April 9, 2012 by: Eric Mac Inerney

Solar Panels on Front

Solar Panels on the Front roof Area

There is a 5.76 KW solar array on the Purple Heron House.  Given that the house is a 5-star rated (or will be when Autsin Green Building finishes its process), we looked into Solar as a way to make the house even more effiecient (with the current efficiencies of the solar panels, it is usually better to conserve first and then look to generation).  At the time between the rebates from Austin Energy and the Tax credits from the Federal Government, the system ended up costing about $9500.  Looking at the current rates and the almost certinty that rates would continue to increase, it seemed a good time to try out the system.  From the outset we knew that an array of this size would not make the house net-zero energy, so we tried to get as big an array as we could without going to herculean lengths. Now that things are settling in, it seemed to be a good time to check in on it.  

The array is actually broken into three parts to take advantage of the sunny areas.  There is a lot of shade on the roof and most of my reading says that shade on a roof is far more energy efficient than solar panels, at least currently (sorry for the pun).  Actually, with this roof, the panels are hard to see as the pitch is 5/12, the house sits high on its site, and the aforementioned trees cover a lot (I had to work to get this picture).  The metal roof makes adding solar very easy as there are special clips that attach to the standing seams without putting holes in the roof.  If you are remodeling or building new, it is a good idea to go ahead and plan for solar -- Circular Energy did this design for this house and they have a program for helping you design a "Solar Ready" house that makes it easy to get the panels and wiring in place.  In this case it meant planning boxes that the roofer installed to alllow the wiring to get into the attic.  The panels came about a month after the house was complete.

Solar Panels on RackRear Panel Rack on North Facing Gable

One of the interesting aspects of this install was that we placed panels on the north facing roof because the south facing roof gets so much shade.  Of course, the north facing roof does not get much sun, but by building a reverse slope rack on the dormer, we could achieve a good amount of panel room with no shading.

Another cool piece to this install is the use of microinverters (which you can see in the picture of the rear rack).  These microinverters convert the DC energy of the panels to AC at the individual panels rather than the traditional method of having one big inverter.  This has two advantages, both of which came in handy on this project.  First, in a system with one inverter, all of the panels function at one level of efficiency (the lowest), but with the microinverters, each panel can perform according to the sun it gets.  This helps in this installation becuase some of the outlying panels get a little more shade.  The image (below) from the Enphase website for this array shows how the panels generate different levels depending on thier location.  The second advantage is that the ac wires from the panels are allow to travel inside the attic rather than across the roof, so the install is much cleaner.Solar Panel Overview

Display showing energy generated per panel.  Note the bottom left and the top right panels produce less energy because they are starting to get into the shade from the trees.

HOW IS IT WORKING?

That is an interesting question.  Here is the February bill from Austin Energy.  The house used 619 KWH (The previous house used 583 KWH and 535 KWH in the pervious two years, but that early 80s tract home was about half the size) which is really great (but keep in mind February is one of the open-your-window months in Austin).  The meter read 455 KWH generated.  So overall the house netted 293 KWH ($27 on the Green Energy Program) -- almost half the electricity for twice the house!

Energy Bill

However, the energy produced (as recorded in the meter) is somewhat below expected, and more confusing is lower than the Enphase report from the inverters.  Accroding to the Enphase report, the array produced 598 KWH which would make the house close to zero-energy (for that month).   I will be looking into this and will give an updated report when I know what is occurring.  It may be that some of the generated power is being used by the house and not being recorded in the meter.

I can't wait to see the summer energy production, but the AC will be running then as well.

One last piece of eye candy from the Enphase web site:

Environmental Benefits resized 600

 

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