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Solar Home Fundamentals
God likes to use solar! Do you? Fortunately, there are laws of nature that, if understood, can greatly increase heat efficiency. You will not only save the planet, but you will also save green ($).
Solar Rays are Strongest from the South
Now, in houses with a south aspect, the sun’s rays penetrate into the porticoes in winter, but in summer, the path of the sun is right over our heads and above the roof, so that there is shade. If, then, this is the best arrangement, we should build the south side loftier to get the winter sun and the north side lower to keep out the cold winds (Quoted by Socrates).
For this reason, it is more efficient for homes in the southern hemisphere to use solar. However, it is important to note that it is totally possible to fulfill all of Americas home energy needs with solar. Many people advocate using a large portion of Arizona or Nevada to generate this electricity. It’s a matter of getting political and financial support to make it happen.
Ideally, the south side of your home needs to have a sunny view for maximum efficiency. Shady areas reduce the amount of solar electricity dramatically.
Glass Windows on the South Side
Many solar homes have lots of large windows on the south side. Why? Besides getting maximum sun exposure from the south side, the glass traps in the solar heat. In a study done at Purdue University, they found that the loss of heat through the large windows was less than the retained heat.
A common complaint from people that use passive solar heating through glass windows is that they get too much heat. It’s too hot. The department of energy has said that the glass area should be no more than 12% of the square footage of the room to prevent overheating.
Windows (Panes and Glazing)
Solar people like to use the term glazing; all that means is how many panes the window has. Obviously, it is better to have a high quality double pane window. The more insulation you have, the slighter the variation in temperature. Thick walls and high rated insulation add positively to this effect. This is an important point because early solar homes had wide temperature fluctuations that were unmanageable.
Keep the Windows Covered at Night
The window lets in heat, traps it, and also lets it out a lot more than walls. That’s why you keep the windows open in the day and cover them at night. If you don’t want people to see in your home, simply get the windows tinted.
You can cover your windows with various automatic or manual methods. Many people use shutters or canvas blinds. The better you cover the window, the more heat that will be retained.
There are many types of collectors to gather solar energy. Perhaps the most popular type is the photovoltaic collector that was pioneered by NASA. These are the typical solar panels you often see on peoples roofs, even though they can be assembled on the ground; as well. The general rule of thumb, for photovoltaic, is to have half the area of the home in solar panels. This is for an average home. You can often reduce it from half to a third with an efficient home.
Passive solar collectors can be built by most do it yourselfers. There are a lot more ways of creating passive collectors. Among these are water drums, rock pits, water piping, and hot air. Many of the choices you face are determined by the ground and home architecture.
Photovoltaic Technology / Solar Panels
The solar industry will often use the term PV as a short way of saying photovoltaic. Most of us just call them solar panels.
Photovoltaic technology consists of two thin wafers of silicon. One of the wafers emits electrons in sunlight while the other wafer accepts the electrons. The passage of electrons from one wafer to the other creates electricity.
The wafers are enclosed in glass with a waterproof seal. The frame is usually aluminum; for lightweight and strength.
There are three types of photovoltaic cells.
This is the oldest and most expensive way. You cook a loaf of single crystal silicon, slice it into wafers, and then dope the wafer. Conversion efficiency is highest.
Smaller silicon loaves are produced with a less exact production method. However, it is much cheaper with a slightly less conversion rate.
It sounds like a science fiction movie. Amorphous is the process of vaporizing silicon material and depositing it on glass or stainless steel. The cost is lower for production (cheap for you), but the conversion rate is around 50% less than single crystal. Amorphous panels have a big advantage in partial shade environments. They also require more space for mounting.
You can install stick on PV material to metal roofs. You simply peel off the backing, like a sticker, to install the solar panel.
Nobody can give you the exact payback time to recover the initial solar investment cost. For one thing, every municipality charges different utility rates. Taxes on solar can also fluctuate. The price of the equipment can fluctuate and change with technology improvements. The other large factor is the overall design of the home; it needs to be efficient. Factoring all this in, we can take a guess that it will take you 1-10 years to gain back the investment.
Let’s say you need to spend $10,000.00 on solar equipment and installation. For example, if your utilities are around $200.00 per
month than you will save $2,400.00 per year with solar. That means it will take a little over four years to gain back the investment.
Keep in mind that you will not do as well with solar as manufacturers claim. The reason is that manufacturers base their calculations in laboratory conditions. You should consider that these calculations are probably about 15% more optimistic than claims made.
Necessary Photovoltaic Parts
It’s not just the solar panels that you need. The panels will be connected to wires to carry the electricity. The electricity will go through a safety disconnect, charge controller, battery bank, inverter, DC load center, and a system monitor; not all these features will come with every type of setup.
This is why the system is considered active. It takes a certain amount of knowledge and maintenance to make it work.
Passive Solar Technology
Water is good at retaining heat and radiating it off at cooler temperatures. Want your tomatoes to grow faster? All you need to do is put a gallon of water next to your plant. You will find it will grow much faster due to the fact that the water gives off heat at night. This will keep that plant warmer and it will grow faster.
Drums work in the same way. Many do it yourselfers will take a large number of oil drums and fill them with water. You can stack them up and put them against a south facing wall. They will gather heat during the day and warm the home at night.
You can produce many variations of this type of solar technology. Some people may use fans to draw the water over the drums. Another option is to use two liter bottles inside the home with the help of a fan.
Have you ever been to the desert in the summer? When you touch a sandstone rock it can almost burn you. Rocks, like water, retain heat.
You can dig a large hole. Most rock pits will need to be at least six feet deep and 8-10 feet wide in each direction. You fill the pit with three inch sized rocks. Many people use smaller rocks (like one inch), however, there is no agreement as to the best size of rock.
How it works is that you draw air into the home over the hot rocks. There needs to be a good flow of air to make this work. The rocks can also be used, in reverse, to cool the home.
Stone or concrete homes have much better insulating capacity than stick built homes. This means they keep you naturally cooler in the summer and warmer in the winter.
A good choice for a rock bin is in the basement of your home. You already have two walls to work from and the hole is already dug. Put the bin by a window so that it is easy to get the rocks in there. Then make sure the outside walls are insulated well. You can insulation to the walls or mound up dirt around the walls on the outside of the structure.
This type of collector is fairly easy to build yourself. It consists of a wood frame. You can use a ¾ inch piece of plywood, 2*6 boards and 2*2 boards to make the frame. Then you will insert aluminum sheeting onto the board. Then you build a series of tubing that proceeds up and down (similar to radiator tubing). You will have an inlet and an outlet hole on each end of the wood frame.
Copper tubing is the best choice, but the most expensive. You can also use plastic tubing. Just make sure that the plastic tubing is of the type that can handle hot water (Polybutylene or CPVC).
You will need to put insulation under the tubing and metal sheeting. You can actually buy specialty insulation at a solar store to perform this job, but it isn’t necessary because much of the foam insulation at hardware stores works fine.
The final product will have a wood frame, glass or Plexiglas (double pane preferred), tubing that will sit on the metal sheeting, insulation that sits under the tubing and under the metal sheeting.
Metal roofing material or corrugated siding are good materials to use for a hot air collector. The idea is to take two pieces of sheeting material and sandwich them together. Hot air gets trapped between the sheeting and can move through the open pockets.
The ends of the material must then be ducted into the area where you want the air to go. Both ends of the material should be ducted to move the air through the channels.
You might use this technique in combination with other techniques like rock pits.
Jonathan Hammond, in 1974, designed a roof pond home. The pond on the roof has an insulating lid. During the winter, you open the lid and it reflects solar into the pond. The pond naturally gives off heat for your home. The pond will also work in reverse. In summer months, simply keep the insulating lid closed. At night, open the lid and the pond will radiate out the hot air it collected from the home during the day.
Passive Solar Design Tips
Overhangs keep high summer sun out and low winter sun in. This is especially important on the south side.
Thermal mass refers to the thickness, insulating properties, and or size of walls. The thermal mass acts like a battery that collects energy during the day and uses energy at night. Get a high thermal mass.
Deciduous vines and trees can keep out heat in the summer, while allowing sun in the winter. An arbor with vines is a good item to have for south facing windows.
Don’t worry about your roof pitch. You can even put solar panels on a flat roof. Most panels can be easily adjusted.
The general rule of thumb is the latitude of your area plus or minus 10 degrees. You will also need to readjust the panels for winter and summer.
The US is divided into four latitudes. The northernmost latitude is 45 degrees and the southernmost latitude is 30 degrees. Here is a summary of US latitudes: 1- Northernmost (45 degree latitude) set solar panels at 35 degrees in summer and 55 degrees in winter. 2- Mid north tier: (40 degrees latitude) set solar panels to 30 degrees in summer and 50 degrees in winter. 3- Mid south tier: (25 degrees latitude) set solar panels to 25 degrees in summer and 45 degrees in winter. 4- Southernmost (30 degree latitude) set solar panels to 20 degrees in summer and 40 degrees in winter.
DC and AC
DC energy systems use either 12 or 24 volts. If you are producing less than 2000 watts per day, a 12 volt system is the best choice. For larger systems 24 volts is recommended.
DC stands for direct current and AC stands for alternating current. Since AC power can’t be stored, alternative energy requires the use of DC power. Many systems will require an inverter to convert AC to DC. The reason is that it is easier to create AC than DC.
It doesn’t really exist; so why bother? Wrong! A phantom load is the energy that is used by appliances that are simply plugged in when not in use. What people may not realize is that this actually uses up a lot of energy. Electric razors and electric toothbrushes have historically been some of the worst offenders. If your appliance has a display, it needs energy to run the display. How many displays do you run constantly? Power adapters also suck energy. These are large black square plugs that get warm when plugged in. If you touch them and they are warm, it means it is using energy. Solar homes have a goal of no load. To achieve no load, outlets can be put on switches; a power strip can also do the job. To figure out what power phantom loads are using, simply check your meter.
How Much Electricity Do I Need?
A 2500 square foot home will use around 1000 KWH per month. Ideally, you will have a higher load potential to account for spikes. On the other hand, you may cut out many KWH through energy efficiency.
Let’s say you have a PV module that produces 90 watts of electricity. This means that a 2500 square foot home may need 12 modules. These twelve panels may cost in the neighborhood of $6,500.00. On top of this cost, you will have installation and other parts like inverters, wiring, and monitors. You could expect to pay around $12,000.00 to complete the job. You may consider performing the labor yourself to keep cost down.
Solar material is roughly $4-$5 per square foot. That is pretty cheap considering the fact that most roofing, siding, and stone construction materials run about the same price.
Another way to figure this would be to take half the home square footage (1250) and multiply this by $5.00 per square foot. This calculation produces a cost of $6,250.00 for solar equipment. This estimate is very close to our previous estimate of $6,500.00.
Many of the larger kits come with a wind turbine. However, many homes simply do not have a good wind site. Wind is generally best in rural areas with lots of wind.
Mounts or Trackers
You will get more out of your photovoltaic cell if the solar module follows the movement of the sun. That is what a tracker does. Freon, in the tracker tubes, adjusts the angle of the solar module; this is a passive tracker.
Active tractors use a controller and suck power. Active trackers may use 10-15 watt hours per day (this isn’t very much).
If you have shade, move higher up. You will need photovoltaic to be 30 feet higher than the tallest structure nearby. Poles are the solution.
Almost 95% of solar panel buyers will not get a system with batteries. The main factor is whether there is a reliable grid in your area. It is also less expensive and most efficient to tie into the grid. To intertie, is the word solar people use for hooking into the grid. If you can’t tie into a grid, then batteries are a good source of backup power.
If you do get batteries, use sealed batteries. They are a little more expensive, but well worth it. Wet cell batteries tend to become chemically resistant. In addition, you may (probably) forget to add water every few months.
You may have heard of volts, amps, and watts. And, you probably aren’t sure how they all fit together.
Electricity works by electrons being arranged in the right order. The faster the electrons move the more potential electricity we have. This potential energy is called volts. Turbines and chemical reactions move the electrons to gain volts. Volts are analogous to water pressure.
Amperage is how much electricity will pass through the wire. Amps are analogous to how large your water pipe is. Larger pipes can carry more water than smaller pipes. With electricity, larger wire can also carry more amps (safely) than smaller wires. Large pipes also increase water pressure (amps). Therefore, high pressure volts can use smaller wire to get the job done.
Watts are the power that you get at the end of the wire. You can increase watts by adding larger wire or increasing volts. You can decrease watts by using smaller wire and decreasing volts.
The bottom line is that if you start with higher volts you can use smaller wire or if you start with lower volts larger wire can help you maximize watts.
Simply check the wire you are purchasing to see if it can carry the number of amps you want to run.
Equations: volts * amps = watts; watts / amps = volts; watts / volts = amps.
Most appliances have an amp rating on them. If you take a typical outlet of 120 volts and multiply by the amps you will get the watts of that particular appliance. You can also figure out amps from watts (highly useful).
Solar Rebates and Interest Rate Buy Downs
Many states give out rebates to homeowners for solar installation and may also buy down your home interest rate; as an incentive. You will need to check with your individual state.
Some states will give you a smaller rebate for self installation. In many cases, for two reasons, it makes sense to hire a professional: 1- They will often do the rebate paperwork for you. 2- The larger rebate may pay for the installation.
Check with local solar stores. They often know about rebates and financial incentive information.
Some areas of the country get more lightning than others. At the very least, the aluminum module should be grounded to the frame.
High lightning risk areas may also want to install a lightning rod and/or lightning arrestors.
Solar is perfect for pools. The heat of the summer is when you get the most solar electricity and when you will use your pool the most (outdoor pools). Pools must circulate the water and are already plumbed to have the water moving. All you need to do is have the piped water go through a solar collector to get heated up. You should install a collector that is about half the size of the pool.
Universities and Solar Homes (source: The Solar Home Book)
This is probably the first solar house (1939). It used flat plate collectors made of blackened copper sheets.
In 1947, MIT built a second solar home. This home used water drums that sat behind glass of a south facing wall.
In 1948, MIT takes on another solar house. This house had a flat plate collector on the roof and a water tank in the attic to store solar heat. Radiant ceiling panels distributed heat to the rooms. In addition, 180 square feet of windows covered the south wall (The Solar Home Book).
In 1959, MIT builds its last solar house. Aluminum was used as a collector plate with copper tubes on top. Double pane glass was used on top of the collector plate. The collector sent heated water to a storage tank and then through a heat exchanger. A fan blew over the heat exchanger to get hot air into the home.
In 1940, Purdue built two solar homes on campus. They were basically passive solar homes that used large south facing windows.
In 1945, Dr. George Lof built a functioning solar system within a conventional gas heating unit.
In 1948, Glaubers salt was used as a heat storage medium. It would be great for cloudy days because it could store up to nine times more heat than water. The down side is that the salt deteriorated after one year.
Desert Grassland Station
In 1954, Raymond Bliss and Mary Donovan of Arizona designed a solar air conditioning system. It used a solar collector atop an insulated rock bin. The system worked well to heat the home, but wasn’t an adequate air conditioner.
Bridger’s and Paxton Office Building
In 1956, Bridger’s and Paxton built the world’s first solar commercial building. The system used a flat plate collector that used water to transport heat. The water was stored in a 600 gallon tank and distributed by radiant panels in the floor.
This French house had a south facing wall of concrete one inch foot thick. The concrete was painted black and covered with glass. Hot air between concrete and glass rose up and entered the home through an opening at the top of the concrete wall. Effectiveness data is not available.
The same guy who built the Boulder house gives it another try. This solar home uses solar collectors on a flat roof that put the air directly into gravel storage beds. Then, dampers and blowers move the heat around the home.
This system used a huge storage container of water. The entire roof was covered in a copper tube and plate collector; no glazing involved.
Thomason Solar House
Thomason, a patent attorney, has come up with many simple and effective solar home techniques. His system uses black corrugated aluminum absorber panels on the south roof. A fraction of an inch above the aluminum is a layer of glass. A hot water tank, in the basement, is filled with rain water that runs off the roof. The water tank is surrounded by stones. The water tank heats the stones. Fans blow over the stones to get the air flowing throughout the home.
In 1960, in Massachusetts, Norman Saunders built a 2700 square foot solar home. The home has earth banked walls on the north, east, and west walls. The walls are massive one foot thick pumice block. The south wall has 325 square feet of double paned windows. This home obtained 63 percent of its heat from solar.
This is a unique solar house. The roof has a pond in it. The pond is 10 inches deep and covered with plastic to prevent evaporation. A lid goes over the pond. In the winter, you open the lid during the day to gather sunlight and close it at night to keep the heat in. In the summer, you close the lid during the day (keep out heat) and open it at night (let out heat).
According to Hammond, the home builder, the home produced 90% of heating needs.
This home in Oregon has a huge reflecting surface made of household aluminum foil. The foil is held in place by an asphalt roofing compound.
In Oregon, it is overcast most of the time. This makes it a challenging area for solar. Inventor, Henry Mathew, showed that it can still be done.
The Mathew house collector is also made of galvanized pipe, aluminum panels, and plate glass. In addition, the home has a huge 8000 gallon tank located beneath the house. Henry estimates that this home is heated 50 to 70 percent by solar.
Van Dresser House
In 1957, Peter Van Dresser converted an old adobe house to solar. The home uses galvanized sheets that are insulated with double pane glass. There is a one inch gap between the metal and the glass. This makes the warm air the medium for warmth.
Yale professor Everett Barber, around 1975, built this home. It gets 70 percent of the heat from the sun and 80 percent of electricity from wind.
The home uses passive solar techniques. It has south facing windows with overhangs. It also has a water storage tank, rocks under the concrete slab, shutters, and three inches of sprayed on polyurethane foam.
The home also uses active solar techniques. It has 400 square feet of solar collectors. The collectors are blackened copper plates.
Ouroboros (named after a mythical dragon)
Near the University of Minnesota and around 1975, Dennis Holloway and 160 students built a solar home. The home has three unique features: a sod roof, a windmill, and a composting toilet.
The home has a trapezoid base with the longest side facing south. Dirt is piled against north, east, and west walls. The walls and roof have at least nine inches of insulation. There is a large water tank surrounded by rocks for heat storage in the basement. . The south wall has a sandwich type double glazed collector made of two sheets of steel. Water is pumped up through the sandwiched collector to for heating. In addition, the lower south wall has a greenhouse.
University of Florida House
In 1973, this home was updated to have 12 flat plate collectors that total 500 square feet. It also has a 3000 gallon water storage tank. Heat is distributed by forced air convection. This home can supply nearly 100 percent of its energy needs.
Colorado State University Houses
Around 1974, the University of Colorado built three solar homes. They each built the collectors differently to see which one would work best.
The first home used tube in plate collectors. The second home has an air type collector that absorbs sunlight with galvanized steel plates. In the third home, the collectors are parallel arrays of concentric glass tubes. The outer tube is evacuated and the two inner tubes carry the heat transfer fluid.
These three homes also used a water storage tank, and heat exchanger.
University of Delaware House
This home used cadmium sulfide photovoltaic cells located in rooftop panels. This house used sodiumthiosulfate pentahydrate to store heat during the winter and Glaubers salt when temperatures were less than 120 degrees. The salts work in much the same way as an insulated water tank. The salts give off heat when they solidify to heat the home. And, since they absorb heat well, they can also be used for air conditioning.
Grassy Brook Village
Grassy Brook Village is one of the first community based efforts at solar. 10-20 homes will be heated with solar on a centrally based system of collectors and water tanks. The system will use a water glycol solution to carry heat to storage tanks. The solar array will be 4500 square feet. The village also plans to use wind power.
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