My rudimentary logging has been working pretty well, and I’ve accumulated a bit more than a week of continuous solar charging data. It hasn’t been the best time to do it – after months of drought we’ve had some seriously cloudy (and rainy) weather! Despite this, I’ve been able to put 963 Wh of solar-charged energy into my battery over the last 8 days.
Frustratingly, on October 7 my logging script hung and didn’t exit at the end of the day – so I lost that day’s data. Still, 963 Wh is 1 kWh when stated to 1 significant figure. While it’s tempting to say that I’ve saved a full 24.22 cents, that’s probably a slight exaggeration! Since my logging data is coming from the charge controller, it is measuring what is going in to the battery. If there are any self-discharge losses in the battery itself (I think this is negligible – data coming soon), or any conversion losses in the inverter (almost certainly around 10% losses) then this ~1 kWh of charged energy will correspond to slightly less “useful” energy in my devices.
Still, its probably a solid 20.99 cents or so. Only another 2400 weeks to pay off the solar panels and charge controller at this rate! Yet again the conclusion is obvious: I need to increase my battery size.