by Dr. Tom Lombardo
You may also be interested in reading Energy Conservation at Home Part 1 and Energy Conservation at Home Part 2
Ask a few homeowners about renewable energy and they’ll probably talk about solar panels and rooftop wind turbines. They might even use the term “off-grid.” In reality, there are many more possibilities, each with its own advantages and disadvantages. Let’s start with a brief overview of renewable energy on a residential scale. Each topic below is worthy of a thorough discussion, which I’ll provide in future articles.
Why Renewable Energy?
Homeowners typically install renewable energy for one of three reasons: to decrease their energy costs, to reduce their carbon footprint, or to become self sufficient (AKA “off the grid”). Often it’s a combination of those reasons, and while all three are valid, the first reason – decreased energy costs – must be treated as a long term investment.
While you may think your energy bills are high, the US has some of the lowest energy rates in the world. That means a renewable energy system won’t pay for itself right away – it could take anywhere from five to twenty-five years to recoup the cost, depending on where you live. Using ballpark estimates, a solar photovoltaic system would take about fifteen years to pay for itself if your electric rate is 12 cents per kilowatt-hour, the current national average. That, of course, assumes that electric rates won’t increase. It’s likely that they will, which shortens the payback period and adds value to your investment.
Of course, reducing your carbon footprint and being self sufficient are noble causes by themselves, so even if it’s not the best financial decision you may decide to do it simply because it’s good Karma. In effect you’re casting your “economic vote,” which carries more weight than you might think!
Hey! You! Get Off of My Grid!
(Apologies to The Rolling Stones…)
Living off the grid is easier said than done, especially when it comes to renewable energy. When it’s not windy your turbines won’t generate energy. Solar panels generate nothing at night and very little when it’s cloudy. No problem – generate more than you need during the day and store the rest in batteries! While that’s technically feasible, it’s incredibly expensive, at least for now. Batteries could double the initial cost of a renewable energy system and batteries require maintenance. Also, you’ll need to replace them about every five to ten years. If you have access to grid power, I suggest you use it along with your renewable energy sources. With net-metering, you can use the grid for “virtual storage.”
A Watt Saved is a Watt Generated
Image: US Environmental Protection Agency
Before you consider investing in energy production, make sure to reduce your energy consumption. Energy efficiency is much cheaper than generating energy and it has a quicker payback period. Here are simple things you can do:
- Replace your incandescent or CFL lights with LED bulbs
- Replace old appliances with new energy-efficient models
- Invest $30 or so in a programmable thermostat (and actually USE it!)
- Replace CRT or plasma TVs with LCD or LED models – not only are they more efficient, they look better too!
- Be sure your house is properly insulated and doesn’t have air leaks
- Turn off, or unplug, electrical devices that aren’t being used.
While it’s possible to do your own electric load analysis, a complete energy audit – one that examines your heating, cooling, ventilation, and insulation systems – is normally done by a professional because it involves specialized, and often expensive, equipment. The good news is that you can get a federal tax credit (USA) for energy efficiency upgrades and renewable energy systems, so that will defray the costs of hiring professionals when necessary.
Once you’ve made sure that you’re using energy efficiently, you can then start thinking about ways to generate the energy that you need. There’s no single answer to which technology is best; they all depend on your local conditions.
More about energy efficiency:
Passive solar involves capturing the sun’s heat and light and moving it directly to where you need it. South-facing windows can gather warmth from the low winter sun, and a large overhang will block the high summer sun to keep you cool in the summer. Smart placement of trees can help too. If you have a south-facing wall that doesn’t have many windows, you might consider installing a passive solar heating system. I’ve seen off-the-shelf models for a few hundred dollars and I’ve also seen some DIY versions that work well too, even in cold climates.
Windows and skylights let in a lot of light, but they’re poor insulators – even the super-efficient ones. (They’re “super efficient” compared to other windows, but they’re nowhere near as good as an insulated wall or ceiling.) However, light tubes can bring in a lot of sunlight with a small opening, which reduces heat loss.
Passive solar is one of the oldest heating/cooling/lighting technologies. In some climates, that’s all you need; in others, it can greatly reduce your energy bills. While some techniques lend themselves best to new construction, others can be retrofitted to an existing house.
Generating electricity from sunlight is more practical than you might think. Germany is one of the world leaders in solar power production, and it gets less sunlight than the northern United States. Before designing a solar power system, you’ll want to do a site assessment. Among other things, a site assessment looks for a spot that has unshaded access to the sun all year round, with no obstructions during the peak sun hours (9AM to 3PM). Photovoltaic (PV) panels can be mounted on your roof or on the ground. There are even shingles that have PV cells built into them.
A PV system costs about $4 per watt, including installation. A typical house may require a 4 kilowatt (4000 watts) system to meet all of its electrical needs but if you’re grid tied, you can start with a small system now, to lower your energy bills, and add to it later. Prices are dropping!
By the way, I’ve heard some people say that it takes more energy to manufacture a solar panel than the panel will produce in its entire lifetime. That was true … fifty years ago! Today’s solar panels have about a two-year energy payback period, which means that it takes two years for the panel to produce the same amount of energy that went into manufacturing it. Solar panels come with 25-year warranties and continue producing energy well into their forties and beyond! And I’ll admit that the manufacturing process isn’t as “green” as I’d like, but it’s still more eco-friendly than drilling, refining, transporting, and burning petroleum. Also, engineers are developing ways to make solar panels out of more Earth-friendly materials and with cleaner processes.
If you’re considering solar electricity, here’s an article with more information about the process.
Solar Water Heating
A solar water heater can serve all of your water heating needs all year long if you live in a warm climate. For those of us in temperate zones, a solar water heater does the job in the summer, but can also pre-heat water in the winter so your gas or electric water heater doesn’t have to work as hard. Solar water heating is one of the quickest returns on investment. The biggest downside is that you have to run plumbing to the roof.
I’m a big fan (no pun intended) of wind power … on a utility scale. For residential sites, not so much. Wind power is great, but it requires steady, strong winds, and you only see those at very high altitudes in open fields. Those little rooftop wind turbines may promise high energy production, but look carefully at the wind speeds required – you’ll never see those wind speeds sustained on your rooftop. We have a neighbor with a rooftop turbine; even on windy days it hardly spins. On my way to work I pass by a house that has a wind turbine – looks like a 1 kW model – on a 30 foot tower next to the house. The tower is too short and too close to the house. The turbine almost never spins.
If you want to see a detailed analysis of small wind turbines and their energy production, check out my article on ENGINEERING.com.
By the way, don’t be afraid of wind turbines or wind farms. There’s no scientific evidence that they cause harm to people. And while birds do occasionally run into them, birds also run into buildings. Many more birds are killed by domestic cats than by colliding with wind turbines. Pollution and oil spills are far worse for wildlife than any form of renewable energy!
If you happen to have a stream on your property, you might be able to take advantage of a microhydro power system. But to make good use of it, you need a large volume of water falling from a significant height. Your shallow stream might look like it’s flowing fast, but like a small breeze in your backyard, there’s not a lot of usable energy in it.
Heating with Wood
Wood is a renewable resource and it’s carbon-neutral. As trees grow, they remove CO2 from the atmosphere. When they die and decay, they gradually release that accumulated CO2. Burning wood simply releases it more quickly.
If you have a traditional heating system like a furnace, consider a wood-burning stove as a supplemental source of heat and a backup in case the power fails. (Gas furnaces require electricity too.) We bought a wood stove a few years ago and it keeps our home nice and toasty for much less than the cost of electricity to run our heat pump.
More to Come!
As I said at the beginning of this post, I’ll give a thorough coverage each of these items in future articles. I also write about renewable energy at ENGINEERING.com, so if you’re interested in the technology, please check out my articles. There’s some cool stuff happening in renewable energy!