My house uses natural gas for space heat and domestic hot water. When analyzing the benefit of my solar collectors, the obvious thing to do is to examine the actual change in my gas consumption. To answer this, I've plotted the amount of gas I burned per heating degree day (HDD) per month. Using HDDs adjusts for the variability of the weather and allows an apples-to-apples comparison between different years.

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I thought I'd share some graphs showing the output of my solar collectors and the results of my recent renovations (collector installation included) on my home energy use.  Here is the heat collected (measured in kwh) plotted with the maximum daytime temperature:  read more... »

Unlike vehicles where it is easy to compare efficiency by comparing the mileage (expressed in either miles per gallon or litres per 100 km), comparing efficiency of two houses - or comparing efficiency before and after improvements to a house - is much more difficult.  If a homeowner makes an investment in improved energy efficiency it is difficult to compare the effect of the improvement from one month to the next due to seasonal changes.  Comparing a months worth of post-improvement energy consumption with the same month of the previous year or even the average of that month over the previous X years is an improvement but still doesn't really provide a direct “apples to apples” comparison as the month immediately following the improvement may have been warmer or colder than usual.  read more... »