Solar PV Course

7/31/2019 Solar PV Course

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Course written by Keith Taylor

Course contents

How PV works & the components The benefits of solar electricity Is solar installation suitable for the property How to make the most of the energy Cost savings and maintenance Selling your own generated electricity Free solar schemes Planning permission How to install a system Roof fixings and considerations Cable requirements Safety procedures Calculating how many panels are required Testing and inspection Commissioning Servicing & maintenance FAQS


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There are 3 main types.

Monocrystalline Made up from 1 type of crystal

Polycrystalline Made up of more than 1 type

Amorphous

Whats the difference?


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A Monocrystalline Solar Panel is one of 3 common solarpanels manufactured today.

They are the most efficient and the most expensive.

These panels are made of a large single crystal (cut from

ingots). They perform better than its counterparts in low light

conditions, such as cloudy days, but not by much.

When there is low light, there is low energy to be captured.

15 21% efficient.

Generally black in colour


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Polycrystalline or Multicrystalline Silicon Cells:Made from cells cut from an ingot of melted andrecrystallized silicon.

In the manufacturing process, molten silicon is cast into

ingots of polycrystalline silicon, these ingots are then saw-cutinto very thin wafers and assembled into complete cells.

Multicrystalline cells are cheaper to produce thanMonocrystalline ones, due to the simpler manufacturingprocess. However, they tend to be slightly less efficient, with

average efficiencies of around 12%-16%. They have aspeckled crystal reflective appearance, and again need to bemounted in a rigid frame


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cells are manufactured by placing a thin film ofamorphous (non crystalline) silicon onto a wide choice ofsurfaces. These are the least efficient and least expensive toproduce of the three types. Due to the amorphous nature ofthe thin layer, it is flexible, and if manufactured on a flexible

surface, the whole solar panel can be flexible. One characteristic of amorphous solar cells is that their power

output reduces over time, particularly during the first fewmonths, after which time they are basically stable.

The quoted output of an amorphous panel should be that

produced after this stabilisation.


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A Voltageexits if there is adifference in the amount ofcharge between any twopoints. Voltage is the electricpotential energy per unit ofcharge, measured in joules

per coulomb (= volts).However it is the difference inthe voltage quantity, which isphysically meaningful.Conditions must be metbefore any charges \ electriccurrentwill flow.


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It is useful at this stage to remind ourselves about the relationship between Volts (V),Amps (I) and Resistance (R). This can be best explained by using the Ohms lawtriangle

Ohms law states that if you have two of the values you can always find the third. Inorder to see this we can use the following example.

Let us say that we have a circuit where we know the current is20A and we have a resistance of 1.5 Ohms.

To apply Ohms law we need to cover up the valuethat you are looking for and use the resulting formulato find the value. Here we need to find the voltage andhave covered up the V in the triangle, this leaves uswith I * R as a formula, we can then say:V = I X R which gives us the sum V = 20 X 1.5 = 30VThis method can be repeated to find any value if we have the other two

V

I R


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The same method can be applied when weneed to calculate the power in a circuit but weuse a slightly different triangle that contains

the values Watts (W), Amps (I) and Volts (V). As with Ohms law we need to cover up the

value that we wish to find and we will be leftwith a formula to apply to find the missing

value, in this example we are going to wantto find the voltage (V) when we have thewattage (230W) and the current (7.93 A)

W

V I


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The difference between AC and DC is that AC is an alternating current(the amount of electrons) that flows in both directions and DC is directcurrent that flows in only one direction; the product that is flowing being

electrons.AC power is what fuels our homes. The wires outside of our house areconnected to AC generators. DC is found commonly in batteries andimportantly for our purposes, solar photovoltaic cells.Both AC and DC employ magnets to repel electrons. Electrons arenegatively charged particles that are one of 3 components that make up

an atom. Negative charges will repel negative charges and positivecharges will repel positive charges, so one only needs to introduce anegatively charged item next to electrons to force them to move in theopposite direction.


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Likewise, you can attract electrons by introducingsomething that is positively charged into theirenvironment drawing the electrons to it. This property ofelectrons is what allows for AC power to work; that is, theyswitch directions constantly. The picture above is ademonstration of AC power at work.

DC power was invented by Thomas Edison and first usedto power our homes in the late 1800s. Its main drawbackbeing that in order to receive DC power from a generatingstation, your home had to be located within a one mileradius of the station. DC power degrades as it moves awayfrom its generating source; the further away, the less

power. This is an important fact to remember whenconsidering the position of inverters in relation tophotovoltaic modules


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To produce more power cells can be wiredtogether.

When cells are connected in series thevoltages add and the current remains thesame as in one cell.

When cells are connected in parallel theindividual currents add and the voltageremains the same as in a single cell.


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The current and power output is greatly affected by the irradiancelevel but the voltage is only marginally affected as shown by thefollowing IV curves for various solar irradiance levels.

Solar cells are also affected by a change in temperature. An increase intemperature causes a decrease in voltage and power and an insignificantincrease in current. For crystalline cells the voltage is changed by an

average of -0.5% per deg C change from 25C.


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When selecting a Module type for installation it is

important that the modules selected have the relevant typetest approval depending on the type of module to be used: BS EN 61215:2005 Crystalline silicon terrestrial

photovoltaic (PV) modules Design qualification and typeapproval or

BS EN 61646:1997 "Thin film terrestrial photovoltaic (PV)

modules Design qualification and type approval"

(standards are currently being developed for glass/glassmodules)

Type testing involves the manufacturers sending a moduleto an approved test house and they will apply certain teststo verify the modules resistance to external influences(weather, impact etc) and they will measure the modulesperformance under standard test conditions (STC) of 1000Wm2 at 25C.


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In the UK, when wanting to claim the feed in tariff forsystems less than 50kWp, as well as ensuring that themodules meet one of the above type test standards it mustbe ensured that the manufacturing process can make surethat each module can meet these standards, this is calledFactory production control (FPC). All modules that have

MCS approval must have had a factory inspection against arecognised FPC standard, this will help to ensure thatevery module that is installed under the FiT scheme hasmet minimum performance standards.

A module is an environmentally and structurally protected

unit consisting of solar cells wired together. The cells arenormally wired in series to create a higher voltage andoccasionally wired in parallel to increase the current.


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Modules can be of any size but due to its large size areusually limited to 300 Watts (>2m2). A typical module is 36cells wired in series framed in aluminium and covered withglass.

This produces an output of 125 watts (17.3v and 7.23 amps).This type of module is frequently used to charge 12vbatteries. Some modules are sized to charge 24v or 48vbattery banks and some modules made for grid tie systemshave voltages as high as possible to minimize voltage drop.


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All modules have a nameplate on the back showing its ratedoutput in standard test conditions (stc).

STC is when 1000W/m2 of irradiation is exposed to themodule at a temperature of 25C.

This allows modules to be compared together but is not to beconfused with the expected output of the modules which isnormally lower due to system losses and less than idealweather conditions.


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A 1kWp grid connected PV system will achieve approximately 850kWh(SAP 2009) of energy over 1 year average across the UK (regionalvariations).

The 1kWp PV array will require approximately 9-12m2 of roof orexposed area; this is dependant of the type of module and cellconstruction to be used.

We also have to take into consideration the type and output of theinverter to be used. Sizing the array and inverter are very important ashaving an undersized inverter could cause installation failure and in

the worse case the inverter may break down and cause a fire.


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Note the most southerlypart of England in red is

actually 1300

Variations in solarradiation across the UK(figures are averagekWh/m2 per year


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The array itself should be installed pointing totrue or grid south not magnetic south and angledat 30to 40 to horizontal (in UK) to achieveoptimal performance. It can be tilted more or less

to maximize production in summer or winter. Quite often this angle is controlled by the slope

of the roof and the aesthetics. Most customersare unhappy with panels standing up off the roof

and this can also cause problems with windloading and planning permission.


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Example 1:

In the ideal world you would find a rooffacing due south at an inclination of 35degrees. As long as there are no shadingeffects a 2kWp array should produce1700kWh per year (2 x 850kWh as per SAP).


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Example 2:

In the real world you may find that the onlyavailable roof space is facing east. Assumingthe same array and inclination the arraywould only produce (1700kWh x 79%) = 1343kWh. A system loss of 21% and remember the

initial outlay of money is exactly the same.


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Example 3:

On a bad day you may find that the onlyavailable roof space is north facing with aninclination of 60 degrees. A 2kWp arraywould then only produce (1700kWh x 37%) =

629 kWh a loss of 63%.


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Example 4: If you wish to produce a specific output it can be

determined as in the following example. A 1200kWh annual output is desired for an array mounted

on a SE facing roof with an inclination of 45 degrees. Thedesired output is then divided by the % of loss caused by

orientation and inclination (8% or 0.92) and then thatnumber is then divided by 850kWh to find the kWp of thearray: (1200kWh/0.92) x(1kWp/ 850kWh) = 1.5345 kWp.

The number of modules used can then be found by

dividing the array size by the module size. In this examplelets assume that the module size is 180Wp this wouldgive you 15345Wp/180Wp = 8.525 modules. Thus to gainthe output desired 9 modules would be needed.


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SAP calculations are used to provide an estimate of the

annual yield of a PV system using standard data. Whilst insome cases this may not be the most accurate the MCSscheme requires that all installers use this methodtherefore allowing the consumer to compare standardcalculations across all quotes that they may receive

For SAP calculations, the energy produced per year dependson the installed peak power (kWp) of the PV module (thepeak power corresponds to the rate of electricity generationin bright sunlight, formally defined as the output of themodule under radiation of 1 kW/m at 25C). PV modulesare available in a range of types and some produce more

electricity per square metre than others (the range forcurrently available types is from about 30 to 125 Wattspeak per m), and the peak power depends on the type ofmodule as well as its effective area.


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In the UK climate, an installation with 1 kWp typicallyproduces about 850 kWh of electricity per year (atfavourable orientation and not over shaded). At timesof high solar radiation the PV array may generatemore electricity than the instantaneous electricitydemand within the dwelling.

The procedure for PV is as follows. 1) Establish the installed peak power of the PV unit (kWp). 2) The electricity produced by the PV module in kWh/year is 0.8 X kWp X S X Zpv = Total kWh output per year (given

average irradiation)

where S is the annual solar radiation from Table H2(depending on orientation and pitch),

Where Zpv is the over shading factor from Table H4pg34/35


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The potential for any PV system to be shaded has to becarefully assessed as any amount of shading can have aserious effect on the overall output of the system.

Even shading of one module or even a single cell, canaffect the output of the whole array as this places anincreased resistance in the circuit therefore making itharder for the electrons to flow, in very extreme conditionsthis can lead to the overheating of cells and modules andresult in premature module failure.

This has to be considered when calculating the overalloutput and the following factors from table H4 of SAP2009 should be used.


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If there are two PV strings, e.g. at different tiltor orientation, apply the previous equation toeach string and complete the calculation foreach one independently of the other and then

sum the annual electricity generation.


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An inverter converts a DC (direct current) into a usable AC (alternatingcurrent). There are several types of outputs possible from an inverter.Square wave, Modified square wave and true sine wave are available butthe true sine wave inverter is the only one that is allowed to be utilityinteractive. The modified square wave inverter is commonly used due toits lower cost in off grid applications.

The power from the array converted by the inverter is then connected viaisolators into the consumer unit via an MCB (miniature circuit breaker).

Deciding on the type of inverter is down to the installation and theinstaller. The inverter must be sized not only for the maximumcontinuous output but also the range of DC voltages and currents fromthe array. Cost and efficiency are also major factors in choosing aninverter. In the UK an inverter must meet the standards set in ER G83/1and ER G59/1. Some of these operating limits are shown on the nextslide.


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Limits for operating voltage or operating frequency

230V + 14.7%/-10% (207 264V) and 50Hz =1%/-6% (47 50.5 Hz)

Anti islanding/ loss of mains protection Minimum reconnection time of 3 minutes after supply is

restored

Maximum trip time of 5s for PV systems or 0.5 secondsif the inverter cannot withstand being re-energized from a

source that is 180 degrees out of phase. Electromagnetic compatibility (EMC)

DC current injection max. 20mA


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An unusable DC waveformA waveform matched to

supply, synchronised to ausable waveform back to

grid.

From this. To this.


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The sizing of the array for mains connected PV systems is relativelysimple due to the fact that it is connected in parallel with the utility. Thisallows the system to be of any size because the loads will always besupplied no matter what the output of the array is. This means the arraysize is only limited by the space available, the requirements needed toobtain market incentives, and of course the clients budget.

When we select an inverter we must take account of the size of the arrayand the energy level requirements. Over sizing the inverter will increaseinstallation costs and the inverter will not be used efficiently. Invertersizing should always be done alongside manufacturers guidance andmost manufacturers have online or downloadable sizing programs thatare very effective. When we dont have the manufacturers data weshould size an inverter typically to be 80% of the PEAK POWER (Wp) ofthe PV array. We undersize the inverter in the UK due to the relatively

low solar radiation levels and expected losses such as soiling andvoltage drop. As an example a 1kWp grid connected system generatingaround 800kWh a year will require an 800W inverter.


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The output of the PV system should be estimated using theGovernments standard assessment procedure for energy ratingof buildings (SAP 2009). For PV systems Appendix M is to beused taking into account orientation, pitch and shading. Variousprograms are available using this procedure and others tosimplify your life. SAP is the most commonly used and isaccepted by MCS but this does not mean that it gives the most

accurate results. The inverter should be installed on a solid vertical surface with

adequate surrounding space for ventilation as the inverter willget warm during operation. This may require strong board to beinstalled. Some inverters are appropriately rated for outdoorinstallation and then AC cabling has to be routed into thebuilding. For inverters only rated for indoor use the DC cablinghas to be routed into the building. The DC and AC isolatorsassociated with inverter should be easily accessible from theinverter position.


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Inverter location must be acceptable withregards to: Weight bearing capacity of support IP rating of inverter

Access (maintenance and testing) Ventilation Any displays / indicators clearly visible Live wiring precautions are to be followed if

connecting up the inverter necessitates working

around live DC connections. AC system to be installed and tested to BS

7671:2008.


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Normally all grid connected inverters have a circuit that useselectronics to change the output of the array so that input of theinverter is continuously operating at the maximum power pointeven when temperature and irradiance are changing. Due to thisthe voltage at the input of the inverter will be lower than whatwould be normally expected. This voltage is approximately 80%of Voc.

Most grid controlled inverters are rated at 90% to 98%efficiency over the majority of the operating range. The efficiencyof the inverter drops drastically below 25% of the maximuminput.

The warranties on inverters range from 1 year to 20 years due

to the different technologies used and production techniques.The most common is 5-10 years. Inverters come in many sizes. From a small one of a few watts

for solar lighting to a few megawatts for utility generation.


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All systems installed in the UK under 16A perphase must conform to G83 in respect of therequirement to disconnect form the grid,most inverters available are tested to achieve

the requirements set out in G83. However great care must be taken to ensure

that the inverter selected for the job, has gotthe correct certification to G83 as not allinverters are designed to meet thisrequirement.


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When you are considering installing a PV installation on a roof,you will have to understand that the connections and cabling arenot going to be the usual PVC/PVC twin and CPC cable used fordomestic internal wiring. The PV wiring does have to be durableand protected against voltage constraints, mechanical damage,movement, wind, rain and solar radiation. (This is not anexhaustive list). Therefore maximum values need to be assessed.

To safely assess and size the cables we have to look atconditions that need to be satisfied.

The values originate from two key module ratings which is the

open circuit voltage and the short circuit current Themanufacturer's instructions for PV modules will give youstandard test conditions that apply to that specific module.Below is a multiplication that needs to be used when sizingcables.


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DC main cables (to and from the whole array)should be rated as a minimum at:

Voltage: Voc (STC) x M x 1.15 (M = thenumber of series connected modules)

Current: Isc (STC) x N x 1.25 (N = the

number of parallel connected strings) STC=Standard test conditions.


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MC3 Cable &Connectors

Type 3 MC Branch Plug

Top: PV-Male cablecouplerBottom: PV-Female

cable coupler

MC4 connectors


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DC Cable Installation- General Guidelines Cable should always be double insulated and polarized. DC Connectors should always be used Cables and connectors will be expected to last for up to 25 years Cable or fuses should never be disconnected when under load. Cable from the solar PV modules should follow the shortest route to

the array connection boxes. All DC cable should be clearly identifiable Cables should be laid in parallel and loops should be avoided - except

where they enter a building Cables should never be laid in a hazardous space Cables should never be in contact with sharp edges

Cables should never be installed near lightning conductors. Cables should always be tested for polarity in accordance with

specified regulations. Care must be taken when connecting modules as they will generate if

there is light. (correct PPE is essential)


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Voltage drop must be calculated to avoid anyunder sizing of the PV cables which wouldhave a deleterious effect due to overheatingand break down of the insulation. There

follows a table with typical resistances ofdifferent size cables

4mm 0.0046

6mm 0.003110mm 0.0018

16mm 0.0012

25mm 0.00073

35mm 0.00049

Conductor cross sectional area (mm2

)Resistance in Ohms per metre


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Example:- A 4mm2 cable, 100m long, carrying a current

of 20A. The voltage drop = 20A x 0.0046

. For a cable length of 100m the volt drop

A


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Due to PV arrays being constructed of metal components and thestructure being of metal, there is a possibility of lightningstrikes. The Structure therefore needs to be safe guarded againstthese occurrences and earthing needs to be in place to carry anyvoltage disturbances that may occur. The two main areas thatneed to be considered for lightening and earthing protectionare:-

The PV Array The Inverter

Reasoning behind earthing the Array is that ordinary personswithin the property could touch the array either by climbing onthe roof system or through an access window fitted in to the roof

system such as a Velux window. The earthing system employedcan also act to provide a degree of protection against lighteningsurges, even though it is generally considered in the UK that therisk is very low


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The Inverter would be earthed under normalinstallation practices through the wiring systememploying a C.P.C .

As can be seen in the following DTI earthing decisiontree the array frame for most installations in the UKcan be left floating as long as class II modules,cables, connectors, enclosures and a isolatingtransformer is used between the DC and AC sides ofthe inverter.

Lightning protection is not required in UK unless agreater than normal risk of a direct strike is presenti.e. if it is the highest structure in the area or covers alarge area.


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Note the Isolators!


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Overcurrent Protection - Protection of power supplies,conductors, and connected equipment from excessive flow ofinput or output current, including the short circuited current.

Overcurrent protection is afforded by Fuses and MCBs (MiniatureCircuit Breakers. We also have to consider overcurrent and shortcircuit current within the PV array to see if string fuses are

applicable.

For crystalline silicon modules all d.c. components must be rated@ a voltage of(Voc(stc) x 1.15)and a current of(Isc(stc)x1.25).For other module types all DC components must be rated @Voc(stc)and an Isc(stc)for a temperature range of -15 to 80oC.

Double (basic + supplementary) insulation must be used forvoltages greater than 120V DC.


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String cables of 3 or fewer stings must be rated at a voltage ofVoc(stc)xmx1.15and current ofIsc(stc)x(n-1)x1.25if no stringfuses are used.

(m = #of modules per string and n is the # of strings) (The module must be able to withstand a reverse current of

2x1.15xIsc) If string fuses are used or if there is more than 3 strings the

cable must be rated at a voltage ofVoc(stc) x m x 1.15andcurrent ofIsc(stc)x1.25. This also applies for the DC main cable.

DC connectors must be rated DC and properly labelled. In a PV array formed from a number of strings, fault conditions

can give rise to fault currents flowing through the DC system.Two key problems need addressing

overloaded string cables significant module reverse currents


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Refer to hand out Planning permission


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You'll need a roof orwall that faces within 90 degrees of south, and isn'tovershadowed by trees or buildings. If the surface is inshadow for parts of the day, your system will generate lessenergy.

Solar panels are not light and

the roof must be strong enough to take their weight,especially if the panel is placed on top of existing tiles. Ifin doubt, ask a construction expert or an installer.

you don't need planningpermission for most home solar electricity systems, as

long as they're below a certain size - but you should checkwith your local planning officer, especially if your home isa listed building, or is in a conservation area or WorldHeritage Site.


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The General Permitted Development Order of2008 grants the right to carry out the installationof most PV systems without obtaining planningpermission. Permission must be obtained if:

The array protrudes more than 200mm from aroof top.

The array is visible from the highway in aConservation Area or World Heritage site.

To be mounted on a listed building The ground mounted array is more than 4m in

height or within 5m from a boundary.


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The surveyor must as a minimum measure the size of the roof they areproposing to install the solar panels on. This is occasionally done from theground using a laser distance meter, but it is more common to measure thelength of your wall and then the height of your roof space from inside ofyour loft.

Have you looked at the fuse board or consumer unit, a spare breaker isrequired along with a 30mA RCD.

If this is not present a new dedicated consumer unit will require fittingadjacent to the existing board.

Have you assessed and explained where the inverter and associated cableswill be positioned.

Is a Type B RCD required? [Transformer less inverter] HANDOUT REQ.


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Documentation for the existing electrical installation Visual check of earthing arrangements Confirmation of suitability of protective equipotential bonding (to incoming gas,

water and other extraneous conductive parts where necessary). This should becompliant with the latest edition of BS 7671 (IEE wiring regulations)

Confirmation of a suitable earth loop impedance for the given earthing system Availability of a spare way in distribution board and that the distribution board can

take any additional load OR a means to provide a dedicated distribution board forthe AC side of the PV circuit.

Suitability of the protective device in accordance with the latest edition of BS 7671 Identification of the district network operator (this will be needed to notify them of

the installation of the PV system)

Mpan number, this is the 13 digit number that identifies that installation to thedistrict network operator (DNO) as is usually most easily obtained from theinstallations electricity bill


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Location for the Inverter and DC isolator if required, as near to the PV modules aspossible, clear area where it can be easily reached and worked on for maintenanceand where it will have good airflow around it to avoid issues with overheating (seemanufacturer's instructions for guidance)

Cable runs to the inverter from the distribution board

Location of AC isolators Identification of restrictions that may be placed on the methods of installation,

such as times when the power cannot be switched off Identification of other hazards (both to the installer and the installation) that may

be present such as asbestos, confined spaces, sharp objects, rodents etc. Internal check of roof construction for structural capability to accept PV array and

internal roof assessment to ensure that the work can be carried out within the roofvoid safely

Any additional cabling or positioning of data processing units and digital displaysthat may be attached to the system


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When considering the external survey we need to look at the availabilityof roof space or area for mounting (if at ground level) and its suitabilityfor a PV system to be mounted. We also need to consider access issuesfor the installation to be completed. As with the internal survey we havelisted below the key points that we think need to be addressed, againthese may need to be added to dependant on any particular site specificissues.

Orientation of roof (SE to SW) or orientation of module mountingsystem when ground of flat roof mounted

An assessment of the structures strength and fixing of the modules tothe existing roof support system must be taken into account. An olderproperty may have a thin roof support system so adding a heavy PV

generator may have a detrimental effect on the whole property.Construction of roof to be able to take additional loads (static & wind)following where available the manufacturer's instructions

Ctd


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Roof type (type of slates so that the appropriate fixing and

flashing kit can be selected) Roof construction so that a suitable number and type of

fixings can be chosen for the frame Angle of roof or mounting frame Any shading that may cover all or part of the proposed

mounting area, this needs to account for the angle of thesun at all times of the year and times of the day as well asany seasonal variances (trees etc)

Access to the area under the roof for the erection ofscaffolding

Suitable areas for the storage of materials andequipment (if required)


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Costs for installing a solar electricity system have come down quite a bit inrecent years with an average system (2.7kWp) costing around 12,000(including VAT at 5%). Solar electricity systems can cost in the region of4,000 to 5,000 per kWp installed, but costs per kWp should reduce assystem size increases.

In general: The more electricity the system can generate, the more it costs but the more

it could save

Solar tiles cost more than conventional panels Panels built into a roof are more expensive than those that sit on top but, if

you need major roof repairs, PV tiles can offset the cost of roof tiles Savings can be considerable - around 1.2 tonnes of CO2 a year. A 2.7 kWp

system can generate around 50% of a household's yearly electricity needs. Ifthe system is eligible to receive the Feed In Tariff it could generate savingsand income of around 1,100 per year.

Maintenance is generally small - you'll need to keep the panels relativelyclean and make sure trees don't begin to overshadow them.


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Feed-in Tariffs (FITs) became available inGreat Britain on 1st April 2010. And isntavailable in Northern Ireland - although thisis under review.

Under this scheme energy suppliers have to(compulsory for big six suppliers) makeregular payments to householders andcommunities who generate their ownelectricity from renewable or low carbonsources such as solar electricity panels(PV) orwind turbines.


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If you are eligible to receive the FIT then you will benefit in 3 ways:

1. a set rate paid by the energy supplier for each unit(or kWh) of electricity you generate. This rate will change each year fornew entrants to the scheme (except for the first 2 years), but once you

join you will continue on the same tariff for 20 years, or 25 years in thecase of solar electricity (PV).

2. - you will receive a further 3p/kWh from your energysupplier for each unit you export back to the electricity grid, that iswhen it isnt used on site. The export rate is the same for alltechnologies.

3. you will be making savings on your electricitybills , because generating electricity to power your appliances means youdont have to buy as much electricity from your energy supplier. Theamount you save will vary depending how much of the electricity you useon site.

Domestic FIT installations are likely to have their export deemed

(estimated) at 50% in most cases until smart meters are rolled out.


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The Department of Energy and Climate Change (DECC)have announced they are bringing forward their review ofFeed-in-Tariffs which will be completed by the end of2011 (originally scheduled for 2012).

The comprehensive FITs review will: Assess all aspects of the scheme including tariff levels,

administration and eligibility of technologies Be completed by the end of the 2011, with tariffs

remaining unchanged until April 2012 (unless the reviewreveals a need for greater urgency)

Fast track consideration of large scale solar projects (over50kW) with a view to making any resulting changes to

tariffs as soon as practical, subject to consultation andParliamentary scrutiny as required by the Energy Act 2008.


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The FITs Order provides for the total cost ofthe FITs scheme to be shared amongelectricity suppliers according to their marketshare (the levelisation process).

We expect that the costs are ultimatelypassed on the electricity consumers. As wellas the payments actually made, these costsinclude qualifying FITs costs (these are thereasonable costs incurred by a supplier as aresult of the FIT scheme, excluding FITpayments).


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The company installs the solar panels on south, south-west or south-east facing roofs The company pays for the installation, connection charges

and the maintenance of the panels The home owner benefits from free electricity from the. Any electricity that is not used is exported into the local

electricity network. Any income associated with this islikely to go to the installation company As the owner of the solar panels, the company receives the

full Feed-in-Tariffs income (approx. 1,000 per year for atypical 2.7kWp system)

These free solar PV offers are also referred to as "rent my

roof space" schemes with the solar panel owner simply'renting' the roof space from the customer.


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Your roof has been specifically designed to take theload generated by the roof tiles and chimney if youhave one. There are two forces that act on your roof.The gravitational pull with the tiles bearing down onstructure and the force of the wind lifting the roofupwards. This means that your roof is supporting the

weight and at the same time preventing anything onthe roof being blown away. When you introduce a new structure to your roof you

need to be sure that it will not compromise theintegrity of your roof. Solar panels are typically fixeddirectly to the roof rafters or the roof battens. Addingsolar panels to your roof could potentially increasethe load by a quarter.


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Typically this increased load will not cause yourroof to collapse but if the panels are too heavyfor the roof it can cause the roof to sag overtime. The other danger is that a strong windcould lift the panels off the roof damaging theroof itself.

It is important that a structural engineer certifiesthat your roof is strong enough for the size ofthe solar array being fitted. It may be that yourroof needs strengthening which can cost up to500 for the work to be professionally done. Thisneeds to be taken into account when consideringbuying your own panels or taking up one of thefree solar panel offers.


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If you are considering installing solar panels on theroof you may be concerned about any damage thepanels may do to the structure of the building. Thereare two forces at work on the roof, gravity pushingdown and wind trying to lift the roof or panels.

The roof is designed to take a normal expected load

such as the weight of the roof tiles and the weight ofequipment and people working on the roof and layersof snow. Prior to panel installation a structural surveywill be done to see if the roof supports needstrengthening. You should not expect any roofdamage due to the solar panels baring any naturaldisasters.

It would be wise to check building insurance, youshould also advise them if panels are installed.


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What do you think is the main disadvantage

of installing a solar panel system ??


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High initial installation capital costSales technique needs to talk about off setting the equity release

from property and the return on their investment.


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When assessing the installation of a PV system, considerations need tobe given to the way in which modules and inverters are stored, handled

and moved. As the module are made up of many different cells whichare joined together under stringent conditions within a factoryenvironment they need to be handled with care to ensure that nodamage occurs to the modules before, or during the installation process.

As with any technology this means simply following manufacturer'sinstructions as to how to store, and handle the modules and invertersbut in the absence of such instructions the following should be

observed: Modules should be stored horizontally The storage area should be clean and dry The modules and inverter should be stored in such a way as to avoid any possible

mechanical damage Sudden variances in temperature and humidity should be avoided especially where

the inverters are concerned Modules are made of glass, therefore handling of them should take into account the

fragility that glass panels have When exposed to daylight the modules will produce a voltage and current, when

handling and connecting the modules care must be taken to minimise the risk ofelectric shock


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When commencing the installation of the system it is important to complete the work in the

safest and most effective way possible. One of the largest hazards, apart from potentiallyworking at height, is the installation of the modules during daylight when they will have anelectrical output. To minimise this risk the following sequence should be applied to eachstring:

1. Secure DC isolator (or inverter where the DC isolator is integral) in place

2. Attach DC cables to the isolator or inverter(where integral)

3. Ensure that no other connections are made to the isolator / inverter, in the case of inverterswhere the isolator is integral do not wire up the AC side until all DC cables have been installedand terminated

4. Run the DC cables to the roof 5. When the first module is installed connect it to one of the cables that have been run from

the DC isolator.

6. As successive modules are installed connect the cables between them

7. When the final module is installed connect it to the other cable from the isolator (as well asits adjacent module)

8. The remaining connections to the DC isolator or AC connections to the inverter can then bemade

If the above sequence is followed then it will ensure that there will not be any live cables, un-terminated, in the building. It will also ensure that connections are not made under load duringthe assembly of the array.


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Roofing is an extremely important factor to considerwhen installing a PV system as an old building havingthin rafters and purlins may not have the desiredstrength to facilitate a full PV array through weightand the natural forces of wind in which the roofstructure will be under. An assessment of the roofing

structure, the age of the building and the capacity forthe building to take the new system is essential.

PV modules have a general weight ofapproximately 15kg each with the added weight of

the fixing structure; this may be too heavy for someinstallations. PV arrays have a life span of 20+ years.If the roofing is in need of replacement in the nearfuture it should be done before the array is installed.


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There are options such as free standingsystems and consoles that can be erectedpretty much anywhere where there issufficient space. We must now consider the

roof structure. Generally there are sevenelements to a roof structure.


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Felting used beneath the battensfor weather and insulation


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Timber strips where the tiles andslates are fixed

Battens


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Near vertical supports for rafters

Strut


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Horizontal beam across the roof atthe eaves


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Horizontal beam along eaves


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Horizontal beam along ridge


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Horizontal roof beam supporting therafters

Purlin


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These components can be seen on the next page and thecondition of all of these must be assessed to ensure theroof integrity and structure can be maintained during andafter the installation, and also that the safety of theinstallers and the householders can be ensured whilst thework is being carried out. If it can be seen that the roofcomponents are in poor repair then advice and guidance

should be sought from a roofing professional via theNational Federation of Roofing Contractors (NFRC).

Where practicable the modules should ideally be no closerthan 500mm to the roof edge and if less than 300mm thenadditional consideration needs to be given to fixingpoints, wind lift and wind noise as well as rain overshootbeyond the guttering.


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Calculate wind pressure using the following

formula

Where: w is the wind pressure in Pascals qp is the peak velocity pressure derived in

steps a-c

cp is the pressure coefficient for theparticular installation


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Apply correction factors for site altitude (h) in meters:

Note: the altitude correction formula for sites over 100mabove sea level calculates a 20% increase for each 100mabove the initial 100m. Hence a site at 180m above sealevel would have a correction factor of 1.16


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Above roof PV array, mounted away from edges in centralzone of roof (Cp uplift = -1.3)

Site located in central London (more than 2km from edgeof town) Site more than 20km from the sea

Building height = 10m Site altitude = 20m Topography = not significant

a) Site in in zone 1 (22 m/s) Table gives value for qp = 763Pab) Altitude correction factor = none

c) Topography correction factor =d) W uplift = 763 x -1.3 = -992Pa (value excludes safety factor)


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Used to firmly hold panels in placeat each end


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Mounting rail


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Roof rail spacer


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Roof tile removed for roof hook

Pilot hole drilling ready for tile hook

Tile hooks MUST be bolted downwith supplied fixings


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Note tile grinded away


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Strings are lengths of arrays wiredin series and parallel.

String 1, 2 & 3.


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An array is simply

the WHOLEcollection of panels.


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An Integrated PV array is one which is built into the fabric of the roofsystem or single tiles which can be installed similar to a traditional rooftiles. It is important with an integrated system that an air gap is provideddue to the heating effect caused by the PV array. Integrated systems alsohave to form a waterproof seal to prevent leakage in to the array or thebuilding


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A non integrated system relies on external mountings to set the

PV array on. This mounting system is usually made up ofhorizontal rails fixed to the roof structure or the rafters beneaththe tiles. Mounting the rails horizontally so they cross manyrafters means that the fixing will distribute the weight and givemore fixing and strengthening options especially in windy areaswhere the wind can create lifting beneath the array so strength isimportant. The rails will normally be fixed via a roof hook.


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When installing the DC cable systems it is important to ensure that the cables arewell secured to avoid them being able to move during their lifetime. Problems

surrounding cable movement can lead to excessive noise in the building due tothe cables knocking on the roof structure (tiles / train slates) and the obviousstrain that this can put onto connections and the cable itself. One of the easiestways to achieve the security of the cables is to use cable ties to tie the cables tothe array frame, if this method is chosen then this MUST be undertaken during theinstallation of each individual module as to undertake this after the moduleinstallation would be a near impossible task.

Where the cabling systems enter the building it must be ensured that thepenetrations are watertight and do not adversely affect the structure of thebuilding. When using roof mounted systems the most common way of enteringthe building is through the tile or slate that the system is installed on, where thisis the case there are a number of proprietary slate adaptors and entry systems tosuit most types of roof structure.

Alternatively you could choose to form your own slate adaptor using one or moresections of lead, however the proprietary slate adaptors are more reliable andshould be used in preference where available. Where the cable entry point isthrough a wall then in addition to the water tightness of the building we also needto consider the structural integrity of the wall and that, after the hole has beendrilled, it won't compress, cut or damage the cabling in any way; for this reasonthe same methods of protecting the cabling system that apply to AC cables shouldbe applied to DC cables, dependant on the wall construction.


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PV tracking systems also work best when youhave a high proportion of direct irradiation whichallows for accurate tracking and the bestpossibility to gain from the tracking system,where diffuse irradiation is most dominant it maywell not be so viable to utilise a tracker.

For the size of systems that we cover within thismanual it is unlikely to be financially beneficial toinstall a tracking system due to the cost andcomplexity that can be involved, it may well bethe case that where the customer is considering a

tracking system there is a case to spend theadditional money on more static modules so longas there is the available space to do so.


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The best angle to fit solar panels is SouthEast facing & at 30 inclination

How do we measure inclination?

We use a measuring tool attached to rafter toobtain angle.

Many different types are available


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Painted end is ALWAYS north.

Smartphone apps dontreplace a compass!


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With all electrical installations there is a requirementby the regulations to inspect and test all newcomponents that make up the installation to verifythat all equipment has been installed and selected inaccordance with BS7671 and the appropriatestandards. The inspection and testing process is to

confirm before energising that there are no unduefaults on the system and the integrity of the electricalinstallation is not compromised.

Inspection and testing must be carried out on boththe AC and DC side can be summarised into thefollowing key points for the DC side, for moredetailed information please refer to BS7671 and theDTI guide to installing PV:


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The inspection process precedes the testing and can be broken down as

follows. A visual inspection of the system and components is required and the

following items should be inspected:- AC wiring and connections AC isolators and junction boxes Full labelling of the AC and DC supplies Earthing and lightening protection Inverter/s DC wiring and connections including PV cabling DC isolators and junction boxes PV modules Overcurrent protective devices Array mounting system (secure and properly weather sealed) Confirm that the modules comply with the international standards IEC

61215 (crystalline modules) or IEC 61646 (thin film modules) Confirm that the inverter has a type test certificate to the requirements

of ER G83/1


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There are a number of tests that need to betaken before the installation can be safely putinto service and these can be broken downinto groups of tests.

Module testing Array Testing

Inverter testing, AC and DC

AC testing

DC testing


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The testing of a PV system should begin during the Installation phase. As each module is

installed it should be tested as this saves time in troubleshooting and the need to dismantlethe array to find a faulty module. Below is a sequence for module testing:-

1. Place the module in constant sunlight and then measure the open circuit voltage on theoutput of the module

2. Remove the module from the sunlight (preferably by covering it). Then short the output ofthe module and then once again place it in sunlight. Use a clamp on dc amp meter to thenmeasure the short circuit current. (Not all clamp on meters will measure DC amps)

3. At the same time the irradiance and temperature should be measured

4. The Isc is then multiplied to (irradiance @ standard test conditions / irradiance measured).

The Voc is then corrected for the temperature change (-0.5% change for each degree ofincrease from 25oC).

These numbers can then be compared to the electrical ratings on the module nameplate to findif the module is operating to its design parameters or is faulty or out of spec.


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A simultaneous reading of the in-plane irradiance, GI, should betaken.

Divide the measured value of Isc by the measured value of thein-plane irradiance and multiply the result by 1000 to normalise

the measured value of Isc to STC radiation (1000 W/m2).

Verify that the normalised short circuit current value agrees withmanufacturer's data for the module.

Switch the DC isolator to the OFF position before removing the

amp clamp and the shorting link. Record the current, voltage andradiation values in a table.


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b. There are two ways to measure the insulation resistance. The first being tomeasure the resistance of the Negative cable to earth and then the Positive cableto earth.

The second is used if there is a possibility of damaging the modules. To do thisthe negative and positive cables are shorted together and then insulationresistance to Earth is measured.

The following table shows the minimum resistance for various system voltages.The test voltage must not exceed the module or cable rating. Test method

System Voltage (Voc stc X 1.25) Test Voltage Minimumimpedance Array Positive and Negative Shorted Together


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3. Polarity Verified by the Voc test and

observing the polarity displayed on the testinstrument

4. Functionality of switchgear Verified byuse of DC isolator


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The inverter tests are to be completed after the array DC and the

AC supply have been connected. Some inverters will have digitalread out monitors built into their units which will show ACvoltage, DC array voltage, AC and DC current, and frequency.

Below is the sequence for energisation of the inverter. Turn on DC isolator (PV array output) Turn on the AC isolator (grid connection)

Check inverter operations (LEDs, status indicators)

Under G83/1 the inverter should be in standby mode for the first3 minutes.

The inverter should have a DC voltage input of approximately80% of the measured PV open circuit voltage indicating the

inverter is tracking the maximum power point (MPP)


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The testing of the AC side of the system mustconform to BS 7671 so each of the followingmust be satisfied as a minimum; the specifics ofeach test are not covered by this course.

1. Continuity of protective conductors 2. Insulation resistance 3. Polarity (live and dead) 4. Earth fault loop impedance (TN systems) or

earth electrode resistance (TT system)

5. Prospective fault current. 6. Functionality of RCDs and switchgear.


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. Depending onthe type, composite and size of the PV module being used, this willdetermine the output voltage and current. A typical 36 cell modulemeasuring 1mtr x 0.5mtr will have a Voc (voltage open circuit) of21.4volts (approx.) and an Isc (short circuit current) of 4.45Amps(approx.)

. We will be required to input the time and date of the

tests as every day can have different characteristics so comparing thetests results can give us an indication of the overall efficiency of thegenerator over a long period of time.

. The temperature of the modules at time of test isrequired as there will be a difference between temperature of themodule on a specific day and the STC (standard test conditions)temperature we use for the calculations. STC temperature is set at 25C.

. STC irradiance levels are set at 1000W/m2(1000 watts per metre square) in the UK. It is very unlikely that theselevels will be achieved or constant in the UK. We measure the irradiancelevels by the use of an IRRADIANCE METER


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Maintenance & fault finding with PV systems is a relatively straight forward

process that can often pivot around any message that may appear in the inverter,however before we detail these we must first consider the risks involved whilstworking on these systems. Often the module will be generating an amount ofpower whilst we are working on them as it is very difficult and it can often bemore dangerous to attempt to isolate the modules before working on them.

The risks that we may encounter are as follows: DC voltages present Working at heights

AC voltage present Generation when not expected (if for example the modules were not showing a

voltage then the sun came out whilst you are working on them)

Confined spaces (roof spaces) Asbestos High ambient temperatures (roof spaces) Working platforms (either external scaffold or within the roof space)

It is vital that you assess any of the above that may apply, or indeed any othersthat may apply that are specific to the site that you are working on, prior toundertaking any work on the system.


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When undertaking maintenance it is important to ensure that the system is

performing, and has the output, that was originally specified (dependant onannual irradiance levels). To enable this, personnel that undertake maintenancemust have access to the PV array test report and the declaration of expectedannual output from the original quotation or documentation.

A basic maintenance check list can be drawn up and used to check the system andshould include as a minimum the following:

Check to see if the customer is aware of any issues Electrical installation periodic inspection report on the AC side as per BS 7671

Verification that the array fixings are still in a suitable condition Verification that any roof penetrations are still watertight Verification of the condition of the DC supply cables Check the inverter data log (where possible) to verify actual output against what

might be expected Module inspection. An inspection should be made for physical damage, the

entrance of water into the module, delamination or any form of degradation of cellconnections.

Array mounting. The mounting system should be inspected for corrosion orweakness. The weather sealing of the roof penetrations must also be checked.


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Solar PV Course