Solar panel fancier

//www.nrel.gov/gis/images/map_pv_us_annual_may2004.jpgAh, spring. The weather is warming up, the sun is shining, and a young man’s fancy turns to solar panels. Well, perhaps not all young men, but now that the weather is nice, the Evergreen development just south of us has been finishing up their solar installations. It doesn’t take much to get me to look at solar panels again. They look cool, they’re pretty green, and they’re basically magic, which is all appealing.

Figuring out how big a solar panel you need for a given project can be complicated, though. Just because a panel is rated for 15 Watts doesn’t mean that you’ll get 15 Watts out of it continuously. I’ll take you through the steps to discover what you’ll actually need.

First, you’ll need to use something like a Kill-A-Watt (cheap right now at about $22) to figure out how many kWh your device uses over the course of a day. For example, my cell phone charger uses 0.5 Watts over a period of 6 hours for a total of 3 Wh (Watt-hours) per day of use. However, I only use it about once a week, so the overall use is 0.43 Wh per day. My laptop uses 15 Watts while it’s on and I use it for about 8 hours a day. This adds up to 120 Wh a day.

Next, use an insolation map to figure out how much sunlight you’ll get in an average day. If you’re worried about a minimum value (like if you were planning to go totally off the grid), then you’ll want to find a winter map so that you’ll know that you should always get that much sun. This map shows how many “sunlight-hours” you get during the day. Each sunlight-hour is equivalent to one hour of direct sunlight. For example, here in central Indiana, we get about 10 hours of sunlight a day. However, much of it is at an angle so this is the equivalent of 4.3 sunlight-hours. These numbers assume that your solar panel isn’t shaded and is angled according to your latitude. If that’s not true, you’ll have to adjust this number down.

Using your insolation number, you can figure out what you’ll need as a Watt rating for your device. My cell phone charger needs 0.43 Wh per day. I get 4.3 sunlight-hours per day, so I need a solar panel with a Watt rating of 0.01. My laptop, on the other hand, needs 120 Watts per day, so its minimum requirement is 28 Watts.

Now you can start looking for solar panels. You can often find lists organized by Watt, which makes it easier. Depending on your needs, you may want to build in a safety factor. For example, if I don’t want to have to worry about my laptop running out of batteries after a couple of rainy days, I might want to get a panel rated for more like 40 or 50 Watts. In my case, I’m not going totally off-grid (like I would if I were hiking, for example), so it wouldn’t bother me to have to plug stuff back in under that sort of circumstance.

A 1-Watt panel runs about $30, so a full kit with battery and inverter would probably cost about $100. That would be enough to charge both my cell phone and Maggie’s. That only replaces about 13 cents’ worth of electricity, so the payback is on the order of 750 years, but it’s a reasonably affordable way to play around with solar. A 30-Watt panel and inverter runs about $400 and would allow me to run my laptop off-grid. That has a much more reasonable payoff of about 100 years.

Obviously, solar panels at this scale are never going to pay for themselves. However, the convience, greenness, or just plain coolness might make them worth it for you.

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My laziness gets me in trouble

Fire in a fireplaceIn my last post, I pointed to Wired’s article on heating vs cooling as a singular good article in the lackluster series. I did admit that they didn’t give much in the way of detail, but figured that was just a result of the space limitations.

Well, I should have been less lazy and taken a closer look. The online version of the article includes links to their sources and it turns out that Wired is comparing a one-room AC unit in Phoenix versus a whole-house furnace in New England. No wonder the New Englander fares so poorly!

I can see why they did that, though. It’s a lot harder to compare actual numbers than to fil out a state in an online calculator (that doesn’t explain how it arrives at its numbers). Apart from the difference in size, it also seems odd to me that they chose fuel oil, since most homes (that aren’t heated by electricity) are heated by natural gas.

With those criticisms in mind, I ran my own numbers, often using the same sources as the Wired article. Here’s what I turned up.

The Wired article says that the New Englander produces 13,000 lbs of CO2 in a season. Based on their source for pollution figures, that comes out to 80.55 million BTUs for the season. If they used natural gas instead of fuel oil, it’s only 115 lbs of CO2 (rather than 161 lbs) per million BTU, meaning that a home using natural gas instead produces only 9290 lbs of CO2 a season.

However, I found a NYT article that states the average New England home uses 65,000 cubic feet of gas per season. Using Wired’s source for pollution levels, natural gas produces 120.593 lbs of CO2 per thousand cubic feet.

Instead of 13,000 lbs of CO2, the average New Englander probably produces more like 7,840 lbs of CO2!

Now for the other side of the equation, which was quite a bit harder. I tried to estimate the size of the AC unit needed to cool a house but couldn’t find any numbers that matched. Eventually, I hit upon the idea of using the government’s energy efficiency rating (SEER) to figure it out.

In 1997, the average AC SEER was 10.66. Since it’s now illegal to sell AC systems of less than 13, I’ll assume that the average has moved up to 12 by now. As a side note, window units aren’t required to meet this standard, so they tend to be less efficient.

The average American home is 2349 square feet(!) according to the National Association of Home Builders (in 2004, so it should match well with the heating data I had from that year). A 12 SEER air conditioner uses 100 kWh per MBTU (by definition). Dividing the house size by 1000 gets us 2.349 MBTUs required to cool the house. According to a Kansas State University study, houses in the south west use 12 times the base rate per season, so the total MBTU needed is 28.188. Times 100 kWh gives us 2819 kWh for the season.

Arizona’s power is relatively clean compared to other states, since it mixes coal (bad) with nuclear (good). In terms of lbs of CO2 per kWh, Arizona is maybe a little high at 1.56, much higher than Idaho, which is far and away the best at 0.03, but significantly better than the worst, North Dakota at 2.24.

Given the energy usage for the season, the typical Arizona home will produce 4400 lbs of CO2 (2819*1.56).

Wired’s final numbers were 900 lbs for cooling and 13,000 lbs for heating, an incredible win for cooling. My numbers show that it’s much closer, with 4,400 lbs of CO2 produced while cooling and 7,840 lbs for heating. It’s sad that Wired couldn’t run the real numbers, since they support its point, although not by such a ridiculous amount.

Of course, the real numbers are much more nuanced. If you use passive solar in New England, you’ll cut your emissions considerably. By the same token, a geothermal heat pump in Arizona would significantly decrease your AC usage. And, in either place, a smaller home reduces your emissions. A better point than encouraging cooling over heating would have been to encourage people to get smaller houses.

Too bad that conclusion wasn’t sensational enough for Wired.

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Running the numbers on dishwashing

Will measures water

For a long time, I’ve idly wondered how dishwashers compare to hand washing.  I don’t like washing dishes (the counters in our kitchen are low enough that my back starts to hurt after a while), but there are always some dishes that either just don’t fit or seem too dirty to clean automatically.

I guess I have numbers on the brain after thinking about travel (in specific and more generally), because the last time I hand washed, I decided to measure how much water I actually used.

First, I should explain how I wash dishes. Like most people, I fill our sink halfway with warm water and toss some soap in. Anything that’s really dirty sits in the water as I fill the sink for some extra soaking. I plug the other half of the sink as well to capture rinse water, which I keep cold. I still usually have to use the tap to get more rinse water for pots and pans, but small items like utensils or plastic containers I can just dunk, which is faster anyway.

My extremely scientific method of measurement was to use a measuring cup to put the rinse water into the rest of the water, then dump all of the water down the drain using the same measuring cup. Finally, I subtracted the amount of rinse water from the amount of total water. Okay, it’s not super accurate, but it’s accurate enough to give a reasonable estimate. In this particular situation, I was cleaning four or five very dirty pots/pans as well as some miscellaneous smaller items. Together, they probably would have made up a dishwasher load, but only because pots take up so much space.

For the entire process, I used 26 cups (1 1/4 gallons) of warm water for cleaning and 14 cups (3/4 gallon) of cold water for rinsing. For comparison, I use about a cup of water to wash my hands (turning off the tap while soaping, naturally). I can’t figure out a good way to figure out how much electricity was used to heat the warm water, since it’s not all hot and the water heater runs all the time. It seems pretty negligible, though.

Washing dishes in the dishwasher also uses a small amount of electricity, about 0.56 kWh (or over a day of running a CFL) as long as you air dry. Using the heat dry setting increases that a lot. Since we air dry, I’d call the electricity difference a wash.

A modern dishwasher uses about 6 gallons per load, while older machines can use as much as 8-10 gallons. Our dishwasher uses three times as much water as I did. That also doesn’t take into account pre-washing. We rinse anything with food on it before putting it in the dishwasher, which would make the dishwasher even worse. A larger family could fill and run a dishwasher in a day or two, which would make pre-washing less necessary. Since we only run the dishwasher once or maybe twice a week, the scraps begin to smell if we don’t pre-wash.

On the other hand, this analysis also doesn’t take into account that I wasn’t washing the items that I normally put in a dishwasher. It would probably take me at least twice as much water to clean all of the plates, silverware, and cups that fit into one load. Washing all of that myself would also take much longer and require a lot more kitchen space for drying.

I always thought that dishwashers had gotten pretty efficient and would give hand-washing a run for its money, but that doesn’t appear to be the case. Although dishwashing is probably about as good as hand washing for lots of dishes, it’s worse for larger items or if you use heat drying.

I’ll keep using the dishwasher for most things because it’s much more convenient and, as Maggie will attest, I hate washing dishes. However, I’ll make sure that the dishwasher is always full and I’ll continue to wash our larger, dirtier items by hand.

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Communal travel decisions

HighwayIn my last post, I wrote about carbon emissions for different modes of travel on my trip to WI. Arduous picked up on my last paragraph about how these are potentially unreliable estimates and expanded that into a thought-provoking piece on calculating carbon emissions.

Basically, the problem relates to fixed versus marginal costs. For you non-economists, marginal costs are the cost for one more unit, whether producing another widget at your factory or, in this case, adding one more person to a bus. My article focused on fixed costs, but the real question is which marginal cost is more. Even if a bus produces more CO2 per person on average than a full car, it’s going to produce basically as much whether I ride in it or not. As Arduous puts it:

… driving a car is only the most carbon efficient method IF the carbon emissions Will and his friends’s weight cause on a plane, bus, or train is GREATER than the TOTAL emissions of the car. Which seems pretty unlikely.

Since none of us weigh much, especially compared to a bus, I think Arduous makes a really good analysis. The problem at an individual level is that your decision depends on factors you can’t know about in advance (basically, how many people will join you on a bus, plane, or train, and whether or not these trips will be cancelled if you don’t go). This seems like a good place to apply rule utilitarianism, even if it doesn’t make sense in the general case.

In basic utilitarianism, you do what creates the most happiness (or in this case, produces the least CO2). Since it’s so hard to figure that out, rule utiliarian provides some simple rules that help you act in a timely manner. Things like “don’t kill innocent children” or “always ride the bus when possible” increase happiness overall but also makes it so that you don’t have to actually spend the time to run the calculations every time. Which is good, because we can’t, as I mentioned above.

To move from utilitarianism to rule utilitarianism in this case, we need to stop looking at it from an individual point of view and start looking at it communally. The question changes from “how can I travel to reduce my CO2” into “how can I travel to reduce my community’s CO2?” It’s a subtle distinction, but it makes the math easier. :)

To decide that, let’s calculate the break even point between a bus system and a system of cars. Unfortunately, the source for my carbon calculator determines the CO2 production of planes and trains by dividing their total CO2 production by the total number of passenger miles which makes the data useless for this. For buses and cars, I was able to grab the Greenhouse Gas Protocol Initiative (GHG Protocol) data that my calculator from the other day uses.

According to their spreadsheets, a 30mpg car produces 186.6g of CO2 per km (yeah, different units from last post, but it doesn’t matter; it’ll all come out in the wash). A bus, on the other hand, produces 1492.5g of 2! The difference is so large because buses get terrible mileage (6.7mpg average in the US). This difference between running a bus and running a car is almost exactly a factor of 8. This means that it takes eight cars driving the same distance to equal the emissions of one bus.

If you assume that there are generally about two people in a long-distance car trip, then the bus will have to have 17 people in it before it actually reduces carbon emissions.

This gives us a good break-even rule for travel. If you take a bus and it has much fewer than 16 people in it, don’t ride that route anymore. That’ll discourage the bus company from keeping that route going. If the number is closer to 16, it might be worthwhile to keep riding the bus and encouraging others to join you. If it’s more than 16, you can relax, secure in the knowledge that not only are your carbon emissions low individually, but you’re helping reduce your community’s emissions. Note that this is true no matter how many people you would otherwise cram into your car because whether or not the bus produces less CO2 depends only on how other people would act, not on how you’re acting.

On a community-wide scale, this helps you make decisions about when to add buses and, perhaps more importantly, what type of buses to get. Small buses, like those sometimes used as school buses, can never be better than cars. It only makes sense environmentally to create a route with a large bus and only if over 16 people will ride each direction.

Increasing bus mileage would help too. Bloomington has started trying out hybrid buses and some nearby parks use propane-powered vehicles. These methods can help reduce the break-even point.

This same analysis should be possible with planes and trains if you can get hold of overall emissions rather than data per passenger-mile. And, naturally, carbon emissions are only one facet of the much larger issue of sustainable living. Even if a bus produces more CO2 than a car, it might be worth it for other reasons, like traffic reduction.

Personally, I find the carbon calculators valuable for determining which technologies are approximately the same. Driving a packed car versus riding a bus are approximately equal, so I don’t feel bad about the occasional long roadtrip and I also feel good about encouraging additional buses.

On the other hand, rail and plain emissions are so much higher than car emissions that I don’t feel like we’ll be able to meet their break-even points anytime soon. So while it’s true that I, individually, won’t produce more CO2 if I fly, I’m helping support an industry that might require up to 60 people to break even.

The break-even point is also a sliding scale. As cars get better, it requires more and more people on a given flight, train, or bus to reduce the overall amount of CO2.

To make a long (and perhaps boring) story short, it makes sense to encourage high-volume busing and discourage low-volume busing even if that puts some more cars on the road. At least from a carbon perspective.

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What’s the best way to get from here to there?

HighwayThis past weekend, I drove up to Wisconsin by way of Chicago to participate in PlayExpo 2008. It’s too late now, but in the car I got to wondering what the most environmental way to travel up there would be. There were three of us in the car through Chicago and then four from Chicago to Whitewater, so we’d reduce the carbon emissions per person that way. The best would probably have been to run veggie oil from Maggie’s car, but none of us drive shift. A car with better miles per gallon (like a Prius) would also have been good, but we were stuck with Ian’s car, which gets about 30 mpg highway.

With Ian’s car as a base, I used the Native Energy CO2 emissions calculator to figure out how much pollution each mode of transportation would produce.

There were three main legs to the trip: Bloomington to Indy (50 miles), Indy to Chicago (186 miles), and Chicago to Whitewater (106 miles). The first and last had to be done by car (either our own or in a rented taxi sort of situation which would be worse in terms of pollution). The drive from Bloomington to Indy produced 32 lbs of CO2, while the Chicago to Whitewater leg produced 70 lbs, or 102 lbs overall. The car emissions are computed per vehicle though, while plane, train, and bus are computed per passenger. There were three of us going from Bloomington to Chicago and four from Chicago to Whitewater, so the per-person numbers are 10.6 lbs and 17.5 lbs or 28 lbs total.

Those 28 lbs of carbon would be produced no matter how we got from Indy to Chicago, so we’ll ignore them for now. Our drive between Indy and Chicago (186 miles) put 70 lbs of CO2 in the atmosphere. That’s 23 lbs per person.

The flying distance from Indy to Chicago is about 25 miles less than the driving distance. However, planes create a lot of CO2 and they create it in the upper atmosphere, which multiplies its impact. A plane ride would have create 212 lbs of CO2 per person. That’s almost ten times as much as driving!

Okay, conventional wisdom is upheld. Planes are bad. Surely trains are better.

Sure enough, trains are better. Travelling from Indy to Chicago by train produces 108 lbs. per passenger. The travel distance is slightly less with the train than when driving, which helps. If we’d had to take the train as far as we drove, the train would have produced 122 lbs. per passenger.

Even the smaller amount is 5 times as much as driving.

There’s a cool European bus company, Megabus that now services Indy to Chicago. If you order far enough in advance, you can get your tickets for $2.50 (that’s $1 plus their $1.50 service fee)! Unfortunately for us, we didn’t know we were going until the las minute, so the tickets would have cost us $20 each.

But enough of cost. How much CO2 does the bus produce? Travelling over the same mileage as the car, the bus produces 68 lbs. of CO2 per person. That’s a lot better than even the train, but it’s still 3 times as much as driving. Hmm… 3 times. That sounds familiar. In fact, that’s how much I divided the driving portion up because there were three of us in the car. It seems like it would have produced about as much CO2 for a single person to drive as to take the bus.

I have to admit that I’m pretty astonished with these results. I knew flying would be bad, but not that bad. The train was also worse than I’d expected. The big shock was that the bus was almost as bad as driving by yourself! Apparently, the average mpg in the US is about 23, which would adjust things in favor of the bus. If you have a decent car, or a hybrid, you’re better off driving even if you’re by yourself! And if you’re sharing the ride, driving is by far the best option.

Here are the final results, including travel to Indy and Whitewater:

Plane: 240 lbs. of CO2
Train: 150 lbs. of CO2
Bus: 96 lbs of CO2
Car: 51 lbs. of CO2

Overall, the trip would have produced twice as much CO2 if we’d taken the bus rather than the car, three times as much if we’d taken the train, and five times as much if we’d flown.

This really underscores the idea that protecting the environment is a many-faceted concept. Even if cars produce less CO2 for a trip like this, there are other problems connected to them like all that wasted space used for parking lots and garages. Even worse is all the frustration and wasted time caused by gridlock, which would be alleviated by reducing the number of cars on the road.

Of course, I’m aware that these are all estimates. A plane, train, or bus isn’t going to produce that much less CO2 just because we’re not riding. Still, the concept is useful when trying to decide what sort of long-range travel options we should support!

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