Next Step: Natural Gas

As seen in my recent post, I've addressed our electric energy use with solar panels.  Excellent.  So it's on to the next thing - natural gas.  I haven't thought about natural gas much because, well, it's harder to do anything about it.  The gas we use goes toward either heating the air during the winter, or heating the water year round.  We have a water-efficient shower head (saving on hot water) and we don't use the heater in the winter unless it's really cold (We set the temperature to ~64 F).

It occurred to me that I'm pretty ignorant about the natural gas use of our home.  What is the carbon footprint relative to the electricity use?  What fraction of the gas goes to heating air, what fraction to water?  

So I decided to dig a little into the data.  My natural gas provider allows us to download a spreadsheet with our past usage, and a bunch of other relevant information. In particular, the average daily temperature of the billed month is tabulated along side the average daily use.  So I made a plot.  

Natural gas rate of use plotted as a function of average daily temperature. Use above ~62 F is purely water heating. 

Not surprisingly, as the weather got cold, our use went up dramatically as we ran the heat.  However, I was surprised by the shape of the curve at temperature above 62 F.  Above that temperature, we don't turn on the heat, yet our natural gas use is going up.  

To me, that meant that this could have meant a number of things:  1) the ground water is getting colder so it takes more heat to get it to the same desired temperature and/or 2) we take longer showers when it's cold in the house.  Both of these things are probably true at some level.  But is there more to it?

Solar Panels (1 Year Update)

So my solar panels have been on the house for a year (summarized here).  Because there are very large seasonal changes in both power production and usage, the one year anniversary is a nice time to summarize the performance.

Seasonal Changes:

Obviously, there are large seasonal changes.  In the summer, the days are much longer and the Sun is higher in the sky so the panels produce much more energy in the summer than in the winter.  It's almost a factor of two difference - ~15 kWh/day in the Summer, ~8 kWh/day in the winter.  

Of course, my consumption varies with the season as well.  In the late summer it is very hot here and the air conditioning can often use more energy than the panels can produce, even on their best days.  In the Winter, there is some additional power associated with running the fan on the central heat.  

Basically, I consumed slightly more than I produced in the peak hot months (Aug./Sept.), was even during the winter, and produced more than I used during the other months (especially May/June when days are long but I don't need to run air conditioning yet).  

Daily Changes:

Clouds

There were remarkable day-to-day changes.  Obviously clouds are a big culprit.  Generally, they are decreasing power but they can also scatter additional sunlight from other angles onto the solar panels.  The highest instantaneous power the panels ever produced was when cirrus clouds had just cleared, allowing direct sunlight, but also scattering additional light onto the panels.  One thing to note is that the  energy produced only went below 3 kWh in five days out of the whole year.  This is about how much my house needs per day if I don't run the A/C and I'm being very frugal about everything else.  

Smog/Humidity

As mentioned before, humidity and smog have a fairly large (~5-10% effect) on the amount of power produced.  On clear, windy days the power can be significantly higher.  Notice that very high energy point on April 17th.  That was a day with high winds that cleared out humidity and smog the whole day.  

Temperature

The panels are actually less efficient when they warm up.  I notice this effect as well.  It's small, of order 5% day-to-day.  That peak day in April where the panels produced the most energy?  Yes, it was windy, but it was also not too hot.  

Annual Total:

So, I designed this system to produce more power than I consume throughout the year.  I was actually hoping for a little surplus because I will want a plug-in car in the near future.  [There is a whole side story here that the city will not approve permits for systems which produce more than the house consumes because they're required by the state to pay for that excess power.  They almost didn't approve the permit for my system because they claimed that it would produce 60% more than I consumed.  I argued that the system was the right size, if slightly too big.  They were being too optimistic about how much power the panels would produce (I think they were doing this on purpose) and they were using energy usage from the previous owners, who weren't in the house all summer!  Anyway, I argued and they finally approved the permit. Now back to our regularly scheduled blog.]  So, how did it do?  After exactly 1 year, here are the stats:

Energy produced:  3915 kWh 

Energy consumed:  3613 kWh 

Net:  -302 kWh 

The panels produced 8.4% more energy than I consumed!  I actually put a decent amount back on the grid - enough to charge a standard Tesla Model S five times and drive it 1000 miles!  

Savings

Electrical energy in my town is cheap (10.4 cents per kWh), especially for California.  Because I didn't use any net energy, I didn't have to pay a dime of the $375 I would have had to pay for electricity this past year.  Furthermore, I have a credit for $31 for future use (for when I buy that plug in car in a few years).  

The greatest thing about these panels is that they require no effort.  Often, doing the right thing environmentally might require a sacrifice or an inconvenience.  Once these panels are on, they just sit there and ensure that your home isn't contributing to the increase in greenhouse gases or the smog in your community.  And they'll do that for 30+ years!

Now, are you inspired?  Go do this to your home. You can either purchase panels, or lease them.  The federal government will pay for 30% of the cost and you may be eligible for state or city rebates as well.  Go look into it, get several estimates, and make it happen.  The costs have come down dramatically in the past five years.  Now is the time.  

Solar Panels!

I haven't posted here in a while.  Last you'd heard from me was a little over a year ago when I was getting ready to have my solar panels installed.  Well, they are on my roof and have been producing power for over a year!  Here's what they look like.

And here are the details.  There are ten panels which each can produce 240 watts of DC power on a clear day when the Sun is at zenith and the Sun's rays are normal (perpendicular) to the panels.  There are some losses when transmitting and converting the signal to analog, but this should still result in 2.07 kW (2070 Watts) of AC power at peak.  This is enough to run my microwave, TV, several light bulbs, and my dishwasher at the same time.  It's only about a quarter of the power used by my air conditioner.  The whole thing is connected to the grid.  If it's producing more power than my house uses, it puts the excess power onto the grid so my neighbors can use it (and causing my meter to run backwards).  When I'm using more power than my panels are producing (at night or when running my air conditioning), I take power off the grid.  The net amount that I produce/consume is monitored by a new "net meter."

So yes, it's still using the grid.  And even when I produce the same amount of power as I consume, I still have to pay for upkeep of that grid ($18/month in fees).

The whole thing is hooked up to a monitor which determines the power output of each panel every five minutes and uploads it to the web.  Here is the data from two days last August.

The first day was partly cloudy and the second day was clear.  You'll notice that the peak power does not reach 2.07 kW.  That is due to a number of things.  The Sun isn't at zenith, its rays aren't quite perpendicular to the panels, but most importantly, some of the light is being absorbed by smog and water in the atmosphere.  I can see a big 10-15% boost in power when we have strong Santa Ana winds which blows away all moisture and smog.

One really interesting fact about the solar panels.  The total area of the install is 175 sq. ft, or about 9% of the total roof area!  And it will supply all of the energy I ever need.  My installation is about half of the size of other similarly sized homes with solar power in the area (because my house is very efficient).  But still, the point is that even in a way less efficient house, in the American southwest, it is easy to produce power for your house with ~20% of the area of the roof or less.  Of course, in cloudier areas, you will need more.

Now go read about how the panels did after one year in my next post!