Our Solar Roof Hot Water System was installed on 28th February 2007.
The main reading of interest is the temperature of the Hot Water in the morning. The "morning"
temperature is after the night time cooling of the water in the tank, but also represents our peak
personal hot water use time (e.g. morning showers).
We witness that the typical morning temperature is "on average" well above the 120F temperature
recommended by the EPA and EnergyStar as a typical heat to tempertaure for Hot Water. This pie
chart shows data in increments of 10F with values less than 120F dedicated to their own slice.
We in fact see that around 70% of our morining readings are over 140F, which is a great
temperature for our Dishwasher (it is too hot for our Shower without cooling).
We witness great solar heating performance for our hot water. The following plot shows the percentage of
days where our hot water was heated by the sun only (i.e. no supplemental heating). When we planned the
system we estimated an average performance of 80% over an entire year, we actually witness a few points
above this over the year. In the winter months solar heating is around 50%.
The plot below is the distribution of the temperatures in our Solar Hot Water System.
The key items in this plot are the 10th percentile, 25th (or first quartile), 50th (Median) 75th (or third quartile), and 90th percentile
Or expressing this another way, 80% of all readings are between the 10th and 90th percentiles, and are between the upper and lower limits of the plots
The red dots on the plot represent the "outlier" values, i.e. values in the 20% not included in the main plot
The plot of all the measure T3, which is the temperature at the top of the hot water tank. This is where we draw hot water from
Peak Heating occurs between noon and 2pm. Peak Cooling occurs between the afternoon and morning records, with the morning typically demonstrating the lowest temperature. The plots are shown in the order of MIDDAY, AFTERNOON, MORNING
Even allowing for the cooling through the night, the typical water temperature the following morning is well above the 120F "heat to" temperature for domestic hot water as recommended Energy Star Home Saving Tips
Plot of data
The same data can be seen in the following animated GIF. This shows a plot of the readings in the Morning, at
Noon and in the Afternoon along with the corresponding "box and whisker plot". Every 2 seconds the image will
change, the fourth image being the combination of all the plots.
