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.

Pouring the Concrete Piers

   Concrete is wonderful stuff.  Just add a little water, mix and pour.  During the pouring, I paused every 6 inches of depth or so worked the concrete with the end of a stick to make sure there were no voids, particularly on the outside edges were the concrete will be visible once the sonotube is removed.

 In the top of each concrete pier was placed two 8 mm threaded rod sections.  These rods needed to be placed 100 mm apart.  To maintain that spacing, an aluminum bar was machined on a Bridgeport with exactly the right spacing.  A second aluminum bar was also made and buried in the concrete with most of the 100 mm (4 inch) long sections of threaded rods.  This assembly makes it impossible for the threaded rods to be pulled out of the concrete.  This assembly was carefully positioned relative to the level lines so all the the bolts would fit in a straight line.  Each concrete pier was finished with a trowel.  I later learned that I should have worked the edges of the concrete to remove the sharp edge.   Perhaps I can stone this edge off later.

 

    The aluminum bar shown in the image will be removed and discarded once the concrete dries.

   With all the concrete piers in place,  it is time to get the aluminum extrusions from Misumi USA.  Let's hope they all fit properly.

Diggin' It Part 2.

Possibly the only thing duller than watching the grass grow is watching holes being dug.  I will spare you the details except to say that it took about one month of weekends just to dig the holes.  But through the magic of blogging, we can quickly move on to the next steps.

    With the holes dug, the next step was to install the sonotubes (cylindrical cardboard forms) in the holes.  In order to get the holes in the right place, new lines were installed so that the height of the lines would be at the top of the forms.  This was accomplished using 12 long stakes on the outskirts of the work area.  On each stake, the height was marked using a laser level that I purchased for about $70 at Home depot.  The really cool auto leveling laser was $500, so I passed on that.  The laser level that I purchased had to be leveled by hand.  Also, the laser intensity was so weak, that it could not be seen when rotating at full speed.  I suppose I could have waited until night, but instead, I manually pointed the laser at a location on each stake an marked it with a pencil.  With all the marks in place, the lines could be installed as can be seen in the photo.

   One unfortunate thing about the sonotubes is that they are only 4 feet long, yet the holes had to be 4 feet deep.  This would mean that the concrete piers would stop right at the dirt surface, which is not where I wanted them.  To get the required length, two sonotubes were duct taped together and then cut to length with a hand saw.  You can seen just a little bit of the white duct tape in the picture right at the dirt level.

     With all the sonotubes in place, the work-site no longer looks like it has been bombed.  Each tube was covered with plastic wrap (green, left over from Christmas I guess).  This was to protect the sonotubes from water damage.  Sonotubes degrade quickly when wet and must be protected right up to the time they are used.

    Into each sonotube was placed three long vertical pieces of steel called rebar.  This steel greatly strengthens the finished concrete piers.  To keep the rebar in the right position, I added two triangles of steel, one at the top and one at the bottom as shown in the picture.  This assembly could be just dropped into the sonotube without need of additional support or positioning.  Each assembly of rebar had to be cut to a custom length for each sonotube because the concrete piers are not on level ground.

   Now the concrete piers are ready to be poured.

Diggin' It, Part 1

   Like all constructions, you have to start with a firm foundation.  In this part of the world, that begins with digging holes that are four feet deep (below the frost line don't cha know).  Hard experience has shown that this is the best way to build a firm foundation for any project here in the frozen north.  For this project, eight holes were needed for eight sonotubes.  Sonotubes, if you don't already know, are cardboard forms that can be placed in the ground so that concrete can be neatly pored into them.  The cardboard is later removed.

   Before the holes could be dug, their locations had to be marked.  A set of wooden stakes were purchased from HomeDepot along with some high quality and high visibility line (string).  Using information from the CAD model, the stakes were located around the perimeter of the location where the holes were to be dug.  The intersections of the strings located the center of each hole location as can be seen in the photographs.

   Having previous dug post holes, and found it to be no fun, I was looking for an easier way.  Previously, when I lived in Utah, I had seen people use a gasoline powered auger to dig holes and it looked so much easier than digging by hand.  So off I went to Home Depot to rent one.

  Since the concrete piers were to be 8" in diameter, 10" diameter holes needed to be dug which required a 10" auger bit.  This in turn required the larger "two-man" version of the power auger which can be seen in the picture below.

  This tool is an absolute beast.  It takes two strong men to try to work it.  At first, it seems like the answer to my dreams.  The first 2.5 feet of the hole were dug in a matter of seconds, but then it happened.  A large rock jammed the auger and it became completely unusable.  An attempt to dig a second hole met with almost the same fate, but this time only 1 foot of depth was achieved before the auger was stuck.

   The power auger ended up being a waste of $75.  Here in New England, the soil is very rocky and there just doesn't seem to be a good way to dig holes.  In some other location where the soil is sandy or clay, the power auger would probably be great.  For me, the holes would have to be dug the old fashion way, with a post hole digger.  But first, I needed to get the rock out of the hole.

   I worked for hours trying to dig around the rock, removing many fist size rocks in the process.  The rock extended down into the hole to a depth of about 3 feet.  Even working on the rock was a challenge.  I had to lay on my belly and dive into the hole and dig with a small hand trowel.  It was very annoying.  Eventually I realized that even if I could free the rock, there was no way to pick it up out of the hole.

  So I devised a plan to lift the rock out of the hole.  Using a hammer drill (nice one from Bosch, about $300), a 3/8" diameter hole was drilled through a corner of the rock and an I-bolt was fastened to the rock.  A chain was then connected to the I-bolt and then to a 2x4 wooden beam.  Unfortunately, pulling as hard as I could only resulted in destroying the I-bolt.

 It was time for plan B (or C or D, I lost track).  The I-bolt was replaced with a steel cable.  The steel cable was looped through the hole in the rock and then connected to the chain which was again connected to a 2x4.  But no matter how hard I tried, the rock wouldn't budge.  So, I got out the 2 ton car jack.  I used the jack to work as a lever to free the rock, as shown in the photograph.  Then my family of four all lifted on the 2x4s to get the rock out of the hole.  Success!  Well, perhaps not, because I still had another foot of depth to dig on that one hole.

  It was clear that it was going to take a number of weekends to finish digging the holes.  Worried that the rain might fill in the holes or cause them to collapse, I decided to put up an awning, of sorts as shown in the photograph.  My Eagle Scout son make some awesome taught hitches in the lines.

The picture also shows the PV solar panels that are on the roof at the location just above were the new thermal solar panels are going in.

Preparing the Site

   OK, so clearing away the site is not the most interesting of jobs.  But just for a sense of completeness, I am going to tell you anyway.

  The site contained two very large bushes, but unfortunately I forgot to take a photograph.  The bushes were easy enough to cut down with an electric chainsaw.  The stumps on the other hand gave me my first taste of working in the dirt which would last for the next several weekends. 

   I am sure there are better ways to remove a stump, but I decided to use my muscles rather than my brain.  To get started, a sort of moat was dug around each stump to gain access to the root structure.  When a root was encountered, it has to be cut with lopping shears, a bow saw, or the electric chain saw.  None of these techniques worked very well and I ruined not one, but two, chainsaw blades in the process.  Did you know that roots can grow to encapsulate rocks?

    Anyway, eventually the stumps were removed leaving large holes like the one shown in this picture.

Out of that hole came a stump.

The stump and all the remains of the bushes made for a large pile of debris.

All the debris needed to be hauled to the compost center (yes it will get reused by local gardeners).  So what vehicle does the eco-conscious home improvement guy take?  Why the Prius of course.

Although, given that it took me four trips to the compost center with the Prius, it would probably have been "greener" to take my neighbors pickup truck.  However, you have to love a hatchback for its flexibility.

   After all was said and done, a clean piece of dirt was available for me to build on.

   Well it was not quite ready yet.  As I have mentioned before, the concrete piers that support the solar panels will interfere with the concrete walkway.  Some of the walkway also needed to come out.  The eight pound sledge hammer got pressed into service.

   For my day job, I work at a desk.  The heaviest thing that I lift is a 20 ounce Diet Coke.  So while I can swing a sledge hammer well enough, I cannot do it for more than about 10 times before I need a break.  The only thing saving my ego was that my 6'3" 180 lb, 16 year old son couldn't do any better.  Also, my 19 year old daughter swings like a girl and her use of the sledge hammer was completely ineffective.

As can be seen in the picture, steel wire mesh was embedded in the concrete.  This is the so-called six-six-ten-ten mesh.  These are six inch squares of ten gauge steel, and it is very effective at keeping the concrete together.  Even once the concrete was cracked all the way through, the walkway was difficult to breakup because the wire mesh held it together.  After a day's struggle, one section of walkway was cleared.

    One of the more frustrating aspects of using a sledge hammer is that most of the energy is absorbed by the dirt underneath the concrete slab and wasted.  If the concrete slab could be lifted off the ground, it would be much easier to break up.  Eventually, I figured out how to create a lever out of a 2x4, lifted a section of concrete off the ground by a few inches, and supported it by pieces of 2x4s.  Now with the slab supported like a beam in bending, the impact with the sledge hammer was much more effective at breaking up the concrete and the rate of progress increased by about four times.

    Only a segment of the walkway was to be taken out and it would be nice to have a clean break at the end.  Using a Bosch hammer drill (with drill motion turned off), I created a set of cracks in the expansion joint to force a clean break. 

 This technique worked very well and the edges of the work area looked clean.

  Now with the work area prepared, it was time to mark out the locations for the "sono-tubes" or cardboard concrete pier forms.

Solar Path Finder

   Trees are just a fact of life here in New England.  If you don't keep mowing your lawn, the trees will completely reclaim the area in about 10 years.  After a while, the trees will be 40 or 50 feet tall and casting wonderfully large shadows to keep you cool in the summer sun.

   Wonderful, that is, as long as you are not interested in collecting solar power.  Putting solar PV (electric) panels on my house necessitated turning this beautiful tree...

 

into this less than beautiful trunk.

    This time around, I was trying not to lose any more trees.  On the other hand, I do need good "solar coverage."

     Solar coverage is the percentage of the time that the site of interest has unobstructed exposure to the sun.  To measure this, there is a clever little device called the "Solar Path Finder" which can be rented or purchased.   The device costs about $300, but I rented my from Real Goods for $50.  They don't seem to advertise the rental, but if you call them they seem happy to rent.  Later on, I found one on ebay for $89, so I bought it.  If you are in the Boston area, perhaps I can help you out with a loan or site visit.

     The Solar Pathfinder comes with set of (optional) legs to support it on flat ground.  The device must be leveled, using the integrated bubble level, then it must be turned to face due north with the integrated compass.  There is also an adjustment for magnetic declination to adjust for the difference between true north and magnetic north.

      So if you are like most people, you are probably thinking that you put the solar pathfinder out in the sun for a day and it record the shadows.  But that is not how it works at all.  In fact, given that the angle of the sun changes month by month, you would have to record data for a full year using such a method.  The solar pathfinder does not have to see the sun to work.

      In fact, it is best to use the pathfinder on a cloudy day!  Yes that is right, you don't actually want the sun for this measurement.  The top of the solar pathfinder is covered with a partially reflective clear plastic dome.  If you look down at this dome you can see a hemispherical image showing all of the sky in one image.  This shows if any trees or structures are shading the area.

  So that all by itself is pretty clever, but there is one more piece of cleverness that makes this all come together.  Underneath the plastic dome is a piece of paper with two series of lines.  One series of lines represents the time in hours, as can be seen in the closeup image below showing 10 am, 11 am etc..  The other series of lines represents the months, which can also be seen in the image marked by the months June, July, May, etc.

    
   If a photograph is taken from directly above the solar pathfinder, it will show a reflection of the shading trees overlaid on the template showing the months and the hours as shown in the enhanced picture below for my preferred site.

 

The image clearly shows the location is far from ideal.  On the left side of the image, you can see that for most months, the sun starts to reach the site at about 9:00AM, which is great.  On the right side, you can see that sun continues until about 3:00 or 3:30 pm until shaded by an maple tree on the west side of my property.   At the top of the image, the real problem can be seen which is the winter months.  For these months there is almost no solar coverage.  

     In the closeup of the solar pathfinder chart, there are little numbers like 5,6,7 which are the percentage of time allocated for that 1/2 hour period.  For each month line, these number add up to 100%.  The 1/2 hour segments in the morning and evening are worth a lower percentage because the sun intensity is lower.  These number can be used to calculate the solar coverage for each month of the year.  My numbers are below.

January	22%
February	49%
March	71%
April	84%
May	91%
June	87%
July	91%
August	87%
September	80%
October	55%
November	36%
December	0%

The good news is that from April to August, the site will get more than 80% of the available sunlight.  The bad news in that in December, the site will not get any sunlight.  However, sunlight is a greatly diminished resource in the winter anyway.  Even with 100% solar coverage in the winter, the amount of energy is significantly less than in the summer due to the shortened day.

Despite the shortcomings, the chosen site on the ground will be used.

Next time, the location will be prepared to being the installation process.