Photovoltaic power. The mere word makes some futurists smile. Limitless clean power from the Sun making all our worries go away. Reality tells a different story about this energy source.
First, let’s consider the idea of limitless clean power. There is a limit. The amount of sunlight reaching the Earth’s surface amounts to 2.68e16 watts(1). This equals 8.45e23 Joules/annum (J/a), a huge amount. Even considering a 30% efficiency, this amounts to 2.5e23 J/a which is much greater than our current power consumption of 4e20 J/a. The limit certainly seems high enough to not be a concern. Let’s assume so for now.
Now consider the cleanliness. First consider the direct detriments. To get all the power, we’d have to cover every square kilometre of land on Earth with photovoltaic cells. There’d be no room for plants, animals or people. On the plus side, skin cancer would be a thing of the past. On the negative side, the ecosystem would be destroyed and so would end our dominion. Let’s see how.
We’d subtract the land area needed for cropland and urban areas, about 15% (1). Though possible, it is not probable that we could cover the ice regions like Greenland and Antarctica. Thus reduce the value by another 39%. The remaining 46% consists of forests, grasslands and inhospitables like deserts. We cover these with solar panels and we’d push almost all other life to extinction. This is hardly a clean power supply.
Next for cleanliness is the consideration of logistics. Photovoltaics don’t use a chemical reaction to make power so in this they are clean. But, they need energy for fabricating the necessary components as well as a means for their delivery to the end user. Fabrication means silicon, steel and plastic get shaped into panels. And aside from the ancillary inverters and power metres, we need a storage capacity. Batteries! Today, off-grid homes need over 700 kg of lead and acid to store their captured energy(2). If all houses in the United States (3) were using photovoltaic they’d need 7.75e10 kg. True there’s likely enough lead and acid available. But it would need processing, transporting and recovery to and from each home. The same goes for the panels which need be fabricated, transported and recovered. Undertaking this process leads to heat and chemical waste. Hardly clean.
Another problem with photovoltaics is its inability to provide the energy when and where needed. Most of the habited world is in the temperate northern hemisphere. In their winter there’s little Sun for energy but a great need for heating. In a quick review of current off-grid houses in this region(3), none have photovoltaic as the primary heat source. Most use wood. A large percentage of humanity lives in this region and unless they move to warmer climates, they will have to look for their energy supplies from other than purely photovoltaic.
Yes, photovoltaics are a means to extend our technological ability. It can provide power for lights, refrigerators and non-essentials like computers and stereos. It’s woefully inadequate for interior air conditioning whether heating or cooling. It’s equally inadequate for massive energy needs such as aluminium smelting (4). It can’t replace the transportability and energy density of petroleum and natural gas. Photovoltaics aren’t the answer for tomorrow’s energy needs. Our worries shouldn’t go away just yet.
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- Karahnjukar Power Station