It’s a miserable, shitty, overcast day here in Otaki, and what better way to use it than to generate some fodder for my blog. And I had hoped to put my washing out today – oh well. At least one silver lining in this is I get to get some forward intel to help me plan ahead for the winter months, to see how our energy use will be affected.
A Sunny Day:
While no two days of solar power generation are exactly the same, here’s what a typical summer day looks like. Keep in mind that the system we have set up is a fairly basic 1.5 kWh system, but with six high quality micro inverters.
On this day our solar power system produced 10.8 kWh of which 5.6 kWh were exported to the grid. On the flip side 12.9 kWh were consumed (across the whole day, including night time usage), of which 7.7 kWh were imported from the grid.
You can see how we have a system that creates a bit of a predicament for us. On sunny days it generates way too much power for us to realistically use during the peak times. The remainder gets exported back to the grid at no benefit to us.
Rainy days have the flip problem, however. Often, the system generates too little power relative to a fairly consistent daytime base level of demand for household energy.
Not to mention, one’s usage is generally far higher on rainy (and particularly cold) days relative to sunny days. That is one of the many predicaments that occurs with solar, but on the scale of some of the world’s problems, it is not the worst problem to be having.
At 9am:
Barely even a trickle of energy coming through. Damn. I had hoped to put the washing on and get the power component done for free.
Our peak so far has been 34 Wh between 7.45am and 8am. This is realistically less than 10% of its generation potential, but not unusual for this time of day. All of the energy that the panels have generated has been used by our household.
At midday:
So the sun has come out from behind a cloud and the rain has abated. All in all this project looks like it might turn into a bit of a waste of time as the sun has come out anyway. It’s still pretty overcast though.
We’re coming up to reasonable levels of solar generation again. As you can see we’ve actually had some surpluses, although not as many as usual. The main thing is that most of our energy needs are being met by solar production.
I’ve already put through the washing load. I even feel comfortable enough to switch on the slow cooker at this point, and get some extra juice out of my solar surplus.
At 3pm:
So the sun did come out for a bit but has now retreated into a mostly overcast although not rainy day. We’re starting to see some more regular patterns of energy production although there is still some huge variability there. And of course we are back into surplus territory.
It is likely that, despite the overcast weather, we are actually getting additional solar power production because some of the trapped light is reflecting from the clouds back down on the solar panels. So all in all, despite some overcast, it’s not a bad day for energy production.
At 6pm:
By 9pm:
Ok, so I skipped the 6pm lookup because I got carried away doing other stuff. So sue me. Nevertheless, the 6pm results are included in the 9pm results, and by this point the weather has fined up and solar generation is back up to standard. We did have a mostly overcast day, but the energy generation was still there consistently in the afternoon and evening.
Daily Summary
I wrote this blog article to help people understand some of the practical day to day problems that you encounter with a small scale household solar power installation. Hopefully this can give you a taste of the reality of solar, if you don’t already have an installation.
An overcast or even rainy day does not mean that solar power generation will be entirely wiped out – just that it will patchier than usual. And for the majority of households during summer, provided you plan it right, the amount generated on a worse-than-usual day should still be about enough to cover your daytime energy needs.
The only real difference is that it does not produce a ‘smooth curve’ of energy generation that you normally see on sunny days. But the result can be more or less the same.
Keep in mind that although the day was overcast with some bouts of rain, it did occur during the summer, so the number of solar hours would nevertheless be longer.
So I don’t have anything really mind-blowing to say. Frankly this exercise was screwed up by the fact that the weather got better towards the end of the day and I ended up going down the beach.
