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OFF GRID Rainwater Harvesting System

By September 21, 2020October 9th, 2020No Comments

This is a continuation of my series on installing rainwater harvesting tanks. In this post I’ll show the excavation and pouring of a low retaining wall, or curb if you like, for the foundation of this 500 gallon tank.

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In the previous post I showed all the steps I took to install a 1200 gallon tank. This smaller tank sits in our garden and collects water from this timber frame style pavilion I built a few years ago.

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And I’ll be adding an off grid 12 volt solar system and pump to supply the drip irrigation to beds and hanging planters around the pavilion.

See the Youtube Video Part 1 or Part 2 or Part 3 or Part 4

Off Grid Rainwater Harvesting System – PART 1: a concrete footing and gravel foundation

(this is a transcript from the video)

There will be some similarities in the installation of these two tanks so if you’ve already watched the first series then you may see me repeating a few of the steps. So I’ll try to move quickly here.

In the next few episodes I’ll detail the construction of the cedar and corrugated panels that surround the tank. And then cover all the plumbing and fittings to take rainwater from the pavilion and deliver it to the tank. Then finally I’ll install the solar panel and set up the pump and other off-grid electrical parts in a mini pump house at the back of the tank.

A flat and level spot is excavated behind the pavilion and a concrete curb is poured.

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Then filled with pea gravel.

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4×4 posts sit in galvanized saddles that are secured to the curb with anchor bolts.

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2×4 and 2×6 rails are added between these posts on all sides.

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Corrugated galvanized panels are attached to these rails to complete the tank surround.

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So the real work starts with shovel and wheelbarrows — with the occasional break to pet a cat.

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When this spot is flat and level I then dig a trench for a drain.

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Water that accumulates inside the curb walls needs to drain away. This trench will move water from under the tank and to a dry well where it will absorb into the ground — more on that later.

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I’ll build the forms from 1×8’s. With the inside form walls made in two pieces.

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They have a 45 degree cut to make stripping the inside forms easier.

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A mending board across this cut will hold the form together during the pour.

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Cleats added to these 1×8’s will make attaching stakes easier as well as clamping the forms together on the ends.

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And then I can screw the outside form walls together.

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And I’ll line up this wooden box to the pavilion piers.

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Then pound in stakes and screw them to the form cleats.

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Checking and adjusting for level and square as I go along.

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Then the inside walls are clamped then screwed together.

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They are levelled and squared and temporary spacers added.

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Some of the stakes were too tall so I trimmed them with a hand saw.

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With the forms in place I then add the pipes to the dry well.

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There will be a perforated pipe to collect water under the tank and this is connected to a pipe for the tank overflow.

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With the pipes and fittings cut and layed out I’ll add some drain fabric.

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And the cats come to inspect the work.

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I can start to glue the pipe and fittings and add some drain rock as I go. And then cover with more fabric.

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I applied some vegetable oil to the inside of the forms so the concrete would not stick. The curb will be reinforced with rebar, and it’s suspended from wire to keep it centered in the forms during the pour.

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We fired up the concrete mixer and spent a few hours filling the forms.

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I added anchor bolts before the concrete set up. Then covered the forms with plastic and left overnight.

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Here’s the mending board coming off an inside form wall.

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I found this worked well and made it easy to strip the inside walls.

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I’d say the best part about concrete work is stripping forms. Very satisfying!

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With that done I’ll dig the hole for the dry well.

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Then line it with fabric and add some drain rock.

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I set half a rain barrel in the hole and ran the drain pipe into it. Then filled in rock around it.

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Then finally topped with some dirt and sod.

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I keep the new concrete damp and covered with plastic for a few weeks while it cures. I roll out fabric and fill the space with coarse drain rock.

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Then top this with pea gravel.

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I pack and level this then we can set the tank in place.

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Off Grid Rainwater Harvesting System – PART 2: red cedar and corrugated metal fence surround

The surround has five 4×4 posts that support 2×4 and 2×6 rails.

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The posts are screwed to adjustable galvanized saddles. These lift the post up off the concrete by an inch.

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The top and bottom rails on the sides of the surround have a rabbet cut in them. So I can flush mount the galvanized corrugated panels.

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Around the back of the tank I created a space for a mini pump house. This will hold the solar controller, battery, fuses, etc for the DC water pump.

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We wanted the tank and surround to feel like an extension of the pavilion. So we adopted the timber frame look with full dimension rough sawn red cedar. And we used the same stain for the surround as well.

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What I’m building here is beyond what is needed for a rainwater collection tank. But, we wanted to do something different and dress them up sorta speak. And for this particular tank the fence surround is also functional as it will support some of the plumbing and wiring later.

Our property is sloped and there’s not many truly flat and level spots. And in the winter with our heavy rains the soil can get soft and saturated. For those reasons we decided on pouring a concrete curb to hold the gravel and then this acted as a foundation for the fence surround.

We are blessed to have lumber milled from our own trees for many of these projects. When we poured the curb I embedded some anchor bolts to hold these post saddles.With the Sketchup model done I can start cutting the parts.

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I’ll cut all the 4×4’s first. Behind me there is the 1200 gallon tank that I covered in the first rainwater collection series.

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Next I’ll cut the 2×6’s for the bottom rails. And then the 2×4’s for some of the mid and top rails. I can get away with cutting everything to final size here as I was careful to set the forms and pour the curb square and level.

And then I cut a rabbet in the top and bottom side rails. A viewer in the previous series commented that I should have made the horizontal cut on a slight angle for water drainage. And that is totally true.

With all the parts done I roll on some stain. This is a one coat Sikkens semi-transparent stain. It dries overnight and , with only a single coat, the parts are not oily to handle and work with.

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I do add a few extra coats to the tops and bottoms of the posts and to the ends of the rails. And I was thinking that I’d like to add a low profile, simple, galvanized cap for the posts. If I can find or order some somewhere. Maybe I could just cut a square of galvanized sheet metal and epoxy it on. The hardware stores in my area don’t carry a post saddle for a full dimension 4×4 so I need to trim mine down to three and a half inches. I love this western red cedar whenever I pull out a chisel or need to shave it down.

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A single screw through the post saddle holds the bottom in place while I clamp a temporary brace to one side. Then plumb with a spirit level. Then I can repeat that on the second post. With the addition of another temporary brace.

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I use small blocks clamped to the post to support the rails. And a long pipe clamp pulls them together and holds them in place while I drill pilot holes then run in the screws.

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I’ll be toe screwing the rails into the posts. And I think this will do for this particular project.

Once I got a feel for how this was going together I drilled all my pilot holes in the rails ahead of time. And sometimes started the screws in the holes. This can make working solo a lot faster and easier.

Next I’ll add the middle rail. Again, blocks support the rail while I bring the posts together with a pipe clamp. And run in more and more 3″ screws.

A post is added to the East side, plumbed, and supports added. This side has two taller posts and a higher rail. I needed this additional height to support the 3″ pipe from the pavilion gutters and to support some of the plumbing setup.

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For the rest of the sides I’ll add rails starting at the bottom and work my way up the post. Then the mid rail followed by the rabbeted third rail. And a 2×6 at the top.

And around the West side all of this gets repeated.

At the back South facing side I’ll add three 2×6’s.

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We have consistent wind coming from the west so I though I’d add some additional protection for the pump house with this short section of fence.

I’ll jump ahead in time here to show the corrugated panels being added. Eighth inch spacers lift the panels to center them vertically. I used 1″ roofing screws that have a metal and rubber washer. I set my post spacing so I could overlap these a few corrugations and not have to cut them.

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Except for the last panel. I have an attachment for my drill that cuts sheet metal pretty well. But not as good as I hoped for these corrugated panels. It left a rough edge but I was able to straighten it somewhat with a hand seamer.

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Later I made some cuts with an angle grinder running against a straight edge that was clamped to the panel. And that worked much better.

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The mini pump house will be a box with a sloped hinged lid. I made some walls with 2×3’s and 1×8’s. Then screwed these together. And I’ll add an exterior grade plywood bottom.

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And I can cut the end walls for the sloped top. I stained the box and added a top from plywood and attached it with gate hinges.

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This plywood has a synthetic roofing felt tacked on then corrugated panels attached.

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We temporarily set this box in place to see how it fits. And that’s pretty much all the carpentry work done.

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Off Grid Rainwater Harvesting System – PART 3: plumbing and tank fittings

This tank came with a 2 inch bulkhead fitting already installed. It’s for connecting more tanks together and for draining the tank quickly. Or, we can use it for drawing off water. I’ll be adding a float and screen to this tank so I can draw off the cleanest water that’s just below the surface and away from any sediment in the bottom.

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I’ll add a ball valve to this existing bulkhead fitting. I first add a reducer down to one and a half inches. I didn’t have channel lock pliers big enough for these so I used the biggest wrench I had. Then I’ll add this short nipple, and then the ball valve.

Before I can add the float and screen I need to assemble the parts first. I BOUGHT some of the tank parts and decided to MAKE some of them from existing fittings.

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I cut the float hose down to a length I though appropriate for the height of this tank. About 2 feet taller than the tank I thought would be good. There’s a barbed fitting that goes into the inside part of the bulkhead fitting first. Then the clear flexible hose goes onto that. It was a tight fit and tough to get this on, even with some soapy water as a lubricant. And a stainless steel hose clamps secures it.

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Then the screen and float goes on the other end. And a lanyard is tied to the float. This will keep the screen up off the bottom of the tank when the water level gets low.

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I’ll need to drill a hole in the tank for a bulkhead fitting for the hose that’s connected to this float. It will be around the back at the southeast corner. I’ll use a hole saw for this and drill this hole 4 about inches off the bottom.

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Getting the bulkhead fitting through this hole can be tricky. I first screwed in a barbed fitting into the bulkhead fitting. Then I tied a string to the barbed end. And taped it too.

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The other end of this string is taped to the end of a pipe.

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Then this pipe is set in the tank with the string end resting on the hole I drilled. I then carefully remove the tape and pull the string through the hole.

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I remove the pipe from the tank and lay in the hose and float assembly. Being sure that the end of the lanyard on the float is still outside.

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I now pull the string to bring the bulkhead fitting through the hole and attach the nut. I snug this up with a wrench.

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I’ll be connecting this fitting to the mini pump house later. But for now I’ll add a ball valve so I can make the tank water tight. I detailed the construction of the pump house box in Part 2.

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To find the best spot for the tank inlet I sighted down a large speed square. I lined up one edge to the curb and marked the point where the 45 degree edge contacted the tank.

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Then I can mark my center point for the inlet hole.

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I marked this location this way so I could use standard 45 degree elbows to connect the pipe to the surround wall. I tried to position this hole as high up on the tank as possible. Not so high that it would not run into the thread lip where the lid screws on.

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You don’t get a lot of second chances drilling holes in a big tank. So I took my time planning and thinking this through.

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I used a large hole saw for the inlet and overflow pipes. On the slow setting, I drilled until the pilot bit pierced the tank, then clicked the drill in reverse to cut the big hole. This keeps the hole saw from grabbing. And this worked really well.

A rubber grommet fits in the hole and the pipe expands the rubber to make the seal against the plastic watertight. Then I push in a short piece of pipe. It’s tight and a bit of soapy water helps.

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So that water entering the tank does not stir up sediment, I’ll run a pipe to the bottom with two elbows to create a calming inlet.

This will keep the water from splashing as the tank fills. I glue up a 90 and 45 fitting and attach it to one end.

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Then add a 90 to the other end.

Then set this in the tank and attach it with a stainless steel screw. In case I need to remove it at any time later.

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Now, I can drill the hole for the overflow siphon.

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It’s just slightly lower than the inlet hole. And I needed it to rotated around this access hatch wall so it didn’t run into the inlet pipe.

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Then a short piece of pipe is convinced strenuously that this is it’s new home.

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For this tank overflow I’ll use standard fittings to create a siphon. It’s made from three 90 degree elbows and an angled pipe.

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When the tank is full this siphon will skim water off the surface and send it down a pipe to the dry well that I dug in Part 1 of this series.

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Now I’ll glue that in place.

You can buy a siphon formed from one piece but my suppler was out of stock. I think it works out to be cheaper than making your own when you add up the cost of the fittings. And there’s options without a siphon that use a simple 90 degree fitting with screen to keep mosquitoes out.

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In case the siphon dries out I’ll add a screen on the pipe end that runs into the drain just in case. And that’s done later.

Next I’ll tie the tether for the float to one of the pipes to keep it off the bottom.

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On the other side of the tank I’ll add a gauge. It’s a float on a spring coiled spool that you set to your low and high water points.

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Now I’ll start to put together my assembly of fittings that will attach to the tank inlet. I bought a first flush diverter kit and need to adapt it to 3″ drain pipe.

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The fittings it comes with are designed for the thicker Schedule 40 PVC pipe. The gate valve I’ll be also adding is designed for this thicker pipe.

So I need to first glue in these sleeves to allow me to connect everything together.

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Let me stop for a minute to explain what I’m gluing up here. Water will first run into this angled downspout screen. This will help keep leaves and debris from the gutter from entering the tank.

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Below that screen is a T fitting. With one of the outlets running into the first flush T.

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Below is a gate valve that will connect to the drain pipe that goes to the dry well. When this gate valve is closed water will back up against the gate and then fill the first flush diverter before it finally ends up in the tank.

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So the gate valve will be closed when I want to fill the tank. And it will be left open when I want water to bypass the first flush and tank inlet and instead go directly to the drain.

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Stay with me here, it will become more clear as I attach this assembly to the fence surround.

Okay, moving on.

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I could only find the black ABS adapter sleeves but they will work fine for this. I just need the right glue that works on PVC and ABS together. And you have very little time, a few seconds really, to get the parts in the right position once you glue them and slide them together. And there’s no going back for a second try. You can only guess how I learned this.

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So I’ll glue these sleeves to the first flush T. Then to the gate valve. Then with short pipes I can attach the gate valve and T’s together.

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I didn’t want all the plumbing and fittings hanging off a post on the pavilion. For one there wasn’t enough room and I didn’t think it would look so good.

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Better in this case to keep it all close to the tank on the taller East wall of the surround.

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This assembly is attached to the inside of the east wall using some brackets. A 90 degree elbow is attached to the outlet of the first flush diverter T. Then a pipe and fitting assembly is secured to the tank inlet pipe with rubber couplings.

For some of the plumbing here I tried to think about having to disassemble things later. So I only glued what I really needed to.

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I like these 3″ flexible rubber couplings with the two screw clamps. They are great for quickly taking sections apart. And to manage tough connection points or those that require some flexibility. I’m not sure how they will hold up to sunlight over time so I may have to add some protection for them later.

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Now I’ll add the downspout screen.

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Here I’m adding another pipe and elbow section for the tank overflow. It will run into a Y fitting below the gate valve.

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A length of schedule 40 pipe is glued into the first flush diverter T then a threaded section glued to the bottom of that. The diverter holds a ball, screen, and pinhole washer and this system is designed to catch the dirty water that is first coming off the roof when it starts to rain. I’ll add a link to a previous video of mine that explains this better.

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Now I’ll glue up the pipe that runs around the back of the tank to the drain. It has a screened flapper end.

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Finally I’ll run a pipe from the gutter of the pavilion to the tank surround. This will dump water onto the downspout screen.

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This was a bit tricky to pull off. But it ended up working very well. Later I spray painted this pipe and fittings to match the brown gutter.

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The last bit of plumbing to do here is to add a vent to the tank. For this I bought an RV tank vent and fitted it with a bug screen.

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I cut a disc of aluminum window screen and siliconed it to the base of the vent.

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I cut a hole in the top of the tank with a hole saw.

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Added some silicone to the base of the vent and attached it with screws.

Off Grid Rainwater Harvesting System – PART 4: solar panel and pump

In this 4th episode of my off grid rainwater tank series I’ll install a solar panel on the roof of our garden pavilion behind me.

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Then wire that to a controller that charges a deep cycle battery. And that will power a 12 volt water pump to irrigate part of our garden. I’m not a solar panel installer or electrician, just a DIY’er that’s enthusiastic about solar. Around 5 years ago I installed a solar system on our RV. And that system is working flawlessly to this day. That was a lot of fun to do so I was looking forward to building another system here in the garden.

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The solar controller and other electrical parts will be first mounted on a piece of 3/4″ plywood. Then this will be attached to the back wall of the mini pump house box. The solar controller must be connected to a battery first before it can be connected to a panel. So this is why I’ll build the control board first. I bought a 100 watt panel and controller kit from Renogy. I have a similar setup on my RV and everything is still working fine.

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I first mounted the controller. Then a fuse block in pretty much the middle of the board.

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From the controller to the fuse block is a red positive wire that has a 40 amp fuse.

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To the left of the fuse block is a ANL fuseholder. I sized the fuse according to the gauge of wire going to the battery and with the option of adding a 750 watt inverter later. Once I have the layout set for where everything goes on the board I attach the components and begin to make up the wires for the connections.

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Here I’m cutting and stripping the wire from the positive of the fuse block to one terminal of the ANL fuse. I want to remove just enough insulation so there’s no wire showing when I slide the lug on.

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I have a simple lug/cable crimping tool and it works really well. It’s cheap and its fast. This one is spring loaded so I just set the lug in the jaws, hold the wire, then hit it with a hammer.

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I check the fit then slide on some heat shrink tubing. This will make the connection water tight.

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I’ll secure that cable with washers and nuts and check that the cover of the fuse block still fits.

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On the other side of the board I’ll add a shunt to the black negative wire that will lead to the battery.

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I fabricated a holder for this shunt from scrap plywood as it didn’t come with one. A shunt will allow me to monitor how much power is going in or out of the battery.

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I’m now making the negative wire from the controller to the fuse block. And then the negative from that same terminal to the shunt.

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The wire from the controller is 8 gauge and the wire to the shunt is 4 gauge.

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Here I’ll add a toggle switch for the water pump. I made a small bracket from plywood for this switch. Then I’ll run a positive wire from the switch to the fuse block. This circuit in the panel will have a 10 amp fuse.

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I’ll strip that wire then crimp on a connector. Then heat the sleeve to shrink it. Then secure that wire to the block.

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I drill two holes through the plywood. Then add two bolts to make terminals for the solar panel wires. Then I’ll make up the positive and negative wires that go from the controller to these terminals.

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I’m doing this to make connection and disconnection of the panel wires easier. The controller that came with the kit has terminal screws at the back. And they will be difficult to get to once I mount this board in the pump house box.

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The monitor displays are attached to the shunt and will show the charging and discharging of this battery in this system. I used speaker wire and crimp connectors for this.

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The displays also need power so there’s wires to the panel for this. I’ll attach these monitors to the plywood with velcro.

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Now I’ll connect the red positive wire to the battery. Followed by the negative. If everything is wired correctly then the solar controller will show the battery voltage. And one of the monitors will show a small draw from the battery as well.

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I’m sure it’s just me but I really like making up these systems and mounting and connecting all the hardware. It gives me a real sense of satisfaction.

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Then I can mount this on the back wall of the box and connect the battery terminals.

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The 12V pump I have won’t draw a lot of amps so for now a single 100 watt solar panel will work for this system. The roof of the pavilion is sloped to the south and the pump will only be used in the summer months when there’s a lot of sun.

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The kit comes with roof mounting brackets.

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And they are attached to the panel with nuts and bolts.

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To protect the panel while I’m handling it I’ll cut some cardboard and tape it to the face. And this will also prevent any shorts or sparks from the wires if I accidentally cross them. I’m not sure if I needed to do this. But, it can’t hurt.

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On the roof of the pavilion I’ll set the panel in place and check that the feet of the brackets sit flat between the ribs.

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Looks like it just fits.

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I cut a strip of eternabond tape and stick it to the roof under the brackets. This should make a water tight seal. And the roofing screws have a rubber washer too.

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Now I can drill two holes in the roof for the panel wires.

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These wires will run through a water tight housing that I’ll silicone to the roof.

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I’ll tape that in place while the silicone cures. Then connect these wires to the panel and tuck the connectors up underneath.

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And I can now attach these wires to a rafter with cable ties.

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The wires run down the rafters, along the downspout pipe, across the top of the surround and down and behind the pump house box.

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I added lugs to the ends of these wires and then connect them to the bolt terminals on the board. And it worked out that the wires that came with this kit were exactly the right length to just make it to the terminals.

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I’ll tape up the bare positive terminal. And now I can remove the cardboard from the panel.

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I have a spin down sediment filter that I will also mount on a board before adding it to the pump house. It has 3/4″ ball valve on either side of the filter and I add 90 degree elbows and a barbed hose adapter. The drip irrigation will have additional finer filters but this spin down will catch anything that makes it past the downspout screen.

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And I can mount that in place.

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Even though these 12 volt pumps have rubber mounting feet they still vibrate a lot. So I though I would try to reduce this with an additional rubber mount. I cut a piece of plywood and glued on a scrap piece of rubber flooring. Then I’ll glue this to the bottom of the pump house box.

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I’ll use contact cement for this. You can also see from this angle that I added a plywood divider to the box. This was to keep the electrical side separate from the potentially wet pump side. In case I had a leak somewhere. I’ll set the pump in place and screw it to this small piece of plywood. The contact cement worked very well and I don’t think this board is ever coming off.

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The spin down sediment filter has a valve at the bottom so you can quickly remove some of the debris that builds up. I’ll drill a hole through the box and connect a half inch house for this sediment to drain.

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A black 3/4″ water line runs in to the box from the bulkhead float fitting on the tank and is connected to the barbed fitting on the filter assembly.

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And the outlet of the filter to the inlet of the pump with a clear braided hose. And another clear hose to the outlet side of the pump.

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The pump is wired to the fuse block and to the switch so now it’s time for the first test. I turn on the ball valve on the tank and flip the toggle switch.

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And the system works! It is really nice when it works the first time.

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And here’s a few more shots of the inside of the pump house.

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Let me know your thoughts here, I’m always interested in viewer feedback. As I’d mentioned, I built this system with room to expand in the future. And to power other lights and appliances around the pavilion next year. I left enough room in the pump house box to add another battery, and maybe a small inverter if needed. And the controller and system can handle more solar panels if the one I started with is not enough. I’d have to look at upping my cables and fuses to handle bigger loads of course.

So I hope you have enjoyed this post, and thank you so much for reading. If I make any further improvements or changes I’ll post them here.

And, while you are here, please hit the Support Link to help us make more projects and videos like this. We really appreciate anything you can do to help us out!

 

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