Monday, March 30, 2009

Switching to the Prius

I have had my current Prius since late in 2003. Since then, my overall MPG figures are like this:

Overall Average MPG (calc) 48.47
Overall Average MPG (Screen) 49.14

Winter Average MPG (calculated) 47.10
Winter Average MPG (Screen) 47.80

Best Tank (calculated) 65.63
Best Tank (Screen) 57.60

Most Recent MPG (calc) 43.47
Most Recent MPG (Screen) 44.00

Summer Average MPG (calculated) 50.76
Summer Average MPG (Screen) 51.38

Worst Tank (calculated) 31.88
Worst tank (Screen) 41.40

Average MPG Actual

Average MPG Screen

Calculated vs. Screen

Percent Difference

Note, this is for all types of driving in all seasons. Also for those who may not know, the Prius currently has a fuel tank bladder (for emissions control) that makes the tank size vary from fill up to fill up. That is why I am tracking both the standard miles travelled since last fill up, divided by fill up gallons as you would do to calculate your own MPG. And I am tracking the Prius’ own on screen prediction for each fill up. I also compare the differences, and as you see over time the difference between methods is not very much. How does the Prius figure its own MPG? As I recall, it monitors the fuel flow at one fuel injector, using that to calculate the total fuel consumed, and then divides by miles traveled. The result of the comparison is that individual tanks vary greatly depending on the temperature of the bladder. But, over time this will even out. You also see differences by winter or summer driving. For my purposes, I am calling the warmer months summer, and the colder ones winter. This is for the sake of simplicity. Also, for the statistically minded people, I am using a weighted average to calculate the overall average from the Prius interior display of MPG. It should also be noted that the Prius, along with all other cars, recently underwent a change in how the estimated MPG for the window sticker of a new car is calculated. When I bought mine, the estimated MPG was as listed under “Old MPG estimates”. At the time, my overall MPG was just at 50 MPG, missing the EPA figures somewhat. Now, with the new predictions as listed, I would make that combined MPG with room to spare, even if my current overall listing is dropping to 49.14 as stated above. Why is my MPG dropping? I have different tires now than when I started, and evidently the MPG is a bit lower than the standard issue. Also, I am making shorter trips now than initially. More on that later. . .

Old MPG estimates
60 City
51 Highway
55 Combined

New MPG estimates
48 City
45 Highway
46 Combined

Thursday, March 19, 2009

After the solar panels were moved...

The move of the 20 solar panel array went fairly smooth. Actually, as far as jobs like this usually go for us, it was flawless except for one brief glitch. When the switch was turned back on, there was an error message on the inverter, and no power flowing. It was late afternoon. Maybe there should have been a bit of power by then, but we waited to see what it would do the next morning. You guessed it; no juice then either.

The installer came back, and after re-tracing it all, he discovered he had wired the individual panel assemblies in parallel instead of series. So we were only seeing the voltage of one group. Once he fixed that, we were back online with only 2 full days of production missed.

You should be prepared if you do anything with alternative energy to become a nitpicker when it comes to counting your production, mileage or electric bills. That couple of days can make a difference if you are off for some reason. For us, it did not matter that much since this is a time it is normally not that sunny anyway, and that we are not yet on the maximum high use charges.

So far, it looks good. We are already surpassing our normal daily production just by having the panels pointed more towards the sun in the afternoon. One glitch in the overall plan was that at the same time we were moving the panels, we were having a small pond put in. That pond has a small waterfall. That requires a pump. You see where I am going here. This is what normally would be considered a waste of electricity. And we have already cut back the run time from 24 hours a day to just 12. For the first month it had been on, it cost us an additional 12 kilowatt hours a day. Part of our reason to get the solar panels was to be able to afford to run our AC in the summer. This pond would tend to cut into our extra capacity, and I think it might lose out in the long run if it goes up against our comfort.

Wednesday, March 18, 2009

My Green Energy- from Hybrid Prius to Solar Panels and Tankless Water Heaters

I was in a volunteer in High School for a group called “Recycle for Survival.” That was around the time of the first Earth Day, to let you know the time frame of my earlier environmental education. I have been interested in photo-voltaic energy technology since I heard about it when I was in college, way before anyone was using it on a wide scale. Even today, it is still in its real infancy as far as total production goes. In 2001, I purchased my first Toyota Prius, which actually was the first one sold in my town. In 2004, my second. Did I tell you I was an early adopter? In 2007 we installed a 2.2 Kilowatt photo voltaic array on our roof. A few years later, we purchased a tankless water heater. Here is a bit about all that. . . Throughout my Prius ownership, I have tracked my MPG results on a spreadsheet I created, which is just under 50 MPG for all seasons, and all driving types. I added a section to that later to track our household energy use for the solar array in particular. For our solar array, our bill is calculated on an annual basis. That is running less than $100.00 a year, including the $60.00 or so of fees everyone pays no matter what they do to try to save. Since adding our tankless water heater, our summer natural gas bills are usually under $5.00 a month. It really does not pay to heat up a tank of water all day when no one is using it. And it does seem to pay to only heat up the water you use, and stop when you turn off the tap.

My main goal in the beginning is to talk a bit about the solar cells, since that is the biggest investment, and probably the biggest commitment of what we have done. Like I said, we have a system that is around 2.2 Kilowatts and is grid tied. That amounts to 20 panels. That same system today would require fewer panels because of efficiency increases in the panels. The cost of this system installed was around $20,000. At the time, there was a program in place that provided us a rebate of around $8,000. It was still pricey. If we had acted six months sooner, our rebate would have been closer to $10,000. If you are considering doing this, and you are in an area that has rebates, putting it off could cost you.

Installed and in use, our system only achieves 1.8 Kilowatts. This is simple internal losses in the panels, and inverter. Your contractor can advise you on your needs, and how many panels you need to get to lessen the impact of the internal losses, and still make sense for your energy needs. You want to get as close to your energy needs as possible without over production. At least for us, if we have a surplus at the end of our annual billing period, PG and E errases it.

Our system came out pretty close. Your contractor will want to see a year’s worth of electric bills to calculate the size of your system. Your electric company may also need to see this if you opt, as we did, to change your meter and rate schedules. Part of why we are only $100.00 a year, is because we applied to change our metering to what is called “TIME-OF-USE” metering. At the same time we did that, we switched to an E7 rate schedule. Normally, in California, residential use is metered at around 18 cents a kilowatt hour. The E7 rate is split in a way that charges you a higher rate in the higher demand hours, and switches to a lower rate to the rest of the day. This lower rate also applies to holidays, and weekends. For us, from May through October, from noon to six, we would pay 32 cents a kilowatt hour, and the rest of the day it would be 9 cents. Where this is important for grid tied systems, is that your heavy production hours are from noon to six. This means that the surplus production during those hours is sent back to the grid showing as a credit on your meter. Of course, you can use anything in your home as this is happening. But, you have to remember that anything you use means less of a surplus. This system would be best for those when either are not home on weekday afternoons, or who are home but do not use much in the way of electricity. It is not so bad really. If you are home, do things before noon, or after six.

As I am typing this, our system is off-line and being moved. Planned construction on the house meant that eight of our panels would be in the way of our new roof. And, as luck has it, our inverter does not allow the system to run in a split configuration unless both of the sets of panels face the same direction. Since we do not have money for a new inverter, we had to change the panels from their original southeast direction to a section of roof that faces southwest. This may eventually work out in our favor. Due south would be the best direction to have the panels, but you can only deal with the way your house or your roof faces, unless you want to add more money to the installation for mounting to the south, or even more money for systems that track the sun. Sometimes you just work with what you have. As I said, it will work out for us. This is because of that E7 rate schedule we have. Moving the panels to the south west will put them towards a place they will get longer afternoon hours of exposure. Since our rates are higher in the afternoon than they are in the morning, this should get us more of a surplus at the higher rates. Maybe with this our next bill will be completely zeroed out. I am looking forward to it.