Solar energy is harvested either passively or actively. The prime requirement for an active or passive solar heating system is a well-insulated and tight building envelope. This will minimize the required heat and make any solar system more effective.
Solar energy can be:
- Passive Thermal Solar Energy
- Active Thermal Solar Energy
- Photovoltaic Solar Electric Power
Passive Thermal Solar Energy
Passive solar energy captures and stores the heat of the sun through architectural features. A passive solar home is designed to allow the rays of the winter sun to deeply reach into the home and heat up walls and floors.
Image by David Parsons
Many large windows are located on the East, South and Western sides. External shading keeps the rays of the hot summer sun out of the home.
The heat of the sun is captured and stored in what is called the building mass. Stone, concrete or brick walls and floors are examples of materials used for storing solar heat.
Some passive solar homes incorporate additional storage, such as water columns used as room dividers, into the design to maximize the passive solar heat storing capacity.
After the sun sets, the solar heat stored in walls and floors is slowly released and radiates its stored heat back into the rooms.
Passive solar heating features are a must in a green home. Maximizing the passive solar heat will help to minimize the energy usage of your heating system.
Active Thermal Solar Energy
Active thermal solar energy systems use collectors to convert the sun’s rays into heat.
These solar collectors can be used to heat air or a liquid. Most often, the liquid is a water/glycol mixture. The glycol prevents the water from freezing on cold overcast days and at nighttime.
The following paragraphs are simple descriptions of the different types of thermal solar collectors and system, which are currently available.
Solar Air Heating Systems
The simplest solar collectors are those used to heat air. Cold air enters the collector at the bottom and rises to the top as it heats up. The heated air is collected at the top and ducted down within the collector and out at the bottom. A small circulating fan pushes the heated air into to the room about 6 inches above the floor.
Sol-Air Company
The collectors are ideally mounted on south-facing walls. However, they can be mounted on the roof as well. Ductwork can be installed to blow the heated air into the rooms located at the north side of your home.
Air heating systems have the lowest first cost of all solar heating systems. The downside is, that excess hot air cannot be stored to be used at night.
Solar Water Heating Systems
Cold water/glycol is pumped through the collectors where it is heated. The hot water is then pumped to the basement and through a heat exchanger. The heat exchanger is used to separate the glycol/water loop from the domestic hot water and the heating hot water loops.
The heat from solar collectors is used to either pre-heat domestic hot water, or it is used to supply the heating system with hot water. Controls automatically divert the hot water to the heating system (during the heating season) when the domestic water has been heated to the desired temperature.
Pete Beverly
Flat plate solar collectors are the simplest of the water-heating collectors. Cold water is introduced into the collector at the bottom. Copper piping is laid out in a serpentine pattern on a black heat absorber panel. The water heats up as it circulates through this pipe to the top of the collector from where it is pumped to the heat exchanger.
Vacuum tube solar collectors are more sophisticated than the flat plate collectors and generally have a higher efficiency. Vacuum tube solar collectors consist of a set of glass vacuum tubes with black absorber plates and copper pipes running through each tube. Again, the cold water enters the tubes at the bottom, heats up and is pumped from the top of the collector to the heat exchanger.
I want to mention one other type of solar collectors: parabolic type collectors. These collectors focus the sun’s rays on the copper pipes through which the water/glycol is circulated. The concept is similar to taking a magnifying glass, or a lense, and focus the sun’s rays on a piece of paper until the paper ignites.
The water in parabolic collectors can reach very high temperatures. Higher than is generally required for residential use. These collectors are mostly used for commercial application and also for solar power plants, where steam is produced to generate electricity. A Spanish company is planning just such an installation in Arizona.
Solar water heating systems can be installed in just about any home, as long as southeast, south, or southwest exposure is available. It is also important that the area where the solar collectors will be installed is not shaded from at least 9 am until 3pm.
Photovoltaic Solar Electric Power
Photovoltaic (PV) solar power systems consist of
- Photovoltaic panels
- DC disconnect
- Inverter
- AC disconnect
- Main electric panel
- Utility Meter
The sun’s energy is converted to electrical energy in silicon-based solar cells. Cells are arranged and wired together on photovoltaic (PV) panels.
Photovoltaic panels produce direct current (DC) electricity. This is the type of electricity used in batteries. An inverter is therefore part of the PV system to convert the DC electricity to alternating current (AC) electricity so it can be used in your home.
A DC and an AC disconnect are installed on either side of the inverter for safety reasons.
The next component is the main electric panel. All homes require this panel, regardless of whether a home has a PV system or not. That is where the electric power is fed into your home from the electric utility company. Your PV solar system feeds into this panel as well. Electricity is distributed through your home from this main panel.
The last component is the utility meter. All homes have a utility meter. The difference between a solar PV and a non-solar PV home is that the meter in your home, with a PV system, can run backwards! In other words, if your PV panels produce more electricity than you are using at that time, you can feed alternative electric power back into the grid. That means that you are selling power to the utility and they have to buy it!
Photovoltaic panels can be integrated into the roof of your home, or into the siding of southeast, south and southwest exposed walls. Some PV systems out on the market today offer PV panels that look like roofing tiles.
One great way to install PV panels is to use them as shading over your south-facing windows or deck and patio doors.
The space required within your home for inverters, disconnects and utility meter, is minimal. An area on a wall, with unobstructed access, of approximately 4 feet by 4 feet (1.2m by 1.2m) is all you need.
Requirements For Solar Energy Systems
The following is a quick list of the minimal requirements to help make a solar energy system feasible and to give you the best results:
- Minimize the heating and cooling requirement for your home by having a well-insulated, tight building envelope and exterior shading for southeast, south and southwest facing windows
- You must have southeast, south or southwest facing roof, walls or land to locate solar collectors
- The areas where you plan to install solar collectors must be without shading from at least 9 am until 5 pm
- The roof structure must be able to support solar thermal collectors are it must be easily re-inforceable
- Minimize the electrical requirements by using low-energy light bulbs, such as LED light bulbs, high efficiency appliances, motion detectors for lights, etc.
- Sufficient space in the basement to locate hot water tanks and pumps.
Ok, so now you know some of the basics about solar energy. Next steps will be to determine what type of solar energy system, if any, is best for your home. Or Learn about other alternative energy systems:
Geothermal Heat Pumps
Wind Power
http://greenandsustainablebuildings.com/wood-heat/
Use the follwong two resources on available tax incentive and utility rebates to help you decide what is best for your green home.
Tax Rebates and/or Utility incentives are available in all states.
Download “The Borrower’s Guide To Financing Solar Energy Systems”
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