Measuring phase angle and power

Just a quick interjection that might (maybe) help you avoid a problem. I tried solid state relays for a high current project, a water heater controller. It was a 240V thing that was optoisolated. Worked great, got hot. It had to have a heat sink and airflow to keep cool enough to touch and couldn't be mounted in a box outside where I live (desert) because the ambient temperature and afternoon sun would destroy it. I switched to an old fashioned contactor controlled by a little bitty relay off a 5V digital pin. This was because an A/C contactor was easily available and ran off 24VAC. It runs nice and cool and has been cycling now for over two years. At first the noise was offensive, now its comforting because I know it's working.

Now, I know it may have been the particular device I got stuck with and your mileage may vary, but keep this in mind when choosing the device. In my case, old school worked best.