A Home Built Modular Solar Array Part 1

Introduction

I decided to design and build a solar array that was modular in nature and would allow a homestead to add modules as needed in 1-2 KW increments. I wanted the arrays to be elevated, and X-Y positional to take maximum advantage of the sun.

The array should be made from available materials a person could get at any hardware store or lumber yard, excluding the solar panels and electronic components, some big outlets such as HomeDepot and Lowes now sell solar array components.

The solar array consists of:

- Solar Panels and mounting hardware

- Solar array mounting frame

- Solar array cradle

- Mounting platform

- Electrical storage and conversion modules

The power capacity of the array depends on the capacity and quantity of the solar panels and if they are wired in parallel or series. I standardizd on 250-watt panels so a 4-panel module will have a maximum capacity of 1 KW (Kilowatt.) Homes with air conditioners, water heaters, TVs, refrigerators, freezers, lights and the other conveniences use 5-7 KW hours of energy per day, in order to power a typical home you would need 20-28 panels. You rarely get the full 250 watts out of a panel and there are other losses to consider, usually you would double that.

What about night or rain or snow clouds or fog? You must be grid connected or have batteries to store energy for when the sun isn't available. As you can see, costs soon skyrocket. It is usual to spend $40-80K on a full house, battery backup, solar power system.

I am only looking to power a freezer, a refrigerator and maybe some lights. I have windows for cooling and a wood stove for heating. All told the load I need to power to keep my food preserved and allow me some light to work by is about 2 KW.

As far as batteries, I used deep cycle 12-volt AGM 26 AH golf cart batteries and 8 would be sufficient to provide power to my loads for about 2 days. I picked a solar charge controller that handles the voltage and amperage of my panels in serial, and a full sine wave 1.5 KW inverter provides the conversion from DC to AC. When placing sources in serial the volts are additive while the amperage remains the same.

Typical specifications for a 250-watt panel:

- Max Power: 250 watts

- Optimum operating voltage: 31 volts DC

- Optimum Current: 8.5 amps

For a 4-panel module, wired in serial, the charge controller would need to handle 8.5 amps and 124 volts DC. The full sine inverter would need to handle an input of 12 VDC, as the batteries are to be in parallel, and provide 20 amps at 110 volts AC output. A full sine inverter is safe to use with electronics while a square or semi-sine wave is not.

This combination gives 186 total amp hours at 12 VDC, you shouldn't run the batteries to lower than 60%. That means I have 112-amp hours to utilize before I need to go to a backup. That would be 1.344 kWh available to be used. From the statistics on my maximum load, my freezer, it uses 0.9 kWh per day. So 1.5 days of use before I would need to switch to another power source.

Okay, enough facts and figures let's get on with the build.

The Best Laid Plans

Before I start, I draw out a diagram, so I have an idea of the materials needed. Whether a scrawl on the back of a napkin or a detailed blueprint depends on the project. I learned drafting so I can put drawing pencil to paper if needed. Figures 1-3 show the diagrams from the actual build. I found that two standard sized 250-watt panels will fit on an 8-foot-wide axle with the pillow bearings and three 4x4 supports.





From the diagrams you get a bill of materials.

Solar Array BOM

4 – 250 watt 60 cell solar panels $600.00

23 – 8 ft 4x4 $236.00

3 – 4x8 ft ¾ inch outside grade plywood $132.00

11 – 8 ft 2x4 $60.00

1 – 8ft 2 inch OD iron pipe (usually 1 ½ inch ID) $47.00

2 – 2 inch ID pillow block cap bearings $64.00

1 – Solar Charge Controller $113.00

1 – 1500 watt, true sine inverter $159.00

1 – Solar positioning unit * $200.00 (including sensor and actuators)

2 – 18 inch linear actuators *

6 – 4 inch diameter cart wheels $56.00

1 – 12 inch turntable $16.00

16 – Z brackets for mounting arrays $30.00

(look for solar array mounting brackets)

1 – 100 count box of 1 ½ inch deck screws $15.00

1 – 100 count box of 2 ½ inch deck screws $15.00

30 – ½ inch by 6 inch lag bolts $60.00

4 – ½ inch by 4 inch lag bolts $10.00

4 – ½ inch by 2 inch lag screws $9.00

4 – ½ inch ID flat washers $3.00

10 – joist hangers for 2x4s $10.00

3 – 2” ID 7-10 inch leg U-Bolts $50.00 (delivered, as of 2018 from Dsuban Spring)

3 – 4 inch ¼ inch by 1 inch flats for U-Bolt closures Made from scrap I had on hand

1 large deck box, lockable. Mine is 52” by 26” $149.00

8 – 12 VDC 26 AH AGM deep discharge batteries $520.00

(UB12260)

7 – sets of battery cables $31.00 (from Wish)

2 sets of long leads to go from solar charge controller $10.00

to batteries and then from there to inverter

1 set of 10 foot long solar cables $23.00

to go from array to deck box.

1 can of silver or white spray paint $5.00

(For use on deck box, most deck boxes are black or dark color, will overheat in the sun so I painted it silver to reflect the heat.)

If desired, appropriate amount of deck or exterior paint to paint array cradle and deck.

*Usually comes together in kits make sure the actuators are as long as possible.

My total cost in 2021 prices was $2,598.00 (prices from net except as noted, as of 1/3/2021)

The second array was grid tie, everything the same except I didn't need batteries, charge controller or inverter and the deck box to put them in, instead I bought 2 – 1KW grid tie inverters for $256.00 and two combiners for $18.00 dropping the cost of the second array to $1,895.00.

Needed tools

- Chainsaw or Sawsall capable of 4 inch cuts

- Bit driver with appropriate bits for driving the deck screws, if other than screwdriver types are required, the boxes of screws usually include one.

- Wrench set or crescent wrench large enough for nuts on U Bolts

- String level

- Large regular level

- Tractor with PTO auger, powered auger or fence post hole digger

- Ratchet strap

- Wrench sized to fit bolts on batteries

- Drill with 6–8-inch wood long drill bit size 9/16ths

- Hand grinder

- 5-gallon bucket

-Portalign or other leveling device for your drill

- folding ladder

The Actual Build

I made the dimensions such that I used the 8-foot 2x4 and 4x4 and 4x8 sheets of plywood intact.

The first step was to build the array platform.

Array Platform Build

1. In the northern hemisphere, southwest to south is the best way for an array to face. Determine what the spread of directions for the year and place it such that it is at the center of the spread, then allow the positioner to adjust the array as needed.

2. Using my tractor's rock rake I cleared the area where I needed to build the platform.

3. Using the plywood sheets as templates I marked the locations for my support posts. The posts need to be centered at 3 inches in from the edges of the plywood to allow for the 4x4 posts plus the 2x4 supports to fit under the plywood.

4. Once the support post locations were marked, I used my tractor PTO auger for the holes making sure each was 2 feet deep. You can use a post hole digger, but believe me, in this rocky soil a PTO auger was the way to go.

5. Cut the needed support posts, I used 4-foot lengths of ground contact treated 4x4, there are 12 suggested support posts, so this requires 6 of the 4x4s from the BOM.

6. Mix up quick dry cement in a 5-gallon bucket and pour it into the holes, you will add this cost to the BOM, about $10 for two 25-pound bags.

7. Set the posts before the concrete dries and make sure they are level and square with each other. You can see from my pictures I did okay with square, not so good with level. While it doesn't seem to affect their stability, being crooked sure doesn't look professional, so learn from my mistake.

8. Fill in the holes with dirt making sure the posts stay level and square.

9. Once the posts are secure, use a string level to mark the height across them for the platform support beams. Using a Sawsall or a chainsaw, cut the posts to height making sure the tops are flat and level.

10. You will need 4–48-inch 2x4s and 4-8-foot 2x4s for the supports for the platform. You will also need 5-2x4 joists cut to fit between the supports, I waited to measure after I got the supports mounted to the posts.

11. You will need 2-4x8 sheets of plywood and one 4x4 sheet of plywood for the platform.

12. Mount the 2x4s so the edges are level with the tops of the support posts and use the 2 ½ inch deck screws to secure them to the posts. The support goes on the outside of the posts.

13. Once the supports are mounted to the posts, measure and cut the 2x4 joists.

14. Mount the joist brackets using 1 ½ inch deck screws positioned as shown, make sure the top of the joist is flush with the top of the support 2x4.

15. Install and secure the joists using 1 ½ inch deck screws.

16. Using 1 ½ inch deck screws secure the plywood to the supports, joists and posts.

Next the array carriage. Build it on the platform, hence why we built the platform first. I built the first array carriage in my work area then had to move the beast by myself 50 yards to the platform and hoist the monster up onto the platform using the lifting beam on my tractor PTO, not fun. Learn from my mistakes.

Building the Array Carriage

1. You will need:

- 4–67-inch 4x4

- 2-3 ft 4x4 with 45-degree cuts on the end (make sure they are both cutting toward the center of the board)

- 4-2 ft 4x4 with 45-degree cuts on the end (make sure they are both cutting toward the center of the board)

- 1 – 8 ft 4x4 with notches cut to fit the notched side boards, notch ½ the thickness of the 4x4, remember they are slightly less than 4 inches by 4 inches so measure the exact notch needed, over notching will result in cracking and failure under wind stresses.

- 2 – 4-inch 4x4 notched at the exact center point to match the 8-foot 4x4.

- 2 – 1-foot 4x4

- 4 – 45-degree angle pieces of 4x4

2. Begin by using the 6-inch lag screws, join 2 of the 67-inch 4x4s to build the support posts by using the 9/16 bit and drilling three holes down the length of the 4x4s being sure that the two 4x4 for each side don't have holes that line up. Lay the 2-4x4s down and screw the lag bolts into the opposing 4x4, do so on both 4x4s so there should be six lag bolts, three on each 4x4 securing it to the other one. Once complete, make sure both support posts are identical in length.

3. Using two of the 6-inch lag bolts to secure the one-foot 4x4 section to one end of the support post, make sure it is centered. Use 2 of the 45-degree 4x4 sections to brace the 1-foot section on each end using the 6-inch lag bolts.

4. Repeat steps 2-3 for the second support post.

5. Next build the base. The base consists of the two notched 4-foot 4x4 side boards and the 8-foot notched 4x4 spine. Fit the 4-foot 4x4 side boards onto the end notches of the 8-foot 4x4 spine, it should look like a giant capital I with exaggerated ends. Secure the side boards to the center spine using the 4-inch lag bolts, two per sideboard use a staggered pattern. Use the 9/16 drill bit to drill through the side boards from the bottom then screw the lag bolts into the spine.

6. The spine is attached to the top of the base you should be able to see its full length. Turn the base over and attach three wheels to each sideboard, one on each end and one in the center.

7. Mount the turntable to two 12x4-inch sections of the ¾-inch plywood on each side.

8. In the center of the spine mount the turntable using the plywood sections.

9. Next, take one of the support posts and using 3 of the angle brackets, mount it flush with the end of the spine at the center of the sideboard. Make sure it is square and straight using the long level then using 2 of the 2-foot 4x4s brace the side post on either side using the 6-inch lag bolts and then use the 3-foot 4x4 to brace on the inside against the spine. Repeat for the second support post on the other end of the base.

10. Take the 89-inch 4x4 and mount it using 6-inch lag bolts 4 foot up the support posts, it will form a center stabilizing brace.

11. Now, see if the bearing will fit on the end of the pipe. If the pipe is slightly too large, use the hand grinder to take a bit off all the way around the end until it can fit completely in the bearing, repeat for both ends of the pipe and mount the bearings until the end of the pipe is flush with the outer edge of the bearings.

12. Carefully place the pipe on the support posts and mount the bearings on the platforms you built there. Use the 4-inch lag bolts and the flat washers.

13. Position the carriage in the center of the platform making sure there is enough forward and back movement of the wheels for the full 18-inch travel of the actuator for the solar positioner. One side will be fully back while the other is fully forward at either full open or full close of the actuator. Once you determine the proper position, use scraps of plywood as needed to mount the bottom plywood pieces on the turntable to the platform.

Okay, time for a story. I left my first array just like it says in step 13, with the only thing fixing it to the platform being the turntable. It weathered several storms that way. Then we got one with gusts of 50 mph. I came home to find the carriage had busted the turntable and was laying off the back of the platform. One panel had gotten pierced and thus ruined by the actuator stabbing it. An expensive lesson. I now use a heavy-duty load securing ratchet strap that wraps around the carriage and the platform at the turntable to secure the carriage so that it will have to rip the entire thing up or break the support posts to do that again. Learn from my mistakes!

End of Part 1