Offgrid solar project part 3a completed

For those of you following this blog, you know that I have been experimenting over the years with offgrid solar (PV). In phase 1 we had a couple solar panels mounted on a skid outside that was simply hooked to a charge controller and a couple batteries. We used these batteries in a couple mobile inverter carts to power such things as the TV and DVD player. Moving the batteries around quickly became tiresome so we moved onto phase 2. Phase 2 added a transfer switch, pure sine inverter and battery box so that we could run 4 small house circuits without having to move the batteries from the central location. This was a HUGE improvement and allowed the batteries to be continually maintained by the charge controller instead of constantly being moved on and off charging. The problem was lack of charging capacity especially in the winter. We have 2 75amp-hour batteries and due to snow load smashing one of our panels we only had a little over 125 watts (8 amps max). This wasn't bad and was able to power our home office for 11.5 hours but it took about 2 days to recharge from this depleted state. This is where phase 3 came in. Phase 3 started as simply getting a replacement panel for the one that got smashed by the snow load, but due to price drops in solar panels, we were able to pick up 2 Evergreen 205 watt panels for the price of the replacement panel. This meant we needed to mount the two new panels and since the old panels were just on a ground skid that had to be tied down it was decided to permantely mount the old panels also. After siting the best location for the panels, it was decided to mount them behind the garage which unfortunately was about 100 feet from the spot in the basement where the batteries / charge controller / inverter are so this meant a long DC run. Because of the work involved in phase 3, it was decided to divide the project in half and get the new panels mounted and running (phase 3a), before moving and remounting the old panels (phase 3b).

Here are the steps we went through in phase 3a:

1. Since the location of the panels was going to be behind the garage, a long conduit run was needed to go from the basement, through the garage and out into the back yard. During the early months of winter 2010 I started installing 1 1/2 inch conduit from the existing PV combiner box, across the basement ceiling and into the garage. In the garage it crossed the back wall and finally went through the wall the outside where it needed to drop about 8 feet into a buried trench. The inside conduit run was completed in the winter of 2010 including pulling the 2 1/0 cables through into the garage.

2. In the Spring of 2010 final siting was done for the array to make sure that maximum sun was obtained in that spot. After siting at over 16 different spots behind the garage, a final location was determined.

3. I started digging the hole for the support pole in the late Spring of 2010, The pole was hardened steel, 10 feet long with a 4 inch diameter. The requirements for mounting meant I needed a hole 2 feet by 2 feet wide and 4 feet deep. The first 2 feet down was pretty easy going, but then I hit rocks and compacted soil. I even hit a small boulder that ended up being a 75 pound rock that had a 2 foot diameter (this is now part of our ever-growing rock wall).

4. After getting the hole to the proper 4 foot depth, I dug a trench from the garage wall to the hole. I then drilled a hole through the garage wall and dropped the conduit down the wall and into the trench eventually ending in the 4 foot hole. The conduit had to run below grade into the hole so the conduit would be held by the concrete as it turned to go up the pole.

5. Next was building the rebar cage that would surround the pole below grade. This rebar cage was 3 feet tall, by 1 1/2 feet wide and deep. These dimensions allowed the cage to float in the hole without touching the bottom, top or sides of the hole.

6. After building the rebar cage, 2 holes had to be drilled throught the pole to allow rebar to pass through the pole and attach to the cage. These rods served the purpose of first of all supporting the cage above the bottom of the hole before the cement was poured and ultimately to tie the rebar cage and pole together as one unit in the cement preventing the pole from spinning in the ground.

7. With the hole dug and pole prepared, it was time to put the pole in the hole. Fortunately my wife was able to help me carry it out of the basement to the hole where we were able to tip it up into a standing position. After lowering the rebar cage into position and securing it to the pole, I secured the pole into a standing position with rope and stakes.

8. After the pole was standing the hole, it needed to be leveled in all directions. This was done by simply adjusting the tension on the support ropes until it was level.

9. Finally we got to the big task of pouring the cement to secure the pole. Any guess on how much cement we needed to fill a 2 foot by 2 foot by 4 foot hole? Well, it ended up being 29 80 pound bags of concrete (my estimate had been 27 bags from which I rounded to 30 to account for loss).

10. Before the concrete set I quickly tied the conduit the pole so it would set properly aligned.

11. After letting the concrete cure for a week I again sited the PV array, this time from the top of the new pole looking specifically for direction the array should be pointing and the prefered tilt of the array. It was determined that the array should be positioned to 184 degrees (South-SouthWest) and at a tilt of 34 degrees from flat.

12. Knowing the angle of the array, I then attached the pole-mount cap at the correct angle (after re-learning that you can't put a magnetic compass on top of a metal pole and get a proper reading). The pole mounts went up rather quickly including the tilt bar and cross-bar supports.

13. Next was the exciting part of actually mounting the panels to the pole. This is always exciting just because you can finally see the final product instead of it just looking like a pole sticking 6 feet out of the ground. The two Evergreen panels went up fairly quickly and with nice gap in between to allow for air flow.

14. After checking that the panels were indeed producing power (since this is the first time these panels were exposed to the sun), I mounted the outside PV combiner box that finally completed the conduit run all the way from the basement (total conduit length from pole to basement was about 80 feet).

15. Wiring was next, and in my opinion, the most fun step (ok call me a geek). I attached a grounding wire on each panel and fed it into the combiner box and then continued it down to a grounding rod that was pounded into the ground. The PV wiring was fed down through the support channels and into the combiner box where it was wired together through a couple 20 amp DC fuses to the 1/0 cable that leads back to the basement. In my configuration, each panel is wired to a seperate fuse allowing shading on one panel to not affect the other panel. I also added a couple 15 amp fuses in the box that will be used in phase 3b when the old panels need to be wired. I left a little bit of extra PV wire to allow for tilting the array up and down in the summer and winter in order to optimize the solar angle.

16. The final wiring step was to connect the 1/0 cables in the basement to the combiner box in the basement to complete the ciruit and allow the power from the new panels to flow into the circuit. After doing a complete electrical check and retightening all connection I flipped the breakers and let the power flow. A quick check indicated that everything seemed to be working normally.

The system hasn't yet been through all it's paces yet since the batteries were fairly near full, but all indications are that it is producing the power it should.

I learned a ton by doing this and I do want to thank my wife for being so supportive through the million trips to the hardware store for yet another part.

Phase 3b is mounting the old PV array on a pole mount and wiring it into the new outside combiner box. I hope to start this this summer and fall with the goal of at least getting the pole in the ground before winter. There really isn't a hurry on this though since the old array is still producing on the ground skid, just not as much as could be.

Until then...this is just Life according to Troy