The Lightbulb Goes On!

[elfs]

Across the street from the incubator is the Pemco insurance building, and one of the big deals is this sign on the side that proclaims in big letters, "The solar panels on the roof of this building are generating 3.3KW of power!" And I used to wonder, exactly how much power is that? What is that in meaningful terms?

Today, it's a grey day and the sign is showing a pathetic "0.11KW of power." And then it hit me: holy chao, that's 110 watts. That's two lightbulbs. The proud LED sign braying out how much energy they're generating probably takes more power to run than the solar cells generate.

Comments

[gromm.livejournal.com]

Let's just assume that those LEDs are 3W each then (which are some of the brightest around, by the way - for comparison, 1W is typically what each bulb in an LED flashlight provides). That means there can be no more than 36.6 LEDs in that sign to break even on a day like today. Or maybe 110, but I'd bet on the former number. If you use CFL bulbs, then that comes out to about 10 light bulbs by the way. ;)

As for what 3.3Kw in meaningful terms is... well, your dryer is probably between 4.5 and 5.5Kw. It would be a much better idea to dry your clothes on a line than to use solar panels *that* way. ;)

Your TV is probably around 200-300 W, and your computer probably between 100 and 250 W depending on what it's doing (I measured that with a kill-a-watt, by the way). Unless the dryer (or the stove, if it's electric) is on, 3Kw is considerably more than your house will draw at any given moment in time.

For example, my house averages about 20Kwh per day in the summer, without AC (according to my hydro bill, which gets that average from two months of usage divided by X days in those months). My dryer probably uses about 1/3 of that, the fridge about 1/3 of that (it uses less when it's on, but it does it way more often), and the rest is light and electronics.

So when it's cloudy, yes, those solar panels produce SFA. When it's sunny, it really does matter.

Oh, no

[ideaphile.livejournal.com]

There's no way in heck those LEDs are consuming 3W each! They're probably more like 20 mW.

If I'm correct in estimating the sign has 32 x 80 LEDs, its peak power consumption is probably around 50W for the illumination, with the average more like 20W given the usual ratio of on-to-off pixels.

I suspect the system controller consumes a lot more than that, but if the whole thing consumes more than 100W average, I'd be surprised. Looking around online, indeed, that seems to be about right for various commercial LED signs.

So 100W continuous is 216 WH over the course of three months-- only a little more than a quarter of the energy generated by the solar cells in the same time.

And I gather Pemco had the sign before the solar panels anyway, so the panels are really a separate issue.

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Re: Oh, no

[gromm.livejournal.com]

Sure it's possible (http://www.mec.ca/Products/product_detail.jsp;jsessionid=1w6DLV9fF09XyRp12s2HhjncyBlnPwjThmnGTLTk2ZW8myLGlB14!-825556489?PRODUCT%3C%3Eprd_id=845524442629488&FOLDER%3C%3Efolder_id=2534374302696981&bmUID=1259732479153).

But then, I haven't seen the sign either.

Re: Oh, no

[ideaphile.livejournal.com]

A sign made of those superbright LEDs would need water cooling and radiators as large as Pemco's solar array! Plus it would blind everyone who looked at it.

Also, mine (http://www.amazon.com/dp/B001H4MWA4) are brighter (http://www.amazon.com/dp/B0020XF0JQ). :-)

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