2013/12/23

Stop power rate hike

‘Stop power rate hike’

By Rey E. RequejoManila Standard Online_Dec 23, 2013
Solons ask High Court to scrap Meralco move
LAWMAKERS on Thursday asked the Supreme Court to stop Manila Electric Co. from jacking up electricity rates by P4.15 per kilowatt hour, the highest increase in the country’s history.
In their petition, Bayan Muna Reps. Neri Colmenares and Carlos Isagani Zarate; Gabriela Women’s Party Reps. Luz Ilagan and Emmi de Jesus; ACT Teachers Party-list Rep. Antonio Tinio; and Kabataan Party-list Rep. Terry Ridon sought the immediate issuance of temporary restraining order, arguing that the rate increase come at the worst time possible, with the country still reeling from the effects of super typhoon Yolanda.
The groups also asked the Court to nullify the Energy Regulatory Commission approval of Meralco’s rate hike.
They also appealed to the justices to declare as unconstitutional a provision of the Electric Power Industry Reform Act or EPIRA of 2001 which declared that the power generation and supply sectors were not public utilities, and therefore not subject to regulation by the ERC.
In its letter to the ERC dated Dec. 5, Meralco said it would have to increase rates by P4.15 per kWh for residential consumers because it needed to buy more expensive power following the maintenance shutdown of the Malampaya gas field.
On Dec. 9, the ERC approved Meralco’s request.
In approving the increase without the benefit of a public hearing, which is required by law, the ERC committed grave abuse of discretion, the lawmakers said.
EPIRA, the petitioners added, was aimed at promoting competition and penalizing abuses of market power in a restructured electricity industry.
Given “the suspiciously sudden and simultaneous shutdown of various power plants” to coincide with the announced Malampaya maintenance, the ERC should not have approved Meralco’s petition barely three days from its submission.
The petitioners accused the ERC of reneging on its duty to protect the public from anti-competitive practices and market abuse when it approved the P4.15 increase despite clear indications of irregularity in the simultaneous planned and unplanned shutdowns, the hefty spike of electricity prices that Meralco sought.
“It is really mind boggling that the ERC hastily approved Meralco’s letter request,” the petitioners said, adding that the commission’s actions were also collusion with vested oil interests.
In the Court of Appeals, the Special 16th Division junked a petition filed by the Foundation for Economic Freedom seeking to stop the ERC from hearing and deciding on a petition filed by the National Renewable Energy Board, which is expected to increase power rates to consumers.
Associate Justice Pedro Corales ruled that the petition was moot and academic because the ERC had already ruled on NREB’s petition in October and November.
The Appeals Court also ruled that the ERC had not committed grave abuse in approving NREB’s petition.
The NREB filed the petition with the ERC on behalf of the renewable energy suppliers to adopt a feed-in-tariff for electricity generated from biomass, ocean, run-off-river hydropower, solar and wind energy resources.
The tax on electricity consumers for a period of 20 years would generate money for a subsidy to encourage the development of renewable sources of energy.
The FEF had warned that the taxes from electricity consumers nationwide would reach P11 billion annually for the next 20 years collectible through their monthly billings.
The Palace on Thursday said it was determined “to uphold and protect the citizens’ welfare” and to carry out its mandate to prevent anti-competitive and market abuse practices.”
“In view of this, we support the current Senate inquiry into the recent power rate adjustments. This runs parallel to the on-going investigation of the tripartite committee composed of the Department of Energy, Energy Regulatory Commission, and the Philippine Electricity Market Corporation, as well as that of the Justice Department’s Office of Competition,” Communications Secretary Herminio Coloma Jr. said in a press briefing.
Coloma said the Aquino administration hoped that “the Senate inquiry will also lead to concrete proposals on how existing laws can be improved so that the protection of consumer welfare will be assured.”
Senate President Frankllin Drilon on Thursday said if collusion is proved in the recent rate hikes, the appropriate criminal charges would be filed.
Also on Thursday, a labor group criticized Senator Sergio Osmena III for concluding publicly that there was no collusion among power generating companies and Meralco on the rate hike, pre-empting the investigtions by the Energy and Justice departments.
“Serge is a consistent supporter of power industry players since his sponsorship of the EPIRA Law which ushered in the era of high electricity rates to his defense of Meralco’s gargantuan rate hike,” said Wilson Fortaleza of the Partido ng Manggagawa.
Fortaleza was one of the signatories to the complaint against Meralco and generation companies lodged by groups last Monday with the Justice Departments Office for Competition.

Justice Secretary Leila de Lima vowed to come up with the findings by January next year. – With Macon Ramos-Araneta, Ronald O. Reyes and Vito Barcelo
***
EastGreenfields post note on NREB petition for power rate increase.
The power rate is expected to increase pending on the implementation of Renewable FIT rates. This is inevitable since Green sources has to be funded by payments from FIT. 
At first look, the FIT will be an increase in each consumers billing but scrutinizing it further will reveal that FIT rates are actually in parity or even lower (for Biomass), see table below:

Solar FIT: P9.68 / kW-hr
Wind FIT: P8.53 / kW-hr
RoR Hydro FIT: P5.90 / kW-hr
Biomass FIT:P6.63 / kW-hr

These rates are not going to be demanded from all grid consumers but rather will be computed and blended with the mixed generation rates, in proportion to it's contribution.

2013/12/21

Batteries for Renewable Energy System

Understanding Batteries for Your RE System
HP 

By: 
Issue Date 
Last Updated: 
Aug 22, 2013

When shopping for batteries for a renewable energy (RE) system, it is important to choose a battery designed for deep-cycling, and one with a track record of long-term reliability and performance. Make sure to evaluate both the battery manufacturer’s reputation for using quality components, as well as the manufacturing process employed to assemble a deep-cycle battery.

While buying cheap batteries may seem a good idea at first, it can cost you much more down the road. Cheap batteries will not withstand the rigorous deep-cycling that is inherent in RE applications. Over time, these batteries will fail and need to be replaced more often than quality deep-cycle batteries, costing you more money in the long run. Lower overall cost of ownership and reducing the need to constantly replace batteries should be the determining factors, not just the initial purchase price.

Battery Types

A battery uses an electrochemical reaction to store energy. Unlike primary batteries that cannot be recharged, secondary batteries can be recharged many times before they reach the end of their life. Several types of secondary batteries are available in sizes appropriate for an RE system, including lead-acid, lithium ion, nickel-cadmium, and nickel-iron. However, lead-acid, deep-cycle batteries, specifically designed to be deeply discharged to 50% to 80% of capacity, are most often used due to their relative low cost and wide availability.
Flooded lead-acid (FLA) and valve-regulated lead-acid (VRLA, or “sealed”) are two types of lead-acid batteries. FLA batteries lose electrolyte as the electrolyte is converted from a liquid to a gas during charging, so the individual cells must be periodically topped off with distilled water to avoid permanent damage. VRLA batteries can be either absorbed glass mat (AGM) or gel and are maintenance-free—they cannot accept the addition of water. AGM batteries feature individual cells that contain positive and negative plates separated by a glass mat separator (see “When to Use VRLAs” sidebar).
Click to enlarge

Batteries to Suit Your System


Lead-acid batteries are made for specific discharge duty cycles. For example, a starting-lighting-ignition (SLI) battery (used to start vehicles) is designed to deliver high amperage for short durations, and then be recharged quickly. Similarly, a lead-acid battery that is part of an uninterruptible power system (UPS) may need to provide energy for just a few minutes when the utility experiences a grid anomaly or outage—usually only a few amp-hours are taken out of the battery. In contrast, a battery in an RE application must run various electrical loads for long durations, and possibly over several days. So for an RE application, choose a battery designed for a marathon, not a sprint.
Charging characteristics also influence battery choice. A SLI battery is designed to charge for a few hours at most (via the vehicle’s alternator) before the next engine-cranking event. Since a UPS battery has to be ready for discharge at any time, it is on a trickle (“float”) charge whenever the source is available. A deep-cycling RE battery will experience constant charging and discharging over several years. Because of this, the ideal battery for an RE application must be capable of delivering many cycles over a longer time than SLI, and can have some charging flexibility—either more slowly from an RE source or more quickly from a backup generator.

Details Make a Difference


Although all battery manufacturers use the same general processes, all batteries are not created equal. There are significant differences in the battery components used during the manufacturing process as well as the quality control processes each battery manufacturer implements within their facilities. Evaluating these differences is key in determining a battery’s longevity and performance, and this information can usually be found on a deep-cycle battery manufacturer’s website. If not, ask your sales rep or the battery manufacturer directly about specific manufacturing processes.
The working components of lead-acid batteries are their plates, which are made of lead. To harden the lead for use in a battery, it is combined with other metals (calcium, in VRLA batteries; antimony, in flooded batteries).
Lead oxide is used to produce the pastes, which include the positive active material (PAM) or negative active material (NAM) that is applied to a grid of lead that becomes the battery’s positive and negative plates. The chemical compositions of PAM and NAM are proprietary. Deep-cycle batteries have PAM and NAM recipes tailored for applications such as RE, propulsion (in EVs), or equipment like electric forklifts. Therefore, it’s important that a user understand what they want to achieve from their batteries—long float life or long cycle life. A battery’s design and paste formulations are customized for one or the other.
The battery’s lead grids are designed to hold the active materials (PAM and NAM). The grids also provide an electrically conductive path that enables the electrons to move in and out of the battery. Positive and negative grids are cast from molten lead alloys, and the patterns used in the design of grids vary from manufacturer to manufacturer. Grid designs and configurations help the current flow through the grid network, enhancing overall battery performance.
Once the positive and negative grids are pasted with PAM or NAM, they undergo curing, in which the paste is dried slowly. During this process, a bond is created between the paste and metallic grid, to develop an electrochemically active mass. Curing must be accomplished under precisely controlled temperature and humidity to produce a high-quality battery. The curing time can take as long as 72 hours to fortify the interlocking crystal structure of the PAM and NAM.
After curing, the plates are arranged in groups, alternating positive and negative. A separator is placed between each plate that prevents them from touching and shorting. The separator material’s quality and design are important factors in determining the battery’s service life. High-quality batteries use glass mat or rubber separators that reduce the chance of stratification, which is a typical mode of battery failure in renewable energy systems. Stratification is the process in which the acid concentration at the bottom of the battery becomes greater than the concentration at the top. If not addressed, stratification will destroy a battery.
After the appropriate number of positive and negative plates are stacked, they are placed into a plastic case, which contains one cavity for a 2 V cell, three for a 6 V battery, or six for a 12 V battery. The number of plates depends on the specific capacity of the battery being built, i.e., the greater the amp-hour capacity, the larger the number of plates. The positive plates are then welded together at the top, as are the negative plates, forming a single cell assembly. In multiple-cell batteries, each cell assembly is welded in series or in parallel to determine the battery’s voltage.
A cover is then heat-sealed to the case. The quality of this seal is important—if poorly done, the seal’s integrity can be compromised, leading to future problems such as breakage and/or separation of the lid from the battery case. 
Once battery assembly is complete, the battery goes through “formation.” The formation process involves filling the battery with a solution of sulfuric acid and distilled water. The battery is then given an initial charge, which preps the battery plates for operation. Formation usually takes several days to complete; the greater the battery capacity, the longer the formation period.
When the formation process is complete, the battery is tested to confirm it meets the manufacturer’s specifications. This is called “end of line” testing, which ensures all electrical connections are working properly and there are no obvious defects. The battery is then cleaned of any residual acid on its external surfaces, labeled to be in compliance with all necessary regulations, and prepared for shipping.

Quality Control

The differences in the manufacturing processes for a deep-cycle battery can have a profound effect on its performance and life, as seen in the images that show high- and lower-quality batteries.
Both had the same rated capacity, were the same age, and experienced identical service under controlled conditions. However, the battery on the left has aged far more gracefully than the one on the right. Why? The battery cell on the left has a moss shield on the top of the plates, which prevents the plates from expanding and shorting out at the top of the cell. The absence of a top shield on the other battery eventually caused short-circuiting, leading to lower capacity and a shorter life span. The battery on the left also featured a paste formulation specifically designed to optimize use of the battery’s active material, resulting in sustained battery performance over a longer period of time.
Besides the presence of a moss plate, the design and use of a battery’s grid and separators are equally important. Corrosion can quickly kill a battery, and the thicker a battery’s grid structure, the greater its resistance to corrosion. It also is important to ensure that the grids are cast, rather than stamped. Cast grids have no hairline fractures, which can cause the battery to fail prematurely.
In addition, separators between the battery plates should feature wide channels to increase the flow of acid, which enables optimum battery performance. Batteries that feature separators with wide-channel designs will also offer greater resistance to stratification.

Outside Parameters


An essential component of determining the quality of a deep-cycle battery is the manufacturer’s investment in independent third-party testing. This data provides valuable information on product performance, and validates a manufacturer’s product claims. Independent, third-party data obtained from testing batteries per industry-recognized standards, such as by the International Electrotechnical Commission (IEC), allows consumers to compare products from different manufacturers, and can be found on some battery manufacturers’ websites.
For an RE application, the two parameters of critical importance are amp-hour capacity (commonly at the 20-hour rate) and the number of cycles the battery can deliver to a given depth of discharge (DOD)—for example, 3,000 cycles at 50% DOD.
Once the short list of possible battery options has been created, the next task should be to ensure the battery manufacturer has not only a proven track record, but also builds quality into each battery it ships.
The type of battery you choose and the vendor you purchase from can have a significant impact on the performance, durability, and total cost of a renewable energy system. The battery bank in an RE system typically represents the largest equipment cost over the life of the system, so proper understanding of deep-cycle batteries is important to maximize the return on your investment.
Click to enlarge





Kalyan Jana is a senior applications engineer for Trojan Battery’s renewable energy group.
***



2013/12/20

Philippine Net Metering FAQs

Philippine Net Metering FAQs

This blog is taken from the "NET-METERING REFERENCE GUIDE" guide book release by Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH

Part 1 of the reference guide is titled "How net-metering works: Understanding the basics of policy, regulation and standards", this blog will try to present Part 1 of the guide as Philippine Net Metering FAQs.

Here's the complete Part 1.

How net-metering works: Understanding the basics of policy, regulation and standards
Author: Atty. Ranulfo Ocampo, President PEPOA, Chairman NREB Sub-Committee on Net-Metering

Q1. What is net-metering?

A1. Net-metering allows customers of Distribution Utilities (DUs) to install an on-site Renewable Energy (RE) facility not exceeding 100 kilowatts (kW) in capacity so they can generate electricity for their own use. Any electricity generated that is not consumed by the customer is automatically exported to the DU’s distribution system. The DU then gives a peso credit for the excess electricity received equivalent to the DU’s blended generation cost, excluding other generation adjustments, and deducts the credits earned to the customer’s electric bill.

Q2. Is net-metering already available in the Philippines?

A2. On 27 May 2013, the Energy Regulatory Commission adopted ERC Resolution 09, Series of 2013 approving the Rules Enabling the Net-Metering Program for Renewable Energy. This resolution was published on 10 July 2013 in newspapers of general circulation in the country and took effect 15 days thereafter. Thus, the Net-Metering Rules took effect in the Philippines on July 24, 2013. The Net-Metering Program is available only to On-Grid distribution systems (or DUs connected to the transmission grid).

Q3. What is the legal basis of ERC in approving a net-metering program for renewable energy in the Philippines?
A3. Section 10 of the Renewable Energy Act of 2008 (Republic Act No. 9513) provides that subject to technical considerations and without discrimination and upon request by distribution end-users, DUs shall enter into net-metering agreement with qualified end-users who will be installing the RE system. The ERC, in consultation with the NREB and the electric power industry participants, shall establish net-metering interconnection standards and pricing methodology and other commercial arrangements necessary to ensure success of the net-metering for renewable energy.

Q4. Why is there a capacity limit of 100 kW placed on RE systems under the net-metering program?

A4. This is because net-metering, as defined under Section 4 (gg) of the RE Law, refers only to a system appropriate for Distributed Generation (DG). DG, as defined under Section 4 (j) of the RE Law, as small generation entities supplying directly to the distribution grid, any one of which shall not exceed one hundred kilowatts (100 kW) in capacity.

Q5. What types of power generating facilities are eligible for net-metering?

A5. RE facilities such as solar, wind, biomass or biogas energy systems, or such other RE Systems not exceeding 100 kW in power generating capacity, capable of being installed within the customer’s premises, are eligible to participate in the net-metering program.

Q6. What benefit will I get if go into net-metering?

A6. By generating electricity for own use, you reduce the amount of electricity you buy from your local DU. The rate of savings (or avoided cost) realized on electricity generated for own use is equivalent to the DU’s retail rate consisting of charges for generation, transmission, system loss, distribution, subsidies, taxes and other charges. You also earn peso credits on any excess electricity exported to the DU equivalent to the DU’s blended generation cost, excluding other generation adjustments. The peso credits earned is then used to reduce
your electric bill/s.

Q7. How will my DU meter my import and export energy?

A7. The DU may opt to install two uni-directional meters – one to meter energy you buy from your local DU, and the other to meter the energy you export to the DU.

The DU may at its option install a single bi-directional meter that can meter both import and export energy if it finds it to be a more economical. The DU may also install a third meter in proximity to your RE facility to meter its total RE generation. The total RE generation shall earn for the host DU RE Certificates which the DU can use to comply with its Renewable Portfolio Standards (RPS) obligations.



Q8. Who are qualified to participate in the net-metering program?

A8. DU customers who are in good credit standing in the payment of their electric bills to their DU are qualified to participate in the Net-Metering Program for Renewable Energy. These customers are referred to in the Rules as “Qualified End-Users” or QE.

Q9. If I am a contestable customer getting my power supply from a competitive Retail Electricity Supplier (RES), am I qualified to participate in the net-metering program?

A9. No. Only distribution end-users (or captive customers) or contestable customers who opted to remain with their DU are qualified to participate in the net-metering program. This is because the excess electricity received by the DU from the QE can only be distributed to the DU’s other customers, and the credit to be given for the excess electricity received by the DU is equivalent to the DU’s blended generation costs. Contestable customers getting their power supply from an RES are thus not eligible to join the Net-Metering program.

Q10. If I am a customer directly-connected to the transmission grid, am I qualified to participate in the net-metering program?

A10. No. Customers directly-connected to the transmission grid are not DU customers but are transmission
load customers of the National Grid Corporation of the Philippines (NGCP).

Q11. How do I determine the DU’s blended generation cost for a particular month?

A11. DUs are required to publish in their websites their monthly generation cost. You only need to access your DU’s websites to get the blended generation cost of your DU for a particular month so that you will know how much credit you are entitled to on any excess electricity you export to your DU.

Q12. Please give an example of a DU’s blended generation cost, say for the billing month of November 2013?

A12. Using Meralco’s generation costs for November 2013 (as downloaded from its website), its blended generation costs, excluding other generation adjustments, for November 2013 is highlighted in yellow (see table).

double click to enlarge image


Q13. Will I incur additional charges if I avail of net-metering?

A13. Yes, DUs shall impose a net-metering charge to all customers who avail of net-metering equivalent to their existing ERC-approved Php/customer/month supply and metering rate based on the exported energy as registered in the export meter. This net-metering charge shall cover the DU’s incremental costs related to system enhancement and additional meter reading and other operating costs. The DUs may also apply before ERC a different schedule of net-metering charges subject to ERC approval after due notice and hearing. Meantime, the net-metering charges cited above shall prevail until a different schedule of net-metering charges is approved by ERC.

Q14. Please give a simulation of how my electric bill would look like if I am a net-metering customer with a 2kW solar-powered facility installed on my rooftop?

A14. See assumptions and simulated electric bill below:

Assumptions:
Rated Capacity of Solar Rooftop                                     2.00 kW
Yield @ 100% Capacity Factor (2kWx720hrs)                1,440 kWh
Yield @ 16% Capacity Factor 1,440x16%                       230 kWh
Own Use @ 60%                                                                 138 kWh
Net Export @ 40%                                                               92 kWh

Double click to enlarge image


Q15. Are all customers ideal candidates for net-metering?

A15. Not all DU customers are ideal candidates for net-metering. Customers with demand-related (kW) charges may not be ideal candidates for net-metering because net-metering displaces only energy related (kWh) charges.
Be that as it may, customers whose peak demand of electricity coincides with the availability of the RE resource may also stand to benefit from net-metering even if he has demand-related (kW) charges. This is because his RE production can potentially reduce his coincident peak demand for electricity.

Q16. Who then would be ideal candidates for net-metering?
A16. Customers with pure energy-related charges will benefit from net-metering.
As mentioned above, customers whose peak demand of electricity coincides with the availability of the
RE resource may also stand to benefit from net-metering even if he has demand-related (kW) charges
because his RE production can potentially reduce his coincident peak demand for electricity.

Q17. What is the optimum size of an RE facility should I install in my premises?

A17. If you consume all of your RE production, you avoid 100% of the retail rate of your electric bill. If you export any excess RE to your DU, you only offset the blended generation cost (or weighted average power production cost) of your DU. This is about 40-45% of the retail rate of your electric bill. So for an RE facility like a solar roof top system, the optimum capacity that you should install in
your premises should not exceed your daytime peak demand for electricity so that you can maximize your savings/avoided cost on electricity, and shorten to the extent possible the payback period of your investment in the solar roof top facility.

***

EastGreenfields post notes:

In EastGreenfields, we can give you proposals with simulated month by month billing schedule.

Email us for details: inquiry@eastgreenfields.com

or visit our website

www.eastgreenfields.com

2013/12/18

Batteries in Series & Parallel

Batteries in Series & Parallel

HP Issue date: 
10/10/12

Hugh Piggott
Connecting two battery banks of different amp-hour capacity together in series is a bad idea. The problem is that the battery charging controls will operate based on the average battery voltage and the two batteries will have very different voltages because their capacities are different. The 100 AH battery will become fully charged long before the larger one. The combined voltage will rise, but by the time the controller turns off the charging sources, the 100 AH battery will be overcharged. Meanwhile, the 200 AH battery will not get fully charged. When the bank is being discharged, the 100 AH battery will go flat and its voltage will fall well before the 200 AH battery. The inverter will eventually cut out but not before the 100 AH battery is excessively drained.

Connecting two banks with different capacities in parallel is technically fine since the batteries will be operating at the same voltage. Charge and discharge current will be shared, based on capacity. It is best if the batteries are of the same type and age. For example, avoid combining a sealed (gel or absorbed glass mat) battery with a flooded (conventional) battery because they have different charging setpoints. Broadly speaking, you can parallel batteries without problems, and the charge controller will look after them. Just make sure you give them plenty of charge. If the system tends to operate at less than a full state of charge, adding new batteries to old will probably just result in the old ones pulling the new ones down and everything getting sulphated.


Choosing the Best Batteries for RE (Solar)

Choosing the Best Batteries

HP Issue date: March 2012
By: 


Whether you need batteries to store energy for your off-grid home, or you want backup power to keep the lights on when the grid goes down, understanding the different battery specifications will help you select the ideal batteries for your application.
To choose the right battery, you first need to know what you are trying to accomplish. What system type are you working with—off-grid or grid-tied? Where will the battery bank be located? How much maintenance are you prepared to do? And how often (or not) do you want to replace your batteries? The answers to these questions will dictate which batteries make the most sense for your renewable energy system.
Budget also plays a big role in which batteries you choose. Buying batteries is a long-term investment, and skimping on these important components can cripple a system. Getting it right the first time will pay off in performance and longevity. However, simply buying the most expensive battery does not ensure you are meeting the needs of your renewable energy system. For your system to operate and perform well, it is crucial to understand the various battery specifications and how they relate to RE system design.
Batteries used in an RE system can be broken down into two basic categories: heavy duty/commercial and industrial. A common heavy duty/commercial-type battery bank may be comprised of several 6 V, 390 AH (L-16 type) batteries. An industrial battery pack will usually be large 2 V cells (with thicker lead plates) pre-wired to 12, 24, or 48 V and encased in a large metal housing. You will pay more for the industrial battery bank than you will for the equivalent battery pack made of heavy duty/commercial batteries, but you gain longer battery life and a better warranty. 
If you are working with an installing dealer, they often have preferences about which batteries they will use. For example, some installers will only work with L-16 type batteries because they are the largest that they can readily move by themselves—each L-16 battery weighs around 120 pounds, whereas industrial batteries can weigh thousands of pounds, making them difficult to maneuver without disassembly. If you have no experience with batteries, shorter-lived, less-expensive batteries may be a better choice to get you up to speed with battery operation. But some installers will still lean toward the expensive industrial battery packs because they want to minimize battery replacement. This can be especially beneficial in an off-grid setting where just getting to the site may be difficult—much less moving the old batteries out, getting the new ones in, and having to haul the old ones away for recycling. However, industrial batteries are only a wise investment if you are confident in your ability to maintain the battery bank.

Choosing Your Batteries

As with any RE system investment, your best bet will be to identify your true needs and design a system around them. Grid-tied battery backup systems generally use low-capacity  banks made up of sealed, non-industrial batteries that will meet your needs for running critical loads like refrigeration and lighting during power outages. They are generally designed to stay at float most of the time with only occasional cycling, and are often made with calcium alloyed with the lead which helps lower battery self-discharge losses.
To properly size a backup battery bank, compute your critical load profile to determine daily watt-hour consumption during power outages. That number can often be your guide for the correct battery size. Most grid outages are less than one day, and a battery bank sized to be discharged to 50% of capacity by the critical load profile will meet most needs nicely.
If you’re off grid and rely on your batteries to meet all your electrical loads, buy a long-lived battery and be prepared to maintain it well. These systems—which cycle the batteries daily—use batteries with a lead-antimony alloy, which performs better under conditions of regular cycling. 
Typically, off-grid battery banks are sized by considering the required “autonomy”—the number of days that the battery will provide for the loads before reaching 50% depth of discharge (DOD). Off-grid systems usually size a bank to provide two to four days of autonomy. For example, if your load profile requires 5,000 WH per day, you’ll want a battery that stores 10,000 WH to achieve one day of autonomy. Four days of autonomy would require a 40,000 WH battery capacity.
Off-grid system designer opinions on maximum DOD vary widely. Some prefer to keep the depth no greater than 20%, while others have no fear of going below 50%. The deeper the regular discharge, the fewer cycles a battery will give you before needing replacement. So if you do not mind swapping your battery bank more often, go with a deeper discharge—it will save you money up front. But if swapping batteries into and out of your system is a royal pain, you might prefer maximizing battery life by buying a higher-capacity battery. For the design choice that will save you money in the long run, calculate the savings from buying fewer batteries up front, plus the cost of more frequent battery replacement (higher DOD)—versus more batteries up front, with fewer replacements (lower DOD).

...And Don’t Forget

To maximize battery life, batteries need to be properly maintained by:
• Making sure the batteries get completely recharged at least once a week by RE generation and/or supplemented with backup generator or grid charging
·                                 Monitoring the electrolyte and adding distilled water when needed if flooded batteries are used
·                                 Keeping the terminals and interconnections clean by removing built-up corrosion and keeping the battery tops clean and dry
·                                 Equalizing the batteries four to six times a year to remove surface sulfation from the lead plates

Specs Definitions

Manufacturer. Battery manufacturers build batteries for many different applications. Historically, RE systems used batteries originally designed for other applications, such as powering electric golf carts. Today, many battery manufacturers list which of their batteries are appropriate for RE systems. All battery manufacturer Web sites listed in this guide, with the exception of FullRiver Battery, list batteries specifically for use in RE systems.
Model name. These letters and numbers are used by the battery manufacturer to “name” a group of batteries that have similar characteristics, and distinguish them from the company’s other battery lines. It is important to not use batteries with differing model numbers within the same battery bank, as mixing different battery types can create an imbalance within the pack which leads to poor system performance and may cause premature battery bank failure. 
Battery type. Flooded lead-acid (FLA) batteries are the most common type used in RE systems, particularly off grid. They are the least expensive per capacity and, if well maintained, can have a relatively long life span. However, they require the most maintenance. Distilled water needs to be added to the cells on a regular basis, depending upon how often and how deeply the bank is cycled, and upon battery charging regimens.
Valve-regulated lead-acid batteries (VLRA, a.k.a. sealed batteries).  Two general types of VRLA batteries are available for RE systems—absorbed glass mat and gel cells. Absorbed glass mat (AGM) lead-acid batteries are similar in chemistry to FLA cells. In their construction, glass mats, placed between the lead plates (anodes and cathodes), allow the electrolyte to be suspended close to the plates’ active material. These sealed batteries offer the advantage of not needing to be watered and greatly reduced gassing during charge cycles. This type of construction—adding glass mats, sealing the cells, and constructing the plates to operate with less electrolyte—increases cost while potentially shortening life span.
Gel cells use a “gel”-type electrolyte—with a silica additive that causes the liquid to stiffen. Gel-cell batteries are also sealed, which means no water to add—less maintenance and less gassing. However, because lost electrolyte cannot be replaced, they also have a shorter life. They are typically more expensive than FLA or AGM batteries.
Because AGMs can’t be watered, they have to be charged more lightly to avoid using up the finite amount of electrolyte they contain. Gel cells also aren’t watered but need to be charged even more lightly to avoid drying out the cell, which will kill it. 
So why would you ever choose shorter-lived, more expensive batteries like AGM or gel cells? The reasons vary, but often portability, poor battery area ventilation, and maintenance are factors. AGM and gel cell batteries have no liquid electrolyte to spill, so they can be a good choice for mobile systems. And because they hardly gas, they can work well in places where adequate ventilation for FLA batteries isn’t possible. Because they are freeze-resistant, they may be a good choice in applications where extreme cold is a factor.
AGM batteries are often the best choice for grid-tied applications with battery backup, since they are designed for float or standby applications. Because low-capacity battery banks are typical in backup applications, both decreased cycle life and increased cost can be offset by the fact that these batteries are rarely cycled. Plus, users with grid-tied systems are usually less inclined to pay attention to the battery maintenance, since they are also unaccustomed to “maintaining” their grid power. Finally, VRLA batteries will outlast FLA batteries that are not maintained properly (i.e. not watered regularly). If batteries are to be deeply cycled (50% to 80% DOD), gel-cell batteries may offer a longer life (more overall cycles) than AGMs.
Nominal Battery Voltage. Lead-acid batteries are built from individual cells with a “nominal” voltage of 2 V. Battery packs for RE systems are made up of combinations of cells to achieve nominal battery bank voltages of 12, 24, or 48. When designing small systems (loads less than 1,000 WH per day), 12 VDC is often selected as a nominal battery bank voltage if that system is not projected to grow. So a system for a hunting cabin that isn’t going to become a vacation home will keep battery costs down by having this low-voltage design.
For systems with heavier load profiles, larger (and more electrically efficient) battery voltages of 24 and 48 are commonly used. With commercial deep-cycle batteries (like golf cart and L16), the basic unit is often a 6 V battery made up of three, 2 V cells. In the medium-to-large systems, these 6 V units are typically combined in series (four for a 24 V string; eight for a 48 V string). To get greater AH capacity at that voltage, additional strings are then paralleled or higher-capacity batteries are selected.
Amp-Hour Capacity. The sizing of the battery bank depends on the storage capacity required, the maximum discharge rate at any time, the maximum charge rate, and the temperatures at which the batteries will operate.
A battery’s storage capacity—the amount of electrical energy it can hold—is typically expressed in ampere-hours (amp-hours, or AH) at a certain discharge rate. One AH represents a flow of electric current of 1 amp for 1 hour. A battery is like a bucket—the larger your “bucket” is, the more AH it can hold. Hence, the larger the AH value of a battery, given a particular discharge rate, the more storage it offers.
Often there’s a choice of selecting a battery with either higher voltage and lower AH, or lower voltage and higher AH. How do you know which is most appropriate for your application? In general, limit the number of battery series strings in parallel to three or less (two are better, and one is ideal). This reduces imbalances introduced by having multiple paths for the current to follow and extra electrical resistance created by paralleled battery cables. In applications where more AH are needed, buy lower-voltage, higher AH batteries so that several low-voltage batteries can be wired in series and the number of paralleled battery strings can be minimized.
The denoted AH capacity of a given battery depends on the rate at which it is being discharged and the amount of time it takes to discharge it. Large industrial batteries, i.e. for forklifts, are often rated at the “6-hour” rate, indicating a high current discharge rate, which brings the battery to its terminal voltage (often at 80% DOD) in 6 hours, about the length of a forklift’s working shift. For RE systems, a 20-hour rate is typically used, because that is closely aligned with the more modest discharge rates that bring the battery to a terminal voltage (again, often at 80% DOD) over 20 hours—more closely approximating daily home use before recharging.
For converting 6-hour rates to an RE system’s more common 20-hour rate, multiply by 1.24. Using this calculation, a 100 AH, 6-hour rating offers 124 AH at the 20-hour rate.
Bulk Charge Set Point Voltage. When charging batteries, the goal is to put as much current as possible into the battery as efficiently as possible. But charging a battery too quickly can cause heat to build up in the battery, as well as excessive gassing, and can shorten the battery’s life. To keep from harming the battery during charging, charge controllers used in RE systems limit the charge rate based on the batteries’ voltage. As the cell voltage increases, the charge rate (the number of amps allowed in) is reduced to prevent overcharging.
The initial phase when all available current is allowed into the battery is referred to as the “bulk” charge phase. Once the battery has reached its initial bulk-charge voltage, the charge controller will hold the voltage there for a programmed period of time (often 2 hours)—the “absorption” charge phase. This is done to assure full charging throughout the many cells of the battery. Note that the set points listed in this guide are per cell, so you will need to multiply it by the number of series-connected cells to determine the appropriate battery charge set points. For example, if you were to use four batteries (6 V each, wired in series for a 24 V configuration) and the bulk charge set point voltage range is 2.4 to 2.49 V for your battery’s cells, the ideal battery bank bulk-charge voltage set point would be between 28.8 and 29.88 V (3 cells per battery x 4 batteries x 2.4 to 2.49 V).
Float-Charge Set Point Voltage. After the absorption period, the charge controller ramps down the charging current to achieve the “float” phase, which is a lower voltage that greatly reduces the batteries’ gassing while still keeping the battery full. To continue the example, the float-charge set point voltage range is 2.20 to 2.23 V for each cell. With 12 cells total, the ideal battery bank float-charge voltage set point for this particular battery bank would be between 26.4 and 26.76 V.
Both AGM and gel-cell batteries will not tolerate voltages that are as high as FLAs. The charge controller’s bulk and float set points must be programmed appropriately to avoid damaging these batteries.
Equalization Charge Set Point Voltage. An equalizing charge cycle is a controlled overcharging of the battery bank to make sure all cells get charged, and to remove sulfate ion bonds on the batteries’ plates and to regain battery capacity—before permanent bonds develop. First, the battery is charged to full capacity by completing a bulk and absorption charge cycle. Then the battery is charged for an extended period of time, typically 6 to 12 hours, at a C/20 rate (charging amps equal to battery’s AH capacity divided by 20). By controlling the charge rate at C/20, the battery is kept from harm. (Uncontrolled overcharging can warp the batteries’ plates, causing it to short out and possibly explode.)
Equalizing an FLA battery is essential to maintaining battery life, but can be difficult to achieve with the limited current available from a PV array. In off-grid applications, a backup engine generator is often used to equalize the batteries through a charger. Off grid, the use of household loads is generally limited during equalization to make sure enough current is available. In utility-tied systems with batteries, the grid substitutes for a generator.
Using the example of the four-battery bank (6 V each, wired in series for 24 V) and an equalization charge set point voltage range between 2.5 and 2.67 V per cell, the ideal battery bank equalization charge voltage set point for this particular battery bank would be between 30 and 32.04 V.
It is commonly believed that sealed batteries should never be equalized, yet some sealed battery manufacturers will provide an equalization voltage set point for their batteries. It is important to note that these values are usually the same as the bulk voltage set point for that battery. Typically, equalizing sealed batteries means merely extending the absorption period for a longer duration than normal. Additionally, sealed battery “equalization” is usually done only if the battery is showing signs of premature capacity loss (i.e., not lasting as long as normal on a charge), and is not part of routine battery maintenance. Regardless, equalization is very battery specific, so it is important to find appropriate voltage set points and charge current ranges for your particular batteries.
Dimensions. When you’re designing your battery bank, the size of the batteries—their length, width, and height—determines the size of the containment that you’ll need to buy or build. In addition to considering the dimensions of the  batteries, it’s a good idea to leave 1/2 to 1 inch of space between each battery. This will help keep the individual batteries operating at the same temperature and allow them to shed heat during heavy charging regimes.
Weight. Even the smallest batteries used in RE systems can weigh as much as a Labrador retriever—50 to 60 pounds. The really big batteries can weigh as much as a small horse. So, adequate trucks, skids, pallet jacks, and forklifts all become more important in moving batteries safely as the bank grows in size. You’ll need to make sure your floor and/or rack is stout enough to support the total weight of the bank.
Warranty. Manufacturers generally guarantee their products to be free of defects and perform as specified for a set period of time, and will replace defective units during this time period. Many manufacturers offer one-year free replacement with additional prorated warranties for two or three years. During this period, the distributor will replace the failed unit for a percentage of the replacement cost.

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Batteries have enabled Christopher LaForge to live and work for more than 20 years at his off-grid, sun- and wind–powered homestead, SunFarm, in Bayfield County, Wisconsin. He is an ISP-affiliated PV instructor with the MREA, a NABCEP‑certified PV installer, and a member of the NABCEP board of directors.