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Monday, March 23, 2015

Reviewing our renewable energy and efficiency investments.

Since my ex-wife and I purchased our home in Maine in 2001 I have been working at reducing our energy footprint as part of my commitment to live as sustainably as practical.  My strategy has been to reduce use of fossil fuel by improving things like building insulation and increasing efficiency in general. But also I have added renewable energy sources such as a solar heating system for the hot water in our home and the 5.8 kW solar array I installed, and the solar augmented heating system for my workshop.  I decided to review my progress so far since I have extensive data on all of our energy sources and costs.  This information is derived mostly from our utility bills.


We use propane to heat the house and also for cooking, clothes drying, and water heating.  The chart below shows our annualized usage and cost for propane per heating season.  As you can see we have reduced our use of propane by about 50% over the years.  The biggest impact was the solar water heating system installed in 2006.



Not factored into our relatively low propane costs is the fact that we burn up to 2 cords of firewood per year at a cost ranging from $300-$500 per year. In 2014 we spent $425 for firewood which brings our recent total heating cost to a little over $1400 which is less than half the Maine state average for home heating costs. 

Some of the things responsible for our diminishing usage are:
I built a solar augmented heating system for my super insulated 1260 sq.ft.workshop in 2001.  Since then I have reduced the use of propane to heat the building by 75% by lowering the thermostats and transitioning to burning (renewable) firewood that I mostly cut from my own 2.5 acre lot. 

Thanks to the solar power system I installed, our average electric bill would be around $10 if we did not have the Chevy Volt electric vehicle which adds approximately $45 per month to our monthly bill.



The $45 average monthly electric cost to charge the Chevy Volt is reducing our gasoline usage by about 26 gallons for that vehicle since we drive in electric mode about 60% of the time.  (The remaining 40% are driven in “range extender” mode at approximately 40 mpg.)  And since a large percentage of the charging power for the Volt comes from our solar array in the summer, we are driving for largely free and carbon neutral during those months.

One can look at all of the investments I have made in reducing our energy footprint in terms of return on investment. In actual dollars most of these investments have already paid for themselves, such as the solar hot water heating system I installed in 2006 which according to my calculations paid for itself in approximately 4.5 years and will save us an estimated $11,000 over 25 years:

 
In general investing in renewable energy yields a better return than investing in the stock market. Even my relatively expensive solar power installation that has cost me over $25,000 will pay for itself within 16 or 18 years (accounting for federal and state incentives) assuming it had been financed at below 5% interest.  Since I have already paid off that system, the energy savings is all pure profit at this point.