Do the math

Since I launched this blog I’ve had a running debate with an old friend from engineering school. He’s not a fan of Ontario Premier Dalton McGuinty, nor does he like the Green Energy Act, and he’s a definite skeptic on the topic of solar energy. His position is that solar won’t meet the world’s energy needs in our lifetime.

Is that so?

Let’s figure it out together.

First, let’s look at just how much energy the world uses. According to the International Energy Agency, the Total Primary Energy Supply for 2009 was 12,150 million tonnes of oil equivalent (Mtoe). That converts to 141,304 terawatt-hours (TWh). The 2009 figure was actually a slight drop from the previous year, but the overall trend has been up, up, up. So, just for the sake of simplicity, let’s say that the annual energy production figure we need to reach is 150,000 TWh.

Now we know how much of a hill we have to climb if we want to replace all sources of energy with solar. Does the sun provide that much?

According to, the sun produces 4×1023 kW. That works out to 23 trillion times more energy than we currently produce from all sources. Now, we’re just one small speck in the solar system, and we’re 150 million kilometers away from the sun, so very little of the sun’s energy output actually falls on the earth’s surface. Above the atmosphere, each square meter receives 1.361 kW (this value is called the solar constant).  Since half of the earth is in darkness at any given time, and most of the other half doesn’t have the sun directly overhead, the average is 0.342 kW per square metre.

Current photovoltaic technology cannot convert all of that sunlight into electricity. Modern solar cells have an efficiency of around 15%, meaning that they can only produce about 0.15W of electricity for each watt of sunlight. Solar cells also get less efficient as they get hot, so sunny summer days are a good-news-bad-news story; more sun means more electricity, but a hotter cell means less electricity. The reverse is true as well, though, so in the winter there’s less sun but the air is a more hospitable temperature. Over the course of the year, it pretty much averages out.

So we know how much sunshine we can expect, and how much of that sunshine we can convert into usable electricity. How many solar cells would we need if we want to replace all other energy sources that make up the global energy supply? Put another way, how much of the earth’s surface would we need to cover in solar cells? Would we need to pave every square meter just to satisfy our appetite for energy?


We’d need a lot of space, to be sure – 3.3 million square kilometers. Assuming we can only build solar arrays on land, we have about 150 million square kilometers available, so that means we’d have to cover 2% of all land area with solar panels if we wanted to replace all of our energy supply. That’s about a third of the Sahara Desert.

Cost is a different matter. Based on current prices, all those solar panels would cost around 445 trillion US dollars, or seven times the entire world’s Gross National Income (GNI). That’s not taking into consideration supply constraints on the raw materials required to manufacture them, the fact that current production capacity could only meet the tiniest fraction of that demand, and the fact that there aren’t enough competent installers to even scratch the surface of such a monumental undertaking.

So it won’t happen tomorrow. But the day after that…maybe. After all, how do you eat an elephant? One bite at a time.

So many look at our energy situation, and throw their hands up in despair. It’s hopeless. We’ve done too much damage already. We’re too addicted to cheap but ultimately self-destructive energy sources like fossil fuels and nuclear. There’s no way we’ll dig ourselves out of the pit we’ve created before global climate change renders our world uninhabitable. So say the despondent as they survey our climate crisis.

It needn’t be so. Okay, covering half of the Sahara in solar panels is not realistic. However, while the cost of fossil fuels continues to climb and public opposition to nuclear energy continues to grow, the cost of solar energy continues to edge downwards. In any case, solar energy itself is not limited to the surface of the tiny pebble on which we live. It powers most of the satellites we use for telecommunications, weather forecasting, mapping, and a host of other services. Indeed, part of the original impetus for the US space shuttle program was a NASA scheme to harvest clean, abundant solar power using giant satellites, ending the energy crisis that the 1970s OPEC oil embargoes had caused.

Other renewable energy sources are being deployed alongside solar – wind, geothermal, tidal, and biomass. Each holds its own promise to play a role in rescuing us from a global warming apocalypse. Little by little, baby step by baby step, each of these renewable technologies will supplant our current unsustainable system.

On May 25, 1961, when John F. Kennedy made his famous speech announcing the NASA manned lunar program, many laughed. “Never in our lifetime,” they jeered. And yet, on July 20, 1969 – days after I was born – Neil Armstrong announced a “giant leap for mankind” as he planted his foot on the surface of the moon.

We will shake off our dependence on fossil fuels, and on the disagreeable nations that supply them. We will put an end to the damage we do with greenhouse gases and nuclear waste. We will find ourselves in a future where we can be prosperous without leaving our progeny poisoned and impoverished.

And it will happen a lot sooner than most people imagine.


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