power (NSP, now Xcel Energy) back in the 80's:

Once electrical energy is on the grid, it's part of the grid total. If the grid total supply exceeds demand, the result is that the system frequency starts to go up. Power plant governors (like in a car) sense the frequency deviation from normal and reduce output of the generators they control. This happens across the entire synchronously AC connected system -- in our case, the entire eastern 2/3 of the U.S. (minus, sigh, Texas) .

So the wind supplied electricity is not rejected (once its on the grid), but rather other generation automatically backs off.

The Eastern interconnection consists of a number of control areas. NSP's control area was basically southern Minnesota including the Twin Cities with some of western Wisconsin. Anyway each control area is responsible for keeping its supply and demand in balance. So what happens if the NSP control area has the offending excess generation? Its control center software will sum the net outflow of electricity on its tie lines to other utiliities, and send signals to control area generators to back off until the net outflow (or net inflow) is what it's supposed to be (scheduled exports minus scheduled imports).

Fine if we have generation that can be backed off, as usually is the case. So basically the energy from the wind generators backs off other generation in our control area. Generally not a bad thing since the wind, being free, is the cheapest resource on the grid (as is solar). (There is a small variable operation and maintenance (O&M) cost to generating). (As for the capital cost of constructing the wind turbine, that's a sunk cost, so it doesn't enter into operational economic decisions).

The automatic control generation keywords are AGC (Automatic Generation Control), and Economic Dispatch, and Equal Incremental Loading.

But what if it is during a night-time or other low-load period (spring weekends) and all the other generators are backed down all the way to their minimum generation setpoints? That means they can't be backed down any further. So we're up shit creek but we do have a paddle -- we can shut down a generating unit(s). Dispatchers aided with software figure out which generator(s) to shut down and when.

If it's one we would have shut down anyway (and restarted some time later), then no biggie -- we are just shutting it down a little earlier than planned and starting it up a little later than planned, typically.

Sometimes it’s a generator whose shutdown is being caused entirely by the wind (or solar) generation -- i.e. without the wind generation, we'd not shut down the unit. So because of the wind generation, we're paying the cost of a shutdown / startup cycle. That causes extra fuel to be burned to reheat the boiler (or keep it on hot standby), and it causes extra thermal stresses which we have estimates for the long term cost of, e.g. $25,000 per shutdown/startup cycle for a large coal unit (700 MW) back in the 1980's in 1980$.

The above is discussing generation other than the wind and solar (I'll just use wind as an example that applies to both). Well, what about shutting down the wind generation when it is causing unwanted and costly shutdowns of some of our units?

Now I'm in dunno for sure territory -- my experience is before we had any wind or solar. But I read that some wind generators can be shut down by facing their rotors into the wind and rotating the pitch of the blades so they are straight-on into the wind, so that the passing wind does not exert a torque on the blades. So the rotor doesn't spin and the attached generator doesn't spin either, so we have no electricity output. Great, problem solved.

But apparently this capability makes wind generators considerably more expensive, I guess, because a lot of them don't have this capability. So for these wind generators, they just generate when the wind blows. To avoid expensive unwanted shutdowns of other (non-wind) generation, we can play "Let's Make A Deal" and try to sell the excess generation to another utitlity. Fine if we can. Not fine if we can't.

Next up, "Let's Make Another Kind Of Deal" and offer to PAY THE OTHER UTILITY to take our excess energy. If they can come up with a (negative) price that costs us less to get rid of the excess energy that way than by shutting down some unit(s), then that's the way to go.

The other utility (if they are honest about their production costs) will incur costs to shut down some unit of their's, but they may have a unit they can shut down at lower cost (considering the whole shutdown startup cycle) than we can, so that's how the deal works out for both parties.

I've seen a lot of articles about e.g. California utitilies "selling" excess solar and wind energy at negative prices to neighboring southwestern utilities.

Why can't we just open the electrical circuit on a wind generator (if it doesn't have the capability to turn its blades into a zero torque position)? Because without electrical load, and with some wind, the rotor will just spin faster and faster and faster, destroying itself. Because there is no "back EMF" electromagnetic force countering the generator-rotor when the circuit is open.

(Don't ask me what happens if the circuit is opened by accident or if an electrical fault (short circuit) appears and the circuit must be opened to clear that fault -- I would think that happens frequently in a world of tens of thousands (a guess) of wind turbines - they must have some mechanism to lock the rotors, but if they do, why don't they do that in normal operations in the situations described above where there is excess generation causing problems? Unless it's so stressful that its only done in emergencies)

As for solar, I don't know that they do. It's mostly solar energy that California sells at a loss (at times) to neighboring utilities, so I read, so they apparently can't simply just open the circuit and all is well. I guess that solar panels they use just heat up to destructive temperatures if energy is not dissipated by energy flow out as electricity. I guess. I don't know.

All's I know is that if there were a simple way to shut down solar generation, they would, because that is cheaper than paying a neighboring utility to take the surplus energy.

Another possibility is dump resistors. At the Navy nuclear test site in Idaho, they dumped their electricity into resistor banks that were submerged in tanks in a circulating water system, creating steam that made clouds visible for tens of miles.

I've never read about that being done by utilities getting rid of excess electrical energy. Or anything useful like using the electricity for hydrogen production.

That's all I know or don't know.

Additionally, re wind energy efficiency: it doesn't convert all the wind passing thru the circle swept by the blades. Similarly with solar energy and the sun striking the solar panels.

But is the wind and solar that is not converted wasted? Or a lost opportunity cost? Or just a challenge to improve the hardware and design to reduce the capital and material costs per KWH of electricity produced?