I made this gif of visible satellite imagery from the NOAA’s Geostationary Satellite Image Archives. It basically shows cloud cover over the last 12 days at about 1 pm (19:15 zulu) each afternoon. This is a high-tech way of saying we’ve barely seen the sun for the last two weeks.
The implications for my 300 watt off-grid solar project are that almost nothing is being produced, and I’m not running anything from the batteries. With no sun in the forecast, I’m concerned about them sitting at a low stage of charge for days (or weeks at this point), which can reduce the life of lead-acid batteries.
In Minnesota in the winter, solar needs a backup, or at least a supplement. It’s great to have a grid. If I were truly off-grid, I would need some other kind of backup unless I was willing to significantly overbuild batteries or panels.
My latest at streets.mn does the carbon accounting which should have been part of the Draft 2040 Transportation Policy Plan developed by the Met Council.
Thrive MSP 2040, the new regional plan for the 7-county metro adopted by the Metropolitan Council, includes moderately strong language about addressing climate change. But the main implementation tool we’ve seen so far from the Council, the Draft 2040 Transportation Policy Plan, doesn’t go nearly far enough. In fact, it doesn’t even start where it should, with a baseline of emissions.
In this and future posts, I’ll try to do what I think the Draft Transportation Policy Plan should have done – identify where we’re starting from and where we need to go in terms of transportation-related greenhouse gas emissions.
It’s got charts, so you’ll want to read the rest.
The 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:
- 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.
- 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.
- 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.
- 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.
Over at streets.mn, 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.
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
With a short appearance by yours truly. Watch the video here. Unforunately, it won’t embed.
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…
My latest at streets.mn 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?
Many of the images in recent posts include “https” in the link, and since I’ve recently stopped using SSL, they seem to no longer work. You can still access the images by deleting the “s” from the URL. I hope to have a better fix soon.
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
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
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.