Author – Page 9 – solar-iraq.com

January 6, 2023 Author No Comments

In an off-grid mini-grid powered by diesel generators and without batteries, PV modules can be used to feed electricity into the mini-grid. The amount of electricity (and thus fuel consumption) that the diesel generators need to provide is reduced.

An example of how a PV-diesel mini-grid without batteries functions.

At night, when there is no sun, all three diesel generators provide power.

Early in the morning, when solar irradiation is low, some power is generated by the PV modules, and one generator is switched off.

Towards the middle of the day, when solar irradiation is high, another generator is switched off, because more power in being generated by the PV modules. One generator always needs to be on to maintain the grid voltage.

In the late afternoon, as the solar irradiation decreases, some power is generated by the PV modules, and another generator is switched back on.

How exactly a system will function will depend on the system load profile and other factors.

Savings of up to 60% in fuel costs can be made, depending on factors such as solar irradiation levels, the load profile (when and how much electricity is used) and the generators. This type of system is very suitable for industrial and agro-industrial applications where power requirements are high during the day when solar power is available. A professional load profile survey is required to size the solar component of the system optimally. System suppliers need to be consulted regarding generator system compatibility and other technical details.

Some of these systems also incorporate small battery banks to cover lighter loads in off-peak periods.

Types of Systems

January 6, 2023 Author No Comments

This type of off-grid solar electric system consists of PV modules, a solar charge controller, an inverter-charger, batteries and a generator. The generator is used perhaps once a week or once a month, saving fuel costs and wear and tear on the generator. Normally the generator is only switched on when heavy power-consuming loads or three-phase loads need to be powered, such as an X-ray machine in a clinic or welding equipment. The batteries are mainly charged by the PV modules. The inverter-charger can also charge the batteries with electricity from the generator when the generator is on.

Installing this type of system consists of 2 stages:

First, an inverter-charger and batteries are installed – the batteries are charged by the generator when it is on; however, this means that the generator can be on for long periods of time in order to charge the batteries fully.
Then, PV modules are installed with a solar charge controller – this means that the batteries will mainly be charged by the PV modules, considerably reducing the amount of time the generator is on.

Solar modules, an inverter-charger and batteries added to a generator electric system. The batteries are charged mainly by the PV modules. This means that the generator needs to be on for much shorter periods of time, for example, only when heavy power-consuming equipment needs to be powered. The PV modules ensure that the batteries are fully charged more often and have longer working lives.

Special switch gear can be used so that only ‘priority loads’ are powered when the generator is off. Priority loads could be lighting, security systems and other essential services. Powering only priority loads from the battery means the inverter-charger and batteries can be smaller (less expensive) and the batteries will have a longer working life. If the batteries become too discharged, because of high power consumption or during periods of low solar irradiation, an automatic start system can switch the generator on to charge the batteries.

Types of Systems

January 6, 2023 Author No Comments

Small off-grid solar home systems can provide electricity where there is no electric grid.

Very small systems provide DC power only, usually 12 VDC. Systems with inverters also provide AC power, but can also provide DC power as well (mainly for lighting).

Electricity is generated during the day and stored in batteries for use at night for lighting and appliances, but the electricity can also be used during the day.

Typical applications:

Lighting (LED, low-energy fluorescent)
Radio and TV
Low-energy fans
Charging mobile phones
Laptop computers
Energy-efficient / low-energy refrigerators

A small off-grid solar system providing DC power for lighting and AC power for other appliances. During the day the PV modules charge the batteries, and provide AC power for appliances. At night, the batteries provide all the power, for both lighting and AC appliances.

DC appliances need to be used in DC-only systems and the range of DC appliances now available (especially lighting) is extensive. DC appliances are generally more energy efficient than AC appliances – they need to be because they are designed to run on batteries. AC appliances are more widely available and usually lower cost than DC appliances. Decisions need to be made on a case-by-case basis.

It is important to appreciate both the potential and the limits of what can be powered using PV off-grid systems. The battery bank, not the PV array, is the main limiting factor as regards the size of an off-grid PV system. It will usually need to be replaced several times during the working life of the system.

The following appliances are generally not suitable for small off-grid systems because they consume too much power: cookers, water heaters, electric heaters, electric kettles (any appliance that produces heat), air-conditioning units, large halogen security lights.

Types of Systems

January 6, 2023 Author 2 Comments

Telecom and mobile phone networks are a vast potential market for off-grid PV systems. System sizes range from a few hundred W to several kW.

The load is constant/predictable, which is ideal for an off-grid solar electric system. The diesel generator is mainly for emergency situations, if there is a problem with the PV system.

DC power is required for the retransmitting equipment, and AC power may also be required for ancillaries such as cooling fans or lighting.

Typical off-grid solar-powered telecom system.

Daytime operation: Power is provided by the PV array, and the batteries are charged.

Night-time operation: Power is provided from the batteries.

Back-up operation: The generator automatically comes on if required.

Telecom systems operators will normally prioritise the security of the power supply over up-front costs. Telecom PV systems are very reliable, and require very little maintenance.

Types of Systems

January 5, 2023 Author No Comments

Utility-scale PV power plants (also known as solar farms, solar parks or solar power plants) are large solar electric systems that generate electricity and feed it into the national electric grid. Such plants can take up large areas of land. Like conventional power plants, they are connected to medium or high-voltage transmission networks.

Solar power plants range in size from several MW to several hundred MW. Some are over 1,000 MW.

Configuration of a solar power plant using smaller ‘string’ inverters to convert the DC electricity from the PV modules to AC electricity for the electric grid. These types of inverters are also used in residential, commercial, and industrial systems which are connected to the low-voltage grid. The transformer steps up the relatively low voltage produced by the inverters to the higher voltages required by the grid.

Configuration of a solar power plant using a large central inverter. This type of inverter is especially designed for use in solar power plants. At very large solar power plants, several central inverters can be used.

The electricity produced is usually sold directly to an electric power utility via a power purchase agreement (PPA), a legal contract defining pricing and conditions of sale.

Solar power plants can also operate in conjunction with other power sources, such as a gas turbine plant. When solar energy is not available, for example at night, the gas turbine plant can be brought online to make up for the deficit. Some solar power plants also have electricity storage facilities.

Types of Systems

January 5, 2023 Author 128 Comments

Grid-connected solar electric systems for businesses and institutions are usually larger than residential systems, are typically in the size range 10-300 kWp, and have several PV inverters. The electricity generated is consumed by the business or institution, and excess is fed into the electricity grid. A business or institution that uses electricity mainly during the day, when the sun shines, can cover nearly all of its electricity needs.

Typical solar electric system for businesses and institutions.

The PV modules are connected to one or more inverters which converts the DC electricity from the PV modules into AC electricity. During the day, this electricity is either used in a main building or several buildings to power electrical equipment, and any excess is exported to the national electricity grid. At night, electricity is imported from the grid. Electricity can also be imported from the grid during the day if the PV modules are not generating enough electricity. An import-export meter records how much electricity is imported from the grid and how much is exported to the grid.

Like residential systems, these types of systems only work if the grid is available (on). If the grid is not available (off), the system stops producing electricity. This is for safety reasons. When the grid becomes available again (comes back on), the system automatically starts producing electricity again (during the day). However, some systems have batteries which enable them to provide electricity when the grid is not available.

Types of Systems

January 5, 2023 Author 294 Comments

Grid-connected residential solar electric systems are systems, usually on rooftops, which generate electricity for private consumption by homeowners and/or for sale to the electricity utility. Electricity fed into the grid is either deducted from electricity bills or payment for it is received.

Typical residential solar electric system.

The PV modules are connected to an inverter which converts the DC electricity from the PV modules into AC electricity. During the day, this electricity is used in the building to power lighting and household appliances, and any excess is exported to the national electricity grid. At night, electricity for consumption is imported from the grid. Electricity can also be imported from the grid during the day if the PV modules are not generating enough electricity. An import-export meter records how much electricity is imported from the grid and how much is exported to the grid.

These systems only work if the grid is available (on). If the grid is not available (off), the system stops producing electricity. This is for safety reasons. When the grid becomes available again (comes back on), the system automatically starts producing electricity again (during the day). However, some systems have batteries which enable them to provide electricity when the grid is not available.

Economics

January 2, 2023 Author One Comment

Solar power can be added to existing small grids or mini-grids which are powered by diesel generators, and the amount of electricity that the diesel generators need to provide can be reduced.

Considerable savings in fuel costs can be achieved depending on factors such as solar irradiation levels and the load profile (when and how much electricity is used). Wear and tear on the generators and maintenance requirements can also be reduced.

This type of system is very suitable where power requirements are high during the day -when solar power is available- such as for industrial and agro-industrial applications.

Solar added to a generator diesel grid. Configuration and technical details vary considerably depending on the specific local circumstances.

To assess the economic feasibility of a project:

A professional load profile survey is required
Possible system sizes and configurations should be investigated
A comparison of the levelised cost of the electricity (LCOE) a system will produce, both with solar and without solar, should be undertaken,

Software can be very useful when doing detailed cost analyses.

Economics

January 2, 2023 Author One Comment

The main applications for off-grid PV are:

Remote households and communities where connection to the grid is not possible.
Where connecting to the grid would be more expensive than using a PV system.
In urban and semi-urban areas where installing low-power systems can cost less than connecting to the grid, which might involve laying underground cables.
Replacing diesel and petrol generators.
Reducing diesel generator running times.
Where the regular supply of diesel fuel might be a problem.
Telecom base stations.
Water pumping for human consumption, livestock and crop irrigation, and other productive uses of energy.

Typical cost breakdown of an off-grid PV system over the service life of the system. The batteries are the most expensive system component because they need to be replaced several times over the life of the system. Note that systems are different and, thus, proportional costs will vary.

The economics of a situation need to be determined case by case, taking into consideration the levelised cost of the electricity (LCOE) that a system will produce. LCOE is the total lifetime cost of the system divided by the total lifetime electricity generated by the system. It will depend on the initial system cost, the subsequent cost of replacement batteries, and on how well the system is operated and maintained, as well as on the level of solar irradiation at the site. A PV system’s LCOE can be compared with the LCOE of a diesel generator system (where a very significant cost factor will be the fuel consumption) to see which is more economically attractive. Software can be very useful when doing detailed cost analyses of larger off-grid PV systems.

Economics

January 2, 2023 Author One Comment

A PV system in conjunction with batteries can provide security of supply in the case of grid power outages.

Example of a backup solar electric system providing security of supply for periods when the grid is off. Several configurations are possible, depending on requirements.

Systems can be configured to supply only priority loads when grid power is not available. This means that the battery bank can be smaller and/or have a longer service life. Some systems will also feed electricity into the grid while others will not. Careful system design and sizing, taking all factors into consideration, is required.

These solutions are especially interesting for critical facilities and for industrial/production processes that require a continuous energy supply.

Both lead-acid and lithium-ion batteries can be used. Lithium-ion batteries have much longer service lives than lead-acid batteries. Lead-acid batteries are cheaper to purchase but need to be replaced more often. The batteries and BESS (battery energy storage systems) market is undergoing major changes in terms of technological advances, efficiency improvements and cost reduction.