Let’s have a look at the energy consumed in producing 1m square of photovoltiac cells. We have to:
- Mine the siicon and metal ores
- Purify the silicon (and the metal ores)
- Make glass fronting (or in this case, whatever synthetic substance they’ve used)
- Make it into a PV cell
Power consumed in construction of 1m2: ~2MWh using current manufacturing processes
Power output: ~160W per m2 in optimal conditions.
Assuming 5 hours of average optimal use per day, this is 800Wh per day, or 292kW per year. So how many years to pay back the construction energy? About 7 years, give or take. More if it’s a climate like where I live and you get probably 2-4 hours full sun per day on average.
How often do you resurface a road? About every 15 years.
So for the first seven years, the solar cells on a road are doing nothing for the energy balance. Assuming no losses or manufacturing costs in the use of the energy they produce, the cells are simply paying themselves off.
So after that, we have another 2MWh of energy produced over it’s life. Let’s put this in terms of a car. A car uses about 120kwh on 12km of travel using 1litre of fuel. So over the course of seven years, our solar panel will drive a car 24000km, saving roughly 1700 litres of fuel.
Now all politicians care about is money. To buy a 1m2 solar cell capable of that output would cost me about $8,000 NZD. The equivalent amount of fuel costs (at ~3$ per liter) only $5100
This isn’t per road either, this is per meter squared. To do a whole road using these solar cells the difference would be staggering. It really is cheaper to buy the fuel. I don’t have access to specifics about solar cell manufacturing in terms of heat produced and CO2 emitted, but I’m willing to bet it’s pretty similar to that of burning the equivalent amount of fuel.
And this is ignoring the installation costs (including pollution from road-working machinery) of said solar cells. We also have to take into account that solar cells are best perpendicular to the sun, and a road is flat. So we can expect an even longer Energy Payback time from solar cells made into roads.
So from a money and energy point of view, installing solar cells is pretty ‘bad.’ I’m all for clean green energy, but check how clean and green it is first. Take for instance New Zealands Hydroelectric plants. They have a very good Energy Payback time, from memory it’s somewhere under two years, and they operate pretty much without further costs for another 40-50 years.
Let’s have a look at solar cells again, this time the energy they produce. Each solar cell produces 160W per m2. How much energy actually falls on it in that time? 1.366 Kilowatts. So about 10% of the energy is converted. The other 90% is either reflected or retained as heat. Bear in mind this 10% retained through conversion to electricity is then converted to heat in, say, a car or a light.
So your argument is that a solar cell doesn’t have much of a difference to asphalt in terms of retained energy? Well, we can tell this using … albedo! The measure of how reflective a material is.
Solar Cell: 0.25
So the amount of light reflected by a solar cell is … higher than asphalt. So solar cells reflect more light/heat than asphalt. So you are correct in saying that replacing asphalt roads with solar cells would drop the energy retained.
As I said in the post, I had not researched it. Now I have, and my guess was wrong.
Oh, and random thing I found out while researching:
The manufacturing of solar panels emits nitrogen trifluoride or NF3. NF3 is a greenhouse gas 17,000 times more potent than CO2.
So what alternatives are there to solar cells? As I’ve shown, they’re a long way from being cost or energy effective. To me it’s a fundamental problem with solar cells. 2/3rds of their life they are in the dark, or at a non-optimal angle. Putting them in space they will recieve a lot more energy, but they are then less useful for us guys on earth.
Nuclear? You could only run the earth for a couple of decades if you replaced every coal station with an equivalent Nuclear one. You’d run out of uranium.
Fusion? Has potential, but I doubt it will be effective when we start running short on fossil fuels.
Hydro is the only feasible one at the moment
But to be honest, I prefer a different option:
- Change how much energy we use.
I’m all for modern comforts such as laptops, housing and heating, but when you look at this graph, you see something: the biggest energy use is in the transportation.
How far do people travel to work each day? - on average 25km.
How far does your food travel to get to you? - the other side of the planet, particularly tropical fruits etc.
See the problem?
- Live close to work
- Buy locally produced foods
Anyone ever seen this short film? Quite long, but worth it, and in my mind, fairly accurate from either perspective.