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Hybrid Power for Your Home

Posted Aug 24 2008 8:11pm

You have access to an inexhaustible nuclear fusion reactor 93 million miles away that generates no waste or pollution. If you can picture your entire yard covered by tightly-spaced barrels of oil, that's a pretty good approximation of the amount of solar energy that falls on your property free of charge each year. How much of that heavenly gift are you grabbing?





The Futureproof Dream Home will be a hybrid powered home that taps this resource in multiple ways for 100% of its power needs (including charging the family plug-in hybrid cars). You don't need to be designing a dream home to take advantage of the power of the sun, however. The principles and the technology can be applied to any home.





Think Passive Design First





My first dream home, The House on the Hill in the Woods , built in 1985, was a passive solar design with a very well-insulated building envelope with high-performance windows. It had a shallow two-story, south-facing solarium with floor-to-ceiling glazing and a black slate floor. The rear brick wall of this space housed two special heat-storage masonry fireplaces, which provided back-up heat, if needed. In the summer time, this space was shaded by the roof overhang and deciduous trees and it was ventilated at night with gravity displacement or stack-effect ventilation augmented by a high monitor with eight large awning windows at the peak of the roof. This nighttime ventilation cooled down all those tons of masonry and kept the house comfortable without air conditioning, thanks in part to its location among tall oaks. In the winter, the sun blasted the atrium space and heated the slate and the brick as the low winter sun angle and the leafless trees turned on the seasonal solar switch automatically. The high performance windows made electric lighting unnecessary during the day while also blocking heat gain, heat loss and UV radiation. They also allowed for effective cross ventilation and great views of the wooded hillside surroundings.



Any energy productive hybrid home should first take into consideration the site, (site selection and orientation be a future post) and a high performance building envelope that uses solar orientation and passive design features to harvest free energy the old-fashioned way; the way we had been doing it for thousands of years before we invented electricity and air conditioning. The more you spend on the passive features, the less you have to spend on expensive technology like solar collectors. This is the number one secret to designing high-performance buildings for about the same cost as regular energy hogs. If you optimize the building envelope, you can downsize the systems and save money up front and for the life of the building. Forget the minimums written in your local building code in terms of recommended insulation values for walls and roofs. If you build to code, you have built the worst building you can legally build and you will pay for that mistake every month for the life of the building. In Indiana, for example, our residential energy code is based on 1992 Model Energy Code and our current commercial code is the worst in the nation (doesn't quite meet 1989 Model Energy Code), which helps explain why Hoosiers are number two on the list of states in terms of coal consumption per capita (96% of the electricity generated in Indiana comes from coal-fired power plants). For every dollar you spend on making your building more energy productive passively, you will save about three to five dollars on alternative energy systems cost . Today we have good energy modeling software to do what-ifs to make intelligent decisions about the optimal combination of insulation and glazing investment verses system costs that results in the most cost productive, energy productive investment.





Optimization also applies to things like energy productive lighting, appliances and other things you plug in. The big three in this regard are refrigeration, water heating and lighting. By choosing an Energy Star refrigerator, by installing the new and improved low-flow shower heads, Energy Star dishwasher and clothes washer, and high-performance water heater (augmented with solar and geothermal in the Futureproof Dream Home), controlling phantom loads (all those things that are turned off, but still drawing juice), and upgrading lighting (to compact florescents or light emitting diodes) you can reduce the system load by more than 60%. This makes alternative energy systems much more practical and affordable.



Let's look at some potential components of a Futureproof Hybrid Home power system beyond the passive systems described above.



Solar Hot Water
If you are looking to upgrade your current home, before you run out and buy a new solar water heater, there are some things you can do with conventional systems that will save big bucks if you don't have the cash to spend on a new system. On average, we use 60 gallons of water per person per day. Water-saving shower heads have a checkered past, but new technology, such as the Oxygenics Skin Care Shower supercharges the water stream to achieve the same wetting effect and feel as regular shower heads, with a 70% water savings. Laminar-flow aerators achieve the same effect on kitchen and bathroom faucets. Install water-saving shower heads, insulate your water heater, insulate your hot water pipes, set the water temperature at a less deadly temperature and watch your electric bill go down.




If you are building from scratch or looking for something to do with your tax rebate check, look at solar hot water. When I specified solar hot water for a new library in Newburg, Indiana, I was amazed at the production of the system in terms of heat and volume and it got me started thinking about other uses for all that free heat. More about that in a moment. For a homeowner trying to hedge against dramatic energy cost increases, solar hot water is a no-brainer. EERE Consumer's Guide to Solar Water Heating is a great resource and they will show you how a solar hot water heater can pay for itself in as little as a 18 months. If you are a heavy user of hot water, for example, if you have a large population of teenagers at home, then this could be an even faster payback. Today's high-tech solar hot water heaters perform reliably with little maintenance and they can be integrated with the architecture less conspicuously than the models from the 70s and 80s.


Geothermal Heat Pumps
A properly designed passive solar home requires little artificial heating or cooling, but if you want to have reliable back-up system, the most efficient option may be a geothermal heat pump or GHP (not to be confused with the systems that make steam from hot rocks beneath the earth in certain parts of the world). Relying on the fact that the temperature of the earth a few feet below ground remains in the mid-50-degree range all year, this system borrows heat from the earth in winter and uses the earth as a heat sink in summer.



This system can save 50 to 70 percent on your heating bill and 20 to 40 percent on your air-conditioning bill and 20 to 50 percent on total energy consumption, especially if you use a GHP that also produces hot water in summer as a byproduct of the cooling cycle. These systems can work elegantly with a radiant floor hydronic heating system or a more typical forced-air system. Initial cost is a major hump to get over, mostly for the installation of the ground loop, which requires vertical wells or horizontal trenches or, ideally, a lake or pond. There are closed-loop and open loop forms, with a close loop being the most common here. Typical payback on a GHP system is five to ten years. Federal and state and utility incentives are available for GHP systems to help get you over that hump as soon as possible and special home financing may be available. Another advantage of this system is that you move from a fossil fuel that is rapidly escalating in price to electricity, which you can make in your own back yard!
Solar Photovoltaic Power
A simple way to make your own electricity is with solar photovoltaic (or PV) panels installed on your home or on a separate structure. As this technology has improved, power output has gone up and cost per watt has gone down. New thin film solar cell technologies now entering the market promise to make PV power ever more popular as fossil-fuel power continues it's rapid rise. PVs convert sunlight directly into electricity that then typically goes to an inverter that makes that energy compatible with your house wiring. If you are powering a remote cabin or want to assure access to power during a grid power failure or have enough solar juice to refuel your plug-in hybrid car at night, you will have a battery pack that is trickle-charged by the PV system. For most applications, however, it makes sense to keep your house tied to the utility grid. If you produce excess power, you can sell it back to the utility through a process known as net metering. In 35 states, net metering laws require investor-owned utilities to provide net metering, but the actual implementation varies widely from state to state and from utility to utility and those on rural electric cooperatives may be out of luck in many areas. In Indiana, where we are bidding two net-zero-energy PV-powered library branches, net metering is only available up to a 10-kilowatt system limit and that only applies to residences and schools up to 1% of the utilities load. For businesses in Indiana, there is no net metering. In neighboring Illinois, that limit is 40 kilowatts and in Ohio, no limit is specified on either the amount or the type of user, other than no more than 1% of the utilities total load may be enrolled. A Federal net metering law is needed that would make more sense of this hodgepodge and open up the floodgates on clean technology distributed power systems development. This floodgate would really open up if a National Renewable Energy Standard is passed. Twenty-five states have renewable energy standards in place (not including Indiana). PV systems work best in bright summer sun, which is exactly the same time our national energy grid is groping for peak power. For a Futureproof Hybrid Home of reasonable size with excellent passive design, the 10 kilowatt system limit would not be a stopper, but it would be good public policy to put clean tech on a level playing field with highly subsidized brown tech, particularly in those states that lack a diverse energy portfolio, such as Indiana. Clean tech industries, a booming sector creating thousands of new jobs, are attracted to states with strong renewable energy standards, generous net metering laws and comparable incentives for clean tech development verses brown tech development.




Wind Power
Some of that energy from the sun that strikes our atmosphere is converted into the kinetic energy of wind. Wind power in Indiana is best during fall, winter and spring, while solar power is best during summer. If you can swing a hybrid wind power/PV system, you can size the solar for one quarter of the load and the wind for three quarters of the load and save on downsizing both. Wind in combination with solar also gives you more around the clock energy generation. Wind power, at least in Indiana, is a very underrated resource, especially in the flatter northern half of the state ( see wind resource map ). The installed cost of wind is $2 to $3 per watt, which is 1/3 to 1/2 half the cost of PV installed cost.



Because Indiana has significant wind resources located convenient to major transmission lines and major markets like Chicago, it has attracted recent investment from the wind industry and over 2000 megawatts of wind power will be put in place here in the next three years. A future drive along Interstate 65 between Lafayette and Crown Point will provide a view of hundreds of the $3 million turbines covering over 100,000 acres of Indiana farmland, which will remain farmland.
This same rich resource is available to homeowners. The drawback to small residential wind power is that the wind turbines currently available work best when they have high, steady winds free of turbulence and that requires some altitude. The rule of thumb is that the bottom of the turbine rotor should be at least 30 feet above any obstruction within 500 feet. A typical tower height for a whole-house power system is 120 feet. That could be an issue in many neighborhoods. You also need room to assemble and erect the tower. As a result, wind power is most popular in rural areas with lots of room and few obstructions. Another drawback is that wind power systems have moving parts that require service on a regular basis. This service typically occurs once or twice a year and can be done by traveling "windsmiths." If you are mechanically inclined and change your own oil, you are well-suited to do your own service (some climbing involved, unless you get a tilt-up tower).


The power of a wind turbine is proportional to the cubed velocity of the wind. In other words, a small difference in wind speed makes a tremendous difference in power output. If you put up a popular Skystream model in an 8 mile-per-hour annual average wind speed, it will generate 1200 kilowatt hours per year. The same unit in a 12 mile-per-hour average wind will provide 4560 kilowatt hours per year. Often, homeowners try to get by with a shorter tower, but wind speed increases with tower height (the commercial units are typically at 300 feet). The top three things homeowners wish they had done was 1) taller tower, 2) taller tower, 3) taller tower. The difference between an 80-foot tower and a 120-foot tower could be four times as much power with the same unit.
As a general rule, the least expensive systems are those that run at high RPM and have relatively short rotors and are light in weight. These smaller systems also tend to be the least efficient, least reliable, and make the most noise. For long-term reliability, power output and quiet, look for relatively low-speed, heavy-duty wind turbines with long rotors. To estimate the size of your wind power system you would add up 12 months of electric bills to get annual consumption, determine the portion of that annual need you wish to provide through wind power, determine your local wind speed at a given tower height suitable for your location and select a turbine based on annual output based on your average wind speed. To pinpoint wind speed in your location, you can get help from an expert or use a combination of state GIS wind maps, local airport wind data, or ideally, measure the wind resource directly with an anemometer from a local tower. The following are good resources for small wind power systems:


That's all I will cover in this post, but stay tuned for information on other hybrid system components that make sense for some sites, such as microhydropower, biomass, combined heat and power and fuel cell systems.
No matter what power system you are considering, don't forget the cheapest, most productive energy is that which you don't use in the first place. If you are starting with bad passive building design, you will be wasting energy and money, no matter how exotic your power source. We'll spend another post on passive design basics. Refer also to an earlier post on Futureproof Buildings .
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