« Is A Fed Sea Lion A Dead Sea Lion? | Main | Olallieberry! What Does Organic Actually Mean? »

May 18, 2007

Back To Our Future: Use That 1.21 Gigawatts To Power Vermont Instead

1.21 Gigawatts! Yes, that's what the Flux Capacitor needs in order to make time travel possible. But it also makes other, more realistic things possible. I use the term realistic loosely, you'll see.

Just as we start looking at solar options for our home, reading the fine print on energy subsidies for early adopters, Google is putting up a 9,200 panel solar system, with a capacity of 1.6 megawatts (I'm surprised they didn't go for 1.21 gigawatts). I'm pleased they're doing this but they say they can offset the equivalent of 1000 California homes.

I started out trying to figure out how many California homes would be offset by 1.21 gigawatts! But I quickly realized I didn't quite "get" Google's numbers...quite. I based my calculations on this solar calculation method.

Step 1: Define our solar system. Heh.

We are building a 1.21 gigawatt! solar system. Take that, Google!

1.21 gW! = 1210 mW = 1,210,000 kW = 1,210,000,000 watts

Incidentally, I asked my husband about the size of solar panels he's been looking into. Panel size tends to be vendor specific, but some reasonably priced 180 watt panels run 5ft x 3ft, or about 12 watts per square foot. I'm sure you could make nicer ones but we go with what we know.

For our system, we will need 6,722,223 panels, which would be about a 2593 panel rectangle. So our fictitious solar panel system would be roughly the size of 2,315 acres, or 2,400 football fields. Probably somewhat larger because of spacing of the panels. A large ranch would do.

Step 2: Where Shall This Shiny Beauty Go?

The Feds provide us with a useful USA map of solar energy potential.

Clearly the Southwest is the best spot, but we're going to pick a couple:

• San Francisco Bay, California (Yellow) - ~ 5.5 hours/day
• Las Vegas, Nevada (it's shiny already, Orange) - 6.5 hours/day
• Conway, New Hampshire (Green) - ~4.5 hours/day
• We won't be putting one in Sequim, WA...

Step 3: Determine our "realistic" energy usage

According to the DOE, the average US home uses 10,656 kWh/year, or 29kWh/day. That said, energy consumption can vary greatly by region. It will also vary by type of energy but for here, we are just going to look at grid-based electricity usage.

I had a real hard time getting statistics for yearly households in specific states. You can click the statistic to find where I got it, but they might not be accurate and I know the data is often several years old (census driven, etc). Also, the definition of a household varies, as does the size of the average household because the square footage of the average New York or San Francisco house is going to be much smaller than the average house size in Nevada or New Hampshire. Still, this is the best I could find. I've put all the math here so you can do it yourself if you have better numbers.

• San Francisco Bay, California - 5914 kWh/year, or 16 kWh/day
• Las Vegas, Nevada (Cheap rates) - ~11,722 kWh/year, or 32 kWh/day
• Conway, New Hampshire - 6,750 kWh/year, or 19 kWh/day

Step 4: Figure your household daily needs

• Nationally: 29 kWh/day / ~ 5 hours of sun = 5.8 kW
• San Francisco Bay, California - 16 kWh/day / 5.5 hours of sun = 2.9 kW
• Las Vegas, Nevada - 32 kWh/day / 6.5 hours of sun = 4.9 kW
• Conway, New Hampshire - 19 kWh/day / 4.5 hours = 4.2 kW

Step 5: Add a quality control fudge factor (dust, solar eclipses)

• Nationally: 1.2 * 5.8 kW => 7kW per household
• San Francisco Bay, California: 1.2 * 2.9 kW => 3.5kW per household
• Las Vegas, Nevada: 1.2 * 4.9 kW => 6kW per household
• Conway, New Hampshire: 1.2 * 4.2 kW => 5kW per household

Step 6: How many local homes can a 1.21 gW system offset?

• Nationally: 1.21 gW / 7kW = 172,857 households
• San Francisco Bay, California: 1.21 gW / 3.5kW = 345,714 households
• Las Vegas, Nevada: 1.21 gW / 6kW = 201,667 households
• Conway, New Hampshire: 1.21 gW / 5kW = 242,000 households

Incidentally, according to these guys, there are only 474,750 households in New Hampshire, so that covers more than Conway, it covers 51% of the state. If Conway sold the power to nearby Vermont, it would power the entire state of Vermont households (240,744 households) and leave just enough to cover the 1300ish households in Conway, New Hampshire itself. Remember, this does not count non-residential use.

Step 7: A little bit of result verification

Google claims their 1.6 mW system offsets about 1000 California homes. By my numbers, a 1.6 mW system would support about 756 California households. Not too far off. Definately within range if they had a different California consumption number, but if they used the national numbers, it would be more like 229 homes...

There we have it.

My next question is, can we see this 1.21 gW baby from space? It seems very unlikely.

Posted by sorsha at May 18, 2007 11:04 AM