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U. of Rochester Solar Table -- 3,846 Years To Break-even

April 2, 2012, 11:04 pm

Professor Rizzo was keen that I check out the $12,000 solar picnic table at University of Rochester

Most kids use this to hook up their laptops.   Here are a few assumptions

  • 3 hours of use per day (heroic, I am pretty sure it is less than this)
  • 65 watt draw from one laptop
  • 160 days with sun (Rochester is apparently in the top 10 US cities for number of heavy cloud days)
  • 10 cents per kw-hour

This means the table would produce 31,200 W-hr per year or 31.2 KW-hr per year.  This yields an annual electricity savings of $3.12, giving the table a payback time on its investment of 3,846 years.  If one assumes a cost of capital anywhere north of 0.026% per year, then the sun will go dark before this table pays itself off.

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Category: Education, Energy, Environment
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  • nofossil

    In all fairness, there is another calculation. Students these days can't go even a few minutes without being connected, so it may be that the administration felt the need to provide emergency 'filling stations' for laptops and cellphones. If a station had to be built anyway, then you'd have to deduct the cost of the cheapest alternative from the cost of this choice, and base payback on the difference.

    My back-of-the-envelope calculation suggests that this would reduce the payback period by about 500 years! 3200 years isn't so bad......

  • Don

    Warren, did you include the cost of replacement batteries (I assume it has lead-acid batteries in that huge box that takes all the foot room)? Considering how little sun they get, those batteries are going to spend far more time discharged than charged, which means they'll be dying constantly, say once/yr.

    Probably 4 batteries, costing about $200/ea... $800/year operational cost. I'm pretty sure that gives you a negative ROI.

  • Dan Hill

    The other problem here is why the hell it cost $12,000. There's maybe 100 sq ft of solar panels on this thing - as I understand it the current price of solar panels is less than $50 sq ft, not $120...

  • chris y

    Looks like 6 solar panels, each producing about 200W peak, for a cost of $1500 ($1.25/W retail today). A nice 2kW inverter with battery charge control runs about $2000. If batteries are included, add another $1000 per kWhr of storage capacity, or about $2000. With wiring, reinforced umbrella (needs to support about 300 pounds of panels), table, the total bill of materials is probably $6500. Union labor will easily jack the price up to $12000.

    The ROI is always negative because panel output degrades by about 1% per year. In wet and freezing climates, solar panel seals leak much sooner than expected. With Chinese panels, a service life of less than 20 years can be expected. The best lead acid deep cycle batteries can last 10 years in climate controlled conditions. Outdoors in Ra-cha-cha, the best quality batteries will likely need replacing every 3 - 5years.

    You can move the ROI positive by renting ad space on the umbrella. A win-win would be to throw out the panels, inverter and batteries to double your ad space and get rid of the highest cost bits. You could provide 24/7 charging power and illuminate the umbrella ads at night by running 120V power from a nearby building...

  • caseyboy

    All I can think to say is, "Yes we have no bananas, we have no bananas today."

  • Jason

    Here's a video we made about the U of R solar bench:

    http://www.youtube.com/watch?v=L7XTpX6lrL0

    Enjoy!

  • admin

    Actually Chris, there are only two solar panels. The other four slots are blanks. My guess is these two looked like 50 watt panels.

  • NL_

    I'm assuming they might only have two panels to focus on southern exposure.

    I guess the solar umbrella could pay for itself if it convinces philanthropists to give money, or makes alumni think more fondly of the school come the next fundraising drive. Which would make it the green-hippie analog of a great sports team.

  • Peter

    Dont forget before the sun goes dark it expands massively. This would greatly increase the usable hours for the table. Yes anybody sitting there would be roasted to a crisp but that isn't included in the payback calculation is it?

  • Steve

    You estimate of 10 cents per KWH is way too low...this baby will break even in 2,000 years.

  • http://harries@free.fr blokeinfrance

    It brings to mind Bastiat's "Petition of the Candlemakers". They asked the gomnt to ban the sun, so as to give more employment to candlemakers, which would give more demand for tallow, which would cause farmers to raise more cattle, which would make more shit to make the land more fertile. Who could disagree with this brilliant scheme for extinguishing the sun?

    Well, 164 years later, some folk have managed to turn this satire on its head.

  • michael

    haha.
    You didn't count the global warming fenomena!!!
    According to alarmists there will be more sunny days pretty soon!
    And therefore the break even date will come sooner.