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Author Topic: Brilliant or nonsense?  (Read 2086 times)
Justme
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« on: March 27, 2012, 10:23:01 PM »

Liquid metal battery.

http://www.ted.com/talks/donald_sadoway_the_missing_link_to_renewable_energy.html

Brilliant or nonsense?
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« Reply #1 on: March 27, 2012, 10:47:21 PM »

Well...... it left me scratching my head because of the gaps in the explanation - to be frank I think he avoided several points - ok it gets hot, but does it work if it isn't hot? If it's getting hot, that would tend to point to inefficiency because it's producing heat - the two metals melt around 650 degrees c, so do I want them under the seat in my shed? (in place of my lead acids?)- I'm baffled! Undecided
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smegal
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« Reply #2 on: March 27, 2012, 10:51:24 PM »

I didn't watch the video but sodium sulphur batteries work fine.
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billi
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« Reply #3 on: March 27, 2012, 11:02:45 PM »

Too much  of a Priest    this Guy is   ....  in my opinion


Time moves so fast  , but i still think   its important to link   Europe's  renewable s  together       and think about that potential  first


The more equalized charging i have the less battery i need 

Battery is not the God ,  Generation is more important and its Management
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dhaslam
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« Reply #4 on: March 27, 2012, 11:04:41 PM »

It sounds OK but  it does seem that there woud be multiple linked smallish  batteries that might increase the cost of a large system.   On the other hand it may  lead to smaller scale applications as well.   This isn't the case with sodium sulphur  battteries.

http://en.wikipedia.org/wiki/Sodium%E2%80%93sulfur_battery
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« Reply #5 on: March 28, 2012, 02:40:25 PM »

Probably has it's place with other large scale batteries.  Flow batteries are good at industrial scale where you can have pretty much unlimited kWh storage as you just need big vats of the two fuels.  The flow batteries are just liquid fuel cells but the spent fuel is collected and stored and then recharging reconstitutes the original fuel.

The liquid metal battery could work the same way but for the danger of pumping liquid metals at 700C!

As the fuel is automatically separated by its density (the magnesium floats to the top), you could keep replenishing the magnesium at the top and tapping off the "spent" alloy at the bottom.  The salt takes no part in the chemistry, just being a separator and an ion transport (like the electrolyte in a lithium cell).

As for the heat of the liquid metal cells, I'd expect the bigger the cell, the more efficient it would become as the heat loss from the cells decreases with volume as the surface area to volume ratio falls.

However we arrive at it, the fundamental issue is the same.  Renewables need grid level storage.  Either in bulk storage like this or in distributed storage like the Grid Buddy we've been debating in another thread or even my own lithium storage system (allthough that's off grid but grid interactive as on bad days I switch loads to grid).

Another way to look at the problem is one of forecasting renewable grid support.  The inhibitor to renewables taking a big slice of the generating mix is the intermittentcy and unpredictability of its ability to deliver base load.  The backup generators have generally slow response times to sags or are expensive per kWh if they can spool up quickly.

We don't need much renewable storage.  Not like for off grid where you would need maybe a few days of autonomy for bad weather.  For grid management you only need as much battery as would provide a few hours of guaranteed renewable energy.  A buffer that allows you to increase the percentage of renewable generating in the mix and be able to guarantee its delivery.  So long as the battery can cover the guaranteed renewable load contribution for long enough for coal, gas and nuclear to then plan their output a few hours in advance, you can remove the dangerous uncertainty that would otherwise exist at high renewable generating mix percentages.

At the moment they are trying to predict the renewable output based on weather forecasting 1-6 hours ahead.  That's not good enough.  It's not a guarantee of xxx MWh available for the next 6 hours.  Batteries give you that assurance based on what WAS collected in the LAST 6 hours, not what you HOPE will be collected in the NEXT 6 hours.  If the renewables don't make enough, you'll know exactly how much you have in reserve and how much coal to toss on the fire to make up the difference.

It's exactly like a capacitor in a AC-DC power supply.  The rectified AC makes intermittent DC.  A suitably sized smoothing capacitor in the DC output  guarantees constant power flow into the DC load.  In a power supply it's easy to calculate the size of the capacitor (buffer), as you know the period of peak input (every 1/100th of a second) and how big the input peaks will be.  The capacitor is only sized big enough to provide the DC designed load with continuous current for the troughs in input (also every 1/100th of a second).  It doesn't have to be any bigger than that to deliver a guaranteed load.

I predict that if PV continues to expand in residential application then, at some point, the DNOs will say that no more installations can be carried out without local distributed storage.  The Japanese are incentivising it now by adding a secondary FIT mechanism for PV with intelligent lithium storage.  The DNOs are already clamping down on over sized installations over 16A feed in.  Because there is no storage in the system.

It makes perfect sense to have a generator with a potential capacity of 10-15kWh per day and maybe 3kWh local storage.  The house can be an exporter of energy when required (day or night, irrespective of weather) or present a reduced peak load when required by self-consuming its stored energy.  Earning the house a credit for providing distributed generation and storage and saving the house import costs.

The Grid Buddy thing is not bad, but it's using the wrong type of battery, that's all.  My battery if used to under 70% discharge per day will (in theory) last over 8,000 cycles or 22 years.  Since installing it in mid February, I've had two 90% discharges (one on purpose for maintenance) and now in the sunny weather we're having, I'm probably not using more than 40% of discharge capacity per day to deliver 80% of my household demand for electricity (average so far in March) plus the odd tank of hot water with no gas use either.

The question is not as small as "Does a grid assist battery make financial sense for me?".  It's "Does grid assist battery form part of a viable strategy for increasing the percentage of renewables in the generating mix?".  If it can be made cost neutral / beneficial to the provider of the storage (you and me), then that's a fringe benefit.  To meet our goals of using renewable energy mix, it needs to become mandatory.  If you want to install PV, you must install pro-rated storage.

Distributed stoarge has drawbacks... Kit is needed in each home that generates.  The batteries are small and inefficient in terms of packaging used (plastics for the cells, etc.).  But it has one very useful redeeming feature.  Automatic scale.  As more residential renewables come on line, the right amount of storage comes on line with it.  No need to find a home for a battery bank the size of a gasometer in every town (like in the days when we needed gasometers as a buffer for gas supply locally).

4kWh of storage fits under the sofa.  Under the stairs cupboard.  In the loft, next to the PV panels and the AC inverter.
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