Power surge

solar farm

My back yard solar farm has doubled in size to a massive 200 watts!

If you remember from the last post, the wooden frame was half empty (who built it like that?), and was feeling really lopsided without another panel.  The frame is now full (Amazon is a marvel of the modern age), so any further expansion will have to happen on the roof or elsewhere.

Untitled

Parallel wiring.

Under optimal conditions I think this will produce 480 watt-hours per day.  For reference, that’s about 60 percent of the power needed to run our chest freezer.  These panels are connected in parallel, meaning the voltage (12) is the same, but the amperage is doubled (to about 10 amps).  I ordered a cheap ammeter, which I’m excited to hook up so I can see real time results.

The last few weeks have been very cloudy, so I think output has been down.  The next week doesn’t look that great either.  When you’re a solar farmer, you start caring about the weather a lot more.

After adding some additional wiring, I now have access to a solar-powered power strip in the living room, rather than just having access in the basement where I could run an extension cord from the inverter.  Now I’m regularly running some lights and the stereo from the battery.  The cable modem and router are small, consistent loads, so I may move those downstairs to become battery-powered.  I’ve become somewhat obsessed about matching load to the production, since I don’t want to “waste” any electricity produced (and also don’t want to run my battery below 50%).

Stay tuned for another update when the ammeter arrives.

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.

On estimating solar output and voltage drops

12.9 volts?! I want 18.9!

12.9 volts?! I want 18.9!

When I started tinkering with off-grid solar one of the first questions I asked myself was “how long is it going to take to charge this battery?” Or, similarly, “how much power will I produce in a day”?  Initially, the answer seemed easy: I’ve got a 100-watt panel, Minnesota gets about 4 hours of peak sun on average per day, so I’ll get 400 watt hours per day!  A 960 watt hour battery should be charged in two and a half days!

Wrong.  Way off.  Maybe more like 250 watt hours per day, and more like four days to fully charged.

I realized this quickly when attempting to charge a fully depleted battery.  In reality, it took into the fourth day for the charge controller to switch to battery maintenance mode (showing it was completely full).

Under perfect operating conditions and when grid-tied, you may actually get close to that nameplate 100 watts.  However, when your system is connected to a battery the voltage drops.  Many charge controllers (except for the really good expensive ones) will match the voltage of the panel to that of the battery to facilitate charging, which is almost always a lower voltage than the panels potential peak.  The rest of that potential is wasted.  So while my panel will produce 5.29 amps at 18.9 volts under optimum conditions (5.29 amps x 18.9 volts = 100 watts), when connected to my battery, it will probably only produce 5.29 amps at between 11 and 13 amps (5.29 amps x 12 volts = 63 watts).

Panels are built this way on purpose to make sure power can continue to flow to the battery even during overcast conditions when voltage may drop a little (gotta make sure that water flows downhill!).  Grid-tied panels don’t have this problem, since the grid can usually accommodate your voltage, and in a grid-tied system you’ll probably opt for one of the fancier MPPT controllers (see link above).

So, in summary, I’m probably getting 65 – 70% of my nameplate wattage (by design), and a realistic estimate for charging a fully-depleted 80 amp-hour battery from my 100 watt panel is 3.5 – 4 days.

Another takeaway for this amateur: it’s about amps, not watts.  The websites where you shop for panels always have the watts in large font, but the small print tells you the optimum operating current, or amps.  This number times hours of sun gives a much better estimate of the output (5.29 amps x 4 hours = 21 amp hours per day) for a battery-tied system.

Home solar update

Dead battery!

Dead battery!

The battery was totally dead this morning (11.4 volts) after about 16 hours powering the freezer.  The charge controller indicated the panel was charging the battery for about 4-5 of those hours, but it was extremely cloudy.  I turned off the inverter and reconnected the freezer to grid power (it’s nice to have a backup to the backup!)  After charging all day today, the battery is up to about 60%.  I hope I didn’t do any permanent damage to the battery.

My estimate of the charge time was pretty close, but my estimate of running time for the freezer was pretty far off.  I don’t think I calculated any loses from the inverter, which the internet tells me can be 15% or more.  It was also a hot day, hotter than when I measured my freezers usage initially, which could have had an impact. Next time I’ll definitely be measuring the total watt hours used (I forgot to hook up the meter) so I can try to estimate what was lost to the inverter.

One more day of charging before I do any more experimenting.

A small experiment with solar

100 watt panel with wood mount

100 watt panel with wood mount

Being carbon-conscious, naturally inclined to tinker, and seeing the falling costs for components, I was curious to know whether I could put together a small solar PV system on my own.  Having experienced a few blackouts this summer and expecting more in the future, I was also curious about providing a small amount of backup power for essential items.  Here’s the story of my first foray into off-grid renewables.

This post at Do The Math (an excellent blog you should read regularly) in which Tom Murphy describes his small, off-grid system really got me started on the whole thing.  I’m not a physics professor, but after reading it and doing some additional google searching, it seemed easy enough for a lay-person armed with a small amount of reading.  A valuable resource (also provided by Tom’s blog) is the Solar Living Sourcebook, available at your local library, which provides all the basics on what solar PV is, how it works, important safety tips, and options for setup.  I also learned a few things from various youtube videos and generally google searching.

The system I put together is 12 volts, which seems very common for small, off-grid installations.  It’s basically only six things: a solar panel, a charge controller, a battery, an inverter, and assorted wires and fuses.  The solar panel provides the electrons, the charge controller controls how those electrons flow to the battery (and makes sure it doesn’t overcharge), the battery stores electrons, and the inverter turns the battery’s 12 volt DC power into 110 volt AC power so it can be used with regular household electronics.  The wires and fuses connect things together and provide safety.

Panel unboxing

Panel unboxing

You can now purchase relatively affordable panels from Amazon or Home Depot in many wattages and sizes.  I chose a 100 watt panel that seemed to receive good reviews and a website that suggested that the company might be around for a while.

Charge controller showing all systems go!

Charge controller showing all systems go!

The other pieces of the system (inverter and charge controller especially) come in a huge range of prices.  After some reading, I decided that it might be better to spend a little more on a charge controller, as many people had complaints about cheap versions, and keeping your battery well-maintained is important (the function the charge controller plays).  I purchased a 30 amp controller from Morningstar, which I think could power up to 300 400 watts of panels if I expand the system in the future.  The battery is rated at 80 amp hours, and is sealed lead acid.  I purchased it from a local battery store, and its a discount version.

80 ah battery

A bad photo of the 80 ah battery

So what can this thing power you ask? That’s a function of how much the panel produces, how much the battery stores, and how much amperage I can draw at one time from the battery and inverter.

According to some assumptions I pulled from NREL’s PVWatts tool, the panel might generate 400 watt hours per day (100 watts X 4 hours equivalent of 100% production) in the peak season and maybe 210 in the low season (November), although I’ve seen higher numbers in other places.  The battery is large enough to store all that daily production and more (80 amp hours X 12 volts = 960 watt hours).  In fact, it would probably take one and a half to two two and a half days of sun to fully charge the battery.

Even in the winter, the daily production of the panel would probably be enough to power a few lights (the LED variety), an efficient laptop, a fan, and a small TV for a few hours.  It won’t run a hotplate, anything but the smallest air conditioner, a heater, or a refrigerator, at least not continuously.  The battery and the inverter could probably handle it (one of these things), but the panel wouldn’t be able to keep up.  As far as a back-up power source, this set up would power my refrigerator for about 12 8 hours, and our 8.8 cubic foot chest freezer for about 24 16 hours.  That’s assuming a fully charged battery, the panel couldn’t keep up with the draw from those appliances for more than a day.  These are just my estimates, I don’t have any real world results yet, but will report back soon.  Right now I’ve got just the chest freezer plugged into the inverter and I’m going to time how long until I get the low battery warning.

Things I’ve learned so far:

  1. It’s all the other stuff that costs money.  At this stage, the panel itself only accounts for 20% of the cost.  If I added two three more panels (which would probably max out the charge controller) to economize, the panels would still only be 40% 51% of the cost.
  2. I need scale to “save” money.  Right now, my costs per watt are about 76% higher than what I have been quoted to put a grid-tied, full size system on my roof.  If I maxed out the charge controller with two more panels and got another battery, I could bring my costs in line with the pros (again, on a per watt basis).  Whether this would continue to scale up I kind of doubt, since batteries get expensive and I would get into more serious electrical work pretty quickly.
  3. I need another battery (or two) for large stuff.  High amperage appliances, like a vaccuum, seem to be within the wattage range of the inverter, but my battery is only 80 Ah.  The internet tells me I should only run things that are 10-12% in amps of that capacity to avoid shortening the batteries life, and indeed I got a low battery warning when trying to run the shopvac.
  4. You should think hard about where to locate a panel before you embark on this kind of project.  I’m still squeamish about getting into roofing for fear I will cause a leak, and others in my household disagree about the aesthetics of a home-built wooden frame.  My goal in the long run is to get this on a roof somewhere.
  5. In the future, our homes should probably run direct current (DC) rather than alternating current (AC).
  6. Solar panels aren’t just for tree-huggers.  If you’ve ever searched youtube for videos about solar back-up systems, you’ll be a lot less surprised about news items like the Atlanta Tea Party teaming with the Sierra Club to promote more solar.  Many of the instructional videos I watched were clearly made by folks of the conservative persuasion who were into solar because they feared the grid would go down or they weren’t comfortable being beholden to utilities/the government.  Maybe there is more common ground here than we thought.

 

In praise of the prairie

DSC00975

As part of the “Our Fair State” series going on at streets.mn this week, I’ve posted a short photo post praising the western Minnesota prairie.

When most people think summer in Minnesota, they think north: lakes, coniferous forests, large noisy black birds.  But Minnesota actually has four biomes, and I would consider the prairie grassland the most neglected when we engage in communal nostalgia for Minnesota summer.  Luckily, we have some great parks on the prairie where you can see a little of what Minnesota might have been like before settlement.  And it’s beautiful.

The greenhouse gas benefits of autonomous vehicles

stanley side view (2005-023-040)

Autonomous vehicles may bring a myriad of benefits, but I anticipate that one of the largest may be the actual reduction in the total size of the vehicle fleet.  Eventually autonomous vehicles will allow “whistlecar” service, and whether fully autonomous or not would, this service is likely to fundamentally change the ownership model of automobiles.  Like present-day car-sharing services or taxis, a whistlecar subscription would mean one car could serve the needs of many people, instead of remaining parked most of the day waiting for its one owner to return.  Once you’re done with a car, it can drive off and serve someone else in the vicinity, drive to a charging station (if it’s electric), drive to a garage for service, or perhaps even deliver packages.  When you can subscribe to an on-demand travel service available 24-7 (and eventually cheaper than owning a car), many people will choose not to own.

Setting aside all the other benefits of autonomous vehicles for the moment, I’ll explore just this one: the benefits of a reduction in the car fleet.  And in a limited way: the greenhouse gas implications of this reduction in vehicles. Continue reading

Water for our future

Over at streets.mn I have a new post on the importance of water supply planning for the next regional plan.

What does all this have to do with Minnesota?  We have tons of water, right?  Well, on the surface yes, but we’re using our groundwater much faster than it’s being replaced, and that’s a problem.  That was one of the main topics at a Thrive MSP 2040 Roundtable discussion I attended a number of weeks ago, and have been meaning to post about since.  The 7-county region now gets70 percent of our water from groundwater sources, up from 15 percent in the 50′s.  In some places this means we’re reducing groundwater levels by over a foot a year.

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

Washington Avenue Traffic Projections

Hennepin County is preparing to reconstruct a portion of Washington Avenue between Hennepin Avenue and 5th Avenue South.  There has been much discussion of this project, in part because the reconstructed road may or may not include some sort of bike facilities.

Today I got an email about an upcoming public meeting for the project, and I noticed the project webpage includes a Traffic Operation Analysis with some traffic projections through 2035.  Hennepin County is projecting a 0.5% annual growth in traffic volumes between 2011 and 2035.

Hennepin County provided traffic volume forecasting information for the Washington
Avenue study area. Several considerations included in the traffic forecasts are:
Minneapolis overall expects to add 36,000 residents and 30,000 employees over
the next 20 years.

  • Closure of Washington Avenue through the U of M, east of the Mississippi River.
  • Construction of the new 4th Street S on-ramp connection to northbound 35W.
  • Reconfiguration of the interchange at Washington Avenue SE/Cedar Avenue.
  • Construction of the Central Corridor LRT line.
  • The impact of continued development in the downtown area including
  • townhomes/condos, office space and retail businesses.

Given the above considerations and through a review of past studies completed within the project area, Hennepin County recommends that the traffic forecasts be based on applying a 0.5 percent per year growth rate (13 percent increase by 2035) to the existing traffic volumes, then adjusting Washington Avenue, 3rd Street S and 4th Street S traffic volumes to account for circulation changes with the future 4th Street S on-ramp connection to northbound 35W.

I don’t feel qualified to speak about hyper-local traffic patterns based on certain street closures and circulation patterns.  That’s traffic engineer stuff.  But here are a few things (and charts) to consider:

  • According to Mark Filipi, who works on regional traffic modeling for the Metropolitan Council, the regional traffic model (based on old comp plan data) projects 0.3% annual growth in total Minneapolis VMT through 2025.  This is lower than 0.5%.
  • Total Minneapolis VMT has basically been falling since 2002, with non-interstate VMT fluctuating around flat growth (all VMT figures from MNDOT).Minneapolis VMT
  • Minnesota total VMT per capita has been falling steadily since 2004 at over half a percent each year, and total VMT has been falling since 2007.  Minnesota VMT and VMT per capita
  • According to the Minneapolis Traffic Count Management System, two of the three traffic count locations on Washington Avenue in the study area show a drop in traffic from their peaks in the late 90′s/early 00′s.  The third shows flat volumes.Washington Traffic Counts Between 3rd Ave & 4th Ave

Does all this mean that 0.5% annual growth rate on Washington Avenue is incorrect?  I’m not sure.  Minneapolis does plan to grow a lot of downtown jobs and housing.  On the other hand, per capita VMT trends have been falling not just in Minnesota, but across the country and world.  In addition, Minneapolis policy makers have stated their goals to shift modes.  It’s troublesome to me that in the “considerations” that Hennepin County used in their traffic forecasts, they didn’t include plans for that mode shift the same way they include plans for development.

Given the severe lack of detail on how the 0.5% growth figure was developed, I don’t think the community should accept any design predicated on that figure without some additional explanation, especially if the capacity needed to accomodate that growth is given as a reason to reject elements that will make this street a livable, vibrant and valuable place, namely, pedestrian and bicycle infrastructure.

Cross-posted at streets.mn