Taking My Living Room Off The Grid

March 2009

My first major step toward energy independence.

 

My small solar array has grown over the past year.  Now at 225 Watts on the roof, 400 Watts by the end of the month.  I'm running my outdoor lighting via an inverter.  More details on that project here.  By about 11 AM, my array has replenished all the power used the night before.  The battery bank is at 100%, and the charge controller switches to a float mode.  All the energy that could be collected over the rest of the day is unused.  Time to make my system start paying for itself.

It's a lot easier to save energy than to create it.  First move was to get rid of the incandescent bulbs, and move to Compact Fluorescent Lighting (CFL).  These take a fraction of the energy to produce the same amount of lumens.  In each of the two lamp fixtures, I'm now using a 20 Watt CFL bulb, which produces 75 Watts worth of light.  I used a Kill-A-Watt meter to verify each fixture was drawing exactly 20 Watts of grid power.

The next step was to run these lamps from an inverter.  I wanted to verify there was no flicker, hum, or any perceivable different in the lighting when on grid power, versus running on a Modified Sine Wave (MSW) inverter.  I couldn't detect any difference.  I then measured the DC current to determine the current draw while running from the inverter.  3.40 Amps.  3.4 A x 12 V = 40.8 Watts.  The inverter has some losses as well, but that's pretty close to the expected 40 Watts.

These lights will be run 5 or 6 hours a day typically.  40.8 Watts x 6 hours =  245 Watts.  Doable, even with my small array running the outdoor lighting, security system (CCTV), LinkPro monitor, and the self consumption power of two charge controllers.  With a 70% derating factored in (typical for solar panels), and my location (5 hours peak sun), my array collects about 787 Watts.  With all my present loads, I consume 376 Watts per day.  Leaving 411 Watts.  It's enough for this project, but I have another 45 Watt solar array waiting to be installed, and another 130 Watt Kyocera panel on order.

 

The heart of this project is a $29.99 Vector inverter.  It is a Modified Sine Wave (MSW) type inverter, but the CFL bulbs don't care.

 

The Test Setup

To verify the quality of the lighting would be the same via a MSW inverter, I temporarily setup the hardware in the living room.  A 400 Watt Vector inverter with a small 12V battery.

With both lamps up to operating temperature, the total current draw (both lamps and inverter losses) measured 3.40 Amps.

Two lamps light up our living room reasonable well at night.  We have skylights, so natural lighting keeps the place bright most days.  The inverter and battery are sitting on the floor for the test.  An extension cord is running to the lamp furthest away.  Both lamps operating from the inverter in this picture.

Each lamp is fitted with a 20 Watt GE CFL bulb.

Close-up of the $29 inverter.

Back panel, not much to see.

CFL bulbs are cheap these days.

They are also available in many shapes & sizes.  I'm using a pair of these in an antique desk lamp.

 

The Installation

The  inverter was placed next to the battery bank, and installed a new outlet in the living room.  It operates from the inverter.  The trick was to remotely operate the inverter.  If the inverter is left on all the time, it becomes a parasitic load.  This can be accomplished by using a relay at the inverter and a switch in the living room.  It can also be done with a wireless remote control, which is the route I've taken.

 

The 12V wireless kit was purchased at Amazon for 34.95.  Includes two remotes.  Very simple to connect.

 

The built-in relay in the remote control is limited to 6 Amps.  I added a 30 Amp Bosch type relay to the output so it could supply 12V power to the inverter when needed.

The wife has some requirements.  The installation must be hidden, and things must operate normally.  Not a problem.  I selected a location on the short wall leading to the patio.  Marked the location for the box.

I punched a test hole with a screwdriver.  I knew there wouldn't be much room behind the drywall since this is an exterior wall, with block construction.

Cleaning up as I go.  Yea, I probably should have used a drop cloth.

No way that deep box is going to fit in the wall without busting out the block behind it.  So off to the bandsaw.

Sliced off the bottom of the box, leaving the mounting wings intact.  Note the inverter on the wall in the background.

Done.

The modified box now fits nicely in the opening.

I drilled a hole at the top of the wall to pull the wire through.  If I had good access, I could have drilled down from the attic.

Wouldn't you know it, there's a wall stud right where I drilled.  I had to keyhole the opening to get in the wall space between the drywall and exterior block wall.  I ran a metal fish down the wall.  The good news is I now have an easy way to route the wire into the attic.  This is when the wife starts asking questions.  ;-)

The end of the fish was pulled out the opening, and a nylon cord was attached.  After I pulled up the cord, I ran another cord through the top hole into the attic.

Not the black cable in the foreground, but the white cable in the background is coming from the living room.  Tough to reach without a pole with a hook on the end of it. 

Once I hooked the cord, I pulled it over to me, and tied the 14 gauge power cord to it.  My wife pulled the cord from inside the living room until the power cord reached the floor.

The end of the cable was then tied to the cord running behind the drywall, and pulled down to the outlet opening.

The cable was pushed into the keyhole slot I made earlier, and the drywall is ready for repair.

Me on top of a ladder filling the hole.  I'll later sand it, texture it (spray product), and paint it to match.  Wife is straw-bossing, so need to do a good job!

Since I hacked off the back end of the outlet box, the cable entry slots are gone.  I drilled a hole in the top of the box and fed the cable through it.  Note the wing on the top right of the box.  There's another one on the lower left of the box as well. 

When the screws are turned, the wings flip out behind the drywall, clamping the drywall between the tabs on the top & bottom of the box, and the wings.

Outlet wired up and installed.  A little tighter than a regular outlet, but still plenty of room.

Sorry for the fuzzy pic, but the job is done.  Looks like any other outlet in the room.  Same style, same color, same height.  I plugged one lamp in each outlet to prevent something else from being accidentally plugged in.  I will place a discreet decal on the faceplate (black on clear lettering) indicating this is an alt-power outlet.

 

Conclusion

The toughest part of this job was having to sneak a power wire down an exterior wall.  I'm sure the pros have specialized tools for making this a simpler task.  But the fact is not even the cable company does inside the wall installations anymore on existing homes.  They simply bore a hole through the outside of the wall, and run the cables outside.  I could have easily done just that, and ran conduit up the patio wall.  But that wouldn't look as nice, and I'm sure the boss wouldn't be happy.  The results were worth the effort.

When it was all installed, I handed the wife the remote.  She pushed the button, a second later the lights came to life.  It was a bit of work to wire it up, but nothing too technical.  As the she noted, we're going green.  My living room lighting is now free.  Nice part is it will work despite what the grid is doing during hurricane season.

We used the lights all evening as we normally do.  Went off to work in the morning, and by the time I got home, the LinkPro monitor showed that the battery bank was 100% once again.  The calculations were correct.  The array makes enough juice to run the lights and the other equipment mentioned earlier.

No more buying batteries for flashlights.  Our lights don't go off when the grid goes down!  Now to move onto another room, and take more lights off the grid.

 

Update!

The night before last, the lights wouldn't turn on via the remote.  Has been working flawlessly for the past two years.  I went into the garage with the remote, and pushed the button.  I heard the relay "click", but the inverter had no power.  A couple more tries, it started working.  Relay contacts were shot.  Hey, I only paid a buck for this relay on Ebay!  No problem, I had ten new ones I purchased a few months back.

Nice part about having the hardware on a piece of plywood is easy access, easy replacement.  I swapped one wire at a time.  The new relay is rated for more current, though I didn't exceed the rating of the old one.

A quick press of the remote, it works!

A view of the old relay just before chucking it away.  Think I'll avoid this brand in the future.  Probably all made in China, no matter the brand.

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Last updated 5/27/11    All rights reserved.