The earth intercepts a lot of solar power. A 173 thousand (173000000000000000) terawatts. That’s two thousand times more power than the planet’s population uses.

So is it possible to be completely reliant on solar energy?To answer that question, we first need to understand how solar panels work and how it converts solar energy to electrical energy.

Solar panels are made up of solar cells. Most of the solar cells are made from silicon, a semiconductor that is the second most abundantly available element on Earth. In a solar cell, crystalline silicon is filled between conductive layers. Each silicon atom is connected to its neighboring atoms by four strong bonds, which keep the electrons in place so no current can flow.

A silicon solar cell uses two different layers. N-type silicon cell has extra electrons, and p-type silicon cell has extra spaces for electrons, called holes. Electrons can move across the P/N junction, leaving a positive charge on one side and creating negative charge on the other side.

You can think of light as the flow of tiny particles called photos, shooting out from the sun. When one of these photons strikes the cell with minimum amount of energy, it knocks an electron from its bond, leaving a hole. The negatively charged electron and the positively charged hole are free to move around. But because of the electric field at the P/N junction, they’ll only move in one way. The electron moves to the N-side, while the hole moves to the P-side. The mobile electrons are collected by thin metal at the top of the solar cell. From there, electrons flow through an external circuit, doing electrical work like powering a bulb, before returning through the conductive aluminum sheet on the back. Each silicon cell only puts out half a volt, but if stringed them together in modules it gives more power. Twelve photovoltaic cells are enough to charge a cellphone, while it takes many modules to power an entire office or house.

Electrons are the only moving parts in a solar cell, and they all go back to where they originally generated from. Hence there’s nothing to get worn out or used up, so solar cells can last for decades.

So what is stopping us from being completely reliant on solar power? There are political factors and reasons at play, not to mention businesses that lobby to maintain the status quo.

But for now, let us focus on the natural, technological and logistical challenges, and the most obvious of those is that solar energy is unevenly distributed across the planet. Some areas ar sunnier than others. It’s also inconsistent and less sunlight is available on cloudy days or at night. So a total reliance would require efficient ways to get electricity from sunny places to cloudy ones, and effective storage of the produced energy. The efficiency of the solar cell itself is a challenge. If sunlight is reflected from the solar panel instead of absorbed, or if dislodged electrons fall back into a hole before going through the circuit, that photon’s energy is lost. The most efficient solar cell yet still only converts 46% of the sunlight energy falling on it to electricity, and most commercial systems are currently 15-20% efficient.

In spite of these many limitations, it actually would be possible to power the entire world with today’s solar technology. We would need the funding to build the infrastructure and a good deal of space. Estimates range from tens to hundreds of thousands of square miles, which seem like a lot, but the Sahara Desert alone is over 3 million square miles in area.

Meanwhile, solar cells are getting better, cheaper, and are competing with electricity from the grid. And innovations, like floating solar farms, may change the idea entirely. Though experiments aside, there is the fact that over a billion people don’t have access to a reliable electric grid, especially in developing countries, many of which are sunny. So in places like that, solar energy is already much cheaper and safer than available alternatives, like kerosene.

And Apollo Power Systems is solving the power requirements through efficient solar rooftop and land based solutions to generate clean and free energy.

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