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The Cambridge, MA Solar Tool

by gmoke Sun Oct 7th, 2012 at 01:14:05 PM EST

You can now estimate with great detail the solar electric potential of any roof in Cambridge, MA by just typing in an address on a webpage, the Cambridge Solar Tool
(http://cambridgema.gov/solar).  For instance, the double triple decker in which I live has six apartments and a total roof area of 2,781 square feet. 1,136 of those sq ft have high PV (photovoltaic) potential.  This could support an 18kW solar electric system providing 22,945 kWh per year, enough to power about a third of the electricity used by those six apartments, if each apartment uses the rough US average of around 11,000 kWh per year (my own annual electric use is around 1,600 kWh/yr).

The estimated savings per year for such a PV system are $9,081. The total cost  is $101,720.  With the Federal tax credit of $30,516 and a MA state tax credit of $1,000, the final cost to the owner would be $70,204.  In addition, the Solar Renewable Energy Credits (SRECs) of 27¢/kWh could produce $6,212 per year (at least that's my reading of the MA SREC program, but I could be wrong).  Such an investment would pay for itself in about 8 years with a return on investment (ROI) of 12.93%, a better return than gold (10.19%) or the stock market (Dow Jones average:  5.50%).  The solar electricity would replace other fuels that now spew 12 tons per year of carbon into the atmosphere.

If the owner did not want to put any money down, they could opt for a Power Purchase Agreement (PPA), buying electricity from a third party which owns, installs, maintains, insures, and monitors a PV system on the roof of our double triple decker at a long term, generally 20 years, fixed and lower cost than what is paid now for power.

Cambridge is the first city in the world where you can go online, type in an address, and get such detailed information.  The Solar Tool is a project of the Cambridge Community Development Department (http://www.cambridgema.gov/cdd.aspx), the Sustainable Design Lab of MIT (http://mit.edu/sustainabledesignlab/), Cambridge Energy Alliance (http://cambridgeenergyalliance.org), Modern Development Studio (http://www.modeonline.com) and others.  Christoph Reinhart, of the Sustainable Design Lab, says that other cities including London and Singapore are interested in this kind of solar tool and that it is comparatively easy to model PV potential on an urban scale.  The Sustainable Design Lab also has a daylight simulation tool, DaySim (http://www.daysim.com/), that "models the annual amount of daylight, glare and electric lighting use in and around buildings."

The Cambridge Solar Tool was first publicly demonstrated at the Cambridge Library on Wednesday, October 3.  Besides the representatives of the city and the developers, a solar installer walked the audience through the process, a homeowner related his experiences in installing 5.64 kW PV system on another Central Square triple decker, and a vendor explained the solar leasing model or PPA.  As the majority of residents of the city are renters, there was a mention of green leases for renters and condo owners.  There is even some planning by the city to establish a solar buying club or coop to reduce costs to individual homeowners and real estate entities.  A new group, SunUp, Cambridge, plans to canvass the top-rated solar sites and connect interested owners of such sites with contractors for energy audits and solar assessments with a discounted pricing system.  The Home Energy Efficiency Team (HEET) (http://www.heetma.com), a group which does weatherization barnraisings in Cambridge, the Boston Area Solar Energy Association (BASEA) (http://www.basea.org), and the Cambridge Energy Alliance are cooperating on this project.  Cambridge also has a house by house infrared mapping of heat loss done in February 2011 through another MIT project headed by Mechanical Engineering Professor Sanjay Sarma and I expect that information will also be used to pick the most likely customers for solarization and energy efficiency.

Before and after the meeting, there were table exhibits by seven local solar and renewables companies.  That evening's presentations will be online at Cambridge Community Development and Cambridge Energy Alliance.

Installers present:
http://www.shconstruction.com - installer speaker
http://nextstepliving.com - PPA speaker

The estimate is that rooftop PV in Cambridge could supply about a third of the electricity that the city and its residents now consume.  With higher levels of energy efficiency, that portion could rise.  This solar contribution does not include solar hot water and space heating, south-facing walls and windows or food production.

Cambridge is not the only city doing interesting energy initiatives.  NYC has finished its first round of energy benchmarking all its buildings over a certain size.  The results are now available at http://www.nyc.gov/html/gbee/html/plan/ll84_scores.shtml

More cities with Solar Tools?
. yes 66%
. no 0%
. not yes 0%
. not no 0%
. neither yes nor no 0%
. both yes and no 0%
. don't understand the question? 33%
. none of the above 0%

Votes: 3
Results | Other Polls
Just imagine the potential in cities where there's lots of sun, like Austin, San Antonio, Phoenix, etc.

'tis strange I should be old and neither wise nor valiant. From "The Maid's Tragedy" by Beaumont & Fletcher
by Wife of Bath (kareninaustin at g mail dot com) on Tue Oct 9th, 2012 at 08:37:26 AM EST
first being a breakout location for bonnie raitt, now this....kudos

'The history of public debt is full of irony. It rarely follows our ideas of order and justice.' Thomas Piketty
by melo (melometa4(at)gmail.com) on Tue Oct 9th, 2012 at 09:14:34 AM EST
I am in a bit of a quandary about this, because Colorado is an obvious spot for solar energy--but also an obvious spot for coal and gas energy.

We have abundant sunshine, with over 300 sunny days a year. Almost all of our electricity comes from coal, which is available in tremendous, high quality, low cost supply in Wyoming, shipped to here on huge trains. Almost all of our heating comes from natural gas, which is available in tremendous, low cost supply from wells just a few dozen miles from here.

We have three choices for solar power.

  • We can pay the city power company a higher rate for our electricity; they use the excess money to purchase sustainable power from the grid. This is the option I am currently using. You can back out at any time.
  • We can make a large investment in a third party company that has a solar PV farm in town. (Actually there are several such companies.) You pay for a certain number of solar panels, they sell the power from the panels to the power company, and you get a rebate based on that payment.
  • We can put up our own solar panels.

Both of the latter two cases mean that you are making a long-term investment in today's PV technology. Once in, you need to wait for ten or twenty years to recover the capital investment. If you sell your house, the cost can be transferred to the buyer in either case. The long-term nature of these solutions poses a problem, because many things could happen in the next twenty years. PV technology could get much cheaper, or maybe wind power will get a lot cheaper. Maybe the whole town will be abandoned due to a combination of dust storm and military disinvestment. Plus the city is arguing about whether the local power system (socialism in action) should be sold for a one-time cash bonanza and then much higher rates for the duration.

I suppose this is the argument for feed-in tariffs, but we don't have such a concept.

So when making a decision, the comparison comes down to a long term commitment versus a monthly charge. Plenty of people would make the move, I suppose, if they had a way to avoid the long-term factor.

by asdf on Tue Oct 9th, 2012 at 11:24:20 AM EST
Here is the primary solar farm outfit...


by asdf on Tue Oct 9th, 2012 at 11:27:34 AM EST
[ Parent ]
Payback here in Cambridge with state and Federal rebates is from 6-8 years from what I've seen.  Power Purchase Agreements can be thought of as leasing PV panels and there may be companies in your area that offer this service.  With no money down, you agree to purchase the electricity from the panels a company will install, maintain, insure, and monitor on your own roof.  You get electricity at a cost lower than what you're paying today and lock in that lower rate from 15-25 years.  This is a financing model that has been successful for commercial and industrial customers for a number of years and is now coming to residential customers as well.  At least, 10 states have PPA companies operating now.  MA is one.  SunRun, a PPA vendor (http://www.sunrunhome.com/), is working in Denver, Boulder, and Louisville.

Solar IS Civil Defense
by gmoke on Tue Oct 9th, 2012 at 06:26:19 PM EST
[ Parent ]
Yes, we have one, but the "lease" can't be terminated. It's more of a financing option, set up to take advantage of the tax laws. If there were a two year, say, lease, that would be more attractive...
by asdf on Tue Oct 9th, 2012 at 08:12:30 PM EST
[ Parent ]
Two years doesn't make sense, especially if it's a roof installation.  ROI here in Cambridge is 6-8 years on average, so any lease would probably be at least 10 years to make money for the provider.  The shortest leasing period I've heard of is 15 years though most are 20 or 25 years.

Solar IS Civil Defense
by gmoke on Thu Oct 11th, 2012 at 04:59:28 PM EST
[ Parent ]

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