My power time-series graphs look funny. Why?

The most common unusual-looking time-series graphs SolTrex.com are typically graphs with horizontally compressed periods with little or no energy production (such as night time) and horizontally expanded periods with greater energy production. (For an example of this type of graph see Mary Street Residence, as opposed to the more normal-looking Calallen High School). This result is caused by the method of sampling data used at the site. For many small sites, instead of saving data corresponding to every 15-minute interval, which would require saving 96 data records per day, we instead record the timestamps corresponding to the completion of each kilowatt-hour of energy production.

For a small 2 kW residential system, this reduces the number of data records stored from 96 per day to somewhere between 0 and 10 per day, depending on how productive the system was during that day. This method maintains an accurate count of energy generated each day, as well as over days, months, and even years, but results in lower data resolution when viewed on an hourly- or shorter time scale. We use this method only on systems with an AC rating of 10 kW or less; the most common examples are our residential systems in Massachusetts installed with MTC support and our commercial systems on BJ's Wholesale Club stores in Long Island, NY.

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