"Spare" solar generation

This is a hypothetical question, because I have a stupid Boilermate that won't take an immersion heater, and when I get around to replacing that I'll be putting up solar thermal too, however...

I was pondering last night on using a proportional method to dump "extra" electricity into an immersion heater (keeping it simple), and thought about using a triac to control the load. For those who don't know, a triac can act like a solid-state switch that will come on when triggered and stay on until the voltage passing through it hits zero, so you can activate it at some point on the voltage sine curve and it'll switch off twice per cycle. You can use them to make dimmer switches, but they don't half upset switched-mode power supplies!

So, taking that into account, if we have a 2kW immersion, and 1kW of export, we could catch the power signal at the peak and trough of each cycle and activate the triac there, allowing an *average* of 1kW through the heater by feeding it 2kW for half the time. So far so simple (to my understanding). The issue with that is that you'll feed 1kW to the grid for 1/200 second, activate the triac, draw 1kW *from* the grid (plus 1kW from your inverter) for 1/200 second, then do the same in reverse. Effectively you're doubling the frequency of the 1kW on your mains feed and making it spikey as hell.

I suppose the question is what does that do to the appliances in the house, and to the local grid section in your street. Is abusing 1kW like this going to have any noticeable effect? And would it upset the meter to have 1kW in phase, then 1kW in antiphase 100x per second? As I say, it's all pretty academic - as Wookey said in another thread, use solar thermal for water heating; it's miles better. It was merely for my own curiosity.

Any clever bods have an opinion?