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For a writing challenge, I'm trying to create a near-future world (2030 or so) where the major Western nations have transitioned to a fully solar economy.

Hence the rub. The realist in me is aware of the fact that the Earth rotates, putting solar out of reach for any ground-based solar-power for a considerable portion of the day, and at awkward angles for most of the day. Assuming it's not cloudy.

Westerners have gotten used to having electricity at night and during rainy days, so I'm trying to come up with a functional solution for the intermittency problem.

I've thought of putting it in space and microwaving it back, but initial back-of-the-Google-sheet calculation made it look outrageously expensive (I could be wrong). I've thought of putting it in deserts (no rain) and transferring it from the day side (no night), but the power lines actually are lossy, so the cost of transporting electricity long-distance (half-way around the world) is rather prohibitive. So I'm currently working on the idea of damming a few Fjords and pumping up water during solar peaks, and using up the water for hydro power during solar lows. Seems rather low tech, but I know it can kinda work (albeit with rather low efficiency).

I would love to hear some better ideas. So, how do I make a solar power economy work given a) Night b) Cloud c) Winter? Plausible moderately futuristic tech allowed.

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  • $\begingroup$ I'm not sure how viable it would be, but I've seen tech that featured a sidewalk where the 'tiles' were on top of small devices that turned the pressure of pedestrians into electricity. There are also flexible metals that generate charge when bent (could be used to power pacemakers via breathing). A field of these instead of wheat could be possible. Also, how much power could be generated at gyms? Instead of resistance by weight/gravity, they were instead turning generators of some kind. All these methods would be like flipping the couch cushions for extra income, but every little bit counts. $\endgroup$ – coblr Aug 11 '15 at 23:52
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    $\begingroup$ Serban - If we could answer this question, oil companies everywhere would be paying us billions to stay silent, power companies everywhere would be paying us billions to talk, and the Nobel Committee would be literally throwing medals at us left and right. @fractalspawn - The gym idea is brilliant, I don't know why we aren't already doing that! $\endgroup$ – thanby - reinstate Monica Aug 12 '15 at 6:26
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    $\begingroup$ unfortunately the energy yield from a gym is actually embarrassingly low compared to a 'normal' home. You'd need several machines generating power at optimal efficiency to run even one household. This has been tested: electricpedals.com/human-power-station $\endgroup$ – Sobrique Aug 12 '15 at 12:15
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    $\begingroup$ A few years ago, Ars Technica did a nice writeup about the most detailed/sophisticated attempt to model a large scale almost entirely renewable power grid. You might try looking up the study authors to read the original and to see if they've published anything since then. arstechnica.com/science/2012/12/… $\endgroup$ – Dan Neely Aug 12 '15 at 14:04
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    $\begingroup$ Some other problems with solar not mentioned in your question: 1) it is extremely diffuse power, requiring lots of hardware and space to collect enough power; 2) (as with other unconventional power) the best places to get it are most often far from population centers; 3) in good environments solar panels wear out in 10-20 years; 4) when combining #1 & #4, it means you'll need vast armies constantly working on this power generation to keep it running (I haven't check to see whether this army is smaller or larger than that needed for convention power generation). $\endgroup$ – Jim2B Aug 12 '15 at 18:18

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You've hit on the major drawback with solar (or wind) power today: availability factor. It's difficult to predict when these will be unavailable, so you need a backup strategy. Currently, energy sources like this are supplemented in a few ways:

Conventional Generation
During peak loads or times when the sun/wind is unavailable, many utilities bring online less-renewable generators to meet demand. Typically this is Natural Gas turbines, since they have good ramp rates (they start generating quickly) and relatively cheap, easily storeable fuel. It may also be coal, hydro, or other types of plants.

Buy from other utilities
If a utility projects that they will not be able to meet the demand of their market, they have the option to buy generation on an energy market. They can also do this if electricity is cheaper to buy than generate for whatever reason. Generation is constantly being bought and sold much like stock in a stock market. In fact, many utilities need to purchase electricity at peak load times (usually 5pm) from regions to the east or west who are pre- or post-peak and have unused capacity. This is made possible by the power grid, a network of high voltage power lines for transmitting power of long distances. In an all-solar economy, this may not be possible at all hours of the night, due to losses over very long distances. You may offset those losses with extremely high voltage lines (higher voltage helps reduce losses) or by hand-waving room-temperature superconductors.

Storage
This is the most plausible place for improvements to make an all-solar grid feasible. Generally speaking, storing energy as electricity (in batteries or capacitors) is not cost-effective at the scales we're talking about. Fortunately, that energy can be converted into a form that's easier to store. Here are a few suggestions:

Thermal
Use the energy to heat up a fluid, such as a molten salt. Some fluids have very good heat capacities, and can store energy effectively over night if kept in insulated tanks. When power is needed, the salt is used to heat water to produce steam and turn a turbine. This is not far from what concentrated solar plants currently use.

Rotational
Use excess energy to spin a flywheel. Later, use the inertia of the flywheel to turn a generator to produce electricity.

Potential (gravitational)
Use excess energy to pump water up a hill to a reservoir. Later, let it flow through a turbine to produce electricity. This is the same principle that hydroelectric dams work on, although we let the water cylce do most of the pumping there. As people have pointed out in comments, there are several examples of this in use.

Pressure
Pump air into a decently-sealed cavern underground. Later, release it through a turbine to generate electricity. There is a plant in the southern US that does this, and at least one more in Germany.

Chemical
Use electrolysis to separate the hydrogen and oxygen in water. Later, burn the two to produce water and heat. Heat steam and turn a turbine to generate electricity.

None of these are particularly efficient, but that's not a big deal. They all use otherwise wasted energy to store a portion of that energy for later. It's difficult to make them cost-effective today, but a breakthrough on that front could make your solar-only world feasible with very near-future technology.

Rolling Blackouts
Currently, if a distribution utility cannot meet demand, they strategically shed load to prevent cascading failure. While less than ideal, it can be a reasonable solution, especially if your customers have access to a schedule.

Unfortunately, I'm limited to two links by my low reputation. I will add more when I'm able.

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    $\begingroup$ Welcome to the site Carl. Excellent first post. $\endgroup$ – James Aug 11 '15 at 18:04
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    $\begingroup$ "Inefficient" is relative. Pumped-storage hydropower, for example, has typical recoveries on the order of 90%, and the efficiency of pressure-based storage depends on your ability to keep the compressed air hot. $\endgroup$ – Mark Aug 12 '15 at 0:00
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    $\begingroup$ You mention existing "Pressure" stations, if you'd like to see a real life "Potential" station here is one such example: google.co.za/maps/@-34.0888216,18.895844,1335a,20y,180h,81.39t/…. It is just outside the city of Cape Town, South Africa. You can see the main dam at the top of the mountain and the catchment dam and turbine housing at the bottom of the mountain. $\endgroup$ – mccdyl001 Aug 12 '15 at 5:57
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    $\begingroup$ There is also one in Wales google.co.uk/maps/place/Electric+Mountain/… It uses energy generated by the grid at night to fill the small lake towards the top right with water and then it runs down to the larger lake very quickly when there is extra short duration demand. en.wikipedia.org/wiki/Dinorwig_Power_Station $\endgroup$ – Wil Selwood Aug 12 '15 at 16:19
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    $\begingroup$ @thanby That is how these schemes work. Large power plants generally don't ramp up or down easily, so during off-peak hours there is often a lot of excess power available on the grid. These pumped storage schemes use that excess power when no-one else wants it to pump the water around. When peak demand occurs, it's relatively quick to open the sluices and get the water turbine up to speed (not instant like a giant battery would be but within minutes) and likewise shut it down again afterwards. $\endgroup$ – mccdyl001 Aug 13 '15 at 7:57
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Have you considered superconductors? If the electrical grids of the world could be networked together with a superconductor infrastructure of sufficient capacity, you could simply transmit power from the sunny parts of the planet to the darker parts of the planet with dramatically less loss.

While superconductors are still fairly exotic, and therefore expensive, materials these days, perhaps within the next fifteen years there could be advances that make them significantly cheaper and easier to work with. And even if the superconducting power network were constrained to today's superconductor technology, the costs of building, cooling, and maintaining that infrastructure might actually be a negligible fraction of the cost required to convert the entire world's power generation to solar.

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    $\begingroup$ If such a line was build from the Gobi desert eastward to Moscow (yes, I mean east, going the long way around the world through the US) it would be well within the range of conventional long range lines of the majority of energy use in the world. The thermal losses would be proportional to the length, and would not increase much with higher capacity, meaning the more power the world uses, the more relative efficiency this method has relative to the others. $\endgroup$ – wedstrom Aug 11 '15 at 17:48
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    $\begingroup$ There's currently an article on Ars Technica about the "ARC" fusion reactor that estimates the price for 5,730 kilometers of rare-earth barium-copper-oxide superconducting tape as $4.6 billion. See arstechnica.com/science/2015/08/…. $\endgroup$ – Doug Warren Aug 13 '15 at 13:59
  • $\begingroup$ The internet is oddly reticent about it, but more research seems to indicate that the "critical current density" of the "common" superconductor yttrium-barium-copper-oxide is somewhere between 9 billion and 290 billion amps per square meter of cross section. Yes, that's a big range, and no, I'm not sure how big the wires from the ARC reactor are. $\endgroup$ – Doug Warren Aug 13 '15 at 15:08
  • $\begingroup$ The load carried by a transcontinental power line would much larger than used in the arc reactor. Also, the cooling systems and site preparations, including thousands of miles of grading. I would think it would be easily 10 million dollars a mile (maglev trains, for instance, are in the 100 million per mile range). That would put the project costs in the hundreds of billions. Potentially worth it, if there is actually a solar/wind etc market available to make use of it. Far cheaper, I think, than grid level storage which I dislike with a nearly religious zeal. $\endgroup$ – wedstrom Aug 13 '15 at 17:00
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Power Grid Batteries

Going for a pure solar based power grid is possible with the addition of batteries to supply power during solar ebb. The Tesla Powerwall will be available in 2016. The Tesla Gigafactory 1 will be online and producing batteries in 2016 or 2017, so by 2030, the price of lithium-ion batteries should be substantially lower than the present.

Improved Solar Efficiency

Solar cells gradually improve efficiency over time. In the late 1970's, the highest solar cell efficiency, of any design, was no greater than 16%. As of 2010, the highest efficiency was approximately 41%. By 2030, the efficiency should be significantly higher, much closer to the Shockley Queisser Limit of around 88% percent for infinitely layered solar cells. (The theoretical maximum is more nuanced that I've described it here. Go read the link for clarification.)

Blended is Better

Of course, you could do a purely solar economy but that leaves your power grid dangerously vulnerable to long periods of minimal solar activity such as winter time in Scotland. Introducing wind, hydro, geothermal or tidal power to the grid will help or completely alleviate these solar minimums.

Climate Repair

Over-production in the current power grid is fairly common and that extra power just goes to waste because there is no way to store it. Using that extra power to convert atmospheric carbon back to hydrocarbons will help alleviate global climate change. That's incredibly valuable.

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  • $\begingroup$ Re 'Introducing wind, hydro... ' but those sources are also unpredictably intermittent $\endgroup$ – Serban Tanasa Aug 11 '15 at 16:44
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    $\begingroup$ True, they are all intermittent but they are rarely unavailable all at the same time. Just like in financial investments, a diverse portfolio is less susceptible to dramatic losses. $\endgroup$ – Green Aug 11 '15 at 16:49
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I think the answer you are looking for could be giant solar mirrors orbiting the earth. They could be positioned or at least moved by thrusters to always be able to see the sun, and turned to focus the energy down towards collection points on Earth.

Night, cloud and winter are not an issue as the mirrors are not in the atmosphere. Cloud and cold air may slightly impair the efficiency of the solar arrays on earth collecting that reflected light, but i doubt the absorption they would cause would be highly significant.

This could be offset easily by making the mirrors GIGANTIC. There is a lot of space in space

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  • $\begingroup$ I should have added that the major benefit of this is that the concave mirrors in space focus the light from a large area down to a small point on earth, and that solves one of the major hurdles of solar energy generation: the amount of space the solar farms take up on Earth. $\endgroup$ – ctravisuk Aug 11 '15 at 15:26
  • $\begingroup$ But wouldn't launch costs be prohibitive? $\endgroup$ – Serban Tanasa Aug 11 '15 at 16:33
  • $\begingroup$ Mirrors can be pretty light weight... or you might build them in space with space materials. Big up front cost in building the infrastructure, but then the marginal cost goes way down as the materials no longer have to eb launched. $\endgroup$ – Adam D. Ruppe Aug 11 '15 at 17:26
  • $\begingroup$ The mirror in space can be made out of foil, so it can be ultra lightweight while being huge. The problem with that is that the lower its weight the easier it is for it to be moved from position by solar radiation pressure as it becomes similar to a solar sail. $\endgroup$ – ctravisuk Aug 12 '15 at 15:08
  • $\begingroup$ I do not see it... either you propose that mirrors point to the solar station back in Earth (but many people will have issues with such a bright night) or to a solar station in space. The problem with such a space solar station is that to get electricity you need a temperature differential, but that is not easy to get in space (you may get the tower very hot, but all of it will be so, because cooling in space is quite difficult). $\endgroup$ – SJuan76 Aug 12 '15 at 19:27
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Working through the night and maintaining enough lights to be seen from space are a phenomenon of the industrial age, not a necessity of life. A solar-driven society would almost certainly follow the diurnal cycle closely. Rather than charge your phone at night, you'd charge it during the day - and your laptop, television, house, car, etc. You'd probably cook during the day and keep food warm in thermos-like devices. It would be less safe at night, although in 2030 you might have IR-camera drones lurking everywhere looking out for crime.

A case study of an industrial society with no nighttime lighting is wartime Britain, where externally visible lights at night were banned in an attempt to hide cities from bombers. Similarly, in the 1970s electrical power was only available for three days a week due to industrial action: https://en.wikipedia.org/wiki/Three-Day_Week

I'm assuming that "fully solar economy" means giving up on fossil fuels, but there would probably be a certain amount of biofuel available. Domestic wood fires would become popular again. Although don't underestimate the scale of this: Drax power station has been partly converted to burn wood, and if it weren't being imported it would consume every tree in the UK within two years.

You might end up saving most of the liquid biofuel to run aircraft. There is also already at least one project to produce fuel from atmospheric CO2 and spare energy, such as on a nuclear-powered aircraft carrier.

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    $\begingroup$ This would mean giving up much of the comfort we have gotten used to. Unless there is some enormous pressure (like during a war) i doubt the population of any industrial country would accept that without a lot of protest. Since you will need to provide power to hospitals at the absolute minimum, and most likely to the military, you will already be using means of energy storage. I fail to see why there should not be larger scale storage to preserve the convenience we got used to? I do agree that the change in energy cost would possibly shift activity to daytime, where it is feasible. $\endgroup$ – Burki Aug 12 '15 at 9:57
  • $\begingroup$ @Burki I don't think the scenario assumes any volunteering or democratic acceptance. And we really don't need to power the hospitals, military bases, and some long-running industrial processes. We choose to do so, because it's the optimal economic alternative here and now. $\endgroup$ – kubanczyk Aug 13 '15 at 11:38
  • $\begingroup$ @kubanczyk yes we do need to power hospitals at night, lest we want to let people die just because we are not willing to spend some money. Hopefully i will not live to see such a society. $\endgroup$ – Burki Aug 13 '15 at 11:48
  • $\begingroup$ @Burki You already live in a society which lets people die because of "some money". This is a matter of economics, as it was through all of our history. $\endgroup$ – kubanczyk Aug 13 '15 at 12:17
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I'm not entirely sure this is a worldbuilding question because there are solutions already being implemented. But heres a go.

Diversification

it doesn't make sense to go 100% solar, there are other resources, that are easier to match demand with. It means fossil fuels will be around for a long time, but hydroelectric power stations can be ramped up and down, and even run in reverse: https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity . Wind can also complement solar reasonably well in some parts of the world.

Daily storage

Peak electric consumption occurs in the first hours of darkness. Only about 6 hours of storage are required. This can be met with batteries, but this is expensive. There are several types of battery for large scale storage being developed, for example https://en.wikipedia.org/wiki/Beta-alumina_solid_electrolyte and https://en.wikipedia.org/wiki/Flow_battery

Concentrating solar plants use a field of mirrors to heat a thermal fluid, which is then used to generate steam for power generation. The thermal fluid (often a molten nitrate salt) can be stored for several hours.

Longer term storage

The only viable option for seasonal storage is chemical, and even that is a bit impractical / expensive.

Water can be split into hydrogen and oxygen, but hydrogen is bulky, and expensive to compress or liquefy. Extracting CO2 from the atmosphere to make synthetic hydrocarbons is not practical, because the CO2 concentration is so low.

There are several industries that use large quantities of hydrogen, the most relevant of which is the ammonia industry. Nitrogen from the atmosphere can be reacted with hydrogen to make ammonia, which is much easier to compress and liquefy than hydrogen. Ammonia is currently used in the fertilizer industry, but it can be used as a fuel, or decomposed back to nitrogen and hydrogen. Unfortunately ammonia from solar hydrogen will be several times more expensive than ammonia from plants that use hydrocarbons as feed and fuel.

Solar energy could be harnessed in several other ways. One way is the enrichment of biomass. Wood and similar fuels are carbohydrate, which means that their chemical structure contains a lot of hydrogen and oxygen. On heating the material chars, which means the hydrogen and oxygen are given off as water:

sugar C6H12O6 ---> 6C + 6H2O

The resulting charcoal has about double the energy content of the original wood, so converting wood to charcoal using solar energy would halve the amount of wood that needs to be collected.

Solar thermochemical plants

People tend to think of converting solar energy to electricity, and then using it to hydrolyse water, but the process can be carried out using just chemistry and solar heat. It's more efficient that way, but the plants are quite complex.

One of the more promising reaction schemes is the Sulfur-Iodine cycle https://en.wikipedia.org/wiki/Sulfur%E2%80%93iodine_cycle

As I said before, such plants are currently undercut by hydrogen produced from hydrocarbons. In the future this may change.

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  • $\begingroup$ "Peak electric consumption occurs in the first hours of darkness" is true now, but it's a cultural thing that can be 'fixed' in an imagined future. Switching the general socially-active-time from 8:00-23:00 to 5:00-20:00 requires some adjustment, but if there are serious economic incentives then it will happen, just as it used to be back when artificial lighting was possible but rather expensive. $\endgroup$ – Peteris Aug 13 '15 at 8:46
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I think it should be fairly simple.

First, it is unrealistic to rely on solar power alone (when wind power is at least as cheap as solar, and provides good additional power on cloudy but windy days, and in windy nights.

But to your actual question:

Batteries
I am not speaking of triple-a's, of course.

Even today we have a lot of pumped storage hydro power stations. And they work exactly as you need them for your setup: They use excess electricity to pump water up to a high reservoir, and let it flow back to produce energy.

There is even the benefit of rain adding to your energy reserves.

There are different approaches, too, of course:

Turn electricity into fuel
and store that fuel. Use any method that is conveniently available to transform some matter into hydrocarbons. When your other reserves are running low, fire up a conventional diesel (or similar) with the fuel you created in times of abundance. You can, of course, also do hydrogen electrolyse, either to use it in a fuel cell or to burn it. Yet a liquid fuel is easier and safer to store.

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  • $\begingroup$ Another kind of battery is heat. Some of the real world solar stations now focus the sunlight on a big container of sand and melt it. The heat runs a steam turbine and the sand doesn't cool off instantly, so it keeps running overnight. If demand is lower overnight, it might just be ok anyway, and if not, perhaps some electricity can be transmitted from a few hours away or other methods combined to make up the difference. $\endgroup$ – Adam D. Ruppe Aug 11 '15 at 17:27
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While pump storage (hydropower) is probably the best available storage method, a possibility for your paper might be the "zinc economy", where excess electrical energy can be used to refine zinc (which can later be used to power zinc/air batteries). http://encyc.org/wiki/Zinc_economy

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There is a lot of good answers here. I would like to add 2 additional.

  1. Change charging culture, i assume most of us charge our cellphone at night. Charging your cellphone, laptop and electric car during the day so the power last most of the night. Maybe even distribute storage. (1 HUGE government power-bank = expensive, 10.000.000 personal power-banks is more expensive but only for individuals) the power banks would be charged during day and used during nights, fail-over power would be available during night in case the power-bank would run out but at a higher cost.

  2. I see where you are going, but i would like to point out that having eco power could also include wind-power, checkout french tree turbine and tell me it isn't awesome.

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you might want to have a look at this TED talk: http://www.ted.com/talks/donald_sadoway_the_missing_link_to_renewable_energy?language=en

This guy basically developped a new kind of battery, and it sounds good. The talk is from 2012, and you can't buy these things yet, so maybe it's a bit too good to be true. Still, it might just be the solution for your problems :-)

As others mentioned, you can turn the electricity into fuel like hydrogen.

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    $\begingroup$ Could you add a bit about the battery in your answer? Answers need to be able to stand alone and the links should be there for more in depth interest and reference. $\endgroup$ – bowlturner Aug 12 '15 at 13:00

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