60-80% lost in the mechanical conversion in all probability.
But m.g.h for a 20kg weight would only be ~ 20.10.5 = 1000J
Enough to light a 100W lamp for 10s. (with 100% efficiency in practice you will be lucky to get 2-3s)
More like a 1T rotor at 1000rpm if you are serious about a mechanical UPS - that really will store a decent amount of kinetic energy. Used at some remote telescopes to stow them in the event of storm mains failure.
Are you going to winch it up with an electric motor? ;-)
The amount of electricity a human can generate is pretty meaningless.
Think how hard work it is to drill a hole with a hand drill - and how easy it is with a cordless drill. You get the idea? So the amount of work needed to winch a weight up to the top of the house then use that to generate electricity might light a small efficient bulb for a while. But it's not going to produce enough to do anything useful.
"GravityLight is installed to provide a 6ft/ 1.8m drop of a 12kg weight. This weight is lifted and on release starts falling very slowly (about 1mm / second).
What is the output of GravityLight?
To this question there are two answers: the power output of the GravityLight in Watts, and the light output of GravityLight in Lumens.
Our first version, GL01 has 3 power / speed settings, which can be adjusted via a power dial on the front. A 12kg load on High power provides 0.1 Watts, on Medium 0.075 Watts and on low
We bought one of those wind-up dynamo radios with a built-in torch, a few years ago when they were all the rage, to cover power cuts. I was surprised by the amount of effort you had to put in to wind the thing up and get any useful playing time or light out of it. Bloody hard work!
Because, come the day of the apocalypse, we may well want to (eventually if we survive) create electricity by some crude means for those gadgets we simply can't do without.
I doubt electricity generation will be a priority, post Apocalypse. Read The Road, by Cormac McCarthy.
Plot summary
An unnamed father and his young son journey across a grim post-apocalyptic landscape, some years after an unspecified disaster has destroyed civilization and most life on Earth. The land is filled with ash and devoid of living animals and vegetation. Many of the remaining human survivors have resorted to cannibalism, scavenging the detritus of city and country alike for flesh. The boy's mother, pregnant with him at the time of the disaster, gave up hope and committed suicide some time before the story began, despite the father's pleas. Much of the book is written in the third person, with references to "the father" and "the son" or to "the man" and "the boy."
Realizing they cannot survive the oncoming winter where they are, the father takes the boy south, along empty roads towards the sea, carrying their meagre possessions in their knapsacks and in a supermarket cart. The man coughs blood from time to time and eventually realizes he is dying, yet still struggles to protect his son from the constant threats of attack, exposure, and starvation.
They have a revolver, but only two rounds. The boy has been told to use the gun on himself, if necessary, to avoid falling into the hands of cannibals. During their trek, the father uses one bullet to kill a man who stumbles upon them and poses a grave threat. Fleeing from the man's companions, they have to abandon most of their possessions. As they are near death from starvation, the man finds an unlooted hidden underground bunker filled with food, new clothes, and other supplies. However, it is too exposed, so they only stay a few days.
In the face of these obstacles, the man repeatedly reassures the boy that they are "the good guys" who are "carrying the fire". On their journey, the duo scrounge for food, evade roving bands, and contend with horrors such as a newborn infant roasted on a spit and captives being gradually harvested as food.
Although the man and the boy eventually reach the sea, their situation does not improve. They head back inland, but the man loses blood after being shot with an arrow. He dies, possibly due to his long-standing respiratory ailment. The father tells the boy that he can continue to speak with him through prayer after he is gone. The boy holds wake over the corpse for a few days, with no idea of what to do next.
On the third day, the grieving boy encounters a man who says he has been tracking the pair. The man, who is with a woman and two children, convinces the boy that he is one of the "good guys" and takes him under his protection.
For a science lecture on "energy" we hooked a static exercise bike up to a car alternator and inverter to drive a 60W light bulb or a 10W CFL.
Few people could sustain 100W for long and it made some younger members of the audience more inclined to switch off lights when they became aware of how much physical work it took to keep a light bulb on!
Well, quite. And the same applied to any task we are now used to having electricity do for us. Like, as I said, simply drilling a hole.
Or doing the washing by hand and using a mangle to remove most of the water.
So doesn't take much to realise that only a small amount of electricity can be generated by human power alone - and even less if it's from some form of mechanical storage.
Other way to look at it is a small car alternator takes over 1 horse power to deliver its maximum output.
sometime in the '70s I was checking on coverage of a new transmitter in the Western Isles. Parked near one house and a lady came out (thinking I was a detector van) "It's no use you looking here, we haven't got the electric."
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.