The Effect of Soiling on PV Performance Webinar

welcome you to this afternoon's session

of the effect of soiling on pv

performance please bear with me because

this is the second time only that I've

delivered this this content so I'm sure

still trying to get the delivery correct

my name is Michael middlemist I am the

category manager for renewables here at

the sea wood group I operate out of our

office here in Tampa Florida but our our

main headquarters and manufacturing

plant is in the northeast of England my

role is to oversee our renewable testing

range so I look after our solar testers

and I travel to sites around the US and

around the world training on our

products and also getting feedback from

the community the solar community on how

we can improve our offering including

our instruments and our our software

package now recently something that

really came to my attention on a site

out in California was soiling and the

panels were really badly soiled so this

kind of inspired me to create this

presentation that I'm gonna give to you

today about soiling we're gonna cover

what it is how it happens where it

happens what we can do to fix it and how

we can prove to the user of the PVC so

the owner of the plant how we can how we

can prove that the soiling is really

causing a loss of generation and in turn

a loss of return on their investment so

before we get started I must just read

out this brief disclaimer to you ok so

basically this presentation is not to be

considered any replacements for any of

the standards that I reference reference

figures are correct at the time of this

presentation for any clarification

please contact me or a representative

representative see would we don't accept

any responsibility for any of the

information we give here that is used in

error and no part of this presentation

shall be deemed a form of contract or of

training and please do refer back to me

for any queries persons performing any

electrical tests I must be fully

competent to do so and the safety of our

operators is the absolute paramount

subject we should be we should be

looking at your safety is paramount ok

so in this presentation I'm going to be

describing PV testing we're going to be

connecting the PV systems I'm going to

show you examples of that so please do

be careful and one of the things we do

need to cover when you are in the field

is your personal protection equipment ok

so do be very aware of what you're

connecting to

we need rubber insulated gloves it's

your first line of defense use leather

gloves also PV systems can operate up to

a thousand volts 1500 volts so our flash

is a real concern and unfortunately not

all PV systems are clearly labeled and

that means you might not be aware of

what you're connecting to so perform an

on-site evaluation before you connect

the unit ok so now that's the health and

safety kind of stuff out of the way

what exactly is soiling ok what what is

soiling we say this word soiling and we

need to really narrow down what that

covers because it does cover a broad

spectrum of things so the term soiling

is used to describe an accumulation of

snow of dust of dirt of leaves and bird

droppings on PV panels so that's what we

call soiling ok now the performance of a

PV module decreases by surface soiling

and the PV power loss increases with an

increase in the quantity of soiling on

the PV panel so in real terms all that

means is if you have a little bit of

dust you have a little bit of loss

if you have a lot of dust you have a lot

of loss so it scales up

okay so soiling is a big issue and I

don't think the end user okay maybe the

homeowner the business owner of the

plant owner they don't realize how bad

it is okay and we need to quantify that

for them so that's what we're going to

talk about today

what is soiling and how do we prove it

to that end user well I have a nice

little phrase here which hopefully could

help us okay soiling equals shading

which equals power loss okay and one

thing I did not own here which I

probably should have power loss equals

loss of cash okay so that's where it's

going to affect you the most in whatever

kind of system you have installed for

instance if you're a utility scale

installer and your panels are soiled

you're not going to be able to output it

enough power and therefore you will

bring down the R or Y similar for a

residential kleiner definitely for a PPA

a power purchase agreement okay when we

have that on a commercial building or

utility scale we need to guarantee power

output and if we can't do that well then

we're not going to be able to to honor

the the power purchase agreement that

we've made so soiling equal shading

which equals power loss soiling also

does a couple of other things which

we're going to cover a little bit

further on in the presentation so as I

mentioned in the previous slide that

soiling differs okay so it's very rare

that we immediately get one hundred

percent 80% soiling on the panels so it

accumulates the dust buildup and

aggregates over time okay and dust

layers so the layer of dust on the

panels could vary depending on your

environment in your location and does

can be generated by many sources so

obviously when traffic cattle maybe even

volcanic fallout which is not you know

entirely common but it does happen but

the purpose of this slide is if dose

gets worse over time then we need to

schedule our maintenance

to prevent that does that soil a over

that time period okay so when we first

install the panel's perhaps there will

be no soiling okay a month later there

will be two months later there will be

even more so we need to plan in our

schedule of cleaning maintenance in line

with the environment that you're dealing

with so if you have if you're in an area

where you have a lot of dust okay a lot

of sand

perhaps you're in the Middle East you're

in a very hot country perhaps you're in

the Mojave Desert in California or

you're somewhere in the middle of

Hyderabad or Buda Pradesh in India all

very hot dusty locations we should be

very very careful and we should monitor

that does and what kind of time scale we

think that it's going to increase with

okay but not only environmentally but

kind of where we are in position to

other things around us so if we're very

much near a highway okay and the plant

is right there we could have pollution

that is affecting in causing soil a onto

the panel's themselves so be very

conscious of where you are this picture

on the right-hand side that you can see

of the presentation this actually was

just north of Fresno in California and

this was again we're in the middle of

the desert here and this client in

particular was having issues with his

instrument his solar see with solar

instruments and he was telling me

Michael your instrument is not giving me

accurate results I should be getting

this from these panels but it keeps

showing me that I'm getting less output

your instrument is wrong so we had a lot

of backwards and forwards and we got the

instrument here too in Florida to test

we recalibrated it we did everything the

client asked we sent it back out still

he was getting the same results and he

wasn't happy so what I did was I

traveled out to the site and I could see

straight away the problem was soiling so

you can see in the bottom left hand

corner I rubbed the panel and

immediately

he was admitting that it was to soiling

that was causing the problem but how do

I prove that to him okay how do I prove

it well I have a method to prove how

soiling is affecting output a little bit

later on in the presentation for now

just getting back to the location and

how we could understand how dust and

soiling gets worse over time there are

some resources available to us okay so

this article online at ScienceDirect

comm is a great article all about

soiling and here we have the cause of

dust accumulation now we're not going to

go through all of this but you can see

the environmental factors the dust type

the location and installation factors

okay and we can kind of determine what

is going to be affecting our plant and

as such we can maybe plan in a little

bit better what our maintenance and

cleaning schedule should be similarly we

can look at dust intensity around the

globe with this dust intensity map now

this is measuring the micron layer of

dust and it gives us an average for each

area so the darker the zone here on this

map the the worse the dust and the

soiling will be so here if we look at at

North Africa we can see that we have

force it's very dark ok so we've got we

got very high intensity of dust there

similarly in Argentina Chile we're in a

three parts of Mongolia

but we can also see areas that are quite

misleading because number two is the

United States and it said the dust

intensity is quite low but then we have

to localize that to maybe California

okay and then if we look at Greenland

Iceland these are going a very low for

dust but they will be high for snow

coverage okay so what I would like you

to do is when you're considering this in

your own M plans really consider where

you are and it shouldn't be uniform

across all your projects that's my kind

of

point here if you do a project in

California it's not going to be same as

a project in Minnesota so we need to

localize our maintenance schedules the

image here on the right this isn't one

of mine I picked this up from some one

of the community members on LinkedIn and

you can see just how severe the dust

layer can get in a zone for it really is

very pronounced and it's going to cause

us some very big problems moving forward

so the takeaway from this is okay

consider your location both on a global

scale

with regard to dust intensity but also

on a local scale with regard to what's

around you okay are you in a desert are

you in a temperate climate where are you

situated I in the world so I mentioned

that soiling does cause shading but it

doesn't just cause Shay ok soiling

causes us some other problems so take a

look at this you can see that the

soiling is causing a hot spot so we can

see this with any old thermal camera you

don't need a very expensive IR or

thermal imaging camera to to get this

sort of picture but a thin layer and

you've probably seen this as PV Free

Press

professionals has accumulated on the

bottom row of cells of the panels ok and

at first glance you may think well

that's probably not going to cause any

problems it's it's only a little bit of

the panel but what happens is the

current can't flow properly in the panel

and we get increased resistance which is

then dissipated as in thermal energies

as heat so that's essentially those

glowing yellow spots are is power loss

ok so we're not only losing it because

of shading but also because the soil is

causing hot spots now the shading is

lowering the amount of irradiance that

hits the panel and the hot spot is

bringing down the voltage because

voltage is directly affected by cell

temperature so it's a double whammy now

if this was

across an entire table can you imagine

if we had a very large hundred 200

megawatt plant even a small plant if we

multiply up that hot spot across the

whole field we're losing a heck of a lot

of generation now this could be caused

by rain hitting the ground splashing up

onto the panels it could be that there's

been vehicles driven down the middle of

the table which is splashing up and

covering the panel's it could be that we

had dirty rain whatever it may be we

need to find a way to overcome it so the

thing I noticed about this picture is

the panels are very low to the ground

okay so if we lifted the Bob I got some

clearance for the ground we wouldn't

have that splash up so maybe that's a

solution I'm looking at this second

picture so I mentioned soiling isn't

just dust and dirt right it's also bird

droppings leaves etc so you can see the

impact that this bird dropping has on

this panel this is one small bird

dropping okay and imagine that again

scaled up across one hundred to two

megawatts no matter what the size we

have to scale up this problem so you can

see that not only is dust intensities

snow whatever it may be causing shading

but also we're getting quite severe hot

spots on the plant so soiling causes

shading and hot spots which means power

loss which means money lost so soiling

equals lost money but again how do we

prove this to a layman how do we prove

this to the client okay I could show

them this picture and your old PV

professionals here and you can probably

see straight away well that that's not

good

but what does that actually mean to the

end-user to the homeowner mr. Smith miss

mrs. Smith how do we prove it to them

what we're going to cover that shortly

but first we need a solution to that

soiling problem okay so I'm going to go

on to how we prove it but first I want

to tell you what the solution is so

we're going to work a little bit

backwards the solution

is cleaning very simple if something's

dirty you should clean it so we have

many tools available there are a lot of

innovations in this sector there are

automatic robots that are doing cleaning

further - the feedback from the first

presentation I give this morning there

is also a vacuum units available so if

you're in the middle of the desert and

you can't get any water ok

then of course vacuuming off the dust

would be a better consideration also and

in California where I do a lot of work

there's loss there are a lot of areas

that have water shortages ok

so again that means that vacuuming or

another method might be a good solution

for you now I have prepared just a small

video of some cleaning happening in the

Middle East so when I try to do this

this morning the video didn't actually

work so I'm going to try again so

forgive me if I go off if the audio goes

off for a second please bear with me I

will be back with you in a second so I'm

going to try and get this video to run

here ok so hopefully this runs

I'm not sure this is working if the

video doesn't work I don't know if you

can see the the pictures here but

basically the we have a JCB big tractor

with a cleaning brush and what we found

was as the brush was sweeping across the

panel's the dust is just thrown up in

the air and that's really just moving

the problem to another part of the site

and when you have a 260 watt megawatt

plant to take care of and this is the

Mohammed Alban rock tomb solar farm in

Dubai then it's a real issue

I'm really sorry folks it looks like the

video again isn't working so we will

we'll have to give that one a Miss but I

will send out the link it's on our

YouTube channel so I do apologize for

that

ok so getting back to our presentation

and I really will have to get those

videos to start working so to get a

cleaning contract we first got to

convince people ok so how do we convince

people to to do that how do we convince

them to sign us up to doing some

cleaning well using our range of testing

tools what we can do is we can test

prior to your first cleaning session ok

clean the panel's thoroughly with the

appropriate method for the location and

then we can test when they're clean and

what that will do is that will give us

an exact an exact real direct result of

performance increase because we can take

voltage we can take short-circuit

current we could run an IV curve trace

and we can compare the two so you can

sure your clients directly the

difference there and then you don't have

to wait for a report for instance if

this was a residential project you could

invite mr. and mrs. Smith out and say

listen your panels are really dirty look

when I test them this is what I get but

if I was to clean them there

is what you can get so using a handheld

test tool like the c-word pv 210 or 200

we can prove that in real terms for the

client so what I prepared for us today

is actually a little case study around

this an example in the field if you will

so in order for us to convince the plant

owner to clean their modules and show

our expected values ok sorry we need to

show them our expected values versus our

measured values ok so what I'm saying is

here when I look at these solar panels

this is what they should be outputting

okay but this is what they're actually

outputting using my test device so we

could do that for string voltage so as a

quick example if we have a 40 volt panel

and we have 10 panels in series we

should see 400 volts okay not taking

into account the temperature coefficient

for string current at a thousand watts

per meter squared if we have 9 amps then

if 500 watts per meter squared

we should have 4.5 amps using the

irradiance factor so very quickly we can

tell just from voltage and short circuit

current what the output should be so

this is the case study and the example

of where I was ok so this is in Clovis

California in Fresno and standard test

conditions as you probably all know are

1,000 watts per meter squared 25 degrees

Celsius and the standard test conditions

value for these panels that we were

going to test was thirty seven point

four VDC and ISC was 9 amps ABC so

that's what we should have been seeing

because the average irradiance in that

area on that day was round about 900 900

to a thousand watts per meter squared ok

and you can notice in the top right hand

corner there is a good picture there of

when we went up on the roof there was

actually a ground fault on this system

as well which we managed

to detect with the c-word PV to Ted but

you can see that handprint on the panel

okay so that's how badly shaded by

soiling these panels were that you could

put your hand on and you could quite see

clearly see it was very blue underneath

now again I have another video here of

me actually performing the tests in the

field again it didn't work this morning

and the last video didn't work but we're

gonna try again yeah we're going to try

these things so if you bear with me one

second we'll see if we can make this

video available for you and no it looks

like I'm sorry it looks like that video

was also failure to launch so what we'll

do is we'll head into the values which

we extrapolated rather than the video so

using the the formula that we've we

talked about on the previous slide we

calculated that under this temperature

and this irradiance we should see 37.4

volts v OC and we should see 8.1 amps

short-circuit current that's what we

should have seen using the pv 202 tang

rather device which should give us

around about 336 Watts approximately

estimate so when we actually tested the

panel which you can see is incredibly

soiled we actually came out with 33

volts okay and we measured 5.6 for is C

so we've lost nearly 4 apps ok we've had

a 30 percent loss in current and all in

all that we kind of estimated that as

the client was looting losing 44 percent

of their generation okay so with the pv

150 or the pv 200 or 210 we can

demonstrate to the client how much

they're losing in real terms there and

then here you go you got this I cleaned

it test you've got this

you can show the client in real terms

using a very professional device what

their losses were so we will send to you

the videos which I've tried to get going

as I say the first one was the module

cleaning in the desert the second was

this image of me here is the video of

this doing the test and you can see it

in real-time for yourself but there is a

problem here what if we can't clean the

panel's what should we do so here is a

scenario for you you have a plant that

you need to Commission okay and the plan

has been installed for a couple of

months you were just waiting for a

connection and over those months the

dust and dirt is accumulated on the

panels all for instance you're going

back to a job site that you need to do a

performance verification on you may not

have access to clean those panels

machines are very expensive there could

be water shortages you may not have the

personnel they may not be the budget so

you might not be able to clean all of

the panels in the site so what can we do

to make sure that the results we get

using our see what instrument are

accurate like this gentleman I mentioned

earlier who had the problem and said

that his see what instrument working

correctly

he couldn't clean his plant so what we

have to do is work out what our soiling

factor is okay what offset from STC

values should we use okay for this plant

so what we do is we remove a single

panel we don't need all of them okay

we're going to extrapolate up and this

is a very soil panel and what I want to

do is measure that panel while it's

soiled okay and make sure it's in the

same inclination as the rest of the

array

sometimes Tofana on a tracker I

appreciate so we have then the results

we have the dirty results so clean off

that single panel okay and then measure

the clean panel okay and then using

those clean results in the dirt

for a single panel we can then figure

out what the percentage difference is

and we can use that as a soiling factor

for the entire plant okay

so I'm not saying get two data sets here

I mean maybe spend a day in half a day

testing a variety of panels across the

site using this method that we can

aggregate the results but if you can't

clean all of them at least clean one and

figure out what you're soiling factors

should be and how much you should offset

from V or C there are a couple of other

things we need to incorporate the IEC

standard recommends that we should

incorporate 0.5 percent natural

degradation for every year the system

has been installed lig sorting there are

a couple of other things but really

soiling I found in most cases is the

biggest drain from the from the system

so what can we use to test well I've

mentioned throughout the presentation

the c-word PB 210 so this will give us

voltage is see continuity of earth we

will get insulation resistance and also

a curve trace the PB 150 is really a

workhorse unit it'll do everything apart

from the the curve tracing and it's more

cost effective and then the sole utility

Pro is really our larger unit so it's at

1500 volts 40 amps okay so you can test

multiple strings in parallel with that

instrument and you can test 1500 volt

sites so with these units and these

instruments and the the backing of us

here at C wit you can prove to your

clients that there is an issue with

soiling on their plant so what I would

like to do now is I I'm quite active on

on LinkedIn I like talking with other

members of the solar community and I

asked them three questions and the first

question was do you factor cleaning into

your OEM schedule are your clients aware

of production loss due to soiling and do

you clean panels prior

to testing or do you add in that soiling

factor after the fact okay so these very

three three questions about how

operators are currently dealing with

with with soiling and you can see from

this image on the right hand side that

was the home that had forty three

percent reduction in power output due to

soiling

okay you can see how bad that looks so

first of all we had a comment from from

Brian and clean your solar clean your

solar or a great company based out in

California I believe who were doing

cleaning and an installation work he

says Michael production loss will vary

by region and other factors as we

discussed earlier here in Southern

California the soiling factor can be

higher in areas that are dry and dusty

not to mention other factors bird

droppings tree sap pollen etc the

problem that Brian saw in the O&M side

of the residential installations is that

he feels that window cleaners okay not

electricians but window cleaners

recommend that people get their solar

cleaned every three months brian says

that unless the soiling is that bad he

thinks that's overkill so again this is

what I mentioned earlier Brian is

confirming that we need to localize what

our O&M and cleaning schedule should be

he also goes on to talk about commercial

systems where PPA is very much a bigger

factor and so we need more

considerations and more cleaning we then

got some comments from John Nessler he's

the CEO of psi da they they work in the

solar and the wind and power storage

industry

his answer to the first question was he

always cleans the panel's prior to

testing which is good practice he

factors in the cleaning cost of onm and

rigid to try to reduce the frequency of

cleaning and he really talks about it

openly with his customers so I think

John there those are the three perfect

answers we should

do we should really give sorry to those

questions

be honest clean prior to testing and

factor in the cost of cleaning whenever

we can I also got a comment from a

friend of mine Aaron iron is the CEO of

bonds I saw that great company they do

drone inspections he also has some good

innovative products in the work it's

really he's had an underserved area of

the OEM space and where water

availability water availability isn't an

issue it really is a problem and he says

design really plaid design is where we

should be compensating for the soiling

remember in the beginning I suggested

that we raise the table rather than have

water splash onto the panels so it's a

great great comment there by Aaron and

you can of course get drone inspections

in the RGB spectrum to point out

specific areas of shady and then you

could send someone directly to that

point with the instrument Haley the

managing director of solar panel

cleaning services is actually based in

the United Kingdom and he comes across

this a lot now the main point here that

Haley raised is that panels are left for

long periods of time without cleaning

occurring and what happens is the

modules become permanently stained okay

so if you're leaving the the soiling on

the panels for a long period of time it

could actually affect your warranty

because you haven't taken care of them

and for larger commercial systems he

says we should definitely put it into

our cleaning costs and also the

equipment hire forgetting to those sites

not just the labor cost etc so um today

we've covered what soiling is how to

think about how it affects us in our

particular area and where we're

installing we then looked at our

expected and our measured values and

what they can show us in terms of

generation loss we then looked at a case

study Eric

California which was very dusty I also

tried to show you a couple of videos

which didn't work but never mind

and I also introduced you to the C word

range of test tools which is available

globally in the United States in Europe

in Asia Africa Australasia really

everywhere Southern America everywhere

our units are available so I'd like to

open up the floor now to any questions

you may have if you don't have any

questions that's absolutely fine as well

you can contact me at Michael M at C

would calm that's Michael M at C would

calm please do get in touch with any

questions I'm more than happy to to take

follow-up questions you can also link up

with me on LinkedIn if that's somewhere

that you're active I post up interesting

so things there are presentations on

their past webinars you can access and

also you can ask questions and get

involved in the discussion because quite

often we will have nice group talks

going from from a post I asked for

comments and questions to be asked so

does it look like any questions are

coming through right now which is a

little bit different to this morning

which we had we had a lot of questions

coming through so it just leaves me to

thank those people that joined today

thank you

Claudio Thank You densa how you doing

there mate I hope you do well thank you

dr. Robinson Elizabeth the Erik George

Jonathan Joshua Keaton Christopher

marina Michael Sinjin Simon sauna and

and everyone else that is joined oh we

do have a couple of questions here how

to calculate sewing losses before the

installation of the rooftop projects

various installations okay keep them

that's a very good question really we

can't okay we can take a best guess so

what I would suggest is take an

aggregate of the all of the

installations in the similar area of

so maybe we could have a data-based of

soiling okay or maybe we could install

the system and then monitor it for the

client for a couple of months so that's

something you could put in the package

in your proposal you know one of the

lines could be this price includes

soiling protection for three months and

where you'll go and monitor their system

frequently to see how much it effects

but it is really quite difficult but you

can get a larger view of it by saying

okay I'm in the middle of the desert I'm

gonna have a lot of soiling or okay I'm

in the build-up residential area there's

concrete everywhere there's not going to

be as much dust so so you can kind of

get a feel for where where sonic should

be thank you denser for your for your

cracker for your for your thanks and

comments I think I don't see any more

questions coming through so I'd like to

thank everyone for your attendance today

the slides will be sent out and

eventually we're going to get a

recording on YouTube as well so if you

have any questions contact me Michael M

at sea would calm that's Michael m at

sea would calm and do be aware we have

distributors everywhere these are

available worldwide so I can put you in

touch with your local distributor or

indeed if you're in the United States

you could come to us here we include

online training with every purchase so

we can tell you how to use it when to

use it what to use it for we cover IV

curve tracing so on M techniques we do

cover a lot with our free training

that's included with the instrument so

again no questions there so thank you

very much for your time this afternoon I

hope you have a great weekend wherever

you are and see you again on the next

one thank you