Putting the Sidewalk Back In.

     Life (and engineering) is full of compromises.  To put the solar panels at the location that I wanted them, I had to take out the sidewalk.  This was a ton of work and I would have loved to avoid it.

    Sadly, it was only half the work.  Now I need to put the sidewalk in at a new location.  There has been nothing but dusty dirt there for a while, and I cannot believe how much dirt has been tracked into the house.  It is time to fix that.  Also I would rather get the concrete in before the panels go in, rather than the other way around.  Seems like mixing concrete so close to new solar panels is a bad idea.

   To get started, I had to dig out about six inches of soil and cart it away in a wheelbarrow.  Then I had to put in forms made out of 1x3 strapping with stakes holding them in place about every 25 inches.  I worked to match the slope of the soil on the grassy side of the walkway.  If the sidewalk is too low, soil will wash on to it if it rains.

   With the forms in place, I went over to Home Depot and purchased 1000 pounds of gravel.  I took two trips in the Corolla so that I didn't risk overloading the suspension.  I would hate to break a spring in the process of doing this project.  The level of the gravel was flush with the bottom of the form so I would have approximately 3" thick concrete when I was done.

   To hold the concrete together, I added, so called, six six ten ten mesh.  This is steel mesh of 6 inch squares with ten gauge wire.  I purchased a small pair of bolt cutters to cut the material.  Bold cutters are so cool.  I wonder if I will ever use them again.  When I poured the concrete, I periodically pulled up on the mesh to get it in the middle of the concrete.

     Starting at 6am, I went to work.  I made two trips to Home depot to purchase 24 bags (80 pounds each).  That is a total of 1920 pounds or just short of a ton.  The bags of concrete were in place on the site just before 8am.  That is my son in the picture, but he was heading out to Maratha's Vineyard with the girlfriend for the weekend.  So no help there.  I am not complaining.  I am glad he went.

  And so it began.  Pour the concrete into the wheelbarrow, add water, mix, dump into forms, compact, screed, float, trowel, edged, add brushed finish, repeat, until just about noon and it was done.  I had two bags of concrete left over which I returned to Home Depot because concrete does not keep well.

  I am very happy to have the concrete in.  I am not sure I like the surface finish that I left on it, but I will know better once is hardens.  I wanted a little bit of texture for traction.

   Underneath the solar panels, I would like to add a stone bed.  I think this will be good for keeping down the weeds.  By next weekend, the three solar panels should be here.  Actually, they should be at my work because if I shipped them to my home there would be a $200 added charge.  Hopefully my buddy Doug will help me get them home using is big F-150 pickup truck.

Aluminum Frame Work

    Now that the concrete part is out of the way, something is needed to attached to solar panels to, like a frame.  I considered a range of ways of doing this.  The frame could be built from pressure treated lumber, or welded steel, or even plastic.  However during my reading of a "lessons learned" paper from the 1970's solar hot water systems failures, I read a little piece of advice.  The advice was to use only very durable materials for the harsh outdoor environment.  Specifically, the authors of the article had great experience with aluminum and stainless steel.

    The panels that I am planning on purchasing are from a company called Heliodyne.  They make a great frame for about $500.  The frame has aluminum posts and stainless steel fasteners.  It is very nice.  However, the frame didn't offer much flexibility for mounting other objects.  So if I wanted to mount a heat dump on the same frame, it would be tricky because there are no additional mounting points.

   So I decided to make my own frame which is inspired by the Heliodyne frame.  My frame is made from aluminum extruded sections from Misumi and has stainless steel fasteners.  It also cost roughly $500.  The Misumi extrusions are very similar to a competitor's offering called 80/20 which will be familiar to most Mechanical Engineers.  It is the adult version of Legos or Erector sets.  All the pieces are pre-cut to your specified lengths and all you need to do when they arrive is assemble them as shown below.

 

  The aluminum extrusions and their mounting brackets bolted directly to the threaded rod sections that are anchored into the concrete.  Assembly was easily.  I just needed to adjust a little bit for the concrete piers not being of exactly the right height.

 

    To reduce the risk of a lateral load bringing down the framework, diagonal braces were placed on the left and the right.  The commercial Heliodyne framework didn't have this feature and that made me a little nervous about buying them.  Normally, there shouldn't be any side load on the frame, but it is still nice to have some added support.  

    The biggest annoyance that I had was with the 12 foot long aluminum extrusions.  These were too long to ship by normal UPS.  So they had to be shipped with a trucking service for $170 which is more than the $150 I paid for the parts.  In hind-sight, I should have made these into two shorter lengths.  That is how Heliodyne ships these pieces.  Live and Learn.

 

  The aluminum extrusion have T-slots down their length.  This allows a T-nut to be dropped into the slot and I will be easily able to screw in the panels.

   Up next, time to put that sidewalk back in.