Solar/wind straight to resistance heater?

Yes, it can be done... But details matter.

First, solar and rectified wind alternators output DC current & voltage. DC power requires DC rated relay or switch to cycle power. If you use a standard AC rated switch, the arcing of switching DC power can ruin the switch contacts pretty quickly (DC "arcs" much more easily than AC power).

For wind turbines, they are typically 3 phase output power. So if you want to use turbine's AC output--You would need 3 heaters to each phase connection to get 100% of turbine output power.

Other issues too... Horizontal Axis Wind Turbines usually need to be connected to loads 100% of the time. If load is disconnected, the turbine can over-speed and self destruct in moderate to high winds. Placing a switch across the turbine output (shorting the alternator) can be used to "shut down" the turbine if heating is not needed (shorting the turbine should make the turbine spin very slowly in the wind).

Solar panels and wind turbines have variable output--So connecting a "matched" resistive load will not be always be "optimum".

Wind turbines can be problematic for users... Need good windy conditions, typically a tower >=30 feet tall, and no tall trees/buildings/etc. up wind.

A solar thermal system (using water or antifreeze, or drain back system) may be better solution for heating.

Here is a thread that has some discussions on solar heating systems:

https://forum.solar-electric.com/discussion/1819/newbie-here/p1

-Bill