No one is giving you numbers for why this is wrong, so let me ballpark.
Typical solar irradiance is 1000W/m^2. Mean sunshine hours where I live is 3000hrs/y. Assuming 100% efficiency, 100% solar irradiance, perfect angle etc for those 3000hours, we get ~10^10J of energy. Those are bad assumptions, but very generous.
In a gram of deuterium, per e=mc^2, we get ~10^12J. There is 100x more energy in a single gram of deterium than a year of intense sunshine. Deterium is far from rare -- 1 part in ~10,000. Consider the vast amounts of deterium in the oceans and realize if fusion becomes a reality, nuclear, solar, oil, wind etc all become irrelevant overnight.
If energy density were proportional to cost, nuclear fission would already be dominating by a factor of 2,000,000x over fracked gas and coal. The reality is that complexities of systems needed in energy conversions end up coming into play. Getting net energy out of fusion was done in the 1950s (explosively, but still). Even given sustained controlled fusion, you still have to build a power plant around it and 'break even' on costs.
The comment is mostly about energy scales -- Getting into the actual conversion rate, system efficiency, amortization etc is beyond the scope of a comment, especially when it's still an area of very active research.
> In a gram of deuterium, per e=mc^2, we get ~10^12J
Deuterium is not antimatter, where they entire mass of the substance is converted to energy. In nuclear reactions only a very small percentage of matter (~1%) is converted to energy.
Also (too late to edit my previous comment), this assumes fusion converts all of the deuterium mass to energy, but actually it's only the change in nuclear binding energy between D + T and n + He-4, which is 17.6 MeV per reaction, or 2.8e-12 Joules (note minus sign). So this assessment above seems to be off by about a factor of 10^24, or 1 trillion trillion.
To get all the energy out of a deuteron, you need an anti-deuteron. This is dramatically less practical than thermonuclear fusion because we have no credible source of meaningful amounts of anti-matter fuel.
Typical solar irradiance is 1000W/m^2. Mean sunshine hours where I live is 3000hrs/y. Assuming 100% efficiency, 100% solar irradiance, perfect angle etc for those 3000hours, we get ~10^10J of energy. Those are bad assumptions, but very generous.
In a gram of deuterium, per e=mc^2, we get ~10^12J. There is 100x more energy in a single gram of deterium than a year of intense sunshine. Deterium is far from rare -- 1 part in ~10,000. Consider the vast amounts of deterium in the oceans and realize if fusion becomes a reality, nuclear, solar, oil, wind etc all become irrelevant overnight.
I recommend this https://dothemath.ucsd.edu/2012/01/nuclear-fusion/
for a layman's introduction of the energy scales involved here.