This article describes a 50% reduction of the US primary energy by
means of energy efficiency measures, and build-outs of wind and solar
systems, so that the energy available to provide for the residential,
commercial, industrial, and transportation energy requirements remains
nearly unchanged. These efforts would take at least 25 to 30 years.
EXISTING CONDITIONS
The
US required about 97.141 quads of primary energy in 2013. About 60% of
this energy was rejected as heat and as other losses. See URLs. About
97.141 x 0.4 = 38.86 quads were available to provide for the
residential, commercial, industrial and transportation energy
requirements.
NOTE: A quad = 10 to the fifteenth Btu.
In 2013, the US primary energy consisted of the sources in the below table. The values of energy returned on energy invested, ERoEI, are from published sources.
......................PE, quad........ERoEI.........EI, quad
Solar................0.320.............7.0.................0.05
Nuclear............8.270...........60.0.................0.14
Hydro..............2.560..........100.0................0.03
Wind................1.600............18.0...............0.09
Geoth...............0.201............20.0................0.01
Nat gas...........26.600............30.0................0.89
Coal................18.000............40.0................0.45
Biomass...........4.490...............3.0................1.50
Petroleum.......35.100.............25.0...............1.40
Total...............97.141............21.4...............4.55
The
weighted average ERoEI of the US economy calculates to 21.4 The energy
available for economic activities, other than obtaining energy, was
about (97.141 – 4.55) x 0.4 = 37.04 quads.
Declining ERoEIs: As
ERoEIs decrease, an increasingly greater energy establishment is needed
to produce the same quantity of NET energy, i.e., wind turbines, solar
panels, etc., everywhere. Gusher oil wells of 100 years ago had ERoEIs
of 100 or greater. Shale oil in Canada has an ERoEI of about 3!! As
harvesting each unit of energy requires more and more units of energy,
it becomes increasingly important to arrange the US economy for minimal
energy consumption to preserve standards of living.
In this example, the net energy is a constant 100 units of energy.
ERoEI.....Net Energy..................EI.........................ER..................Net
..................(ERoEI-1)....{100/(ERoEI-1)}.... (ERoEI x EI).......(ER – EI)
1.2...............0.2.....................500.00.....................600..................100; ethanol from corn
1.5...............0.5.....................200.00.....................300..................100
2.0...............1........................100.00.....................200..................100
3.0...............2..........................50.00.....................150..................100; biomass, shale oil
4.0...............3..........................33.33.....................133.33.............100
5.0...............4..........................25.00.....................125..................100
7.0...............6..........................16.67.....................116.67.............100; PV solar, unbuffered
18..............17...........................5.88......................105.88.............100; wind, unbuffered
20..............19...........................5.26......................105.26.............100; geothermal
25..............24...........................4.17......................104.17.............100; petroleum
30..............29...........................3.45......................103.45.............100; natural gas, well-head
40..............39...........................2.56......................102.56.............100; coal, mine-mouth
60..............59...........................1.69......................101.69.............100; nuclear, centrifugal enrichment
100............99...........................1.01......................101.01.............100; gusher oil well and hydro
NOTE: The
heavily subsidized, ethanol-from-corn program has an ERoEI of about 1.2
- 1.3, depending on growing conditions, even with co-product credits!!
The lower the ERoEI, the more energy (and environmental impact) it takes
to produce a net quantity of energy.
ENERGY EFFICIENCY
Nationwide efficiency
measures at about 1.42%/y for 25 years could reduce the 97.141 quads by
about 30%, or 0.3 x 97.141 = 29.14 quads. The 1.42%/y is based on the
primary energy. Transportation: In May 2012, the
US finalized new standards to increase the corporate average fuel
economy, CAFE, standard for light duty vehicles, LDVs, from the current
27.5 MPG to 35.5 and 54.5 MPG EPA Combined by 2016 and 2025,
respectively. Europe is well ahead of the US. Already millions of LDVs
are sold each year that get 35 MPG or better.
Below is a comparison of the 27.5 MPG and 54.5 MPG standards:
Travel Mileage
Energy/yr Emissions*
miles/y MPG
lb CO2/y g CO2/km
Present CAFE 12,000 27.5 436 gal 10,647 250.36
2025 CAFE 12,000 54.5 220 gal 5,372 126.33
* Includes upstream CO2 emissions.
Whereas
the higher-mileage vehicles would be more expensive, the amortizing of
the cost difference over 10 years (the average life of US LDVs) would be
more than offset by the significant reduction in annual fuel cost,
i.e., there would be a net reduction in annual owning and operating
costs.
Residential Housing: The US needs to
implement a federal energy code for residential housing to ensure
significant reductions of primary energy for heating, cooling and
electricity. The code should be climate-zone specific. Each state could
opt to have a stricter code. It is economically feasible to have zero-energy or energy-surplus buildings with existing technologies.
BUILDING OUT WIND AND SOLAR SYSTEMS
If
the 97.141 quads were to include 14.25 quads of wind energy and 4.75
quads of solar energy, then, combined with the efficiency measures, the
traditional energy sources could be reduced by 50%, from 97.141 quads to
48.57 quads. Due to the increased wind and solar energy, the US
energy system would produce a greater percentage as electrical energy to
meet the requirements of future plug-in light duty vehicles and heat
pumps for space heating and cooling, and for domestic hot water heating.
The energy available for economic activities would be 48.57 x 0.4 + 14.25 + 4.75 = 38.43 quads.
The
weighted average ERoEI would become 67.57/4.92 = 13.73; see below
table. The energy available for economic activities, other than
obtaining energy, would be about (48.57 – 2.27) x 0.4 + (14.25 – 1.19) +
(4.74 – 1.06) = 35.26 quads. With slightly greater energy efficiency, the same economic activities could be performed as before.
Traditional........... 48.57..........21.4............2.27
Wind.....................14.25..........12.0............1.19
Solar.......................4.75............4.5............1.06
Total.....................67.57.........13.73...........4.52
NOTE:
It is assumed the remaining traditional energy mix continues to have an
ERoEI of 21.4, and 60% as rejected heat and losses*. Wind and PV solar
energy are assumed to have no heat losses, but CSP does have heat
losses. See below.
*The 60% losses would be reduced due to the
above energy efficiency. By how many percent would be a complicated
calculation beyond the scope of this article.
NOTE:
The ERoEI of wind was reduced from 18 to 12, and of solar from 7 to
4.5, their buffered values, because the increased variable, intermittent
wind and solar energy would require:
- Back up generating capacity adequacy, MW, to provide energy when wind and solar are insufficient.
-
Back up flexible generating capacity adequacy, MW, for inefficiently
ramping up and down, at part load, to balance the variable energy.
- Transmission and distribution systems adequacy.
- Energy storage adequacy.
In
2013, wind and solar energy were a minor part of all energy, and the
costs of buffering and ERoEI adjustments were minor as well. As wind and
solar energy become a major part of all energy, buffering costs and
ERoEI adjustments become increasingly significant.
These buffering
costs usually are socialized, i.e., not charged to wind and solar
energy, which, with the various subsidies, makes solar and wind energy
much less costly, enabling owners to enter into power purchase
agreements, PPAs, at near-wholesale prices in some areas of the US. See
below section on federal subsidies.
IMPLEMENTING 14.25 QUADS OF WIND ENERGY
At
end 2014, the installed US wind turbine capacity was 65,879 MW, which
produced 181,791 GWh = 0.621 quads*, at a capacity factor of 0.315. The
estimated invested capital for the wind turbines was about $132 billion,
at $2 million/MW, not including grid, generator and storage
investments.
A wind turbine capacity of 1,489,445 MW, 22.6 times
greater than at end 2014, would be required to achieve 14.25 quads of
wind energy. This section describes the wind turbine capacity and
capital cost required.
* The EIA energy flow chart indicates 1.600
quads, which implies about a 60% loss. This may be an error, as wind
energy does not have such a loss.
Assumptions:
Onshore CF = 0.32; offshore CF = 0.47
Onshore wind turbine 3 MW @ $6 million, which includes all equipment and systems for a complete installation.
Offshore wind turbine 5 MW @ $20 million, which includes all equipment and systems for a complete installation.
Example of Offshore CF: Alpa
Ventus, 60 MW, began full operation in April 2010, average production
during 2011, 2012, 2013 was 253.14 GWh/y, for a 3-year average CF of
0.481. Not all locations would have such high CFs. http://earthtechling.com/2014/02/offshore-wind-powers-eye-popping-capaci...
Alternative No. 1
If
all wind turbines were onshore, 496,482 of 3 MW wind turbines would be
required, for a total of
.................................................................................................$2979
billion
Grid investments, 15% of turbine costs, or ...............................$447 billion
Generator investments, 5% of turbine costs, or .........................$149 billion
Energy storage, 5% of turbine costs, or .....................................$149 billion
Total..........................................................................................$3724 billion
Alternative No. 2
If 50% of the energy were generated onshore and 50% offshore,
248,241 of 3 MW wind turbines would be required........................1489 billion
101,409 of 5 MW wind turbines would be required........................2028 billion
Grid investments, 15% of turbine costs, or.....................................$528 billion
Generator investments, 5% of turbine costs, or.............................$176 billion
Energy storage, 5% of turbine costs, or ........................................$176 billion
Total............................................................................................$4497 billion
The WHOLESALE cost of the wind energy likely would be about:
Onshore: 10 - 15 c/kWh, WITH existing subsidies; about 15 – 20 c/kWh, WITHOUT such subsidies.
Offshore: 20 - 25 c/kWh (based on Cape Wind, et al., projections), WITH existing subsidies; about 25 – 30 c/kWh WITHOUT such subsidies. The
wholesale cost of energy on the US grid has been about 5 c/kWh for the
past 5 years, kept low due to an abundance of domestic, clean, low-cost
natural gas.
IMPLEMENTING 4.75 QUADS OF SOLAR ENERGY
At end 2014, installed capacity of PV solar was 18,321 MW and of CSP
was 1,700 MW. CSP plants, with thermal storage, steam turbine, and, in
the desert, air-cooled condenser systems added to their solar thermal
energy collection systems, have typical overall efficiencies of 25% or
less, and capacity factors of about 0.25.
The estimated production
was 18,321 MW x 8760 h/y x CF 0.18 + 1700 MW x 8760 h/y x CF 0.25 =
28,889 + 3,723 = 32,612 GWh = 0.111 quad*. A solar capacity of 42.8
times greater than at end 2014 would be required to achieve 4.75 quads
of solar energy. This section describes the solar capacity and capital
cost required.
* The EIA energy flow chart indicates a primary
energy of 0.320 quads. This may be an error, as PV solar energy does not
have such a loss, but CSP does have a loss due to heat rejection of the
steam cycle. Below is a primary energy and loss calculation. It
appears, EIA has overstated the PE.
............................PE................Useful..............Loss
PV + CSP...........0.3200............0.1113..............0.209; per EIA
PV.....................0.0986............0.0986......................; actual
CSP...................0.0508............0.0127..............0.038; actual
The estimated capital cost would be about:
PV capacity 18,321 MW x 42.8 x $3,500,000/MW...........................$2738 billion
CSP capacity 1,700 MW x 42.8 x $4,200,000/MW..............................$305 billion
Total...................................................................................................$3043 billion
Grid investments, 10% of system cost.................................................$304 billion
Generator investments, 5% of system cost..........................................$152 billion
Energy storage, 5% of system cost......................................................$152 billion
Total.................................................................................................. $3652 billion
HIERARCHY OF ENERGY NEEDS
If
the EROEI of oil were 1.1, then one could pump oil out of the ground
and look at it. If it were 1.2 one could both extract it and refine it.
If it were 1.3, it could be distributed to where it is useful, but all
you could do is look at it. It would take, AT THE WELLHEAD:
- An ERoEI of at least 3 to build and maintain a truck and the roads and bridges, including depreciation.
- An ERoEI of about 5 to grow and process foods and deliver products in the truck.
-
An ERoEI of about 7 to 8 to include depreciation of the oil field
worker, refinery worker, truck driver and the farmer, and to support
their families.
- An ERoEI of about 9 to 10 to educate the children of these families.
- An ERoEI of about 12 to provide families and workers with health care and higher education.
- An ERoEI of about 14 to provide families and workers with the performing arts and other social amenities.
A
modern civilization needs not just surplus energy but lots of it, and
that requires either high ERoEI energy sources, or an abundant supply of
moderate ERoEI energy sources. Low ERoEI sources, such as biodiesel and
ethannol from corn, etc., would not qualify, i.e., they are more
trouble than they are worth.
REASONS FOR THE HIGH ERoEI OF THE US
The
US would need an ERoEI of about 14 to have a high level, modern
society. However, it has an ERoEI of about 21.4. There are several
reasons for this difference:
- The 60% primary energy losses, such as due to inefficient buildings and transportation.
- Repair/mitigate environmental impacts, such as oil spills, and wind, flood, fire and drought damages.
- Inefficient healthcare and education systems, as reflected in higher costs than in other nations.
- The military-industrial-intelligence, MII, complex with which to exert leadership in the world.
Without
the extra ERoEI, the US would not be able to have its huge,
energy-guzzling, MII complex. Russia, which has an abundance of energy
sources, has a similar, albeit much smaller MII complex, largely to
protect its vast natural resources from foreign takeovers*. Europe, an
importer of energy sources, can have only a “helper” MII complex, hence
its underfunding of NATO. China and Japan, also importers of energy
sources, are similarly handicapped to have major MII complexes.
*Russia’s
suspicions of NATO and EU ambitions in East Europe should be
understood, as France invaded Russia in June 1812; Japan in 1905; the US
with 8,000 troops in 1918 – 1920 (a failed attempt to overthrow the
Communists); Japan in 1939 (Manchurian-Mongolian frontier), and Germany
in June 1941, and NATO is moving its assets adjacent to the Russian
border.
FEDERAL SUBSIDIES FOR ENERGY IN 2013
Below is a table of federal subsidies
for traditional and renewable energy for 2013. Some of the “As
Published” values are from the references, and do not agree with the “As
Calculated” values. RE received 72.5% of the subsidies, but produced
only 13.1% of all the energy. Wind subsidy was 3.522/0.67 = 5.3 times
greater than gas. Solar subsidy was 23.121/0.67 = 34.5 times greater
than gas.
Source........................Subsidy.......Production..........As Calculated.....As Published
....................................million $.....billion kWh...............c/kWh...............c/kWh
Coal..................................901..............1586....................0.057................0.057
Gas + Petro Liq..................690..............1141....................0.060................0.067
Nuclear............................1660................789....................0.210................0.210
Other........................................................20
Total Trad.......................3251.............3536...................0.092
Biomass...........................118..................60.....................0.197................0.207
Geothermal......................245..................17.....................1.441................1.480
Hydro...............................392................269.....................0.146................0.147
Solar, Utility + Distr...........4393.................19...................23.121..............23.121
Wind...............................5936................168....................3.533................3.533
Other RE...........................594
Total RE.......................11678................533....................2.191
Smart Grid + Trans............1184
Total.............................16113..............4069...................0.367
DRAWBACKS OF WIND TURBINE SYSTEMS ON RIDGELINES
Wind turbine systems would:
- Cause major environmental damage to mostly pristine ridgelines.
- Be highly visible, and highly damaging to tourism and ambiance.
- Expose tens of thousands of people to excessive noise, affecting their sleep, health and overall wellbeing.
- Have higher capital costs/MW, compared to Great Plains and Panhandle
- Have higher O & M costs/MWh, compared to Great Plains and Panhandle
- Have lower capacity factors, compared to Great Plains and Panhandle
-
Have shorter useful service lives (15 – 25 years) compared to
traditional power plants (40 – 100 years), i.e., high replacement rates.
FUEL AND CO2 REDUCTION DUE TO WIND ENERGY IS LESS THAN CLAIMED
With
increased wind energy on the grid there would be reductions in fuel
consumption and CO2 emissions, but to a significant percent they would
be offset by:
- The increased inefficient, part-load operation of the traditional generators.
- The increased hot, synchronous spinning requirements of traditional generators.
- The less efficient scheduling of traditional generators.
Example: New England, if foolish enough to invest about $80 billion in wind turbines
to have about 40% percent of its annual energy from wind, would need
major HVDC connections to the Quebec, Labrador and New Brunswick grids
for balancing and backup of its wind energy. Doing it with NE gas
turbines would require them to operate inefficiently due to ramping up
and down, at part load, i.e., more Btu/kWh, more CO2/kWh. In any case,
the NE gas turbine balancing and backup capacity would be inadequate for
balancing and backup.
Example: Ireland had an
island grid with a minor connection with the UK grid until October 2012.
Eirgrid, the operator of the grid, publishes ¼-hour data regarding CO2
emissions, wind energy production, fuel consumption and energy
generation. Drs. Udo and Wheatley made several analyses based on 2011
and earlier Irish grid operations data that offer clear evidence of the
effectiveness of CO2 emission reduction decreasing with increasing
annual wind energy percentages.
The Wheatley study of the Irish grid shows: Wind energy CO2 reduction
effectiveness = (CO2 intensity, metric ton/MWh, with wind)/(CO2
intensity with no wind) = (0.279, @ 17% wind)/(0.53, @ no wind) = 0.526,
based on SEMO data.
If 17% wind energy, wind energy promoters typically claim a 17% reduction in CO2, i.e., 83% is left over.
If 17% wind energy, actual performance data of the Irish grid shows, 0.526 x 17% is reduced = 8.94%, i.e., 91.06% is left over.
What
applied to the Irish grid would apply to the New England grid as well,
unless the balancing is done with hydro, a la Denmark.
Europe is
facing the same problem, but it is stuck with mostly gas turbine
balancing, as it does not have nearly enough hydro capacity for
balancing.
VARIABLE WIND ENERGY ADVERSELY AFFECTS GRID STABILITY
Phasing
out the above 38% of energy on the NE grid will eliminate the grid
stability (frequency, voltage, phase) provided by the SYNCHRONOUS
inertia of their large, rotating turbine generators. Frequency dynamics
are faster in power systems with low rotational inertia, such as when
significant wind and solar energy has been added, making frequency
control and power system operation more challenging.
Performance Curve of a Wind Turbine:
Wind turbine manufacturers publish wind turbine performance curves with
the familiar shape. At a given wind speed, there is a given energy
output. In reality, the wind speed AND direction are constantly
changing, especially in hilly areas, such as on ridgelines.
The published performance curve of a wind turbine shows:
-
Zero output for wind speeds of 0 to about 7 mph; 1 mph = 0.44704 m/sec.
Wind energy intermittency is unpredictable, as it can occur anytime the
wind speed is less than about 7 mph. The intermittency of traditional
generators is highly predictable, except in the rare event of an
unscheduled outage.
- Continuously variable output with the cube
of the wind speed for wind speeds from about 7 mph to about 33 mph, the
maximum speed to achieve rated output.
- A near constant output from about 33 mph to 55 mph.
- A shutdown speed of about 55 mph, which can occur during wind gusts, which are unpredictable and can occur at any time.
Wind Speed and Direction:
Whereas an 8” anemometer quickly indicates wind speed and direction,
that is not the case with a multi-ton nacelle quickly reducing the yaw
angle to perpendicularly face the wind, and 175-ft long blades of a
373-ft diameter rotor quickly changing speed and pitch.
As a
result, the wind turbine output is constantly changing at a indicated
anemometer wind speed. The resulting performance curve is a scatter
diagram that has the shape of the published performance curve, but may
have output variations of plus or minus 20% for an indicated anemometer
wind speed. Adding such scatter diagrams gives a scatter diagram as the
output of a multi-turbine installation.
Variable updrafts and
downdrafts upstream of the rotor, common in hilly areas, also add to
such output variations; nacelle and blade adjustments would not be
effective to reduce those additions to output variations. Grid stability
would be made worse by phasing in increasingly larger quantities of
such variable, intermittent wind energy.
To reduce excessive
output variations and grid disturbances of a wind turbine installation,
various output control strategies are being developed and tested using
some later model wind turbines. The strategies attempt to control output
variations within preset limits by continuously varying the nacelle
orientation, and the speed and pitch of the blades.
As an alternative, synchronous-condenser
systems, upstream of the substation that feeds into the high voltage
grid, are used to “clean up” frequency and phase variations, as with the
$10.5 million, 62-ton, synchronous-condenser system for the Lowell
Mountain wind turbine installation in Vermont.
NOTE:
Grid stability would also be made worse by phasing in variable,
intermittent solar energy to distribution and high voltage grids. Solar
energy is particularly variable during variable-cloudy weather, common
in New England.
NOTE: The moment energy is fed
into a distribution grid or high voltage grid, it immediately spreads,
as electromagnetic waves, at near the speed of light, and gets consumed
along its many ways. The electrons migrate very slowly; mostly they
vibrate in place at 60 Hz. The notion RE fed into the grid is locally
consumed, and use that as a basis for awarding subsidies or other
preferential treatment, is entirely wrong, as moving at near the speed
of light means from northern Maine to southern Florida, about 1,800
miles, in 0.01 second.
NOTE:
- Denmark has
built its entire wind turbine set-up around the hydro plants in Norway
and Sweden, which balance its wind energy; Denmark has the highest
household electric rates in Europe, about 30 eurocent/kWh.
- Ireland expensively balances its wind energy with gas turbines; the gas is imported.
-
Spain and Portugal expensively balance their wind energy with gas
turbines and pumped-storage hydro plants; the gas is imported.
-
Germany expensively balances its wind energy with flexible coal plants,
gas turbines and “borrowing” the spare balancing capacity of nearby
grids; the gas is imported; Germany has the second highest household
electric rates in Europe, about 29.5 eurocent/kWh, due to the ENERGIEWENDE program.
WIND AND SOLAR ENERGY ARE VARIABLE AND INTERMITTENT
People should know by now, in New England:
-
Wind energy is zero about 30% of the hours of the year (it takes a wind
speed of about 7 mph to start the rotors), minimal most early mornings
and most late afternoons, about 60% of all wind energy is generated AT
NIGHT.
- Solar energy is zero about 65% of the hours of the
year, minimal early mornings and late afternoons, minimal much of the
winter, and near-zero with snow and ice on the panels.
- During
winter in New England, solar energy, on a monthly basis, is as low as
1/4 of what it is during the best month in summer; 1/6 in Germany.
- Often both are at near-zero levels during many hours of the year. See URL, click on Renewables. in the Fuel Mix Chart to see the instantaneous wind and solar %.
-
Germany has excellent public records for the past 12 years showing the
variability and intermittency of wind and solar energy, i.e.,
denial/obfuscation of the facts is not an option.
That means, in
Germany and in New England, ALL other existing generators must be kept
in good running order, staffed, fueled, ready to go, to provide varying
quantities of energy almost all hours of the year, including for
balancing the variable solar and wind energy. The end result: Two energy
systems to do one job!
RURAL HIGH VOLTAGE GRIDS AND VARIABLE WIND ENERGY
The
current Northeast Kingdom, NEK, grid in Vermont is perfectly adequate
to serve the NEK demands, but feeding variable (voltage, frequency,
phase), intermittent wind energy into that grid would cause excessive
instabilities, as was found with the Lowell project.
It is well
known by various government entities, the NEK would need at least $300
million of grid upgrades before significant variable, intermittent, grid
disturbing, wind energy could be added. Just adding the cancelled
SENECA system would have cost $86 million in grid upgrades. GMP had to
spend a total of about $20 million to connect the Lowell system to the
grid, including a $10.5 million, 62-ton, synchronous-condenser system.
ENERGY ON THE GRID
The
instant renewable energy is fed into a distribution grid or high
voltage grid, it immediately becomes part of the existing mix of the New
England grid, and the NEW mix spreads as electromagnetic waves, at near
the speed of light, and gets consumed along its many ways. The
electrons migrate very slowly; mostly they vibrate in place at 60 Hz.
Some
patriotic enthusiasts absurdly claim a state, say Vermont, has its very
own energy mix!! Their claim locally-generated RE fed into the grid is
locally consumed is a feel-good, RE-promoting ploy to make lay people
think they are consuming their locally generated RE. Those claims have
nothing to do with physical reality.
Government entities even use
that ploy as a basis for making analyses to show off the benefits of RE,
and for awarding subsidies, or giving other preferential treatment.
There
is nothing local about energy after it has been fed into the grid, as
moving at near the speed of light means from northern Maine to southern
Florida, about 1,800 miles, in 0.01 second. Depending on the quantity of
RE fed into the grid, it could be consumed as part of the NEW mix
almost anywhere within 5, 10, 50 or 100 miles.
BATTERY SYSTEMS FOR ENERGY STORAGE AND GRID STABILITY
Using Batteries For Storing Energy Now for Later Use:
Economically viable energy storage systems, other than hydro, have not
yet been invented, and would take many billions of dollars and decades
to deploy AFTER they are invented. At present, using batteries for
energy storage during the day and using the energy at night costs about
23 c/kWh JUST FOR STORAGE, per a David Hallquist study for the DOE.
Using Batteries For Reducing Grid Disturbances:
Increasing the capacity, MW, of PV solar systems tied to a distribution
grid will decrease its stability, because energy from PV solar systems
significantly varies from minute to minute, especially
during variable-cloudy days, common in New England. Battery systems tied
to the distribution grid are used in California and Germany to smooth
excessive energy variations. They act as dampers, which work as follows:
- The DC energy of the PV panels is sent as AC into the distribution grid.
-
If necessary, some of the energy is converted to DC before charging
into the utility-owned battery system to maintain distribution grid
stability.
- If necessary, some of the battery energy is converted
to AC and sent into the distribution grid to maintain distribution grid
stability.
- DC to AC inverters are about 85%, 50%, and 10%
efficient at 20%, 10% and 2% outputs, respectively, i.e., much of the
converted energy is lost as heat.
- Such charging and discharging
has very little to do with storing PV solar energy during the day for
use at night, as is sometimes claimed.
- If a battery system has
sufficient capacity, it can perform its stabilizing function during the
day while storing energy for use at night.
http://www.theenergycollective.com/willem-post/2264202/reducing-us-primary-energy-wind-and-solar-energy-and-energy-efficiency
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