[Greenbuilding] Energy and Power...

[Richard Garbary]

Still confused. Please see attached file.

=========================================================================================================
On Sat, Aug 6, 2011 at 4:25 PM, Gordon Howell -- Howell Mayhew Engineering <
ghowell at hme.ca> wrote:

>  Greenbuilding List:
>
> Further to the interchange below highlighting people's incorrect use units
> for energy and power,
> though it may seem reasonable on the surface to say "almost every Canadian
> on this list (including myself) and, I suspect, most others in North America
> and around the world either know or have the capacity to figure out what
> your original message meant":
>
> it is the same as mixing up speed (km/h) and distance (km), or volume
> (litres) and flow (litres per second) (which we would never do and would be
> disparaged by society if we did)
> and
> then we get these same people who "apparently" understand how to "figure it
> out" then making huge calculating errors when the look at solar PV economics
> or sizing (as I've seen many times) because they don't fundamentally know
> the difference between energy and power.
>
> *I would suggest that it is extremely important to not mix up these units.
> *A watt is a rate of energy flow -- it is like speed, which is a rate of
> distance "flowing".  A watt means a joule per second.  Whenever you use "W"
> think of "joule per second"... so a 230 W solar PV module generates 230
> joules of electrical energy per second (at rated solar conditions of 1000
> joules per second per m2).
>
> A kWh (or preferably joule) is an amount of energy -- it is like distance.
>
> kWh means "thousand times watts times hours", which is a correct energy
> unit.
>
> kW/day means "thousand times watts per day", means "thousands x joules per
> second per day" -- it is a unit of energy-production acceleration.  It is
> never used on a small scale as in kW or days.  The electric utilities and
> regulators use MW/hour units, because it speaks of the rate at which
> generators can ramp up or down (which is an acceleration) the rate (MW or
> millions of joules per second) at which they can produce energy.  We also
> use MW/year to describe the capacity of a PV factory, because it also
> implies the acceleration of PV energy generation in the world due to that
> factory.
>
> So I made the attached PowerPoint presentation to help (I hope) people
> understand the difference between the two and the importance for not mixing
> them up.
>
> I have to say that when I see people mixing up energy and power units, then
> immediately my mind starts to discredit them and their professional
> expertise... and I've even seen engineers, electric regulators and electric
> utilities mix them up!
>
> I am quite fascinated that peoples' mixup in all this fundamentally arises
> because we have non-metric time, and this is due to the Sumerians of some
> 4000 years ago who gave us the sexagecimal system, which we use for hours,
> degrees, minutes and seconds.
>
> I would value anyone's comments on this.
>
> +Gordon Howell
> Edmonton
>
>
>
> Please see my replies to your questions, below. You may not comprehend
> all of my answers, but that is all right.
>
> > We've mounted 13,000 watts DC panels, in agreement with the Ontario
> > Power Authority to sell, at max., 10 Kw per hour.
>
> I mean that we have 52 Solar Worldphotovoltaic modules, rated at 250
> watts Direct Current output each, mounted in four strings, feeding two
> SMA 5,000 watt output inverters, and that the Ontario Power Authority
> will buy 10 Kilowatts of electricity, maximum, per hour, produced from
> these modules.
>
> > These sunny summer days, we vary from 75 to 92 Kw per day...
>
> Each day varies, as does the weather, and we typically sell between 75
> kilowatt hours to 92 kilowatt hours per day, to the Ontario Power
> Authority.
>
> > They pay 81 cents per Kw produced, up to a maximum of 10 Kw per hour...
>
> Each day, the Ontario Power Authority pays $0.81 Canadian Dollars for
> each kilowatt that they buy from us. However, they will only pay for 10
> kilowatts per hour, even if we produce more than that. The limit of 10
> kilowatts per hour is a part of the definition of the Ontario microFIT
> distributed generation program.
>
> > This means we produce more full 10Kw each hour than the standard
> > 11,000 watts arrays
>
> I am impressed by your courteous (and slightly humorous) response to what I
> considered a rather inappropriate email.
> Almost every Canadian on this list (including myself) and, I suspect, most
> others in North America and around the world either know or have the
> capacity to figure out what your original message meant.
>
>
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