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Energy Efficiency
February 11, 2023 No Comments
The efficiency (ƞ) of a machine or electrical appliance is ratio of the useful work produced by the machine or the electrical appliance to the energy consumed by the machine.
efficiency (ƞ) = Output/input.
Efficiency ƞ (%) = (energy output in watts ÷ energy input in watts) x 100.
The energy wasted (losses) during the process is usually in the form of heat.
Energy efficiency refers to using less energy (input) to provide the same result and perform the same task (output).

All engines, machines and electrical appliances have energy losses. The fewer the losses, the more efficient the energy use

A simple example is to compare two lamps, a non-halogen incandescent lamp (old type) and a fluorescent lamp, both providing the same level of illumination. The incandescent lamp wastes 90% of the energy it consumes as heat, while the fluorescent lamp wastes only 25% as heat. Thus, the fluorescent lamp consumes about 85% less energy than the incandescent lamp while providing the same level of illumination.

Energy efficiency / energy losses, comparing incandescent lighting with fluorescent lighting.

Energy efficiency, comparing lamps. Energy consumed = lamp wattage x quantity of lamps x hours of operation.

Energy efficiency, comparing computers. Energy consumed = computer wattage x quantity of computers x hours of operation.

The above or only examples for demonstration purposes. The same basic principles apply to non-electrical equipment.

Energy Efficiency
February 11, 2023 No Comments
تمثل الكفاءة (ƞ) للآلة أو الجهاز الكهربائي النسبة المئوية لإجمالي الطاقة المستهلكة بواسطة الآلة أو الجهاز الكهربائي (المدخلات) والتي تمكنها من تأدية عمل ذو قيمة (المخرجات).
الكفاءة ƞ (%) = (مخرجات الطاقة بالواط ÷ مدخلات الطاقة بالواط) × 100.
عادةً ما تكون الطاقة المفقودة (المهدرة) أثناء العملية على شكل حرارة.
تشير كفاءة الطاقة إلى استخدام طاقة أقل (مدخلات) لتقديم نفس النتائج وإجراء نفس المهام (مخرجات).

جميع المحركات والآلات والأجهزة الكهربائية معرضة لفقدان في الطاقة. كلما قل فقدان الطاقة، ازدادت كفاءة استخدام الطاقة.

أحد الأمثلة البسيطة على ذلك يتمثل بالمقارنة بين مصباحين، مصباح متوهج غير مهلجن (من النوع القديم) ومصباح فلورسنت، وكلاهما يوفر نفس مستوى الإضاءة. تفقد المصابيح المتوهجة 90% من الطاقة التي تستهلكها على شكل حرارة، بينما تفقد مصابيح الفلورسنت 25% من الطاقة التي تستهلكها على شكل حرارة. وبالتالي، فإن مصباح الفلورسنت يستهلك طاقة أقل بحوالي 85% من المصباح المتوهج مع توفير نفس المستوى من الإضاءة.

مقارنة كفاءة الطاقة/فقدان الطاقة ما بين الإضاءة المتوهجة وإضاءة الفلورسنت.

مقارنة كفاءة الطاقة للمصابيح. الطاقة المستهلكة = القوة الكهربائية للمصباح × عدد المصابيح × عدد ساعات التشغيل.

مقارنة كفاءة الطاقة لأجهزة الكمبيوتر. الطاقة المستهلكة = القوة الكهربائية للكمبيوتر × عدد أجهزة الكمبيوتر × عدد ساعات التشغيل.

الشكل أعلاه أو الأمثلة فقط لأغراض التوضيح. تنطبق نفس المبادئ الأساسية على الأجهزة غير الكهربائية.

Main Component
January 8, 2023 1,629 Comments

PV modules are rated in peak watts (Wp), which is the power they are expected to produce under standard test conditions (STC). STC are defined as the solar irradiance of 1000 W/m2, a module temperature of 25°C and an air mass of 1.5.

The electrical energy output of a PV module can be roughly calculated thus:

PV module energy output (Wh) ≈ PV module power rating (Wp) x peak sun hours (PSH) x performance ratio (PR).

The performance ratio accounts for system losses, and varies according to system type, local temperatures, and quality of installation. For a grid-connected system, 0.7 (70%) would be expected if the module is near optimum angle and orientation.

So, for example, what would a 100 Wp PV module be expected to produce at a location in Iraq on a day with 4.5 peak sun hours (kWh/m2 per day of solar irradiation)?

Answer: 100 Wp x 4.5 PSH x 0.7 ≈ 315 Wh

Basic formula for estimating the electrical energy output of a PV module.

Using the same example, with 5 x 100 Wp PV modules, the total peak power of the PV array would be 500 Wp; and under the same conditions, electrical energy output would be approximately 1,575 Wh per day (or 1.6 kWh). Which over a year would be 1.6 kWh x 365 days ≈ 584 kWh.

Average energy output in kWh per kWp of PV modules in Iraq. Values range between 1,600 kWh per kWp in the east and 1,800 kWh per kWp in the west.

Source: © 2020 The World Bank, Source: Global Solar Atlas 2.0, Solar resource data: Solargis

In an off-grid system, there would also be losses associated with the batteries and other equipment.

Main Component
January 8, 2023 2 Comments

A fault in a battery can cause a fire or an explosion (a release of energy in an uncontrolled manner). With lead-acid batteries there is the danger of acid spillages and explosive hydrogen gas. Damaged or incorrectly operated lithium-ion batteries can be a fire and/or explosion hazard. Strict compliance with manufacturers’ installation, operation and maintenance instructions is essential.

Purchasers of PV systems with batteries need to consider:

  • Where in a building are the batteries going to be installed?
    • Batteries are large, heavy and contain hazardous materials.
    • A special room may need to be constructed for larger systems.
  • Who is going to maintain the batteries?
    • Only trained persons should do so.
  • How are the batteries going to be disposed of at the end of their service life?
    • Batteries are considered to be toxic waste.
    • Some companies have comprehensive recycling schemes for equipment.

Deep cycle 2 V lead-acid batteries in a battery room. Each battery cell is 0.5 metres high. The nominal output of the PV array is 2,000 Wp.

Warning signs used with lead-acid batteries.

 

There are international standards regarding the installation requirements for batteries, battery enclosures and battery rooms. Reputable manufacturers will incorporate these into their installation and operation manuals/instructions, which should always be rigorously adhered to. The requirements for lead-acid batteries and lithium-ion batteries will be different.

There are also issues regarding battery fires (especially with regard to lithium-ion batteries) that firefighting services need to be aware of.

Main Component
January 8, 2023 2 Comments

A range of monitoring equipment and data collection systems are available for grid-connected and off-grid PV systems. Monitoring system performance is invaluable for detecting under-performing and faulty equipment. In large systems, monitoring is essential, since undetected system failures or under-performance can lead to considerable revenue losses.

In a grid-connected PV system, energy output can be checked regularly at the meter or inverter. However, more detailed information is required to assist with fault finding.

Typical performance indicators monitored include:

  • Power output of PV module arrays (with reference to solar irradiation levels).
  • Battery state of charge over time in off-grid systems and back-up systems.

PV inverter display showing power output, 1302 W; daily energy output, 14.75 kWh; and total energy output since the system was installed, 196.42 MWh.

Radiation sensor at a solar power plant. Source: SMA Solar Technology AG.

Monitoring systems fall into the following general categories:

  • Energy meters
  • Monitoring integrated into equipment such as PV inverters, other inverters and solar charge controllers
  • Equipment-specific monitoring, specific to particular PV inverters, charge controllers and battery inverters/inverter-chargers, with remote monitoring
  • Monitoring systems that can be used with a range of system types, also with remote monitoring

Many companies offer remote monitoring services over the internet.

Main Component
January 8, 2023 No Comments

PV modules can also be installed on sloping roofs. However, the roof may not have an optimal orientation or inclination for maximum electricity production.

The combined weight of modules, the mounting system, and any additional wind-loading needs to be considered to avoid damaging the roof. A space needs to be left between the roof and the PV modules to ensure ventilation because high temperatures will reduce the output of the modules. The installation will also need to comply with national building regulations.

PV modules being installed on a tiled roof. Mounting structures are available for different types of roofs.

PV modules being installed on a metal roof, which can get very hot on sunny days. Note the space under the modules for ventilation, and that the modules are not at the same angle as the roof.

Scaffolding will most likely be required for the installation, which adds to the cost. Working on roofs is one of the main cause of accidents in the solar industry, so special safety precautions need to be taken during installation work.

Main Component
January 8, 2023 No Comments

Flat roofs can be very good for installing PV modules on. Access for maintenance and repair is also easy. Mounting structures are either ‘free-standing’ (held in place by ballasts) or fixed to the roof (if the roof cannot bear the additional weight of ballasts).

PV modules on a flat ‘green’ roof: mounting stucture held in place by brick ballasts.

Larger system on flat roof, mounting structure fixed to building structure.

Is is easy to overestimate how many PV modules can fit on a flat roof. Structures on a roof can cause shading, the rows of modules need have enough distance between them in order that they not shade each other, and the orienation of the roof may not ideal.

Main Component
January 8, 2023 3 Comments

Ground-mounting structures for PV modules are the easiest type of mounting structure to install, and optimal inclination angles and orientation can be achieved. The PV modules do not have to be lifted onto a roof and access for maintenance and repair is also easy, but may require heavy machinery for trenches and foundations.

Ground-mounting structure for PV modules. Ground mounts are usually the easiest to install and maintain – access is easy for cleaning the modules (when required) and for carrying out regular inspections and repairs. Ground mounts also provide good airflow/ventilation; high module temperatures reduce electricity output. Smaller ground-mounting structures are also available.

Installing PV modules at ground level also makes it easier to avoid shading by buildings, other structures and trees. However, there needs to be enough distance between the rows of PV modules so that they do not shade each other.

Structures are usually made of galvanised steel, but also aluminium. Common methods of fixing structures to the ground include concrete foundations, concrete piers, ground screws or ram foundations. A ground survey is usually necessary to choose an adequate method.

The installation should be in a fenced enclosure to prevent unauthorised access and protect against theft. Cables should be laid in conduits or trunking to protect them against UV radiation and the environment.

Main Component
January 8, 2023 One Comment

PV modules need to be securely fixed to a mounting structure exposed to the sun and these structures need to be securely fixed to the ground or the building on which they are installed. Mounting structures should be shade-free and be able to withstand high winds.

There are many different types of mounting structures:

  • Ground-mounted structures in fields/open areas.
  • Mounting structures on flat roofs.
  • Mounting structures on sloping roofs.
  • Pole mounts.
  • Mounting structures on building facades.
  • PV slates and tiles integrated into a roof.
  • Tracking PV arrays (automatic, single or double axis).
  • Tracking PV arrays (manual adjustment and turning, single or double axis).

The mounting structures are usually  made of galvanised steel or aluminium.

Ground-mounting support structure for PV modules.

PV modules are fixed to mounting structures with frame clamps (as above), bolts or other means.

The optimum inclination angle for PV modules in Iraq is approximately 30° to 35° +/- 10°, however it can be different and will very much depend on the system’s type and location and therefore expert advice should always be sought.

Orientation in Iraq should be towards the south.

Structures are usually made of galvanised steel, but also aluminium. Special ‘solar cables’ and connectors are used to connect the PV modules to one another and to other equipment, and cables should be laid in conduits or trunking to protect them against UV radiation and the environment.

Main Component
January 8, 2023 2 Comments

Solar charge controllers are used mainly in off-grid PV systems, but also in other systems with batteries. Their main function is to protect the batteries from overdischarging and overcharging, and to ensure efficient charging of the batteries. Battery voltage decreases as the battery discharges. The charge controller protects the batteries by disconnecting the DC loads if the battery’s state of charge gets too low, and switching on the DC loads again when the batteries have recharged.

Charge controller wiring in an off-grid PV system powering DC lights.

Charge controller from Steca, note the very clear battery state-of-charge (SoC) display. Source: Steca.

Most charge controllers currently on the market are designed for use with lead-acid batteries. However, charge controllers are also available for lithium-ion batteries, and some charge controllers can be used with both types.

Charge controllers range in size from very small in simple lighting systems to several thousand watts in larger systems, and there are many different types.

If there is a battery inverter in the system, the charge controller will not disconnect the AC loads being powered by the inverter, which can lead to the batteries being overdischarged as they are usually connected directly to the battery inverter. The system either has to be carefully managed by the system owner or an automatic solution implemented (some have integrated low voltage disconnect or overdischarging detection) to protect the batteries. Having DC lights in an off-grid system with an inverter can act as a warning mechanism – the charge controller will disconnect the DC lights before the battery discharges to such an extent that it can be damaged.

Wiring diagram of a system containing a 24 V battery inverter.

Having DC loads (lights) in the system can act as a warning mechanism –  if the battery state of charge is too low, the charge controller will disconnect the batteries.

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