Renewable Energy

Photovoltaic Cells and Wind Turbines

Gaining passive solar energy to heat our homes is a fairly basic endeavor. In its simplest form, we can open our curtains and let in the sun's energy. Gaining electrical energy from the sun is not so easy. There is a misconception that going solar means energy is "free." To gain electricity from the sun, there are a whole series of components that are necessary and they come with fairly high price tags. The pay-off will come later when not paying monthly utility bills that will probably rise for on the grid users. There is also the important pay-off that results from knowing that energy blackouts won't affect one's home, and from not contributing to CO ₂ in the atmosphere. For every kilowatt hour of electricity produced at the typical power plant, twenty pounds of carbon is released into the atmosphere. For every watt used in one's home, approximately nine watts are lost in the transmission lines [24]. For people moving into the country where there are no utility connections, the solar option can be immediately cost effective as utility companies usually charge a high premium to run lines to a new building site.

Photovoltaic cells are usually grouped together in modules. They convert sunlight into electrical charges. The charged electricity then travels through wires to storage batteries in the home. This is the major difference in living off of the grid. We are accustomed to switching electricity on and off as it enters our homes from the power lines. Off-grid users must store their energy in batteries or it will be lost. These batteries look like the ones we use in our cars, but are a heavier, deep-cycle version.

Now things get tricky. At this point, it is a good idea to remind students that they are studying electricity. This is not something to go home and play around with. The first step is to assess how much electricity (wattage) is going to be used. More usage requires the purchase of more photovoltaic (PV) panels (arrays) and storage batteries, which can significantly raise expenses and affect maintenance issues. More batteries will also affect construction cost, as they should be stored in a separate room inside the house. So, how much energy will you need? First, calculate your current usage. Consult your electrical bills and divide the kilowatt hours from the bill by the number of days in the billing cycle. The average home will probably be in the range of 15 to 30 kilowatt hours per day (without air conditioning) [25]. "Consider that the modules for a solar array will cost you somewhere in the neighborhood of $3.50 to $5.00 per watt [in 2003] (and each of those watts will give you, on average, .004 to .006 kilowatt hours per day, which is to say that a 1000-watt array will yield 4 to 6 kilowatt hours on a good day) [26]."

Obviously, conserving energy will be cost effective. Calculate the amount of electricity that is essential and then look for ways to eliminate usage. Older appliances are energy hogs. Look for newer, Energy Star-rated models to save wattage. Don't use items such as plug-in clocks when wind-up or battery operated will work just as well. Eliminate phantom loads. The modern home contains several items that are always "on," even when they are turned off. The television is the best example. It comes on instantly, because it is waiting in an "on" condition. Other examples are VCRs, DVD players, cable boxes, laptop computers, and electronic chargers [27]. These items should be unplugged when not in use or plugged into a power strip that can be turned off. Switching from incandescent to compact fluorescent light bulbs will save wattage. Every bit helps and reduces set up cost. Once the system is up and running, there are other wattage saving measures that can be undertaken. Don't use big energy consumers at night or on cloudy days. Wait for days when the sun is out and constantly charging the batteries.

It might seem that having extra PV cells and batteries would just be easier, despite the cost. But, that is not necessarily true. With too few batteries you will be wasting available solar and wind energy. With too many, the batteries themselves will suffer due to maintenance issues [28]. Sulfates can accumulate on batteries that are not brought to full charge. This will lessen the life of the battery. So, the batteries need to be taken to full charge (filled up with energy) on a regular basis. Too many, and that may not be possible [29].

The solar array of PV cells should be oriented towards the sun in the same manner as a house utilizing passive solar energy. There are several components necessary to bring solar electric energy into the home. Energy from the PV cells needs a charge controller to ensure that the electricity is the appropriate DC current for storage in the batteries. American homes operate off of AC current, so an inverter is needed before the energy can be put to use. Meters are useful for monitoring usage, and fuse or breaker boxes are needed to regulate energy to the outlets. If including energy from a wind turbine, that electricity will also have to flow through the charge controller, or converter, for storage in the batteries (see Figure 3). This all serves as a reminder that the start-up costs of "free" solar electricity are more than those associated with contemporary construction.

Figure 3. Reprinted with permission of the publisher from Logs Wind and Sun by Rex A. and LaVonne Ewing: PixyJack Press.

Wind turbines can be large or very small. Check YouTube for numerous variations in style. The advantage of using wind energy is that it supplements solar production when the sun is not shining and at night. Of course, for this to work, wind is necessary. A turbine requires wind speeds of between 8 to 10 mph to produce electricity. It is wise to monitor wind velocity in an area before investing in a turbine system. Since wind speed increases with height, most turbines are raised on towers. Here again, there is more start-up cost. The turbine should be free of any obstacles that can limit wind access such as trees, buildings or geographical formations. In his book, Logs, Wind and Sun, Rex Ewing recommends that the blades of a turbine be mounted at least 20 feet higher than the highest point within a lateral radius of 300 feet [30]."