Batteries role in stable energy supply and their storage

Balancing power supply and demand is always a complex process. When large volumes of renewables such as solar PV, wind and tidal energy, which can change abruptly with weather conditions, are integrated into the grid, this balancing process becomes even more difficult.

Energy storage can be a valuable resource for the power system in maximising the efficient use of this resource, and add flexibility for electric utilities. Effective energy storage can match total generation to total load precisely on a second by second basis. It can load-follow, adjusting to changes in wind and solar input over short or long time spans, as well as compensating for longterm changes. While fossil plants may take 10 minutes or more to come online, and will consume fuel even on "spinning reserve" standby, storing renewable energy for later use effectively produces no emissions.
 If you have some terrain resp. altitude difference and some water in the vicinity of the generation facility and cheap labor you will be better off pumping water to a reservoir for energy storage. Pump storage is not particularly efficient unless you are talking about MWs.
Ultracapacitors (or supercapacitors) store energy electrostatically by polarising an electrolyte, rather than storing it chemically as in a battery. Ultracapacitors have a lower energy density but a higher power density than standard batteries: they store less energy (around 25 times less than a similarly sized li-ion battery) but can be charged and discharged more rapidly. Although ultracapacitors have been around since the 1960s, they are relatively expensive and only recently began being manufactured in sufficient quantities to become cost-competitive. Ultracapacitors have applications in 'energy smoothing', momentary-load devices, vehicle energy storage, and smaller applications like home solar energy systems where extremely fast charging is a valuable feature.

Batteries have their uses. They are relatively inexpensive, relatively easy to maintain, but if your requirement is a constant load such as database centers or factories, then batteries are not valid UPS sources. If you only need occasional power, then batteries are ok.

Invented in 1859, lead-acid batteries use a liquid electrolyte and are still in common use. They store rather small volumes of energy but are reliable and, above all, cheap. In renewable energy systems multiple deep-cycle lead-acid (DCLA) batteries, which provide a steady current over a long time period, are connected together to form a battery bank.

Several types of batteries are used for large-scale energy storage. All consist of electrochemical cells though no single cell type is suitable for all applications.
In a dry cell battery, the electrolytes are contained in a low-moisture paste. Lithium-ion (li-ion) batteries in particular are the subject of much interest as they have a high energy density, and larger-scale production due to emerging electric vehicle applications is expected to bring down their cost significantly.

Lead acid is the old standby with a proven track record though and is the most used option. Lead acid battery is the popular one that people are using in solar system. Of course, Li-ion or LiFePO4 (and others) battery can be used as well. At this moment, however, performance-price ratio wise, lead acid battery is the best one now. Even in lead acid battery, there are still different technologies. tubular one is like normal flooded lead acid battery, which requires a battery maintenance every 6-8 months. And this battery is also quite popular in India. It's cheap comparing with Gel and AGM lead acid battery. Gel and AGM batteries are maintenance free during the life time. with better performance on deep discharge. If you only have low power consumers you might try lead acid, lithium might be to expensive and your facility to small for flow batteries

Check into Lithium Iron Phosphate batteries. Less impact on the environment (Do not contain Mercury and any heavy metal that do harm to enviromental and human beings).

At today's situation LiFePO4 is a good option. More expensive initially but more cost effective over its life. With LIFEPO4 you would have more cycles but also calendaric lifespan and temperature problems, so really a lot depends on the circumstance. I would also think in alternatives like potential energy if feasible. LiFePO4 batteries can handle wide working temperature (-20°C--60 °C) much better than other. Long-lasting technology: lithium-ion batteries last three times longer than lead-acid batteries.
The advantage of lithium-ion batteries compared to lead-acid batteries is their greater storage capacity and energy density along with low weight and, above all, their long life.The high peaks and extreme loads placed on the accumulator would cause lead-acid batteries to quickly run down. A typical lead-acid battery has a maximum life of 2,000 cycles, In contrast, lithium-ion batteries last around 7,000 complete cycles. For a typical household this would represent more than 20 years - as long as the solar module itself. Lithium-ion batteries are also 50 to 80 per cent less likely to self-discharge and have much higher cycle efficiency, meaning fewer losses and more output for the user."

Lithium batteries. Flat plate (automotive) wet cells are rated for C20 discharge. Tubular (traction) batteries are rated for C10 discharge but can be discharged at higher rate, but the effective capacity decreases. However, LiPO4 batteries can be charged and discharged at C3 and even C1 rate and the loss of capacity is much lower. They can also be discharged down to 80% without significant loss of life and can operate at higher temperatures. They have a flatter characteristics compared to lead acid.

One technology that is now attracting considerable interest is large-scale battery storage.

Vanadium Redox Batteries (VRBs) are a particularly clean technology, with high availability and a long lifecycle. Their energy density is rather low - about 40 Wh per kilogram - though recent research indicates that a modified electrolyte solution produces a 70 percent improvement in energy density. Vanadium prices are volatile, though, with the increased demand for battery use likely to stress supply.

Flow batteries are emerging energy storage devices that can serve many purposes in energy delivery systems. They can respond within milliseconds and deliver significant quantities of power. They operate much like a conventional battery, storing and releasing energy through a reversible electrochemical reaction with an almost unlimited number of cycles. The active chemicals are stored in external tanks, and when in use are continuously pumped in a circuit between the reactor and tanks. The great advantage is that electrical storage capacity is limited only by the capacity of the tanks. Flow batteries have existed for some time, but have used liquids with very low energy density (the amount of energy that can be stored in a given volume). Because of this, existing flow batteries take up much more space than fuel cells and require rapid pumping of their fluid, further reducing their efficiency. 

Molten salt batteries (or liquid sodium batteries) offer both high energy density and high power density. Operating temperatures of 400-700°C, however, bring management and safety issues, and place stringent requirements on the battery components.

Researchers at Case Western Reserve University are using iron to create a scalable energy storage system that can service a single home or an entire community. Robert Savinell, professor of chemical engineering at Case Western, calls it the rustbelt battery. Since the cost of iron is as little as 1 percent of that of vanadium, the iron-based battery is estimated to cost US$30/kWh, well below a $100/kWh goal set by Sandia National Laboratories. A large-scale 20-MWh iron-based flow battery would require two storage tanks of about 250,000 gallons (950 m³), and could supply the power needs of 650 homes for a day.

Estimating Size For A Solar System

Rooftop Solar Panel array at the Kuppam i-Community Office (Photo credit: Wikipedia)

Sizing a system includes the following steps:-

Step 1 Estimating Electric Loads

Qty X Volts X Amps X Hours(h) = Watts(W) X Hourss (H) = Watt- Hour(WH)

Step2 Sizing & Specifying Batteries

BC ={(Power of the appliance X Working time)/System Volatage} X Consecutive rainy days X System safety factor (1.4-1.8)

Step3 Sizing and Specifying an solar array

Power of the solar module= {(Power of the appliance X Working time)/System Voltage} X Attrition factor(1.6-2.0)

Step 4 Specifying a controller

The controller must operate a system efficiently while meeting the needs of the user. According to manufacturer's specification. The controller must handle under a short circuit of array and normal working.

Step 5 Sizing and specifying inverter

Calculate the total connected watts, determine the maximum surge watts required. The choosing inverter should meet the system's wattage specifications, budget, and other requirements.

Step 6 Sizing System Wiring

System wiring should be designed to endure system current, minimize voltage drop, meet safety codes, and provide protection from environment.

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Photo voltaic Technology

Scientists have known of the photovoltaic effect for more than 150 years. Photovoltaic power generation was not considered practical until the arrival of the space program. Early satellites needed a source of electrical power and any solution was expensive. The development of solar cells for this purpose led to their eventual use in other applications.

DISCOVERY AND DEVELOPMENT OF PHOTOVOLTAIC POWER

The photovoltaic effect has been known since 1839, but cell efficiencies remained around 1% until the 1950s when U. S. researchers were essentially given a blank check to develop a means of generating electricity onboard space vehicles. Bell Laboratories quickly achieved 11% efficiency, and in 1958, the Vanguard satellite employed the first practical photovoltaic generator producing a modest one watt.

In the 1960s, the space program continued to demand improved photovoltaic power generation technology. Scientists needed to get as much electrical power as possible from photovoltaic collectors, and cost was of secondary importance . Without this tremendous development effort, photovoltaic power would be of little use today.

Early photovoltaic development

YEAR	DEVELOPMENT
1839	Antoine-César Becquerel, a French physicist, discovered the photovoltaic effect. In his experiments he found that voltage was produced when a solid electrode in an electrolyte solution was exposed to light.
1877	W.G. Adams and R.E. Day observed the photovoltaic effect in solid selenium. They built the first selenium cell and published “The action of light on selenium,” in Proceedings of the Royal Society.
1883	Charles Fritz built what many consider to be the first true photovoltaic cell. He coated the semiconductor selenium with an extremely thin layer of gold. His photovoltaic cell had an efficiency of less than 1%.
1904	Albert Einstein published a paper on the photoelectric effect .
1927	A new type of photovoltaic cell was developed using copper and the semiconductor copper oxide. This device also had an efficiency of less than 1%. Both the selenium and copper oxide devices were used in applications such as light meters for photography.
1941	Russell Ohl developed the silicon photovoltaic cell. Further refinement of the silicon photovoltaic cell enabled researchers to obtain 6% efficiency in direct sunlight in 1954 .
1954	Bell Laboratories obtained 4% efficiency in a silicon photovoltaic cell. They soon achieved 6% and then 11%.
1958	PV cells were first used in space on board the Vanguard satellite.

CONVERTING SUNLIGHT TO ELECTRICITY

A typical photovoltaic cell consists of semiconductor material (usually silicon) having a pn junction as shown in figure

Sunlight striking the cell raises the energy level of electrons and frees them

from their atomic shells. The electric field at the pn junction drives the electrons into the n region while positive charges are driven to the p region. A metal grid on the surface of the cell collects the electrons while a metal back-plate collects the positive charges.

POWER OUTPUT AND EFFICIENCY RATINGS

The figures given for power output and efficiency of photovoltaic cells, modules, and systems can be misleading. It is important to understand what these figures mean and how they relate to the power available from installed photovoltaic generating systems.

Power Ratings

Photovoltaic power generation systems are rated in peak kilowatts (kWp). This is the amount of electrical power that a new, clean system is expected to deliver when the sun is directly overhead on a clear day. We can safely assume that the actual output will never quite reach this value.

System output will be compromised by the angle of the sun, atmospheric conditions, dust on the collectors, and deterioration of the components. When comparing photovoltaic systems to conventional power generation systems, one should bear in mind that the PV systems are only productive during the daytime. Therefore, a 100 kW photovoltaic system can produce only a fraction of the daily output of a conventional 100 kW generator.

Efficiency Ratings

The efficiency of a photovoltaic system is the percentage of sunlight energy converted to electrical energy. The efficiency figures most often reported are laboratory results using small cells. A small cell has a lower internal resistance and will yield a higher efficiency than the larger cells used in practical applications. Additionally, photovoltaic modules are made up of numerous cells connected in series to deliver a usable voltage. Due to the internal resistance of each cell, the total resistance increases and the efficiency drop to about 70% of the single-cell value. Efficiency is higher at lower temperatures. Temperatures used in laboratory measurements may be lower than those in a practical installation.




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Illuminance

When it is necessary to access lighting objectively and quantify the lighting ambience of a space, i.e. Low, soft or strong lighting, the concept of illuminance is used. For instance, the luminous intensity which is provided on a single gray wall by a lamp of identical power decreases according to inverse of the square of the distance. The illuminance, in other words the quantity of light incident upon this surface, is a function of the distance to the source (d), its luminous intensity (I), and the angle that exists between the incident light which reaches the material and the perpendicular to the surface.

The illuminance is expressed in terms of lux (lumen/m²). This is a means of comparison which lighting engineers often use to describe the functionality of lighting.

Common Light Levels Outdoor

Common light levels outdoor at day and night can be found in the table below:

Condition	Illumination (lux, lumen/m2)
Direct Sunlight	100000- 500000
Full Daylight	10000-40000
Overcast Day	20,000
Twilight	400
Full Moon	100
Quarter Moon	0.01- 20
Starlight	0.001-10
Overcast Night	0.0001

 Common and Recommended Light Levels Indoor

The outdoor light level is approximately 10,000 lux on a clear day. In the building, in the area closest to windows, the light level may be reduced to approximately 1,000 lux. In the middle area its may be as low as 25 - 50 lux. Additional lighting equipment is often necessary to compensate the low levels.

Earlier it was common with light levels in the range 100 - 300 lux for normal activities. Today the light level is more common in the range 500 - 1000 lux - depending on activity. For precision and detailed works, the light level may even approach 1500 - 2000 lux.

The table below is a guidance for recommended light level in different work spaces:

Activity	Illumination
	(lux, lumen/m2)
Public areas with dark surroundings	20 - 50
Simple orientation for short visits	50 - 100
Working areas where visual tasks are only occasionally performed	100 - 150
Warehouses, Homes, Theaters, Archives	150
Easy Office Work, Classes	250
Normal Office Work, PC Work, Study Library, Groceries, Show Rooms, Laboratories	500
Supermarkets, Mechanical Workshops, Office Landscapes	750
Normal Drawing Work, Detailed Mechanical Workshops, Operation Theatres	1,000
Detailed Drawing Work, Very Detailed Mechanical Works	1500 - 2000
Performance of visual tasks of low contrast  and very small size for prolonged periods of time	2000 - 5000
Performance of very prolonged and exacting visual tasks	5000 - 10000
Performance of very special visual tasks of extremely low contrast and small size	10000 - 20000

Reference Efficacy Info

 The  following is a guide of efficacies one might expect from common lamp and luminaire combinations:
Lamp Efficacy:

Incandescent General Service lamps:
50 watts or less-- 11 L/W
50 to 125 watts-- 17 L/W
Over 125 watts-- 20 L/W
Halogen lamp to 250 watts-- 18 L/W
Fluorescent Lamps (based on mean lumens, all at 3,000k color):
Up to 26 watts, retrofit screw base-- 48 L/W
Up to 42 watts, plug in triple tube -- 55 L/W
Long Twin Tube-- 57 L/W
T12 Energy Saving-- 72 L/W
T8 Energy Saving-- 87 L/W
T5 Energy Saving-- 90 L/W
T5 HO -- 86 L/W
High Intensity Discharge Lamps (based on mean lumens):
Up to 100 watt Metal Halide, coated lamp-- 40 L/W
150 to 250 watt Metal Halide, coated lamp, pulse start-- 55 L/W
400 watt Metal Halide, coated lamp, pulse start-- 72 L/W
Up to 250 watt High Pressure Sodium-- 98 L/W
400 and 1000 watt High Pressure Sodium-- 114 L/W

Luminaire Efficacy:

Incandescent downlight with 60W A19 lamp-- 9 to 11 L/W
Incandescent reflector lamp downlight with PAR lamp and reflector trim-- 9 to 17 L/W
Incandescent reflector lamp downlight with PAR lamp and black baffle-- 5 to 12 L/W
Halogen downlight with elliptical reflector and baffle --10 to 15 L/W
CFL Downlight 42W triple lamp-- 28 to 36 L/W
Metal Halide downlight-- 32 to 37 L/W
Fluorescent lensed troffer with T12 lamps-- 41 to 47 L/W
Fluorescent parabolic troffer with T8 Lamps-- 60 to 67 L/W
New generation direct/indirect recessed fluorescent with T5 lamps-- 82 L/W
High Bay Industrial reflector, Metal Halide lamp-- 36 to 47 L/W
Low Bay Industrial reflector, Metal Halide Lamp-- 40 to 50 L/W
Parking Garage luminaire, Metal Halide Lamp-- 38 to 45 L/W
Parking Garage luminaire, High Pressure Sodium Lamp-- 64 to 80 L/W
Decorative wall sconce-- white acrylic diffuser, CFL plug-in lamp-- 13 to 20 L/W
Decorative wall sconce-- white acrylic diffuser, incandescent lamp-- 4 to 7 L/W
Fluorescent under-cabinet light, T5 lamp-- 35 to 47 LW

Comparison Matrix Between LED versus HPSV Street Light

 

Item	60 w LED Street Light	150w HPSV Street light
Cost of electricity (KWh)	8	8
Operations in hrs(1 day)	10	10
Operations in days(1 year)	365	365
Annual KWh	219	547.5
Annual Cost of Electricity	1752	4380
Lifetime	30000 hrs/3000 days	6000 hrs/600 days
Comparative Cost	21000	4500
Total Cost of Ownership over LED lifetime keeping cost of electricity same	35400	49500

Over All 40% cost saving in LED street Light

 

Salient features of LED lighting

 

1. High energy efficiency & savings- High power factor> .95
2. Safe light- no UV or IR in the beam
3. Low heat dissipation/sink
4. Vibration resistance- no filament to break.
5. Instant on - reaches full brightness in nanoseconds.
6. Long lifespan- 30000- 100000 hrs.
7. Low -temperature friendly-no issue starting in cold temperature.
8. Excellent colour rendering
9. High Brightness- no compromise between efficacy and CRI.
10. Option of colours
11. Eco friendly green products-contains no mercury, lead or other heavy metals.
12. No maintenance cost.
13. Directional - no wasted light; any pattern possible.

LED Lighting

The use of LED, an acronym for Light Emitting Diode, has greatly spread in the last few years within many diverse fields of application, from traffic lights to infrared TV controls. The increasing use of LED within industry is primarily due to technological progresses, which have permitted LED to be produced in colours other than the original red (which in the beginning was the only colour available), as well as the  fundamental characteristics which LED can boast: being trustworthy, highly efficient and with a long-life span. 
LED today also plays an ever increasing role in the field of technical lighting, as LED lighting systems offer various advantages in respect to traditional sources of illumination:

• long life
• no maintenance costs
• greater efficiency in contrast to halogen and florescent lights
• secure operation
• a clean light as it is without IR and UV components
• easy of installing light points
• absence of mercury
• the possibility of a strong spotlight effect
• no problems switching on
• insensitivity to humidity and vibrations
• ease of achieving efficient and effective optics in plastic or glass

LED illuminations have the following characteristics:

• small
• dynamic effects (variations of the RGB colours)
• cost effective shape and size
• long life and robust
• concentrated colours

Due to the characteristics of LED and of the LED lighting systems, light is increasing its value in its ability to create diverse ambiances both publically and privately: such as in the illumination of museums, restaurants, health centres, bars, road signs, safe routes as well as becoming increasingly useful in the naval sector.
The versatility of LED lighting systems make this form of technical lighting particularly adapted to scenography and set design as well as creating original and personalised spaces. Monochrome or multi-colour LED systems perfectly integrate with buildings and their surroundings, becoming an integral part of the design, offering solutions for internal space as well as external spaces, whether in humid environments or very hot atmospheres.
Choosing an LED lighting system brings with it numerous economic advantages in terms of lower costs; the possibility to achieve four times as much light in respect to tungsten flurescent and filament lamps; the increased effeciency and reliability of led is also highlighted in its life span, which is one to two times greater than that of cl;assic lighting sources. 
The Geospec technical team produces and sells a wide range of led lighting systems, which include:

• LED light fittings
• LED lighting profiles
• LED devices
• LED spotlights
• Path lamps
• LED spotlights for swimming pools
• LED spotlights for gardens and small paths
• Spotlights for light fittings and/or lighting for stairways and steps
• Monocrome SMD LED stips
• SMD RGB Led strips
• Internal and external Wall Washers
• Supplies
• Colours for RGB spotlights