Tuesday, 13 September 2016

One Year of Solar Energy

One Year of Solar Energy

Dodecahedron Books is your best bet for sustainably produced ebooks, with nearly all of our electricity produced by solar power.  :)  You can see that in the graph below.

Actually this graph represents a single household’s power production and use throughout one year, from summer solstice to summer solstice – that’s because we run Dodecahedron Books from our home.  But, all the energy used to write and format the books is in there somewhere – of course the energy that Amazon uses to distribute the books and that readers use to read the books is another matter, but we can’t control those things.

Our system consists of 16 panels, each about 1 meter by 2 meters (a bit smaller  actually), that are rated to produce 280 watts each when perpendicular to the sun’s rays under a clear sky, on a temperate day.  The panels are located in two arrays on the garage, east and west side, with a roof pitch of about 25 degrees.  The garage centre line runs north-south.  So, in the morning, the east side generates the most power, in mid-day both sides do, and in the afternoon it is the west side that produces the most power.  The house is located in central Alberta, Canada, so it is pretty far north – at about the 54th parallel of latitude.  That means we produce a lot more in the summer than the winter, but over the course of the year we send almost as much to the grid as we receive, as the graph above indicates.

In our area, we have a grid-tie system.   Basically, when the panels produce power, the power goes to the house, which gets first call on the power.  Any excess is sent to the grid, adding to the system’s total power, just like any other power generator.  When the house uses more power than the panels produce, power is drawn from the grid.

The graph above includes that “phantom power” that goes directly to the house, and is not captured by the electric meter.  I estimated the amount produced to the house, from electrical bills in previous years, assuming that the house’s usage has remained approximately constant. Operationally, this is calculated as:

average daily KWhrs for that time period – KWHrs taken from Grid

So, for example, if the house had historically used 13 KWHrs per day during the first half of April, and drew 7 KWhrs from the grid, that would imply that the solar panels supplied 5 KWhrs directly to the house, and the remaining power that they produced went out to the grid.

Obviously, this means that power production peaks during the height of summer and drops very low during the depths of winter.  However, as the graph shows, even in December and January, the panels send power to the house, though not enough to supply all needs.  Our winters are cold, but they are often sunny.  Tiltable panels, that could be optimized for the different seasons, would help quite a bit. 

Of course, from day to day, the power production fluctuates according to the cloud cover.  This can be seen in the graph below.  As you can see, on some days no power is produced (extremely rainy and overcast days), while on others a substantial amount is produced (bright sunny summer days).

If we look at a 7 day moving average (that’s the average of the three days before and after a given day, as well as that day), the data is smoothed out considerably.  The graph below shows that data.  That would be most relevant for someone considering going off the grid, via something like Elon Musk’s Powerwall batteries.  However, even with that, at norther latitudes you would still have a problem generating sufficient power, likely needing a backup supply of some kind (e.g. a small diesel generator).

The graph above also shows a nice summary of the local weather.  The long days of June and July don’t produce nearly as well as one might expect; that’s because we often have quite a bit of rainy weather during those times (it does make for an excellent climate for growing crops and gardens, though).  Conversely, though autumn days are relatively short, they can be very sunny and clear, with very little obscuring dust or haze, and therefore can generate more power than expected.

I will look at some other aspects of the data in another blog.

In Kati of Terra’s universe, the more advanced planets make great use of sustainable energy.  Read them and find out more  :).

Kati 1 - Escape from the Drowned Planet
Kati and Mikal's escape from the alien slaver Gorsh.
Amazon U.S.: https://www.amazon.com/dp/B00811WVXO
Amazon U.K.: https://www.amazon.co.uk/dp/B00811WVXO

Kati 2 - On Assignment on the Planet of the Exalted
Kati and Mikal follow the trail of justice to the planet Vultaire.
Amazon U.S.: https://www.amazon.com/dp/B00D0H15CC
Amazon U.K.: https://www.amazon.co.uk/dp/B00D0H15CC

Kati 3 - Showdown on the Planet of the Slavers
Kati and Mikal must battle Gorsh on his home turf.
Amazon U.S.: https://www.amazon.com/dp/B00KHBN8FG
Amazon U.K.: https://www.amazon.co.uk/dp/B00KHBN8FG

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