Title: Automatic SPV Array Cleaning System
Field Of The Invention:-
The invention relates primarily to cleaning of Solar Photovoltaic (SPV) arrays, and
to automatic cleaning system for SPV arrays in particular.
Background and Prior Art:-
At present large number of solar systems/installations are installed and are being
installed to meet the energy requirement in villages and remote areas. Such
system/ installation relies on seasonal cleaning of the modules during rains and
is sized at a much higher rating than actual requirement of load. Moreover the
system is often encountered with deep discharge of the solar battery and the
eventuality of the battery getting damaged in the extreme dust conditions as the
modules with dust accumulated on it does not generate energy sufficient to meet
up the load.
Usually in practice, a manual cleaning schedule is recommended for such kind of
installations but the said cleaning procedure is cumbersome or difficult as the
solar modules are installed at the top of the solar installation to avoid shading
effects and thus are not easily reachable to make quick cleaning.
A lot of work has gone into ways of solving this problem. Willard S. Macdonald
has used pressure from air tank for the blowing of dust. This is useful in less

dusty and wet environment. Majumdar, Sims and Wilson have used
electromagnetic field for dust removal on a dust shield, which is again a less
efficient process. Sergey A. Biryukov has used a moving electrostatic conductor.
The life pf such system does not match with the life of the module/array due to
moving components.
The proposed invention is aimed to develop a real time and cost effective
installation and method by cleaning the modules automatically on water spray on
the solar array for a predetermined short time without detaching any module of
array or disturbing the continuous operation of the SPV system once the
integrated and electrically interconnected modules are formed into an array and
mounted.
Solar photovoltaic products/systems as a source of renewable energy are very
popular nowadays in view of their inherent advantage. However, due to high
cost of solar modules, it is not yet affordable by general public. Lot of efforts are
required to increase the efficiency of a SPV Module/system. However, very little
attention has been drawn towards the deteriorated performance of the Solar
Systems in the dusty areas, though it has been reported that if regular cleaning
of modules is performed, then an absolute gain of 10% on an average in
temperate Zone and 20% in tropical zone areas is achievable. It has been

observed in temperate regions that 5-15 % of the SPV output gets reduced due
to the problem of deposition of dust on the modules/systems (refer CEC
published A Guide to PV System). In tropical regions this can go upto 12.38%-
52.54% after storms (refer report dated 09.10.05) by Hamdy K. Elminir and
others of NRIAG Egypt). Automatic cleaning system using pressure from air
within a tank has been made with some success (refer USPTO application no.
11/786,674 by Willard S. Macdonald) on a smaller scale. Another invention for
tackling dust deposition in dry/windy climate through a transparent Self-cleaning
dust shield (refer USPTO application no. 10/253,625 by Majumdar, Sims and
Wilson) uses electromagnetic field on irregular basis only in case of
transmittance being reduced below a threshold level. An apparatus with a
moving electrostatic conductor over the surface using electric field has also been
attempted (refer USPTO application no. 08/905,512 by Sergey A. Biryukov).
However, using water spray a non automatic way of SPV module cleaning by the
way of having the module itself with perforated frame for removal of
snow/volcanic ash has been made (refer Japanese Patent Application no.
19950247810-19950926 by Morioka Nobuyuki). Manual cleaning is quite
cumbersome and at some times not practical also. However, an automatic
system for the cleaning of modules/system through water on daily basis can
alleviate this problem to a great extent.
The present invention seeks to overcome the drawbacks of the prior art.

Summary Of The Invention:-
An automatic cleaning setup for cleaning a SPV array has been developed. The
system works fully in automatic mode. Special nozzles have been designed to
increase the area of cleaning without wasting water and arranged in a way so
that least number of nozzles can clean the entire array. The system works on
220VAC thereby reducing system cost and increase reliability.
Brief description of the accompanying drawinas:-
Fig.1 shows the automatic SPV array cleaning system in accordance with the
invention.
Fig. 2 shows the electrical schematic diagram of the system of Fig. 1.
The invention will now be described in an exemplary embodiment as depicted in
the accompanying drawings. It is however understood that there can be other
embodiments of the invention, all of which are deemed covered by this
description.
Description Of The Invention:-
The invention is being described in an exemplary embodiment, that is suitable
for cleaning the SPV modules of a 1000Wp array of a solar power plant which

has 120VDC output. The modules are of amorphous silicon type. The automatic
cleaning system draws its own power needs from the power generated by the
solar array, the modules of which its cleans. The solar power plant has its own
battery bank.
Fig. 1 shows the various components of the automatic array cleaning system(A).
The SPV array (1.01) of the solar power plant generates solar power which is
stored in battery bank (1.10) through a power conditioning unit (1.09).
The out put of the battery bank is given back to power conditioning unit or
PCU (1.09) for providing 220V ACpower necessary to drive AC pump (1.05). The
main components of the array cleaning systems are:
1. ½ hp 220VAC Pump (1.05)
2. A container/tank to hold water (1.06)
3. Piping network (1.03)
4. Nozzles to spray water over array (not shown)
5. Sensor Module of 2-4W capacity (1.04)
6. 4AH battery (1.08)
7. Automatic control circuit alongwith relays and timer for operation of pump
(1.07)
8. 220VAC input from PCU connected to array
9. Battery bank connected to PCU (1.10).

For carrying out the cleaning of module and/or system automatically, a scheme
has been made (refer figure 2) where a commonly available AC pump (1.05) is
powered through the system for a short duration ~ 1-3 minutes in the morning.
The motor consumes a small amount of power which is about 360W, and is very
rugged as well. The water lifted by the pump is sprayed through a system of
nozzles especially designed for reducing the consumption of water as well as
increasing the area covered by the water spray (1.02).
When photovoltaic solar cells are illuminated, a solar cell acts like a battery,
pushing positive and negative charges to opposite sides. These charges are
collected by conductive films and are available as electrical currents.
A solar array (1.01) is an assembly of one or more solar modules that are
electrically interconnected. A module is generally sealed in a frame or
encapsulating substance by known art , to protect the cells from damaging
effects of dirt, moisture and other environmental hazards. Electrical connections
are provided to pass electrical currents out of the frame or encapsulant. A single
solar module is designed to provide enough potential difference to charge a 12
volt battery. Solar modules when assembled and electrically connected together
in series and parallel to increase the total output voltage and current, form an
array.

But in spite of such protection of the mounted solar cells, the frame or
encapsulant cannot prevent the hazardous atmospheric conditions and the
performance of solar cells gets deteriorated in the extreme dust conditions. The
effect was noticed in other applications also, such as the operating hours in solar
street lights have been very low if regular cleaning was not performed.
According to the invention, an Automatic Cleaning system for solar array has
been developed which improves the performance of the solar system by water
sprinkling through an AC pump (1.05) for a preset time of a timer, by a sensor
circuit on sensing a preset level of voltage of a module (1.04) to run the said
pump. The water is sprayed through a group of nozzles which are designed in a
way to give adequate water spray without wasting water and /or choking on
account of hardness in water.
A small capacity solar module (1.04) is used as a sensor for "dawn condition" on
incidence of sunlight producing power to control operation of loads.
The control circuit (1.07) on sensing a preset level of voltage of the sensor
module (1.04) runs the small AC pump for a time period set by a timer.

The pump (1.05) is connected with the load through a connector via the control
circuit. The pump stops after a predetermined time and the solar power plant
continues to operate its usual connected loads.
The timer can be preset or can be varied from 30 seconds to 5 minutes through
a preset timer located on the control circuit. It has been observed that 120-180
seconds of running of the pump is enough to clean the solar array, but about 60
seconds serves most purposes.
Actual testing of a 70Wp solar module was carried out under clean and dusty
conditions. The results obtained are given in tabular form below.



It can be seen easily from the above table that the cleaning system gives an
improvement of about 20 to 25% in the power generated by a module/ an array.
Fig. 2 shows scheme of the cleaning system, which operates as described below.
Steps of operation for automatic cleaning setup:
1. At dawn, relay R3 starts and remains on till dusk.
2. R3 operates timer which also remains powered till dusk.
3. Timer operates relay R2 for a preset period ranging 0.5- 5.0 minutes.
4. R2 in turn connects neutral to the pump and also operates R1. Thus both
Relays operate the pump for the time it remains on.
5. Pump sprinkles water on the array for cleaning for preset time.
6. The cycle repeats next day and so on.

Working of the automatic cleaning system of SPV array:-
Figures 1&2 represent an automatic cleaning installation of a solar array. In the
morning sensor module (1.04) senses SPV insolation and gives signal for the
control circuit. It also charges a small battery (1.08) for keeping the timing
constant. The timer gets a signal on the control circuit through relay R3 which in
turn starts relay R2. R2 connects neutral of AC supply to pump (1.05) and
operates R1 relay which in turn allows 220VAC input from PCU (1.09) to power
the pump for a predetermined period.
The cleaning operation should be carried out once a day, and in the early
morning, so that nightly dust deposit which forms a thick coating in association
with dew is cleaned. That is why the cleaning is carried out as soon as sensor
module (1.04) senses dawn.
A 220VAC pump (1.05) is installed for spraying of water (1.02) on the array. As
the pump runs only for short time (about 120-180 seconds), it consumes small
amount of power, which is much less than the power generated by the solar
power plant (5000 watt hours per day).
The present invention is applicable to a number of integrated solar photovoltaic
arrays and can be used optimisingly to an array.

We Claim:-
1. An automatic SPV array cleaning system (A) comprising of:
- an SPV array (1.01) connected to a battery bank (1.10) through power
conditioning unit (1.09),
-a sensor module (1.04) which charges a battery (1.08) through automatic
control circuit (1.07) and feeds signal to automatic control circuit (1.07), and
- an AC pump (1.05) which pumps water stored in water tank (1.06) through
water pipes (1.03) to create water spray (1.02),
characterized in that the automatic control circuit energizes the water pump
(1.05) for a preset time period once everyday, to clean the SPV array by the
water spray (1.02).
2. The automatic SPV array cleaning system as claimed in claim 1, wherein the
water spray (1.02) is created only after the sensor module (1.04) senses
incidence of sunlight or dawn condition every day.
3. The automatic SPV array cleaning system as claimed in claim 1, wherein the
pump (1.05) is operated between 120-180 seconds, preferably for 60 seconds.

4. The automatic SPV array cleaning system as claimed in claim 1, wherein the
electric power required for cleaning the SPV array (1.01) is given from the
battery bank (1.10) through the PCU (1.09), and wherein the said battery bank is
charged by the said SPV array through the said PCU.
5. The automatic SPV array cleaning system as claimed in claims 1 and 3,
wherein the drawn condition is determined by a pre-set voltage generated by the
sensor module (1.04) upon incidence of sunlight on the sensor module.
6. The automatic SPV array cleaning system as claimed in claim 1, which results
in 20 to 25%, improvement in the power generated by the SPV array.

An automatic SPV array cleaning system (A) which comprises of an SPV array (1.01) connected to a battery bank (1.10) through power conditioning unit (1.09),a sensor module (1.04) which charges a battery (1.08) through automatic control circuit (1.07) and feeds signal to automatic control circuit (1.07), and an AC pump (1.05) which pumps water stored in water tank (1.06) through water pipes (1.03) to create water spray (1.02). The automatic control circuit energizes the water pump (1.05) for a preset time
period once everyday, to clean the SPV array by the water spray (1.02).