What is the cheapest board with WiFi + solar option?

[kingneil]

What is the absolute cheapest way to get a Raspberry Pi-style board, which has WiFi, and the ability to provide constant power using solar or other renewable means?

Or even just a really long-lasting battery rather than even renewable energy?

I am looking for links to products that I can buy

1. Board

2. WiFi

3. Power source

By the way, the WiFi chip must have the ability to run a relay... i.e. to be used to receive WiFi from a hotspot, and also to be used as a hotspot itself at the same time.

[W. H. Heydt]

Cheapest? Pi0W. Providing power is up to you as that's not a feature of SBCs. As for "Pi-like"...there aren't any. No other boards use the Broadcom SoCs. Acting as both a WiFi client and hotspot simultaneously is handled in software.

[davidcoton]

You need to work out a power budget. Measure the current used by your particular combination of hardware, convert to watts. Now work out the sunlight availability at your location, and the size of panel you need to provide average power (much) greater than the power you require. Work out the size of battery to cope with nights, several dull days, and any other non-availability of sunlight. Remember that voltage conversion and battery charging/discharging are not 100% efficient. Work it all out, and you will realise that it is anything but cheap.

[mikerr]

Absolute cheapest ? Look at esp8266 based boards - they can be had for under $3 with onboard flash.