How Does It Work?
PV cells are normally fabricated using special semiconductor materials that allow electrons, which are energized when the material is exposed to sunlight, to be freed from their atoms. Once freed, they can move through the material and carry an electric current. The current flows in one direction (like a battery), and thus the electricity generated is termed direct current (DC). The energy generated by PV modules can be used immediately or stored in batteries for later use.
What are the benefits of Net Metering?
Net Metering is a simple way to get the full value of the electricity you generate. For example, if you are a residential customer, you may not be home during the day when your system generates electricity. Net Metering allows you to "store" this excess electricity on the grid, reducing or offsetting the electricity you would otherwise have to purchase.
Another benefit of Net Metering is the "baseline" rate you are charged for the net electricity you consume. The baseline is a given amount of electricity for your home or business; you are charged a lower rate for each kilowatt-hour of electricity you consume below the baseline, and a higher rate above it. If your system is sized to offset most of your electricity needs, you are charged a lower rate for the minimal electricity you purchase from your utility if your annual net consumption falls at or below a baseline.
Net Metering offers additional benefits, depending on the size of your generating system. If you purchase a smaller, less expensive system, you can still offset most or all of your electricity needs because of the higher value of your excess electricity. If you purchase a larger system, you can "bank" or store your excess electricity on the grid and offset all of the electricity you would otherwise purchase from your utility or ESP.
You will be asked to demonstrate that your system was installed to certain building codes and electrical standards, prove that your system is insured, and show that your utility has access to a disconnect in case they need to shut your system down to service the grid --- line repair men need to be kept safe from your system when they are working on the grid.
What do you mean by roof area needed?
For a solar installation, you need a roof area with sun exposure. The amount we give you is a typical amount (10 watts per square foot), but the actual amount may vary based on the roof angle, shade, type of PV cells installed, etc.
How do you calculate the payback time?
Years to break even occur when the total utility savings equal the value of the installed renewable energy system:
Years to Breakeven = (Net cost - property value increase) / ("Pretax" average annual utility savings). For this calculation, we use PRE-tax dollars for the utility savings, and we assume you have a 40% effective tax rate: Pretax Utility savings = Average annual utility savings / (1 - 40%).
For this calculation we also assume the Net Cost to you is "YOUR ESTIMATED NET COST" minus (-) the expected increase in property value.
NOTE: When you install solar, the value of your property will generally increase -- in some cases your "on-paper" breakeven period can be immediate (a "0" or negative number) if the cost to install solar increased your property value by the same amount, or more.
How is Lifetime Savings from solar calculated?
To calculate life time savings from a solar system, we take the first-year utility savings and multiple it by the expected life of the solar system (assumed to be 25 years for PV). We also assume a annual increase in utility prices (see note, below. Our initial assumption is 3.78% utility inflation). You may change the assumed utility inflation rate.
NOTE: According to the US Department of Energy, on a national level during 2003, the retail price of electricity averaged 7.40 cents per kWh, up 2.6% from 7.21 cents per kWh in 2002. Electricity prices in the United States fell every year between 1993 and 1999, but this trend reversed in 2000, 2001, and 2003. For the first eight months of 2004, electricity prices were up 1.7% year-over-year, to 7.57 cents per kWh. In the first five months of 2005, electric utility rates increased an average of 3.78 percent from 2004 rates.
References:
http://www.bls.gov/cpi/home.htm#data
http://www.eia.doe.gov/emeu/cabs/usa.html
What are the environmental benefits?
Renewable energy technologies are a lot friendlier to the environment than conventional energy technologies, which rely on fossil fuels. Fossil fuels contribute significantly to many of the environmental problems we face today ? greenhouse gases, air pollution, and water and soil contamination ? while renewable energy sources contribute very little or not at all.
Why is renewable energy important?
Renewable energy is important because of the benefits it provides. The key benefits are: (1) Energy security (2) Energy for our children and grandchildren (3)Jobs and the economy (4) Environmental benefits.
Typical Power Ratings of Some Common Appliances
| Power Rating | (watts) | | (watts) |
| | | | |
| 12-V DC loads |
| Auto stereo | 6 | CB radio: Receive | 4 |
| Fan, portable | 115 | Transmit | 6 |
| Digital clock (LED) | 2 | Coffee-maker | 140 |
| Drill (3/8 inch) | 144 | Portable TV: |
| Lighting: Incandescent | 25 | Black and white | 20 |
| Compact fluorescent | 4?20 | Color | 60 |
| Four-foot type (double-ended) | 40 | Vent fan (15-cm blade) | 24 |
| Water pump | 50?300 | Hair dryer | 400 |
| | | | |
| 120-V AC loads |
| Block heater | 600 | Clock | 2 |
| Clothes washer, excluding hot water | 300?500 | Front-loading washer | 160 |
| Coffee-maker | 900 | Dishwasher, excluding hot water | 1300 |
| Drill (3/8 inch) | 300 | Saw | 400?1000 |
|
| Furnace fan motor (varies greatly) | 350 | Hair dryer | 1000?1500 |
| Curling iron | 25 | Iron | 1000 |
| | | | |
| Lighting: |
| Incandescent | 25?100 | Compact fluorescent | 4?20 |
| Four-foot type (double-ended) | 40 | Microwave oven | 600?1500 |
| | | | |
| Personal computer: |
| Desk model | 250 | Laser printer (while printing/standby) | 600/30 |
| Laptop in use | 25 | Laptop charger | 100 (max.) |
| Radio | 5 | Radio-telephone (transmitting/idle) | 96/12 |
| Single-side band radio (idle) | 4 | Stereo | 30 |
| | | | |
| TV (19 inches): |
| Black and white (in use) | 60 |
| Color (in use/standby with remote control) | 100/5 | Remote control (standby) | 5 |
| Toaster | 1100 | Vacuum cleaner | 200?1400 |
|
| VCR (on/standby) | 30/5 | Water pump (?-hp jet) | 1000 |
Note: These are typical values only. For exact numbers, consult product literature or Dealer / Installer.
Unfortunately there is no per square foot "average" since the cost of a system actually depends on your daily energy usage, how many full sun hours you receive per day; and if you have other sources of electricity. To accurately size a system to meet your needs, you need to know how much energy you use per day. If your home is connected to the utility grid, simply look at your monthly electric bill. If not, you can fill out the "load evaluation form" Using this information, your authorized Dealer / Installer - Solar Mountain Inc. - can design a system to meet your needs.
There are many state, federal and local incentives available to help pay for the cost of installing renewable energy systems. Here is a Database of Grants and Rebates - http://www.dsireusa.org/
Tips for Saving Energy
Plant deciduous trees (ones that lose their leaves in fall/winter) on the south and west sides of your home. Planting deciduous trees in these areas will help block the sun's rays, keeping the exterior walls of your home cooler. In the winter, the deciduous trees allow the sun to shine through to heat up your home.
Attic insulation. The heat that radiates through your roof is tremendous. If you have a dark colored asphalt shingle roof and little or no attic insulation, the air temperature in the attic can reach 140-150 degrees. That heat has to go somewhere and that somewhere is down into your interior living space. This makes your air conditioner work harder and longer to cool down your rooms.
Need a new roof? If you live in an area that's hot pretty much all year round and it's time to resurface your roof, try to get a material that's light in color and has insulation properties to help keep heat from radiating into your attic and living space.
Doing It Yourself
Self-Installation is a lot of work because there are so many details. It is worth familiarizing yourself with the technology to whatever extent you are interested or you can pay someone else to worry about all the details. At a minimum some electrical experience is necessary for a whole house-sized installation. Trial and error is not an effective approach. Planning is very important to avoid electrical code problems with clearances in battery rooms for example. (DO NOT put your batteries in front of the power panel!)
Be aware that un-permitted or un-licensed modifications to your home may void insurance coverage.
Also be aware of the large number of highly conductive parts in a solar electric system. The module frames and all equipment chassis need to be well grounded.
With a good design, installation should be fun. We at Solar Mountain Inc. are ready to work with you or your electrician to provide the level of support you need.
HOW BIG?
Big Fairgrounds Array
Solar electric systems are often described by the nominal power rating of the solar panels. I have twelve 75W modules so I can describe the system as a "900W system," or almost a kW. A one kW system is an average size for a small stand-alone home system powering a good assortment of typical AC loads. However, this oversimplifies the situation.
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We need to size:
1. Panel array
2. Battery bank, if applicable
3. Inverter
To do this we need to know:
1. Load analysis - average and surge
2. Real world performance of components
3. Budget
It is common to do a load analysis and find that a system to match is out of the budget. By increasing efficiency and planning for later expansion a compromise can be reached.
AC vs. DC
Trace Inverter Stack and Generator
Solar electric panels produce DC. Batteries store only DC. Thus for an off-grid system we need to get from solar DC, to battery DC, to household AC.
If you are setting up a solar system please be aware that an electrician may be unfamiliar with some components and techniques necessary for high current DC systems. This is simply because these things are not a concern in normal residential or even commercial work.
DC-rated disconnects, cable, circuit breakers, etc., are not always sitting on the shelves at the local supply house. In some cases standard items will work and I will refer to those items when possible.
Note: That a high-current DC system requires a greater attention to detail than a typical residential AC-only system.
This is because:
1. DC electricity is harder on connections and has a greater tendency to arc than AC.
2. A series of DC connections must be perfect to avoid overall loss of power. There is no Megawatt grid pushing power through the system if there is a marginal connection.
3. DC circuits are typically operating at lower voltages than household AC, again putting a premium on correct connectors and adequate wire size.
4. DC circuits often operate at higher currents than are commonly found in residential wiring, putting a premium on safety.
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