FAQs - Solar Energy How do solar cells generate electricity? Photovoltaics cells (PV) is a direct current (DC) generator which gets its power from the sun. When light energy hits a solar cell, they knock electrons free in the silicon crystal structure forcing them through an external circuit , 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 . Typically 30-36 cells are wired in series in each solar module. This produces a solar module with a 12V nominal output (~17V at peak power) that can then be wired with other solar modules to form a complete solar array, the more solar modules you use the more power you can generate. [TOP] Will solar work in my location? Solar is universal and will work virtually anywhere, however some locations are better than others are. 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 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). Different parts of the world receive more sunlight from others, so they will have more "full sun hours" per day. Conulting the solar insolation area map will give you the "full sun hours per day" for your location. [TOP] How much will a system cost for my 200 square metre home? Unfortunately there is no "average" since the cost of a system actually depends on your daily energy usage, how many sun hours you receive per day and what other sources of electricity you may have available, IE wind or Hydro power. To accurately size a system, we need to know how much energy you use per day. If your home is connected to the electric grid, your monthly electric bill will usually give you a statement of daily consumption. With this information, coupled with detailed discussion on your power usage profile a system can be designed to meet your needs. Usually a combination of Solar and secondary power generation ( IE diesel/petrol or wind) is designed to get a balance between capital cost and affordable running costs. It would be true to say that a renewable energy system to meet your power needs is directly related to the amount of money you want to spend. Such a system is referred to as a “Hybrid” Solar system. [TOP] Can I use all of my normal 240v ac household appliances? When you 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. Appliances such as electric water heaters, electric ovens and hobs, heaters and air conditioners are costly loads to run on solar. Where possible using alternatives such as LP or natural gas for water/space heating and cooking should be considered, Refrigeration, lighting and pool pumps are typically the largest energy users in a home, electric heating loads can use up all the stored energy in a system very quickly therefore these should be looked at very carefully in terms of getting the most energy efficient units available. Over recent years advances in technology has made big improvements in the efficiency of electric refrigerators/freezers and especially aircon units, with inverter technology significantly reducing load requirements.A complete range of low power consumption lights are now widely available and use up to a tenth of the power of a standard bulb for the same light output and last ten times longer. The rule of thumb in the renewable energy industry is that for every Euro you spend replacing your inefficient appliances, you will save three Euro’s in the cost of a renewable energy system to run them. Energy conservation plays a crucial part in designing a renewable energy system that is both efficient and cost effective. [TOP] What components do I need for a stand alone renewable electric system? There are many components that make up a complete solar system, but the 4 main items are: solar modules(PV), charge controller(s), batteries and inverter(s). The solar modules are mounted where possible to capture the most sunlight and the DC power they produce is transferred to a charge controller and then to the battery bank where it is stored for later use. 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. The battery bank stores the energy produced by the solar array during the day for use at anytime of day or night. Batteries are the heart of the system and come in many sizes and grades, it is important that sufficient battery capacity is installed to meet power requirements . The inverter takes the DC energy stored in the battery bank and converts it standard electric power to run your AC appliances as if connected to the electrical mains. Well designed systems will also have a series of safety fuses and trips to ensure the system and your house is protected from failure. [TOP] What type of solar module mounting structure should I use? There are four basic types of mount structures: roof or ground, medium height mast and tracking mounts, each installation requires its own type of mount. For example roof mount structures may keep the wire run distances between the solar array and battery bank to a minimum, which is good. But they also require roof penetrations (a potential source of leaks) and they require an expensive ground fault protection. On the other hand, ground mounted solar arrays require fairly precise foundation setup, are more susceptible to theft/vandalism. Mast mounted systems are relatively easy to install. Mast mounted PV arrays reduce the risk of theft/vandalism. They are also a better choice for cold climates because snow slides off easily. Solar trackers, significantly increase the daily number of full sun hours. Trackers are extremely effective in the summer time, but typical home energy usage peaks in the winter when a tracker mount can make a difference compared to a fixed mount. Sometimes having more modules on a less expensive fixed mount will serve you better than fewer modules on a tracker. [TOP] Where should I mount the solar modules and what direction should I face them? You need to aim your solar modules to the true south direction to maximize your daily energy output. 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 simple method would be to set latitude minus 15° in the summer, exact latitude in the spring,Autumn and latitude plus 15° in the winter. It is important to ensure that your proposed array site will not be shaded at any time of the day or year. [TOP] Should I set my system's battery bank up at 12, 24 or 48 VDC? The PV industry really began with the 12V recreational vehicle market. These systems were typically small (1-2 PV modules) with 12 VDC loads mainly to run a couple of 12V lights and maybe a small TV. As the solar industry developed systems became much larger (16+ solar modules) and with modern day inverters can efficieny convert the DC power into usable home power. Most home systems 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 a smaller and less expensive wire for your solar to battery and battery to inverter wire runs, Should aheavy duty load be placed on the system (IE pump load) this will also reduce voltage drop over the cables and system, minimising potential system trips. Most grid-tied systems operate at 24 volts or higher, with a 48V DC system being the optimum. [TOP] Should I wire my home for AC or DC loads? DC loads 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. [TOP] Can I use PV to heat water or for space heating? Not recommended. Photovoltaics converts the sun's energy into DC electricity at a relatively low efficiency level compared to Solar water heaters, 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. [TOP] Should I fit a Wind generator to my system. A wind generator (Typically 1000W) can be a valuable cost effective addition to a medium sized PV based system, providing additional power during night time and low sun availability periods. These tend to work best in mountain or coastal areas providing a lot of power relatively quickly. Modern day generators (24V/48V) can also be wired in such a way as to provide power to an auxiliary load (IE electric water heater) when the batteries have been fully charged, further improving system efficiency. Careful consideration should be given to the location of wind generators. [TOP]
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