36

Because a playground equipped with generators would probably not be much fun. The merry-go-round would grind to a stop the moment it is no longer being pushed. The swings would not swing; they would glide back to their resting place then sit idle. The jungle gym would require children to follow a prescribed exit that could capture their stored gravitational ...


20

It depends on what power you can produce and the efficiency of the equipment you use to convert that mechanical power into electrical power. As a moderately fit 50+ cyclist, I can produce over 200 W for five or so hours, 300 W for much shorter periods, and levels around 1 kW for less than a minute. A commonly quoted efficiency for electrical generation is ...


14

Summary: in the US about 150 hours a day, in Australia only about 90. Solar panels are better. Power Generated Most people who cycle regularly can produce between 150 and 250 watts for an hour. More for shorter periods or fitter people, obviously. Indurain is believed to have peaked at 2kW but he was exceptional even for a world champion (some people are ...


14

A better target would be gym exercise machines Indoors, not exposed to elements, controlled environment so less chance of theft and vandalism. Customers stay on machines for a prolonged period instead of kids who would play on 1 thing for 5 minutes or less before moving on to the next one Arrays of identical machines can be connected to same grid tie ...


13

No. There is no readily available supply of net-positive-energy hydrogen on Earth, where most human power usage takes place. Hydrogen fuel cells may be a useful component of a total energy system but they are not a source of generation capacity. Hydrogen is more like a battery than a supply of energy. Hydrogen can be liberated from water by using energy. ...


11

This is built on, and directly quotes from, my answer and user26165's answer to a similar question over on Physics.SE. No, fresnel lenses are not widely used for solar power. Occasionally, but rarely. The issues are engineering and economics. Other solar competitors The big economic story is the amazing speed at which ordinary photovoltaics have reduced ...


11

Playground equipment is very expensive and not typically something that local councils have large budgets for. Hooking it up to the electrical grid for minor amounts of electricity generation would increase the cost substantially and require an ongoing electrical maintenance contract.


10

BBC1's "Bang Goes the Theory" demonstrated a human-powered home in a TK programme. In this segment, 8.5 kW of power required 70 cyclists, of fairly typical fitness, or about 107W per cyclist. The full programme shows running a household of four for twelve hours utilising 80 cyclists, working with breaks. The example isn't highlighting low-power draws, but ...


10

No, you cannot get more energy out than you put in. No, you cannot invent a perpetual motion machine.


9

It's possible, but the best way to do it was devised over a century ago: hydro power. Let the high land collect and channel lots of rain, and then put a turbine on the channel. The problem is that raindrops, as they fall, have very little energy - very little mass, and pretty low velocity too. Once they've fallen on high land, they've still got a lot of ...


9

DC motors: The most suitable motors are those which have permanent magnets in their rotors. Traditionally these were pure DC motors - where DC was fed into the motor rather than AC such as is obtained from AC mains or via a transformer, but the boundary has become blurred as a BLDC motor or BLDCM = "Brushless DC Motor" uses electronics to take supplied DC ...


9

Why did you rule out Solar? Solar is effective even in the state of Alaska. According to this article a 16 panel 2.5KW system in Fairbanks Alaska can provide you with around 500KWh/month of power during the summer, and 10KWh/month during the dark winter months (when daylight only lasts 3 or 4 hours). A laptop that consumes 40W of power would use around 7....


6

The big advantage of GravityLight is that you can pull the weight once and then you have electricity for a relatively long period (I read somewhere it's 30 minutes). This is ideal when you need to have both hands free to do some work. This long period is also a must if you want it to replace the kerosene lamps that are currently used in rural Africa. The ...


6

I asked my late father (an electrical engineer) this very question years ago and he said that essentially, the entire cost of a solar panel is the cost of the energy to make it. You dig dirt out of the ground and apply energy to turn that into metal, glass, etc, then you use energy to ship parts around and to assemble them into a panel and ship the panel, ...


6

TL;DR: Wind is not dead, but a diverse set of economic, technical, and political factors have resulted in a leveling off of the rate of new construction. The cost to build new wind declined for years but has leveled off From the U.S. Energy Information Agency: Early wind project developers snagged the best sites As costs declined, developers ...


6

TL;dr -- it's most economical to operate nuclear plants at a fixed output level, so other fuels are used to adjust for variations in demand. Nuclear output at any given time is limited by outages, which are driven by the need for refueling and routine maintenance. Nuclear plants aren't load following, so other sources are needed From Wikipedia's article on ...


5

I'm going to assume you'e in the USA since you're using Imperial units. 1) Is 3 phase power more efficient to generate/use? In bulk, yes. Three phase (or sometimes 6 phase/3 phase 220V in low-voltage countries like the USA) has more options for direct driving motors and generators, and the higher voltages mean lower currents and hence lower losses. This ...


5

In this question about rooftop hydro I covered the efficiency question almost as an aside. I can't find an actual plant with efficiency over 80%, only claims that that might be possible. The average efficiency will be much lower than the peak, as a lot of plants are old and have efficiencies around 60% (although some have been refitted to boost efficiency). ...


5

The very reason solar energy is exciting is that it is not scarce at all. So, instead of making the best use of any photon, we use twice the surface area and cover it with cheap solar panels. Pros Cheaper Higher output Better scalability Minimum need for structure. Otherwise, you need to elevate a very heavy lenses Cons If you live in Monaco, you want ...


5

The validity of your assumptions depend very much on your location and on the amount of energy you want to generate. Some small-scale solutions do not suffer from the same drawback as large-scale solutions. Biomass The CO2 emitted by burning biomass is CO2 from the atmosphere that was taken up by plants and trees. This means that energy from biomass can be ...


5

Before you worry about charging, consider this: It takes about 85W to propel a 75kg cyclist at 20km/h under ideal conditions. Thin film (i.e. flexible) solar panels have an efficiency of ~9% and when deployed as an overhead canopy would likely deliver no more than 50W/m² in mid-latitudes. To generate the required 85W you thus would need a panel 1.7m² in ...


5

The second slide of the presentation linked by you actually shows the issue with wake very clearly. You could also talk about turbulences instead of wake (my company actually does). Wake is simply the pertubation of the flow of the wind by wind turbines (or any other object, like hills, trees, buildings, airplane noses, the grill on the new SUV by Chrysler, ...


5

In 2018, global wind capacity increased from 515 GW to 564 GW - a 9.5% increase. 20 GW of that 49 GW increase was in China, 11 GW in Europe, 3 GW South America, 8 GW North America. A 9.5% year-on-year increase is pretty good. It's not dead. It's not merely stable. It's growing. It's not growing fast enough for the good of the world. There's a huge resource ...


5

tl;dr -- For the west coast of the U.S., a 20% decrease in heating demand and 18% increase in cooling demand results in a 5% reduction in carbon emissions from electricity and natural gas usage Here's the approach I came up with to try and answer this question with some hard data. 1. Find a region of the U.S. which had a cold winter and mild summer, ...


5

Wouldn't it therefore be better to have a small rise in global temperature? No. The radiative forcing by carbon dioxide does not increase solar radiation that can be captured by solar cells. The warmer temperatures actually decrease solar cell output, because solar cells really like cold temperatures and lots of radiation. You can't have both optimal ...


5

There are two main areas to consider here: Safety. Anything put near children has to be safe, and mains voltage and generators generally aren't. Damaged wires could electrocute somebody, a generator rotor could kick back, injuring a kid. Durability A regular playground will be used in every possible unintended way, and there will be often damages. Not a ...


5

If the amount of radiation stays the same, solar panels produce more energy when they are cooler. Heat causes efficiency to suffer. However, this is assuming the radiation amount is the same. Usually it isn't. If you consider a place that's very cold, so cold that there's snow, usually there's a reason for that. The reason being that it's winter season and ...


4

I did some digging and found data with a bit more resolution. First, polysilicon prices since 2010: Source: Fu, et al, Economic Measurements of Polysilicon for the Photovoltaic Industry: Market Competition and Manufacturing Competitiveness. Then, crude oil prices since 2010: Source: www.macrotrends.net, Crude Oil Prices - 70 Year Historical Chart. Note ...


4

No. As the graphs provided show, the prices both spike during the GFC, loosely speaking, but the oil price spikes later and declines faster, then continues a general slow rise while the price of silicon falls. Note that in late 2005/early 2006 oil drops abruptly while silicon is rising sharply, but during the 2011 blip in silicon prices you see a similar ...


4

Here's a quick answer; hopefully we'll see some more in depth answers too. Looking at the given charts closely, the price of polysilicon appears to decline from around $75 in early 2010 to $17 in 2014, but the price of oil appears to gradually rise from $80 to $100 over the same period. This is very different behaviour, and says to me the relationship ...


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