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 Post subject: Solar panels atop my university's supercomputer center.
PostPosted: Fri Nov 03, 2006 5:19 pm 
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Location: Buffalo, NY
http://www.buffalo.edu/UBT/features/energy.html

My first reaction was "hey, cool!".

Then I read the details. $800k of photovoltaics putting out 100kW of power. Then the power will be converted to AC, and fed into the grid. It'll provide 6% of the building's power consumption.

Photovoltaics produce DC. Computers use DC. So why not skip the ineffeciencies of inverting then converting it? Create a +12VDC grid, and power it with these solar panels, plus a large, very efficient AC-DC converter for when it's dim out.

But there's a bigger problem here: the sun seldom shines in Buffalo. We're on the leeward side of one of the Great Lakes, which means cloud cover. Plus the panels will be covered with snow several months a year, but never mind that, since we're 43° north of the equator and when we do get light, it's dim anyway.

They admit this is a demonstration project and that it would not have made economic sense were it not for a grant from the state. Okay, fine, but then why were we allowed to hire Chevron to do the job? Shouldn't we have made some EE students do it?

Also, this amuses me: "Ironically, a worldwide push to develop alternative energy sources, especially in Europe, has driven up prices for the photovoltaic panels used in solar arrays, as well as components for wind turbines, making some alternative energy sources temporarily even more expensive."

I do hope that the price of solar panels comes down to the point where offices and for-profit entities install them on their roofs. Even if the price were ~10% higher, the difference could be made up by the fact that solar panels generate DC power, which can power computers more efficiently than AC. Sadly, photovoltaics are around two or three times the required price.


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PostPosted: Fri Nov 03, 2006 6:01 pm 
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Interesting,

Given sufficient sustained demand for panels, somone will put on the additional manufactuing to compete and drive down the price.

It's not the raw materials that are the problem - they are cheaper than ever. Silicon ignots, which they then slice and make into components such as CPUs, RAM and other semiconductors are far more pure in the centre then they are on the outside. The inner bits get used for high quality semiconductors (RAM/CPUs etc) and the outer bits (which oftgeh go to waste) are lideal for low-mid quality solar panels.

Getting sufficient interest to build a market AND get the manfacturing sector to build is a problem - the latter is quite expensive


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 Post subject:
PostPosted: Fri Nov 03, 2006 6:07 pm 
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Oh, yeah, almost fogot to add...

Transmitting DC power at low voltages (12V) is quite inefficient and required large wires. 1KW at 12V is 83A - and needs cables as thick as what you see coming out of the battery in your car (about as thick as your finger).

Hence, it's an efficiency problem of bumping up to AC, and then coverting back to DC.


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 Post subject:
PostPosted: Fri Nov 03, 2006 7:38 pm 
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Although the price of solar panels may be temporarily up (?), I read this article in The Economist a few weeks ago. I think it's likely that the cost of solar power will continue to drop and the efficiency at which they convert sunlight to electricity will improve.

That being said, it's debatable if solar cells make much sense in that climate anyways.

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 Post subject:
PostPosted: Sat Nov 04, 2006 2:55 am 
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Quote:
Photovoltaics produce DC. Computers use DC. So why not skip the ineffeciencies of inverting then converting it?


It's actually not that inefficient; inverters, transformers and rectifiers can be up to 95% efficient, so you have to weight that against the resistive losess you will get running up to 83A through cabling.


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 Post subject:
PostPosted: Fri Nov 10, 2006 5:02 pm 
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Location: Buffalo, NY
The also built a kiosk in the library that overlooks the solar panels. Turns out they run several PV cells in series, and it's something like 180VDC they run down to the inverters inside the building. I'm willing to bet that 180VDC -> AC -> 12VDC is less efficient than 180VDC -> 12VDC. However, I admit it would be very expensive to convert the computers to use 12V power supplies, and that would translate to them not being able to install as many solar cells.


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 Post subject:
PostPosted: Fri Nov 10, 2006 7:49 pm 
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Converting a DC voltage to another DC voltage requires a switched converter, with unavoidable switching losses, in a similar what that modern power supplies switch AC to DC. Hence, DC->AC->DC is most likely l;ess efficienty than 180VDC -> 12VDC.

But, there are significant cabling and logistical advantages of pusing that power into the AC supply. Firstly, cabling, let alone the installation is expensive - especially retrofitting a building, with speciualist power outlets. Secondly, computers would need to be retrofitted with 108V-12V DC/DC converters at considerable expense.

Therefore, you're better off going back and purchasing some more solar panels in the first place, cost-wise and I daresay material wise as well.

Or, pour the money into domestic solar hot water supplies, which make direct use of the sun's heat, and makes a very significant reduction in the energy used in domestic how water (or even have one or two at the cafeteria/shower block/dorms...)


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 Post subject:
PostPosted: Wed Nov 29, 2006 1:53 pm 
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It's too bad they didn't try wind power instead.

Also, you go to Buffalo? Your guys played a great game against us (Auburn).

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PostPosted: Wed Nov 29, 2006 3:11 pm 
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Last time I read up on solar power, the most cost effective solar power were the big heat reflectors that use mirrors to heat up some sort of heat carrier that drives a steam turbine. There's a Wiki page that tells a little bit about it[/url] but I know there's better information sources out there. The wiki doesn't address it in detail, but from what I could gather the last time I read up on it, the two main benefits over PV are that you can build thermal reserves, so even in cloud cover and in fact total darkness you can be producing electricity from the thermal reserve tank. I believe Solar One ran for something like 180 hours straight at one point without a single interruption when used in that configuration.

Also, I believe the other advantage is that since it's using the sun's heat, or UV or whatever which is largely unaffected by cloud cover, it still performs very well in heavy overcast conditions, much like you can still get a bad sunburn almost as quickly in overcast weather as you can in direct sunlight. The downside is of course that it doesn't scale down like PV does. In order to get the economies of scale, it must be a very large installation. That does bode well for the future though, as oil, coal, and natural gas supplies run out we'll be able to use sunshine to replace the energy produced by fossil fuels.

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 Post subject:
PostPosted: Wed Nov 29, 2006 4:20 pm 
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During the Carter administration you could take a tax write-off (forgive me -- I can't remember the formal term for it) if you built or installed solar panels on your house. We're talking about the 70s here.

When Reagan came along, that quickly disappeared, along with a lot of other progressive economic practices.

You can't expect alternative energy technologies to do much elbowing their way in against the fossil fuel industries unless governments take deliberate steps to encourage them by tax breaks and subsidies. That's the reality of the situation -- if you're looking for market forces to accomplish this it'll go along at a snail's pace at best.

I'm sure more could be done to encourage research as well.

I'm impressed by Japan, which, according to the chart in the Economist article, has had about half of all the installed solar power in the world for a few years.


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 Post subject:
PostPosted: Wed Nov 29, 2006 4:41 pm 
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Quote:
I'm impressed by Japan, which, according to the chart in the Economist article, has had about half of all the installed solar power in the world for a few years.


It's not that surprising, considering they have zero domestic fossil fuel resources. They've developed alternative energy sources out of necessity rather than out of environmental conscientiousness, after all, necessity is the mother of invention. :wink:

Quote:
That does bode well for the future though, as oil, coal, and natural gas supplies run out we'll be able to use sunshine to replace the energy produced by fossil fuels.


a couple of points:

1) There's a lot of coal in the world (ie many trillions of tonnes). So it could be a while (like 200 years+) before it runs out.

2) Solar power is a no-brainer for places like Arizona and California which have abundant sunshine. But a lot of world energy demand is situated in places that don't get enough to make it practical (like Northern Europe for example). So they will have to use nuclear (a la France) or wind or clean coal or whatever. Also, a lot of world energy demand comes from transportation, which requires energy-dense liquid fuels; it's hard to see how solar power would replace these.


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 Post subject:
PostPosted: Sat Mar 10, 2007 11:48 am 
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Brian wrote:
The also built a kiosk in the library that overlooks the solar panels. Turns out they run several PV cells in series, and it's something like 180VDC they run down to the inverters inside the building. I'm willing to bet that 180VDC -> AC -> 12VDC is less efficient than 180VDC -> 12VDC. However, I admit it would be very expensive to convert the computers to use 12V power supplies, and that would translate to them not being able to install as many solar cells.

Couldn't they use high voltage DC at about 340v and set the power supplies to "240v" mode so they accept DC?


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 Post subject:
PostPosted: Sat Mar 10, 2007 1:07 pm 
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star882 wrote:
Brian wrote:
The also built a kiosk in the library that overlooks the solar panels. Turns out they run several PV cells in series, and it's something like 180VDC they run down to the inverters inside the building. I'm willing to bet that 180VDC -> AC -> 12VDC is less efficient than 180VDC -> 12VDC. However, I admit it would be very expensive to convert the computers to use 12V power supplies, and that would translate to them not being able to install as many solar cells.

Couldn't they use high voltage DC at about 340v and set the power supplies to "240v" mode so they accept DC?


way to resurrect an old thread :). the 240V switch on a PSU is for 240VAC. it's not a DC 'mode'. it's so they don't have to build different PSUs for north america (120VAC) and europe (240VAC) markets.

i don't mean to ignore the rest of the world's electrical grids, but those are the only two areas i know the specs for.

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 Post subject:
PostPosted: Sat Mar 10, 2007 4:50 pm 
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flyingsherpa wrote:
star882 wrote:
Brian wrote:
The also built a kiosk in the library that overlooks the solar panels. Turns out they run several PV cells in series, and it's something like 180VDC they run down to the inverters inside the building. I'm willing to bet that 180VDC -> AC -> 12VDC is less efficient than 180VDC -> 12VDC. However, I admit it would be very expensive to convert the computers to use 12V power supplies, and that would translate to them not being able to install as many solar cells.

Couldn't they use high voltage DC at about 340v and set the power supplies to "240v" mode so they accept DC?


way to resurrect an old thread :). the 240V switch on a PSU is for 240VAC. it's not a DC 'mode'. it's so they don't have to build different PSUs for north america (120VAC) and europe (240VAC) markets.

i don't mean to ignore the rest of the world's electrical grids, but those are the only two areas i know the specs for.

In the 240v mode, virtually all PC power supplies will accept 340v DC. I actually have an automotive power adapter for a laptop that simply outputs about 300v DC. It does work and it actually makes the laptop wall wart run cooler than it does on 120v from a regular outlet or 170v peak squarewave power inverter.
The next time you come across a broken PC power supply, take it apart and carefully trace the input wiring for 120v and 240v mode. It usually operates as a voltage doubler for 120v and a bridge rectifier for 240v. There are a few that have preregulators, which operate as bridge rectifiers all the time.


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 Post subject:
PostPosted: Wed May 23, 2007 12:53 pm 
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If the government would get beind it, it is much are money and energy efficient to build a 1.5GW nuclear plant, or a cluster of plants outside a city than to have distributed solar generation. Solar could handle peak A/C demand in the SW though.


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