1

General Science / Re: So how big a nuclear bomb would it take to cover the UK with a tsunami anyway

« on: 04/05/2022 20:05:24 »

I mean it's basically a tsunami bomb:

https://en.wikipedia.org/wiki/Tsunami_bomb

Which does raise the question: What, exactly, has the "nuclear deterrent" deterred? The Soviet Union was an ally of the western powers until they acquired nuclear weapons, since when there have been wars all over the world, mostly with little point and no desirable outcome.

I know what it didn't deter. It didn't deter Russia from invading Ukraine. There was no deterrent, after Ukraine agreed to give up the nuclear weapons they actually had to Russia, shortly after the USSR fell.

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General Science / So how big a nuclear bomb would it take to cover the UK with a tsunami anyway

« on: 04/05/2022 00:21:12 »

Apparently in Russian state media they're threatening to do this. Is this even remotely practical? I'm doubting they've got a big enough bomb to do that, but I'm prepared to accept a worked example proving otherwise.

3

Question of the Week / Re: Can the Earth be used as a dynamo?

« on: 29/04/2022 02:36:55 »

Linda asks: Can the spinning of the Earth be used as a source of electricity, similar to the spinning of wind turbines?

The spinning of the Earth itself can't be the source of electricity, since the Earth has to conform with conservation of angular momentum. Unless something left the Earth or joined the Earth or another external body changed speed, or the Earth radically changed shape, no closed cycle can result in the Earth simply slowing down and electricity being generated, as it will always have the same angular momentum.

4

Technology / Re: Are electric cars responsible for natural gas demand?

« on: 25/04/2022 23:32:26 »

I'm afraid money rules, if renewable where economically superior we would have converted to them already.

It will in a few years, and the progress is exponential.

Exponential,

At this point I'm assuming you're just here to troll all of us.

While an exponential decay is indeed an exponential, this is what the worldwide solar power looks like on a semilog graph:

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Technology / Re: Are solar panels worthwhile?

« on: 25/04/2022 21:29:54 »

Conspiracy theories can be fun

6

Technology / Re: Are solar panels worthwhile?

« on: 25/04/2022 21:01:35 »

Solar panels aren't scrapped after 25 years, they have about 0.5% loss of output per year, so they're still outputting nearly 90% of their original output after that. That's just the suggested lifespan, but they're clearly going to go a lot longer.

Whilst this is somewhat  true of current panels, many older panels are significantly worse, plus there is the lifespan of associated equipment/faults/ servicing.

https://news.energysage.com/how-long-do-solar-panels-last/#:~:text=The%20industry%20standard%20for%20a,below%20what%20the%20manufacturer%20projected.

But given this degradation that is reported widely at 1% a year and the lack of cloudy sky generation, I have to think this is being rushed into. When cloudy sky generation  is improved  most solar in the uk will be replaced.

No.

And because there's been little installation so far, most panels that will be installed will be new panels, and they give 0.5% a year:

https://www.nrel.gov/state-local-tribal/blog/posts/stat-faqs-part2-lifetime-of-pv-panels.html

Note that the UK may well be a lot less even than that, a lot of the degradation is due to stuff like high temperatures and damage from sunlight. The UK has less sunlight than many places (like Hawaii!) and is not a particularly hot country, so the calendar degradation should be much less.

7

Cells, Microbes & Viruses / Re: Can some one here explain the biology of aging?

« on: 25/04/2022 03:23:33 »

There's almost certainly not any one thing. Ageing is caused by the build up of damage of one kind or another; and is in turn related to how well protected the organism is. Animals that are very well protected age much more slowly.

For example a tortoise has a hard shell, so can live for centuries, so has evolved genes for ageing very slowly. Humans are very good at looking after themselves so have evolved to live quite a long time. Birds can fly away, so live decades. Mice and bats are both mammals, but mice have short lives usually ending in crunchy squeaks when they get predated, whereas bats are a similar size but fly extremely well, and thus can largely avoid danger; again they can live for decades.

Ageing slowly is thought to require extra genes. If an organism is going to die anyway before those genes make much difference, those genes will not be selected for, and they will disappear from the organisms genome.

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Technology / Re: Are electric cars responsible for natural gas demand?

« on: 25/04/2022 01:46:39 »

This must be an odd definition of 'subsidy', both natural gas and coal power are uneconomic compared to the unsubsidized price of solar and wind power in the UK. At the moment at least, increased use of solar and wind reduce the cost of electricity.

That certainly wasn't historically true not even a few years ago, but it is right now.

9

Technology / Re: Are electric cars responsible for natural gas demand?

« on: 24/04/2022 20:35:06 »

Problem with solar is that all the sources go off line at the same time, and windmills may not work at all for several days at a time - the primary sources are not independent.

But you know it's doing that before it happens, because of something called a 'weather forecast'.

This wouldn't be a problem if renewable generators were backed up with adequate storage, but that would not be profitable, so grid integrity relies on fossil fuels to maintain the profitability of renewables.

Thing is, backup generators are relatively cheap, and the grid already has them anyway. It costs fuel, but hydrogen and perhaps other things like ammonia is looking promising for that.

10

Technology / Re: Are electric cars responsible for natural gas demand?

« on: 24/04/2022 17:57:39 »

Solar panels are made using electricity that comes from whatever is on that factories' grid.

These days significant fractions of that electricity in China are made using solar panels and wind, and whatever is on that grid is what's used to make solar panels.

ALL grids, everywhere are powered by UNRELIABLE sources: ANY power plant can fail or get disconnected at ANY time.

11

Technology / Re: Why are solar panels not curved?

« on: 24/04/2022 01:37:53 »

The best angles to have your solar panels at is complex. Since about 2014 the cost of the panels are low enough that having more solar panel capacity than inverter capacity became cost effective. I believe I'm correct in saying that you would ideally want your panels facing north-east and north-west in your case; the cost of the extra panels is a small proportion of the cost of the system. When I ran the numbers on a system I was planning here, it was something like the cost went up by 15% and the productivity went up by 20%.

East-west systems approximate solar tracker outputs and may be optimal near the equator, and if you're not on net metering where the feed in tariff is small compared to the normal usage tariff if you're doing any significant self usage of the electricity.

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That CAN'T be true! / Re: Does the IVO thruster violate Newton's third law?

« on: 23/04/2022 04:32:20 »

There are classes of propulsion that don't require fuel, for example, interacting with the Earth's magnetic field. But I don't know what this is supposed to be, many of these things are bullshit.

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Technology / Re: Are solar panels worthwhile?

« on: 23/04/2022 04:22:12 »

The retail cost of electricity is the renewables subsidy. The retailer gets a profitable 27p per unit  whether the wind is blowing or not, so there is no incentive for the wholesaler to build the storage system needed for a fully renewable supply.

If the retailer is getting 27p/kWh then it's still in their interest to get the electricity for the lowest possible average cost. Note that wind power is usually sold on Contract For Difference, which is essentially a fixed price of 7p/kWh or whatever.

In practice, retailers are in competition with each other for customers, so they try to hold their price down- the 27p is not a given.

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General Science / Re: Do rockets violate conservation of energy?

« on: 22/04/2022 21:26:00 »

coe

hi again. other people on different fora have been debating the question. member "uatu" on the german allmystery.de forum has provided what I consider the definitive solution with a graph illustrating the key parameters. my primitive derivation indicated an initial parabolic rise in ke, followed by an asymptote at around 3/4 fuel consumption. the rigorous expression provided by "uatu" does the same followed by a sharp downturn. this derivation seems to be rock-solid, in my limited mathematical abilities. bottom line: the coe is safe and emmy noether can rest peacefully.

FWIW this is somewhat subtle stuff. There was actually some disagreement about the relationships between rockets and energy but it was laid to rest by Hermann Oberth.

He reported that at one point in his investigations of rocketry he believed he had completely disproven conservation of energy too, but he later was able to show that he hadn't.

See:

https://en.wikipedia.org/wiki/Oberth_effect

This links to 'Ways to spaceflight' which describes his mathematics which covers this and other topics.

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Technology / Re: Are solar panels worthwhile?

« on: 22/04/2022 18:12:26 »

The retail cost of electricity has very little to do with physics and a great deal to do with profits, taxes and subsidies.

There are not really any solar subsidies anymore in the UK. They pay you what is basically cost (or more accurately, they pay the electricity supplier, most of them just pocket this, but Bulb gives you the money.)

Having lived through many, I understand a good deal about UK summers. Yes, the sun is above the horizon for over 16 hours in June, but the solar angle never exceeds 62 degrees in London, 59 in Inverness, which is why it is generally colder in Scotland than in England and the north pole (24 hour sunlight) stays frozen.

Gee, if only someone could work out a magic way to deal with that issue, such as tilting the panels at ~30 degrees. But apparently you can't think of any way. Must be impossible.

And we do have a lot of cloud over these Atlantic islands.

Yeah, except not so much in summer. Solar is quite predictable in summer, and isn't permanently hidden by clouds in the UK.

The value of mains electricity and gas is 24/7/365 availability at any level from zero to the supply rating. Until the cost of renewables includes that of maintaining an adequate overnight and strategic (say 10 day) reserve, you are not comparing apples with apples.

Wrong. Dispatchable electricity is certainly useful to have, but you want to use it as little as possible because: it's always £££ and high CO2 emissions. But a lot of our electricity is predictable and highly correlated with the daytime.

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Technology / Re: Are solar panels worthwhile?

« on: 22/04/2022 10:49:01 »

Note that solar panels work better in the UK than Australia during their respective summers, because the UK is such a long way north. We get over 14 hours of sunshine.

Not according to the folk who sell solar power systems - see the attached chart of annual equivalent sun hours. The polar regions get 24 hours of sunshine in the summer but remain covered with ice! And of course demand is maximised in winter, not summer.

That's averaged over the entire year. Which bit of 'summer' didn't you understand?

The more I learn about renewable sources of electricity, the more I am convinced that their commercial success so far depends almost entirely on the flexibility of fossil fuels. If it wasn't possible to fire up a gas-powered generator quicker than coal, wind and solar would never have featured in the energy market.

As opposed to what? Nuclear?

.

The fact that the panels are only producing about 10% of the time doesn't matter, because they DO produce during the day, when people are using more energy

And they do produce during the winter when people need energy by far the most.?

No, but wind does.

Apparently in your heads, the UK has no electricity demand in summer, and you think that using natural gas, which gives a current electricity price of over 14p/kWh is only superior to solar which costs around 5p/kWh in the UK right now and wind that costs about 7p/kWh.

Hint: if solar panels are attached to your house, you can reduce your bills because any electricity you use only costs 5p/kWh instead of ~27p/kWh and any you don't use gets exported to the grid and reduces the electricity price.

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Technology / Re: Why are solar panels not curved?

« on: 22/04/2022 05:39:16 »

In operation, solar panels are more or less constant voltage, largely independent of illumination. The current depends on the illumination. Because of that, panels with different illuminations work well in parallel, less so in series. You want panels in series to all have similar illuminations, to all be at the same angle to the sun.

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General Science / Re: Do rockets violate conservation of energy?

« on: 22/04/2022 02:12:47 »

Hi.

Nice diagram  @wolfekeeper .    Out of interest, what was the blue line?

Blue line is the instantaneous energy efficiency (force times vehicle speed/half the exhaust velocity squared) of the rocket engine expressed as a percentage of the internal engine efficiency at turning available chemical heat energy into fast moving exhaust.

19

Technology / Re: Are solar panels worthwhile?

« on: 22/04/2022 00:53:22 »

Solar panels aren't scrapped after 25 years, they have about 0.5% loss of output per year, so they're still outputting nearly 90% of their original output after that. That's just the suggested lifespan, but they're clearly going to go a lot longer.

The fact that the panels are only producing about 10% of the time doesn't matter, because they DO produce during the day, when people are using more energy, that increase is mostly carried by natural gas, so it directly reduces the amount of natural gas burnt. Spoiler: natural gas is a LOT more expensive right now than solar power.

Note that solar installations have got a LOT cheaper. Payback can be as little as 5 years now, but 7 is probably more common. The actual panels are stupidly cheap at about £0.3/watt peak and still falling. What kind of investment pays back the initial investment in 7 years? A good one, that's what.

Note that solar panels work better in the UK than Australia during their respective summers, because the UK is such a long way north. We get over 14 hours of sunshine.

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General Science / Re: Do rockets violate conservation of energy?

« on: 15/04/2022 03:42:17 »

FWIW here's a graph of energy efficiency versus final velocity (in red):



To generate the graph you use the rocket equation to calculate the remaining rocket mass after reaching a particular velocity. You can then calculate the kinetic energy of the vehicle at that speed. The loss of mass (i.e. the fuel burnt) will happen at a particular exhaust velocity, so you can calculate how much energy was used and divide one by the other to get the red line.

The scale along the bottom is in multiples of the exhaust velocity and the scale up the left hand side is in multiples of the engine efficiency. It obviously never reaches 100% and in fact carries on going down.