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Comment Re:The big problem with PV (Score 1) 167

So a peak that lasts 10 hours?

Again this is not about the peak power source but the replacement of a base power source by an intermittent one. The 10 hour number is a number that wouls allow the lack of an intermittent source to be replaced by battery for a reasonable period of time.

So storage is even further away from being needed?

As the title of the article is "Solar Could Lead In Power Production By 2050" and the only way Solar can do that is to replace a base power source then storage is needed to make an intermittent source like Solar look like a base source from the grids persepective then yes storage is needed.


Comment Re:The big problem with PV (Score 1) 167

Understand I work for a power company, and as I said I'm giving the electric companies perspective.

And energy use goes down on cloudy days (less A/C used). You are looking for a problem that doesn't exist. There are plenty of battery technologies out there. They aren't used because they aren't economical, not because they don't exist.

I'd say you live in a warm climate.. Cloudy days means more energy in colder climates. France uses at its peak about 100 GWatts of electricity. Say you'll need at least 10 hours of battery storage, then you are talking about 1 TWh of power storage for 100% replacement by PV. You can't seriously imagine that any current battery technology can supply that type of storage. Hydro can get you part of the way there, but the largeset damn in France has 800MW of generation and can only supply about 2h at that level. As well that dam is not a STEP (Pump water up hill when power is cheap to store energy) and there are only 5 such dams in France for geographical reasons. So as I said there is not storage technologies that are suitable

I never meant storage technologies don't exist just as you say they are not economically viable or available in large enough quantities to make any meanful difference.

There isn't enough solar production to make storage save anything.

Storage is not about "saving" anything, its about making the supplied energy meet exactly the demand. With an intermittent source such as PV you absolutely need another means to ensure demand meets supply, with the ultimate means availble to the power grid being of course a blackout.

And it's what, about 80% of usage during the day? So until that 40% approaches 80%, they obviously don't have over-production of solar that would allow storage. If they had "perfect" storage now, it wouldn't be used. So that's obviously not the problem..

If fact the 40% peak PV is for a Sunny Sunday afternoon, so a lot further away from 80% than you think. .

"Production" needs to be 100% of usage before storage without parallel generation would be feasible. 40% is well below the ability to serve those areas, no matter what the storage was.

Why ? Storage already exists in the grid in reasonable quantities by pumping water up hill. I really think you have no idea how a power grid works.

The supply of electricity must meet the demand at all times, with a little bit of slack taken up in voltage or frequency drops. To meet this simple supply/demand equation, traditionnally there the power production means were split in the two types; "Base" and "Peak". The optimal base energy source is extremely cheap, in Europe on the order of 50€ to 100€ per MWh but with frakking in the US a bit cheaper on the other side of the pond, but difficult to put online, with lead times from hours to days. "Peak" power is optimised for the time it take to put online, of the order of minutes but not cost. A gas turbine might, basically a jet engine with a 200Wh inline generator, costs 1000€ or so for a MWh of prodution. PV and most other renewable energy sources are "Intermittent", so in periods where the base supply is sufficent, they subsitute foe the base supply source, but without storage you can you remove the base source because the source is intermittent. Any amount of storage can allow the removal of some base power source, but to make a meanful reduction in the base source you'd need at least 10h of storage of that base storage. For example to get rid of a 900 MW nuclear reactor at replace it with 900 MW of PV you'd need 9GWh of storage.


Comment The big problem with PV (Score 0) 167

From an energy companies perspective the big problem with solar is that you need to think about what happens on a cloudy day or at night. Basically that means you need to have altenative capacity to produce energy that is in most cases 100% of the installed PV capacity, as the power storage technologies that are available now just aren't up to storing the PV from sunny days for later use. For example PV represents upto 40% of the power for the French operator SEI ( who supply power to Corsica, Martinique, Guadoloupe, etc. However, they have enormous diesel generators they replace the PV at night and cloudy days.

Until we have better power storage technologies, wind and solar can never represent more than a fraction of the power mix because it is just not economically feasible to have the replacement generation capacity that is sitting around doing nothing when its sunny.


Comment Maybe they should stop sleeping with the partners (Score 1) 365

as well as they the human body radiates about 100Watts or 500 times more power than the maximum allowed power from a WiFi access point. Going out it sun is definitely out as at 1kW per square meter of 5000 times strong than WiFi that definitely going to be fatal...

What a load of Bollocks!


Comment Re:Funny, I heard the same thing about their camer (Score 1) 252

You do of course realize that DSK was the man most likely to be the next president of France up until this accusation? French politics is not really that clean either. Lookup "clearstream sarkozy" and look at how another party infight turned to corrupt means to taint Sarkozy's image before the last election, which backfired and ended up even boasting his popularity, eliminated the other presidential candidates.

The next presidential election in France is in May 2012 and the socialist party is just about to select their candidate. The timing of this scandal is just "too" convenient. If he is guilty most French people I know say "let him hang", but most also have serious doubts given the political context surrounding the case.


PS: Though I live in Paris, I'm not French

Comment Re:Godzilla (Score 1) 1148

BRAZIL = Cheap labor + Lots of Sun + Low population density = Cheap biofeul

Sorry Brazil's model applies to very few countries in the world. Read the report "Without the hot air" (url if you want to see how Brazil's model would fair went applied to the British situation, which is fairly a rather depressing read.


Comment Re:rock in water... (Score 1) 244

Except that from my days working with ADCs and coherent demodulation I know that 1deg of phase error between the two transmit signals will reduce the isolation between the two transmitted signal to 40dB. That 1deg of phase difference is 0.3mm at 2.4GHz

The authors say they need 50dB of isolation, whereas as my guess they need more like 60dB for a reasonable transmit power. There is a need to precisely place three antennas probably about 10cm apart with a positioning error of a very very small fraction of a mm. Difficult to do and mechanically fragile

Not to speak about the fact that the positioning is frequency dependent and so this is going to be an extremely narrowband radioband system.


Comment Re:Actual information (Score 1) 244

And have you seen that their first active component in the receive path is an intersil qhx220 that is a noise cancelling LNA. The IIP3 of this LNA is about -21dBm at 2.4GHz, so the P1dB will be about 10dB under that, and OFDM signals typically needing 5dB backoff from the P1Bb to get in the PER specs of 802.11x. So lets assume they are transmitting 15dBm from their transmit antennas (typical for a portable WiFi device) to avoid your LNA going non-linear you want to the cancellation of the transmit signals at the receive antenna to be more like 60dB of cancellation. Even if they get that in the antennas I hope their receive electronics are well shielded because even ignoring the antennas, getting the isolation between the transmit and receive paths better than 60dB is going to be a challenge in a low cost and/or small device. So this thing is going to be gold plated and hand tuned to even get it to partially work


Comment Stargate = Satimo SG64 (Score 1) 229

These things have been sold for over 10 years by the French company Satimo for the type of rapid antenna measurements that are needed when you're measuring in the presence of a human. Look at the website

This is hardly a sign that Apple is modern, but rather they are following behind the antenna measurement industry,


Comment Re:Hmmm... (Score 1) 320

Except supratentorial gilomas being tumors that form outside the membrane of the brain are a type of tumor that is more likely to be in close proximity to the ear (rather than deeper in the brain) where the specific absorption of microwaves will be the highest.. Seems like a good type of brain tumor to base a study of the effects of mobile phones on the brain on.


Comment Re:Use only channel 1,6 and 11. (Score 1) 451

Yes its standard practice, but no it doesn't produce the best strategy in the context of 802.11. The problem is that the 802.11 MAC clear channel assessment minimizes the opportunity for interference but in fact reduces the opportunity to transmit even in cases that won't interfere. That is I might be trying to communicate with an AP that is 10 metres away, but can see a transmission on the same channel from an AP 100 metres away and the CCA will prevent me from transmitting, even though I probably won't interfere with the other transmission and he certainly won't interfere with me.

The CCA in 802.11ag is defined in two different manners. The first is that if I can synchronize with a preamble in the channel then I consider the channel occupied. This basically means that anything I can hear at the receiver sensitivity (-85dBm for 802.11ag) in my channel I won't transmit. However this doesn't help for the issue of overlapping channels or non 802.11 transmissions in band. So the second definition is a simple RMS power measurement at 20dB above the receiver sensitivity level. That is if I hear something at -65dBm in my band I don't transmit regardless of what type of signal it is. So I'd rather have someone transmitting on the same channel as I am as far away as possible, and adding more, but overlapping channels, giving the frequency planner more opportunities to do that.

Therefore a better frequency plan in the 2.4GHz band that gains a 20dB advantage from the CCA definition is 1, 7, 13, 2, 8, 14, as that minimizes channel overlaps while maximizing the distance. However channel 14 isn't always available and so 1, 6, 12, 2, 7, 13 is a compromise that is reasonable.

Note that the 802.11n "green-fields" preambles have a better definition of the CCA that is basically the same whether or not your on the same channel. However, I don't think anyones really using these new preambles in 802.11n yet.



Submission + - Forensic computer targets digital crime (

coondoggie writes: "A European consortium has come up with a high-speed digital forensic computer dedicated to the task of quickly offloading and analyzing all computer records from email or picture files to database contents and file transfers.The TreCorder is a rugged forensic PC able to copy or clone up to three hard disks simultaneously, at a speed of up to 2 Gb/min. The same transfer would take 30 to 60 minutes using alternative equipment. The PC not only provides a complete mirror image of the hard disk and system memory — including deleted and reformatted date — but also eliminates any possibility of falsification in the process, Hermann said. It uses the FireWire high-speed serial bus to connect the host computer and provides support for IDE, SATA and SCSI hard disks."

Submission + - Stampedes can be predicted by CCTV software

An anonymous reader writes: Analysis of footage from the Jamarat Bridge stampede tragedy during the 2006 Hajj pilgrimage has shown up new processes that can be used to predict when such a disaster will occur. Sharp waves move through a crowd before a turbulent phase when people are jostled in unpredictable directions, when they are likely to fall, leading to a stampede. Software used by the researchers could be used to provide warning before this stage is reached.

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