stallation as they relate to
the Solar Decathlon. A battery system can be hazardous because it is a continuously energized source of electricity and contains
corrosive electrolytes. Also, batteries can be heavy, can cause fires, and can produce explosive or corrosive gases. Solar Decathlon team
members need to be aware of these inherent hazards to minimize the risk to themselves and the public when transporting, installing,
maintaining, using, or replacing a battery. Although this document focuses on lead-acid batteries, most of the information and discussion
applies to all battery chemistries.

Because this competition has a strong public outreach component, the Organizers are providing these guidelines to reinforce the
importance of safety at the Event. The public viewing the Solar Decathlon homes may choose to incorporate some of the features and
technologies in their own homes. Because solar-powered homes will be new to many people, the homes need to demonstrate safe
photovoltaic (PV) and battery systems. Although most people are familiar with automotive batteries, the batteries in the Solar Decathlon
homes will be larger, and they are subject to additional regulations and considerations.

General Applicability and Interpretation

This document lists and discusses most of the codes, standards, and recommendations that apply to batteries typically used in solar-
powered homes. Although the list may look exhaustive, some codes, standards, or recommendations have been left out intentionally or
may have been left out inadvertently. Also, state and local jurisdictions and the sponsoring school may have additional requirements
beyond the international or national codes listed here.

Interpreting the codes, regulations, and recommendations is ultimately the responsibility of the individual Solar Decathlon teams and their
institutions. In this document, the Organizers have established a minimum level of battery safety consistent with published codes,
regulations, and recommendations. Individual teams or their sponsoring institution may add their own additional requirements.

Battery codes, regulations, and recommendations have only a minor impact on the homes energy usage. Batteries are emphasized here
primarily because they represent an important safety issue. Teams must make safety a priority throughout the competition.

In addition to safety, proper interpretation of codes, regulations, and recommendations can improve a batterys performance and extend its
lifetime. Although the Solar Decathlon competition on the National Mall takes place over a brief period of time, a battery system should
be designed, installed, and operated as if the house were to be occupied full time and the battery system lifetime needed to be maximized
2005 Solar Decathlon Rules and Regulations
Battery Requirements and Guidelines
March 12, 2004
Page 1 of 15 through proper operation and maintenance. The public will scrutinize the Solar Decathlon homes and the schools they represent, so all
battery systems must be properly installed and operated.

Battery Terminology

Commonly accepted terms will be defined to interpret the codes and to discuss the issues within the context of the Solar Decathlon Rules
and Regulations and with other battery industry experts. The cell is the smallest electrical unit capable of producing voltage. In the lead-
acid battery chemistry, the cell produces 2 V nominally. The battery consists of ALL the cells that are series or parallel connected.

Confusion begins when referring to the homes battery. Many of the codes and standards refer to batteries as the collection of individual
batteries that comprise a battery. This publication, when discussing the Solar Decathlon competition, regulations, and suggested best
practices, will refer to the house battery as the battery bank or battery system.

State-of-charge (SOC) is the percent of electrical energy stored in a battery compared to the manufacturers rated capacity of the battery.
A full battery has a 100% SOC and a discharged lead-acid battery has a 20% SOC. Most batteries are not fully discharged to 0% SOC,
even though the manufacturers rated capacity is based on a full discharge. Depth-of-discharge (DOD) is the inverse of SOC. A fully
charged battery has a 0% DOD whereas a discharged lead-acid battery has an 80% DOD.

Battery Chemistries

There are several electrochemical battery types available for solar-powered homes. The most common battery type is lead-acid because of
availability and cost. Other battery types that have been used are nickel-cadmium (NiCd), nickel-iron (NiFe), nickel metal hydride
(NiMH) and lithium-ion. Each battery type has its own specific operating, transportation, cleanup, and disposal requirements. The battery
manufacturer should supply this information along with a Material Safety Data Sheet (MSDS). Whereas some of the discussion in this
document focuses on lead-acid batteries, most of the discussion is applicable to all types of batteries.

Most of the battery chemistries can be incorporated into vented or sealed battery configurations. Figure 1 shows the different types of
lead-acid batteries. The vented (or flooded) configuration contains liquid electrolyte (either acid or base). During normal operation,
electrolyte or electrolyte film may be present on top of the battery case because of the venting of hydrogen gas, overcharging, or
overfilling vented configuration batteries. Standard maintenance requirements for a vented battery include visually checking the
electrolyte level and adding distilled water, if needed. In the vented configuration, electrolyte can spill out if the battery is tipped, or if the
case becomes damaged. A vented battery should come with spark arrestor vent caps for each cell. After-market hydrogen recombinant
and spark arrestor vent caps may also be available to help reduce water loss. Check with the battery manufacturer before replacing any
vent caps.

2005 Solar Decathlon Rules and Regulations
Battery Requirements and Guidelines
March 12, 2004
Page 2 of 15
Lead-acid battery
Vented or
Flooded
Sealed or
Acid
(VRLA)
Valve Regulated Lead
Absorbed Glass Mat
(AGM)

Gel


Figure 1. Different types of lead-acid batteries

The sealed (or valve-regulated lead-acid [VRLA]) battery configuration avoids many of the vented battery configurations disadvantages
by immobilizing or minimizing the electrolyte. Absorbed glass mat (AGM) batteries are different than gel batteries, even though both are
sealed lead-acid batteries. An AGM battery immobilizes the electrolyte by absorbing the electrolyte into a fiberglass mat. A gel battery
immobilizes the electrolyte by adding silica gel creating a semi-solid mass.

Under normal operating conditions in a sealed battery, the hydrogen gas that is generated during charging and discharging is recombined
with oxygen inside the cell. Depending on the manufacturer, sealed batteries can usually be placed in any orientation (with the battery
terminals on top or on the side). Some manufacturers claim that certain orientations of their sealed battery improve battery-recharging
efficiency. Check with the manufacturer before placing a battery in an orientation different than as received. Sealed batteries are
generally more convenient to install and operate, even though the initial and operating costs may be higher.

Battery Hazards and Risks

A battery presents many hazards and risksall of which can be minimized through proper design, installation, operation, maintenance,
and disposal. A battery is always energizedthere is no on/off switch. Even a battery that is discharged still contains a lot of energy.
2005 Solar Decathlon Rules and Regulations
Battery Requirements and Guidelines
March 12, 2004
Page 3 of 15 The corrosive electrolyte inside the battery can cause physical injuries to the user or additional damage to the battery if the electrolyte
leaks out of the case, spills from the battery in an accident, or vents to the atmosphere. A battery can be heavy and awkward. Poorly
designed battery rooms with limited space can hinder safe lifting and installation (or removal) of a battery. If improperly manufactured or
maintained, a battery can cause a fire. Also, a fire near the battery can be started if the wiring and connections are improper or maintained
poorly.

A vented or flooded battery will produce hydrogen gas during normal operation. A vented lead-acid battery with antimony-containing
lead plates will produce more hydrogen than a battery with calcium-containing lead plates. A sealed or VRLA battery should contain all
gases during normal operations. However, during abnormal circumstances, excess pressure inside the sealed battery will cause the battery
to vent hydrogen gas. A sealed battery contains a one-way pressure relief vent that can release excess pressure from inside the battery
case if the battery is overcharged or overheated, or if there is a battery failure. The total amount of hydrogen gas that can be generated
from a vented or sealed battery can be similar but depends on the total amount of electrolyte inside the battery. The rate of hydrogen
evolution is a function of the SOC, battery age, and current.

In summary, the risks to be considered when installing, utilizing, and maintaining a battery bank are:

Explosion/flammability of hydrogen gas
Electric shock and electric current hazards
Acidic o