Harvesting Massive Amounts of Power: A Look into Solar Farms and Grid-Connected PV Power Plants

Harvesting Massive Amounts of Power: A Look into Solar Farms and Grid-Connected PV Power Plants

What is a Solar Farm?

Solar farms are made up of PV modules, inverters, Power Conditioning Unit, and grid-connection equipment. They are made to supply electricity to the power grid and are mostly owned by utility companies to supply power in their areas of coverage. The following image depicts a solar farm and its energy transmission to the homes:

Diagrammatic Representation of a Solar Farm
Figure: Diagrammatic Representation of a Solar Farm 

The arrays contain several PV modules that directly convert the energy from the sun into electricity. This electricity is then supplied to the grid. Solar farms are usually decentralized. What this means is that they are located closer to the area where the power they generate will be supplied to as opposed to having a larger plant in another place and having the power sent through the national grid. This is beneficial as it reduces power losses associated with transmission. This article aims at highlighting the different concepts related to solar farms and other grid-connected PV power plants.

Rooftop v/s Community Solar Power

Another concept that has arisen in recent times is that of a community solar power. Community solar power is based on the idea that not everyone can/wants to have a solar power system installed at their rooftop. A community solar power project (sometimes also known as a solar garden or roofless solar) is a localised solar power plant. The electricity generated by a solar garden is shared by more than one home. It is usually a large ground mount installation built over a piece of land near the homes of the community. In terms of appearance, community solar plants resemble utility-scale solar farms. However, they are usually smaller in size. How community solar works is that customers can either purchase a share of the overall array or they can lease energy from the solar system. This allows them to switch from paying monthly utility payments to monthly community solar payments that are typically lower prices. The following table summarises the comparative analysis between community solar and rooftop solar:

 Community SolarRooftop Solar
        How it works?Can be owned or subscribed. When owned, it is usually a share of the project. In subscription, the system is owned by the utility company or the solar company and consumers can buy cheaper electricity from themCan be owned, financed or leased
                  Billing and SavingsBillings are administered by the utility company, the project administrator or a combination of both. Consumers benefit from either of these two: Virtual net-metering or other credits on their monthly electricity bills. Or An arrangement with the community solar supplier. Here, the  utility bill is reduced using solar credits and community solar developer sends a separate billBillings are administered by the utility company. Consumers benefit from net-metering credits on their electricity bills. Also, costs of purchasing electricity from the  utility company are avoided
    Lease Contract DurationLeasing contracts vary for community solar. Some contracts allow ease of entering and exiting while others are long-termContracts are usually for 20-25 years depending on the company leasing the system
      MaintenanceMaintenance is the responsibility of the project’s developer or administratorIf the system is owned by the house owners, they maintain the system. If it is leased, maintenance is the responsibility of the solar company that provided the PV system
      Location OptionsCan be built on land (or roof of a building) which is owned by the community or a third-party’s property. Mostly built on the ground for optimal access to sunlight.On the roof or elsewhere of the home or commercial building
    LifespanExpected to be usually around 25-30 years however, some community solar projects may exceed this lifespanExpected to be usually around 25-30 years
    Environmental ImpactIdeally should be located close to existing grid establishments and unusable land for being environmentally considerableUtilises space that would otherwise be unutilised

Site Topology, Physical Layout and the Use of Land

The selection of a suitable site for a solar farm is extremely important. The land needs to be selected depending on the desired power output. The factors that need to be kept in mind while selecting how much land is required are:

  • Location
  • Efficiency of the PV modules being used
  • The slope of the site
  • Type of mounting being used

It is quite rare to have a large land which is completely flat in regards to the ground level. Hence, some work might be required initially in order to level the area where the modules are meant to be mounted. The support structures of the PV modules in the array are fixed to pilings in usual circumstances. However, sometimes the ground does not support this and hence, ballasted supports can be used. If the existing slopes of the ground are not too severe, they can be made use of too.  Brown field sites are considered the most suitable location for solar parks in terms of land use. Also, where there is no other use of the land, it is feasible to choose that land for a solar park. A considerable amount of area of the land that is used to build a solar farm can be used optimally for biodiversity or crop-growing. A concept where a piece of land is used for both PV power generation and agriculture is called agrivoltaics. The following image shows crops grown in a land where PV modules are mounted in a solar park:

Agrivoltaics being practiced in a solar farm
Figure: Agrivoltaics being practiced in a solar farm 

Array Arrangement, Spacing and Effect on Shading

Usually, solar parks use ground-mountings for the modules. These are known as free-field solar power plants. They can be either fixed at a tilt or can use solar trackers (devices used to orient a module towards the sun). The use of a tracker improves the overall performance of the plant. However, the installation and maintenance cost increase by the use of a solar tracker. A small number of utility-scale solar farms are laid on buildings. These use building-mounted solar arrays. These are called Building-Integrated PV (BIPV) Systems. The majority of solar farms are free-field systems. There are three types of free-field systems:

Agrivoltaics being practiced in a solar farm
Figure: Bellpuig Solar Park in Spain using dual axis trackers 
  1. Fixed Arrays: A lot of solar plant projects use mounting structures where the PV modules are mounted at a fixed angle. This angle is calculated to provide the most optimum power output throughout the year. The PV modules are normally faced towards the Equator. The angle is slightly less than the latitude of the site. Different tilt angles can also be used depending on the local climate, topography or electricity-pricing strategies. The arrays also can be offset from the usual east-west axis in order to favour the output either in the morning or evening. Sometimes the tilt angles are also adjusted twice or four times in a year for the optimum output of the seasons.
  2. Dual Axis Trackers: Solar panels should be at an angle normal to the sun’s rays in order to maximise the intensity of the incoming radiation. This can be achieved by designing arrays using dual axis trackers. These can track the sun in its daily orbit and its elevation as it changes throughout the year. These kind of arrays need to be spaced out more. This is to make sure that they do not inter-shade while changing their orientation. This implies the need of a bigger area for the plant. Dual axis trackers are most commonly used in subtropical regions because of the high levels of radiation.
  3. Single Axis Trackers: This type of technology uses tracking but with lesser required area of land, reduced capital and operating cost. Since this is only tracking one axis, it tracks only the sun’s movement across the day and not across the seasons.

Consider the following image:

Depiction of Ground Coverage Ratio (GCR)
Figure: Depiction of Ground Coverage Ratio (GCR)

The Ground-Coverage Ratio (GCR) is the ratio of the module area to the land area. This can also be represented as the ratio of array length to row to-row pitch (L/R). GCR depends on the spacing between the row, along with the tilt angle and panels’ size. GCR itself is not location-dependent but the effect of GCR on system losses is dependent on the location to an extent. This is because it relates to the proportion of the sunlight that is received by the panels at low incidence angles.

Advantages and Disadvantages of Solar Farms

Grid-connected PV power plants have many advantages. For instance, some utility providers use schemes such as net-metering and feed-in tariff. This can offset the electricity usage costs for customers. Also, grid-connected plants are relatively simple and cheaper to install as there is no need of an energy storage system (which is usually very expensive at such a large-scale). There are also no storage losses involved in these systems. Environmentally, a PV power plant is carbon negative over its lifespan.

Even though grid-connected solar parks are advantageous, there are also some disadvantages to them. For example, grid-connected PV systems can cause problems regarding voltage regulation. Feeding electricity into the grid increases the voltage. This can drive the levels outside the acceptable range of ±5%. Grid-connected PV can also compromise the quality of power. This is because there is rapid change in voltage because of PV’s intermittent nature. This wears out voltage regulators due to adjustments which happen too frequently. This results in voltage flicker as well.

Conclusion

This article has highlighted what a solar farm is. Grid-connected PV power plants are often known as solar farms or solar parks. We also looked at community solar power and did a comparative analysis between rooftop and community solar power. We then looked at site selection, topography and the use of the land in terms of solar farms. We then looked at the array-arrangement and the types of technologies used to create solar farms. We finally looked at the advantages and disadvantages of grid-connected solar power plants. Overall, we can say that grid-connected PV power plants are really advantageous because of their eco-friendliness, consumer-satisfaction, and independence of storage systems. They are sources of massive amounts of power and thus, governments around the world should promote more and more of such projects.