The shift from fossil fuels to renewable energy sources is inevitable and had already begun, but what will be the impact of this change? Obviously the point of making that shift is to reduce our reliance on energy sources that are becoming harder and harder to access while at the same time being kinder to our planet. Shifting to renewable energy will slow climate change, and that's a good thing, but it's impossible to predict all outcomes but it is useful to talk about the possibilities. Let's take solar power as an example.
If you put solar panels on your roof tomorrow, a lot of things would change on an immediate, personal level. Depending on how much sun you get, you would see an immediate reduction in your power bills, or you might even start earning money from the power companies as they buy back the excess energy you produce. With that in mind, it might not take long to recoup the costs of installing and maintaining those panels. It might not take long for your neighbors to take note and follow suit, putting solar panels on their roofs as well.
It's an effect that grows exponentially. If everyone put solar panels on their roofs tomorrow, the entire energy industry would transform. Obviously the money drains out of power plants that rely on fossil fuel, but that money doesn't go away, it just moves. Suddenly there's a boom in jobs maintaining the grid and the solar panels that fuel it. Suddenly there's no one power station that puts a whole city in darkness if it goes down, everyone is their own power station. There would be vastly increased demand for better battery technology to store all the extra energy from sunny states, moving that power to areas with less solar potential and just as much demand for power.
Any fossil fuel has the potential to run out. As coal or oil becomes scarcer, the cost of getting it rises because you have to dig deeper, or get it from abroad. Being reliant on external resources is a risk, both for the country that needs it and the country that supplies it. It can be mutually beneficial in the short term, but all too often it leads to conflict, colonialism, and war. Reducing the reliance on foreign oil reduces risk for the world.
Long-term environmental impacts are precisely the point of changing to renewable energy sources. While solar panels alone cannot save the planet, solar panels alone can reduce carbon emissions and give us time to figure out how best to repair the damage that's already been done. On top of the environmental long term effects, widespread decentralized power production means a completely different kind of power grid. It's hard to say what exactly the long-term effects would be, but it seems likely that a decentralized grid would be both more robust and less vulnerable to attack or natural disaster. Imagine a world where the power doesn't go out just because there's a storm passing by and remember that power outages may be an inconvenience for some but they're an emergency for others.
That said, there will, of course, be unforeseen negative effects as well as unforeseen positive effects. Solar panel production, for example, produces pollution, and old solar panels are their own kind of toxic waste. There will always be problems to tackle and unforeseen environmental effects. The important thing is to recognize those effects as they are happening and take steps to counter them.
To be clear, just because shifting to renewable energy will have unintended side effects doesn't mean we shouldn't do it. There is no reason to delay any longer than we already have. A change away from non-renewable energy to renewable energy sources is just that: a change. All changes come with side effects, some anticipated and others, unanticipated. That doesn't mean that the change isn't needed, and needed urgently.