Re: electricity from a gym: quick calcs

On Sep 13, 7:41 am, ehsjr <eh...@xxxxxxxxxxxxxxxx> wrote:
mrdarr...@xxxxxxxxx wrote:
I had a conversation with a co-worker about harnessing energy from
folks dancing on a dance club, and from folks walking in a mall during
the shopping season. I was skeptical, thinking the capital costs
would outweigh any benefit, but decided to run the calcs just to be
fair.

I was *sure* I'd posted similar calcs on sci.physics or sci.chem a few
years ago, but can't find them. So, I re-derived them.

Let's say we have a gym with 100 pieces of equipment, with generators
on each of them. And let's also say the gym is open 24 hours a day,
fully packed at all times.

Let's say each person exercises at a rate of 100 W (pretty hard work),
or 0.1 kW.

Let's say electricity costs $0.10/kW per hour. (More in the bay area,
less here in wintertime...)

So, each person generates $0.10/kW/hr x 0.1 kW, or one cent per hour.
(Much less than minimum wage, I might add.)

That's 24 cents/day/piece of equipment.

$0.24/day x 100 pieces of equipment = $24/day, or $8,760/year in
electricity back to the grid.

Now for the equipment costs. Let's say that each generator thingie
costs $100, including installation labor costs. $100 x 100 pieces of
equipment = $10,000.

Breakeven time is just over a year.

Key assumptions:
- gym is fully packed at all times. Not gonna happen.

- each generator thingie, plus grid-intertie-converter, breaks down to
$100/piece of exercise equipment. That's awfully generous. Probably
more like $1,000/piece of equipment is closer to the mark...

- 100% credit from the electric company for electricity. Probably in
Minnesota, but not here...

Any thoughts, folks?

Michael (I'm *not* an electrical engineer, by the way)

In a typical gym you wouldn't recover the energy needed
to light the place, let alone sell power back to the grid.


Yep. 10 kW *maximum*, assuming 100 pieces of equipment. That already
is a lot. *Can* one pack more than 100 pieces of exercise equipment
into a gym?

24 Hour Fitness is downright empty at times... not always fully
packed, as my optimistic calcs assumed. If only 10% occupied, 1kW...
can that power the fluorescent lights...? It definitely won't keep
the indoor pool heated...

Then it just boils down to the economics of reduced electricity
purchases - never mind the grid intertie. Hmm... replace the
inverter with a shelf of deep cycle batteries to store energy from the
peak crowds, and just use that energy to heat the pool...???

M

.

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