You can't switch an inductive load on and off many times a second. You will blow it or something else in the circuit up.
Have a read of the instructions for an SSR.
From the Fotek SSR25DA spec sheet:-
"specially suited to control resistive, capacitive and non-saturated inductive loads"
From a Crydom Whitepaper:-
"Solid State Relays (SSRs) and Solid State Contactors (SSCs) are ideally suited for
controlling dynamic loads such as motors"
http://www.crydom.com/en/tech/white-papers/ac_mc_whitepaper.pdfI have a Resol Controller for my Solar Thermal, and it can vary the speed of the pump - I can set it in 10% increments from 30% to 100%. It uses a Solid State output, not a mechanical relay. Can you advise how this is achieved?