Environmentally sustainable base load power

[Jarhyn]

Really? At what scale? Could you refer me to an example of such a facility that is not pumped storage hydro?

http://news.nationalgeographic.com/...0403-fuel-cells-hydrogen-wal-mart-stationary/


Electricity for Homes and Businesses

The world’s largest fuel cell plant, a 59-megawatt facility in South Korea that opened earlier this year, provides both power and heat to homes in Hwasung. Another fuel cell “park” is set to be built in Seoul. Those cities join several municipalities and companies that are using fuel cell power plants to provide baseload electricity for homes, data centers, fulfillment centers, and similar applications.

Well it's a start; but 59MW wouldn't pull the skin off a rice pudding.

Sure, but it's well in advance of a prototype. It's an established commercial technology.

And as I was saying, big is worse in this case. Small plants are exactly what you need. One big plant is asking for trouble.

That's a one megawatt supply for not much more than two days. A base load plant is maybe a gigawatt. To reproduce that with solar, you need at least 2GW of generation capacity plus a GW of storage - just to cope with nighttime. More if you expect to ever see heavy cloud.

Still cheap, though. And it's not like you're hurting for space to put up collectors.

On the other hand, Gen III ABWR nukes in the 1.06GW range are up and running - there are IIRC half a dozen such in Japan alone.

Just not very suitable for this situation.

Are you kidding? We're being trolled, right? A gigawatt is 2 orders of magnitude more than that shitty fuel cell plant pumps out, and even a 70% reduction of electrical consumption across the board means that it would take 10-20 of those to fuel a decently sized city. That's a lot of fugly solar arrays eating up prime building top real estate. Not to mention the material hazards produced by that much hydrogen kicking around, or the loss of transmitting such low voltage on city sized scales.

High power lines are as efficient as they are because they can crank the voltage up so high.

Not to mention what others said about the downtime demands. We need lots of nuclear, and if you want to press for progress, breeder nuclear. Nothing else has been discovered that even MIGHT work.

 

[steve_bnk]

Large sCcle fuel cells have been around for a while. I know about Ballard because they are in the region..

http://ballard.com/files/PDF/Distributed_Generation/CLEARgen_Spec_Sheet.pdf

It potentially addressees distribution, but not energy supplies. Solar to hydrogen to electricity is also inefficient.

Nuclear is the only practical alternative to fossil fuels. New architectures involve clusters of small plants that intrinsically safe, they can not go runaway critical.

Sandia is supposed to be developing a small encased rector for distributed power.

http://www.greentechmedia.com/articles/read/sandia-joins-race-for-mini-reactors

https://share.sandia.gov/news/resou...-developing-right-sized-reactor/#.U6nYxpjn8hw

 

[Togo]

Just not very suitable for this situation.

Are you kidding? We're being trolled, right? A gigawatt is 2 orders of magnitude more than that shitty fuel cell plant pumps out, and even a 70% reduction of electrical consumption across the board means that it would take 10-20 of those to fuel a decently sized city. That's a lot of fugly solar arrays eating up prime building top real estate.

Alice Springs is short of desert?

Not to mention the material hazards produced by that much hydrogen kicking around,

If material hazards can't be overcome, nuclear power has it's own problems.

or the loss of transmitting such low voltage on city sized scales. High power lines are as efficient as they are because they can crank the voltage up so high.

The technology already exists to feed solar into a national grid, which uses high voltage transmission.

Nothing else has been discovered that even MIGHT work.

You feel the discussion is a waste of time, because you believe there is only one answer?

 

[bigfield]

Sure, but it's well in advance of a prototype. It's an established commercial technology.

Is it scalable to city-wide power demands?

 

[Togo]

Sure, but it's well in advance of a prototype. It's an established commercial technology.

Is it scalable to city-wide power demands?

Well, it's presently being used in a city, as a combined heat and power plant. You generally can't have combined heat and power on a large scale, which is why it's so small, and only running a local area. There's no obvious reason why you can't have a larger scale plant if that's the way you want to go. Or you can convert light industrial uses of electricity to run off fuel cells directly - Wallmart uses it to power forklifts in their warehouses, the oft-mentioned 'air conditioning in a hospital' would be an obvious application, since hospitals are already set up to handle volatile substances anyway - a large sophisticated user like a hospital could probably just use synthesised hydrogen directly.

 

[bigfield]

Sure, but it's well in advance of a prototype. It's an established commercial technology.

Is it scalable to city-wide power demands?

Well, it's presently being used in a city, as a combined heat and power plant. You generally can't have combined heat and power on a large scale, which is why it's so small, and only running a local area. There's no obvious reason why you can't have a larger scale plant if that's the way you want to go. Or you can convert light industrial uses of electricity to run off fuel cells directly - Wallmart uses it to power forklifts in their warehouses, the oft-mentioned 'air conditioning in a hospital' would be an obvious application, since hospitals are already set up to handle volatile substances anyway - a large sophisticated user like a hospital could probably just use synthesised hydrogen directly.

I'm primarily interested in power plants which can replace the fossil fuel plants we currently use for nationwide base load power generation. So the plants would need to be able to service everyone, like the current plants do.

The reason I ask about scalability is because 59MW is a such a tiny fraction of the total power even a smaller country like Australia would need.

 

[Togo]

Sure, but it's well in advance of a prototype. It's an established commercial technology.

Is it scalable to city-wide power demands?

Well, it's presently being used in a city, as a combined heat and power plant. You generally can't have combined heat and power on a large scale, which is why it's so small, and only running a local area. There's no obvious reason why you can't have a larger scale plant if that's the way you want to go. Or you can convert light industrial uses of electricity to run off fuel cells directly - Wallmart uses it to power forklifts in their warehouses, the oft-mentioned 'air conditioning in a hospital' would be an obvious application, since hospitals are already set up to handle volatile substances anyway - a large sophisticated user like a hospital could probably just use synthesised hydrogen directly.

I'm primarily interested in power plants which can replace the fossil fuel plants we currently use for nationwide base load power generation. So the plants would need to be able to service everyone, like the current plants do.

The reason I ask about scalability is because 59MW is a such a tiny fraction of the total power even a smaller country like Australia would need.

Ok, well that's a very different question to how to power Alice Springs, and goes back to my original point, which is that the ecological approach is to move away from just ramping up base load as high as possible.

Back when fossil fuel was all there was, just ramping up the base load made sense - you could easily turn it on and off, and there weren't really any alternatives. You got the occasional brown out if demand peaked, and potential disaster threatened every time a really popular TV show came on, and everyone switched out the lights. Balancing power load was tricky, and entire coal plants might get switched on or off.

Since then, we've become more sophisticated, and power management is much easier, but it's still an issue. Power storage is the most obvious way, so you get people pumping water up the mountain when there is too much electricity compared to demand, and letting it run down through a turbine, generating power, when there isn't. It's not very efficient, but it's a lot better than trying to bring up and bring down a power station several times a night.

However, there is only so much hydro power out there, and it can be expensive to maintain. One of the reasons why gas-fired power stations are so popular is that they are easy to switch on and off - more so than coal, and much more so than nuclear, which tends to be inefficient unless it runs all the time. However, the easiest to switch on and off are renewables - it can be as easy as disconnecting a solar array, or unshipping a wind turbine's blades.

By the far the most ecological approach is energy efficiency - there are huge gains to be made there. Beyond that, using local power wherever possible, saving on transmission costs, and reducing the fluctuations on the main grid. Beyond that we have renewables, with their near-zero emissions and high switchability. And beyond that, some form of energy storage. Only once all that is has been used to it's greatest extent should you reluctantly turn to some form of base-load generation to meet the residual energy needs. Because they're ecologically expensive, and not nearly as flexible.

Which is why the question is such a strange one - when you ask what the most ecological source of base load power is, you're asking what the most ecological source of power is once you've exhausted ecological alternatives. The ecological approach is to make base load as small as possible, because it's about matching generation to demand.

 

[bilby]

Sure, but it's well in advance of a prototype. It's an established commercial technology.

Is it scalable to city-wide power demands?

Well, it's presently being used in a city, as a combined heat and power plant. You generally can't have combined heat and power on a large scale, which is why it's so small, and only running a local area. There's no obvious reason why you can't have a larger scale plant if that's the way you want to go. Or you can convert light industrial uses of electricity to run off fuel cells directly - Wallmart uses it to power forklifts in their warehouses, the oft-mentioned 'air conditioning in a hospital' would be an obvious application, since hospitals are already set up to handle volatile substances anyway - a large sophisticated user like a hospital could probably just use synthesised hydrogen directly.

I'm primarily interested in power plants which can replace the fossil fuel plants we currently use for nationwide base load power generation. So the plants would need to be able to service everyone, like the current plants do.

The reason I ask about scalability is because 59MW is a such a tiny fraction of the total power even a smaller country like Australia would need.

Ok, well that's a very different question to how to power Alice Springs, and goes back to my original point, which is that the ecological approach is to move away from just ramping up base load as high as possible.

Back when fossil fuel was all there was, just ramping up the base load made sense - you could easily turn it on and off, and there weren't really any alternatives. You got the occasional brown out if demand peaked, and potential disaster threatened every time a really popular TV show came on, and everyone switched out the lights. Balancing power load was tricky, and entire coal plants might get switched on or off.

Since then, we've become more sophisticated, and power management is much easier, but it's still an issue. Power storage is the most obvious way, so you get people pumping water up the mountain when there is too much electricity compared to demand, and letting it run down through a turbine, generating power, when there isn't. It's not very efficient, but it's a lot better than trying to bring up and bring down a power station several times a night.

However, there is only so much hydro power out there, and it can be expensive to maintain. One of the reasons why gas-fired power stations are so popular is that they are easy to switch on and off - more so than coal, and much more so than nuclear, which tends to be inefficient unless it runs all the time. However, the easiest to switch on and off are renewables - it can be as easy as disconnecting a solar array, or unshipping a wind turbine's blades.

By the far the most ecological approach is energy efficiency - there are huge gains to be made there. Beyond that, using local power wherever possible, saving on transmission costs, and reducing the fluctuations on the main grid. Beyond that we have renewables, with their near-zero emissions and high switchability. And beyond that, some form of energy storage. Only once all that is has been used to it's greatest extent should you reluctantly turn to some form of base-load generation to meet the residual energy needs. Because they're ecologically expensive, and not nearly as flexible.

Which is why the question is such a strange one - when you ask what the most ecological source of base load power is, you're asking what the most ecological source of power is once you've exhausted ecological alternatives. The ecological approach is to make base load as small as possible, because it's about matching generation to demand.

It might be possible, to some extent, to match demand to generation; but matching generation to demand is basically impossible with the major renewables. Solar power is available during the day, but not at night or when it is heavily overcast, no matter what the demand at night might be. Wind is available when the wind blows, but not when it is calm. Tidal is available on a fixed cycle, with peak supply roughly four times daily at most sites. Wave power varies in a similar pattern to wind, but with some offsets in both time and location.

Not one of these is amenable to matching with demand, which tends to be driven by at best only loosely correlated drivers. The best fit is probably the correlation between solar power availability and demand for refrigeration and airconditioning; but these things are closely coupled to atmospheric temperature at ground level, rather than to the level of ambient light - so demand is low during the daytime in winter, and high at night in summer.

There is some ability to do energy intensive things at times when power is plentiful; and some factories and refineries already take advantage of cheaper electricity prices at times of peak generation. But this is not practical for most users of power.

Electric cars are a good example; most drivers use their cars during the day, and charge them at night - exactly the reverse of the most efficient way to use solar power.

Matching generation to demand is not about base load at all - by definition, base load is the portion of demand that does not vary. Matching generation to demand can be done with renewables; but requires massive redundancy in order to guarantee availability of peak load at peak times.

The idea that nuclear plants are inefficient unless run all the time is seriously out of date by the way. Modern nuke plants have good load-following capabilities with little loss of efficiency; in Germany, nuclear plant load following was in widespread use prior to Fukushima, necessitated by the highly variable supply situation created by their large number of wind farms. In France, nuclear load following has been used for decades, due to the large proportion of nuclear (vs traditional load following technologies such as gas turbines) in their generating mix.

The main objection to using nuke plants for load following is one of low utilisation, rather than low efficiency; The ROI on the construction cost of a plant is lengthened if the plant is not run 24x7. However in the German scenario, where the effective return from generation is negative during windy conditions, that economic consideration goes out the window - even with the very low variable cost component in a nuclear plant, it is cheaper to shut down than it is to keep running when total nationwide supply is far in excess of demand.

All that wind power, that is overproducing on windy days, is completely useless when conditions are calm, so other sources need to be available (even if they are mostly on standby); adding wind farms is good for cutting CO₂ emissions by offsetting the burning of coal on windy days, but they are not much use for any other reason - You can't replace 1GW of coal with 1GW of wind power, but you can use 1GW of wind capacity plus 1GW of coal capacity to get 1GW of power out, while burning half the amount of coal that the coal plant alone would use.

Of course, you can get 1GW without the windmills in that scenario, but only at the cost of generating a lot of CO₂. Replace the coal plant with a nuclear plant, and suddenly the CO₂ is not an issue. Uranium is dirt cheap - so why bother with the windmills at all in this scenario?

 

[bigfield]

Of course, you can get 1GW without the windmills in that scenario, but only at the cost of generating a lot of CO₂. Replace the coal plant with a nuclear plant, and suddenly the CO₂ is not an issue. Uranium is dirt cheap - so why bother with the windmills at all in this scenario?

To reduce toxic waste, and to prolong uranium supplies even if they are plentiful.

 

[bilby]

Of course, you can get 1GW without the windmills in that scenario, but only at the cost of generating a lot of CO₂. Replace the coal plant with a nuclear plant, and suddenly the CO₂ is not an issue. Uranium is dirt cheap - so why bother with the windmills at all in this scenario?

To reduce toxic waste, and to prolong uranium supplies even if they are plentiful.

Fair enough; but is that saving worth the cost of all those windmills?

There really is plenty of uranium; and we are only talking about using it as a better option than coal until the storage and/or transmission technology needed to fix the intermittency problem can be developed and brought up to scale.

One of the big benefits of nuclear power is just how little fuel is used, and how little waste generated, per unit of power supplied.

 

[bigfield]

Which is why the question is such a strange one - when you ask what the most ecological source of base load power is, you're asking what the most ecological source of power is once you've exhausted ecological alternatives. The ecological approach is to make base load as small as possible, because it's about matching generation to demand.

That makes sense but it does not eradicate the need for base load supply. Even maximum efficiency doesn't remove that requirement.

What is the base load supply in a system using renewables? Pumped hydro storage is dependent on geography.

 

[bilby]

Which is why the question is such a strange one - when you ask what the most ecological source of base load power is, you're asking what the most ecological source of power is once you've exhausted ecological alternatives. The ecological approach is to make base load as small as possible, because it's about matching generation to demand.

That makes sense but it does not eradicate the need for base load supply. Even maximum efficiency doesn't remove that requirement.

What is the base load supply in a system using renewables? Pumped hydro storage is dependent on geography.

A LOT of geography

A hydro plant like Dinorwig, in North Wales, can generate nearly 1.8GW, which sounds great - until you realise it can only do this for a maximum of six hours at a stretch, for a total storage of less than 40TJ. To cover the mean UK demand of 1,500TJ for 12 hours (and solar power generation would struggle to operate consistently for 12 hours per day, so you might need twice this amount of storage) would need another forty such sites - and it is doubtful that that many suitable locations exist in all of Western Europe, much less in just the UK.

Fuel cell sites like the one mentioned up-thread are currently much too small scale, and much too expensive per unit of energy stored, but they do at least have the advantage of being suited to a much wider range of potential sites.

 

[bigfield]

Fair enough; but is that saving worth the cost of all those windmills?

Well we in Australia have plenty of space to dump toxic waste, which means that we can almost pretend that it's not even there. But elsewhere in the world, toxic waste disposal is potentially a huge pain in the ass.

There really is plenty of uranium; and we are only talking about using it as a better option than coal until the storage and/or transmission technology needed to fix the intermittency problem can be developed and brought up to scale.

One of the big benefits of nuclear power is just how little fuel is used, and how little waste generated, per unit of power supplied.

Fair points.

 

[Togo]

Pumped hydro storage is dependent on geography.

A LOT of geography

A hydro plant like Dinorwig, in North Wales, can generate nearly 1.8GW, which sounds great - until you realise it can only do this for a maximum of six hours at a stretch, for a total storage of less than 40TJ. To cover the mean UK demand of 1,500TJ for 12 hours (and solar power generation would struggle to operate consistently for 12 hours per day, so you might need twice this amount of storage) would need another forty such sites - and it is doubtful that that many suitable locations exist in all of Western Europe, much less in just the UK.

This is a very strange form of argument. A single power plant, generation or storage, was never going to be enough for an entire country, so why compare them? No one is suggesting the UK meet all it's energy needs through solar power, so why use that as a base assumption? Why base your consideration of hydro on a single large scheme in wales, when there are other pumped storage plants in Ffestiniog, Foyers, and Cuachan?

And you realise that these schemes were originally built to try and solve the power generation problems caused by a reliance on large inflexible power plants like the ones you're suggesting?

Fuel cell sites like the one mentioned up-thread are currently much too small scale,

Too small scale for what? I'm not sure why small=bad. You just build more of them. Now that our power balancing technology is more sophisticated than a guy with a gauge, a dial, and a cup of coffee to keep him awake at night, we can handle multiple smaller sources. Unless there's something I'm missing here?

My in-laws have just installed a new solar array on their roof in the north of England. They're selling electricity back to the grid most days, cloudy or not. Storage heaters used to run at night for the same reason the pumped storage hydro plants were built - to counter the inflexibility of large power plants that ran at night because they were too expensive to shut down. Now they've switched their storage heater from running at night, to running during the day, dropping their night-time electricity use to almost nothing. That's solving the problem at a tiny scale - the scale of an individual house.

and much too expensive per unit of energy stored,

Cost is another matter entirely. None of the solutions I've suggested are particularly expensive, (or particularly cheap). The cheapest option is going to be to keep our existing power stations going as long as possible. I'd rather stick to the original topic of what is more ecological, because cost is a topic in it's own right.

 

[bilby]

Pumped hydro storage is dependent on geography.

A LOT of geography

A hydro plant like Dinorwig, in North Wales, can generate nearly 1.8GW, which sounds great - until you realise it can only do this for a maximum of six hours at a stretch, for a total storage of less than 40TJ. To cover the mean UK demand of 1,500TJ for 12 hours (and solar power generation would struggle to operate consistently for 12 hours per day, so you might need twice this amount of storage) would need another forty such sites - and it is doubtful that that many suitable locations exist in all of Western Europe, much less in just the UK.

This is a very strange form of argument. A single power plant, generation or storage, was never going to be enough for an entire country, so why compare them? No one is suggesting the UK meet all it's energy needs through solar power, so why use that as a base assumption? Why base your consideration of hydro on a single large scheme in wales, when there are other pumped storage plants in Ffestiniog, Foyers, and Cuachan?

Because you need a LOT of Joules, and Dinorwig is by far the biggest in the UK - those other three put together add up to 0.75 of Dinorwig - which is the entire point. You need dozens more; but you can't manage to find a site for another like it, and having built three more tiddlers, you still haven't doubled your capacity.

Pumped storage hydro is as good as storage gets right now. And it ain't close to good enough to handle a 'mostly solar and wind' generating strategy. It's OK for knocking a few percent either way off demand to make nukes super efficient. But it is not even close to being OK for smoothing a supply that goes to zero for 12 hours at a time or more (often much more).

And you realise that these schemes were originally built to try and solve the power generation problems caused by a reliance on large inflexible power plants like the ones you're suggesting?

Indeed. But asking them to do the much larger job of smoothing wind and solar supply peaks is too big an ask.

Fuel cell sites like the one mentioned up-thread are currently much too small scale,

Too small scale for what? I'm not sure why small=bad. You just build more of them. Now that our power balancing technology is more sophisticated than a guy with a gauge, a dial, and a cup of coffee to keep him awake at night, we can handle multiple smaller sources. Unless there's something I'm missing here?

Cost. Cost is what you are missing. Money supply is non-infinite. So is the supply of materials used in fuel cells. Cheaper catalysts need to be developed; or we all need to win the lottery simultaneously, so we can afford the storage needed.

My in-laws have just installed a new solar array on their roof in the north of England. They're selling electricity back to the grid most days, cloudy or not. Storage heaters used to run at night for the same reason the pumped storage hydro plants were built - to counter the inflexibility of large power plants that ran at night because they were too expensive to shut down. Now they've switched their storage heater from running at night, to running during the day, dropping their night-time electricity use to almost nothing. That's solving the problem at a tiny scale - the scale of an individual house.

and much too expensive per unit of energy stored,

Cost is another matter entirely. None of the solutions I've suggested are particularly expensive, (or particularly cheap). The cheapest option is going to be to keep our existing power stations going as long as possible. I'd rather stick to the original topic of what is more ecological, because cost is a topic in it's own right.

OK; ignoring cost (which won't go away), how do you propose to get, say, 150GWdays of storage organised, while having less environmental impact than 65GW of nuclear power? Which do you think has the best chance of providing the 50GW or so average consumption of the UK with the fewest blackouts? If 150GWdays is not enough - and it isn't if you expect more than a few days of still, overcast weather - then how much is?

 

[Loren Pechtel]

A hydro plant like Dinorwig, in North Wales, can generate nearly 1.8GW, which sounds great - until you realise it can only do this for a maximum of six hours at a stretch, for a total storage of less than 40TJ. To cover the mean UK demand of 1,500TJ for 12 hours (and solar power generation would struggle to operate consistently for 12 hours per day, so you might need twice this amount of storage) would need another forty such sites - and it is doubtful that that many suitable locations exist in all of Western Europe, much less in just the UK.

Fuel cell sites like the one mentioned up-thread are currently much too small scale, and much too expensive per unit of energy stored, but they do at least have the advantage of being suited to a much wider range of potential sites.

12 hours? The sun shines every day???

One cloudy day and you need probably 100 such sites, not 40.

 

[Togo]

This is a very strange form of argument. A single power plant, generation or storage, was never going to be enough for an entire country, so why compare them? No one is suggesting the UK meet all it's energy needs through solar power, so why use that as a base assumption? Why base your consideration of hydro on a single large scheme in wales, when there are other pumped storage plants in Ffestiniog, Foyers, and Cuachan?

Because you need a LOT of Joules,

What for?

And it ain't close to good enough to handle a 'mostly solar and wind' generating strategy.

You may be right, but I'd like to see the working. So far all you've considered is an entirely solar powered UK, which does nothing to support your conclusion.

If it helps, I'm not convinced you have enough storage to support a 100% nuclear strategy either.

It's OK for knocking a few percent either way off demand to make nukes super efficient.

It's not about making nukes 'super efficient', it's about making them viable at all. The way it works at the moment, the fluctuating demand gets handled by switching plants off and on. It's much hard to do that in nuclear power than it is in fossil fuel plants, particularly natural gas plants. Renewables are the easiest of all. If you want a lot of nuclear plants, which work best when they're just on all the time, you'll need a lot of renewables or storage to handle the changes in demand.

But it is not even close to being OK for smoothing a supply that goes to zero for 12 hours at a time or more (often much more).

Can you give an example? Because even on a cloudy day, you get solar, and even on a still night, you get wind.

Indeed. But asking them to do the much larger job of smoothing wind and solar supply peaks is too big an ask.

But you don't need to smooth peaks with renewables. You can just, cheaply and efficiently, turn them off when not being used.

Cost is another matter entirely. None of the solutions I've suggested are particularly expensive, (or particularly cheap). The cheapest option is going to be to keep our existing power stations going as long as possible. I'd rather stick to the original topic of what is more ecological, because cost is a topic in it's own right.

OK; ignoring cost (which won't go away), how do you propose to get, say, 150GWdays of storage organised, while having less environmental impact than 65GW of nuclear power?

How much energy storage are you assuming for the nuclear option? And is this one site or a grid?

What I'd probably do for a 65GW peak requirement is to get 15 GW from energy efficiency spending, a further 5GW from site-specific generation, Load the demand onto the daylight side to generate a daytime peak, and cover maybe 30Gw with solar, and follow up with maybe 30GW of wind. Maybe get another 2-3GW from heat exchange pumps and run of the river, depending on the site. Obviously if we can get a small hydrogen synthesis plant going, we can use that for storage. It really depends on how you want to run it. That gives you a little over 65GW of generation on a 50Gw demand, say it drops to 45GW once every 5 years or so when you get a real dearth of wind, so you need maybe 10GWdays of storage. Set up a reservoir, or import it.

Now it would be better if you could find a use for that extra capacity, in the form of some kind of storage, but it's essentially free just to switch the panels/turbines off.

How would you deal with the storage requirements using nuclear? You've got a 65GW daily peak demand, falling to 40GW at it's low ebb. Assuming you meet peak demand, you're looking at a forced scaledown or efficiency loss unless you can arrange to lose that extra 25GWs that aren't being used during peak periods. Assuming some seasonal fluctuations, you're looking at a storage requirement of 25GWs per day for, say three days, so 75 GWdays. You also need to compensate for safety shutdowns, 3 days isn't that uncommon, so that's 150GWdays on top of that (because you have to retain the 150GW as an 'always filled' reserve'.

 

[Togo]

Fuel cell sites like the one mentioned up-thread are currently much too small scale, and much too expensive per unit of energy stored, but they do at least have the advantage of being suited to a much wider range of potential sites.

12 hours? The sun shines every day???

One cloudy day and you need probably 100 such sites, not 40.

Yes, the sun shines every day. That's why solar panels continue to produce electricity even when it's cloudy.

I live in England. We get 'overcast' skies lasting for a month or more without seeing the sun. Solar works just fine. It's not blocked by clouds.

Which makes sense if you think about it. If clouds did block all light, then the horizon to horizon solid cloud that we get would make it as dark as night, and all the plants would die.

 

[Loren Pechtel]

Fuel cell sites like the one mentioned up-thread are currently much too small scale, and much too expensive per unit of energy stored, but they do at least have the advantage of being suited to a much wider range of potential sites.

12 hours? The sun shines every day???

One cloudy day and you need probably 100 such sites, not 40.

Yes, the sun shines every day. That's why solar panels continue to produce electricity even when it's cloudy.

I live in England. We get 'overcast' skies lasting for a month or more without seeing the sun. Solar works just fine. It's not blocked by clouds.

Which makes sense if you think about it. If clouds did block all light, then the horizon to horizon solid cloud that we get would make it as dark as night, and all the plants would die.

Solar panels produce *SOME* power under clouds. Not as much power, though.

http://en.wikipedia.org/wiki/Exposure_value#Tabulated_exposure_values

Yeah, I hear you complaining that that's about photographic exposure, not solar power. Photographic exposure 101: A difference of 1 exposure value represents twice (or half, if you're going down) the light.

Note full sun is EV 15. By the time there aren't shadows is EV 13 and heavy overcast is EV 12.

EV 13 means 1/4 of the light--and thus a quarter of the power. That drops to 1/8 if it's really cloudy.

 

[steve_bnk]

You can find tables that give average surface solar power in watts/meter^2 by latitude and longitude by month in the USA.

Assume a total system efficiency of say 5% and calculate how much area you need to equal the total energy used in the USA per year.

Try searching on on 'USA average solar irradiance' and 'total energy usage USA'.

If we had a unified coordinated national electric utility based on distributed solar stations it could havee a major impact.