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Power Problems
Power problems can occur in two forms:
· problems or disturbances that occur with a mains supply. Here we are concerned with Power Quality issues.
· when the mains supply completely fails. Here we are concerned with how to keep systems running and business continuity.

Power supply problems are caused by various sources, for example distribution network faults, system switching, weather and environmental conditions, heavy plant and equipment or simply just faulty hardware. Regardless of the cause of the problem, the result will include one or more of the following types of power problems:
Sags: are short duration decreases in the mains supply voltage which generally last for several cycles. They are one of the more common forms of disturbances. When sags occur sensitive equipment can lock or hang causing data loss and system resets.
Surges: are short duration increases in the mains supply voltage which generally last several cycles. When surges occur equipment can suffer from premature failure. The high voltage causes wear and tear and general component degradation. This may not be noticeable until failure, though heat out is a good sign.
Transients and Spikes: these are very fast high energy surges lasting only a few milliseconds. When transients or spikes occur equipment can lock or hang, crash and even suffer damage which inevitably causes data loss and corruption. Large transients can occur from local or worst case a direct lightning strike.
Electrical Noise: this is a high frequency noise either common or normal mode which can cause severe disruption and damage to circuits and equipment.
Brownouts: are long term sags in the mains supply voltage which can last up to several days. During a brownout equipment can reset or even shutdown.
Blackouts and Mains Failures: when the mains supply fails completely this is known as a total mains failure or blackout. A break in the mains supply of only several milliseconds is sufficient enough to crash, lock or reset many of the components that make up a typical data or voice processing IP network, such as PC, terminal, console, server, PBX, printer, modem, hub or router.
A survey can be used to identify the types, duration and magnitude of power problems experienced on a site.

 

 

Power problems cause voice and data processing errors, hardware damage and expensive downtime. When an Uninterruptible Power Supply (UPS) as your power protection solution it is important to consider two elements:
· How clean is my mains supply when it is present ?
· Does the application need to be kept running when the mains fluctuates wildly or fails and if so for how long ?
Power Quality without battery back-up
Solutions vary in the power quality they provide and include:
Filters
A filter will attenuate spikes and electrical noise down to predefined levels. A very basic economic form of power protection.
Transient Voltage Surge Suppressors (TVSS)
A TVSS will clamp and divert the excess electrical energy of transients away from downstream loads. A TVSS is superior to a filter and can cope with lightning strike surges in some instances. They are commonly used within heavy industrial complexes and mobile base stations. When placed before Uninterruptible Power Supplies a TVSS will provide protection for the Uninterruptible Power Supply itself from local transient surges.
Voltage Stabilisers
Smooth out sags, surges and brownouts in an attempt to provide a near stable supply and are typically used in combination with a filter. They provide a form of power protection used typically in third world countries for non-critical loads such as fridges and freezers. A voltage stabiliser (also known as an Automatic Voltage Stabiliser or AVR) can be electronic or electro-mechanical.
Power Conditioners
The ultimate power protection without battery back up. They can be either transformer or electronic based and provide conditioning in the form of filtering, stabilisation and regulation. Some power conditioners can also provide Galvanic isolation. This is more commonly associated with Constant Voltage Transformers (CVTs).
 

 

Uninterruptible Power Supplies (UPS)
Offline / standby
Offline / standby UPS. Typical protection time: 0–20 minutes. Capacity expansion: Usually not available
The offline / standby UPS (SPS) offers only the most basic features, providing surge protection and battery backup. The protected equipment is normally connected directly to incoming utility power. When the incoming voltage falls below a predetermined level the SPS turns on its internal DC-AC inverter circuitry, which is powered from an internal storage battery. The SPS then mechanically switches the connected equipment on to its DC-AC inverter output. The switchover time can be as long as 25 milliseconds depending on the amount of time it takes the standby UPS to detect the lost utility voltage. The UPS will be designed to power certain equipment, such as a personal computer, without any objectionable dip or brownout to that device.
Line-interactive
Line-interactive UPS. Typical protection time: 5–30 minutes. Capacity expansion: Several hours
The line-interactive UPS is similar in operation to a standby UPS, but with the addition of a multi-tap variable-voltage autotransformer. This is a special type of transformer that can add or subtract powered coils of wire, thereby increasing or decreasing the magnetic field and the output voltage of the transformer.
This type of UPS is able to tolerate continuous undervoltage brownouts and overvoltage surges without consuming the limited reserve battery power. It instead compensates by automatically selecting different power taps on the autotransformer. Depending on the design, changing the autotransformer tap can cause a very brief output power disruption,which may cause UPSs equipped with a power-loss alarm to "chirp" for a moment.
This has become popular even in the cheapest UPSs because it takes advantage of components already included. The main 50/60 Hz transformer used to convert between line voltage and battery voltage needs to provide two slightly different turns ratios: one to convert the battery output voltage (typically a multiple of 12 V) to line voltage, and a second one to convert the line voltage to a slightly higher battery charging voltage (such as a multiple of 14 V) Further, it is easier to do the switching on the line-voltage side of the transformer because of the lower currents on that side.
To gain the buck/boost feature, all that is required is two separate switches so that the AC input can be connected to one of the two primary taps, while the load is connected to the other, thus using the main transformer’s primary windings as an autotransformer. The battery can still be charged while "bucking" an overvoltage, but while "boosting" an undervoltage, the transformer output is too low to charge the batteries.
Autotransformers can be engineered to cover a wide range of varying input voltages, but this requires more taps and increases complexity, and expense of the UPS. It is common for the autotransformer to cover a range only from about 90 V to 140 V for 120 V power, and then switch to battery if the voltage goes much higher or lower than that range.
In low-voltage conditions the UPS will use more current than normal so it may need a higher current circuit than a normal device. For example to power a 1000-watt device at 120 volts, the UPS will draw 8.32 amperes. If a brownout occurs and the voltage drops to 100 volts, the UPS will draw 10 amperes to compensate. This also works in reverse, so that in an overvoltage condition, the UPS will need less current.
Double-conversion / online
The online UPS is ideal for environments where electrical isolation is necessary or for equipment that is very sensitive to power fluctuations. Although once previously reserved for very large installations of 10 kW or more, advances in technology have now permitted it to be available as a common consumer device, supplying 500 watts or less. The initial cost of the online UPS may be slightly higher, but its total cost of ownership is generally lower due to longer battery life. The online UPS may be necessary when the power environment is "noisy", when utility power sags, outages and other anomalies are frequent, when protection of sensitive IT equipment loads is required, or when operation from an extended-run backup generator is necessary.
The basic technology of the online UPS is the same as in a standby or line-interactive UPS. However it typically costs much more, due to it having a much greater current AC-to-DC battery-charger/rectifier, and with the rectifier and inverter designed to run continuously with improved cooling systems. It is called a double-conversion UPS due to the rectifier directly driving the inverter, even when powered from normal AC current.
In an online UPS, the batteries are always connected to the inverter, so that no power transfer switches are necessary. When power loss occurs, the rectifier simply drops out of the circuit and the batteries keep the power steady and unchanged. When power is restored, the rectifier resumes carrying most of the load and begins charging the batteries, though the charging current may be limited to prevent the high-power rectifier from overheating the batteries and boiling off the electrolyte.
The main advantage to the on-line UPS is its ability to provide an electrical firewall between the incoming utility power and sensitive electronic equipment. While the standby and line-interactive UPS merely filter the input utility power, the double-conversion UPS provides a layer of insulation from power quality problems. It allows control of output voltage and frequency regardless of input voltage and frequency.

 

Introduction to Solar in Non-Technical Terms
There are four major components to solar electric systems; Solar Panels, Charge Controllers, Batteries and Inverters. All of these components are necessary to have a functioning Solar Electric (PV) system. The solar panel is the basic building block of the system. This is your battery charger. If you have several solar modules wired together you have created a solar array. The size of the solar array determines the amount of power or energy that will be produced. Your location is also a factor in the amount of energy produced. If you live in Florida, Southern California, or Texas you will produce more than if you live in Oregon, Maine or Maryland. In general the closer to the equator you live your system will produce a larger amount of energy. Charge controllers come in many different sizes and types. They all basically do the same thing. The charge controller prevents the solar panel or array from overcharging your battery. Batteries are the energy storage for your system. Without batteries there is no way to store the energy your solar panels produce during the day. Typically loads receive their power from batteries instead of directly from the output of a solar panel. A solar panel produces a high voltage that will damage electronics if loads are powered directly. A common application for solar panels directly powering a load is water pumping. Instead of storing energy you store water. This way you can pump during the day and have water all night. Batteries will provide you with the energy you need at night. The last major component is the Inverter. The inverter converts the DC energy stored in your batteries and turns it into the AC power you use in your home. Inverters are rated by wattage and the quality of their output. You can use a 50 watt inverter that plugs into your car 12 volt outlet to power a computer, or you could have a 4000 to 11,000 watt inverter system that powers your home. These major components can be put together in many different ways. Minor components like wire, disconnects, circuit breakers, and fuses are also needed for a complete system.
Introduction of how these different components are used in systems
Stand Alone or "Cabin" Systems
Solar/ Charge Controller/ Battery/ Inverter/ AC Loads
or
Solar/ Charge Controller/ Battery/ DC Loads
A Stand Alone solar system is just as it sounds. It is not connected to the utility or other types of charging sources. This type of system is used when utility power is not present and is to costly to bring in from the nearest pole. If you have a shed set off from the house, a cabin in the mountains, or a summer home by the lake that is without power this type of system can often be very cost effective. When compared to bring in the power lines the initial cost can be less. Some of the pros of this type of system are: The lack off reliance on the utility. Potential cost savings. Some of the cons of this type of system are: Even thought there maybe a cost savings over running utility line, there can be a high initial cost. You have to know your loads and have the system designed correctly since you don’t have utility power for backup.
Utility Tied System
Solar/ Inverter/ Utility
This system is the newest addition to our site. The system utilizes an inverter that does not require batteries. During the day, the power generated is fed back into the utility. If you are producing more power then you are using your meter can even spin backwards. Due to the simplicity of the system, it has the lowest cost per watt. The downfall of this system is that when the utility grid fails the system will shut down.
Battery Backup System
Utility/ Battery Charger/ Batteries/ Inverter/ AC Loads
This is a system that does not involve solar power. This system utilizing an inverter that has a built in battery charger. It will charges batteries and hold them at 100% waiting for a power outage or a brownout. Your critical loads will never see the power outage. Computers, home health equipment, and lights will continue to operate when the utility grid fails. This is a system that is great for areas where power is lost for short periods of time. The limit on this system is the amount of battery capacity that you have. The larger the batteries the longer your run time will be.
Utility Tied Battery Backup System with Solar
This system operates on the same principal as the Battery Backup System. The difference is the addition of solar. The solar is used to charge your battery bank. When the batteries are full the excess power is fed back into the grid. In the event of an outage, your critical loads are powered by the system, and the solar panels continue to charge the batteries. The benefit of this system is that you have the ability to sell power back and have the piece of mind that you critical loads will continue to operate. The drawback is the cost per watt is higher then a Utility Tied System.
More Technical Terms
Solar energy systems fall into two categories:
1. Solar Electric
Also called photovoltaic (PV) systems, these convert sunlight to electricity. PV systems can provide all the electricity needed by a home or business, or they can be used as backup or to supplement energy needs.
Photovoltaic (PV), often called solar cells, are semiconductor devices that convert sunlight into direct current (DC) electricity. Groups of PV cells are electrically configured into modules and arrays, which can be used to charge batteries, operate motors, and to power any number of electrical loads. With the appropriate power conversion equipment, PV systems can produce alternating current (AC) compatible with any conventional appliances, and operate in parallel with and interconnected to the utility grid.
 

 

How PV Cells Work
A typical silicon PV cell is composed of a thin wafer consisting of an ultra-thin layer of phosphorus-doped (N-type) silicon on top of a thicker layer of boron-doped (P-type) silicon. An electrical field is created near the top surface of the cell where these two materials are in contact, called the P-N junction. When sunlight strikes the surface of a PV cell, this electrical field provides momentum and direction to light-stimulated electrons, resulting in a flow of current when the solar cell is connected to an electrical load.
Regardless of size, a typical silicon PV cell produces about 0.5 - 0.6 volt DC under open-circuit, no-load conditions. The current (and power) output of a PV cell depends on its efficiency and size (surface area), and is proportional the intensity of sunlight striking the surface of the cell. For example, under peak sunlight conditions a typical commercial PV cell with a surface area of 160 cm2 (~25 in2) will produce about 2 watts peak power. If the sunlight intensity were 40 percent of peak, this cell would produce about 0.8 watts.
PV Cells, Modules & Arrays
Photovoltaic cells are connected electrically in series and / or parallel circuits to produce higher voltages, currents and power levels. Photovoltaic modules consist of PV cell circuits sealed in an environmentally protective laminate, and are the fundamental building block of PV systems. Photovoltaic panels include one or more PV modules assembled as a pre-wired, field-installable unit. A photovoltaic array is the complete power-generating unit, consisting of any number of PV modules and panels.
The performance of PV modules and arrays are generally rated according to their maximum DC power output (watts) under Standard Test Conditions (STC). Standard Test Conditions are defined by a module (cell) operating temperature of 25 degrees C (77 degrees F), and incident solar irradiance level of 1000 W/m2 and under Air Mass 1.5 spectral distribution. Since these conditions are not always typical of how PV modules and arrays operate in the field, actual performance is usually 85 to 90 percent of the STC rating.
Today’s photovoltaic modules are extremely safe and reliable products, with minimal failure rates and projected service lifetimes of 20 to 30 years. Most major manufacturers offer warranties of twenty or more years for maintaining a high percentage of initial rated power output.
How a PV System Works
Simply put, PV systems are like any other electrical power generating systems, but the equipment used is different than that used for conventional electromechanical generating systems. However, the principles of operation and interfacing with other electrical systems remain the same, and are guided by a well-established body of electrical codes and standards.
Although a PV array produces power when exposed to sunlight, a number of other components are required to properly conduct, control, convert, distribute, and store the energy produced by the array.
Depending on the functional and operational requirements of the system, the specific components required, and may include major components such as a DC-AC power inverter, battery bank, system and battery controller, auxiliary energy sources and sometimes the specified electrical load (appliances). In addition, an assortment of balance of system (BOS) hardware, including wiring, over current, surge protection and disconnect devices, and other power processing equipment.
Why Are Batteries Used in Some PV Systems?
Batteries are often used in PV systems for the purpose of storing energy produced by the PV array during the day, and to supply it to electrical loads as needed (during the night and periods of cloudy weather). Other reasons batteries are used in PV systems are to operate the PV array near its maximum power point, to power electrical loads at stable voltages, and to supply surge currents to electrical loads and inverters. In most cases, a battery charge controller is used in these systems to protect the battery from overcharge and over discharge.
Batteries
One of the most misunderstood parts of a solar power system is the battery or battery bank,Some solar battery banks use wet cells, like golf cart batteries, while others use sealed or gel cell batteries, and each have different temperature, mounting, and ventilation requirements.
Every battery is designed for a specific type of charge and discharge cycle. Car batteries have thin plates to keep their weight down and are designed for a heavy discharge lasting a few seconds, followed by a long period of slow re-charge. A 6-volt golf cart battery (size T-105) is the minimum battery recommended for a residential solar application. You will need to buy these in "pairs" to make 12 volts. Golf cart batteries have very thick plates and are designed for hours of heavy discharge each day, followed by a fast recharge in only a few hours each night. This is similar to the duty cycle of a residential solar application, only in reverse. A solar battery must be able to provide long periods of deep discharge each evening and night, followed by a full recharge in only a few hours of sunlight each afternoon. Very few batteries can take a deep discharge-recharge cycle every day, and the 6-volt golf cart battery is the least expensive and easiest to find locally that can.
For some reason, everyone wants to use a sealed marine battery for their homegrown solar system. I strongly recommend that you do not. Even though this was a small 12-volt DC 5-amp solar charge controller powered from a single 50-watt solar photovoltaic module, this was enough energy to gradually overcharge the battery and evaporate all of the electrolyte even though this battery was "sealed." A low electrolyte level can expose the plates which will gradually warp or "grow" in thickness as they oxidize. This can cause an internal short circuit and ignition of the hydrogen gas.
Plate damage can also occur when there is a large buildup of sediment after the upper plate areas become exposed from reduced water levels and begin to "flake" off. Most liquid acid batteries do not vent gasses while discharging. However, near the end of a typical charging cycle, when the battery is almost "full," the sulfuric acid and water electrolyte will begin to break down into hydrogen and oxygen-a very explosive combination.
When ignited by a nearby spark or flame, an "explosion" can result, but this flash lasts only a fraction of a second, which is usually too fast to ignite nearby walls. However, this is still a very explosive reaction, with plastic battery parts becoming acid-covered shrapnel.
Always wear eye protection and acid proof gloves when working around batteries, and have lots of water and baking soda nearby. This will neutralize any acid spills from battery refilling and prevent further corrosive damage.
A typical 6-volt golf cart battery will store about 1 kilowatt-hour of useful energy (6 volt X 220 amp-hr X 80% discharge = 1056 watt-hours). Since this would only power two 50-watt incandescent lamps for 10 hours (2 X 50 X 10 = 1000 watt-hours), your alternative energy system will most likely require wiring several batteries together to create a battery bank. Since each golf cart battery weighs almost 65 pounds, there are weight considerations as well as battery gas venting issues to think about.
An area of a garage or storage building having a concrete floor is the most common location for a battery bank, although some large systems have their own specially designed battery room. Assuming you are installing a much smaller system and will only require four to eight batteries.
If you need more than the 220 amp-hr capacity contained in each golf cart battery, It is suggested switching to the larger "L-16" size traction battery, having a 350 amp-hour rating, which may allow using fewer batteries. This battery is the same length and width as a golf cart battery, but is much taller and twice as heavy. This is an excellent battery for solar applications and can take very heavy charge-discharge cycling. This industrial rated battery may be more difficult to find, as it is only available from battery wholesale distributors.
Batteries can lose over half of their charge when exposed to extreme temperature swings, so be sure your proposed battery location stays in a 50° to 80° F range, or you will need to insulate the battery box. Since liquid batteries require refilling and battery terminal cleaning to remove corrosion several times each year, the floor area selected should be able to take an occasional acid spill and water wash down.
Battery venting is very important as discussed earlier, and if you build an enclosure around your batteries, it should be designed to direct all vented gasses to the outside. A 2-inch PVC pipe makes a good vent, but be sure it is located at the highest point in your battery enclosure where the lighter hydrogen gas will accumulate. Be sure it also includes a screened vent cap to keep out rain and insects. Do not locate your battery bank near a gas water heater or other open flame appliance that could ignite any accidental hydrogen accumulation.
A battery box can be built using standard 2 x 4 framing construction, with pressure treated plywood lining the interior surfaces. A hinged top door is needed for periodic battery maintenance, and should include a gasket to prevent gases from entering the room. Note how the top of the site-built battery box shown in these photos slopes up to a high rear area where two PVC vent pipes are located. The interior plywood surfaces of this wood frame construction were painted with several coats of fire and acid resistant paint. Since batteries lose capacity with lower temperatures, your batteries should not rest directly on a cold un-insulated concrete floor.
Pressure treated 2 x 4s on edge, spaced every 6 inches and covered by a fiberglass laminated concrete board, makes an excellent base for your battery box. This heavy sheet material is sold in most building supply outlets as a backing behind ceramic tile work in wet shower stalls, and is usually available in smaller 2-foot by 4-foot sizes. By careful planning, you may be able to use the entire sheet without cutting or splicing.
If you can afford to invest in the more expensive gel or absorbed glass matte (AGM) batteries, you will have more flexibility in locating your battery bank, since these batteries do not need to be refilled and do not normally generate explosive gasses. The photo shows a large battery bank with the batteries mounted close together in a vertical steel rack. You do not need a vapor proof enclosure or vent pipe when using these batteries, however they cost almost 30 percent more without providing any additional life or storage capacity.

 

Types of PV Systems
Photovoltaic power systems are generally classified according to their functional and operational requirements, their component configurations, and how the equipment is connected to other power sources and electrical loads. The two principle classifications are grid-connected or utility-interactive systems and stand-alone systems. Photovoltaic systems can be designed to provide DC and/or AC power service, can operate interconnected with or independent of the utility grid, and can be connected with other energy sources and energy storage systems.
Grid-Connected (Utility-Interactive) PV Systems.
Grid-connected or utility-interactive PV systems are designed to operate in parallel with and interconnected with the electric utility grid. The primary component in grid-connected PV systems is the inverter, or power conditioning unit (PCU). The PCU converts the DC power produced by the PV array into AC power consistent with the voltage and power quality requirements of the utility grid, and automatically stops supplying power to the grid when the utility grid is not energized. A bi-directional interface is made between the PV system AC output circuits and the electric utility network, typically at an on-site distribution panel or service entrance. This allows the AC power produced by the PV system to either supply on-site electrical loads, or to back feed the grid when the PV system output is greater than the on-site load demand. At night and during other periods when the electrical loads are greater than the PV system output, the balance of power required by the loads is received from the electric utility. This safety feature is required in all grid-connected PV systems, and ensures that the PV system will not continue to operate and feedback onto the utility grid when the grid is down for service or repair.
Stand-Alone Photovoltaic Systems
Stand-alone PV systems are designed to operate independent of the electric utility grid, and are generally designed and sized to supply certain DC and/or AC electrical loads. These types of systems may be powered by a PV array only, or may use wind, an engine-generator or utility power as an auxiliary power source in what is called a PV-hybrid system. The simplest type of stand-alone PV system is a direct-coupled system, where the DC output of a PV module or array is directly connected to a DC load. Since there is no electrical energy storage (batteries) in direct-coupled systems, the load only operates during sunlight hours, making these designs suitable for common applications such as ventilation fans, water pumps, and small circulation pumps for solar thermal water heating systems. Matching the impedance of the electrical load to the maximum power output of the PV array is a critical part of designing well-performing direct-coupled system. For certain loads such as positive-displacement water pumps, a type of electronic DC-DC converter, called a maximum power point tracker (MPPT) is used between the array and load to help better utilize the available array maximum power output.
Pros & Cons of PV
Photovoltaic systems have a number of merits and unique advantages over conventional power-generating technologies. PV systems can be designed for a variety of applications and operational requirements, and can be used for either centralized or distributed power generation. PV systems have no moving parts, are modular, easily expandable and even transportable in some cases. Energy independence and environmental compatibility are two attractive features of PV systems. The fuel (sunlight) is free, and no noise or pollution is created from operating PV systems. In general, PV systems that are well designed and properly installed require minimal maintenance and have long service lifetimes.
At present, the high cost of PV modules and equipment (as compared to conventional energy sources) is the primary limiting factor for the technology. Consequently, the economic value of PV systems is realized over many years. In some cases, the surface area requirements for PV arrays may be a limiting factor. Due to the diffuse nature of sunlight and the existing sunlight to electrical energy conversion efficiencies of photovoltaic devices, surface area requirements for PV array installations are on the order of 8 to 12 m2 (86 to 129 ft2) per kilowatt of installed peak array capacity.
Can photovoltaic systems operate normally in grid-connected mode, and still operate critical loads when utility service is disrupted?
Yes, however battery storage must be used. This type of system is extremely popular for homeowners and small businesses where critical backup power supply is required for critical loads such as refrigeration, water pumps, lighting and other necessities. Under normal circumstances, the system operates in grid-connected mode, serving the on-site loads or sending excess power back onto the grid while keeping the battery fully charged. In the event the grid becomes de-energized, control circuitry in the inverter opens the connection with the utility through a bus transfer mechanism, and operates the inverter from the battery to supply power to the dedicated loads only. In this configuration, the critical loads must be supplied from a dedicated sub panel.

 

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