What is kWp?
kWp stands for Kilowatt Peak or in other words the maximum peak performance obtainable from a solar PV system when operating under perfect conditions.
The actual output of a solar PV array is dependent on three main factors;
1. Light level
2. Temperature
3. Air quality
In the UK under normal operating conditions a PV array will rarely reach it's kWp potential; for example a 3kWp system will not run at 3kWp all of the time, instead the Solar PV array output fluctuates based on the environmental conditions as mentioned above.
What is the difference between a kilowatt (kW) and a kilowatt hour (kWh)?
A kW is a thousand watts, and a unit of power. A kWh is the amount of energy used when a kW of power is consumed/used for one hour.
We use Watts (W), kilowatts (kW) and kilowatt peak (kWp) to measure power when sizing a Solar PV and or Battery Storage system to ensure that all of the different components will work efficiently and safely together when connected.
We use kilowatt hour (kWh) and kilowatt hours (kWh's) to measure how much usable power will be generated and or available for storing and or export/sell. Electricity bills are measured and payable based on kWh's, the Smart Export Guarantee payments are based on kWh's exported to the grid.
Accurate solar PV kWh production estimates will be prepared in advance of an installation based on historical solar radiation data combined with the characteristics of the installation and the location. Along with this the household annual electricity consumption in kWh's and the consumption profile of the property (i.e. how many people live in the house and when is the energy being used) enables us to give a comprehensive financial analysis for your return on investment. In the UK we typically see that for every 1kWp of installed PV you get a return of between 800 and 1000 kWh's of electricity per year. The better the system design in relation to it's location the greater the kWh's return will be.
What are the components of a solar photovoltaic (PV) system?
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Solar PV Modules (solar panels): these make up the PV array(s) within a solar PV system and they converts daylight into electricity, direct current (DC)
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Solar PV Mounting Systems: can be in-roof, on-roof, ground mounted, wall mounted, carports, canopies as well as integrated into buildings.
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Power Optimisers: these are either integrated into the solar PV modules (solar panels) and or connected to each solar PV module. Power Optimiser enable increased Solar PV production, module (panel) level monitoring and system alerts, enhanced safety.
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Solar PV Inverter(s): convert direct current (DC) into alternating current (AC), control grid interaction and are the hart of any solar PV system.
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Solar Cables & Connectors: are used to connect the DC components of the system
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Isolators: are used to disconnect parts or all of the system for maintenance and/or in an emergency
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PV Junction Boxes: are sometimes used to combine multiple solar PV strings before the inverter
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Monitoring & Displays: Used to provide real-time module level performance data and automatic alerts from the PV system.
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Batteries: used to store excess solar PV production and maximise self-consumption
How does a solar PV system work?
Daylight hits the photovoltaic cells and is converted to direct current (DC) electricity. The inverter converts the DC electricity to alternating current (AC). This AC electricity is then used automatically by the property/site demand while any excess energy can either be stored in a battery (even a car battery EV) or exported/sold to the grid under the Smart Export Guarantee, assuming the system is installed by an MCS or equivalent certified installer and so is eligible.
What does energy conversion efficiency mean?
Energy conversion efficiency is an expression of the amount of energy produced in proportion to the amount of energy consumed or in our case available to a device. The sun produces a lot of energy in a wide light spectrum, energy conversion efficiency for Solar PV modules (solar panels) in general are typically from 15% to 23% efficient.
The energy conversion efficiency of a solar panel has a direct effect on the kWh yield and is a key differentiator between different solar PV Modules (solar panels) when specifying or choosing which is the best equipment to use.
How is a Solar PV system connected to the national Grid?
Connecting a PV system to the distribution network is arranged by the installer working with the Distribution Network Operator (DNO). The DNOs are the power companies that run the power distribution networks (EDF, Scottish & Southern, UK Power Networks etc). There are two engineering recommendations (G98 & G99) that are followed by both the installer and the DNO to ensure that the solar PV system will integrate safely with the national grid.
Solar PV systems under 16A per phase (i.e < 3.68kW inverter) come under engineering recommendation G98. Solar PV systems installed under G98 can be installed without prior notice to the DNO, with the DNO being informed afterwards (within 30 days).
Solar PV Systems over 16A per phase will need to consult the DNO before the Solar PV system is connected to ensure that the distribution network can handle the extra power being provided. Depending on the system size and the DNO's preferences, larger systems may be installed either under G98 or G99 but generally this will fall under G99.
What is net metering?
Net metering allows buildings with PV systems to use any excess electricity they produce to offset their electric bill. As the PV system produces electricity, the kilowatts are first used for any local requirements within the building. When the PV system produces more electricity than the building needs, the extra kilowatts are fed into the utility grid.
Does a solar PV system need batteries?
If the solar PV system is connected to the National Grid then technically your system will not need batteries as any excess energy can be sold to and fed into the grid under the Smart Export Guarantee (SEG). However more and more system owners are choosing to add battery storage to their solar PV system, increasing the self-consumption from their PV system (how much they use of what the solar PV system generates) but more importantly reducing their overall house/site consumption and reliance on the grid. Even with battery storage the average household will still sell some excess energy to the grid and receive the SEG payment, assuming the system has been installed by an approved MCS or equivalent installation company. Added to this some energy suppliers now offer dynamic energy tariffs meaning you can also charge your battery storage during low rates and sometime even free. This is very useful in the winter/leaner solar PV production months as you can charge the batteries at lower rates and discharge at higher rates. The key to note with this is selecting the right energy management system that's user friendly with everything at your fingertips.
Batteries can also be integrated into hybrid grid tie / battery systems as a backup, protecting against mains power cuts.
What does energy conversion efficiency mean?
Energy conversion efficiency is an expression of the amount of energy produced in proportion to the amount of energy consumed or in our case available to a device. The sun produces a lot of energy in a wide light spectrum, energy conversion efficiency for Solar PV modules (solar panels) in general are typically from 15% to 23% efficient.
The energy conversion efficiency of a solar panel has a direct effect on the kWh yield and is a key differentiator between different solar PV Modules (solar panels) when specifying or choosing which is the best equipment to use.
What are the effects of shade on solar PV Panels?
Shading has a disproportionate affect on a systems performance. This is because the cell with the lowest illumination determines the operating current of the series string in which it is connected. This is one of the areas that must be covered in a survey carried out before the installation.
Modern arrays can bypass the effected diodes to minimise shade effects; but these effects must still be considered as system yields (kWh's) as well as other factors will be affected.
How does the angle a solar PV Panels installed affect it's performance?
The maximum total annual solar radiation available in the UK is usually at an orientation of due south and at a tilt from the horizontal equal to the latitude of the site minus approximately 10-15 degrees. For example 30 degrees is an optimal tilt at the tip of Southern England, increasing to around 40 degrees in Northern Scotland.
If the optimum angle is not achievable, over 90% of the maximum annual energy can still be achieved at 10 degree and 50 degree tilts. South-facing vertical facades generate around 70% of the maximum. This is why we only install SolarEdge as it allows for installing solar panels on multiple orientation and minimising shading losses due to module level electronics (optimisers).
What other points should be considered with a solar PV installation?
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Method of fixing/ integration into the building
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Ensure that the fixings do not cover or shade any part of the PV cells
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The fixing must allow for thermal expansion without breaking the glass
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Weather sealing
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The mounting option must allow for safe maintenance and possible replacement of individual solar PV panels and power optimisers.
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The life of the support structure must be at least that of the PV array.
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Protection from corrosion
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Wind loading
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Any extra weight
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How and where to run electrical wiring
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Where to place junction boxes, meters and inverters