Adding a 3 kW DIY Solar Array Without Another Inverter


Bob Bruninga, WB4APR - lastname@usna.edu

Adding another 3kW array to the Garage (without a new inverter):

Our original southeast facing three-array 8 kW system is visible on the above right. It favors the southeast because of a clump of shade trees to the west that begin shading the panels after 2 PM. Comparing this to similar arrays, this limits our array performance to about 90% of what an ideal array would produce. In addition, having switched from heating oil to Geothermal Heatpump to stop burning another 1000 gallons of fossil fuel every year, our electrical load went up. To compensate for both of these factors, we added an additional 3 kW array facing southwest on the garage roof as shown. Once the original southeast facing system was permitted, approved, in place and grid-tied, adding these additional panels was very cost effecitve as they did not need an additional inverter. These new panels are diode-paralleled to the most east facing of the southeast arrays (to minimize Sun overlap). As the southeast array becomes shaded by a bunch of trees, then this southwest array is just beginning to get sun. This way, we get dual use from the same inverter, as it now has Sun twice as long each day due to the second set of panels. See shading image in summer.

Multifaceted Project: There were several wide ranging factors involved in this project, not the least of which was overall maintenance and repair of this 90 year old garage which was falling down, full of leaks and rotting foundation. As you can see to the right, there is a lot of cleanup in progress. The half finished roof array can be seen here, as well as the terrible need for a paint job (which entail siding and a vacuum cleanup of all the surrounding dirt to capture all the old lead paint). Another significant effort to be able to access the lower edge of the solar panels on the high roof, I had to build a stairs and walkway. Instead of a walkway, I changed to a small trolley platform that can roll across the entire width of the building.

Eagles Nest: Since the wasteland of junk trees-of-paradise had to be topped above 30 feet to get sun to the garage, the 30' stumps looked pretty naked. As a result, we spent a day building an eagle's nest in case anyone was looking for a home. So far, it is mid spring (April) and no Eagles nor Osprey have ventured near, though it has been occupied. A live camera sticks above the nest so we can watch for activity.

There are several other overlaping and related pages to our solar and energy projects:

  • My other ramblings on alternative energy
  • Panels on Piers now possible in Maryland
  • Grid-tie is the way to go (if you have it)! See why.
  • Geothermal Heatpump that eliminates our 1000 gal/year oil burning.
  • Solar augmented Salvage Prius eliminates 500 gal/year oil burning.
  • Using the Prius for emergency field power
  • Misinformation about EV's holds back EV adoption
  • Building a DIY Charge cord for 120v for under $100
  • Solar Power (powerpoint) Presentation

    Click to join SolarDIY . . . Click to join our SolarDIY email discussion group

    Roof Repair Avoided!: The other reason for this project was to fix the roof. Rather than spending lots of money repairing the roof and then covering it with expensive solarpanels, we designed the solar panel system to be water proof so that we did not need a new roof. As you can see in the above picture, the big holes in the roof (one as big as a football where a Raccoon was nesting in the attic) were simply covered with extra shingles. The wooden 2x6 rails for mounting the solar panels can also be seen to be slightly notched on the bottom edge to allow for the added shingle thickness. You can also see how the top row of solar panels was designed to overlap the bottom row by one inch . This assures that water flows across the junction and there was no need for any weather profing between the panel rows. The crack between the vertical columns of solar panels is less than 1/16th inch and are raised above the surface of the panels so it is unlikely that any significant water will get between them. If so, a simple caulk gun can seal the gap.

    Panel Raising Pulleys: Also visible in the above picture is the wire-rope and pully system used for rasiing the panels the needed 30' to the roof. A sliding block slides along the wire rope (supported between the Eagles Nest and my car bumper 60 feet to the left) and also supports a 2-to-1 mechanical advantage rope/pulley system for raising the panels from the ground. Then they were stacked on the roof for later install.

    Attachment Scheme: The panels are held in place by screweyes into PVC blocks as shown here. I assume wood can also be used, but I had the PVC so used it. The screweyes pass through the pre-existing mounting holes as shown far right and then hang down between the 2x6 rails and are attached to the rails with 1" drywall screws. To facilitate single person installation, an upper placement jig with nails in the right places was placed between the two rails to temporarily hold the upper panel in place until attached from underneath. The upper panel is installed first so that all four screweyes can be secured by reaching under.

    Then the bottom panel is slid into place from above and caught at the bottom by a second set of nails on the lower jigs. Then moving to the trolley system to reach under from below the lower panel, the panel is pushed up the 1" under the top panel and then the lower two screweyes are secured. Of course, installing the last lower panel was a challenge for a single person, so it was slid down into place against the temporary lower jig using wires from above..

    Background - Grid-Tie is the only way to go: Going Off-Grid makes NO SENSE (if you have access to it): If you don't have access to the grid, solar is a still a great source of energy... but at about 3 times the cost of grid-tie. In addition, it condems you to a life of sacrifice, and maintenance issues due to having to maintain your own batteries. If you DO have the grid, it is Golden! Never give it up! Even if you consume no net power from the grid, just using it as storage more than DOUBLEs the efficiency of your system compared to being off grid. Do not be mislead into going OFF-GRID if you have it!

    Temporary Array: The image above was my original temporary placement of the southeast 8kW of panels just propped up in the backyard on 2x4's because of my years long struggle to get county and state approvals to put some of them on a pier in the creek. They are now properly permitted and permanently installed in my yard, though the original plan has been to put them on floating piers in the creek. Now (summer 2013) 4 years later the state has finally dropped its prohibition to solar on piers but my system is working fine where it is. Pictures below show my 3 inverters and basement wiring.

    Grid-Tie Inverters: The image above shows the three 2.8 kW inverters. I chose to go with three separate identical 2.8 kW inverters (2 new ones with updated larger DC disconnects on the left) rather than one large inverter for redundancy and reliability. Notice that all indoor high voltage solar DC wiring must be in metal conduit due to the fire hazard when HV DC is disconnected or the result of a bad connection.

    Distribution Wiring: The next photo shows how the inverters are connected to the distribution panel. I combined the 240v AC outputs via three 15 amp dual breakers in a combiner box and sent the combined 240 VAC outside to the "solar Disconnect" switch by the electric meter required by the utility. Then it comes back inside and simply goes to a 50 amp breaker in my normal distribution panel shown on the right.

    Solar on Piers, in the Critical Area, HIgh Voltage Distribution and other topics: To see the 4 years worth of wrangling with the state to get the able DIY arrays installed and the fight over installing them on a pier and in the Chesapeake Bay critical area which prohibits any such structure within 100' of the water, please see my alternative energy web page.

    Bottom line - Reducing our Carbon Footprint: . The time is now to go solar! We cannot continue to burn fossil fuel as if there is no tomorrow nor to send billions of dollars a day overseas to buy foreign oil for our energy needs when energy is right there outside our door. Also consider all of your energy needs, not just electricity and driving. This plot shows how we have reduced our annual 3000 gallons of fossil fuel burning down to under 300 by investing in three salvage Prius, then solar, then geothermal, and then this final 3kW array. All that is left to get down to our final 100 gallons a year is when one of the decade old Prius dies and we can switch our local travel from 55 MPG down to zero with an all electric car (the Truck-E).

    Yes, we can do this... and it is even cheaper than doing nothing!

    Bob Bruninga, WB4APR,