2015/03/10
Make a DIY solar power generation plant in your roof
by: EastGreenfields blog
While summer heat is now knocking at your door, you probably is asking yourselves how to deal with the upsurge in electricity usage to run your electric fans during the day.
Then why not make yourself a DIY on-grid solar power plant on your roof?
Micro solar power generation can power electric fans, LCD TVs, laptops and charge cellphones without breaking the bank or ripping your wallets off.
A 500 watts system (2x 250 watts) can provide around 1960 watts-hr free electricity during the summer months.
This is roughly equivalent to running one of the following appliances:
16" Electrifan -- 10 hours or whole day
2x Air cooler / Humidifier -- 10 hours or whole day
10x 18 watts CFL Lighting -- 10 hours or whole day
10 Cu Ft Refrigerator -- 12 hours or whole day
40" TV Set -- 9 hours or whole day
Desk top computer -- 9 hours or almost whole day
Cellphone chargers -- Whole day
Its so easy a houswife can figure out how to install the system and it only needs a solar panel, a micro-grid inverter, and a breaker, its almost plug and play!
Install micro on-grid and beat the heat!
Email us: inquiry@eastgreenfields.com
POWER RATES DOWN BUT MAY GO UP AGAIN THIS SUMMER
Gonzales, I. (March 10)
MANILA, Philippines - There’s a slight reduction in electricity rates this month, but consumers should still brace for high electricity bills due to higher demand during the hot months and the month-long maintenance shutdown of the deepwater gas-to-power Malampaya natural gas field in offshore Palawan.
Manila Electric Co. (Meralco), the power distributor, yesterday announced a reduction in electricity rates by P0.095 per kilowatt-hour to P10.42 per kwh for March.
For a typical household consuming 200 kwh, this is equivalent to a decrease of around P19 in their electricity bill.
The decrease was driven by lower power cost during the February supply month, which translated to a lower generation charge of P5.209 per kwh in March from P5.238 per kwh previously.
“Generation charge, or the portion of the bill that goes to the generation companies or power producers, decreased by P0.029 per kwh from P5.238 to P5.209. This was driven by the 30-centavo reduction in the average rate of Meralco’s Power Supply Agreements (PSAs) for the February supply month owing to higher dispatch of the plants under the PSAs,” Meralco explained in an advisory.
Meralco said that the PSA’s share to Meralco’s total requirements went up to 54 percent from 49 percent previously.
But Meralco still purchased from the Wholesale Electricity Spot Market (WESM), the country’s trading floor for electricity, which saw an average price increase of P1.14 per kwh, and from independent power producers (IPPs), which saw an increase of P0.18 per kwh.
“WESM’s share to Meralco’s total power requirements went up from 4 percent to 4.5 percent due to Quezon Power Philippines Ltd. (QPPL)’s maintenance outage. The share of IPPs, on the other hand, went down from 47 percent to 40.5 percent due mainly to the QPPL outage,” Meralco said.
But the transmission charge went down by P0.045 per kwh due to lower ancillary charges.
Other charges, including system loss charge and subsidies, registered a decrease of P0.010 per kwh, resulting in corresponding decreases in taxes such as value added tax and local franchise tax of P0.011 per kwh.
Meralco’s distribution charge, however, remained unchanged and had been at the same level since July 2014.
But the Malampaya natural gas field, which supplies power to three natural gas-fired power plants in Luzon, will go on maintenance shutdown from March 15 to April 13.
“As a result of the use of liquid fuel, rates are expected to increase in the billing months affected by the shutdown and the impact of higher energy demand during the summer months. This includes both April and May 2015,” Meralco said.
Power plants bogged down
Other power plants have also bogged down and are on forced outage or extended outage even as the critical supply period is fast approaching.
According to the National Grid Corp. of the Philippines, GN Power’s unit 1, with 302 megawatts and which has been unavailable since Oct. 26, 2014, will go on extended shutdown until March 19. Similarly, unit 2 (53 MW) of the Tiwi plant in Albay has been unavailable since March 8 due to valve trouble.
Energy Development Corp. yesterday disclosed that unit 3 of its Bacon-Manito geothermal plants, with a capacity of 20 MW, is also unavailable due to line tripping.
Several plants are also on scheduled outage. These are the unit 3 (90 MW) of the Magat plant, which is on planned shutdown until March 21; unit 1 (250 MW) of the Sta. Rita plant also on planned shutdown from March 7 to 11; and unit 2 (302 MW) of GN Power, which will be out until March 25 on maintenance shutdown.
The Limay plant in Bataan (60 MW) will be unavailable until March 12 as well as the Magat Plant (90 MW), which will be out until April 19. Two units of the Makban plants (63 MW and 17 MW) will also be out until March 31.
According to the Department of Energy (DOE), an average of 631 megawatts to as high as 858 MW are expected to disappear from the Luzon grid from March to June 2015 as a result of forced outages of power plants.
Specifically, an average of 631 MW in capacity would not be available in March as a result of forced outages, while an average of 712 MW would not be available in April. This is predicted to go down to an average of 642 MW in May and rise again to an average 858 MW in June.
Reference:
Gonzales, I. (March 10)http://www.philstar.com/headlines/2015/03/10/1431961/power-rates-down-may-go-again-summer
MERALCO SAYS RATES LOWER IN MARCH
Flores, A. M. S. (March 10)
Manila Electric Co., the biggest electricity retailer, said Monday rates have dropped by P0.095 per kilowatthour in March compared to a month ago due to lower generation charges and other bill components.
Customers with a monthly consumption of 200 kWh will experience a decrease of around P19 in their March electricity billing.
Meralco, however, said power plants relying on natural gas would shift to the more expensive liquid fuel in the wake of the shutdown of the Malampaya production from mid-March to mid-April.
“As a result of the use of liquid fuel, rates are expected to increase in the billing months affected by the shutdown and the impact of higher energy demand during the summer months. This includes both April and May,” it said.
Meralco said he generation charge, or the portion of the bill that goes to the power producers, decclined P0.029 per kWh to P5.209 for March from P5.238 in February.
“This was driven by the P0.30 reduction in the average rate of Meralco’s Power Supply Agreements for the February supply month owing to higher dispatch of the plants under the PSAs,” Meralco said in a statement.
The PSAs’ share to Meralco’s total power supply rose to 54 percent from 49 percent.
Meralco said the reduction in the PSA rates, however, was dampened by an increase of P1.14 per kWh in the average price at the Wholesale Electricity Spot Market and P0.18 per kWh in the charge of independent power producers.
WESM’s share to Meralco’s total power requirements increased to 4.5 percent from 4 percent due to the maintenance shutdown of Quezon Power Philippines Ltd.
The share of IPPs, meanwhile, dropped to 40.5 percent from 47 percent due mainly to the QPPL outage.
Despite the lower rates from the Sta. Rita and San Lorenzo natural gas plants, the average IPP rate was pulled up by QPPL.
The balance of Meralco’s power requirements was accounted for by the interim power supply agreements.
Meralco said transmission charge also rose by P0.045 per kWh due to lower ancillary charges. Other charges, which include system loss and subsidies, registered a decrease of P0.010 per kWh. The reductions resulted in corresponding decreases in taxes (VAT and local franchise tax) of P0.011 per kWh.
http://manilastandardtoday.com/2015/03/09/meralco-says-rates-lower-in-march/
2015/03/05
MPPT Charge Controllers
MPPT Charge Controllers
Z Yewdall
Published In: HP online
In a battery-based PV system, a charge controller is used between the PV array and the battery bank to monitor battery voltage, optimize charging, and keep the array from overcharging the batteries.
There are a few common types of charge controllers: single or two-stage (shunt or relay type); pulse-width modulated (PWM); and maximum power-point tracking (MPPT). While non-MPPT charge controllers are less expensive and still have their place in the battery-based PV market—especially for lighting and small developing-world systems—just about all modern home- and cabin-scale PV systems include an MPPT charge controller, as they offer several advantages.
MPPT Advantages
More watts. Recall the power equation—volts × amps = watts. The more voltage captured from an array, the more power (watts) can be sent to the battery bank. An MPPT charge controller keeps the array operating at the peak of the current-voltage curve, and converts array voltage above battery voltage into extra amperage, thus absorbing more watts from the array. A non-MPPT charge controller chains the array’s voltage to the battery’s voltage, effectively limiting the array’s power output.
Array voltage varies with cell temperature. For example, when the cells are cold during winter, yet receiving full sun, the array voltage is higher. Higher array voltage translates into greater wattage. Here’s an example: Considering average winter and summer temperatures in Boulder, Colorado, there would be about a 12% difference between average winter versus summer array power output, and up to a 25% difference on a cold winter day versus a hot summer day. For off-grid systems that have higher loads in the winter, the extra energy input offered by MPPT-based systems can be a big benefit. At higher temperatures, which usually occur in the summertime or year-round in mild climates, array voltage drops, and an MPPT controller may be less advantageous.
Step-down. Voltage conversion is another benefit that is built into MPPT charge controllers. An MPPT charge controller is a DC-DC converter—with computerized controls. It can take a higher voltage and lower amperage, and convert those to a lower output voltage at higher amperage. For example, instead of an array producing a nominal 24 V and charging a 24 V battery, an MPPT controller can step-down an array producing 60 V to charge that battery. This frees the array from having to be matched to the battery voltage, and mitigates some wire-sizing (and cost) issues.
In that example, pushing 30 A at 24 V a distance of 40 feet would require large-gauge (expensive) cable—2 AWG—to keep voltage drop under 2%. For the same amount of power, pushing 12 A at 60 V that same 40 feet with 10 AWG will keep voltage drop under 2%, with the MPPT charge controller stepping the output voltage down to 24 V for the batteries. THHN #2 wire retails for about $1.24 per foot, and #10 sells for about $0.19 per foot, saving $84.00 on that two-way wire run, even without considering conduit size and the physical difficulties of pulling large wire.
Higher Input Voltages
Until recently, most charge controllers could accept a maximum input voltage of only 150 V. Today, one manufacturer has models that accept 200 or 250 V input, and two have models that accept up to 600 V input. Having these options provides more flexibility in designing module strings for battery-based systems. For example, instead of designing strings of three modules in series, strings of six modules in series are possible. This reduces the number of strings needed by half. At half the amperage and twice the voltage, the same size wire can be used, but at four times the distance—without losing power.
A 600 V charge controller may be able to accommodate a single series string of 12 modules, negating combiner boxes completely. This translates into less equipment, wire expense, and labor.
The 600 V charge controllers may be used for transforming batteryless grid-tied PV arrays to grid-tied with battery backup. In many cases, rewiring the array is unnecessary.
A disadvantage to using a controller with a higher input voltage is that the disconnects and combiner boxes (if required) are typically more expensive and harder to find. Note that one of the 600 V input charge controllers (Morningstar’s TS-MPPT-60-600) has an optional integrated DC disconnect, which can help mitigate sourcing and finding space on the wall for an external 600 V DC disconnect, though the controller’s additional cost is similar to the cost of a separate DC disconnect.
Single-Module PV Systems
Most module manufacturers have switched to a 60-cell design, resulting in modules in the 200 W to 300 W range with a maximum power point of 25 to 35 V. Nominal 12 V and 24 V modules (having 36 and 72 cells, respectively) are harder to find and more expensive per watt. Several manufacturers have introduced MPPT charge controllers to accommodate a single 60-cell module on a 12 V battery system (which might power, for example, remote lighting or communications, or an off-grid cabin). Blue Sky Energy offers several products for 12 V systems, and MidNite Solar and Morningstar have introduced smaller (30 A) MPPT controllers, which will work for a single module on a 12 V system.
These charge controllers cost more than a simple PWM charge controller that you might use on a system with 36-cell (12 V nominal) modules. However, when you take into account the total system cost—PV module(s) plus charge controller—it can be 10% to 20% less expensive to use the 60-cell module with the MPPT charge controller. Plus, you get the advantage of MPPT. In addition, the wiring of the system often is simpler, since it involves one large module and no combiner boxes.
Matching Controllers to Inverters
For off-grid systems, matching the brand of charge controller to the inverter isn’t usually important, since there is very little coordination between these two. The charge controller routes energy into the battery, and the inverter takes it out—neither of them really cares what the other is doing. However, for a grid-tied system, synchronizing them can matter. While there are thousands of battery-based grid-tied systems that operate without communications between the charge controller and inverter, system programming can be simplified and efficiency can be improved if they are matched. Compatible communications systems enable the inverter to tell the charge controller that the grid is available. At this point, the charge controller’s job is not to regulate battery charge but to track the array’s MPP and get the most energy out of the array that it can. (The inverter will regulate the battery voltage by selling excess energy to the grid.)
Monitoring & Data Logging
All but the most basic charge controllers come with some system monitoring. All of the charge controllers included offer remote display options, enabling you to monitor the system’s operation in the house, for example, rather than at the controller’s location. Most of the MPPT charge controllers include a digital display on the controller as well. If your system has multiple charge controllers (from the same manufacturer), they can communicate with each other to coordinate charging, and can all send data to a single remote monitor.
MidNite Solar offers an amp-hour-counting state-of-charge meter with their Classic charge controllers, and as an option on its smaller KID controllers. Battery state-of-charge (SOC) metering, which shows battery SOC as a percentage, is an important tool that enables users to easily see how full (or empty) their batteries are. But it is often left out of systems because it comes at an extra cost.
Data logging can be another important feature, especially with systems that are not monitored daily. The larger MidNite Solar, Morningstar, OutBack Power, and Schneider Electric charge controllers include data logging, so you can see how many kWh the system produced over a period of time. Having access to this data can be useful for installers when troubleshooting a system.
MidNite Solar, OutBack Power, and Schneider Electric’s charge controllers can be connected to a computer or smartphone (directly for MidNite Solar, and through an extra communications device for OutBack Power and Schneider Electric charge controllers) for monitoring, programming, and accessing historical data.
Z Yewdall
Published In: HP online
In a battery-based PV system, a charge controller is used between the PV array and the battery bank to monitor battery voltage, optimize charging, and keep the array from overcharging the batteries.
There are a few common types of charge controllers: single or two-stage (shunt or relay type); pulse-width modulated (PWM); and maximum power-point tracking (MPPT). While non-MPPT charge controllers are less expensive and still have their place in the battery-based PV market—especially for lighting and small developing-world systems—just about all modern home- and cabin-scale PV systems include an MPPT charge controller, as they offer several advantages.
MPPT Advantages
More watts. Recall the power equation—volts × amps = watts. The more voltage captured from an array, the more power (watts) can be sent to the battery bank. An MPPT charge controller keeps the array operating at the peak of the current-voltage curve, and converts array voltage above battery voltage into extra amperage, thus absorbing more watts from the array. A non-MPPT charge controller chains the array’s voltage to the battery’s voltage, effectively limiting the array’s power output.
Array voltage varies with cell temperature. For example, when the cells are cold during winter, yet receiving full sun, the array voltage is higher. Higher array voltage translates into greater wattage. Here’s an example: Considering average winter and summer temperatures in Boulder, Colorado, there would be about a 12% difference between average winter versus summer array power output, and up to a 25% difference on a cold winter day versus a hot summer day. For off-grid systems that have higher loads in the winter, the extra energy input offered by MPPT-based systems can be a big benefit. At higher temperatures, which usually occur in the summertime or year-round in mild climates, array voltage drops, and an MPPT controller may be less advantageous.
Step-down. Voltage conversion is another benefit that is built into MPPT charge controllers. An MPPT charge controller is a DC-DC converter—with computerized controls. It can take a higher voltage and lower amperage, and convert those to a lower output voltage at higher amperage. For example, instead of an array producing a nominal 24 V and charging a 24 V battery, an MPPT controller can step-down an array producing 60 V to charge that battery. This frees the array from having to be matched to the battery voltage, and mitigates some wire-sizing (and cost) issues.
In that example, pushing 30 A at 24 V a distance of 40 feet would require large-gauge (expensive) cable—2 AWG—to keep voltage drop under 2%. For the same amount of power, pushing 12 A at 60 V that same 40 feet with 10 AWG will keep voltage drop under 2%, with the MPPT charge controller stepping the output voltage down to 24 V for the batteries. THHN #2 wire retails for about $1.24 per foot, and #10 sells for about $0.19 per foot, saving $84.00 on that two-way wire run, even without considering conduit size and the physical difficulties of pulling large wire.
Higher Input Voltages
Until recently, most charge controllers could accept a maximum input voltage of only 150 V. Today, one manufacturer has models that accept 200 or 250 V input, and two have models that accept up to 600 V input. Having these options provides more flexibility in designing module strings for battery-based systems. For example, instead of designing strings of three modules in series, strings of six modules in series are possible. This reduces the number of strings needed by half. At half the amperage and twice the voltage, the same size wire can be used, but at four times the distance—without losing power.
A 600 V charge controller may be able to accommodate a single series string of 12 modules, negating combiner boxes completely. This translates into less equipment, wire expense, and labor.
The 600 V charge controllers may be used for transforming batteryless grid-tied PV arrays to grid-tied with battery backup. In many cases, rewiring the array is unnecessary.
A disadvantage to using a controller with a higher input voltage is that the disconnects and combiner boxes (if required) are typically more expensive and harder to find. Note that one of the 600 V input charge controllers (Morningstar’s TS-MPPT-60-600) has an optional integrated DC disconnect, which can help mitigate sourcing and finding space on the wall for an external 600 V DC disconnect, though the controller’s additional cost is similar to the cost of a separate DC disconnect.
Single-Module PV Systems
Most module manufacturers have switched to a 60-cell design, resulting in modules in the 200 W to 300 W range with a maximum power point of 25 to 35 V. Nominal 12 V and 24 V modules (having 36 and 72 cells, respectively) are harder to find and more expensive per watt. Several manufacturers have introduced MPPT charge controllers to accommodate a single 60-cell module on a 12 V battery system (which might power, for example, remote lighting or communications, or an off-grid cabin). Blue Sky Energy offers several products for 12 V systems, and MidNite Solar and Morningstar have introduced smaller (30 A) MPPT controllers, which will work for a single module on a 12 V system.
These charge controllers cost more than a simple PWM charge controller that you might use on a system with 36-cell (12 V nominal) modules. However, when you take into account the total system cost—PV module(s) plus charge controller—it can be 10% to 20% less expensive to use the 60-cell module with the MPPT charge controller. Plus, you get the advantage of MPPT. In addition, the wiring of the system often is simpler, since it involves one large module and no combiner boxes.
Matching Controllers to Inverters
For off-grid systems, matching the brand of charge controller to the inverter isn’t usually important, since there is very little coordination between these two. The charge controller routes energy into the battery, and the inverter takes it out—neither of them really cares what the other is doing. However, for a grid-tied system, synchronizing them can matter. While there are thousands of battery-based grid-tied systems that operate without communications between the charge controller and inverter, system programming can be simplified and efficiency can be improved if they are matched. Compatible communications systems enable the inverter to tell the charge controller that the grid is available. At this point, the charge controller’s job is not to regulate battery charge but to track the array’s MPP and get the most energy out of the array that it can. (The inverter will regulate the battery voltage by selling excess energy to the grid.)
Monitoring & Data Logging
All but the most basic charge controllers come with some system monitoring. All of the charge controllers included offer remote display options, enabling you to monitor the system’s operation in the house, for example, rather than at the controller’s location. Most of the MPPT charge controllers include a digital display on the controller as well. If your system has multiple charge controllers (from the same manufacturer), they can communicate with each other to coordinate charging, and can all send data to a single remote monitor.
MidNite Solar offers an amp-hour-counting state-of-charge meter with their Classic charge controllers, and as an option on its smaller KID controllers. Battery state-of-charge (SOC) metering, which shows battery SOC as a percentage, is an important tool that enables users to easily see how full (or empty) their batteries are. But it is often left out of systems because it comes at an extra cost.
Data logging can be another important feature, especially with systems that are not monitored daily. The larger MidNite Solar, Morningstar, OutBack Power, and Schneider Electric charge controllers include data logging, so you can see how many kWh the system produced over a period of time. Having access to this data can be useful for installers when troubleshooting a system.
MidNite Solar, OutBack Power, and Schneider Electric’s charge controllers can be connected to a computer or smartphone (directly for MidNite Solar, and through an extra communications device for OutBack Power and Schneider Electric charge controllers) for monitoring, programming, and accessing historical data.
MPPT - Finding the Sweet Spot
Finding the Sweet Spot
HP Online
All PV cells, modules, and arrays have conditions under which they will perform optimally. Two of the most important of those conditions—amount of sunlight and PV cell temperature—are difficult to control. Ambient temperatures and heat from sun’s rays increase cell temperature, affecting how well a cell converts available light to electrical energy. To date, beyond providing an air gap behind an array, no practical, cost-effective means of cooling cells have been found. Our only recourse is to adjust the module’s electrical condition.
Maximum power point tracking (MPPT) optimizes a module’s power output within the range allowed by its temperature and available sunlight. Every PV module has particular characteristics that are described by I-V curves—a graphed representation of current (I, in amps) versus voltage (V). Power is a product of current and voltage (watts = amps × volts). While the curve changes based on temperature and sunlight, there is only one maximum power point (MPP) on an I-V curve.
Different electronic algorithms can achieve MPPT, but what all methods do is periodically vary electrical conditions and test power output. If the power increases, it is varied a little more until the maximum is attained. If the tested power decreases, then the condition is varied in the other direction to find that maximum power point. That “sweet spot” is maintained until it’s time to again vary conditions and retest. A re-sweep of the I-V curve typically happens every few minutes or when there is a significant power change, though it can vary depending on the tracking method. Since the array is not operating at the MPP during the I-V curve testing, it makes sense to spend as little time as possible during the sweep.
MPPT equipment also varies. Most batteryless grid-tied systems use string inverters, which test and adjust to the MPP for the entire array. Most battery-charging systems rely on a single MPPT charge controller to adjust the entire array. But no two PV modules share the exact characteristics—slight differences between I-V curves, cell temperature, and sunlight (including shading) vary from one place in the array to another. That’s where module-level MPPT comes in.
Microinverters, which are paired to each module, do this automatically. But in a system with a central string inverter, a DC optimizer would be required for each module. A system using optimizers might enjoy an increase of a few percent up to 25% or more in power output, depending on shading and other specifics. A battery-based system would similarly benefit from optimizers. In the case of module-level MPPT, the expense of the equipment should be weighed against the potential gain in energy harvest. Each module will require an optimizer, which can add from a few to several hundred dollars to the system’s overall cost. Optimizer implementation also adds complexity, installation time, and more points of potential failure.
Understanding what MPPT is (and what your equipment options are for various PV system types and scenarios) will help you make an informed choice for your particular situation.
HP Online
All PV cells, modules, and arrays have conditions under which they will perform optimally. Two of the most important of those conditions—amount of sunlight and PV cell temperature—are difficult to control. Ambient temperatures and heat from sun’s rays increase cell temperature, affecting how well a cell converts available light to electrical energy. To date, beyond providing an air gap behind an array, no practical, cost-effective means of cooling cells have been found. Our only recourse is to adjust the module’s electrical condition.
Maximum power point tracking (MPPT) optimizes a module’s power output within the range allowed by its temperature and available sunlight. Every PV module has particular characteristics that are described by I-V curves—a graphed representation of current (I, in amps) versus voltage (V). Power is a product of current and voltage (watts = amps × volts). While the curve changes based on temperature and sunlight, there is only one maximum power point (MPP) on an I-V curve.
Different electronic algorithms can achieve MPPT, but what all methods do is periodically vary electrical conditions and test power output. If the power increases, it is varied a little more until the maximum is attained. If the tested power decreases, then the condition is varied in the other direction to find that maximum power point. That “sweet spot” is maintained until it’s time to again vary conditions and retest. A re-sweep of the I-V curve typically happens every few minutes or when there is a significant power change, though it can vary depending on the tracking method. Since the array is not operating at the MPP during the I-V curve testing, it makes sense to spend as little time as possible during the sweep.
MPPT equipment also varies. Most batteryless grid-tied systems use string inverters, which test and adjust to the MPP for the entire array. Most battery-charging systems rely on a single MPPT charge controller to adjust the entire array. But no two PV modules share the exact characteristics—slight differences between I-V curves, cell temperature, and sunlight (including shading) vary from one place in the array to another. That’s where module-level MPPT comes in.
Microinverters, which are paired to each module, do this automatically. But in a system with a central string inverter, a DC optimizer would be required for each module. A system using optimizers might enjoy an increase of a few percent up to 25% or more in power output, depending on shading and other specifics. A battery-based system would similarly benefit from optimizers. In the case of module-level MPPT, the expense of the equipment should be weighed against the potential gain in energy harvest. Each module will require an optimizer, which can add from a few to several hundred dollars to the system’s overall cost. Optimizer implementation also adds complexity, installation time, and more points of potential failure.
Understanding what MPPT is (and what your equipment options are for various PV system types and scenarios) will help you make an informed choice for your particular situation.
Citation:This article appears in HP online magazine.
Battery Venting for Small Systems
ASK THE EXPERTS: Battery Venting for Small Systems
Dan Fink • Buckville Energy Consulting
HP Online
I have a small 75 W solar-electric system that I use to charge three marine lead-acid batteries. I use it to power my ham radio station, minimal lighting, and a small inverter so we can watch TV during occasional power outages.
The battery’s capacity is about 350 Ah, and the maximum PV short-circuit current is about 5 A. I have a charge controller that prevents battery overcharging. There seems to be no battery gassing from this setup, so I have not worried about ventilation and have the batteries in my house. However, I am thinking seriously about increasing our solar capacity—not to the point of replacing our normal electricity usage, but to have enough charging and storage to run the motors in our pellet stove during a winter power outage or keep our freezer running during a summer outage.
Should I be worried about keeping flooded lead-acid batteries inside the house? Should I either provide a vented enclosure or put the batteries outside? Is there a rule for an acceptable ratio of charging current to Ah capacity for using batteries as I am now using them?
Albert S. Woodhull • Leyden, Massachusetts
Keeping your batteries indoors in their own enclosed, ventilated space is usually the best practice, since this protects them from potentially damaging temperature extremes. Most renewable energy installers recommend a sealed, vented battery enclosure, no matter how small the battery bank or what battery technology is used.
Article 480.9 of the National Electrical Code (NEC) states that provisions for ventilation must be made to prevent the accumulation of explosive gases, but the NEC doesn’t go into the specifics. Under the NEC, sealed battery technologies don’t require venting. American Boat and Yacht Council (ABYC) guideline 10.7.9 recommends a sealed, vented enclosure no matter what the battery type. Some local electrical codes even require power venting of the battery enclosure.
A properly designed and installed power system with a modern, three-stage charge controller keeps hydrogen gas emissions to a minimum (as with your present system), and battery technologies like sealed lead-acid don’t gas during normal operation. But what happens when the situation becomes abnormal? A poorly programmed or malfunctioning charge controller can cause any battery to gas, and even “sealed” batteries have internal valves to release the gas and prevent a case from rupturing.
Battery banks also pose other hazards—exposed high-amperage terminals and wiring; corrosive buildup on the terminals; thermal runaway (with certain battery technologies); and the danger of spilling acid electrolyte. A mishandled wrench that shorts out a battery can turn red hot in a moment, not to mention giving a dramatic sound-and-light show for the unfortunate person who dropped it. Battery banks should be securely isolated from anyone who doesn’t have any business with them.
So, that’s the logic behind always using a vented battery bank enclosure. Most recommendations call for a minimum 2-inch-diameter PVC pipe vent from the top of the box, and a hinged, slanted lid, so any hydrogen gas rises to the top and out the pipe. Hydrogen is so light that it will find its way out even with a flat lid, but the slant also prevents the homeowner from piling things on the battery box lid. That makes access for regular battery maintenance easy, and gives quick emergency access.
For a typical flooded lead-acid renewable energy battery, the maximum recommended charge rate is usually about a C/5 (battery capacity in amp-hours divided by 5), tapering down during the final charging stages. But there are so many different battery technologies and manufacturers that you should be sure to follow the manufacturer’s recommendations. Some modern charge controllers let you tell them the battery bank type, capacity, and recommended charge rates. Their circuitry then does the math for you, and sets up the controller automatically to keep your battery bank healthy.
Things aren’t always normal, and lots can go wrong. Keep your batteries accessible but secure, and check on them regularly.
Dan Fink • Buckville Energy Consulting
Dan Fink • Buckville Energy Consulting
HP Online
I have a small 75 W solar-electric system that I use to charge three marine lead-acid batteries. I use it to power my ham radio station, minimal lighting, and a small inverter so we can watch TV during occasional power outages.
The battery’s capacity is about 350 Ah, and the maximum PV short-circuit current is about 5 A. I have a charge controller that prevents battery overcharging. There seems to be no battery gassing from this setup, so I have not worried about ventilation and have the batteries in my house. However, I am thinking seriously about increasing our solar capacity—not to the point of replacing our normal electricity usage, but to have enough charging and storage to run the motors in our pellet stove during a winter power outage or keep our freezer running during a summer outage.
Should I be worried about keeping flooded lead-acid batteries inside the house? Should I either provide a vented enclosure or put the batteries outside? Is there a rule for an acceptable ratio of charging current to Ah capacity for using batteries as I am now using them?
Albert S. Woodhull • Leyden, Massachusetts
Keeping your batteries indoors in their own enclosed, ventilated space is usually the best practice, since this protects them from potentially damaging temperature extremes. Most renewable energy installers recommend a sealed, vented battery enclosure, no matter how small the battery bank or what battery technology is used.
Article 480.9 of the National Electrical Code (NEC) states that provisions for ventilation must be made to prevent the accumulation of explosive gases, but the NEC doesn’t go into the specifics. Under the NEC, sealed battery technologies don’t require venting. American Boat and Yacht Council (ABYC) guideline 10.7.9 recommends a sealed, vented enclosure no matter what the battery type. Some local electrical codes even require power venting of the battery enclosure.
A properly designed and installed power system with a modern, three-stage charge controller keeps hydrogen gas emissions to a minimum (as with your present system), and battery technologies like sealed lead-acid don’t gas during normal operation. But what happens when the situation becomes abnormal? A poorly programmed or malfunctioning charge controller can cause any battery to gas, and even “sealed” batteries have internal valves to release the gas and prevent a case from rupturing.
Battery banks also pose other hazards—exposed high-amperage terminals and wiring; corrosive buildup on the terminals; thermal runaway (with certain battery technologies); and the danger of spilling acid electrolyte. A mishandled wrench that shorts out a battery can turn red hot in a moment, not to mention giving a dramatic sound-and-light show for the unfortunate person who dropped it. Battery banks should be securely isolated from anyone who doesn’t have any business with them.
So, that’s the logic behind always using a vented battery bank enclosure. Most recommendations call for a minimum 2-inch-diameter PVC pipe vent from the top of the box, and a hinged, slanted lid, so any hydrogen gas rises to the top and out the pipe. Hydrogen is so light that it will find its way out even with a flat lid, but the slant also prevents the homeowner from piling things on the battery box lid. That makes access for regular battery maintenance easy, and gives quick emergency access.
For a typical flooded lead-acid renewable energy battery, the maximum recommended charge rate is usually about a C/5 (battery capacity in amp-hours divided by 5), tapering down during the final charging stages. But there are so many different battery technologies and manufacturers that you should be sure to follow the manufacturer’s recommendations. Some modern charge controllers let you tell them the battery bank type, capacity, and recommended charge rates. Their circuitry then does the math for you, and sets up the controller automatically to keep your battery bank healthy.
Things aren’t always normal, and lots can go wrong. Keep your batteries accessible but secure, and check on them regularly.
Dan Fink • Buckville Energy Consulting
Expect hike in March generation charge
by Lenie Lectura - March 4, 2015
Generation charge for March electricity bills is expected to go up due to higher prices at the Wholesale Electricity Spot Market (WESM), an official of the Manila Electric Co. (Meralco) said on Wednesday.
“We are still waiting for billings from independent power producers/power supply agreements [IPPs/PSAs], but WESM results appear to point to higher market prices,” Meralco Utility Economics Head Larry Fernandez said in a text message.
A Meralco bill is made up of many charges. The largest component is the generation charge, or the portion of the bill that goes to the generation companies or power producers.
Meralco sources its power requirements from the WESM, PSAs and IPPs.
Fernandez explained that higher demand for electricity and the lower dispatch levels of power plants that went offline could be the reasons for higher WESM prices recorded during the supply month of February that will be reflected in the March billing of Meralco customers.
“This maybe due to an increased demand, as peak went up by around 200 megawatts from January to February, coupled with more capacity on outage like the Masinloc and Quezon Power,” the Meralco official added.
The utility firm, which recorded 5.6 million customers at end-2014, will release next week the final adjustment for the March power bills.
Last month Meralco announced that all bill components for February shoot up to P10.51 per kilowatt-hour (kWh). The upward adjustment also translates to an increase in overall power rates by P168 for consumers with a monthly consumption of 200 kWh; P252 for 300 kWh; P336 for 400 kWh; and P420 for 500 kWh.
Generation charge went up by P0.52 per kWh to P5.24 per kWh due to a P1-per-kWh increase in the rates of generation companies under the PSA, as capacity fees normalized from a low level in the preceding month.
Transmission charge also went up by P 0.12 per kWh to P0.99 per kWh. Taxes increased by around
P0.08 per kWh to P1 per kWh, while other charges such as system-loss charge and lifeline subsidy increased by P0.08 per kWh to P0.55 per kWh and P0.14 per kWh, respectively.
The February 2015 billing will also reflect the new Feed-in Tariff allowance charge of P 0.04 per kWh, a uniform charge that will be billed to all on-grid electricity consumers nationwide in support of the Feed-in-Tariff Program.
Meralco reiterated that it does not earn from the pass-through charges, such as the generation and transmission charges.
Payment for the generation charge goes to the power suppliers such as the plants selling to Meralco through the WESM and under the PSAs, as well as the IPPs. Payment for the transmission charge, meanwhile, goes to the National Grid Corp. of the Philippines. Of the total bill, only the distribution, supply and metering charges accrue to Meralco.
Distribution charge remained at P2.20 per kWh.
http://www.businessmirror.com.ph/expect-hike-in-march-generation-charge/
Generation charge for March electricity bills is expected to go up due to higher prices at the Wholesale Electricity Spot Market (WESM), an official of the Manila Electric Co. (Meralco) said on Wednesday.
“We are still waiting for billings from independent power producers/power supply agreements [IPPs/PSAs], but WESM results appear to point to higher market prices,” Meralco Utility Economics Head Larry Fernandez said in a text message.
A Meralco bill is made up of many charges. The largest component is the generation charge, or the portion of the bill that goes to the generation companies or power producers.
Meralco sources its power requirements from the WESM, PSAs and IPPs.
Fernandez explained that higher demand for electricity and the lower dispatch levels of power plants that went offline could be the reasons for higher WESM prices recorded during the supply month of February that will be reflected in the March billing of Meralco customers.
“This maybe due to an increased demand, as peak went up by around 200 megawatts from January to February, coupled with more capacity on outage like the Masinloc and Quezon Power,” the Meralco official added.
The utility firm, which recorded 5.6 million customers at end-2014, will release next week the final adjustment for the March power bills.
Last month Meralco announced that all bill components for February shoot up to P10.51 per kilowatt-hour (kWh). The upward adjustment also translates to an increase in overall power rates by P168 for consumers with a monthly consumption of 200 kWh; P252 for 300 kWh; P336 for 400 kWh; and P420 for 500 kWh.
Generation charge went up by P0.52 per kWh to P5.24 per kWh due to a P1-per-kWh increase in the rates of generation companies under the PSA, as capacity fees normalized from a low level in the preceding month.
Transmission charge also went up by P 0.12 per kWh to P0.99 per kWh. Taxes increased by around
P0.08 per kWh to P1 per kWh, while other charges such as system-loss charge and lifeline subsidy increased by P0.08 per kWh to P0.55 per kWh and P0.14 per kWh, respectively.
The February 2015 billing will also reflect the new Feed-in Tariff allowance charge of P 0.04 per kWh, a uniform charge that will be billed to all on-grid electricity consumers nationwide in support of the Feed-in-Tariff Program.
Meralco reiterated that it does not earn from the pass-through charges, such as the generation and transmission charges.
Payment for the generation charge goes to the power suppliers such as the plants selling to Meralco through the WESM and under the PSAs, as well as the IPPs. Payment for the transmission charge, meanwhile, goes to the National Grid Corp. of the Philippines. Of the total bill, only the distribution, supply and metering charges accrue to Meralco.
Distribution charge remained at P2.20 per kWh.
http://www.businessmirror.com.ph/expect-hike-in-march-generation-charge/
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