Grid-Tied PV For $1.25 Per Watt


Inside this Article

A build-it-yourself, adjustable ground-mounted rack and DIY installation provided deep savings on a PV system for this Wisconsin family.
The author got his start with renewable energy by building wind turbines with his father. Now he shares wind and solar projects with his own son.
The author got his start with renewable energy by building wind turbines with his father. Now he shares wind and solar projects with his own son.
The 6.1 kW array of Helios Solar Works PV modules (shown) was sized to maximize the Wisconsin rebate and match the ideal voltage for peak efficiency from the Power-One Aurora 6000 inverter.
The 6.1 kW array of Helios Solar Works PV modules was sized to maximize the Wisconsin rebate and match the ideal voltage for peak efficiency from the Power-One Aurora 6000 inverter (shown).
Once the footing locations were laid out, a post-hole digger with an 18-inch-diameter auger drilled the three holes for the I-beam footings.
With the help of friends, levels, ladders, stakes, and 2-by-4 supports, the I-beams were centered in the footing holes and leveled.
The two pivot pipe/pillow block assemblies were set up beforehand to their correct lengths and then used as fixtures to properly space the I-beams.
The finished rack assembly, ready for paint before the modules are mounted.
Modules were positioned accurately before the mounting-hole locations were transfer-marked onto 1-by-4 wooden stiffeners and mounting holes were drilled. Stainless steel hardware was used to secure the modules to the wooden frame.
Each rack’s tilt angle is adjusted via a set of metal arms. This tilt feature enables the array to produce 4.6% more energy on an annual basis.
Willi’s engineering background enabled him to design a custom tiltable rack for his family’s PV array, saving them money upfront and reducing the system’s payback period.
In its first year of operation, the PV system has produced within 1% of the original estimates.

A build-it-yourself, adjustable ground-mounted rack and DIY installation provided deep savings on a PV system for this Wisconsin family.

In 2006, I refurbished a classic Jacobs Wind Electric wind turbine and installed it on our family’s property in Merton, Wisconsin. The “Jake” produces an average of 110 kWh per month, offsetting about one-third of our household’s total electricity use on a yearly basis. However, in the summer months, when winds average 8 mph, the Jake was only generating about 40 kWh per month. That’s when I started thinking about installing a PV system to boost our renewable energy production.

In 2011, the prices of PV modules were continuing to drop. I began researching system components, incentives, and permitting requirements. I set an aggressive goal of designing and self-installing an adjustable, ground-mounted PV system for $1 per watt (after incentives), and began my PV project in earnest.

Choosing a Site, Capturing Incentives

A rooftop array was ruled out for several reasons. First, there was the shade caused by a 70-foot-tall tree near the west side of the house, which severely limited the available solar window. But we were loath to cut it down—the summer shade it provides helps reduce our air-conditioning loads. The largest roof sections face east and west, and while not a deal-breaker, orienting the array to meet Wisconsin’s Focus on Energy (FoE) program rebate requirements, which states that modules must be installed within 45° of due south, would have meant mounting them in an aesthetically unpleasing way.

Fortunately, although trees border our property, there was still plenty of room on our 1.3 acres to find a suitable solar window for a ground-mounted system and meet the town’s minimum 20-foot setback requirements (see “Finding True South” sidebar). The window wasn’t “perfect”—my analysis showed that some shading of the array would occur in December and January from maple trees that lie just outside of our south property line—but that energy loss could be offset by adjusting the array’s tilt monthly (see “Optimizing the System”).

Once we’d determined that there was a good solar window, we examined our electricity loads (see “Electrical Loads” table) to arrive at a reasonable PV system size. According to our utility bills, our household consumes an average of 321.5 kWh of electricity per month, or 3,858 kWh per year, which costs us about $630. (We use natural gas for our forced-air furnace, water heater, oven, and cooktop. We also have two wood heaters, both of which are used often in the winter.) But besides meeting our existing electrical loads, we also wanted the system to generate enough electricity to recharge a plug-in hybrid vehicle or electric vehicle in the future.

Wisconsin’s FoE program offered a cash-back rebate (up to $2,400) for grid-tied PV systems, and we could also take the 30% federal tax credit. Balancing these economic and energy goals, I arrived at a 6.1 kW system, which would max out the FoE rebate and provide extra electricity for an EV. This system size would also maximize the inverter’s energy-conversion efficiency and stay within the weight parameters of the wooden rack structure I had in mind.

On January 2, 2013, I applied for Wisconsin’s FoE Renewable Rewards program. To be eligible for the program, I had to retain the services of a PV installer to oversee and sign off on the installation. I hired Trang Donovan, who provided me with design reviews, recommendations, and a final system inspection for compliance to the National Electrical Code.

Solar energy systems are eligible for a federal tax credit of 30% of the system cost, with no upper limit, until December 31, 2016. I also applied for solar renewable energy credits (sRECs) through Ethos Renewable Power, which would pay $13 per megawatt-hour (MWh) generated.

After the Rewards program appli­cation was approved in February 2013, I began sourcing PV system components. The $1-per-watt goal was an aggressive cost target set to achieve a return on investment (ROI) of at least 18%.

Optimizing the System

I implemented several strategies to make the most of every solar-generated electron at my site.

Adjustable, ground-mounted rack. Although mounting the PV array at a fixed tilt is the most straightforward strategy (and the least amount of work, since you don’t have to adjust the rack), it incurs energy penalties. The sun changes its angle from the horizon, being higher in summer than winter, so annual energy output can be increased by seasonally adjusting module tilt. From the sun-path chart I generated (, I determined an array tilt to maximize the system’s energy output for each month. I’d need to be able to adjust the array tilt from a minimum of 19.6° in June to a maximum of 66.5° in December. Over the course of a year, I calculated that the monthly tilt adjustment would yield about 4.6% more energy compared to a fixed array (see “Estimated Production” table).

In snowy regions like Wisconsin, a steeply tilted array sheds snow more quickly, which is important for maximizing the system’s overall production. Following a 4-inch snowstorm, for example, our steeply tilted array is snow-free the following sunny day, while I’ve observed that it can take more than a week for the snow to melt from a fixed-tilt, ground-mounted PV array that’s on a church property 1.5 miles away. 

In the summer, a ground-mounted system has better airflow around the array, which means lower module-cell temperatures and higher energy production compared to a similarly sized roof-mounted system. Since PV modules have a negative temperature coefficient, keeping them cooler increases their power output. For example, my modules have a temperature coefficient of -0.41% per degree Celsius (i.e., for every degree above 25°C, the PV modules’ power output is derated by 0.41%). Roof-mounted PV modules typically run 25°C or more above ambient temperature, while ground-mounted modules typically run slightly cooler (i.e., my estimate is 22°C above ambient). The annual average high temperature for my region is 13.5°C. For a roof-mounted system, the production hit due to heat would be 338 W [6,100 W × -0.41%/°C × (13.5°C + 25°C) - 25°C]. With a ground-mounted array, the average power decrease would be 263 W [6,100 W × -0.41%/°C × (13.5°C + 22°C) - 25°C]. So in my case, a ground-mounted PV system results in 75 W (338 W – 263 W) more power output per peak sun-hour of operation. This translates into an additional 124 kWh per year (4.52 sun-hours/day × 0.075 kW × 365 days/yr.).

No batteries, a high-efficiency inverter, and high-wattage modules. I chose a batteryless grid-tied system for several reasons:

  • It minimizes system cost (batteries are expensive);
  • It increases overall system efficiency (batteries and charge controller inefficiencies reduce the system efficiency by 5% to 10%);
  • Our utility’s electricity delivery is very reliable, so battery backup would rarely be needed.

There are many batteryless grid-tied inverter choices, but since I was already satisfied with the Power-One 4.2 kW Aurora transformerless inverter used with my Jake, I decided on an Aurora (Power-One) 6 kW inverter for our PV system. The 6 kW inverter can process two PV strings with independent maximum power point tracking, and has a CEC-rated efficiency of 96.5%.

I chose Helios Solar Works 7T2 (305 W) modules for several reasons. First, I wanted to keep my hard-earned dollars in the United States, and these modules were manufactured in Milwaukee—close to home. I could rent a trailer for $20 and drive to the Helios Solar Works factory (a mere 25 minutes away) to pick up the 20 PV modules, saving significantly on shipping costs. Second, putting 10 of the PV modules in series hit the Aurora 6 kW inverter’s voltage “sweet spot.” And, third, dimensionally, these modules allowed for a reasonable rack wooden header length that would minimize module deflections caused by wind and snow loading.

Maximizing PV output. The voltage of PV modules in series is additive, but the string’s current is limited by the lowest module current (Imp)—so it is best to place all the modules with the highest Imp in the same string. Using the manufacturer-provided data measured for each module, I methodically went through the list to select modules to string together. This allowed each series array to perform within 0.3% to 0.4% of their theoretical maximum power output.

Minimizing electrical losses. Properly sizing PV electrical conductors can decrease power loss from voltage drop. Generally, the total DC voltage drop should be less than 2%. I used #10 copper PV wire in the PV output circuit, which results in only a 0.7% loss. A tolerable AC voltage drop (inverter output circuit) is between 1% and 1.5% for grid-tied systems. For the inverter’s maximum output of 25 amps, the AC voltage drop was 0.7% using #2 AWG aluminum wire.

Build-It-Yourself Rack

I knew I could economize and improve my system’s return on investment by building a custom rack structure using locally available, relatively inexpensive lumber and readily available metal components. Had I purchased a manufactured ground-mount rack, I would not have had any chance of achieving my $1-per-watt goal. The most similar manufactured option was a metal rack (about $4,892, with shipping). Besides being more than twice the cost of a home-built rack, this rack would have been much bigger (46 lineal feet versus 33), subjecting the array to more shade because of its length, and was not as adjustable, as it only went to 50°—I wanted my rack to tilt to 66.5°.

The most complex part of the custom-rack design process was calculating loads (see “Design Loads” sidebar). I also needed to create a simple yet durable tilt method that would accommodate some design imperfections, since nothing would be dimensionally “perfect.” Pillow blocks—bearings used to provide support while allowing rotation—used with 2-inch-diameter, schedule-40 pipes, would allow each of the roughly 1,500-pound rack assemblies to be adjusted. The additional cost for this method was $360; it will likely be recovered in about seven years when assuming the additional 4.6% output that results from being able to adjust the array monthly. During the array’s expected 25-year lifetime, the tilting feature has an ROI of 14.3%—well worth the extra design effort and expense.

The racks that hold the PV modules each consist of two 2-by-12 headers mounted onto a 2-inch-diameter pivot pipe. Six 2-by-12 joists sit on joist hangers between the headers, and were glued and screwed together. Eight 1-by-4 stiffeners were glued and screwed to the joists. Joints were sealed and the counter-bored lag screws were topped with silicone caulk before the entire rack was coated with deck stain to protect it from degradation.

The support structure had to be robust to support the two wooden racks. The horizontal force of the wind on the center I-beam support was calculated to be 3,470 pounds. A 4-by-8 inch I-beam made from ASTM A992/A572 (grade 50) steel provided a two-to-one safety factor. The 18-inch-wide, 4-foot-deep concrete footings were also designed to handle this wind loading with sufficient margin, and were excavated below the 4-foot frost line to ensure that the structure would not shift from freezing and thawing. Rebar in the bored holes increased the loading capability.

Both wooden racks were pre-assembled to ensure proper fit, then taken apart for assembly on the tilt structure. Before mounting the PV modules, a strip of aluminum-foil tape was bonded to the top of each 1-by-4 stiffener. Each module was mounted to the wood frame using 5/16 stainless steel hardware through four of the specified module mounting holes. Modules were spaced 1/4 inch apart. A #6 bare, stranded copper wire serves as an equipment-grounding conductor (EGC); each module was connected to the EGC with a WEEB ground lug. The 10 modules in each string were connected in series using their MC4 quick-connect plugs.

The inverter was installed in the existing wind turbine inverter shed. The shed already had 240 VAC and a subpanel with a spare circuit breaker location. Mounting the inverter in the shed gave a short PV output circuit cable run (approx. 58 ft.) and protection from the weather, animals, and vandalism.

Economics & Performance

My original target for the PV system was $6,100 (or $1 per watt), after incentives. The final cost came in at $7,661 (or $1.25/watt)—not too far off-target. The tilting feature has been working flawlessly. Adjusting the two arrays takes less than five minutes; I actually look forward to it, as I know tilting increases our PV array’s monthly electrical output. Our grid-tied system is net-metered with a monthly true-up. Rather than paying electric bills, we are now receiving monthly checks from the utility. In its first full 12 months, our grid-tied PV system generated 8,618 kWh—within 1% of that predicted by PVWatts. In that time, the system has earned $1,286 [($0.136207/kWh × 8,618 kWh) + $13/MWh × 8.618 MWh)] worth of electricity, resulting in a system payback of about six years. Under our grandfathered net-metering agreement with the utility, we are paid at the residential retail electricity rate for any surplus electricity that our PV system produces each month. If the earned credit for our PV-produced electricity is less than $25, it is carried over to the next bill. So far, though, we’ve been receiving monthly checks from the utility.


Comments (38)

Timothy Heywood's picture

Finally finished my version of this design, for which I give kudos to Willi for the inspiration and the design pointers. Started at Memorial Day and hoped to be done in early August. A busy summer and work travel pushed it out past Labor Day. Now done and producing as expected. Great family project! Here are some pictures:

Willi Hampel_2's picture


Your PV system looks great - glad to hear it is producing power. My wife loves the picture of your son in the hole - she took one just like it of our son! Thanks for sharing the photos.


Timothy Heywood's picture

Thanks for the kind words. The kids loved digging the holes. I considered renting equipment, but they jumped right on it and dug the three holes to spec in no time. It helped that we had our self-propelled 48" depth reference (Alex) ready at all times! If you're ever near Rochester, NY look us up and I'll show off the system. And I'm going to do a little writeup for HP soon describing the project - just have to do the final tally on costs. Expect very similar to yours per watt.

Willi Hampel_2's picture

I'll make it a point to stop over if I'm ever in the Rochester, NY area; thanks for the invite. Looking forward to reading your upcoming HP write-up.

Back in April of this year, we purchased a used 2013 Nissan LEAF EV. We've put almost 7,500 miles on the car in 6 months and just love driving it. So now, rather than pumping all that extra PV generated electricity back into the electric grid, approx. 280kWHrs/month goes into the LEAF instead. The LEAF replaced an old ICE vehicle which averaged about 35 mpg. Since we're making double the price of electricity (present electricity cost = $0.13/kWHr) by using it in the LEAF vs. sending it back into the grid, our PV system's ROI (Return On Investment) actually improves! Here's how I calculate this result (based on 5 months of our actual LEAF's efficiency as well as actual local average regular gasoline prices):

Equivalent Electricity Cost = (Cost of Gasoline / IC Car Fuel Efficiency) x LEAF Efficiency

Equivalent Electricity Cost = ($2.30/gal / 35 miles/gal) x 4.1 miles/kWHr = $0.27/kWHr

So the higher gasoline prices go, the faster our PV system pays for itself.

Andreas Dutschke's picture

When it comes to moving the array, could you not use some sort of pulley system to move it? You can buy 2 ton units for very little.
One on each side, controlled from the centre.

Michael Welch's picture
You could, but that requires more attention than most people are willing to give. For example, if you moved the array to capture the sun first thing in the morning, then for whatever reason don't move it during the day, then your late day output will be much lower than it could have been, and your total output for the day would likely be less than if the array were fixed, facing south.
kipcanderson's picture

Great project!

I will be using it as the basis for a single axis azimuth tracking installation.

Willi Hampel_2's picture

Sounds great - please send us photos once you have completed your installation!

Timothy Heywood's picture

I am planning on a similar size ground mounted array installation this spring/summer (moving my little 1.5kW array from the roof to the ground and expanding to about 5kW). This innovative design seems the best I've seen, especially the tilt capability since in Western NY the efficiency gain and snow shedding benefit are similar to the author's locale. If the author is still monitoring this thread, I'm curious after living with it through a couple of seasons he has any thoughts on enhancements, things he wished he'd done differently, etc. Or if anybody else who has built a similar system had any feedback on the mounting. Thanks in advance!

Willi Hampel_2's picture

Timothy, thanks for the excellent question. Yes, I would likely change one aspect of the design: it takes two people to tilt the structure (note: I am able to do it by myself with some counterweights added/removed from the structure, but this method takes significantly longer than with the 2-person method; see option #3 below). It's a 2-person job because the C.G. (Center-of-Gravity) of the entire tiltable assembly is above the tilt pivot point, causing a moment (i.e. the turning effect of a force) which needs to be counteracted by the second person during the tilt adjustment process.

I positioned the pivot point on the 2" x 12" header's neutral axis (the axis through a beam where the stress is zero, that is, there is neither compression nor tension) in order to minimize the stresses in the wooden beam. However, the ten PV modules weigh 572lbs (per tiltable array) and they are mounted on top of the rack assembly; this causes the C.G. of the structure to be above the pivot point which causes the turning moment. There are three ways I thought of to resolve/minimize this turning moment:

1) shift the tilt axis up slightly (i.e. closer to the PV modules) to make the entire tilt structure's C.G. align with tilt pivot point.
2) add 572lbs of counterweights to the bottom side of the wooden tilt structure to counteract the PV module's weight.
3) add/remove counterweights (10lbs to 40lbs, depending on the tilt angle) during the tilt process to minimize the moment.

So if I had to do it all over again, I would choose option # 1 above and make the tilting process a one-person job. Fortunately for me, my wife or son are always happy to help with this simple 5-minute job!

Good luck with your upcoming ground mounted solar project!

Timothy Heywood's picture


Thanks for the great input. As a electrical engineer with not much mechanical aptitude, I definitely wouldn't have thought of that. Been a while since Statics & Dynamics class. In moving the tilt axis up some, would you reinforce the 2x12 more (looks like you're using some kind of plate/collar for the penetration as it is from one of the pictures)? Is the pivot pipe diameter you used around 1 1/2"? Since the pipe is only bearing load between the 2x12 and the pillow block, I guess the important thing is that the pillow block is rated for the load, with any reasonable pipe size. Haven't looked into steel suppliers around here, but curious if your supplier added the top plates for pillow block mounting or you had that done separately or yourself (I'm no welder).

I'm hoping to get my design finalized before mid-June so I can hopefully do the install by mid-July and not miss too much summer sun! Thanks again, Tim

Willi Hampel_2's picture


Yes, I would definitely reinforce the 2 X 12's, when shifting the tilt axis up, with a much larger plate than I used on my original "pivot-centered" design.

I used a 2" structural pipe (2-3/8" actual outer diameter) but had a friend weld a steel transition piece onto each end in order to mount the pipe to each of the 1.5" inner diameter pillow blocks. Each pillow block has a radial static load rating of over 4000 lbs. I also had a friend weld the pillow block steel mounting top plate onto each steel I-beam.

Send us some photos of your design once it's up and running.


Timothy Heywood's picture

That was helpful. When I was looking at different pillow block sizes, nothing seemed to line up with structural pipe OD's so the transition piece on each end explains it. If I may continue to impose, there are just a couple of final details on your rotation design I want to make sure I understand: I assume the pipe runs for each rack are separate and there are two pillow blocks side by side on the center I-beam? And can you elaborate a bit on the process of getting the headers on the pipe and then getting the pipe ends into the pillow blocks (before reassembling the rack in place). I can't quite picture the sequence, which makes me think I might be missing something. And the plate on the header 2x12 that the pipe goes through is just a metal plate with an appropriate hole size cut out? Thanks again, and I'll post a link to pictures once we've finished!

Willi Hampel_2's picture


Correct, there are two separate pipes, one for supporting each tiltable rack assembly, and there are two pillow blocks side-by-side on the center I-beam.

Here's how I mounted the 2 x 12 headers onto the pipe (starting point: pipe and the two pillow blocks mounted to the I-beams):
1) remove one pillow block from its shaft and rest the shaft of the pipe on top of a small 2 x 4 placed on the far I-beam top plate.
2) using a longer 2 x 4 (i.e. from the ground-to-pipe in length; also cut a v-notch or half-circle in 2 x 4 so pipe doesn't slide off), lift up the pipe high enough to slide the first 2 x 12 header onto the pipe. Slide 2 x 12 all the way to the center I-beam support.
3) slide the second 2 x 12 header onto the pipe and place in by the far I-beam support.
4) Re-attach pillow block to correct dimension on the shaft and Loctite pillow block attachment bolts to the I-beam top plate.
5) Position the center I-beam support 2 x 12 header to its proper dimension from the center I-beam support pillow block and attach the shaft locking plate.

This shaft locking plate has the pipe O.D. hole size cut through it. The shaft locking plate is actually two pieces (split through the center of the hole) that are bolted back together so that this plate actually locks onto the pipe AND bolts onto the 2 x 12 header to prevent the 2 x 12 header (really the entire wooden tilt structure) from shifting/rotating relative to the pipe.

Hope this helps and I will look forward to seeing your photos.


ksvik's picture


Inspiring work for all us extreme diy'ers. What kind of fun would it be to shell out for an off the shelf setup?? :)

I'm having a hard time finding any kind of "spring clamp plate" or split shaft collar like you used. Where did you source yours from? If I'm able to weld in the field do you see any problem with welding a plate to the pipe rather than having a clamp? Does the removable spring clamp have advantages?

Also, did you consider using 6"-8" SCH 40 pipe instead of i-beams? Seems like they're used for single top of pole mounts so should have the structural integrity. I may be able to get my hands on those easier than the I beams. As far as I beam sizing, what web dimensions are your beams or what per ft weight? Are they true I beams or h beams?

Thanks so much for writing this up,

Willi Hampel_2's picture


I custom designed the pipe-locking plates and had them manufactured by a local machine shop. The four pipe-locking plates are all identical and relatively simple to make (manufactured from 3" wide x 3.5" long x 0.5" thick 6061-T651 aluminum bar stock):
1) machine a 2-3/8" diameter hole through the plate (centered on the 3" x 3.5" side of plate) - hole used to clamp onto pivot pipe.
2) machine four equally spaced 0.323" diameter thru holes on a 3.281" diameter bolt circle (centered w.r.t. the 2-3/8" diameter hole) - holes used for 5/16" dia. x 3" long lag bolts screwed into 2 x 12 header.
3) drill two 1/4" dia holes through the 0.5" x 3.5" surface, spaced 3" apart and centered w.r.t. the 2-3/8" diameter hole) - these holes enable the clamping force to be exerted onto the pivot pipe.
4) saw the plate in half (parallel to the 3.5" surface) - can now clamp both halves of the pipe-locking plate onto pivot pipe using two 1/4-20 X 3.5" long SHCS.

I'm not a big fan of welding this type of locking plate onto the pivot pipe in the field for the following reasons:
1) My concern is that if not properly done, welding could weaken the pivot pipe (which is supporting thousands of pounds of weight)
2) One should really assemble the entire wooden tilt structure, square it up, and position it properly before locking it in place with this plate. Welding the locking plate too close to the 2 x 12 headers could cause a fire/burn the surface of the wood.

Yes, I did investigate using a 4" SCH 40 pipe originally. Unfortunately, the stresses in this 4" pipe were too high for the loading (even if filled with concrete). I also looked at using 4" x 7" tubes - they would have worked from a stress point of view but were more expensive than the I-beams. Doing a quick calculation on a 6" SCH 40 pipe, it should work. However, it will likely be more expensive than the I-beam and weigh significantly more (19lbs/ft vs. 10lbs/ft).

The vertical beams used in my design are not officially I-beams; they are really called "Wide Flange" beams. I used a W8 x 10, ASTM A992/A572 (Grade 50) WF Beam. For a cost reference, the three WF beams cost $9.41/ft.

Good luck with your project!


goli0024's picture

It looks like you calculated the 30% before the FoE grant. I think you would need to take the 30% off the total after all grants and reabates, otherwise you will need to report the grants and rebates as taxable income. Still an awesome project and THANKS for sharing!

Willi Hampel_2's picture

I expect the operating and maintenance costs of the rack to be one gallon of deck stain ($25/gallon) every 5 - 7 years and the lifespan of the wooden rack to match the expected system life of 30 years. I designed and built an outdoor wooden picnic table from non-pressure treated lumber 22 years ago and it is still going strong (with only 2 applications of stain to date) so it is reasonable to expect the wooden solar support structure to last at least 30 years.

Paul K. Hearsey's picture

Just curious, Will, about the stain you prefer for your outdoor wood projects. I have almost finished an all-wood ground mount for our 2.75kW array, built with pressure treated 6 x 6's. it's a fixed mount, because I worry about high winds, so the focus was on anchoring it securely to the ground. No concrete.

I've tried a variety of stains on several outdoor projects, like my very nice picnic table in heavy cedar planks, but nothing seems to endure the 35C summers and minus 35C winters. All suggestions welcome!

Willi Hampel_2's picture

Congrats on building a ground-mounted PV array; sounds like you've put together a low-cost PV rack as well.

I used Thompson's Water Seal Deck and House Solid Oil Stain on my tiltable wooden solar array structure. After almost 2.5 years now, the Thompson's stain is holding up well. After researching stains, my take was that solid stains are better than semi-transparent or transparent stains due to their superior UV wood protection.

chaolysti's picture

Curious what the author expects regarding the O&M and lifespan of the rack vs. the overall system lifetime. Really ingenious, though, and goes to show how "barnraising" solar projects can be a decent way to get solar installed and build interest in the technology. No other way this would have reached the $1/watt goal.

Back in my way early days working on solar projects I did a pressure-treated support system with Unirac rails for a customer. I shudder at the thought now of how well that rack is holding up.

bnther44's picture

Please don't take this the wrong way, but is that wooden mount legal? I asked my solar guy about building my own mount - as I am, like everyone - limited on funds. His comment was, "The UL listing component is important because with the most recent iteration of the National Electrical Code all solar mounting structures must be UL listed as such to be code compliant. Mounting structures that are made of wood or site designed and built can no longer meet the newest code requirements."

Can anyone comment on this?

Justine Sanchez's picture
Hello and good question! Per the NEC, if the mounting structure is used to provide grounding as well as mounting, then yes it need to be identified for the purpose of grounding per 690.43(D) section (2014 version): "(D) Photovoltaic Mounting Systems and Devices. Devices and systems used for mounting PV modules that are also used to provide grounding of the module frames shall be identified for the purpose of grounding PV modules." However in this case there is a separate equipment grounding conductor connected to each module that performs the equipment grounding function. Cheers, Justine Sanchez Home Power Magazine
bnther44's picture

Justine, thanks so much for answering.
My experience with PV has only been through salesmen. I've met some great guys offering a great service, but generally the quotes come in at $5 to $5.5 per Watt - and that's grid-tied. Finding out that it can be done for less than half of what I've been quoted, it's exciting and sickening at the same time. My thanks to Willi Hampel and Homepower for sharing this success story. I'm from Kzoo, MI, so the sun paths chart was of special interest to me.

tlutrick's picture

Great job on the install. I especially liked the negative temperature coefficient illustration, as your -0.41% number caught my attention. I went back and looked at my Kyocera 210w panels and they're -1.20% at the same temperature of 25 degrees C. Here in the deep south of muggy Louisiana we see high temperatures frequently, so it shocked me about the loss that I'm seeing and that panels are becoming more efficient. The newer Kyocera panels are -0.46%. Oh well, technology improves a little bit every year, my 19.34kW have been working great for 5 years, and produce about 70% of my total usage. So hat's off to your install.

BTW, I too would love to have Richard Taschler post a website to his insulation techniques. I struggle to think that my home is not insulated correctly or enough and would love to see some ideas to improve my efficiency. Please post if you can.

Great article...

Richard Taschler's picture

See new posting

Richard Taschler's picture

Sorry, we do not have a web site on super insulation. We are retired and kept busy enough as volunteers teaching local home owners how to re-insulate. And our summers are reserved doing what us 75 year old seniors are supposed to do, pedaling our bicycle-built-for-two (a Tandem) around much of the world. We are fortunate indeed. Our best trip ever was 4 months pedaling Australia & New Zealand.
Your home is under insulated? You're not alone, at least 90% of all homes in the USA are woefully underinsulated. Our seminars normally run 2 hours and is more than I can give you here so I'll attempt to compress some info.
Winter 1975/76 - our experiment. Took one wall in a room and built half the wall using 2x6 studs, the other half using a DOUBLE WALL (2x4 and 2x3 staggered studs) which was also 6" deep. Used 6" and 2 layers of 3 1/2" fiberglass batts for insulation. Then the High tech approach - waited till the temperature outside dropped to 5 degrees and walked into that room putting 1 hand on the 2x6 wall and the other hand on the Double wall. The difference was astounding, I knew that wood conducts heat but surely that great a difference in warmth had to be more than the wood transmission of heat, Somewhere, I learned that the University of Saskatchewan was doing a lot of research so I contacted them. They sent us the answer. Where the fiberglass meets the wood, MICRO CHANNELS form and that is where the rest of the heat is lost. The double wall with staggered studs stops that. That's it, we did our house with double walls. Took down the sheet rock and added a second interior wall of 2x3" studs and a vapor barrier. We were amazed when completed that we turned our furnace off. So was our local natural gas supplier who sent a crew truck AND a supervisor's car to investigate these people who were probably stealing gas and they did it in a sneaky way in that each year they used lesss and less gas (corresponding to our progress doing one or two rooms each winter):::::or their meter was defective. They were not smiling but we've beem smiling ever since.
Each and every no-furnace home I've ever seen or learned about uses the double wall concept with the only difference being the farther north you live, the thicker the walls. Proof? 31 years later we went to a brand new passive solar home near us. It was fabulous. The achitect was there and he gave me a personally conducted tour. He used the same concept. Chatting, he requested a visit to our home and we complied and also gave him a copy of our power point presentation. The day after he sent us an Email informing us he was also a professor teaching environmental architects and would we give our seminar to his classes? Of course.
Our attic we did as soon as we moved into the house. Took out the blown in fiberglass (it settles too easily-yuk) and installed 15" of fiberglass batts. We kept graphs each month for each year of our therms used, A picture is worth a thousand words.
25 years later the wondering was laid to rest, did we cause damage to the house with mold or whatever forming? I took down the sheetrock from 2 walls and looked. Everything looked like the day we installed it. The vapor barrier, insulation and wood.

Other types of insulation:
Spray on foam - Costs 3 to 5 times as much but we liked it UNTIL we learned that after a period of years, it lost its adhesion. OH-OH, not for us! Years later they got it right, But last year we attended a seminar and learned that they are back in the laboratory testing because of all the new building materials with associated adhesion concerns. So be careful if you use it.
Cellulose - We decided against it because it tends to settle if not PROPERLY installed which would eventually leave a gap at the top of the studs. Even more so if you modify the walls as we did when we remodeled the kitchen. My brother in California had it installed in his walls (they obviously didn't do it properly) and a few years later he found the settling problem. Sorry.
Thermal breaks - an article in this very Email from Home Power addresses that problem. We did a minimal, not trusting caulk (despite the claims of longevity), I got out the putty knife and filled between the studding around the doors and windows with pieces of fiberglass.
Did it work? Again, all I can say is that our total energy bill for all of 2013 was $518 for our 3000 sq. ft. house. P.S. Our next door neighbor with an identical house after 25 years living next to us is finally having their house retrofitted, BUT they sent their contractor to us to give him our presentation. They just finished their large family room and were estatic about how warm it is.
Sorry I can't give you more but this is taking a lot of space. Thank you, Home Power magazine.
And good luck to you home owners. Remember, Patience and Persistance, it takes a lot.

Paul K. Hearsey's picture

Richard, I must put in a plug for blow-in cellulose. It's a great product. My wife and I did a loose blow in our attic (18 inches) and a dense-pack in the walls (12 inches). Dense-packing takes skill, perhaps more than most folks have, but we rented the blower machine for an entire week, and practiced and practiced until we were very good at it. At 3.5 lbs/cu. ft. it does not settle. It cannot.

Attic blowing: yes, it does settle. But everybody in the business knows and understands that. Our supplier, an Edmonton Alberta firm that recycles newsprint, supplied a chart allowing us to blow in extra depth to allow for eventual settling. Easy. I think we blew in about 21 inches of cellulose to end up with 18 inches.

This is an environmentally friendly product, entirely fireproof because of the added borates, light, easy to transport and handle, affordable....I just cannot say enough good things about it. Our next project, a garage/workshop, will be insulated with cellulose too. We're off next week to help a neighbor insulate his garage. Cellulose.

Herman A Newman's picture

Richard, How do I send and email to you? I attempted and the system will not allow me to send you an email at this address - Help!

tlutrick's picture

Wow! thanks Richard. Your write up has inspired me to dig deeper into what I can do more with my home. I know that I need more blown insulation in the attic, but will begin looking harder into your suggestions. If you have any more suggestions, please email me at trey.lutrick at gmail dot com. Would love to hear from you and thanks.

Richard Taschler's picture

My compliments, Here in Virginia (known as the "Dark State" because it has NEVER provided rebates on alternative energy, We took another path. We, as self taught DIYers experimented on how to best insulate walls in the winter of 1975/76 on our 2 year old home we just purchased. Experimenttion completed we went to work on the walls completing them in 1983 at which time we turned our furnace OFF, we simply didn't need it for our 3000 sq. ft. house. The retrofit cost us $300 with a Federal rebate of $2000. By 2011, we had saved so many $ due to no heating bills and reduced Air Conditioning bills, we had saved enough to have solar PV installed. We have neighbors 80' trees and our house faces east/west. So we get about 5 hours sun for our 3.9KW system.
Our total energy bill for all of 2013 was $518.
We never advertised our house but via word of mouth we found ourselves in the newspaper and then on TV across the country. Next we received requests to give seminars on what and how we did it. We have 4 seminars scheduled now (2 at diferent universities), have had hundreds of people tour our home and have helped numerous people turn turn their furnaces OFF, just like we did.
The biggest bang for the buch is super insulation,
We always start our seminars with a question to the audience which is "Is anyone in the audience aware of the fact that since 1980 they have been building homes in Canada and across the northern USA that are so well insulated that furnaces are not needed nor installed?". In all these years only a single person has called out "I have". To which we respond "Today we'll show you pictures of a few of these homes."
Our seminars are always 'standing room only'.
Again, our compliments on your efforts and success. It's a GREAAT FEELING, isn't it?

Craig Gates's picture

Do you have a website? I'd like to hear more!

Richard Taschler's picture

New posting

Richard Taschler's picture

My compliments, Here in Virginia (known as the "Dark State" because it has NEVER provided rebates on alternative energy, I took another path. We, as self taught DIYers experimented on how to best insulate walls in the winter of 1975/76 on our 2 year old home we just purchased. Experimenttion completed we went to work on the walls completing them in 1983 at which time we turned our furnace OFF, we simply didn't need it for our 3000 sq. ft. house. By 2011, we had saved so many $ due to no heating bills, we had saved enough to have solar PV installed. We have neighbors 80' trees and our house faces east/west. So we get about 5 hours solar.
Our total energy bill for all of 2013 was $518.
We never advertised our house but via word of mouth we found ourselves in the newspaper and then on TV across the country. Next we received requests to give seminars on what and how we did it. We have 4 seminars scheduled now (2 at diferent universities), have had hundreds of people tour our home and have helped numerous people turn turn their furnaces OFF, just like we did.
The biggest bang for the buch is super insulation,
We always start our seminars with a question to the audience which is "Is anyone in the audience aware of the fact that since 1980 they have been building homes in Canada and across the northern USA that are so well insulated that furnaces are not needed nor installed?". In all these years only a single person has called out "I have". TO which we respond "Today we'll show you pictures of a few of these homes."
Our eminars are always 'standing room only'.
Again, our compliments on your efforts and success.

Stephen Hackney_2's picture

Willi, thanks for the response. I couldn't see that the headers were also beams. That explains a lot, as I also had concerns about the pipe size running through all the joists. I was just being pedantic about the snow load calculation. I don't doubt that the wind load would be on the whole array as if it were a solid wall perpendicular to the wind. My only other concern was the size of the braces used to tilt the array. How did you calculate there size?

Willi Hampel_2's picture

Stephen, here's how I determined that the steel braces would be adequate:
1) Determine longest length of brace required for the seven operating positions (length between longest mounting holes): L = 41.50 inches
2) Calculate the moment load (due to the worst-case 105 mph wind load), using pressure calculations performed during the ASCE7-10 Wind Load Calculation. The two braces must resist a moment of M = 6409 ft-lbs.
3) From the tilt structure geometry, this 6409 ft-lbs moment translates into a buckling force of 1307 lbs on each steel brace.
4) Using a column buckling calculator (can be found on multiple websites), the engineering critical load for each column was calculated to be: Fcr = 3500 lbs (note: this assumes a "clamped-hinged" boundary condition).

Since the actual worst-case force on the steel column (a.k.a. steel brace) of 1307 lbs was significantly less than the calculated critical load (3500 lbs), the steel braces should not buckle under the worst-case 105 mph wind load (and have greater than 2.5X safety factor).

Stephen Hackney_2's picture

I went straight for this article since I'm planning to build my own. I first noticed that the author used the area of the array to calculate load. However I think that the horizontal span is the dimension required by IBC. Unless of course one expects the array to be allowed to be in the horizontal position during a significant time during the winter. I would also like to know more about the calculation for the braces that tilt the array. They look inadequate for the job. My other concern is the pivot point. There are only two 2X12s supporting the whole weight of the array and the support point is in the center of those boards. That leaves less than a 2X6 on the top side to prevent crushing and shearing forces causing failure. Think of this as a floor joist supported on both ends with the entire live and dead loads hanging from a hole drilled through the center of the joist. For the same reason I'd have run the joists parallel to the headers and drilled the pivot hole through them all. That would relieve the load on the headers and the pivot hole. I would probably also use a steel plate, 12X12 or longer drilled for the pivot hole and bolted securely to the joist(s). There were pillow block bearings to secure the pipe to the I beams but how was the rack attached to the pipe?

Willi Hampel_2's picture


Thanks for reading the article; it's great to hear you are planning to build your own ground-mounted PV array support structure!

In Step 6 of the ASCE7-10 Wind Load Calculation, one needs to determine the external pressure coefficient, Cp or Cn. It should be noted that these pressure coefficients are defined as perpendicular to the surface of the "roofline" (in my case, the PV panels) as depicted in Fig. 27.4-4 of the ASCE7-10 code. When calculating the wind pressure in Step 7, the calculated worst-case wind pressure of 23.2 lb/ft3 is also then acting perpendicular to the PV array surface. Therefore, since the wind pressure is defined perpendicular to the PV array, using the actual PV array area (vs. horizontal span (L) area) to calculate the force on the PV panel array is appropriate. Note: using the actual PV array area causes the calculated force on the array to be greater, which is a more conservative approach for making a safe structure (i.e. safety margin is your friend!).

In regards to your pivot point strength concern, there are actually four 2X12s (i.e. two on each end of the pivot pipe) supporting each tiltable array. There is also a 3" x 4" split clamp aluminum plate (can barely be seen on pg 43 of article, center photo) which ties each set of two 2X12s to the pivot pipe. These aluminum plates serve two functions: a) prevents the wooden structure from rotating relative to the pivot pipe and b) increases the shear loading that the wooden structure can handle.

I also considered running "the joists parallel to the headers and drilled the pivot hole through them all" as one of the design options I analyzed. I would not recommend running joists perpendicular to the pivot pipe for the following reasons:
1) If one would keep the same 2" diameter Schedule 40 steel pivot pipe (16' long), the maximum array deflection (just taking into account the weight of the wooden tilt structure plus the PV panels) would increase from 0.08" on today's design to a theoretical 20.8" (note: a 2" diameter steel pivot pipe would permanently deform/break well before this theoretical 20.8" deflection has been reached)!
2) If the pivot pipe diameter were increased significantly (requires at least a 10" diameter Schedule 40 steel pipe size) to reduce this theoretical 20.8" deflection back down to approximately 0.08" of today's design, the cost and weight of the PV array pivot structure would have increased significantly.

The answer to your final question, "how was the rack attached to the pipe?": through the two 3" x 4" split clamp aluminum plates described earlier.

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