Stand-Alone Power Supply (SPS) System Module 2

What’s in a SPS System?

There are 5 main components of a stand-alone power supply system. SPS systems generally consist of:

Power Supply Components (e.g. photovoltaic array, wind turbines, diesel generators, microhydro turbines)
Energy Storage Components (generally lead acid batteries)
Power Conditioning Components (regulators, inverters)
Control Systems (to supervise the energy flows in the system)
Also needed is a Load, which consumes the electricity generated

Figure 1 There are many possible SPS configurations. This is a series switched system.

Other common configurations are Hybrid systems (see Figure 2).

Figure 2 A Hybrid SPS system.

Options for Energy Sources

There are a variety of options, some of the more commonly used options are:

Diesel or Petrol only
Or Hybrid Systems...
Diesel & Wind
Diesel & Solar
Diesel, Wind & Solar
Diesel & Microhydro

There are a number of options which can provide the energy for a RAPS system. Single fuel systems which are usually based on a diesel or petrol generator, or multi source systems which typically combine a fuel and a renewable energy source. These systems are known as hybrid systems.

Diesel / Petrol Generator

Low capital investment
High ongoing cost of operation and maintenance
Diesel ~$1.40/ L
ULP ~ $1.25 / L
Well established technology
Widely available

Historically, RAPS systems have been based around a single energy technology, usually a diesel or petrol generator. There are many reasons for this, including the relatively cheap price of fuels, existing mechanical knowledge of diesel and petrol systems, available in a wide range of sizes for a wide range of applications.

However, as the price of liquid fuels increases, single fuel systems based around diesel or petrol generators have an increasingly large operating cost.

Figure 2 A typical diesel generator

Solar - Diesel

Solar photovoltaics provide some of the energy requirements. Diesel and batteries used as back up when energy is not being generated by the PV array. This is generally during night time and when the demand exceeds the supply of what the PV array can supply.

One hybrid combination popular in WA is the solar – diesel system where photovoltaic (solar) panels offset the fuel used by generating electricity from sunlight. The energy generated during daylight hours is stored in a battery bank and used when sunlight is not available or when the demand exceeds the available supply from the solar system.

Systems typically start at ~ $25 000 for a 1.5 kW system
Maintenance costs range are lower than for diesel
System life is typically greater than 25 years(most PV modules are guaranteed for 20 years)

Figure 3 A PV array

Wind - Diesel

Wind turbine provides some of the energy requirements in a similar fashion to PV arrays. Diesel and batteries used as back up when energy is not being generated by the turbine. This is generally in low wind conditions, extremely high wind conditions, or when demand exceeds the supply that can be supplied by the wind turbines capacity.

Systems typically start at ~ $20 000 for a 3kW turbine
Maintenance costs less than $100 per year (<1% purchase price)
Some components will need replacing at intervals ranging from 5 – 10 years
Average 5 yr replacement cost $ 500 (2% purchase price)
System life is typically greater than 25 years

Figure 4 A wind turbine in a grain paddock

Wind – diesel systems are similar to solar – diesel systems, except the wind turbine provides some of the energy requirements. As with other hybrid systems, diesel gensets and batteries are used to store energy for use in high demand or low / high wind conditions. Most small wind turbines have an operating range of between about 10 and 50 km/h winds. In higher wind conditions, such as during storms, turbines are fitted with a furling system which turns them out of the wind to reduce damage to the generating components. In very strong winds, some smaller systems can be lowered using a tilt tower system.

Solar – Wind – Diesel

This is a combination of PV array, wind turbine and a diesel generator in one system. This is a great solution for locations where there is a good wind and solar resource. Hybrid systems can also use a combination of solar, wind and diesel equipment, and are best suited to locations where there is both a good solar and wind resource.

Figure 5 A Hybrid SPS system (system 2) installed at RISE

This is the end of Module 2.

Click here to Return to the Stand-alone Power Supply (SPS) System Page to attempt the Module 2 Quiz.