Battery bank design for 1KW solar stand alone system at Barmer (Rajasthan)

Battery bank design for 1KW solar stand alone system at Barmer(Rajasthan)

The stand alone solar system works only in day, generally from 9.00 to 3.00 hours solar time. Rest of time it generates negligible energy to suit owner requirements. So for other times some storage device essential for running lights, fans, motors, freeze, etc.

Battery is a electric storage device. It sores electricity in the form of chemical energy. Generally there are two types of batteries, first is automobile battery or thin plate battery and other is deep cycle battery or thick plate battery. For our application in solar system deep cycle battery is used.  We can use 80%  of its capacity.

Example:  A 48Volt DC has an AC loads of 6 tube lights 40watts, 5 fans60watts, freeze, water pump etc.

(A)Average daily energy (Wh)

1.   (No. of tube lightsxwattsxNo. of hoursxno.of days /week)/7days/week

(6x40x5x7)/7-Wh

1200Wh

In this way calculate Wh for fans, freeze, motors etc. Suppose total  it came 4600Wh, than add extra 20% . Now it became (4600+20%x4600) 5520Wh.

2.   The  other method is electric bill, if you have electric connection. See how much unit you have consumed per month. Take average of all months and calculate per day electric consumption . Wh. Suppose it came 5500Wh.

(B) If there is cloudy days, the solar energy will not be available that day. So we keep the reserve energy for three days autonomy. Now the battery bank is designed for:

 (Average daily consumption)x3

=5520x3

=16560Wh

=16.560KWh

The battery capacity is denoted by AH, so divide 16560Wh by 48Volt

=16560/48 Ah

=345Ah

This 345Ah is usable capacity of battery, It is only 80% of battery bank capacity. So total capacity of battery is :

=345/0.8

=431.25Ah

Temperature correction:

The battery is designed to operate at room temperature 25°C. Below this temperature the effective capacity decreases as rate of chemical reaction slow down. So the storage capacity must be corrected upward for condition of use. In winter the room temperature go down to 10°C. The effective capacity reduced to 1%/°C below 25°C. Thus the differential is (25-10=15°C).Thus the 15% capacity reduced. Our battery capacity 431.25Ah is corrected to

=431.25/0.85

=507Ah

So we shall use 500Ah at a discharge rate C/20, placing it at room temperature 25°C.

Take 24 cells of two volts and 500Ah to connect in series to make battery bank 48Volt, 500Ah. The other combinations are eight six volt and 500Ah, Four 12Volts and 500Ah, connected in series. Donot use more than two parallel connections.

   Effect of discharge rate  

As the discharge rate increases the capacity decreases and vice versa. For example Surrette S460 has a capacity of 360Ah at C/24. Meaning the 15A load discharges in 24 hours. (100% discharge). If discharge rate C/100 than capacity increases 466Ah, as there is more time to active material for participating in chemical reaction. If the discharge rate increases to C/4, than less time is available to active material for participating chemical reaction. The battery capacity reduced

Solar Dish Cookers for sale

Solar Dish Cookers- For Sale 

Rate Rs. 7000.00 only for SK-14  Solar cooker

Solar dish concentrator concentrates radiations of sun on receiver / cooking pot through all the day from 9 a.m. to 6 p.m. It tracks the radiations of sun manually. Parabolic dish consists of set of high reflective Aluminum Sheets. Normally, dish cookers has an area 1m^2, 1.4 m^2, 3 m^2 or of 4 m^2 of elliptical or parabolid shape.

1. SK 10 Dish Cooker: Cooking capacity for 5 to 8 person (3 liters)

2. SK 14 Dish Cooker: Cooking capacity for 8 to 12 people (5 liters) 

3. SK 30 Dish Cooker: Cooking capacity for up to 40 people (25 liters)

4. SK 40 Dish Cooker: Cooking capacity for 50 people (35 liters)

Applications in Rural Families who use traditional Mud Stoves, uses Fire-wood, Cow-dung and Crop residue etc. Residential schools, mid-day meal program, Military & Defense teams deployed in remote and urban areas, Small Canteen facilities to Employees, and many more Catering up to 50 persons daily.

(ii)  Dish Type Cookers

It is useful for joint families, small establishments etc. catering to about 15 persons at a time. The cooker can be easily assembled and dismantled and can also be packed and transported easily. The cooker is user-friendly as the place of the vessel to be kept for cooking is at a level convenient for people to use.

Configuration

It is a concentrating type parabolic dish cooker with aperture of 1.4 m diameter and focal length 0.28 m. The reflecting material used is anodized aluminium sheet with a reflectivity of over 75 %. The parabolic dish is made of reflecting sheets supported on suitable rings for holding them in fixed position. The sheets are joined together in such a way as to form a parabolic shape. The structure and frame of the bowl should be strong so that the reflectors do not get deformed while turning in various directions. The reflector stand is made of mild steel with powder coating.

Manual tracking arrangement is provided and adjustments may be made once in 15 to 20 minutes at the time of cooking. The stand is designed in such a way that the reflector could rotate 360° around horizontal axis passing through the focus and centre of gravity. It will also rotate around the vertical axis so as to turn the reflector in the direction of the sun.

Working Principle

The cooking vessel is placed at central point where all the sun’s rays are concentrated through the reflecting sheets to deliver energy equivalent of 0.6 kW to boil 2 – 3 litres of water in ½ hour. The temperature achieved at the bottom of the vessel is about 350°C to 400°C sufficient for roasting, frying and boiling. The cooker has a thermal efficiency of about 40 % and can be used on clear sunny days from one hour after sun rise to one hour before sun set.

Potential for use 

·         Cooking for individual house holds

·         Small catering establishments like dhabas, tea shops etc.

·         Small size canteens in industries.

·         Remote locations.

Economics  (Tentative)

Payback period is  2 years  against a life period of 10 years.

Principles of electric generation by solar cell

Introduction: Solar energy is god gift to human beings. Daily trillions KWh of energy falls on earth. The solar energy is in the form of different sizes of solar radiations. Among these are 7% ultraviolet (200nm – 380nm- Neno meter means 10^-9M), 47% visible wavelengths (380nm – 780nm) & 46% infrared (780nm – 5000nm). The average irradiation falls on the outside of earths’ atmosphere is 1367 watts/M^2. About 25% energy is absorbed or scattered by ozone, water vapors, dry air, upper & lower dust and rest of extraterrestrial direct normal irradiation  1000watts/M^2 reaches to earth surface.

The India is getting good share of it due to its position on the earth. The Barmer a western district of Rajasthan the state of India is receiving solar energy 6-6.5 KWh/M^2/day (Killo-watt hour per meter square per day). There are two processes to generate electricity . One is solar thermal and other is photovoltaic. Our discussion is towards electric generation by photovoltaic.

The solar radiation also called “PHOTON”. The meaning of PHOTO is “produced by light” and VOLTAIC is “electricity produced by chemical reaction”. Thus a photovoltaic cell means a device which produces electricity by light. The device by which electricity is produced is called solar photovoltaic cell.

Solar cell: Solar cell is made of 0.9999% pure silicon doped boron & phosphorus. Silicon has 4 electrons in its outer bond.  Boron has three electrons in his outer bond so there is vacancy for one electron , so it is positive & phosphorous has 5  electrons in outer bond so it is has extra electron , it is negative. Thus constituted silicon with boron & phosphorous is  P-N junction diode and  is called solar cell.  The movement of free electron are  always from p side to N side of P-N junction diode even in night also.

Types of Solar cells:

There are two types of solar cells generally used one is Crystalline and second is thin film.  Further Crystalline solar cell is divided as mono crystalline and poly crystalline depends upon their manufacturing processes. The mono crystalline cell has 13.5% to 15% efficiency, where poly crystalline has 0.5% less efficiency to mono crystalline. The poly crystalline is cheaper than mono crystalline solar cell. The amorphous is thin film solar cell, but it has 6 % to 7% efficiency. So space required for thin film solar cell is double the space required for crystalline solar cell for same power output. In my opinion always use poly crystalline solar cell.

Principles of electricity generation: Keep the ‘N’ side of solar cell parallel to sun so that sun rays fall perpendicular to surface of cell. The sun rays constituted of photons falls on the cell. Sum photons reflected back, sum passes through cell and some are absorbed for generation of electricity. The photons dislodge the electrons from ‘N’  surface  (CONTINUE)