Off Grid and Grid Battery Backup Solutions

img_2424.jpgTo go solar off-grid, a battery bank will be needed to store your power for use when the sun isn’t shining.  The first thing people want to know when talking about a battery bank is how much space will it take up?

That of course depends on how much power you’ll need to store.  For a normal family home of 4 bedrooms, approximately 24 cells will be required.  Every three months the batteries will need to be topped up with demineralised water if they are a flooded lead acid battery – gel batteries, are a little more expensive but don’t require any maintenance.

Overall, your battery bank should last around 12 to 15 years if properly cared for and kept above 80% depth of discharge.

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Waterfront-geelongRadiant Energy Systems are based in Geelong and work across the Ballarat, Western District, Otway Ranges, Bellarine and Melbourne areas.  The team have been lucky enough to work on some of Geelong’s premier renewable energy projects, including the the City of Greater Geelong, St John Of God and Surf Coast Civic Centre wind turbine.

Victorians are some of the biggest users of renewable technologies, with two Melbourne suburbs – Hoppers Crossing and Werribee – among the top five in Australia to install roof mounted solar panels.

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There are a number of types of solar heat collecting systems, but for water heating we are concerned with a tried and proven system called flat plate collectors. Firstly though, let’s distinguish between solar electric (photovoltaic) modules which convert sunlight into electricity; solar pool heating panels, which are designed to raise a large mass of water a few degrees; and flat plate collector panels, which are designed to raise a smaller amount of water (say 250 to 400 litres) to useable hot water temperatures (of about 70 degrees Celsius).

Construction

The typical flat plate collector consists of a glass covered box containing vertical copper pipes (called risers) welded onto a flat sheet of aluminium or steel or copper in the higher quality units. At the top and bottom of the sheet are larger diameter horizontal pipes (called headers). The water from the hot water tank typically enters the bottom left hand corner of the collector casing, travels along the header pipes, up the riser pipes as it becomes hotter and exits out of the top right hand corner, where it returns back to the insulated storage tank for use when required.  Solar systems – how they work

Materials

The best solar panels are made from quality components which include: copper pipes and flat copper plate; an “AMCRO” selective surface (which absorbs 95% of the available solar energy); and low iron Solar systems - how they workglass (which improves solar acceptance by about 10%).

Location

A suitable north facing mounting spot must be found for the solar panels. Generally this will be on the roof, but they may be located on a wall over a north-facing window, on a deck or even on the ground. Ideally the solar panels need to be as close as possible to, but below the storage tank.

Roof Angle

Any angle between 15 degrees and 30 degrees is OK. On flat roofs we install a galvanised angle frame to raise the panel angle to around 25 degrees​

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Typically, a flat-plate collector is used with a number of types of hot water storage systems. Generally though, there are three main kinds of tank/panel arrangements used in domestic dwellings. They are:

Pumped or Split System solar hot waterSplit system solar hot water
A mains pressure tank is located at ground level and the solar collectors are mounted on the roof. With this system, when the water in the collectors is hot enough, the circulating pump is activated and water is pumped through the collectors’ water tubes where it absorbs the sun’s heat.

Advantages: The tank can be located (either internally or externally) at ground level and the panels can be above the tank. Good for roofs that do not have the strength for a close coupled system.

Disadvantages: Needs electricity to run the circulating pump and can’t be connected to a wood stove.

Close Coupled System

Both the solar panels and tank are mounted on the roof. The panels are located just below the storage cylinder and water rises into the tank through a principle known as ‘natural thermosiphon’.

Close coupled systemClose coupled system Advantages: Usually the most cost-effective system to install. Provides water at mains pressure or low pressure. Has no moving parts and has the highest efficiency. Can also be used as a waterproofed gravity -feed tank for wood heater backup in winter. Also, a good option if a position for a ground mounted tank cannot be found.

Disadvantages: Roof needs to be designed to withstand the combined weight of tank and water. ​May not be aesthetically pleasing to some.

Gravity or low pressure system

The tank is located in a roof cavity or if waterproofed, on the roof itself, with the solar panels installed on a north facing roof. The panels must be below the tank to allow for natural thermosiphon of water from tank down to panels and returned in an upwards flow to the tank.Gravity / low pressure system.Gravity / low pressure system

Advantages: Usually the most cost-effective system to purchase. May be directly connected to a wet-back in a wood-stove or heater. The tanks lasts from 30 to 40 yrs, as they’re made of copper and it operate at much lower pressures than mains pressure.

Disadvantages: The house must be plumbed for gravity pressure requiring larger pipe diameters. The flow rate from the taps may not be to the liking of some.

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