Why hasn’t solar energy been harnessed as primary source of energy?
Our investment so far has been away from solar and back into fossil fuels. Politics determines where we invest R&D money. Go to your local big box store and look where our solar products are made. The bulk of them are imports from countries whose governments subsidized building factories to produce them. Our government would rather rely on imported oil and imported solar cells than invest in solar development.
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Large scale solar energy operations are very expensive to build. Costs to make industrial/commercial grade solar panels are actually going up. Then you also have the problem that not every day is going to be sunny and you can’t make electricity at night.