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Comment by HereBeBeasties | Hacker News Reader

There's nothing wrong with solar per-se, but it's just not sufficiently power dense if you're talking national scale power usage. https://www.finder.com/uk/solar-power-potential seems to think that countries like the UK would need more than 10% of their area covering with solar panels to cover their energy needs. I think you'd need to be talking about an order of magnitude improvement in efficiency to really start making it look really feasible as a significant way to change our fossil fuel usage, no?

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UK would do best supplementing wind with solar, rather than going wholly solar. UK is famous for many things, consistent reliable sun isn't one of them. Maybe in 20 years we'll have a more Spanish climate, though I would hope not. Adding solar on every roof that's suitable should be plenty for starters.

There's probably dozens of spots around the UK suitable for Dinorwig 10 GWh pumped storage style solutions. NIMBYs permitting.

If the UK fully built out offshore wind it would probably have enough to power the whole of Europe. Same goes for Ireland.

Actually the estimates are that the Irish coast alone has enough potential wind energy to power all of the planet, during peak seasonal wind, and at least all of Europe during the less windy summer season.

Building the infrastructure to transmit that power would be a massive undertaking though. Ireland and France are currently cooperating to build an undersea power cable which is going to cost $1Bn, take 5 years, run 575km and have an annual transmission capacity of 6.1 TWh.

Annual global energy usage in 2013 was 19,504 TWh, or 3,197 times that.

Here is a source which says otherwise, and includes references: https://withouthotair.com/c18/page_103.shtml

Warning this book is quite old now. While the discussion of theoretical limits should probably still hold up, all the economics has been turned upside down since then.

Solar and wind costs dropped faster and further than most people's best case estimates, while nuclear costs and timescales just keep going up.

Methodology is flawed. If you switch from burning oil in ice engines to electric you use at least 50% total energy less.

So they overestimate area needed.

What's that due to? Less energy lost to dissipation?

Carnot cycle limiting maximum ICE efficiency to ~40% (can be obtained if you're big electric power plant) vs 95% electric engine efficiency.

For practical purposes, ICE has way lower efficiency than 40% and electrics lose some due to the transmission and battery recharge.

Thermodynamic cycles and engineering constraints. ICE engines are about 30% efficient at best. Operationally they're usually a lot worse. Where modern combined cycle power plants are pushing towards 60%. A big part of the difference is that stationary plants use multiple stages to wring the last bit of energy out of the fuel. Where piston engines use one stage.

They also suffer from mechanical and thermal losses due to their small size. Small size means higher internal surface area to volume and higher operating speeds. Contributes to higher friction and thermal losses. Friction in an ICE is actually significant.

For the same kind of reason solar panels only access about 15-20% of the energy that hits them.

I was serious. Solar cells are like solid state heat engines in that they’re fundamentally limited by Carnot Efficiency (which is theoretically high for solar cells as the effective temperature of sunlight is high). If we’re going to use “primary energy” and not useful electrical or mechanical energy, then we’d need to include the energy of sunlight falling on the solar panels, which is about 5 times the useful electrical energy produced.

And just like actual heat engines, solar cells are improving. The best cells have achieved 47% efficiency in the lab, comparable to a high performance combined cycle natural gas plant (note that thermal power plants often cheat a bit by listing the efficiency in terms of the low heating value of a fuel, ie the heat produced not counting condensing the water vapor out).

Electric cars need about 15-20kWh/100km. A liter of gasoline has about 9kWh of energy. The average car needs about seven liters per 100km, so around 60kWh/100km.

Similar improvements can be had for heating. You get a little less than 1J of heat in your room per Joule-equivalent of fuel you burn, but with an electric heatpump you get 3-5J of heat per Joule of electric energy.

>Methodology is flawed

The end product of those efficiency is still Twh. I don't see how the Methodology is flawed.

You're burning 1kg of gasoline with 46MJ/kg energy at 20% efficiency gives you 9.2MJ of work done.

Do you need to replace 46MJ energy embodied in gasoline with 46MJ worth of electricity?

No. Electric engine has 95% efficiency so you need 9.68 MJ of energy.

We also need batteries. But that's why solar is only part of the solution. No single source will solve all the problems in all the areas. I'm a big proponent of nuclear but it's only part. Solar is also what I want to see. But more than the other two I want batteries.

From what I heard from people in the solar business battery is generally not a good idea. Better to invest in a good grid where we can transfer electricity from one place to another (there’s always windy somewhere). And have some sort of backup power plants on the lowest days (like natural gas, biofuel, etc, not co2 free but they wouldn’t be used very often from what I understand). Or alternative “batteries” like pumping up a lot of water in some dam.

I like to point out the efficiency gains and load shifting will also reduce off peek demand somewhat. Industrial users will chase lowest cost if possible. If electricity costs 3X at 1am the price at 11am, no ones going to be running an electric furnace at 1am.

Either way I'm actually rather confident that the whole storage thing is more or less solvable. Since there are a host of technologies that are workable.

So it's slightly pointless argue as some do that lack of current solutions is a reason not to move forward with renewables. Worst comes to worst we already have peaking plants that could substitute for baseload power.

I think there's miscommunication.

> lack of current solutions is a reason not to move forward with renewables

No one is saying we shouldn't move forward with renewables. Well maybe a certain canine news network, but not anyone here.

> Either way I'm actually rather confident that the whole storage thing is more or less solvable. Since there are a host of technologies that are workable.

What people are saying is there isn't good enough technology yet. So that means that we need to continue funding research. Not being solved means that just building won't be the solution. That we need to spend some serious money researching. That's what people mean by "battery tech isn't there yet". It isn't a defeatist attitude, it is a "continuing and doubling down on research is an important part of the equation" type of attitude. This is typically because that kind of research isn't done by the private sector, but rather government. DOE does a lot of this funding, and even funds a lot of the research being done in the private sector. So being vocal about this means we care and hopefully those in control of allocating that money (probably not by Rick Perry) will spend more on fixing that part of the equation while the private sector does the building out part.

There's significant power loss in transmission on grid and to avoid power loss, you need fairly expensive equipment to convert to and from high voltage. If you are adding wind to the mix and working on an AC grid as normal, phase sync is also tricky. Electricity supply on grid has to be very closely matched to demand and the problem will likely become fairly complex with lots variable sources. A lot of problems potentially go away if you push renewable to significant battery storage first and you also get a much more resilient grid to natural disasters (see Puerto Rico's situation)

For an interesting graphic along these lines see [0].

The parent of this comment is talking about increasing the efficiency (reducing rejected energy) and the gp is talking about just increasing the total amount of energy. Both are solutions. But I wouldn't say it is a good thing we reject more than half the energy we create.

[0] https://flowcharts.llnl.gov/content/assets/images/energy/us/...

As an addendum - explanation of the electricity distribution losses on grid:

https://electrical-engineering-portal.com/total-losses-in-po...

Because there's confusion I'm adding an addendum to the addendum. Here's an LLNL scientist explaining the graph. Which he does talk about the rejected energy [0]

[0] https://www.youtube.com/watch?v=G6dlvECRfcI

> But I wouldn't say it is a good thing we reject more than half the energy we create.

The meaning of "Rejected Energy" in that graphic is obscure but it certainly doesn't relate to energy which has been created and rejected. It may relate to excess capacity of fossil fuel plants (how much more they could produce if ordered to burn more fuel).

The US is thankfully not "rejecting" twice as much energy as it is producing as those figures of 68.5 vs 32.7 lead you to believe. Curtailment of wind and solar generation in the US is recently around 2-4%

[1] https://blog.ucsusa.org/mark-specht/renewable-energy-curtail...

Sfifs has an accurate link. But your comment really isn't correct. You suggest it is solely to fossil fuels. There is inherent waste to any electrical system as some of the energy produced goes into heating the wires (unless they are super conductors, but as far as I'm aware solar panels and wind farms don't use ultra high temperature super conductors. Don't even know any that exist tbh). Heat is just the simplest example, but Sfifs liked more information.

> There is inherent waste to ..

What has inherent waste to do with your reference to "Rejected Energy" ? What do you now understand of that graphic ? Transmission losses are generally in the range 5-10% for modern grids. Your interpretation of that ambiguous reference wrongly indicated 66% losses. Thats not reasonable and doesn't support your advice on energy storage. I suggest gaining more familiarity with the general subject before judging it.

The graphic's term for rejected energy includes a multitude of things. Thermodynamic loss is part of it but not all. It was mentioned because it is one of the easiest for people to understand. There has been another link provided that I have already referred you to that includes a more comprehensive breakdown.

But yeah you can act all knowledgeable, or you can listen to the group leader of the LLNL staff that put this chart together using the same exact example I used.[0]

I, again, will say that this is only a portion of the rejected energy. But thermodynamic loss (i.e. heating wires, heating your ICE engine, etc) is part of that rejected energy.

[0] https://www.youtube.com/watch?v=G6dlvECRfcI

I watched the explanation of the chart and it is still ambiguous both what it is, and its purpose. That narrator explains: "Rejected energy is the portion of energy that goes into a process and comes out generally as waste heat" - waste heat is not just as you wrote: "part" of it, it is explained to be "generally" (all of) it. Really neither of us should need to clarify the difference between "part of" and "generally all"

So then "rejected energy/waste heat" can not be used or as we are saying here -"accepted" by better battery storage, which was the opinion that you brought this ambiguous chart and presentation to explain. This chart is irrelevant to battery storage.

Also, most of the energy in the chart is thermo-electric derived from fossil fuel and nuclear plant. Wind turbines and solar "reject" heat energy in completely different manner and lesser degree than thermo-electric plants - it is truly nonsensical to mix the two together under the vague heading of "rejected". It makes so little sense, I do wonder about the credentials or motivation of this LLNL to educate on energy issues.

I think that most rejected energy is on the majority from thermodynamic losses. At least for electric power production. Converting heat to work has large theoretical losses (See Carnot Cycle) and loses due to engineering limits (Turbines aren't 100% efficient). Losses end up as waste heat.

Rejection is an action - whatever it means in that graphic its not a thermodynamic factor. My bet is the figures shown relate to capacity factor, they have no connection to what they have been presented as - a potentially reclaimable amount. Of course the proof should lie in the article which the graphic comes from - its a very messy idea to link and debate graphics which have no clear sense without their article.

Personally I'm not really very happy with that graph since it combines energy inputs into black boxes instead of groupings. Take natural gas, solar, wind, nuclear, and hydro and combine those into an electric power generation' 'fruit basket.' It makes you think you know something, but at the same time makes sure you don't know enough.

Succinctly put, thanks.

Energy loss in the grid is not that dramatic. Average losses are typically well below 10%.

Matching demand to supply is not that hard. If you have oversupply you run pumped hydro, batteries, and power-to-gas plants and store the extra energy. If you have even worse oversupply you disconnect your solar panels, or your wind turbines. If you have undersupply you use the energy you stored previously.

Conventional power plants fail first because they are big and centralized. When a plant goes down temporarily you have a huge gap to fill. With renewables 100 turbines stopping out of 1000 is not a big deal because they don't all fail at the same time.

The problem is that if you have a completely renewable grid (note I'm not saying a zero or low carbon grid) you can't provide large parts of the world (even the US) with that energy unless you direct it from some big hub. An easy to see example of this is that certain parts of America aren't very sunny and/or windy throughout the year (PNW, NE, Midwest, Alaska). Other parts are very sunny and very windy (think desert areas like CA and southwest). This leads to centralization even with renewables. It isn't an easy problem to solve and that's why people suggest things like nuclear, to fill in the gaps. Hydro has been a great filler in many places, but not all of these regions have access to large enough rivers, so again we get some centralization (see Tennessee Valley Authority, who also still use a lot of nuclear).

The problem is 100% solvable, but that doesn't mean it is currently solved or what's left is trivial. We're almost there, but it is hard to finish fixing things when you slap a sticker on it saying "done" and stop addressing the remaining issues.

The battery business is a great idea today for grid stabilization, is getting there for peak demand shaving for customers, and the cost is falling.

from what i understand (and i could be wrong), you could make biofuels using atmospheric co2, alguae, heat from the grid during low demand... when you burn it, it releases that co2, but when you’re not it acts as a big carbon sink

could be totally off base, or very much a “not yet industrialised” process... but the idea is super cool none the less

The efficiency is too low for day to day storage but for month to month storage it might work.

Or other forms of energy storage.

Your own link says that about 6% of the UK has been built over; although I am unclear exactly what that means [1], this is an achievable level. Of course, I would still agree that it’s good to have a mixture, for example the British Isles have a lot wind power (I’ve heard, but can’t find a reference for the claim, that it could supply most of the European continent).

[1] the percentage sounds high enough that I assume it includes all gardens and roads not just the buildings themselves

Here's a good link for you: http://gridwatch.co.uk/

It shows current UK grid demand and generation sources as well as historical data.

Thank you, though — while interesting — that doesn’t tell me how much wind power the British Isles could produce if UK and Ireland built the wind farms necessary to exploit it.

The problem with solar isn't that it isn't power dense. The problem is that the capacity factor compared to something like wind energy is very low. I'm skeptical of that 10% area claim. They probably made a very basic mistake of replacing all chemical energy with the electricity generated by solar power plants. This completely ignores that we can only turn that chemical energy into heat and then have to convert it to electricity. Depending on the size of the engine the efficiency of this step can range from anywhere between 25% to 50%. So you need 2 to 4 times more primary energy than if your power source generated electricity from the start.

Take a look at this chart [0]. As you can see, renewables produce barely any primary energy at all with the exception of biomass, because they don't need to. [1] If we really did increase our renewable deployment 8 fold then Germany would be at 400% renewables at current consumption rates which clearly isn't necessary even if every single car is electric and all industry switched away from fossil fuels. There will still be some processes that depend on fossil fuels as input material but those do not burn the fuels to obtain their energy. Oil products like plastic will most likely dumped in the oce- I mean in landfills.

[0] https://www.cleanenergywire.org/sites/default/files/styles/p...

[1] https://www.cleanenergywire.org/sites/default/files/styles/p...

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