Laying out the support frame.  As mentioned before, the south facing roof on our house is taken up with the solar hot water system.  The only mounting option for the photovoltaic system was to build a sun shade type support frame in the yard.

The first thing that was needed was the size of the array.  For this system, we will be installing 20 Sanyo HIP-205N modules.  These measure 62.2″ x 31.4″.  I would like these to be installed landscape style, four deep by 5 wide.  The total array size is 311″ or 25.9′ X 125.6″ or 10.4′  I am leaving a little room around the edges for a safety factor, so my support frame will be 27 x 12 feet.

I also want  to tilt the array to latitude, which around here is 42 degrees.  There have been studies that show that the tilt angle is not a critical as once thought, however, since I can do it, I might as well.  Therefore, I will install a total of six support posts, making the structure 26 feet x 7 feet.  The front of the structure will be about 6 feet above ground level, the back will be about 12 feet above ground level.

PV system location marked with stakes

I staked out the frame and aligned it to true south.  It is only a few degrees off from the property line, so it works out well.  Since we have had a lot of rain this year, I decided to dig a test pit to see where the water table is in relation to the bottom of the footings.  Local code requires 48 inch deep footings, my test pit reached 46 inches deep before I saw some seepage.  I left it over night and the next morning there was about 2 to 3 inches of water in the bottom.  Over all, not too bad, I put some crushed stone in the bottom of each footing before I put the form in.

Test pit to see where the ground water table is

It rained most of the day on Saturday, however, I still managed to dig four of the six holes.  On Sunday, I dug the last two.  Then, by this post, I knew that it takes about 2 2/3 80 pound bags of ready mix to fill an 8 by 48 inch sonotube.  I picked up 16 bags of 4000 PSI ready mix.  This time, I borrowed a cement mixer, which made things much easier.  I also used one #4 (1/2 inch) rebar down the middle of each footing, tied to the J bolt on top.  I used 1 gallon of water per 80 pound bag, as the directions on the bag stated.  This made a good stiff mix.

Holes completed, string crosses mark footing locations

To make all of the forms the same level, I used a 14′ 2 x 8 and a level.  Going from hole to hole, slowly putting more packed crushed stone in each hole, I think I got pretty close.  Also, the crushed stone will aid with drainage around the bottom of the footing.  Any differences in level can be made up by trimming the posts.

Footing hole, somewhat deeper than 48 inches

This was a miserable job.  It was wet and muddy all day long.  One of the hole had a lot of water in it, which needed to be pumped out before I could put the form in.  Our soil is thick clay, which caked on everything, shovels, boots, rocks, etc.  The weather forecast was for sun on Sunday, which turned out to be false.  Still, it is done.

Footings completed and backfilled

I was going to use the excavator to dig the trench for the conduit, however, I decided that a ditch witch would be a better idea, less back fill, less mess, etc.  For conduit, I think I will go with two inch.  This system has microverters, which means the feed from the solar array will be 240 VAC.  I could use #12AWG with this and come in at just under 2% voltage drop.  Since I have spools of #8 AWG already on the truck, I will used that cable instead.  That makes the voltage drop 0.6%.  Since there are two 240 VAC branch circuits, plus two neutrals and one ground wire, that makes the total number of conductors 7.  According to the latest version of the NEC (2008), table C.10, 1 1/4 inch schedule 40 PVC conduit is acceptable for this installation.

Once the concrete hardens for a couple of days, we’ll put up the frame.

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