Basics of Photovoltaic Solar Power

                           What is a solar cell and how does solar power work? Here you will find a simple introduction to the technology for the uninitiated.

What is a Solar Cell?

A solar cell or photovoltaic cell is a device which generates electricity directly from visible light by means of the (sun) photovoltaic effect. In order to generate useful power, it is necessary to connect a number of cells together to form a solar panel, also known as a photovoltaic module. The nominal output voltage of a solar panel is usually 12 Volts, and they may be used singly or wired together into an array. The number and size required is determined by the available light and the amount of energy required.

                              Can the power be stored?

The amount of power generated by solar cells is determined by the amount of light falling on them, which is in turn determined by the weather and time of day. In the majority of cases some form of energy storage will be necessary.

In a Grid-connected system, the solar array is connected to the mains. Any surplus power is sold to the electricity company, and power is bought back from them when it is needed.

In a Stand-alone system, however, this is not possible. In this type of system the usual choice for energy storage is the lead-acid battery. The number and type of batteries is dependent on the amount of energy storage needed.

                            Power Control

No matter what, sometimes there will be too much power. Other times there won't be enough. In a stand-alone system the battery will be damaged if it is allowed to be overcharged or over discharged, so a controller is needed to protect it.

The smallest systems may have only a few 12 Volt lights, but in bigger systems 230 or 110 Volts will probably be needed. An inverter is used to transform the low voltage DC generated by the solar panels into voltage AC. A different type of inverter is needed in a grid-connected system to convert the surplus power in order to export it to the grid.

                                                              How solar hot water works:

 Aside from cost and greenhouse gas emissions savings, the beauty of a solar hot water system is its relative simplicity and durability!

 There are two types of collectors used in a solar hot water service:

·         flat plate collectors (suitable where tank roof mounting is required)

• evacuated tubes (more efficient and great for frost prone areas)

 

Flat plate solar collectors

Flat plate collectors work on copper pipes running through a glass covered collector, often connected to a water storage tank (sometimes on the roof). The hot water can then thermo-siphon itself in and out of the tank, thus heating the water.      

    Evacuated tube solar collectors                   

Evacuated tubes use a glass tube with a vacuum inside and copper pipes running through the centre. The copper pipes are all connected to a common manifold which is then connected to a slow flow circulation pump that pumps water to a storage tank below, thus heating the hot water during the day. The hot water can be used at night or the next day due to the insulation of the tank.

The evacuation tube systems are superior as they can extract the heat out of the air on a humid day and don't need direct sunlight. Due to the vacuum inside the glass tube, the total efficiency in all areas is higher and there's better performance when the sun is not at an optimum angle - such as when it's early in the morning or in the late afternoon.

The evacuation tube systems are superior as they can extract the heat out of the air on a humid day and don't need direct sunlight. Due to the vacuum inside the glass tube, the total efficiency in all areas is higher and there's better performance when the sun is not at an optimum angle - such as when it's early in the morning or in the late afternoon.

          Evacuated tube vs. flat panel - which is more efficient?

The water tank and thermal mixing

          As heat rises, hot water delivered to the tank from the solar collector is drawn from the top for use in the house

As the temperature of the water may exceed 60 degrees Celsius (a requirement to kill bacteria), in order to ensure a safe temperature at the taps, a tempering valve will reduce the temperature to around 45 degrees Celsius..

Electricity and gas boosters

While the sun can provide sufficient energy to provide you with plenty of hot water for most of the year, there may be extended periods of cloudy, cold days where your system will need a helping hand. This can provided with an electric backup, oil backup or gas backup system from your existing heating source.

Using a tankless gas water heater is the most efficient boosting method as boosting only occurs when hot water is used. With an electric system, the tank is heated as soon as the internal temperature drops.

      Retrofitting for solar hot water

If your current hot water system has plenty of serviceable life left or you've recently purchases a gas/electric hot water system, you can still go solar with a Metund retrofit kit!

Hot water and household energy usage

Electric and gas hot water systems account for approximately 20% of a household's greenhouse gas emissions. You can reduce these emissions and also save up to 75% of your water heating costs! the table below is sourced from the Department of Environment and Climate Change NSW.

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