Some quotes:
"Off-grid solar PV systems often charge lead-acid batteries."
Nobody is using lead-acid anymore, which shows how out of touch these idiots are with reality. For 5, if not 10 years LiFePO4 batteries have been the best option even for DIY systems.
You lose half the power you put into them, the deeper you discharge them the more you wear them out which means you have to buy far more capacity than you need, whereas LiFePO4 you can discharge down to 10% and charge to 90% and still get thousands of cycles out of them before they degrade to maybe 80% of their nameplate capacity. You also get higher working voltage - 13-13.8v for much of the battery's state of charge. I'm not kidding when I say that from efficiency losses alone you DOUBLE your effective solar generation by switching to LiFePO4 from lead-acid.
"At the other extreme, resistance on the pedals is too high when powering a kettle or a refrigerator."
It would take three hours for the average person to put enough energy into a "perfect" kettle to get it to boil, using a "perfect" bike that could convert the roughly 100W of mechanical effort into 100W of heat in the kettle....
Between mechanical and electrical losses, heat loss in the kettle, and energy inefficiency of the human body, I would rule it nearly impossible for even some of the world's most elite cyclists to power an electric kettle long enough for it to boil.
The handcart article goes to explain at length why a multitude of other options are inferior, but then they act like an electric generator bike would provide any sort of meaningful amount of power compared to just putting a solar panel outside.
Especially if you're willing to buy used, solar is dirt cheap. You can get NEW panels 300-400W panels on clearance for ~$100. You can get a nice-but-cheap 1-1.3kWh 12v battery for about $250. A top-notch solar controller, $75-100. And that battery will fully charge from dead in one day worth of sun in non-ideal conditions...
Of course, on a Total Cost of Ownership (TCO) basis, it was already cheaper quite a while ago (for the last 5 years I'd guess). It was a combination of LiFePO4 batteries having such longer cycle lives than any lead-acid chemistry, and the greater depth of discharge meaning you could use a lot more of the energy. So if you build a new lead-acid based system, you'd need almost double the amp-hours of batteries to supply the same amount of energy with a safe depth of discharge, and you'd still have to replace them much sooner. So you'd not only have to factor buying a lot more batteries with lead acid but also replacing all the lead acid batteries at least once while a LiFePO4 system would continue to operate.
Ok, but they often are lead acid batteries. I just bought an inverter off a guy with lead acid batteries. They exist like crazy all over the place because lead acid can be reconditioned effectively forever with proper equalization. If you have lots of solar and you value repairability with simple tools and simple skills lead acid still has a niche