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How many solar panels and what size are enough to meet my needs?
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Each energy consumer has different needs, dependent upon the electric appliances being run. For instance, if you are powering two 27 watt compact fluorescent light bulbs for two hours, you would need to supply 108 watt-hours of energy (2x 27x 2 hours). In San Diego, which has a yearly average insolation of 5 hours a day, one Unisolar 32 watt photo voltaic (PV) module is more than adequate (32x 5 hours=160 watt-hours).
To find out how much energy you use, use our solar calculator <link to calculator> or energy worksheet. The perfect way to help you size the most appropriate solar system.
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What if there is hardly any sunshine for several days?
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In a typical PV system, the solar modules are used to charge a battery bank. Different geographic regions provide various amounts of daily sunshine. It is recommended that a system has enough battery power to account for five days of inclement weather. The American southwest averages 5 sunshine hours per day and the northeast receives about 3 hours of daily sunshine. More solar panels will increase the amount of power generated when the sun is shining.
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How long do solar panels and batteries normally last?
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New solar panels have a manufacturer's warranty of 20 years. With proper care, however, the panels should last many years beyond the warranty. In the case of batteries, basic routine maintenance and discharge rates of no more than 10 -20% means your batteries should function effectively for 10 years or more.
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What maintenance is required for a solar electric system?
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Solar electric systems are elegantly simple. Maintenance includes:
- Checking your deep cycle batteries every few weeks to make sure they have enough distilled water
- Occasional checks of the connections between the solar modules and the inverter(s), and to tighten them when applicable.
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Do some solar panels generate more power per inch than others?
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Some solar panels do generate more power per inch than others. For example,
- Monocrystalline panels have a higher output per square foot than amorphous silicon panels. Traditionally, if square footage was important, monocrystalline solar modules were the best choice due to a higher conversion rate of sunlight to electricity.
- New amorphous silicon panels <link to UniSolar panels in the store> absorb three different spectral wavelengths, which translates to up to 30% more real power per watt from the PV module. This is because the amorphous panels produce energy for longer periods each day than monocrystalline panels. This means the panels produce more amp-hours per amp than other technologies.
New and future hybrid designs employ the best of both technologies
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How can I find out how many watts my appliances use, such as computers and stereo etc.? |
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There are a few ways to determine how much energy your household appliances use including the following:
- The easiest way is to look at a monthly utility bill. This has the amount of kilowatt-hours consumed during the billed month. From there, a consumer can determine how many average kilowatt-hours were used daily.
- Additionally, a typical electronic appliance should have an energy rating sticker somewhere on the product.
- There are devices available including the Kill-A-Watt <link to Kill A Watt in store> that can be used to determine the energy usage of a specific appliance.
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How long does it take for a solar system to pay for itself?
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The payback period for a solar system is roughly 20 years, based on calculations assuming the cost of energy obtained from the utility grid is 10 cents a kilowatt-hour.
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Is the current technology more advanced than a few years ago? |
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The technology behind PV solar energy is continuously improving. Research on thin film materials, processes and devices are leading to increased module efficiencies while using high-throughput, lower-cost plasma processing. Increased module efficiencies coupled with fast deposition rate technologies implies the cost of PV modules will continue to decline
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Do current trends show that solar electricity will become increasingly affordable? |
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Thin-film modules are less-expensive to manufacture because the amount of materials, capital investment and labor are decreased. According to the US Department of Energy's Fiscal Year 1998 Photovoltaic Energy Program Overview, researchers predict that by optimizing processes and using materials more efficiently, the cost of thin-film manufacturing could drop to $50 a square meter
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Why choose solar over wind- or water-power generation? |
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Every energy source has its advantages and disadvantages. Wind- and water-power generation may be appropriate in certain situations. However, these technologies are
- Limited by seasonal variations
- Have moving parts that require maintenance
- Generate noise
- May negatively affect wildlife
PV modules, on the other hand, are:
- Silent
- Have no moving parts
- Non-glass panels are covered by a 20-year warranty.
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Should I use a sine-wave or modified sine-wave inverter? |
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A modified sine-wave inverter is appropriate for most stand-alone household applications. However, for certain technical appliances or for grid-intertied PV systems, a sine-wave inverter is necessary. In grid-intertied systems, energy can be bought and sold to the utility company by the end user.
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What voltage should I consider using 12, 24, or 48 Volts? |
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Solar systems can be sized in 12, 24 or 48 volts. As a general rule, smaller PV systems are run on 12 volts. 24 or 48 volt equipment can handle 4,000 watt systems. 48 volt systems are designed for energy consumption needs of over 4,000 watts. Higher voltage systems use smaller wiring.
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What is the best way to monitor the charge status of a solar system? |
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Battery volt meters <link to volt meters in the store> are the most common way to monitor the charge status of a solar system. However, battery voltage readings can be inflated depending on charge and discharge rates. For this reason, an amp-hour meter is the most accurate way to monitor the system charge status.
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Are prepackaged ready to go systems available? |
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PV systems are increasingly being designed for ease-of-use. Prepackaged turnkey (plug-and-play) solar systems are available, and can be custom-designed by Discover Power. <link to Discover Power consulting services>
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What special considerations should be observed where the batteries are placed? |
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Ideally, storage batteries would be placed in cool, dry and vented locations (batteries release hydrogen gas). <link to battery storage in the storage> Sheds or garages are good places. The contents of batteries should not be subjected to boiling or freezing. Freezing will only occur when the batteries are in a state of discharge.
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