Overview of Renewable Energy Production for off grid systems using batteries.

To select a renewable energy system for your home, boat or camper, you should know what the major parts are called, what each one is for, and how they work together.

The Process Sun shining on solar PV modules, wind or water turning a generator produces electricity in AC or DC format. Wind and hydro turbines uuslay produce AC current and this needs to be converted to DC  and that is done by a rectifier sometimes built into the turbine. DC is the only kind of power stored in batteries. Often this is 12 volt, the standard used in cars. Larger systems may be designed for 24 volt or 48 volt it’s better to try and design your system for higher voltages if you can.

Charge Controllers Sometimes called a charge regulator, is a electronic unit receiving the power from solar, wind, or micro-hydro generators, and controlling the flow of power to the battery. To prevent battery damage from overcharging, the charge control automatically stops the charge or diverts it to a dump load when batteries become full. A charge control may have manual control switches and may have meters or lights to show the status of the charging process.

Batteries This DC power is stored in deep cycle batteries, which give back the electricity as needed, even when no power is being produced. Like a bank account, power put into batteries over a period of time can be taken out more quickly if a lot is needed. Like a bank account you cannot take out more than you put in, or the account will be depleted. Fuses and circuit breakers on every circuit connected to a battery are essential. Battery size is chosen for both surge power requirements and for the amount of reserve power needed.

Inverters The inverter is the major electronic component that converts the DC current from the battery into 220 volt AC current, the same as utility power for standard household lights, outlets, and appliances. Most renewable energy homes use primarily 220 volt AC produced by the inverter. Short, heavy cables with a large fuse or circuit breaker carry battery power to the inverter. After conversion to AC, power from the inverter connects into the circuit breaker box of the house. Sometimes a small renewable energy boat, or cabin may have no inverter, and use only DC wiring and appliances. A stantby inverter/charger is an inverter that also has a battery charger and transfer relay built in. When the input terminals of a standby inverter/charger receive power from an outside source of AC (a generator or utility power) the inverter stops producing AC power from the batteries, and instead passes generator or utility AC power straight through to the house. At the same time it uses the generator or utility power to recharge the batteries. Some standby inverters even auto-start the generator when batteries need charging. A separate battery charger can be used instead of (or in addition to) a standby inverter/charger.

Fuses or Circuit Breakers Are necessary in all DC wiring between the batteries and other power system components. This prevents fires and equipment damage in event of a malfunction.

Meters Like the fuel and temperature gages in a car, are necessary to show everything is working. Meters show how much power is being consumed, confirming how much power is available. These battery system monitors can be located in the power room, or at a convenient spot in the home for easier checking.

Engine Generators Producing 220 volt AC power can be part of the system. This is a second source of AC power and a backup for charging the battery when there is a shortfall in solar, hydro, or wind power.

Solar electricity potential in Europe © European Communities

Solar panels Photovoltaic Cells Converting Photons to Electrons

The solar cells that you see on calculators and road sings are also called photovoltaic (PV) cells, which as the name implies (photo meaning “light” and voltaic meaning “electricity”), convert sunlight directly into electricity.

A module is a group of cells connected electrically and packaged into a frame (more commonly known as a solar panel), which can then be grouped into larger solar arrays.

Photovoltaic cells are made of semiconductors such as silicon when light strikes the cell a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow.

This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off. This current, together with the cell’s voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.

An atom of silicon has 14 electrons, arranged in three different shells. The first two shells which hold two and eight electrons respectively are completely full. The outer shell, however, is only half full with just four electrons. A silicon atom will always look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms.

Pure crystalline silicon is a poor conductor of electricity because none of its electrons are free to move. The silicon in a solar cell usually has phosphorous mixed in with the silicon atoms. Phosphorous has five electrons in its outer shell, not four. It still bonds with its silicon neighbor atoms, It doesn’t form part of a bond, but there is a positive proton in the phosphorous nucleus holding it in place.

The process of adding impurities like phosphorous is called doping the resulting silicon is called N-type (“n” for negative) because of the prevalence of free electrons. N-type doped silicon is a much better conductor than pure silicon.

The other part of a typical solar cell is doped with the element boron, which has only three electrons in its outer shell instead of four, to become P-type silicon. Instead of having free electrons, P-type (“p” for positive) has free openings and carries the opposite (positive) charge.

When light, in the form of photons, hits our solar cell, its energy breaks apart electron-hole pairs. Each photon with enough energy will normally free exactly one electron. The electron flow provides the current, and the cell’s electric field causes a voltage. With both current and voltage, we have power.

This is a PV system we installed in Co Leitrim its 500w and mounted on a tracker. The Panels are made by Solara and they use our photo on their web site www.solara.de

Solara solar equipment makes it easy to convert the Sun’s energy into electricity for various applications including boats, camper vans, holiday homes, commercial and specialist applications. These high performance panels will withstand even the harshest conditions day after day to provide a reliable source of electricity.

Solara 500w PV on a Tracker in Co Leitrim Ireland Installed by Eirbyte

They are manufactured in Germany using high efficiency solar cells. Their textured surface reduces sunlight reflections and increases the yield. The panels have a robust, salt water resistant aluminium frame which provides rigidity and also allows the panel to be easily mounted. The panels also have a waterproof junction box to allow easy wiring.

Each module is individually tested according to STC conditions. The panels are extremely reliable and have a 26 year performance guarantee.  The high quality sandwich with special tempered glass provides the longest life expectancy even under extreme climatic conditions; ice, hail, snow, storms and extreme humidity have no effect on the solar panels.

• Downloads in PDF format
• Ridged Solar Panels
• Marine Solar Panels
• Centrosolar Brochure

You can also download the Planning sheet fill it in and send it back to us or Centrosolar for a quote

News at the moment is we are running a wind turbine building workshop with Hugh Piggott in Ballinamore, Co Leitrim, in September for details please visit our other website http://buildyourownwindturbine.com/

Hugh Piggott Workshop Ireland 2009

Facebook event page 2010