Home Solar Power Outside Peak Sun Hours

How much power can a solar system crank well outside of the “golden hours” for PV electricity generation? Here’s an example.

While peak sun hours generally fall between 10AM – 4PM, even not long after sunrise and towards sunset can see useful levels of power generated.

Making the most of solar power is about maximising self-consumption; running power-hungry appliances during high solar energy production hours where possible in order to minimise mains grid electricity consumption. But lower-power appliances can start running purely off your solar panel output not long after the sun has cleared the horizon.

I recently had a 10kW solar system installed consisting of 24 Trina Solar Vertex S+ panels, a Fronius inverter (Primo 8.2-1) and Fronius smart meter. It’s not a perfect setup in terms of panel orientations (2 roof faces – NNE and WNW) and our current energy consumption profile¹, but not particularly bad either.

During its first week of life on our home’s rooftop, I was keeping a pretty close eye on things, watching system performance under various conditions courtesy of the real-time reporting generated in Fronius Solar.web. This service also offers various daily, weekly and monthly reporting options as well, with reports you can download in CSV or Excel format  to peruse at your leisure.

Spring In Our Solar Step

Spring is a pretty good time for solar energy production given the longer daylight hours, (generally) clearer skies and often mild daytime temperatures (heat is the enemy of solar panel efficiency). While this spring has been a bit crap on the clear skies front to date in Adelaide,  here’s how things panned out in terms of power output on a clear, mild day in late September up to around mid-morning and then from late afternoon.

• Inverter had “woken up” by 5.38 AM².
• Sunrise began at 6.03 am
• 6.04 AM: 10W – enough to power an LED light fixture
• By the time the sun had cleared the horizon (but houses in the way) – around 50W.
• 6.15 AM: 100W – enough to power a few LED lights and a notebook, with capacity to spare.
• 6.50 AM: 1kW – more than enough to start the washing machine (cold cycle) as well.
• 7.15 AM: 2kW – turn on the big screen (LED) TV while waiting on the washing. You’ll still have power to spare.
• 8.10 AM: 4kW – along with everything else above, the kettle could go on – and that only draws for a couple of minutes. Among other appliances that could be used is a microwave oven or a vaccuum cleaner. You could start loading up at this point.
• 8.35 AM: 5kW output.

.. and so on, until around 10.25 AM when the system had reached its maximum output (while I was testing) with various appliances in use and the SAPN-imposed solar export limit of 5kW in play. It reached about 7.93kW output at its best while fiddling.

But we should have whacked on another appliance to see if we could squeeze a bit more out of it; bearing in mind while there’s 10kW of solar panels, the solar inverter is rated at 8.2kW. Having more panel capacity than inverter capacity is a common practice called oversizing – explained here.

Then towards the evening, I kept an eye on output at various stages again:

• 4 PM: 4kW
• 4.15 PM: 3.4kW
• 4.30 PM: 2.8kW
• 4.45 PM: 2.3kW
• 5 PM: 1.8kW
• 5:15 PM: 1.5kW
• 5.30 PM: 750W
• 5.45 PM: 280W
• 6 PM: 196W
• Sunset (sun down over horizon): 6:13pm
• 6:15 PM: 0W
• Last light – 6:38pm.
• 6.47 PM inverter goes offline.

Something I failed to do was set up daily energy³ production reporting (5 minute intervals) in Fronius Solar.web – which was rather silly. It would have been useful to show total energy production for those two periods on that day⁴. But even without this information, the above shows a largish solar power system can make worthy contribution well outside of peak sun hours!