Home Monitoring (home made) – Reborn

I’d previously shared on my blog the home made monitoring application I’d built to aggregate pv, meter and weather data – see: http://blog.v-s-f.co.uk/2014/03/home-monitoring-home-made-overview/.

Over the last few months I re-wrote the app to not only output the data to PVOutput every minute, but store that same data into an HSQLDB on my server. The new code base uses less Java than the previous version and moves a lot of the aggregation into Mule flows. I also took the opportunity to try out Git Hub, so the code is all available online here: https://github.com/vls29/aggregator

So far it’s been running very stable since the start of January and the refactoring enables new data sources to be added very quickly, e.g. Mains Voltage as can be seen below on the graph as a purple line starting above 3000W:


(link to my system on PVOutput: http://pvoutput.org/intraday.jsp?id=4836&sid=4409)

… but solar panels don’t work in the winter!

I’ve had my solar panels since October 2011 (details about my system can be found on this post) and I’m always telling people how good they are. When I tell people about my solar panels, I get one question – “how much do they generate” and the second is a statement that always makes me want to bang my head against a brick wall – “… but solar panels don’t work in the winter!” Don’t they??

When I first started telling people they should buy solar panels, all I could them was how much electricity they would generate and potentially cut from their bill, but since then I’ve added monitoring to the system which uploads the data to the internet. After the person I’m talking to has used the infamous statement about not producing electricity in the winter, I then proceed to show them the stats from my solar panels.

In the UK, winter solstice is a day between 20th and 23rd December and for more than a week each side of winter solstice, there are less than 8 hours of sunshine in a day. It’s quite literally the worst generation time of the year for solar panels in the UK – especially combined with the weather that you can get at that time of year… But when the sun does shine in the winter, you can get very good solar output days!

This December gone, I checked my system from work during lunch (as I do most days! sad, yes I know…) and noticed the solar panels had heated the hot water. To heat the hot water, there has to be enough energy generated by the solar panels to not only cover the house’ standby usage (350 ish W/h), any additional power being used by family members and also the 1kW/h immersion.

What’s more impressive is that the date was 16th December!
(the red block indicates the immersion is switched on)

In fact we even had brief solar water heating on the 19th and 20th but they aren’t as visually impressive…

But what all three of those charts show is that solar panels do work in the winter. They can even generate enough electricity to cause a surplus and power devices around the home!

It is true that the panels do not generate as much electricity during the winter, due to the angle of the sun in the sky and the length of the day, but we still generate in the order of 100kW/h of electricity each December.

And on a perfect day, it’s possible to generate 9kW/h.