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All stand-alone solar electric systems require battery storage.
Solar panels charge the batteries during daylight hours and the
batteries supply the power when it is needed, often at night
and during cloudy weather. Utility intertie systems supply power
directly to the utility grid; no battery storage is needed.
The two most common types of rechargeable batteries in use
are lead-acid and alkaline. Lead acid batteries have plates made
of lead, mixed with other materials, submerged in a sulfuric
acid solution.
Alkaline batteries can be either nickel-cadmium or nickel-iron
batteries. They have plates made of nickel submerged in a solution
of potassium hydroxide. We do not list nickel-cadmium batteries
in this catalog because of their high cost and environmental
problems related to disposal.
 Battery Size
The size of the battery bank required will depend on the storage
capacity required, the maximum discharge rate, the maximum charge
rate, and the minimum temperature at which the batteries will
be used. When designing a power system, all of these factors
are looked at and the one requiring the largest capacity will
dictate battery size.
Temperature has a significant effect on lead-acid batteries.
At 40°F they will have 75% of rated capacity, and at 0°F
their capacity drops to 50%.
The storage capacity of a battery, the amount of electrical
energy it can hold, is usually expressed in amp hours. If one
amp is used for 100 hours, then 100 amp-hours have been used.
A battery in a PV power system should have sufficient amp hour
capacity to supply needed power during the longest expected period
of cloudy weather. A lead-battery should be sized at least 20%
larger than this amount, but a ni-cad battery can be sized to
exactly this amount. If there is a source of back-up power, such
as a standby generator with a battery charger, the battery bank
does not have to be sized for worst-case weather conditions.
Lead-Acid
Batteries
Lead-acid batteries are the most common in PV systems because
their initial cost is lower and because they are readily available
nearly everywhere in the world. There are many different sizes
and designs of lead-acid batteries, but the most important designation
is whether they are deep cycle batteries or shallow cycle batteries.
Shallow cycle batteries, like the type used as starting batteries
in automobiles, are designed to supply a large amount of current
for a short time and stand mild overcharge without losing electrolyte.
Unfortunately, they cannot tolerate being deeply discharged.
If they are repeatedly discharged more than 20 percent, their
life will be very short. These batteries are not a good choice
for a PV system.
Deep cycle batteries are designed to be repeatedly discharged
by as much as 80 percent of their capacity so they are a good
choice for power systems. Even though they are designed to withstand
deep cycling, these batteries will have a longer life if the
cycles are shallower. All lead-acid batteries will fail prematurely
if they are not recharged completely after each cycle. Letting
a lead-acid battery stay in a discharged condition for many days
at a time will cause sulfation of the positive plate and a permanent
loss of capacity.
Sealed deep-cycle lead-acid batteries are maintenance
free. They never need watering or an equalization charge. They
cannot freeze or spill, so they can be mounted in any position.
Sealed batteries require very accurate regulation to prevent
overcharge and over discharge. Either of these conditions will
drastically shorten their lives. We recommend sealed batteries
for remote, unattended power systems.
Caring For
Lead-Acid Batteries
Always use extreme caution when handling batteries and electrolyte.
Wear gloves, goggles and old clothes. "Battery acid"
will burn skin and eyes and destroy cotton and wool clothing.
The quickest way to ruin lead-acid batteries is to discharge
them deeply and leave them stand "dead" for an extended
period of time. When they discharge, there is a chemical change
in the positive plates of the battery. They change from lead
oxide when charged to lead sulfate when discharged. If they remain
in the lead sulfate state for a few days, some part of the plate
does not return to lead oxide when the battery is recharged.
If the battery remains discharged longer, a greater amount of
the positive plate will remain lead sulfate. The parts of the
plates that become "sulfated" no longer store energy.
Batteries that are deeply discharged, and then charged partially
on a regular basis can fail in less than one year.
Check your batteries on a regular basis to be sure they are
getting charged. Use a hydrometer to check the specific gravity
of your lead acid batteries. If batteries are cycled very deeply
and then recharged quickly, the specific gravity reading will
be lower than it should because the electrolyte at the top of
the battery may not have mixed with the "charged" electrolyte.
Check the electrolyte level in wet-cell batteries at least four
times a year and top each cell off with distilled water. Do not
add water to discharged batteries. Electrolyte is absorbed when
batteries are very discharged. If you add water at this time,
and then recharge the battery, electrolyte will overflow and
make a mess.
Keep the tops of your batteries clean and check that cables
are tight. Do not tighten or remove cables while charging or
discharging. Any spark around batteries can cause a hydrogen
explosion inside, and ruin one of the cells, and you.
It is a good idea to do an equalizing charge when some cells
show a variation of 0.05 specific gravity from each other. This
is a long steady overcharge, bringing the battery to a gassing
or bubbling state. Do not equalize sealed or gel type batteries.
With proper care, lead-acid batteries will have a long service
life and work very well in almost any power system. Unfortunately,
with poor treatment lead-acid battery life will be very short.
The chart below gives state
of charge vs. specific gravity of the electrolyte
as well as battery voltage.
|
State of Charge |
Specific Gravity |
12
Volt Battery |
| 100% Charged |
1.265 |
12.70 |
| 75% Charged |
1.239 |
12.37 |
| 50% Charged |
1.200 |
12.06 |
| 25% Charged |
1.170 |
11.67 |
| Fully Discharged |
1.110 |
10.5 |
| These readings
are correct at 75°F |
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| Lead-Acid Battery Designs |
| Form
of Electrolyte |
Cycling |
Application |
Benefits |
Manufacturer |
| liquid, flooded |
deep |
industrial, marine,
remote home, RV |
low cost |
Trojan, Exide, East
Penn |
| sealed gelled |
deep |
industrial, telecom,
remote systems |
transportable, no
spilling or gasses, can mount horizontally, less susceptible
to freezing, non-hazardous classification |
East Penn, Exide,
SES |
| Sealed, absorbed (AGM) |
deep |
Concorde |
Battery Specifications
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Shipping Information:
Concorde batteries up to 70 lbs are UPS shippable. Larger
sizes are shipped via freight trucks.
For residential customers, the best and least-expensive rate
for truck freight shipping is for you to pick the batteries up
at a local freight terminal. They usually will help you load
your vehicle.
The second best rate is a commercial drop point. A fork-lift
should be available.
A residential delivery, if possible, is usually $45 to $95
more than a commercial business delivery. Most residences are
not capable of handling a 40' semi and most don't have the fork-lift
capability to quickly unload.
A lift gate, not always available, (lowers the batteries to
ground level), is usually an additional $75 to $150 in extra
fees.
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Please
Note: California Proposition 65 Warning
Battery posts, terminal, and related accessories contain lead
and lead compounds, chemicals known to the State of California
to cause cancer and reproductive harm. Wash hands after handling. |
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