Frequently Asked Questions
Being a relatively new industry in the United States, Renewable Energy (RE) may seem puzzling to some people that are not familiar with it. To help those of you that are being exposed to solar and wind power for the first time, we have compiled a dozen of the most frequently asked questions (with their answers) that we hear at Sunelco everyday. We hope this FAQ file is helpful to you.
 
F.A.Q.
Q1: How do solar cells generate electricity?
Q2: Will solar work in my location?
Q3: How much will a system cost for my 2000 square foot home?
Q4: Is solar cost effective?
Q5: Can I use all of my normal 120/240 VAC appliances?
Q6: What components do I need?
Q7: What type of solar module mount structure should I use?
Q8: Where should I mount the solar modules and what direction should I face them?
Q9: Should I set my system’s battery bank up at 12, 24 or 48 VDC?
Q10: Should I wire my home for AC or DC loads?
Q11: Can I use solar, wind and hydro together to charge one battery bank?
Q12: Can I use PV to heat water or for space heating?


Q1: How do solar cells generate electricity?
Simply put, photovoltaics or PV for short can be thought of as a direct current (DC) generator powered by the sun. When light photons of sufficient energy strike a solar cell, they knock electrons free in the silicon crystal structure forcing them through an external circuit (battery or direct DC load), and then returning them to the other side of the solar cell to start the process all over again. The voltage output from a single crystalline solar cell is about 0.5V with an amperage output that is directly proportional to cell’s surface area (approximately 7A for a 6 inch square multicrystalline solar cell). This is not enough to do any appreciable work so typically 30-36 cells are wired in series (+ to -) in each solar module. This produces a solar module with a 12V nominal output (~17V at peak power) that can then be wired in series and/or parallel with other solar modules to form a complete solar array to charge a 12, 24 or 48 volt battery bank.

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Q2: Will solar work in my location?
Solar is universal and will work virtually anywhere, however some locations are better than others. Irradiance is a measure of the sun’s power available at the surface of the earth and it averages about 1000 watts per square meter. With typical crystalline solar cell efficiencies around 14-16%, that means we can only expect to generate about 140-160W per square meter of solar cells placed in full sun. Insolation is a measure of the available energy from the sun and is expressed in terms of “full sun hours” (i.e. 4 full sun hours = 4 hours of sunlight at an irradiance level of 1000 watts per square meter). Obviously different parts of the world receive more sunlight than others, so they will have more “full sun hours” per day. We have a “Solar Radiation Data Manual” that lists the average number of full sun hours per day throughout the year for 239 cities across the United States for both stationary and tracking mount structures. We use this data along with your electrical load information (see next question) to accurately size a photovoltaic system to meet your needs. • Go to page 12 for more information on this topic.

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Q3: How much will a system cost for my 2000 square foot home?
Unfortunately there is no per square foot “average” since the cost of a system actually depends on your daily energy usage and how many full sun hours you receive per day. For us to accurately size a system to meet your needs, we 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, otherwise please fill out the “load evaluation form” on page 10. Without an estimate from you, we would only be guessing what your daily energy usage is, which could cause us to under or oversize your system (either of which will not make you very happy). Please fill this load evaluation form out as best you can using amperage of wattage figures from your actual appliances or from the averages listed on the appliance power consumption table on page 9. Once you mail, fax or e-mail us this load evaluation form, we can accurately size a system for you.

Solar Insolation Zone Map
1-800-338-6844 5 Frequently Asked Questions (FAQ)

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Q4: Is solar cost effective?
Yes and no. If your remote home is a half mile or more away from the utility lines, solar can definitely compete with the cost of a utility line extension. Of course when you are comparing the high up front cost of a photovoltaic system with the cost of bringing power to your site, you should also consider the fact that once a PV system is purchased and installed you no longer have a monthly power bill. Over the course of 20 years that could add up to a considerable savings that PV has over utility power especially with rising power prices. If your home is already connected to the utility grid, going 100% solar will probably not be a cost effective move unless your charge per kilowatt-hour (kWh) is very high (25¢+). Of course being connected to utility power doesn’t mean that you can’t use solar. Several states now offer “net metering” which means that the utility company will pay you the same rate per kWh of energy that you sell back to the grid as what you pay per kWh used. Installing a grid-interactive solar (or wind ) system can significantly reduce your monthly electric bill. There are several grid feedback inverters available today (see pages 55-59) that would allow you to produce some or all of your energy from the sun.

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Q5: Can I use all of my normal 120/240 VAC appliances?
Maybe. Many older homes were not designed or built with energy efficiency in mind. When you purchase and install a renewable energy system for your home, you become your own power company so every kWh of energy you use means more equipment (and hence more money) is required to meet your energy needs. Any appliance that operates at 240 VAC (such as electric water heaters, cookstoves, furnaces and air conditioners) are impractical loads to run on solar. You should consider using alternatives such as LP or natural gas for water/space heating or cooking, evaporative cooling instead of compressor based AC units and passive solar design in your new home construction if possible. Refrigeration and lighting are typically the largest 120 VAC energy consumers in a home (after electric heating loads) and these two areas should be looked at very carefully in terms of getting the most energy efficient units available. Great strides have been made in the past 5 years towards improving the efficiency of electric refrigerators/freezers. Compact fluorescent lights use a quarter to a third of the power of an incandescent light for the same lumen output and they last ten times longer. These fluorescent lights are now readily available at your local hardware or discount store. The rule of thumb in the renewable energy industry is that for every dollar you spend replacing your inefficient appliances, you will save three dollars in the cost of a renewable energy system to run them. So you can see that energy conservation is crucial and can really pay off when considering a renewable energy system.

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Q6: What components do I need?
There are many components that make up a complete solar system, but the 4 main items are: solar modules, charge controller(s), batteries and inverter(s). The solar modules are physically mounted on a mount structure (see question 7) and the DC power they produce is wired through a charge controller before it goes on to the battery bank where it is stored. For more detailed information on solar modules, turn to page 17. The two main functions of a charge controller are to prevent the battery from being overcharged and eliminate any reverse current flow from the batteries back to the solar modules at night. Turn to page 32 for more detailed information on charge controller functions and features. The battery bank stores the energy produced by the solar array during the day for use at anytime of day or night. Batteries come in many sizes and grades, which you can see starting on page 39. The inverter takes the DC energy stored in the battery bank and inverts it to 120 VAC to run your AC appliances. For more detailed information on different inverter models and features, turn to page 54.

Frequently Asked Questions (FAQ)
Magnetic Declination Map

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Q7: What type of solar module mount structure should I use?
There are four basic types of mounting structures: roof/ground, top-of-pole, side-of-pole and tracking mounts, each having their own pros and cons. For example roof mount structures typically keep the wire run distances between the solar array and battery bank to a minimum, which is good. But they also require roof penetrations in multiple locations (a potential source of leakage) and they require an expensive ground fault protection (GFP- device to satisfy article 690-5 of the National Electrical Code- NEC). On the other hand, ground mounted solar arrays require fairly precise foundation setup, are more susceptible to theft/vandalism and excessive snow accumulation at the bottom of the array. The top-of-pole mounts are relatively easy to install (you sink a 2-6 inch diameter SCH40 steel pole 4-6 feet in the ground with concrete). Make sure that the pole is plumb and mount the solar modules and rack on top of the pole. Top-of- pole mounts reduce the risk of theft/vandalism (as compared to a ground mount). They are also a better choice for cold climates because snow slides off easily. Side of pole mounts are easy to install, but are typically used for small numbers of solar modules (1-4) for remote lighting systems where there already is an existing pole to attach them to. Last but not least are the trackers, which increase the daily number of full sun hours and are often used for solar water pumping applications. Trackers are extremely effective in the summer time when water is needed the most. In the northern U.S., typicalhome energy usage peaks in the winter when a tracker mount makes very little difference as compared to any type of fixed mount (roof, ground or top-of-pole). In this situation, having more modules on a less expensive fixed mount will serve you better in the winter than fewer modules on a tracker. However, if you are in the southern U.S. and your energy usage peaks in the summer, then a tracker may be beneficial to match the time of your highest energy consumption with a tracking solar array’s maximum energy output.

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Q8: Where should I mount the solar modules and what direction should I face them?
Irregardless of what type of mounting structure you plan to use, if your site is in the northern hemisphere you need to aim your solar modules to the true south direction (the reverse is true for locations in the southern hemisphere) to maximize your daily energy output. For many locations there is quite a difference between magnetic south and true south, so please consult the Declination Map (left) before you set up your mount structure. The solar modules should be tilted up from horizontal to get a better angle at the sun and help keep the modules clean by shedding rain or snow. For best year round power output with the least amount of maintenance, you should set the solar array facing true south at a tilt angle equal to your latitude with respect to the horizontal position. If you plan to adjust your solar array tilt angle seasonally, a good rule of thumb to go by is latitude minus 15° in the summer, latitude in the spring/fall and latitude plus 15° in the winter. Most mount structures provide for a seasonal adjustment of the tilt angle from horizontal to 65°. Roof/Ground Mount Top of Pole Mount

Side of Pole Mount Tracker
Frequently Asked Questions (FAQ)

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Q9: Should I set my system’s battery bank up at 12, 24 or 48 VDC?
The PV industry really began with 12 volt systems. These systems were typically small (1-2 solar modules) and had all 12 VDC loads. As the solar industry matured and entered the home market, systems became much larger (16+ solar modules) and no longer used DC loads exclusively. Most home systems that we design and sell today are 24 or 48 VDC since the higher system voltage gives you a lot more flexibility as to how far away you can place your solar modules from the battery bank as compared to a 12V system. For a given power output, a higher system voltage reduces your amperage flow (but not your power) which allows you to use smaller and less expensive gauge wire for your solar to battery and battery to inverter wire runs. Of course, if you already have a lot of 12 VDC loads, this may be the deciding factor as to the voltage of your system.

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Q10: Should I wire my home for AC or DC loads?
It depends on the size of the system and what type of loads you want to run. DC appliances are usually more efficient than AC since you don’t have to worry about the loss through the inverter, but DC appliances are typically more expensive and harder to find than their AC counterparts. Small cabin and RV systems are typically wired DC while most home systems are wired for AC loads exclusively. With improvements in inverter efficiency and reliability in the last 5 years, AC is the way to go for a home system. Another advantage AC has over DC is that the voltage drop for a 120VAC circuit is much less than a 12 VDC circuit carrying the same power which allows you to use smaller gauge wire.

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Q11: Can I use solar, wind and hydro together to charge one battery bank?
Yes. In fact combining multiple charging sources is ideal since they compliment each other very well seasonally. A solar array’s output peaks in the summer when a wind generator’s output is typically at its lowest. The reverse is true in the winter with the wind generator’s output at its peak while the solar array’s output is at its minimum. Selecting a good site for installing a wind generator is a little more involved than what is required for a solar array. First of all you need to determine if your site has an average windspeed that justifies installing a wind generator. We have a “Wind Energy Resource Atlas of the United States” that maps out the wind power classes for each state, (see example on page 27) so give us a call and we will tell you the wind potential of your area. For more information on different wind generator models and their features, turn to page 27. Hydro systems can produce power 24 hours per day, year round if you have a year round water source. Hydro is very site specific, but an excellent resource to tap into if you have the water rights and can get through all of the government red tape. You can be charging 24 hours per day year round if you have a dependable year round water source. To determine the power potential from a hydro system, we need to know the feet of head and flow rate (gpm) available from your water source. For more information on micro-hydro generators, turn to page 31.

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Q12: Can I use PV to heat water or for space heating?
No. Photovoltaics converts the sun’s energy into DC electricity at a relatively low efficiency level (14-16%), so trying to operate a high power electric heating element from PV would be very inefficient and expensive. Solar thermal (or passive solar) is the direct heating of air or water from the heat of the sun and is much more efficient for heating applications than photovoltaics. Solar thermal is a completely different field than photovoltaics and we do not design or sell solar thermal products. Give us a call and we might be able to refer you to a solar thermal company in your area.

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