That's an interesting concept but the base assuptions are fundamentally wrong, because this is not how the electricity market or the grid work.
There is no classical supply and demand here. There has to always be the amount produced as is used up. More supply than demand and the grid breaks down, more demand than supply and the same happens.
When you add cheaper renewable electricity to an existing system, there is no effect of higher supply reducing the price thus creating more demand like in a classical market. The opposite is true. The base price is usually linked to the most expensive producer via some merit order system (because there must always be enough capacity to fullfill the demand in real time), so the price stays the same. And on top of the produced electricity we now also need to pay some producers to stop production. That cost is also added via some grid fee. So burning fossil fuels is indeed the worst thing to make money here. Instead you can get a lot of money with producing renewable energy on one hand (as you get a high prize for cheap production), or by not producing fossil fuel energy (basically getting paid for not shutting down you power plant in case it's needed while not actually burning fuels most of the time).
Which in the end means you are indeed replacing fossil fuels with renewables. Prices will only drop once you build so much renewables and short term storage to completely eliminate the need for fossil fuel power plants to be kept for the rare moment you need them. So there is no effect of lower prices artificially creating higher demand.