On 20/02/2021 14:28, Theo wrote:
NY wrote:
I'm surprised at how small the capacity of the rechargeable batteries that
are used in most solar lights. Part of the reason that they don't last very
long even in summer is that a lot of solar power goes to waste because the
batteries cannot accept any more charge.

Solar lights require a long cycle life (one charge/discharge cycle a day).
They're also repeatedly cooked and frozen. This is about the worst
situation a battery can be in. It is better to put in a lower capacity cell
that's more robustly constructed than a cell with maximum capacity that's
rarely going to be used, but is less able to withstand the harsh
environment. Carthorse v thoroughbred.

That may be true for some battery chemistries but not most. For example,
lead acid last longer if they don't undergo a deep discharge.

Solar lights will typically flatten its battery during the winter. I
would suggest the choice of battery chemistry is critical.

Having said that, our lights do last a lot less time in winter, so the
amount of daylight is also an issue. I'd have thought that modern solar
cells would be able to produce usable power even on an overcast winter's
day.

The cells probably work less well in the cold.

I would have thought the opposite, diodes have a sharper IV curve at
lower temperatures and reverse current leakage would also be lower.