Re: electricity from a gym: quick calcs

On Sep 12, 11:56 am, 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)

1. Credit for power put into the grid is much higher than cost of
power taken out of the grid in many states. For example, in WA, you
get paid as much as $.51/kW-hr to add solar or wind energy to the
grid.

2. Many exercising machines convert effort more or less directly to
heat. In winter, this can subtract from the heating requirements of
the building, much as waste heat from lighting fixtures does. Of
course, if taken too far, this heat can cause the cooling system to
kick in, even in winter. In summer, the heat from exercising generally
adds to the cooling load.

Paul Mathews

.

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