Distributed Energy and Electrical Line Losses

[jebatty]

One benefit of green energy is that it may be a more distributed energy system resulting in lower transmission losses than current systems powered by distant generating plants and then moving the power over lengthy transmission lines. While doing a bit of reading on this topic, I came across two articles which were quite interesting. One take away from these articles is how inefficient current electrical distributions systems now are. A second take away is that this inefficiency often is subsidized at public expense. A third take away is that this lack of efficiency results in the cost of electricity to users being much higher than it otherwise might be.
Line Losses 1
Line Losses 2

 

[Where2]

One benefit of green energy is that it may be a more distributed energy system resulting in lower transmission losses than current systems powered by distant generating plants and then moving the power over lengthy transmission lines. While doing a bit of reading on this topic, I came across two articles which were quite interesting. One take away from these articles is how inefficient current electrical distributions systems now are. A second take away is that this inefficiency often is subsidized at public expense. A third take away is that this lack of efficiency results in the cost of electricity to users being much higher than it otherwise might be.

And yet some groups still contend that "Net Metering" and grid connected systems raise the costs to those without arrays. In my suburban neighborhood where the next house is 25' away, the line loss through the feeder sized conductors is almost 0% to feed my excess energy next door. If I'm overproducing at mid-day, then there are actually 4 other houses all connected to the same transformer that are likely to use all my excess power. That equals less wear on the local transformer in the heat of the day, and less burden on the dead end spur of the grid that powers my home, and the four neighbors.

 

[DBoon]

Most people would be shocked to know that fossil fuel BTUs convert to electrical delivered BTUs at about 32% efficiency, overall.

 

[HitzerHillbilly]

And yet some groups still contend that "Net Metering" and grid connected systems raise the costs to those without arrays. In my suburban neighborhood where the next house is 25' away, the line loss through the feeder sized conductors is almost 0% to feed my excess energy next door. If I'm overproducing at mid-day, then there are actually 4 other houses all connected to the same transformer that are likely to use all my excess power. That equals less wear on the local transformer in the heat of the day, and less burden on the dead end spur of the grid that powers my home, and the four neighbors.

I like this idea, the scary part for me being a lineman for the utility company is back feed through the transformer if the feeder line goes down. A transformer will work both ways, stepping voltage up or down, so there could possibly 7200+ volts coming out of the top of that transformer to the primary line, which in a storm scenario could be laying across a neighbors fence. Dangerous situation unless someone has the technology to disconnect the primary side of a transformer in the event of storms/power outages.

 

[jebatty]

Truly a scary thought. Solar PV systems are to be equipped with anti-islanding control to prevent this. But people also have backup generators which could backfeed the grid unless their systems are disconnected from the grid when the generator is in operation, such as through use of a transfer switch. Keep safe.

 

[woodgeek]

Most people would be shocked to know that fossil fuel BTUs convert to electrical delivered BTUs at about 32% efficiency, overall.

Indeed. Most people don't know that heat and energy are different things with thermodynamic limits on their interconversion.

Or for that matter how their refrigerator works.

 

[woodgeek]

Somehow the intermittency of renewable power is continuously brought up as an insurmountable problem, while it has a ready technical solution: storage. There are no limits to how efficient or cheap storage can be.

And yet the severe thermodynamic limits to the conversion of FF to useful work (electricity or propulsion) are NEVER brought up.

And then RE is often scored as if it were converted to BTUs and compared to the 'input BTU' side of the energy system, even though it puts energy on the 'work' side of the system. IOW, if wind provide 5% of electricity, some will say it provides <2% of the energy relative to FF BTUs in the electrical grid. Ugh.

 

[HitzerHillbilly]

Truly a scary thought. Solar PV systems are to be equipped with anti-islanding control to prevent this. But people also have backup generators which could backfeed the grid unless their systems are disconnected from the grid when the generator is in operation, such as through use of a transfer switch. Keep safe.

Yep, and all of our customers that use a renewable resource are required to have anti-islanding devices, or transfer switch or for large operations we have automated reclosers which our company has control of. I was thinking on a smaller residential settings. A primary transfer switch, or automated reclosure, would have to be used at the transformer instead of at the customer's house on their secondary side. I guess one option could be to run a secondary grid connecting so many houses. One that does not even inter tie with the utility company. Just kind of brainstorming. I am sure you guys have put a lot more thought into this than I have.

 

[HitzerHillbilly]

I am really looking into a solar back up system for my house. House is all electric. You recommend any one brand or system in particular?

 

[DBoon]

IOW, if wind provide 5% of electricity, some will say it provides <2% of the energy relative to FF BTUs in the electrical grid. Ugh.

It's better than this - thermal conversion is roughly speaking 40-50% on average for a utility's fossil fuel systems, whereas transmission and distribution are more like 10-15%. Don't quote me on the exact numbers (I'd have to look them up...it's been a while), but this is the rough range. So wind generation sourced close to usage probably has T+D losses in the 5% range, but doesn't have the thermodynamic conversion losses.

 

[jebatty]

Some research I did back in 2009 follows. Progress is slow. As to efficiency in converting input energy into output electrical energy, there is little if any cost or adverse impact in input/output ratio when wind and solar PV are considered in large part because there are no emissions or waste heat. Similarly, virtually no energy needs to be expended to obtain the wind and solar energy once the plant is in place, while with coal there is a very large energy expenditure just to get the coal to the generating plant.

From July 2009:

(broken link removed)

In the United States, about 40.5 percent(6) of anthropogenic CO2 emissions was attributed to the combustion of fossil fuels for the generation of electricity in 1998, the latest year for which all data are available.(7)

Coal has the highest carbon intensity among fossil fuels, resulting in coal-fired plants having the highest output rate of CO2 per kilowatthour.

CO2 emissions from coal-fired electricity generation comprise nearly 80 percent of the total CO2 emissions produced by the generation of electricity in the United States, while the share of electricity generation from coal was 51.0 percent in 1999 (Table 3).


http://en.wikipedia.org/wiki/Fossil_fuel_power_plant

Subcritical fossil fuel power plants can achieve 36–38% efficiency. Supercritical designs have efficiencies in the low to mid 40% range, with new "ultra critical" designs using pressures of 4,400 psia (30 MPa) and dual stage reheat reaching about 48% efficiency.

Older nuclear power plants must operate below the temperatures and pressures that coal fired plants do. This limits their thermodynamic efficiency to the order of 34–37%. Advanced designs, such as the Advanced gas-cooled reactor and the Supercritical water reactor, operate at temperatures and pressures similar to current coal plants, producing comparable efficiency.


(broken link removed)

. . . this ideal maximum [thermodynamic] conversion efficiency is never achieved, so a
generous estimate would be 50%. In addition, the "true" cost is a much more
complicated calculation. The "true" cost takes into account the cost of
mining and transporting the coal, and the operating costs of the generation
(plant cost, salaries, environmental costs, and so on). The bottom line is
that the conversion of coal into electricity is very inefficient.

Estimate of 30% efficiency of 30% for transforming the heat energy of the coal
into electrical energy and transmitting it to your home – [does not include the energy used in mining, transporting, and handling the coal before it is burned]


(broken link removed)

DOE estimates: only a third of the energy value of coal is actually converted into electricity, the rest is lost as waste heat.


http://www.energetics.com/gridworks/grid.html

DOE: America operates a fleet of about 10,000 power plants. The average thermal efficiency is around 33%. Efficiency has not changed much since 1960 because of slow turnover of the capital stock and the inherent inefficiency of central power generation that cannot recycle heat.


(broken link removed to http://wattwatt.com/pulses/95/i-challenge-you-on-electricity-transmission-have-we-got-it-right/)

the overall losses between the power plant and users can easily be between 8 % and 15 %,


http://www.groupsrv.com/science/about326877.html

In any country, the network, through losses, is the biggest consumer of electricity. In Europe, these losses amount to 4-10% of electricity generated, with an average of 7%.