Power Storage

updated Sept. 15, 2002.

Click here link for circuit information for creating a "desulfator" that will rejuvinate batteries that have sat around a long time and/or had the plates in the battery heavily sulfated (age). It will not correct a battery with a dead or shorted cell(s). You may save the life of a marginal battery with this circuit or bring one back from the dead. I haven't tried the circuit personally yet but, time permitting, will build one soon.

Information taken from www.energyalternatives.ca

Storage batteries are the heart of an independent power system. They store electricity for use at a later time when a charging source (sun, wind, water or generator) is not available. They also provide a reserve of available energy to run loads that require more power than that provided by the charging source.

Batteries wear out and must eventually be replaced. Regular monitoring and maintenance will extend the life span of your battery bank and save you money. The deeper they are discharged, the shorter their life span will be. Batteries contain toxic materials and should be disposed of properly.

Choosing a Battery
There are many types of batteries available. Many are unsuitable for an independent power system. Choosing the right type of battery is the first step in designing a reliable renewable energy system.

Car Batteries
Car batteries are designed to provide a brief, high current for engine starting, not for deep discharge applications. The “Cold Cranking Amps” rating does not indicate the battery’s storage capacity. The thin plates in these batteries are good for a quick release of energy, but deep discharging will cause rapid deterioration. These are a poor choice for alternative energy systems.

RV and Marine Batteries
These Batteries are a compromise between engine starting batteries and deep cycle batteries. The plates are similar to the engine starting batteries and will not withstand repeated deep discharging. They are adequate for small (under 200 amp / hours) systems and might last 2 to 4 years. These are not a true deep discharge battery despite the claims on the label to be a “deep cycle” battery.

Motive Power Batteries
Motive batteries are deep-cycle batteries used to provide energy for electric vehicles such as golf carts and forklifts. They have thick plates that will withstand many deep discharge cycles. These are used for most independent power systems as they are durable, have good storage capacity and are cost effective. These are usually in a 2, 6 or 12V casing. Typically, the golf cart batteries will last four to seven years, while the Global-Yuasa forklift batteries will last 10 to 20 years.

Stationary Batteries
These cells, common known as utility backup cells are used by telephone companies for back-up power supply systems. They are often designed with calcium alloy plates which are not for deep cycling, so they are poor batteries for a most renewable energy systems. However, they may be suitable for use in systems where there is no requirement for autonomy such as a micro hydro installation. When batteries are used this way, also referred to as “float service”, they are storing reserve energy for peak load demands. Stationary 2V cells frequently come in a clear casing.

Gel (sealed) Batteries
Gel cells are filled with an electrolyte that is in the form of a gel or sponge. It is not possible to service this type of battery or replace the electrolyte. They have a much shorter life and cost considerably more than liquid filled batteries. These batteries require no maintenance, tolerate low temperatures, do not spill and do not produce corrosive gases. They are good at remote sites where maintenance is not possible and cold weather prevails. Precise charge control is critical.

New Technologies
There have been several advances in battery technology over the last few years. Unfortunately, they are not yet available in an affordable manner for large scale use in alternative energy systems.

The Ovonic Battery Company (which is part of the same family as Uni-Solar) is currently gearing up for production of a battery used primarily in electric vehicle applications. This Nickel Metal Hydride (NiMH) battery boasts a fast recharge capability (up to 60% capacity in 15 minutes), ability to deliver high current without dropping cell voltage and most significantly these batteries weigh half as much as lead acid counterparts. We will continue to monitor these advances in battery technology and will add these to our product line when they become readily available and affordable.

Temperature
Ideally a battery bank should be protected from cold and be maintained at a constant temperature. Battery capacity is significantly reduced as temperatures decrease. For example, if a battery is rated as 600 a/h at 60°C, its rating will drop to 300 a/h at -20°C. Batteries must be derated when operated in cold climates. Protecting your battery from cold temperatures will improve the performance of your electrical system.

Capacity
The capacity of deep cycle batteries is measured in amp / hours (a/h). The rate of discharge affects the total capacity. The slower the discharge, the higher the capacity. A 20 hour discharge is often used when labeling a battery for renewable energy use. However, 72 or 100 hour rates are sometimes used. A battery rated at 800 a/h at a 20 hour rate can sustain a discharge of 40 amps for 20 hours before it is completely discharged. When purchasing a battery bank, one should consider price, quality, battery bank size, length of expected service, and weight.

Battery Installation
Generally, batteries receive sufficient protection from west coast weather conditions if they are placed in an insulated box adjacent to the house. In other parts of Canada, many people place their batteries in an underground insulated box. This is a good way to protect them from freezing weather but the pit must be well drained.

Batteries may be installed inside a home if they are vented to the outside. When batteries are charging they give off hydrogen and other gases, which are explosive, corrosive, and foul smelling. To minimize the risk of fire, batteries must be in a vented compartment separate from any other electrical components.

If battery cables to the inverter are run in conduit, it is necessary to seal the conduit at the battery box to prevent gases from rising up the conduit and reaching the other electrical components. Even Gel cells, which are sealed, should be kept away from sources of flame, sparks and heat. Batteries should always be installed so children do not have access to them.

Battery Care

Keep terminals clean and tight.
Keep batteries charged. Do not store them in --discharged state.
Periodic equalization is needed, especially with deeper discharge cycles.
Avoid totally discharging your batteries. This shortens their life considerably
Inspect cells every three months for water loss.

Batteries are often referred to as the heart of a renewable energy system. By monitoring your battery and performing periodic maintenance, it is possible to prolong its life and correct small problems before damage occurs.

Always use caution when handling batteries. Wear gloves, goggles and old clothes. Battery acid will burn skin and eyes and destroy cotton and wool clothing. (Polyester is a good fabric to wear around batteries.)

Battery State of Charge
Knowing a battery's state of charge allows us to answer the two questions foremost in our minds, "How do I know when my battery is charged?" and "How do I know when it¹s time to charge my battery?"

1. An amp hour meter is a simple and accurate way to determine battery state of charge and it simplifies battery maintenance. The cost of an amp hour meter will be easily recovered in extended battery life and improved efficiency of your electrical system¹s operation.

2. A volt meter provides a useful measure of system and battery voltage. However, it is only an approximate indication of the state of charge of a battery. The best time to read battery voltage, is when it is at rest. That is, when no charging or discharging is taking place, and has not for several hours. Battery voltage will fluctuate as charging takes place and as loads are turned on and off.

3. Another way to determine a battery's state of charge is with a hydromete r. A hydrometer measures the density of the battery electrolyte. A fully charged battery will have a higher concentration of acid and a higher specific gravity reading. The extra time, potential for contamination and hassle of a hydrometer tends to make people avoid their hydrometer.

A battery that is constantly discharged will have a much shorter life than one that is regularly charged. If your battery is always discharged you must either increase the charge rate or reduce the loads.

Battery Maintenance
Battery maintenance should be performed every three months. It is very simple and will only take a few minutes to complete.

1. Check the connections and make sure that they are clean and tight. If there is corrosion on the battery terminals, clean them with baking soda, water and a wire brush. You must not allow water or foreign matter to enter the cells, especially soda.

2. Check all electrolyte levels and top up with distilled water. When batteries are at rest, the fluid level should be to the bottom of the split plastic ring or 1/2" above the plates. If water levels are constantly low the voltage of the charge controller is probably set too high. Do not add water to batteries when they are discharged, they may over flow when brought to a full charge.

3. If you are having problems with your battery use a hydrometer to check the specific gravity of each cell in your battery bank. A fully charged battery will read approximately 1.265 on the hydrometer. If any cells are noticeably different from the others (0.02 or more) you may have a weak cell which is an indication of impending battery failure. Equalizing your battery may eliminate the problem.

4. Equalize your battery (non-sealed, lead acid batteries). This needs to be done more frequently when a battery is kept in a partially discharged state or is experiencing deep discharge cycles. Equalizing should be performed for at least two hours when the cell voltage is raised above 15 volts in a 12 volt system. A longer period (up to 48 hours) is necessary when equalizing at between 14 and 15 volts. Audible gassing (bubbling) is an essential indication that equalizing is taking place.

When a battery is discharged lead sulfate forms on the lead plates. If a battery is not fully recharged the sulfate remains on the plates and hardens until a normal recharge will not remove it. This reduces the capacity of your battery by sealing off some of the surface area of the plates.

Even with proper charging some of the cells may accumulate lead sulfate. Equalizing a battery removes the sulfate from the plates and the gassing that results stirs up the electrolyte which tends to stratify. Stratification concentrates the sulfuric acid at the bottom of the cell and corrodes the plates. Distilled water should be added to the battery after equalization has taken place and voltage is back to normal.