DIY Ground Mount Solar

This article is all about installing your own solar panel system using a ground mount, not on a roof. If your roof doesn't have enough area or faces the wrong direction, and you have a ground area with a view of the southern sky you can install the panels on a rugged metal frame that faces the right direction, looks good and saves you a ton of money.

You can either hire a contractor to install it, or you, as a homeowner, can be the general contractor and Do It Yourself, no license required.

By installing it yourself you can save even more money, the total cost will be about a quarter to a third of a professionally installed system.  If you don't mind doing some labor intensive work you can get your system up and running in a month or two (working weekends).  It's not complicated work, just time consuming and back breaking.

However, if you are not comfortable working with electrical equipment or wiring, or you have an aversion to hard work, pay the money and hire someone.

Saving the planet

"You don't do it to save money, you do it to save the planet".

That's a direct quote from JM, an old friend, during a discussion a few years back about electric cars.  As far as electric cars are concerned, he's dead right.  They don't save any money when it boils down to it.  Yes, they save the cost of the gas, but the cost of the car itself vastly outweighs that minor saving in fuel.  They do, however, remove the direct pollution from the tailpipe (notwithstanding the arguments to the contrary about burning coal to produce the electricity) and thus are better for the air.  Living in the San Francisco Bay Area, we can do with all the help we can get to clean up the air.

It so happened that I did jump in and bought an electric car a few years ago.  A nice Tesla Model S, now over 3 years old and still perfect.  I save money on gas, indeed, about $300 per month, and my employer provides a nice free charging perk.  To make it feasible to charge at home, I had to move to Pacific Gas and Electric's Electric Vehicle-A rate scheme (EV-A) which instead of their 4 tier rip-off prices, they put you on a time-of-use rip-off plan that charges much more for the electrons you consume during the day but gives you a much easier to swallow rate after midnight.  When I started on this plan the off-peak rates were $0.10 per kWh and I think the peak was about $0.40.  I just noticed this month that they had surreptitiously increased the off-peak to $0.114 per kWh and the peak is $0.44.  That's about a 14% increase.

The issue with the time-of-use plan is that you can definitely charge the car for a reasonable rate, but all the other electricity (oven, dishwasher, TV, etc.) cost much more than before.  My bill went from about $160 per month to over $250.  And at the rate at which the prices are increasing it will be $300 and over within a year or two.  I was feeling ripped off and needed to do something about it.

Go for it

I'd been thinking about going solar for a while but never had the incentive to do it.  A friend of mine had installed his own system on his roof a few years back and was very happy with the results.  You can't walk through Home Depot these days without being accosted by someone pushing solar installations.  I decided to let them give me a quote for putting solar on our roof.  A couple of different companies came out and either wanted to charge me $50,000 for the system or declined to quote because of the shape of our roof and the shade situation.  We have a 30 year old maple tree that shades most of the roof and I wasn't going to cut it down, so the roof turned out to be a no-go.

So it was going to be a ground-mount system or nothing.  I asked one of the companies for a quote for a ground based system and they reluctantly gave me some completely unreasonable price that included me having to dig the holes and trenches because their "highly skilled installers are too expensive to dig holes".  WTF?  OK, so that was a no-go too.

Years pass by and I'd been keeping an eye on the cost of ground mount systems from the internet. Then, this year I decided that I was going to do it.  I'd kept a few bookmarks of interesting online solar kits and I noticed that GoGreenSolar.com had an offer on.  A window popped up in my browser asking if I wanted some help.  What the hell, I typed something in the chat window.

Steve, the helpful salesman who happened to be online that day answered me immediately and I stated that I was interested in a 6kW system (24 panels).  He said that they had a good deal (that happened to be expiring the next day, of course) that they would throw in the cost of the plans ($500 value) and the PG&E paperwork ($200 cost).  I decided to take it further.

The system I bought from GoGreenSolar.com consisted of 20 panels (my main service panel only has a 125A service so I couldn't do the 24 panels I'd originally wanted), a SolarEdge inverter and "power optimizers" for the panels.  This was a ground mount system so I would also need some Schedule 40 steel pipes to build the frame and lots of large gauge wire.  As an aside, I was expecting the steel framing pipes to be supplied with the kit, but they use the phrase "locally sourced" to mean that they are not included and you have to buy them yourself.  This wasn't clear from the web site and I still think it's a little disingenuous of them to not tell the customer up front.

In April 2016 I took delivery of the kit, over 1000 lbs of it on two pallets.  The panels were in two very large cardboard boxes (about 5 feet by 3 feet by 2 feet).  We spent a couple of hours carrying the panels from the garage to their storage place at in the back yard.  They are not heavy individually but you can't lift the box if it's full.  The box probably weighs more than a panel of two.  And there it all sat for about 3 months while the project was under way.

GoGreenSolar.com says on their web site that a ground mount system can be installed by the average homeowner in a couple of weekends.  This is way off.  My system took about 3 months to complete, working mostly at weekends.  It's not that I'm a slow worker, it's just a hell of a lot of work on a difficult slope in the heat of the summer.  Maybe someone could do it in a week if they worked full time on it and had everything lined up, but a few weekends is not feasible.

My aforementioned friend, JM, had also decided to install a system on his sprawling property in Los Gatos.  His problem was that he didn't want to do the work himself so instead he employed a contractor who insisted that the system needed to be at least 10kW, 40 panels.  This is much larger than he actually needed but the work involved meant that it wasn't worth while for the contractor to do it unless it was a large system.  

For the plans I needed to decide on a location.  I happen to have about half an acre of land that slopes up from the house to the north.  The hill in the back yard is fairly steep but levels off at the top.  This makes for a perfect south facing gentle slope.  I chose the location to be in the north east of the property, about 150 feet from the house.  This would entail digging a long trench to accommodate the conduit containing the wire and the terrain was going to tough, a slope with trees and a concrete wall and pathway to traverse.  But it was the only location I had that was suitable.  The panels would have an unobstructed view of the southern sky.  I drew a diagram for the GoGreenSolar guys and provided all the information they needed to draw up the plans.

I got the plans from GoGreenSolar.com in early May and after few corrections took them to the city planning office and got them approved on the spot, and paid $400 for the privilege.  The plans arrived via email in PDF format and I needed to print out 3 copies in 11x17" format.  A trip to the local Kinkos (sorry, Fedex Office) cost me around $50.  Pretty good service though, all self-serve and easy.

Layout plan for the solar array from GoGreenSolar.com

Then I was ready to start.

First things first, clear the site.  This was May and the El Nino had dumped enough water on the Bay Area to ensure the ground was reasonably damp and the grass was still green, if about 2 feet tall. Lawn mower and chainsaw to the rescue.

Site cleared and ready to go

Being on the ground rather than on a roof, the system needed a custom frame constructed to support the panels and the frame's posts need to be buried into the ground.  I was given a choice of how big to make the holes for the foundations.  The soil around here is a very hard clay type, either a thick sticky black mud or a grey concrete-like material.  From previous experience I knew that digging a deep hole would be onerous so I chose to go with holes that were 2' diameter and 3'6" deep.  My other choice was a 4'6" deep hole, 1' in diameter and I had no idea how to dig that.  There is no way to get a Bobcat with an auger up the hill to the site and I knew it would all be hand dug.  A wider, shallower hole should be much easier to excavate.

Plans for the frame

The city code has rules about how close things can be to the property lines - setback.  In this case the setback was 5 feet so I had to ensure that the back edge of the array was more than 5 feet from the back fence.  The side fence was no problem, I had plenty of room there.  Armed with a long tape measure, some string and a can of red marker paint, I determined the locations for the 10 footings ensuring they were in line, the correct distances apart and oriented in the right direction.

Footings marked

Digging the holes themselves was going to be a challenge.  I'm a really good digger.  As a child, my dad had me digging all sorts of things in his garden, from turning over the soil for a vegetable patch, to grading the large garden.  I even dug out a pond by hand.  I got really good at digging with a spade, especially when I used "Charlie", my favorite spade, so named after my grandfather because I bought it on the last day I saw him alive.  Even so, I didn't think that it would be much fun digging 10 huge holes in clay.  An auger was required.  The local Danville Cresco tool rental store had a good selection of them and on the first day of the school summer vacation I rented one, for about $100.  You should have seen my daughter's face when I asked her to help me use it.

Holes

A two-man powered auger is an awesome tool.  It has 4 handles and a huge, heavy engine (basically a Honda motorcycle engine) that drives a big screw.  Newton's 3rd law is a real bitch as our arms will testify.  Rotating the screw into the ground also rotates the engine and it takes a lot of effort to stop it spinning, especially when the bite of the black mud digs in.  We managed 3 or four holes, each 1 foot wide and about 3 feet deep before we had to take a rest.  By this time my son, the 18 year old high school graduate was awake and decided to help out.  We swapped helpers and we got the other 6 holes done in about an hour.  More than once, we had to fill the hole with water to prevent the screw simply spinning on the hard-pan.  This put even more strain on the operators as the clay was even worse when it was wet.  When we had finished and hosed down the auger for return we had 10 holes that were only half the diameter and not as deep as they needed to be.

For the remainder of the excavation we were forced to resort to Charlie, a couple of steel buckets and a post hole digger.  It was very tough going but we eventually managed to widen all 10 holes to 2 feet and make their depth 3 and a half feet.  We ended up tying two buckets together with a length of rope.  The smaller bucket just fitted into the bottom of the 12" hole so we dropped it in and used Charlie to dig out the sides, dropping the "soil" into the bucket.  When it was full we pulled it up, dumped it and repeated.  When we got to the bottom, below the rim of the bucket we had to use a post hole digger to pull the rest out.  The ground was so hard about 2 feet down that we had to fill the holes with water to soften it.  Mud, glorious mud that was really heavy and a great workout.

Holes, with bucket excavation device

Charlie and post hole digger

Trench

The site for the panels was about 180 feet from the main panel.  The city code says that electric cable must be in a race (conduit) buried 18" under grade.  This means that the trench needs to be at least 18" deep (technically more since the code says it's to the top of the conduit).  The first problem with the trench was the V-ditch that ran just south of the panel site.  This is an ancient (in California terms) concrete channel that was installed before the houses were built to catch storm water and prevent erosion of the hills.  I had to go below it.  I went to Home Depot and bought a thing to attach to a hose to tunnel under pathways,  After installing the nozzle and hose connector onto a sprinkler pipe, I a turned on the water and tried to push it under the V-ditch.  No chance, man.  The clay soil saturated in a matter of seconds and it was impenetrable.  The water shot back and soaked me, nice dirty water.  Well, at least it was a hot day and I enjoyed the shower.

Charlie to the rescue, with the help of a 5' crowbar and a thin trench digging spade.  Eventually I got through, after a couple of hours of backbreaking work.  Now to the rest of the trench.  With a couple of helpers (my brother, son, daughter and nephew), an 80's Rock playlist on Spotify and a lot of Propel water, we managed to dig 144 feet of trench down to the edge of the concrete pathway at the house.  The going was tough, dusty work with the roots of two trees to plough through and lots of hard clay, but we got there after 4 days.

V-ditch vanquished

Roots and dirt

The end at last

First inspection

I was nervous about the first inspection.  We had the holes and trench excavated and (very close to) the correct depth.  I ordered the inspection for a Tuesday morning and waited in anticipation for the ogre of a city inspector to arrive.  Mike, the inspector was actually really nice.  He was about my age and very talkative and friendly.  He did his inspection efficiently and without looking around at anything else on the property.  I think this is a requirement for our city inspectors.  If you get a permit and they come onto your property they are not allowed to find violations of code.  I guess this is because if they did that, nobody would get a permit and they would be out a lot of money.

Anyway, I had no reason to be nervous.  The trench was mostly the correct depth and all I had to do was put some dobies (3" concrete cubes) in the bottom of the holes.  The first signoff was done and we could proceed.

Pulling the wire

When the plans were being drawn up I asked to use PVC pipe for the conduit because I didn't believe that I could dig the perfectly straight trench that would be necessary for a metal pipe.  The code calls for Schedule 80 PVC which is pretty thick-walled but still flexible enough to bend a little (a blowtorch makes it bend further if needed).  I decided to use 1.5" PVC pipe because I needed to pull 5 wires through it.  The wires are:

• #6 green ground wire
• #8 red positive (x2)
• #8 black negative (x2)

The reason for the two extra wires was that there was a mistake in the plan that specified a ground and 3 #8 wires (I wondered what the extra wire connected to...).  I asked for a plan change but that would cost $170 in city planning fees to change the approved plans.  They said that I would just add another wire and say that it was for future expansion of the system.  This actually sounded like a good idea to me anyway.

Now where was I going to get the wire.  Online web sites seemed pretty expensive for the type I needed (THWN-2).  I asked around work and a colleague had a friend who installed solar for a living who he was willing to contact for me. A few minutes later I had the information for Nassau Electrical in New York (http://www.nassauelectrical.com) who were not only much cheaper than other stores, but had everything in stock and provided free shipping.  Fantastic service.  I ordered it immediately.  Although the trench was only 144; long, I ordered 250' to be sure I had enough.

Now I needed the PVC Schedule 80 electrical conduit.  Home Depot seemed the best place so we headed over to pick some up.  I needed about 200' of it and it's sold in 10' lengths.  Unfortunately the local store only had 7 of them.  We hit another Home Depot and found another 7.  Let's see 14x10 = 140, nowhere near enough.  I decided to order some from Home Depot online.  I placed the order and all looked good.  Within an hour I got a call from the local store saying that there was a stock issue and they didn't have any (that's because I had cleaned them out).  I found it strange that they were not going to order any more and they could only suggest that I tried another store.  I ended up using the lengths of 1.5" pipe for most of the trench but bought some 1" for the part that was above ground - it would look better anyway.

Pulling the wire was reasonably easy.  I bought a plastic reel, the type used for an extension cord and cut it in half.  This allowed me to place the electric wire into the reel and secure it with some steel wire without unwinding all 250' of it.  Putting the reel onto an axle made of a 2x4 at the top of the hill, it was easy to walk down the trench pulling it along.  We did one wire at time and got all 5 done in about an hour.

Now we simply ran the 1.5" conduit lengths, one at a time, up the wire and placed them in the trench.  A 12' fish wire (actually a fiberglass rod) help enormously with this task.  I taped the end of all the wires to one end of the "fish rod" and it made it really easy to pass the rod and wire bundle through the conduit.  When all the conduit was placed in the trench, they were glued together using PVC cement (you don't need that nasty purple primer for this like you do with sprinkler pipes).

Wire in conduit

Where the flexibility of the PVC pipe was stretched by the bend of the trench the solution is to use a plumbers torch to gently heat the pipe until it softens (keep the flame moving) and then bend it round the corner.  Here's a photo of one such bend.

Heat bent pipe in not so straight trench

Building the frame

The frame for the panel array is constructed from 2" Schedule 40 galvanized steel pipe.  While you can get this at Home Depot it's an awfully expensive way to buy it.  I found a local store in San Carlos who had the pipe for $57 for a 21' length and who were willing to cut it to my specifications and even add threads.  Total cost was about $600.  I needed the following lengths:

• 5x 6 feet
• 5x 9 feet
• 4x 15 feet

The 6 feet lengths were for the south side of the frame, the side closer to the ground while the 9' ones were for the other side.  The array length was going to about 30' so I got 4 15' sections with threads on one end.  The vertical pieces attach to the horizontal (30' long) pipes using a special connector that uses heavy duty U-bolts.  I asked the provider for the off-cuts because I reckoned they wouldn't be optimal in their cutting strategy to limit the cost and I thought I needed some extra in case of a mistake (turned out to be a great idea).  The supplier gave me a couple of threaded connectors to join the 15' sections together.

The idea is to build the frame in place with the vertical posts dangling into the holes at the correct place and pour the concrete all at once.  This way it can all be levelled before the concrete comes.  I used a bunch of 2x4 boards with 2" holes cut in them for the pipe.  The boards were arranged to support the horizontal pipes at 3 places (both ends and middle) in an "A" shape.  We spent a whole day assembling all the pipes and building the supports.  Getting them straight and level was challenging and heavy work.  On many occasions the supports slipped on the dirt and had to be redone.  Eventually we got them nicely arranged.

The site is not perfectly level so it was a bit of challenge to work out the exact length of the pipes to dangle into the holes.  The pipes can't be less than 3" from any edge or bottom of the hole (code requirement).  I made use of long-lost math skills in trigonometry and geometry to calculate the exact lengths and positions to give a nice 25 degree angle from the bottom to the top rail.  It helped that my son has just graduated from high school so his math was a little fresher.  A Sawzall with a metal cutting blade was the best tool to cut the pipe.

Frames in place and braced

Time for another inspection

To arrange an inspection you call a local number and go through an automated system.  It's pretty efficient and if you call 24 hours in advance you can get a morning inspection for the next day.  I needed a "rough framing" inspection.   Mike, the not-so-ogre inspector arrived promptly at 9.30am and we walked up to the site.  He got his measuring tape out and announced that the west end of the frame was 7'4" when it was supposed to be 7'6".  No big deal I thought but he seemed concerned.  He then went to the other end and said "You are only 6 foot 6 here".  "Can't be" I thought, no way I could make such a big mistake, we checked it constantly.  "Are you sure?", I asked and he measured it again.  As he was holding his tape at the post his sunglasses fell off and landed at the bottom of the hole.  "Shit!", he exclaimed, followed by "Excuse my french".  I got some long wooden laths and he used them like chopsticks to fetch his glasses out of the 3'6" hole.  Took a couple of attempts.  After, embarrassingly,  remeasuring the distance between the posts he looked at me and said "You know, we're all good here".  The posts were the correct, 7'6" apart and he had misread his tape.  He wasn't concerned about the 2" discrepancy at the other end any more.  Maybe it was because he dropped his glasses, or maybe it really wasn't that big of a deal after all.

The pour

I was really nervous about how to get the concrete into the holes.  I had originally thought about buying bags of dry mix at Home Depot (I should have shares in that company) but a quick mental calculation told me that I would need over 200 of them!  10 holes, each is 2' in diameter and 3'6" deep.  Pi R Squared H.  Roughly 3 times 1 squared times 3.5, equals 10.5 cubic feet.  Times 10 = 105 cubic feet.  An 80 lb bag of concrete is 0.6 cubic feet (thanks Google) so that's about 175 bags.  And the holes were not exactly the correct size so I'd need a bunch more.  Even though I could do with the workout, there was no way I was carrying over 200 bags, each weighing 8 lbs up a steep slope.

Nope, the only way was to get it delivered and I reckoned it would be expensive.  I Googled it and found that the average is $97 for a cubic yard.  I needed about 5 cubic yards.  Not too bad.  I was more worried about getting it pumped though.  I had no idea how to organize a concrete truck and pump to be there at the same time, or even if a pump can be obtained that would be strong enough to raise the slurry up to the top of a 40' hill.

I bit the bullet and called up Pleasanton Concrete, a local delivery service.  They quoted me about $900 for 6 yards (they said I needed more than 5).  That was a little more than the national average but this is the Bay Area and we get ripped off left and right.  They were even able to arrange for a pumping guy to be there at the same time.  I would have to pay him separately.  That was easy.  I made sure to tell them that the site was 200' from the road and up a slope, a vertical distance of about 40'.  They didn't seem to be concerned.  Excellent, progress.

The day arrived and I took a vacation from work.  It was a Friday.  The pumping guy arrived early and we climbed the hill to the site.  Uh oh, his pump was way too small to lift the concrete this far. No problem, he called up his friend who had a bigger pump.  An hour later, his friend arrived with his huge pump and laid the rubber pipe up the hill.  The concrete truck arrived a little later and he got started.  He insisted on controlling the pipe himself.  He was able to stop the pump with a button attached to a radio on his belt - pretty nice.  He filled up all the holes in about 15 minutes and we had about a yard left over so I got him to pour it on the ground to make a path up a deck.

One thing I was worried about was how they were going to get all the concrete out of the pipe when we were done.  It turns out that they'd thought of that and they simply pump water up the pipe to push all the remaining concrete out.  No wastage at all, cool.

The pumping cost about $450 on top of the concrete delivery.

Pumping the concrete into the holes

Final framing

The concrete set overnight and the next day was Saturday.  I had already consumed almost every weekend for 2 months on this project and we were finally making progress.  I intended to spend that weekend getting the frame complete and ready for inspection.

Frame with braces removed

Early next morning I removed all the 2x4 braces and admired the straight and level frame.  It was pretty cool.  The instructions from IronRidge (the supplier for the mounting system) says that there are specific torque settings for each bolt.  The vertical frame pieces attach to the horizontal with some U-bolts and two set-screws.  The set screws need to be torqued to 240 in-lb while the bolts need 180 in-lb.  Unfortunately the Husky torque wrenches you can get at Home Depot can't do both torque settings so I had to buy two of them.  Bummer.  I torqued down all the bolts in the frame.  The installation manual for the IronRidge system is available online on the IronRidge web site.

The next task was to assemble the rails that support the panels themselves.  These are supplied as part of the kit and consist of 14' long extruded aluminum shaped pieces.  They attach to the horizontal framing member by strong U-bolts and screws.  The spacing of the rails isn't critical but I chose to place them evenly along the rail.  The panels were to placed in landscape mode, with the longer side being 1640mm long.  This meant that I placed the rails every 820mm (or as close as possible to it).

Panel rails attached every 820mm

Power optimizers

The system supplied by GoGreenSolar used SolarEdge power electronics.  This is a system of "power optimizers" and an 8kW inverter.  I originally wanted to install micro-inverters to avoid having a large, expensive inverter and a single point of failure, but Steve, the GoGreenSolar sales guy persuaded me that the combination of a single inverter and a power optimizer per panel was the state of the art and a better way to go.  After some research I agreed.  The advantage of the optimizer route is the simplicity of the system.  An inverter is a complex piece of power electronics and can go wrong.  Having 20 of them increases the chance of failure substantially.  An optimizer is really simple, basically a DC-to-DC converter.  The theory goes like this.

A solar panel array is like a bunch of batteries, all connected in series.  If you've ever connected some batteries in series you will know that if one of them is dead it affects all the others and you get no power from them.  A solar panel is a variable voltage battery, the more photons hitting it the more electrons are liberated from the silicon crystal to flow to your appliances.  Unless you have a perfect system there will be times when some of the panels receive more sunlight than others, and even nothing when a panel is be totally shaded.  This is like a dead battery in the sequence.  A power optimizer accommodates for this situation by adjusting the output voltage of the solar panel to match the others in the string thus keeping the whole array at it optimum output.  Pretty clever really.

I was going to connect all 20 panels in series, each panel producing about 37 volts.  Without the optimizers that would be 20 x 37 = 740 volts.  This is above the maximum voltage for the inverter so the optimizers also reduce the voltage (and boost the current) to keep the panel producing just the right voltage for the inverter.

The use of DC from the panels to the inverter also allow for the future installation of a Tesla PowerWall or equivalent for power storage, when they become economical enough for me to buy one.

Another feature of the optimizers is that they communicate with the inverter and know when it's safe to ramp up the voltage.  This is important because unless you are installing your panels at night there will be a voltage on their output wires, probably a very high voltage when they are wired in series.  This is dangerous.  The optimizers provide a nice feature that they only output 1V when they are inactive.  The inverter needs to tell them to power up when it's safe to do so.

The optimizers are small boxes, about 6" on square that bolt onto the rails with a star washer to ensure proper grounding.  The bolts are have a T-shaped head so they can be inserted into the top slot on the rail and rotated 90 degrees to provide a nice secure hold.  I placed one optimizer at roughly the center of where each panel would be.  To help with this I measured the panels and marked the rails with a Sharpie at the the future location of each panel.  It took about 20 minutes to install the optimizer and torque them down.

Optimizers attached to the rails

Wiring the inverter

With the 5 wires running down the trench from the site of the panels to the house it was time to connect them to the inverter.

A solar inverter is a piece of electronics that converts the DC voltage from the panels into an AC voltage suitable for driving your house.  My inverter was a single-phase grid-tie inverter.  This means that it produces a single alternating current at 60Hz and the phase of that current was matched to the phase of the supply from PG&E.  This means that it's safe to connect it to the power grid.  This might need some explanation.

In a supply of Alternating Current (or AC) the voltage is created by at the power station by rotating a magnet near a coil of wire.  The magnet induces the highest current in the coil as it passes closest to it.  When it is far away from it there is no current.  The magnet rotates at a constant 60 times a second producing a 60Hz changing electric current. Due to arrangement of the magnets and coils, the current alternates between a positive maximum and a negative maximum,  60 times each second.  The inverter takes a straightforward Direct Current (DC) from the panel array and converts it into an Alternating Current at 60Hz.  However there is one further factor to take into account.  The generators in the power station synchronized and arranged to all produce a maximum current at exactly the same time (and likewise for the minimum).  This ensures that each generator doesn't interfere with all the other generators (if one is generating +200V and another is generating -200V at the same time the result will be 0V).  The inverter needs to do the same thing.  If the grid power is at +240V it needs to be producing +240V at exactly the same time.  In other words, the waves of alternating voltage from the grid and from the inverter need to be phase.  The inverter has a special circuit to sense the grid phase and match its output.  This makes it a grid-tie inverter.

The input to the inverter is the DC output of the optimizers.  When the system is operating, this is around 400V at about 13A.  The output of the inverter is a 240V AC connected to the main service panel.  If the grid power goes off during the day, the inverter is still producing a high voltage and this presents a danger for anyone working on the grid.  For this reason, the inverter has an automatic safety cut off when it detects no grid power.

In addition, there needs to be a big manual AC disconnect switch on the wires between the inverter and main service panel.  This switch is not supplied in the kit and needs to be purchased separately.  I had to order one from Home Depot online and pick it up in the store.  This had to be done when the original PG&E paperwork was completed.  I bought one manufactured by GE TGN3321R.  It cost about $60.

There was a problem with getting the wires to the inverter, however.  The inverter was located on the wall of the house, close to the main service panel.  The wires in were in a trench that terminated at a concrete path.  I had to, somehow, get the wires under the path the along the wall to the inverter.  I knew, from the experience of trying to tunnel under the V-ditch that this was not going to be easy, or even possible, so I decided to cut the concrete.

For this job I needed a concrete saw.  Cresco had some of them so I rented one for 4 hours.  This is another awesomely dangerous machine.  It is a gas engine that drives a diamond blade at some horrendous RPMs.  It's so fast that the gyroscopic precession effects are very noticeable and quite dangerous.  More than once it was heading toward my leg as I raised the machine.  It also generates a lot of concrete dust and you don't want to be breathing that.  It was reasonably expensive to rent, about $130 for 4 hours.

I knew that there was no way I would be able to match the concrete color or pattern if I was to try to replace it after the job was done so I cut a slot wide enough to accommodate some pavers that would look much better than a patched path.

Cutting the concrete took a couple of hours and then there was an additional 4 hours of work with sledge hammer, a crowbar and an air chisel to remove the path segment down to the dirt.  It was very heavy, blister generating work, lucky that my son wanted his workout for the day.

After removing the corner of a retaining well and digging the remaining foot or so of the trench, I had a way to get the conduit over to the wall of the house.  I used 1" Schedule 80 conduit to run the wires under what was the concrete path, up the wall, round a chimney and over to the location where I would attach the inverter.

End of the trench

Conduit up the wall

The next task was to attach the inverter and AC disconnect to the wall.  The inspector told me that nothing was allowed within 3 feet of the gas supply pipe so I chose a location that was outside the 3 foot radius and found a cross brace that would support the weight of the inverter.  Two lag bolts held the mounting bracket to the wall and the inverter was slotted over the bracket and secured with a couple of screws.  I didn't know where the AC disconnect was supposed to be located so I picked a location and attached it temporarily.  I'd have to move this later.

Inverter and AC Disconnect switch (in the wrong place)

Connecting the DC wires to the inverter was easy.  Cut them to length, strip about half an inch of insulation and insert a small screwdriver into the terminal block in the inverter.  While the screwdriver depressed the catch, push the exposed copper into the terminal and release the screwdriver.  In the above photo, the DC terminal is on the left side of the inverter.  There was enough space for the 5 wires.  The ground connected to a ground bar at the bottom.

One final thing to do was to install a bonding ground wire on the panel support frame.  This is a #6 solid bare copper wire that is attached using a WEEB grounding lug on each rail.  I had assumed that this connected to the ground wire running down the trench to the inverter but the inspector told me that it was not connected and was purely to ensure an even electrical potential across the frame.  I was doubtful because the plans showed it connected to the ground, but I didn't want to argue and didn't want to pay another $170 for a plan change so I kept mum.

The thing with WEEBs to be careful of is that they are single use only.  The purpose of a WEEB (still like saying that word), is to penetrate the anodized coating on the aluminum rails and make a good electrical contact.  They are basically a piece of steel that has been stamped out into a special shape with points that stick out and punch through the coating when enough force is applied.  The kit doesn't provide enough of them to account for mistakes so care needs to be be taken not to torque them down until you are sure they are in the right position.

Panel installation

After another inspection it was time to install the panels themselves.  I had bought panels manufactured by GigaWatt (who, incidentally happen to own GoGreenSolar.com).  They are self-rated at 255W per panel, although official ratings are a little lower.  They measure 1640mm by 992mm (about 5' by 3') and have a blue sheen and a black frame.  They are polysilicon panels and are therefore cheaper than the more efficient monosilicon models.  Polysilicon panels consist of thousands of small silicon crystals whereas in monosilicon construction, each cell is a slice from a single silicon crystal.  Monosilicon panels are about 25% efficient versus 20% for polysilicon.  However the polysilicon (mostly made in China) are about half the price.

There were 20 panels and they were in their boxes at the bottom of the hill.  It took all of us to carry them up the hill, two people taking one panel at a time.  The panels are attached to the rails using two different types of clamps.  The panels are arranged in a rectangle and end clamps are bolted to the rails at the top and bottom.  Between the panels, mid clamps are used.  Each clamp uses the same T-bolt that attached the optimizers to the rails.  Some of the mid clamps use WEEBs to provide a good ground contact.

We started at the bottom by running a string along the frame to get a nice straight line.  Then we attached the middle panel on the bottom row, working both left and right.  There were 4 rows of 5 panels.

One snag we hit was during the installation of the mid clamps.  It was hard to reach over to tighten the screws and more than once the T-bolt didn't seat properly in the rail and therefore wasn't attached when torqued down.  This meant that, while it looked secure, the panel was not bolted to the frame and was unsafe.  When installing the panels, we had to make sure that each T-bolt was properly inserted and rotated before torquing them down.  It was easy to spot the ones that were wrong - they stuck up a little higher above the panel surface.  We had to use a small stool and a ladder to reach the mid clamps of the north end of the array as it was raised about 8 feet off the ground.

Also, we had to remove and reorient some panels because we discovered that the wires didn't reach the optimizer.  After a few of these initial mistakes, all the panels were installed and torqued down, a couple of hours of work.

First two panels go in

Mid clamp and WEEB

All panels done

Final wiring

The panels were all properly attached to the frame and now it was time to wire them up.  Each panel attached to the input of its optimizer using MC4 connectors that snap together easily but need a tool to detach.  One output from each optimizer is connected to the next optimizer in the row and the rows are chained together to form one big loop.  One end of the loop is negative and the other positive. Since the optimizers are not activated, the would be 1V per optimizer (20V for this array).

The kit contained 2 60' lengths of #10 PV wire with MC4 connectors.  It turned out that I only needed one of these and had to cut it.  The other wire will for future expansion.  Both ends of the panel string were pulled through some 3/4" PVC conduit to a junction box attached to a post at the top end of the trench.  Inside the junction box the positive wire was connected to one of the red wires and the negative to the black corresponding to the red-black pair.  One tip here is to use different color electrical tape to pair the red and black after they were run down the trench.  The other red and black wires were capped off with a wire nut and left for future use.

The wires were connecting using large wire nuts (blue color) but the ground was attached to the junction box using grounding lug.  I found a voltmeter very helpful here because the wires coming from the panels are not color coded and they had to be connected in the correct polarity (I don't know if the inverter will be damaged or not if it's wrong though).

So much for the panel-end wiring, now for the inverter.

I was told by the inspector that I couldn't put anything within 3 feet of the gas inlet pipe.  I had thought that this meant 3 feet radius, but it actually meant 3 feet horizontal and 10 feet vertically of the inlet.  The AC disconnect switch was in the wrong place and had to be moved.  I moved it down to the bottom right of the inverter and used EMT (metal) conduit to run the 4 AC wires to it from the inverter.  The wires colors are:

• Green - ground
• White - neutral
• Red - hot
• Black - hot

The voltage between the red and black wires is 240V.  Between the red and white is 120V, likewise between the black and white.  The red, black and white wires connect from the like-colored terminals in the inverter to three terminals inside the AC disconnect switch.  The ground wire attaches to the case of the switch (it's metal).

AC Disconnect wiring (ground not connected yet)

Both the main service panel and inverter/AC disconnect switch were located on the garage wall so there was plenty of space to run the EMT conduit inside the garage.  I punched a hole in the stucco and ran 1.25" EMT conduit through from the AC disconnect switch into the garage.  I needed to buy a "hub" to attach to the top of the AC disconnect switch.

From the location of the AC disconnect I ran the conduit over to the back of the main service panel and punched out one of the holes to allow access to the internals.  The conduit was attached using a big nut and the wires pulled through to the main service panel.

I had originally intended to hire an electrician to wire up the main service panel but when I removed the front cover and took a look I realized that it was easy to do.  I had never seen inside one before and had assumed it was ripe with open electrical conductors ready to kill me for just looking. However, it's not that scary.  The main wires come into it from the meter and are huge aluminum beasts.  There are 3 of them, one neutral and two hot.  The neutral connects to a neutral bar (a metal bar with holes and screws), as does a ground wire going to a metal rod buried into the earth.  The hot wires go to the main breaker under a plastic protective shield.  The only hot metal in the panel were two busses that are recessed deep at the back and connect to the other side of the main breaker.  It would be hard to touch them even if you wanted to.  I decided that this wasn't rocket science and I could do it myself.

After running all the wire from the AC disconnect switch, into the garage and out into the main service panel, I had a look at how to connect them up.  The neutral bar was almost full and there were no holes big enough to take the #6 neutral wire.  I did some research and found that you could buy neutral lugs at Home Depot that connect to two adjacent small holes but have a connector large enough for my wire.  I bought two of them for a few bucks each (one for the neutral and one for ground).  I also bought a 20A two-pole circuit breaker for about $10.  Incidentally, a shout out to Gary in the San Ramon Home Depot store.  He is an electrician by trade and is very knowledgeable about what to buy and how to use it.  Thanks Gary.

After switching off the main breaker I connected the neutral and ground to the neutral bar using the new neutral lugs and the red and black wires to the new circuit breaker.  I pressed the circuit breaker into its seating and pushed it onto the hot busses.  Main power back on.  Easy.

Neutral bar with no space for #6 wires

AC Disconnect wired up

New 20A circuit breaker

One final thing was to attach lots of red warning stickers all over the system.  There were 4 at the main service panel, 3 on the AC disconnect switch and one every 10 feet of any exposed conduit.

Main service panel stickers

AC disconnect stickers

One of these every 10 feet

Cleanup

Although it was almost complete, there was still an open trench and a wide swath of concrete missing on the path.  We filled in the trench in about an hour (much easier than digging it) and covered the slot in the concrete with pavers (held in place with 4 bags of ready mix concrete).  The pavers turned out to be a great idea because it looks like a natural separator on the path and we didn't have to try to match the concrete and make it look good.

Wall rebuilt and concrete repaired using pavers

Final inspection

During my rough electrical inspection, Mike had told me that the next one was going to the be final.  He wanted to see it all powered up and working.  I had already connected the inverter to the main service panel but had left the AC switched off.  It was time to commission the system and switch it on.  I was aware that I was not allowed to operate it (generate power into the grid) without first getting permission from PG&E so I was reluctant to switch on the new circuit breaker, however this inverter requires 240V AC to operate (a safety feature - it won't work if there is no grid power).  I powered on the inverter and it booted up.  The first thing to do was comission the optimizers.  This involved holding a switch for about 10 seconds and then letting to.  The inverter communicated with the optimizers and eventually said it was connected successfully.  However the display showed that it only had communication with 19 of them (but could see 20 of them).  This worried me.  Had one of the optimizers failed?  It turned out that it can take up to 10 minutes to connect to them all and receive their telemetry.

The inverter finally showed that it was generating 2.8kW of power and I looked at the PG&E SmartMeter.  It showed that it was receiving about 1.5kW.   I was producing power.  I switched the inverter off so as not the provoke the wrath of the omniscient public utility and ordered a final inspection for Monday morning.

Mike arrived on time as usual and took a look at the work.  All good.  However, he did have to check our smoke and CO alarms in the house so he, apologetically, entered the house and tested them all. Unfortunately, 3 of them were not producing enough of an alarm sound so he gave me a pass on the solar but couldn't sign off until the smoke alarms were replaced.  I had to run down to Orchard Supply Hardware and buy them for about $30 each.  You have to use 10-year battery alarms now, no more replacing 9V batteries.

The next day he came back and signed off on the whole thing.  I immediately scanned and emailed the permit and signed approval sheet to Joy at GoGreenSolar and an hour later I received my approval to operate from PG&E.  It was supposed to be 5 to 10 days, but apparently they have sped things up a bit.

All done.

Relax with a nice glass of wine

Total cost, including installation

So what did this cost?  A couple of hours with my multiple Home Depot receipts (about 30 of them) told me that I paid a total of about $14063 for the system.  The breakdown is (roughly):

• Panels, Inverter, Optimizers and rails: $9,894
• Framing pipes: $663
• Concrete delivery: $948
• Concrete pumping: $430
• Tools, hardware, etc: $500
• PVC conduit: $347
• Wire: $500
• Permit: $450
• Tool rental: $200
• AC disconnect: $64

But, there is (still) a 30% federal tax credit for the total cost of the installation so that gives me about $4000 back in tax breaks.  Factoring that in, a 5.1kW system will have cost me about $10000.  At $250 per month in electric charges, that works out at 3.3 years to pay back the cost.  Remember to keep all your receipt in case you get audited.

Operational

After about 3 months, the system was finally up and running.  I had connected the included monitoring system (a Zigbee radio on the inverter and a box that connects to the house ethernet). This allows me to see the power being generated by the system using a series of charts.  It even shows the output from each panel separately.  It's pretty good.  They even provide a REST API for those programmers among us who what to do their own monitoring.

This doesn't tell how much you are using net.  When you are not generating power you are buying it from PG&E at retail cost.  Here's the catch.  The power you generate goes into the grid where they sell it at $0.44 per kWh but pay you $0.04.  At the end of the year you get a "true up" bill.  If you have used more than you generated throughout the year you own them the difference.  If you generated more than you used they don't pay you anything.  Apparently this is legal.  So you should size your system so that you use exactly what you generate.  If you see that you are generating more than you are using, switch on your air conditioner!

Summary output (operation since Sept 7th)

Today's output per panel (early afternoon)

So far, in September 2016 the system is producing around 25 kWh per day.

Materials and Vendors

Here's all the things you will need to complete your project.  I already had a lot of tools from previous assorted projects around the house so I didn't need to buy much.  Anyway, tools are cheap when it boils down to it.

• Ground mount solar kit
• 2" Schedule 40 Galvanized Steel pipes
• Auger to dig foundation holes (rental)
• Spade/shovel, post hole digger, bucket, and rope for hole excavation
• Measuring tape, string and marker paint
• 2x4 boards to brace frame
• Laths for bracing
• Wood screws
• Spirit level and compass
• Hammer
• Sharpie markers
• 3" dobies
• 2400 PSI pea gravel concrete for foundations (delivery and pumping)
• Approved AC disconnect switch, grounding lug and screw
• PVC Schedule 80 conduit, connectors, glue, brackets
• #6 green THWN-2 ground wire
• #8 red and black THWN-2 wire (for DC side)
• #6 red, black and white THWN-2 wire (for AC side)
• #6 solid bare copper for bonding
• Junction box, wire nuts, ground lug
• EMT conduit, connectors, corners, support brackets
• Neutral lugs (optional)
• Dual pole circuit breaker
• Torque wrench (or two)
• Socket set
• Reciprocating saw for cutting pipes
• Blow torch for bending PVC pipe
• Lag bolts for attaching inverter to wall
• Wire strippers and cutters
• Voltmeter

I have been very happy with the service I received from all my vendors.  I'm listing them here to maybe steer some business their way.  I live in the San Francisco Bay Area so if you want some recommended vendors...

• GoGreenSolar.com, Placentia, CA
• Pleasanton Ready Mix Concrete, Pleasanton, CA
• Maxx Metals, San Carlos, CA
• Nassau Electrical, New York
• Martinez Concrete Pumping, Concord, CA
• Cresco Tool Rental, Danville, CA
• Home Depot, San Ramon, CA