Renewable Power on a budget

Introduction - Off Grid power

Everyone wants to be green but power system costs are high. The small system shown here cost very little as it is mostly made from old salvaged equipment. I opted for solar photovoltaic as the power source. This can be expensive, but I used just 90W of amorphous PV panels. These thin film panels are cheaper than the more popular polycrystalline types. They have a shorter life expectancy and require a slightly larger area per watt. Four panels were required to produce a 48V system. The batteries, cabinet and inverters are all redundant equipment salvaged from industrial applications such as uninterruptible computer supplies.

Photo voltaic panels on garage roof

The batteries where pulled from a large backup system where they were considered 'end of life'. They have worked for a further 5 years in my system. Occasionally I have found that a cell dies and becomes a resistance in the circuit. As the batteries have individual compartments for each cell, these can be cut out and replaced from other batteries. The complete battery is rated at 6V. Eight are wired in series to supply 48V. There is also a tap at 24V for a second smaller inverter.

The large inverter is old and not very efficient but it produces a very clean sine-wave at 220V and is rated to 800W. The second inverter is more efficient but can only produce 250W

Currently the system is used mainly for power cut backup and has easily coped with 5 hour power outages. The 800W output seems like very little power but it is capable of running all the household lighting, central heating pumps, TV etc. Although the fridge/freezer causes problems due to start loads. A 1kW inverter is really required to deal with this.

In the summer months the energy collection is larger and the system is used for periods of off-grid supply when mains is still available. Eventually I plan to integrate it in a more automatic form, as it currently has to be manually switched over.

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On Grid

The main disadvantage with off-grid power is the need for batteries, their added cost and maintenance. Grid-linked systems are a cost effective option which requires less user intervention. The main disadvantage of a grid linked system is there is no power in a power cut. The rule for all grid linked inverters are that they must not be able to "island" themselves. This is mainly for safety as they would otherwise try to feed power into a faulty system.

- on budget grid-linked systems