Renewable Energy

Renewable energy is energy generated from renewable sources such as sunlight, wind, rain, tides, and geothermal, sources that are naturally replenished. In Orange County, the two renewable energy sources that are economically feasible are sunlight and geothermal. While we have wind in Orange County, it is not widely feasible to harness because of its low average energy density here.

Electricity from sunshine

Energy from sunlight can be harvested economically in Orange County by using photovoltaics (PV), a technology that turns sunlight into electricity. The NC Solar Center has more information on this technology and its relevance in North Carolina.

30% Federal and 35% NC State tax credits, plus depreciation, can pay back your investment in a photovoltaic system in less than six years, assuming you have the income tax liability to use the credits. DSIRE, the Database of State Incentives for Renewables & Efficiency, is run by our own NC Solar Center and has up-to-date information on all tax breaks and other incentives.

The tax credits mean that, in exchange for being without your money for just six years, you get free electricity without pollution for the 25-plus-year life of the system. A calculator that shows the financial details can be seen at the Appalachian Institute for Renewable Energy’s website.

If you produce solar power, you can either purchase batteries to store the power, and use your own power in your own home, or you can forego the cumbersome batteries and sell the power to your electric utility. The utility gives you a second meter that records how much power you generate. The electricity you are actually using is coming in from the utility and being measured by your existing meter. So you are not actually running your house on solar power, but the utility has just become a little greener because of your contribution. More information is available from NC Green Power. In addition, you will receive income from Solar Renewable Energy Credits (SRECs). The idea is simple: you put power into the grid and get paid for it and you take it out and pay for it. The grid is like a giant battery.

Typical PV system Diagram (click to enlarge)

Individually-owned PV systems in Orange County are generally located on a south-facing roof, but they can also be mounted on the ground or any other structure. The key to their working is solar access. In general, this means the place where you install them cannot be shaded at any time of the year between about 9 in the morning and 5 in the afternoon. One kilowatt of PV as of this writing will vary in cost from $7,000 to $10,000, depending on the complexity of the installation, or roughly $70,000 to $100,000 for 10 kilowatts (10 kW of installed PV here will produce roughly 12,600 kilowatt-hours of electricity per year).

Some local solar installers are:

Southern Energy Management
Strata Solar
Honey Electric Solar

The installers serving can help you understand the details and install a system for you. They will also help with all of the details of interconnecting with the utility, no simple walk in the park.

A quick note on electric cars: If you buy an electric car without installing a PV system, you will be fueling it with energy from coal-fired or nuclear plants. If you install your own solar electric system
sized to your driving needs, you will not only get your money back but you will have free fuel for the life of the system.

Geothermal energy

A geothermal heat pump or ground source heat pump (GSHP) is a central heating and/or cooling system that pumps heat to or from the ground. It uses the earth as a heat source (in the winter) or a heat sink (in the summer). Wikipedia has more information about geothermal technology.

In Orange County, the common practice is to drill wells and pump a fluid through a closed loop to facilitate the heat exchange. These wells can be 300 to 400 feet deep and there can be multiple wells depending on the size of the system. There are federal and state tax credits for ground source heat pumps that can drastically reduce the upfront costs.

Typical Ground Source Heat Pump Diagram (click to enlarge)

How do ground source heat pumps systems actually save on energy?
Simply put, they transfer energy more efficiently. The ground in Orange County 5 feet below the surface stays at about 55 degrees all year round, whereas the air temperature fluctuates all year. In contrast, an air-to-air heat pump uses outside air as a heat sink or source of heat, so if the air temperature is 90 degrees in the summer and 20 degrees in the winter, there is not much capacity to absorb heat in the summer or give up heat in the winter compared to the 55-degree constant ground temperature.

Ground source heat pumps are not cost-effective under about three tons because the added expense of the wells and equipment does not produce enough savings to pay back the investment in a reasonable length of time. This means that the systems are not practical for residential or commercial buildings smaller than about xxxx square feet.

Some local installers of ground source heat pumps are:

All American Heating and Air Conditioning
Evangelist Service Company
Beaver Brothers, Inc.
Raleigh Heating and Air, Inc.

Questions about renewables? Email us.

Information compiled by Giles Blunden.