Author: Alicia Webb
Contributor: Barry Hendy
A solar park is a large collection of solar panels, essentially similar to a rooftop system but at a larger scale. A solar park can offer more inclusive ownership opportunities to renters or people without suitable roofs like apartment dwellers.
Solar parks can be located on the ground in open spaces, or on rooftops of large commercial or industrial buildings.
Solar park technology
A solar park is a large collection of solar panels. Solar panels capture the sun’s energy using photovoltaic (PV) cells. Each cell is made from layers of semi-conducting material — usually silicon. When sunlight, which contains photons, shines on the cell, it creates an electric field across the layers of silicon, producing electricity.
Each solar panel is made up of multiple small solar cells, arranged together into a carefully sealed panel (or module). A small panel can generate up to 5 watts in the middle of a sunny day, whereas a typical large panel can generate up to 125 watts.
A solar park is connected to the electrical grid and generates electricity during sunny days. It is possible to use battery banks to store energy and export it to the grid 24 hours a day, however batteries can be prohibitively expensive so most solar parks just generate during daylight hours.
Ballarat Solar Park. Source: Ecogeneration
Advantages of a solar park
The two primary advantages of a solar park over rooftop solar are installation efficiency, and more inclusive ownership opportunities.
Installation efficiency
A typical roof top solar installation involves two major expenses. One is the purchase of the solar system including solar panels, inverter, relevant connections and mounting systems. The other expense is the installation cost, which includes the time it takes for a trained installer to affix the panels properly to the roof and complete all the relevant wiring and testing. For a domestic system, the installation costs might be as high as half of the total cost.
Solar parks are able to dramatically reduce the installation cost. Firstly the job would take less time per panel, as all of the panels are in the same place and potentially not mounted on roof tops. Installation cost efficiencies would also apply to the wiring and connection of all of the panels.
More inclusive ownership opportunities
Many Australians have taken advantage of government grants and rebates, and installed roof top solar at home. However, these programs rule out people without suitable roofs, apartment dwellers and renters. In addition, the rebate programs rule out those who may not be able to purchase an entire system but who might like to participate at a lower level. A community owned solar park allows those people to take part in solar energy generation, through the purchase of shares in a solar park at a sunny, suitable location.
Locating a solar park
A good site for a solar park is one that is sunny, accessible, and close to a good connection point to the electrical grid.
Because they require a lot of space, it's a good idea to be creative with location options. Australian solar parks have been sited at airports, show grounds, crown land, and former landfill sites. Solar parks are virtually silent and present very little risk to flora and fauna and as such they can be located close to infrastructure, forests and houses.
Selecting a site for a solar project is less complicated than selecting a site for other forms of renewable energy such as bioenergy, geothermal or wind energy. The path of the sun across the sky in different seasons is well understood by scientists, and the amount of cloud cover an area receives doesn't tend to differ across short distances.
A good source of solar data for your region is the Bureau of Meteorology. This map is of average daily solar exposure over a year, and shows that the Northern Territory and Western Australia have some of the best solar exposure.
Energy production
Generally, solar parks are described in terms of their 'name plate' capacity, which is the total of the DC energy rating of the panels. This number, for example 100 kW, will probably never actually be produced, and certainly not as AC power actually exported to the grid. The name-plate rating of a panel is based on standard lab conditions of 1,000 W/m2 and at a cell temparature of 25 degress. As the cells heat up in the sun, their efficiency and so output drops. Other factors such as air clarity, the sun's angle to the panel, dirt on the panels etc all reduce the actual output of the panels.
As the power flows through the DC wiring in the field, losses from the cables could reduce the power by around 1% depending on the design. Then the Inverter will have a certain efficiency, followed by more losses in the AC cabling, and perhaps a 'step up' transformer to the grid connection voltage that may take a few more % of the energy away.
The rating of the farm will be in power, as kW or MW, but we are really only interested in the energy produced in kWh or MWh. Power is the instantaneous output, but it is only when this output is applied for some time that we see the energy produced. The analogy of water flow helps understand the difference: power is like the flow rate of the water, but energy is the amount of water that flows in a period of time. When you receive a water bill you pay for the amount of water per month. When we discuss a solar farm, we want to know how many kWh or MWh it will produce in a time period like a month or a year.
The common measure of a solar farm is kWh/kWp/yr - or Killowatt-hours per killowatt-peak per year. This is a function of the location (i.e. the solar resource), the panels, the systems design and the losses. The location, and the local meterology, will be the biggest influence. Projects could expect outputs from around 1,300 up to perhaps 1,800kWh/kWp/yr.
At say 1,500kWh/kWp/yr this equals 4.11kWh/kWp/day, meaning the project will produce at the equivalent of 4.11 sun-hours per day. Given there are 24 hours in a day, this is equivalent to a 17% capacity factor (4.11/24) in the common wind-farm metric.
A free PV system design program, Sunny Design, is available from SMA that allows the basic design of a system and can report the expected kWh/kWp/yr output. The program is available here and is a great tool to investigate the basic paramaters of a PV farm. More detailed design tools are discussed below.