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what would a similar system scaled down to average home cost?

K

kimmo

Jan 1, 1970
0
interesting article in nytimes (replicated for those who dont have a signon)

assume average house would want/need a storage capacity for 10kw or 20kw

Wind Drives Growing Use of Batteries
By MATTHEW L. WALD
The rapid growth of wind farms, whose output is hard to schedule reliably or even
predict, has the nation's electricity providers scrambling to develop energy storage
to ensure stability and improve profits.

As the wind installations multiply, companies have found themselves dumping energy
late at night, adjusting the blades so they do not catch the wind, because there is no
demand for the power. And grid operators, accustomed to meeting demand by adjusting
supplies, are now struggling to maintain stability as supplies fluctuate.

On the cutting edge of a potential solution is Hawaii, where state officials want 70
percent of energy needs to be met by renewable sources like the wind, sun or biomass
by 2030. A major problem is that it is impossible for generators on the islands to
export surpluses to neighboring companies or to import power when the wind towers are
becalmed.

On Maui, for example, wind generating capacity over all will soon be equal to
one-fourth of the island's peak demand. But peak wind and peak demand times do not
coincide, raising questions about how Hawaii can reach its 70 percent goal. For now,
the best option seems to be storage batteries.

In New York and California, companies are exploring electrical storage that is big
enough to allow for "arbitrage," or buying power at a low price, such as in the middle
of the night, and selling it hours later at a higher price. In the Midwest, a utility
is demonstrating storage technology that can go from charge to discharge and back
several times a minute, or even within a second, bracing the grid against the
vicissitudes of wind and sun and transmission failure. And in Texas, companies are
looking at ways of stabilizing voltage through battery storage in places served by
just one transmission line.

Renewable goals can be met, many in the industry insist. But if the energy source is
intermittent, "you can't do that without batteries of some sort," said Peter Rosegg, a
spokesman for the Hawaiian Electric Company.

His company has agreed to buy electricity from a wind farm on the northern shore of
Oahu, where the Boston-based power company First Wind has just broken ground.

The spot is one of Hawaii's best wind sites, Mr. Rosegg said, but the supply is gusty
and erratic. What is more, it is at the farthest point on the island from the company's
main load center, Honolulu, and does not even lie on its high-voltage transmission
backbone.

So the 30-megawatt wind farm, which will have enough power to run about 30 Super
Wal-Marts, will have Xtreme Power of Austin, Tex., install a 15-megawatt battery.

Computers will work to keep the battery exactly half-charged most hours of the day,
said Carlos J. Coe, Xtreme Power's chief executive. If the wind suddenly gets stronger
or falls off, the batteries will smooth out the flow so that the grid sees only a more
gradual increase or decrease, no more than one megawatt per minute at some hours of
the day.

The Hawaii installation is designed to succeed at a crucial but obscure function:
frequency regulation. The alternating-current power system has to run at a strict 60
cycles per second, and the battery system can give and take power on a micro scale,
changing directions from charge to discharge or vice versa within that 60th of a
second, to keep the pace steady.

The battery system can also be used for arbitrage, storing energy at times when prices
are low and delivering it when prices are high. It can hold 10 megawatt-hours, which
is as much energy as a 30-megawatt wind farm will produce in 20 minutes if it is
running at full capacity. That is not much time, but it is huge in terms of storage
capacity.

Neither First Wind nor Xtreme Power would say what the project cost, but publicly
disclosed figures put the project in the range of $130 million, with about $10 million
for the battery. The Energy Department has provided a $117 million loan guarantee.

Across the country, it is proving hard to predict the cost and the value of power
storage to consumers. The electricity stored in off-peak hours could be quite low in
cost, and prices at peak hours could be quite high. If the reliance on renewable
energy reduces the need to burn coal and natural gas, that would yield an additional
advantage.

Mr. Coe estimated the battery system's round-trip efficiency - that is, the amount of
electricity the batteries could deliver per megawatt-hour stored in them - at over 90
percent. If that figure is borne out, it would be a significant advance from the
largest form of energy storage now in general use, pumped hydropower, whose efficiency
is put at 70 to 85 percent.

At a pumped hydro plant, off-peak electricity is used to pump water from a reservoir
at a low elevation to one at a higher one. At hours of peak demand the water flows
back down through a turbine, creating electricity.

Electric companies are using other strategies for storage and frequency regulation. In
Stephentown, N.Y., near Albany, a Massachusetts company, Beacon Power, is building a
bank of 200 one-ton flywheels that will store energy from the grid on a
moment-to-moment basis to keep the alternating current system at a strict 60 cycles.

Atop each flywheel is a device that can be a motor at one moment and a generator the
next, either taking energy and storing it in the flywheel or vice versa. The Energy
Department provided a $43 million loan guarantee to assist in the $69 million project.

The Energy Department is also supporting storage projects that rely on compressed air.
Surplus electricity is used to pump air into an underground cavity; when the
electricity is needed, the air is injected into a gas turbine generator. In effect, it
acts as a turbocharger that runs on wind energy captured the previous night, instead
of natural gas burned at a peak hour.

The department is contributing to two projects explored by PSEG Global, an affiliate
of Public Service Electric and Gas, based in New Jersey. It plans to provide $30
million of the $125 million estimated price of a 150-megawatt project envisaged in
upstate New York, perhaps at an abandoned salt mine, and $25 million toward a $350
million, 300-megawatt project to be built in Northern California.

Both will be used to store power made in off-peak periods and deliver it in peak
times, when prices are higher, said Paul H. Rosengren, a spokesman for P.S.E.G.

In Presidio, Tex., American Electric Power and MidAmerican Energy Holdings have just
completed a four-megawatt battery system that is not tied to any particular wind farm
but is intended to improve reliability in the town, served by only one major
transmission line. American Electric Power already has smaller batteries working in
Ohio and Indiana to provide more stability in its distribution systems there.
 
V

vaughn

Jan 1, 1970
0
For comparison you can buy a 12V 105AH deep discharge marine battery
(1.2 KWH) for under $100.

OK, let's do a little "napkin math" to see if this makes any sense. (You are
free to make your own assumptions, but let's start with mine)

First assumption: 50% DOD (More than that will shorten the life of the battery)
So we can store .6 KWH/cycle per battery.
Second assumption: One cycle per day
Third assumption: Battery life = 3 years = 1095 cycles @ 50% DOD (A more
expensive battery will last longer.)

Over its lifespan our battery will store a total of ..6 X 1095 = 657 KWH

Divide $100.00 battery cost by 657 to get storage cost per KWH 100.00/657= 15.2
cents/KWH for STORAGE, you need to add the actual cost of the energy plus the
other costs for the storage system to get your full storage cost.

I don't know about you, but that does not sound like anything that would make
financial sense for a home that has access to the grid. My cost for grid power
is far less than that.

Vaughn
 
OK, let's do a little "napkin math" to see if this makes any sense. (You are
free to make your own assumptions, but let's start with mine)

First assumption: 50% DOD (More than that will shorten the life of the battery)

IIRC, Nick Pine demonstrated that deeper discharges resulted in the
highest amount of lifetime kWhs. He used data from Trojan, for L16s I
think. It wasn't a big difference though.
So we can store .6 KWH/cycle per battery.
Second assumption: One cycle per day
Third assumption: Battery life = 3 years = 1095 cycles @ 50% DOD (A more
expensive battery will last longer.)

I've seen folks with poorly maintained T105s go beyond 5. The usual
assumption for normal maintenance and correct loading is 5 years for
105s, 10 years for L16s, and 20 for industrial quality.
Over its lifespan our battery will store a total of ..6 X 1095 = 657 KWH

Divide $100.00 battery cost by 657 to get storage cost per KWH 100.00/657= 15.2
cents/KWH for STORAGE, you need to add the actual cost of the energy plus the
other costs for the storage system to get your full storage cost.

I don't know about you, but that does not sound like anything that would make
financial sense for a home that has access to the grid. My cost for grid power
is far less than that.

Vaughn

That looks about right, but don't forget to allow for the fact that
with most battery-based power setups, not all the energy makes a trip
through the batteries. At my own place, some days it's virtually none.
For a few it's 100%. Anything over about 2kW generally comes from the
batteries. When welding during daytime while simultaneous loads are
invariably present, it tends to be more than half the power from the
batteries. Quick estimate of the average overall - perhaps a quarter
of the total consumption takes the battery route. Tracking and wind
power helps considerably.

Quick and dirty for 1kW solar, 2kW inverter, 48V string of L16s...
say, $8k total, and 5kWh per day production. Call it an average 20
year life for most of the setup except the batteries = 17 cents per
kWh for generation, and an additional 11 for batteries. Some folks are
already paying more than that for grid energy, without counting the
hookup cost which can be substantial even if it might be buried in the
home purchase price. Add in the generally ignored external costs which
are put off onto future generations, and a very good case can be made
for home power.

Wayne
 
V

vaughn

Jan 1, 1970
0
IIRC, Nick Pine demonstrated that deeper discharges resulted in the
highest amount of lifetime kWhs. He used data from Trojan, for L16s I
think. It wasn't a big difference though.

Like I said, different folks, different assumptions. I do notice I forgot to
figure in the round-trip efficiency of the battery. When you put 1 kWh into a
battery, you unfortunately do not get 1 kWh. I usually se 80% used as an
assumption. Don't know if that includes inverter and other system losses.
I've seen folks with poorly maintained T105s go beyond 5.

With daily cycles?
The usual assumption for normal maintenance and correct loading is 5 years for
105s, 10 years for L16s, and 20 for industrial quality.

Fair enough, but even those assumptions have problems. At the end of life
(whatever that is) you no longer have a battery with the original capacity,
because the battery capacity slowly decreases over its lifetime. So you can't
really use the full factory nameplate capacity as a lifetime figure when doing
your cost calculations.
That looks about right, but don't forget to allow for the fact that
with most battery-based power setups, not all the energy makes a trip
through the batteries.

Yes, but the article was more about storage for time-shifting to take advantage
of excess capacity and to get around peak hour pricing. My point is that
battery energy storage is not free, it can actually be quite expensive.
Quick and dirty for 1kW solar, 2kW inverter, 48V string of L16s...
say, $8k total, and 5kWh per day production. Call it an average 20
year life for most of the setup except the batteries = 17 cents per
kWh for generation, and an additional 11 for batteries.

OK, I was mostly talking about the battery portion of the expense. I came up
with 15 cents per kWh, while your working assumption is 11 cents, so we agree
that battery storage is neither free nor cheap. Last month, I paid just under
11 cents/kWh for my grid power (all inclusive). It would make no sense to pay
11 cents/kWh to store power that costs me 11 cents.kWh.

Thanks for a good response!

Vaughn
 
Like I said, different folks, different assumptions. I do notice I forgot to
figure in the round-trip efficiency of the battery. When you put 1 kWh into a
battery, you unfortunately do not get 1 kWh. I usually se 80% used as an
assumption. Don't know if that includes inverter and other system losses.


With daily cycles?

Yup. One guy I'm thinking of had the most messed up arrangement
imaginable. It didn't look like it was possible that it ever got fully
charged, and yet it had been functioning that way for over 5 years
then, and another year since. I'm thinking that the daily discharges
were always shallow though, and for sure they're shallow now with full
charges most days. The bank may only be a fraction of its original
capacity, but it's still doing the job.
Fair enough, but even those assumptions have problems. At the end of life
(whatever that is) you no longer have a battery with the original capacity,
because the battery capacity slowly decreases over its lifetime. So you can't
really use the full factory nameplate capacity as a lifetime figure when doing
your cost calculations.

That's supposed to be taken into account when purchasing. But the
longer the projected life span, the less likely that the use will be
as expected. About the only thing that's stayed the same with my place
over the last 15 years is that the energy use keeps changing. :) 3
different radio-phone setups over the years, 3 different Internet
delivery methods, 2 different TVs, 3 different time-shifting setups,
daily computer use was originally 1 machine for 1 hour, now it's 3
machines for a total of 15 hours, etc.
Yes, but the article was more about storage for time-shifting to take advantage
of excess capacity and to get around peak hour pricing. My point is that
battery energy storage is not free, it can actually be quite expensive.


OK, I was mostly talking about the battery portion of the expense. I came up
with 15 cents per kWh, while your working assumption is 11 cents, so we agree
that battery storage is neither free nor cheap. Last month, I paid just under
11 cents/kWh for my grid power (all inclusive). It would make no sense to pay
11 cents/kWh to store power that costs me 11 cents.kWh.

Disregarding the battery thing for a moment, the only sense would be
if you wanted to make a "green" statement and a good long-term
investment. Plug your zip, monthly bill, and the name of your power
company into this
http://www.solar-estimate.org/index...solar-calculator&subpage=&external_estimator=
You might want to change the default $8 to reflect your local costs
and/or your DIY skills. Retail is supposedly $5 here according to
local news reports. I did it for my place just for fun - called it $60
per month and $5 per watt. It came up with $5K investment, 9 year
breakeven and nearly 300% return.
Thanks for a good response!

Right back at ya'.

Wayne
 
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