You need to spec your system so at the very least it generates enough power on the worst days of the year to cover your needs, and surplus power on good days. You also should have a second means of power generation, wind works nicely as it's uncommon to have a day that isn't either windy or sunny.
I've used 100% solar for the past 2 years and there has not been a single day that I needed a second source of power.
Also my system is quite modest. Just 500W of panels and about 600Wh of lithium ion battery (lifepo4) energy storage.
The 500W of panels is plenty. Most days I charge my batteries fully before noon.
The 600Wh of batteries is enough to get me through 3 days of heavy cloud weather ( you get about 10% of your maximum generation on a heavily clouded day ).
This system is for two people using our computers and 3g wireless for the entire day. LED lights at night which are bright and warm, water pump, food processor, stereo, iPad, hella gadgets, raspberry pi backup server, etc etc
If I changed something, I'd double the batteries that I use.. going to 24V. You get more of the rated power of the solar panel when using a 24V system. I am considering getting an electric bike & storing extra power there.
The total cost of the system was about $800.
In the summer I can generate about 2 kWh / sunny day -- I only need about 400Wh / day though. You do the math for the cost per kWh. It's damn cheap.
Exactly. It's a total nonsense proposition to offset seasonal swing using battery power. Running a PV system is about conservation first and foremost and some planning second. Your battery is for the day/night cycle and overcast days, not for seasonal variations. Maybe he should run a PV system for a while before writing articles like these.
From the article "Even with these rough numbers it’s hard to see how anyone living any distance from the Equator is going to be able to justify the cost of installing enough batteries to go off-grid with a domestic rooftop solar PV installation."
If you go off grid on purely solar your backup is not a battery, your backup is a genset.
It's a nonsense proposition leading to nonsense conclusions based on nonsense numbers. Very tiring.
With that said, from reading some articles about off-grid living, it's not outwith the bounds of possibility that people are looking at pure solar (or pure renewable anyway) off-grid living, for priniple-based reasons , rather than a more pragmatic rationale.
Back in the real world you wouldn't design your system that way. Instead, you would look at your worst case scenario - mid-winter, and calculate how many solar panels you would need to capture a day's worth of energy in one day. This would also tell you how large your battery would need to be. A prudent engineer would probably introduce a factor of 2 or so both in the size of the panel installation and the size of the battery to allow for a sequence of unusually dark days, but the multiples being talked about in the article are just ridiculous.
Do you mean 600Wh?
The fridge would probably double our power requirements. Add in a stove and we may need 3x our requirements.
The total bill would still be pretty cheap, but I may be running out of roof space on a camper this size.