Summer solstice

Longest day of the year?

PhotoPills screenshot showing time/date for equinoxes and solstices.

Today is the summer solstice (in the northern hemisphere). More precisely, the solstice occurred at 5:15am here in the Eastern timezone. The summer solstice is the moment at which the sun has ‘traveled’ to its northernmost latitude, in its annual cycle of apparent movement to the north in summer and to the south in winter. (It’s a great day for those of us with solar panels, because it means we’re getting hours of sunlight!) Read on.

Continue reading “Summer solstice”


Equal day and night.

Today (22 September) is the fall equinox – when we have equal amounts of the day with sun and no sun. The length of the day is changing fast – indeed, faster than any other time of the year except spring equinox – and it is really noticeable every day. Today was rather cloudy, not a great day for solar power:

Continue reading “Equinox”

Summer Solstice

Maximal sun makes maximal power.

Today is the summer solstice in North America, so I was especially interested to see how our solar tracker managed on the longest day of the year. A few weeks ago we doubled our battery storage so we could extend our independence from the grid. Given the extended daylight (15 hours and 27 minutes, from 0507–2034), and the extra battery, the batteries can now last through until sunrise. Although today’s weather was not purely sunny, the system produced over 50 kWh.

In the graph below, the green line shows the battery level declining in the early hours, and climbing after sunrise. The dark blue region shows the house consumption, and the gold region shows the excess solar production… used first to replenish the batteries, and then, after 2pm, to feed back to the grid.

Today was a good day… but not the best day yet. Two days ago was more sunny, and we set a personal record for solar production: 58.58 kWh:

Spring equinox

Spring is here in the valley.

Today is the vernal equinox – the spring equinox – when the length of day and night are equal (equi = equal, nox = night). Actually, “They are not exactly equal, … due to the angular size of the Sun, atmospheric refraction, and the rapidly changing duration of the length of day that occurs at most latitudes around the equinoxes” [Wikipedia]. Here in New Hampshire, Sunrise was at 6:51am, Sunset at 7:01pm.

For those who welcome the arrival of spring, today is when we are adding more minutes of sun per day than at any other time. We’re on the steep part of the curve! This is great news for our solar tracker, which put in a banner effort today under nearly clear skies, with a total production of 45.57kWh:

Technically, the equinox is “the instant of time when the plane of Earth’s equator passes through the geometric center of the Sun’s disk” [Wikipedia]. This year, that occurred at 0937 UTC, or 5:37am here in Lyme, which happens to be about when I got up this morning.

Interestingly, it has long been noted this is the “day when the Sun rises due east and sets due west, and indeed this happens on the day closest to the astronomically defined event.” [Wikipedia again].

On cue, the Connecticut River decided it is also ice-out day – the day the winter’s ice breaks up and the river begins to visibly flow. I’m pleased to see open water, because it means that bald eagle might be seen more often in our neighborhood once again, now that it has an opportunity to fish.

ice-out on the Connecticut River, in front of our house

The forecast shows nothing but clear skies, warm days (50-60º) and cool nights (20-30º). Great weather for sugaring! More on that to come…

Solar flat

Even on a windy day, we can still generate power.

It was a wild and windy night, as a cold front blew away yesterday’s warm temperatures. Our solar tracker is designed to protect itself by going flat when there are gusty or strong winds, and that’s how I found it this morning.

Solar tracker goes flat in windy conditions.

You can see the anemometer at the far-right corner, which is on a gimble so it can measure horizontal wind speed even as the tracker tilts.

That picture was taken about two hours ago. It’s now quite sunny, and still windy; the tracker is still flat (and thus not pointed at the sun), but still generating enough power to serve the house, charge the battery, and feed the grid:

Solar complete

Solar and battery and generator.

Finally, more than six months after we received the initial proposal from a local solar-power company (Solaflect), we have a complete system installed: last week, they completed the installation of a battery back-up solution from a German company called Sonnen. Our house can now be supplied by solar power, grid power, battery power, or propane-generator power, depending on the situation. Although I won’t dig into all the details, it’s pretty cool, so read on…

diagram of power flowing
A screenshot from the Sonnen battery portal showing power flowing from the solar tracker into the house (supporting its consumption) and into the battery (keeping it charged) and into the grid (selling power back to the electric company). The actual graphic is animated, showing power ‘flowing’ from the top to the other three destinations.
Continue reading “Solar complete”

Self-protecting tracker

Last night it was extremely windy, with large gusts barreling down the river valley. The forecast was for 2-6″ of snow, but we ended up with only a dusting as the nor’easter storm held mostly to the south. Our solar tracker, however, decided it was better to spend the gusty night horizontally.

Seen from above.

The panel has an anemometer on the upper-right corner – seen here in the right-most corner, on a gimbal so it stays upright regardless of the panels’ angle – and when it detects high winds or strong gusts, moves the panels into a horizontal position to protect itself. It spent the night this way.

Seen from the deck.

Normally, it spends the night in a vertical position, to avoid accumulating snow, ice, or dust. This morning, the winds are calm; when the sun rose , though invisible behind the clouds, the tracker steered into its normal sun-tracking mode.

Sun overhead

The sun was directly overhead Bangalore.

Thanks to Prof. John Thorstensen’s excellent JSkyCalc software, I was able to calculate that the sun was directly overhead Bangalore today.

I think this is really cool.  As I live in the north, the sun is always to the south of us. Each year the sun processes further north in summer, and south in winter, but never passes overhead.  Here in the tropics, by definition, the sun passes overhead Bangalore (13° 01′ 23″ north, which I can read from Google Maps) on its way northward to the Tropic of Cancer (23° 26′ 22″ north), and then again on its way southward to the Equator and then the Tropic of Capricorn.  I missed the opportunity, unfortunately, to run outside at noon (local solar noon, of course, not noon IST) to see that my shadow was directly underneath me.  But now it’s kinda cool to think that the sun is north of me!

This post was transferred from MobileMe to WordPress in 2020, with an effort to retain the content as close to the original as possible; I recognize that some comments may now seem dated or some links may now be broken.