- Intro
- Reducing electricity consumption I: Lighting
- Reducing electricity consumption II: vampire/standby power
- Reducing electricity usage III: Major appliances
- Renewable energy for the home
- Cutting the cord
- Reducing heating and cooling costs
- Reducing water consumption
As we've seen the last several days, I've spent a great time thinking about—and doing—various actions to reduce my energy consumption as I head toward a net-zero (and eventually sub-zero) carbon footprint. I've replaced my lights, significantly reduced my continuous vampire/standby/always-on electricity usage, I've chosen my major appliances carefully, and I've adjusted my behavior to minimize usage of the devices and appliances that remain.
But of course, none of that gets me to net-zero or better. It gets me to "consuming less," and since I don't plan on living the caveman lifestyle, any further improvements require that I generate my own clean energy. And I do! So in today's installment, I will talk about the various types of energy you yourself can generate at home. Not just solar, but wind and geothermal.
There is no doubt that these systems are expensive, and payoff times are long (nearly a decade). But incentives and leases exist to ease the financial burden, and there is no better way to wean you and your family off fossil fuels than to eschew them entirely. So head on below the fold, but as I've done every day, one quick reminder before we do so: these are the rules of my energy-efficiency journey:
1. I do what I do to save the world. That's my top priority, bu t...
2. Saving money is important! The upgrades have to make financial sense.
3. Don't sacrifice comfort.
SOLAR
When people think of renewable energy for the home, they immediately think solar. And sure, it's by far the most popular and accessible form of consumer-level alternate energy. Companies like Sungevity and Solar City have done a stellar job popularizing solar, and many companies now offer lease programs that minimize the up-front cash requirements.
I myself went with Solar City. Given the incentive structure in my corner of the world, the size of my array was restricted to 100 percent of my previous-year annual production. For me, that meant a 3.9 kW system, which means that it can theoretically produce that much power at peak sun. However, solar panels aren't 100 percent efficient, far from it, and there are further efficiency losses through the power lines, inverter, etc. Furthermore, my roof slopes east-to-west, so the east-facing panels get more morning sun, while my west panels get more of the afternoon sun. All in all, at peak production in the summer, when the sun is at its highest, my panels generate 3.1 kWh per hour.
Right now, in the darkest part of winter, I'm lucky to get 1.5 kWh per hour.
Time of day matters, and time of year matters. Here's my production this year:
Solar production peaked in May out here, even though the days are longer and the sun is higher in June and July. Why? Because we get heavy morning fog in the summer as cool ocean air collides with hot Central Valley air. May is the sweet spot, the clearest time of the year. The December bar is for three weeks, and it's been a dark and stormy three weeks out here. We need the rain, so huzzah! But it means very little power.
Last December, I averaged 8.36 kWh of generation per day. This December, it's only 4.65 kWh. In May, it was 23.6 kWh per day, so a huge range throughout the year. And that's why we have what's called "net-metering." I don't pay PG&E a monthly bill. Rather, the utility tallies up my entire year net use, and I get a true-up bill in October to pay for the balance. See my usage chart again, this time comparing the green "solar" line to my consunption:
As you can see, I generated significantly more power than I used in the summer, which is then offset by the winter months. This past billing year (October to October), I ended up owing the utility on a net usage of 1658 kWh, or about $300. For the entire year. And that number was exaggeratedly high by a longterm house guest who thought it was a good idea to run the electric space heater in her room at full blast, then open the window to her room at night because "it was too hot." That's what that GINORMOUS spike in December 2013 is all about. She and her baby are wonderful people, but her wasteful energy usage almost killed me. I am SERIOUS OCD about this shit.
The difference is dramatic. While my house used 1200 kWh of electricity in December 2013, we are on pace for only about 440 kWh this December. It's not all our houseguests. We're having a far warmer winter this year than last. But then again, I had a lot more of that usage offset by the sun last year than this, and I'll still come out WAY ahead in 2014.
What's my point? Oh, net metering. Point is, given my continued efficiency gains this year, and given the smaller (and more efficient) household, I should hit net zero electricity use in 2015. In the last year, my solar array has produced 5461 kWh of power. My energy use the past 12 months? 5511 kWh. And like I've noted, more recent months have been significantly more efficient than their year-ago equivalents. Heck, I expect PG&E to write me a check next October which will offset my gas usage. It will be a small check, but hey, better than writting them a check.
So what did this all cost me? I did what was called a pre-paid lease, in that it's a 20-year rental of the panels, but I paid the cost all up front. (Some solar providers have zero-down leases as well.) Total, that 3.9 kW array cost me a shade under $12,000, which also includes an output guarantee, a new inverter when the current one goes bad (they last about eight years), free replacement if any panels go bad, and they have to haul everything away at the end of the lease. I can alternatively choose to negotiate an outright purchase at that 20-year mark, and while no one knows what terms might look like, it's kind of irrelevant to me. In 20 years, the efficiencies of the latest and greatest technologies should be so much higher than what I have now that I'll inevitably want to upgrade.
Since I got the panels (13 months ago), they've produced 5993 kWh of energy. At my $0.19 average rate, that's $1,139 in savings. That puts my break-even point on the investment at 10 years, but that assumes no future increase in electricity prices, which we know is impossible. That probably gets me in the nine-year range which is what most solar providers cite as the pay-back time.
My current household power usage is around 14.6 kWh per day. I project I can get that down over the next several years to a svelte 7 kWh per day. A big part of that is moving my aquariums out of the house, but also includes other efficiencies like cutting the (Satellite TV) cord and further reduction of standby power usage. If I do that, and if my panels continue to average 14-15 kWh of production per day (solar panel efficiencies drop with time), that would give me an excess 7-8 kWh per day in production which would be more than enough to power my future electric car.
So thanks to reductions in our usage and higher efficiencies, our existing solar system will one day power not just our house, but much of our (non-bike) transportation needs as well. (The rest is BART and airplanes.) And that's how I can get closer to a truly net-zero carbon household.
Incidentally, Solar City has a pilot program to install backup batteries (made by carmaker Tesla) so that houses can continue to use stored solar power at night, and even more importantly, to keep power even during utility outages. Currently, solar powered homes lose their power during outages, even if the sun is shining. Why? Because unused solar power is being sent back to the grid, and no one wants an engineer electrocuted while trying to fix downed powerlines. With a battery, my house could retain power despite such outages (though only to a limited number of circuits, not the whole house).
However, my installation was cancelled halfway through after Solar City realized that the batteries performed poorly when installed outdoors. They needed a protected enclosure, and given my small-ish home, there was no space for anything like that. It was for the best, though. The 7 kWh battery cost $7,000, a huge stretch for my budget, and it turns out that using the utility for "storage" of excess power is a more-than-adequate option. I still want a battery for disaster-proofing my house, but I can wait until they get smaller and cheaper.
Finally, you can use solar power to heat your water. Solar water heating is simple tech: slap a tank on your roof, attach it to solar collectors, and let the sun take care of heating that water. There are systems that attach to your existing water tank, so no need for that extra tank in the roof.
These have been extremely popular in the middle east and southern Europe since lizards first crawled the earth, and they are considered a mature and effective source of water heating. I just haven't gotten very far with it for two reasons: 1) I take my showers in the morning (to wake up, since I don't do coffee), before the sun has had an opportunity to heat the water, and 2) our heater runs mostly at night, when there is no sun to heat the water.
Now a large tank loses its heat slowly, particularly if it's well-insulated, so theoretically, solar water proponents say that absent a long string of cloudy days, there should still be hot water in the morning. But given that I need evening heat most of the year (even in the hottest month, the average night-time temperature in Berkeley is 56 degrees), and given that my heat is generated by hot water (via radiant floor heating), I intuitively distrust any promise of hot water in the morning. Furthermore, I got rid of my water tank when I went to a tankless water heater, and in my space-constrained house, I don't want to give up that extra (now storage) space.
But it's not a notion I'm done considering. It's not quite on my bucket list yet, but merits further study. If you want to learn more about solar water heating, this is a good source.
WIND
I live in an urban environment, with houses tightly packed together, small yards in back. The idea of wind power is appealing: generating electricity even when the sun isn't shining. It makes the concept of "off the grid" theoretically possible—sun during the day, wind and batteries at night, and to hell with the dirty utilities. But how does wind stack up?
One Washington newspaper actually compared the two side by side:
The solar panels have produced about five times as much electricity as the wind turbine over the past 14 months. The sun’s ability to generate more electricity than the wind – even during short winter days – has surprised the utility’s engineers.
The utility bought a 35-foot wind turbine and a bank of solar panels. The systems are representative of technology scaled to individual homeowner use, Damiano said. Each cost from $22,000 to $24,000 to install.
Turns out that wind is very erratic, and even in cloudy Spokane, Washington, where the winter days are quite short, solar outproduced a wind setup of similar price. So for overall power generation, solar remains king. But here's the thing: at night, electricity needs are much lower than during the day, at least in my house. My nighttime usage is aquarium pumps, maybe some heating, my internet infrastructure (cable modem and routers), the fridge, and evening TV watching.
Take the aquariums and DirecTV out, because it's in the plans, and my nighttime usage averages out to roughly a steady 100 watts. If I'm watching TV and doing laundry, it'll peak at around 1.2 kWh. Seems like a small-ish wind system could handle that kind of load, right?
There are no Sungevities or Solar Cities for wind. Most articles online about residential wind power are around 2011, click on the companies they talk about, and a surprising large number of them no longer exist. For the do-it-yourself off-the-grid types, there seem to be plenty of options out there. But for those looking for a modern grid-tied smart system (with an iOS app to track production), I haven't found anything compelling.
Furthermore, the siting of a wind turbine is complicated, particularly in urban environments, and the wind speeds needed to make wind really viable, over 10 MPH, rule out lots of places. In Berkeley, wind speeds are highest in the summer, when I'd need the least amount of supplemental power, and lowest in the winter, when I'd need it the most.
GEOTHERMAL
Geothermal heat pumps take advantage of the constant temperatures of the ground around your home in order to provide both
heating and cooling to your home.
Initially a large, ground loop is installed deep in the ground (from 5 to 300 feet deep) and installed in such a way that it has good thermal conduction to the Earth. This loop is filled with water and methanol (an anti-freeze) which is then circulated down into the ground and back up again.
In the winter time, the heat from the ground (56 degrees) is transferred to the fluid in the loop and then transferred again into a refrigerant loop inside the heat-pump. According to the laws of thermodynamics, when the pressure is increased in a closed system, its temperature will rise. A compressor raises the pressure of the refrigerant which causes its temperature to also rise. The now hot refrigerant is fed through a heat exchanger where a blower transfers the heat from the refrigerant into the air, sending it throughout the house in the heat ducts. Once the heat has been removed from the fluid, the pressure of the now cooler refrigerant is released. This causes the refrigerant to become super cool. The refrigerant then cools the fluid in the ground loop which is then pumped back down the loop where the Earth warms it back up to 56 degrees.
I'm not going to pretend to understand the physics behind closed loops, but fact is, it is the most efficient way to heat and cool your home, by a factor of a bunch. The most efficient water heaters right now (generally tankless) hover in the low 90s. The most efficient furnaces are in the high 90s. Impressive! But a ground loop? The Department of Energy
estimates between
300-600 percent on the coldest nights. John Saves Energy put together a
handy chart:
How is that possible? Because you are using some energy—electricity for the pumps—to unlock stored energy from the ground. Just like solar taps a free energy source, ground loops do so, but at efficiencies that solar can only dream of. And while the quote above specifically talks about ground loops heating the air, it can also be used to heat water. Remember my dream to ditch all natural gas from my house? Geothermal would allow me to eliminate my gas-powered tankless water heater. And that hot water also would dramatically lower my home heating bills, since I use radiant floor heating (basically, hot water pumped under my floor).
I highly recommend reading John Saves Energy's detailed recap of his geothermal installation, including photos. He's been through the process and chronicled every step of the way.
The downside is that installation is way expensive, between $30-40,000 before tax incentives (or even higher), and you are drilling multiple holes hundreds of feet into the ground, so it makes a huge mess. If you've got lots of land, there are horizontal versions of ground loops that cost less, but for me, space is at a premium. So yup, expect your entire yard to be ripped up:
Now John installed a big system to cover his big (5K square foot) house in Utah, where the winters are COLD and the summers are HOT. The results after a year?
Amazingly, only 1800 kWh of electrical energy was required to heat our 5000 sqft house and supplement much of our hot water needs this past winter. An additional estimated 9000 kWh was provided for free from the ambient heat in the earth.
John calculated the payback time of his $20,000 investment in geothermal (after rebates and incentives) at between 11 and 14 years, since the more efficient his home becomes, the longer the payoff time for big investments like this one (ironically). On the other hand, once he factored in personal intangibles like greater comfort, he estimated the payoff time at 8.5 years. And that's before even considering the environmental benefits.
There's no doubt that a geothermal ground loop is the biggest investment of any of these options, but the benefits are likewise huge. My journey toward a negative-carbon household runs through one of these. Eventually. Maybe. Perhaps not.
When it comes to residential heating and cooling loads, the trend is toward smaller loads (due to improved building envelopes with reduced air leakage, thicker insulation, and better windows), not larger loads. A home with a good thermal envelope doesn't need much heating or cooling, and it certainly doesn't need a $42,000 HVAC system.
That might be a good point. My house is 2,000 square feet, so relatively small, and is situated in a temperate climate without weather extremes at either end. My heating load is light, my cooling load is zero. The tighter I make my envelope (i.e. insulation), the less I spend on heating. So why would I get an insanely expensive ground loop system to save what few bucks are left heating my home? John's irony above applies to me: the more I spend on making my house efficient, the less sense it makes to spend big on making further efficiency upgrades. I'm rapidly approaching the point where the cost of further improvements is too high for marginal gains at best. It might simply be better to beef up my solar array to heat my water electrically.
It's all academic anyway. I don't have $40,000 for a ground loop system. But if the time comes when I do ... my house will be too efficient for it to make sense.
But for those with bigger homes in climates with extreme temperature ranges? The math might make a lot more sense.
By the way, if you liked John Saves Energy's detailed geothermal rundown, you'll also love his Solar writeup. I mean, this is a guy who performed major surgery on his doorbell to save 4 watts of standby power, and chronicled every step along the way. He's an energy efficiency hero!
NUCLEAR POWER
Just kidding.