Tagged minneapolis

The view from the roof of the Minneapolis Convention Center, which holds a 600 kW solar PV system

How much energy could Minneapolis get from solar?

Solar PV seems to be the current darling of the renewable energy world.  But how much “resource” is really out there?  How much should cities rely on the development of local solar resources to meet their climate and energy goals?  What trade-offs should urban cities make between desirable things like tree canopy and maximizing solar energy resources?  GIS tools and new data resources can help begin to answer that question.

Counties and states are beginning to produce LiDAR data more regularly, which provides the building block information needed to analyze solar resources on buildings and elsewhere (see my previous post for a brief intro to LiDAR, or see here).  Minnesota happens to have LiDAR for the whole state, and Minneapolis has a climate action goal that references local renewable development, so I’ll focus there.

So how much solar electric potential does Minneapolis have?  Enough to supply 773,000 megawatt-hours (MWHs) each year, at the upper bound.  That would mean covering every piece of rooftop with good sun exposure and appropriate pitch (southeast to southwest facing or flat) with the best modern PV panels.  It would also mean solar installations on 68,351 structures, consisting of over 2.3 million individual panels.

773,000 MWhs would represent about 18% of Minneapolis’ total annual electricity consumption (based on 2010 figures).  It would be the equivalent of reducing 392,684 metric tons of CO2 (also based on 2010 figures), which is equal to the emissions from the energy usage of almost 36,000 average American homes each year.

Explore the results for individual buildings in Minneapolis.

There are some limitations to this calculation, and some additional interesting findings, but first a brief description of how I came up with these numbers.

Methodology

Annual solar insolation values shown in a black-white color ramp.
Annual solar insolation values in the Wedge neighborhood shown in a black-white color ramp.

I briefly covered how to calculate solar potential in a previous post, and the process for this analysis was similar.  I was able to get my hands on the solar insolation raster for the whole city thanks to the excellent work of some students in Dr. Elizabeth Wilson’s capstone class at the University of Minnesota’s Humphrey School.  Solar insolation represents a measure of the total energy from the sun reaching any particular point (each square meter in this case) on a building, tree, earth, etc.  To calculate this, ArcGIS has a complex tool called Solar Radiation Analysis.  It takes in to account things like how trees shade buildings, and how the sun moves across the sky at different times of year based on the latitude of a particular point on earth.  It spits out a measure of solar energy hitting that location over the course of a year,  measured in watt-hours per square meter. This gives you a good idea of where exactly on each building a suitable spot might be for a solar PV system.

LiDAR data can also be used to calculate the slope of roofs, another important piece of information to understand solar potential.  This allows a user to pick out areas of flat or south-facing roofs.

Red hatched areas represent areas of rooftop that are good for solar
Red hatched areas represent areas of rooftop that are good for solar

Finally, Minneapolis supplies building footprints, so I knew approximately what was a roof. I confined my analysis to building roofs, assuming we don’t want any of our precious open space filled with solar panels.  I also buffered the roof edges, since I’m told OSHA requires some open space between the panels and the roof edge for safety, at least for flat roofs.  I also considered 1,000 watts to be the minimum size that would warrant an installer to climb onto a roof.

Combine all this with some assumptions about the space needed for installations on flat and sloped roofs (the students helped with that too) and information on the size and power output of panels, and you get a measurement of the total “good” roof area and associated potential energy production from each roof.

That’s enough how-to, here are more interesting findings.

Findings

The 100 buildings (0.14 percent of the total building with solar) with the largest solar potential would provide 14 percent of the total production, or over 109,000 MWhs annually. The 1,000 buildings (1.4 percent of the total buildings with solar) with the largest solar potential would provide 43 percent of the total production, or over 333,000 MWhs annually. Targeting these structures for further analysis and possibly incentives would probably make sense to achieve the largest economies of scale for installation costs.

Buildings symbolized by their total solar energy potential
Buildings symbolized by their total solar energy potential – warmer colors represent higher potential

The 100 highest-potential buildings are geographically concentrated in roughly three areas: the northeast industrial area – roughly north and east of the U of M campus, the Lake Street/Greenway Corridor, and extending from the North Loop along the river into north and northeast Minneapolis.  Unsurprisingly, these are areas that still have many large, flat-roofed warehouse and industrial buildings.  If Minneapolis wants to maximize its solar resource, we may want to think about the trade-offs in redeveloping these areas or developing high density near them that may shade existing rooftops.

Commercial, industrial and single-family residential structures (based on parcel data) each account for almost exactly 23% of the total roof-top solar potential in the city.  The next largest potential was among apartment properties at 9%, and duplexes at 7%.  While the top three were evenly split potential-wise, single-family residences with good solar potential included over 46,000 structures, while commercial and industrial together was about 4,300.  See economies of scale note above.

The fact that 46,000 residential structures have good solar potential means that lots of homeowners, even in leafy Minneapolis, could be empowered to go solar.  This would be a more powerful political constituency than a small number of commercial property owners.  Obviously some would face the trade-off between more trees and their benefits and electricity from solar.

Suburban areas are much more likely to approach energy production equal to energy usage.  With its high density commercial core, Minneapolis uses a lot more energy than it can produce on its roofs.  Residential structures are also smaller and more shaded than many suburban areas.  This isn’t necessarily a bad thing, as density brings many other environmental benefits, like the ability to use transit cost-effectively.

Limitations

Xcel Energy limits the size of solar installations they allow to be connected to their system.  An interconnected solar PV system cannot be designed to produce more than 120 percent of the customer’s total usage from the previous year.  Many homes in Minneapolis, and possibly low-energy warehouse buildings, could accommodate systems larger than that.  This analysis limited system size only based on roof/sun conditions, and not electricity usage in the structure since that wasn’t known.  In some cases, this means this analysis over-represents solar potential.

This analysis includes no information on roof age or structural integrity.  Some flat-roofed buildings aren’t structurally able to accommodate solar without expensive retrofits.  Residential structures may need to have old roofs replaced before putting on a solar energy system (which are typically designed to last 20 years).  Some structures, like parking ramps and stadiums, would require additional structural supports to be added before a solar energy system could be added.  These factors could all further limit solar potential on Minneapolis buildings.

There was a geometry problem I couldn’t solve in GIS.  While I could calculate the size of a roof area that got good sun and had the correct slope, I couldn’t quickly figure out how many solar panels of a certain shape (defined length and width) fit in that area.  I only used total square footage divided by the square footage of a standard solar panel.  Internet forums are filled with many people better at GIS than I discussing this problem (but not providing me with easy solutions).  If anyone reading this wants to take a crack at it, let me know in the comments.

Solar insolation in January

Mapping Minnesota’s solar resource

Boston, New York City, Denver, Cambridge and other cities have created solar potential maps to help their residents understand that solar photovoltaic systems are viable in dense urban areas, and to demonstrate the potential that exists on rooftops.

Of course, I had to try this myself.

Minnesota produces LiDAR data, which is basically micro-scale elevation data produced by flying a plane back and forth in a grid and shooting the ground with lasers a bajillion times.  Skilled/obsessive GIS users can clean from this data information that can be used to make a fairly accurate model of everything on the ground (buildings, trees, etc).  GIS software also makes it easy to produce daily, monthly or annual solar insolation maps.  By taking the position of the buildings and trees, knowing the latitude, and projecting how the sun moves across the sky throughout the year, the software calculates a total amount of solar radiation that will hit a point after shading, angle and other factors are taken into account.

KingfieldSolarAfter much tinkering, the Kingfield Solar Energy Potential map was born.  The extreme density of the LiDAR data limits how large an area I could process (there were 4.9 million individual data points in this one small section of Minneapolis), but you get the idea.  This map shows the area of each roof that might be appropriate for solar, how many panels could fit in that area, and an estimate of the annual production from those panels.

Some roofs are wholly inappropriate for solar, whether due to tree or building shading, orientation or size.  But there is significant potential.  If solar was installed on every appropriate piece of roof in this one-quarter square mile area, it would produce an estimated 2.2 megawatt hours of electricity each year, and avoid 2.9 million pounds of carbon dioxide emissions.

Car2Go first impressions

Over at streets.mn, I detail some of my first impressions of one of Minneapolis’ newest car-sharing options, Car2Go.

According to MPR, by 2014 there will be over 400 vehicles available to car-sharing customers.

The bulk of these will be in the fleet of Car2Go, which operates on a different business model than the rest, offerring “point to point” service.  Walk to a car anywhere in Minneapolis, drive where you want to go, then park it at any curb space in Minneapolis (expect rush hour zones).  Other companies require that you return their cars to a specified location at a specified time.  The trade-off is that their rates are generally cheaper.

Read the rest.

NiceRide2012_cyclopath_routing

2012 Nice Ride flows revisited

For the last two years, I’ve mapped the flows of the Nice Ride bikes.  I’ve always been slightly dissatisfied with the results, since bikes were obviously shown taking routes that any sane Nice Rider would never take (Hennepin Avenue between Lake and the bottleneck, for example).  Try as I might, I could never get ArcGIS to prioritize trails, lanes and bike boulevards sufficiently.

Enter the good people at Cyclopath.  Cyclopath is something like a bike route wiki, in that it is constantly updating it’s database of bike routes using ratings from users.  So every street in their database has a rating from bad to awesome (actually 0 to 4).  And this database includes the whole metro and beyond.  Best of all, they were willing to share it!

The latest version of ArcGIS has a new “restriction preference” setting, meaning there are six levels of preference for a link from “Highly Avoid” to “Highly Prefer”.  So I combined cyclopath’s street ratings with these preference settings and got a new and better route analyzer.  Here are the results:

NiceRide2012_cyclopath_routingAs a reminder, here is what the old version looked like:

2012 Nice Ride FlowsA few changes of note:

  • Hennepin is obviously not so popular anymore, save in downtown where there are more Nice Ride Stations.
  • The Cedar Lake Trail got a little more popular, perhaps 500 trips in some locations, since it was a Highly Preferred route.
  • West River Parkway south of the Washington Avenue bridge got a lot less popular (although crossings at Franklin stayed nearly the same).
  • There is generally just a lot less jigging and jogging on small streets as trips tend to condense onto major routes (see the major difference on Summit Avenue in Saint Paul).

Here is a version with a base street map for orientation:

NiceRide2012_cyclopath_routing_greybase

It’s a bird, it’s a plane, it’s dedicated ROW!

Over at streets.mn, I have a post about everyone’s favorite fictional urban transit revolution, the urban gondola (or aerial tram).

The case history on US urban gondolas doesn’t look good cost-wise, but the travel time savings look great.  The Portland Aerial Tram, which could also be called an urban gondola (if you consider low-slung Portland urban), cost $57 million, or roughly $90 million per mile, if I calculated the hypotenuse correctly.  The Portland Aerial Tram travels at a top speed of 22 mph, which could make an Uptown Transit Station to Hennepin-8th Street trip in 6.5 minutes.  That’s about one-third the posted travel time for the #6 bus, and less than half the travel time of the limited-stop #12.  6 minutes is even less than half the travel time identified by Metro Transit for an upgraded arterial BRT on Hennepin.

Yglesias discovers the comprehensive plan

Matt Yglesias, Slate writer and MOU (market-oriented urbanist), laments Minneapolis’ NIMBYs (emphasis mine):

…if each NIMBY group gets its way, then the “push the costs onto other people” plan becomes self-defeating. Others bear the costs of your NIMBY actions, but you bear the costs of their NIMBY actions. What’s needed is a citywide institutional framework that leads to a less-dysfunctional outcome where valuable projects are allowed to go forward.

Perhaps some sort of community visioning session that combines a look at projected growth, market forces, neighborhood desires, externalities of development, transportation impacts, and comes up with a mutually-agreed-upon document that can guide regulatory land use controls?

Or perhaps he means, as a friend emails, a comprehensive plan and zoning code that aren’t influenced by residents/stakeholders? 1) Good luck and 2) that kind of defeats the purpose.

See my early screed about MOU “solutions”.  MOUs claim market forces can unlock better outcomes for our urban areas, but the big barrier is really one of better process and collaborative decision making, which gets short shrift or no shrift at all in these posts.

20LRTplan

LRT plans, past and present

The Transportationist posts this 1988 LRT plan developed for Hennepin County.  Obviously, the SW LRT route has moved and the “south” alignment has become freeway BRT.  Also note the dotted line, which I assume means tunnel.

In this plan, Minneapolis, especially the most dense parts, is well served by high-quality transit, with the exception of North.  In real life, if Bottineau goes with the LPA, 3/5ths of the regions high-quality, “fixed” guideway transit improvements won’t really serve Minneapolis at all (I’m including freeway BRT in the count of 5 since it’s been “converted” from the planned LRT. I’m also not counting Northstar).

Table1v2

Interlining

Everybody knows that the LRT alignment that would go through the second most dense area of the Twin Cities metro would have fewer trips than one that goes through a railroad trench and parkland, but few have dared to ask why.  Come with me on a exploration of the wild world of transportation modeling.

If you dig deep in the Southwest Transitway DEIS, like a stubborn prospector, you can sometimes find real gold.  And by gold, I mean stinky logic.  Deep in Appendix H, “Supporting Technical Reports and Memoranda Part 1″ is Table 1 in the Transit Effects Appendix (on page 274, to be exact).  Table 1 summarizes the daily LRT boardings by segment.  These segment summaries are based on station-by-station ridership numbers found later in the Appendix.  Here is the table:

Notice anything strange?  That’s right, route 3C-1 is assumed to have zero riders continuing their trip from the Central Corridor LRT.  Chapter 6 of the main DEIS document has a section on “Interlining Assumptions” which goes into more detail, but the key sentence seems to be on page 6-6 and the table following:

The LRT 3C-1 (Nicollet Mall) Alternative is not integrated with either the Hiawatha or Central Corridor LRT guideway for daily operations.

In the table that follows, under “Passenger movement/convenience” while other alternatives are labeled “One-seat ride possible”, the Nicollet alignment is branded as a “Stand alone LRT line”.  That’s right.  When you exit the train at 4th Street and Nicollet Avenue, you step off into an abyss.  You’ve just ridden a stand-alone LRT line to THE END OF THE LINE.  Don’t even try to transfer.

Of course, there are legitimate operational concerns about tracks not aligning and trains not being able to continue on for use on another line.  But to assume that ALL travelers coming from the Central Corridor, when confronted with the idea of a *gasp* transfer literally hundreds of feet away would abandon all hope and just drive a car the whole way (or take a slower bus), seems terribly ridiculous to me.  The ridership projections also assume that the 3C-2 line, which does interline, actually has fewer Central Corridor riders than 3A, because you know, those few extra minutes.  It’s not like there are any attractive destinations along Nicollet and in Uptown.  I’m pretty sure no one from the U of M goes to Uptown for anything.  They’re all, “out of my way mister, I’m headed for Eden Prairie!”

If you add back in those 5,300 Central Corridor travelers to 3C-1, you get 29,850 daily boardings, or the highest of the all the alignments.