My comments on the Draft Transportation Policy Plan

CurrentRevenueThe Metropolitan Council held a public hearing tonight on their draft Transportation Policy Plan. If you care about transit or transportation issues in the region, you should comment (you can do so through October 1). Here are four comments I have on the plan:

  1. Our urban areas are significantly underserved by this plan. Even under the “increased revenue scenario”, we will spend $5 on transit to serve suburban commuters for every $1 we spend on transit improvements to places where transit makes economic sense (see here for my attempt at a geographic breakdown of projects). The Met Council, in the Thrive 2040 plan, has said they want to match transit service to the number of riders and intensity of land use. This plan does not do that.
  2. The plan currently prioritizes projects like Gateway BRT (9,000 riders at $50,000 per rider) over projects like Hennepin Ave BRT (23,000 riders at $896 per rider). This is an example of how our urban areas (that are expected to grow significantly) are underrepresented in this plan.
  3. The Transportation Policy Plan, as an implementation plan of Thrive 2040, should identify how our transportation system will be planned to reduce greenhouse gas emissions (another goal of Thrive). While the plan mentions “reducing vehicle trips”, there is no analysis in the plan of whether the scenarios presented will increase or decrease emissions from our regional transportation system. We can’t wait another 10 years for the next update of the regional plan to take significant action on climate change.
  4. It’s definitely not all bad. The Met Council for the first time has identified regional priorities for a bicycle network, which will give communities the ability to apply for funds to upgrade their local network if it matches the regional plan. Many of the transit projects identified are much needed improvements (Hennepin, Chicago, West Broadway), but are simply not adequately prioritized.

Questions about the northeast water supply plan

Over at, I ask some questions about the Met Council’s new northeast metro water supply plan.  Here is a big one:

Where is the conservation alternative?  The cost and feasibility of  reducing water use are not analyzed as part of the report.  Building nothing and simply asking/incentivizing/requiring people to use less may be the cheapest option.  According to the report, water use in 2010 was 92 gallons per person, per day in these communities. The ratio of peak day demand to average day demand ranges from 1.7:1 in Forest Lake to 5.9:1 in Lexington.  The report hints that this is “mainly attributed to irrigation and outdoor water use needs”.  Sprinkling lawns in other words.  Many options exist for conserving (potable) water – from retrofitting toilets, sinks and showers, to using captured rainwater to irrigate, to simply paying people to remove lawns and replacing them with low-water alternatives.  For the cost of the alternatives to serve all northeast communities with new water supply (~$600 million), you could pay every household over $1,400 to remove lawn, and keep paying them $40 every year after that.  Without an analysis of conservation alternatives, this report seems inadequate.

Read on.

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. Continue reading How much energy could Minneapolis get from solar?

100 days of solar

Watt hours to the battery, first 100 days

Today I noticed that my solar charge controller has been running for 100 days (it logs this among many other data points).  Here are some highlights from the first 100 days:

  • The system has produced 32 kWhs from two 100-watt panels.  This is roughly 2% of the total electricity consumption we saw over the same period last year.
  • Converting from DC current to AC current at low wattages is wildly inefficient.  I usually run the wifi router and cable modem continuously off the battery and I lose about 40% of my produced energy to the inverter.  It is much happier running closer to its peak (1000 watts).  We should probably convert to DC.
  • Something happened to my charge controller settings when I converted to 24 volts.  Although the controller was still charging, I lost about 10 days worth of data (hence the gap in the chart) and wasn’t able to communicate with it over that time.  A firmware reboot fixed this.
  • Although very cold, clear days are when the panels perform their best, the sun just doesn’t shine for that long each day in January and February in Minnesota.  The panels being on the ground doesn’t help either.  Just from the middle of March to the middle of April I’ve about doubled my daily output.
  • All that said, this chart doesn’t really show total potential of the panels on a given day.  If I didn’t use much of the battery the day before, panel production the next day was curtailed by the controller to avoid overcharging the battery.  I’m trying to match the loads I put on the battery with the “capacity” of the season, but that’s sometimes tricky.
  • I recently learned we were accepted into the Minnesota solar rebate program for 2014!  So with the help of a friendly solar installer, we should have a 2.8 kW grid-tied system installed sometime this year. Along with the grid-tied panels, the installer will be adding two panels on the roof dedicated to battery charging.  Now I just have to wait…
RIT Curitiba

Let’s be pro-transit

My latest at is all about positivity:

I’ll start by saying I have strong feelings about Southwest LRT. So do some people on this very blog. You probably do too. However, I won’t be contributing further to the gallons of spilled real and virtual ink or weeks of public testimony.  I’d like to talk about how we can set the stage for some other projects that could be really beneficial for transit-dependent and transit-interested communities. Nothing in this post should be interpreted as diminishing the importance of that LRT project, the upcoming decisions that will determine it’s fate/depth of its tunnel, or the correctness of any particular opinion about it.  But I have this urge to start some positive conversations about other projects that need some support.  Weird, right?

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.

Solar insolation in January
Solar insolation in January

After 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.

The Kingfield Solar Map
The Kingfield Solar Map

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.


Counting every watt hour

This little device is an ethernet to wi-fi adapter. It connects my solar charge controller to my home wi-fi network so I can make fancy graphs.  It uses 1.2 watts per hour.  I know this because I measured its usage using a watt meter.  I do this with everything I power from the solar batteries.

I have a hunch that this is what solar does to you, makes you compulsive about energy use.  Even if (when?) I have a large grid-tied system, I imagine myself checking the daily output, and constantly thinking about how to reduce my usage to match.

On very cloudy days, this little thing has used over 45% of the energy produced by the panels.  I unplugged it.  For now, graphs only on special occasions.

Home solar: adding MPPT and marvelous data


As part of my plan for the eventual expansion of my off-grid solar energy system, I recently added a new charge controller with Maximum Power Point Tracking (MPPT).  Besides being much more efficient, this controller is capable of producing reams and reams of wondrous data, and is network-connected, meaning I can geek out on battery voltage and array current from anywhere in the house!  The charge controller I had was great, but it wouldn’t handle anything beyond a few more small panels.  Now I should be able to go all the way up to 750 watts of panels (my goal).  So, thanks Santa!

While installing the controller, I also took the opportunity to install a breaker box, which should bring me closer to code, and upgrade to larger diameter battery cable, which should reduce efficiency losses.

The MPPT advantage

MPPT is a fancy way of saying the charge controller is able to send significantly more energy to the batteries from the same panels.  How much more? After only a few days of testing, I estimate 40 – 60% more than the Pulse-Width Modulation (PWM) controller on days when the battery is low.  (If you want to know the details of how MPPT works, I found this explanation helpful.)

Here’s some actual data from my system which I think illustrates the MPPT advantage well:

1-5 plain graph

The blue line is the amps, or current, coming from the panels.  The red line shows the amps the controller is putting in to the battery.  It’s higher!  The magical MPPT doohicky converts excess voltage into amperage (remember, amps X volts = watts) so less of your panel’s potential is wasted.  On this particular day, I estimate the charge controller may have been able to wring an extra 100 – 150 watt-hours from the panels.

There are other interesting things going on here, so here’s a little annotation:

1-5 annotated graph

Here’s the next day, when the battery starts out the day almost totally full.  It was very sunny.

1-6 amps graph

The controller limits the array current and current to the battery significantly because the battery is almost fulled charged.  The gentle downward slope in the amperage is a function of battery charging called absorption.  Less current is pushed into the battery as it reaches capacity.

I can track hundreds of days of watt-hour production, so I’ll do another update when I can show some seasonal changes.  How I yearn for the days when the panels get more than 4 hours of sun per day!