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No matter how I slice it, adding solar panels to our house is just plain expensive.  Even with the current tax incentives and credits from the utility companies, I ran the numbers and a system will still set us back about $20,000 by the time it’s all said and done.  With that in mind, we set out to tackle all the passive solar and energy reduction projects that we could before jumping into active solar.  In case you don’t know what the difference is between passive solar and active solar, let’s start with a brief explanation of the two:



Passive Solar

As you might guess, passive solar is the practice of reducing the suns heat load in summer, and increasing it in winter.  The goal is to strike a balance between your home and the seasons to maximize you heating and cooling efficiency.  Here in Arizona, we lean hard towards the cooling side of that equation, but in cooler climates, it makes sense to look at ways to reduce your heating demand by taking more advantage of the sun.  The good news is that many of the same strategies that are employed to thwart heat gain also work to prevent heat loss.

Most passive solar has little to no operating costs and typically requires little maintenance. The tradeoff is that many passive solar techniques need to be designed into the home or office in a way that yields the best performance. By conserving energy, it reduces the required size of any active solar system (solar panels) that needs to be installed.  This means that you get to keep some of the “green” in your pocket.  

Active Solar

Unlike Passive solar, active solar essentially uses the sun’s energy to produce power, hot water, or other energy through the means of employing technology.  Examples of active solar include:

• Photovoltaic solar panels
• Solar how water heaters
• Solar steam engines

There are others, but these are some of the most common.  The problem with active solar is that it’s expensive and therefore takes a while to realize your return on investment.  Not that adding solar panels to your home or office is bad, just that it will take more money up front. 



Passive Solar: Attic Insulation

Since we are going into summer here and the temperatures hit 100 today (May 31, 2008,) I thought I would share with you the project that I have been procrastinating on for a couple years:  attic insulation.  Our house was built in 1938, is 1,137 square feet, and is made of double bonded brick.  This means that the walls have no insulation.  So the only thing I can do to add insulation is beef up what we have in the attic.
 
Our fairly spacious attic has a 1 inch layer of rock wool and another couple inches of fiberglass blown in on top.  And, insulation was completely missing in areas where work was done to duct work, lighting , etc. over the years.  Since the insulation companies claim that 40% of the heat gain/loss is through your attic, I thought that I had a legitimate chance to reduce the heat load coming in from the attic by having more cellulose blown in.  In our neck of the woods, the department of energy suggests that homeowners have R49 in the attic, which is the highest rating listed.  Check out the map below and see where your home should be.

I called around and found that most shops were within a few dollars of each other, so it came down to who offered the “greenest” product.  I settled on a company that uses a cellulose product called Green Fiber.  This product consists of 85% recycled content (newspaper,) and is specially treated for flame resistance.  In fact, they have a pretty impressive video that shows how it compares to fiberglass in a burn test.

 
We have about 1,100 square feet of attic space which cost $744 after tax to bring up to R49.  That’s 14.5 inches of passive solar, cellulose goodness.  But how much money does passive solar via attic insulation save?  Let’s take a look.

Looking at usage history on my power bill, I divided our usage into two segments that roughly translate into summer (June - October) and off-summer (November to May.)   In summer we average 2,221 kilowatt hours of power per month and in “off summer” we average 1341 kilowatt hours per month.  The difference is roughly our cooling load because we run the air conditioning in the summer months.  This is a difference of 880 kilowatt hours per month or 4,403 over the course of the summer months.  Make sense so far?  Good, let’s keep going, because here’s where it gets interesting. 

The Department of Energy says that we lose roughly 40% of our heat and cooling through the attic. Of course that assumes no insulation so I’m going to be conservative and say that we will only save 20% heat loss/gain as the result of adding R49 insulation.  That’s half of what the DOE says we will save by adding R49. Even at 20%, this saves the equivalent of 880 kilowatt hours (4403 * 20%) of the additional power used for cooling each summer.  At a rate of $0.105 per kilowatt hour, this will result in a savings of $92.46 over the course of the summer months.  Assuming no other efficiency gains in heating or cooling during the more mild months, this will provide a 100% return on investment within 8 years.  Less if you factor in the double digit rate increases that the utilities are applying for each year.  Plus, I get a 10% tax credit on my 2008 taxes.  It’s not much, but every little bit helps.   

But what about Solar Panels or Active Solar?

If you want to compare that to installing solar panels (active solar,) that same $744 spent on insulation would buy one (yes one,) 125 watt BP Solar Panel.  This would produce roughly 250 kilowatt hours each year or $26.25 worth of power at our current rate of $0.105 per kilowatt hour.  The problem is that you would need to spend a minimum of another $800 to invert the power from the solar panel and route it into your grid power.  Never mind the mounting system, permit, inspection, and wiring costs.  And since inverters are only about 85% efficient, that means your $26.25 worth of power coming out of the shiny new solar panel will get cut to around $22.31. That pencils out to a 69 year return on investment.  That’s 8 times longer than the ROI for adding passive solar attic insulation.  Hopefully my power bill will reflect a far more significant savings this summer.

Conclusion: Passive Solar makes Sense

 Adding passive solar attic insulation was just one of the items on my list of passive solar projects to tackle before adding photovoltaic solar panels or active solar:

• I have a south facing brick wall that turns into a pizza oven in the heat of the day and radiates heat all night. This needs to be addressed. I’m thinking some sort of green wall like vines.
• I still have more venting to do in the attic to allow maximum air flow. This helps evacuate the hot air that superheats in the attic.
• I have three none air-tight recessed lighting fixtures that need to be replaced so the attic insulation can come in contact with the can and form a tighter seal.
• I have several known leaks that I need to address around doors and windows.
• I want to add sun shades on the south facing windows or at least apply reflective film to the glass.
• Finally , I have a basement to finish that will undoubtedly require a great deal of sealing to ensure the cool air doesn’t escape.

Ultimately, a passive solar strategy will never lead to energy independence, but it is a great partner to the technologies that will.  By adding the attic insulation and saving 880 kilowatts of energy, I can reduce my photovoltaic (solar panels) system by nearly $2600 worth of hardware.  In this example, that’s more that $3 savings for each $1 spent.  Many passive solar projects are far cheaper.  I hope you take a minute and look in your attic, crawl space or basement.  I bet you have some small projects that will net big results. 

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