Reliability
–Uninterrupted Power Supply (UPS). In effect, no blackouts due to power failures

Durability
–PV modules typically last 25 years.
–Good batteries last 10 to 15 years.

Low maintenance
–Panels have to be cleaned once a month.
–Battery water has to be checked once a month and replenished if necessary.
–Batteries have to be “equalized” or charged up every ten weeks to three months.

No fuel cost
–No monthly bills.
–No purchase, storage, or transportation costs for fuel.

No Sound Pollution
–PV systems operate silently.

Safety
–PV systems use no combustible fuels and are safe if properly designed and installed.

Independence
–PV systems allow users to live even in remote regions.
–City dwellers gain independence from the grid.

Initial Cost
–PV systems are initially expensive.
–To offset the high initial cost, some adjustments are necessary in home appliance selection.

Reliance on the weather
–PV systems require sunlight, which may not be available for stretches of time because of cloudiness.

Energy Storage
–PV systems usually require batteries to store energy for use when the sun is down. Batteries are bulky and increase the system’s size and complexity.

Module
Better known as a solar panel, it is a configuration of photovoltaic cells laminated and framed in the shape of a panel. Modules convert solar radiation into electricity.

Array
One or more modules with mounting hardware wired together at a specific voltage.

Charge Controller
A power conditioning device that regulates battery voltage.

Battery
A medium for storing direct current electrical energy so that the PV system can provide electricity at night or when it is cloudy.

Inverter
A device which changes direct current (DC) to alternating current (AC) to operate alternating current powered loads.

DC Loads
Appliances, motors, and equipment powered by DC.

AC Loads
Appliances, motors, and equipment powered by AC.

Alternating current has electron flow in both directions in a circuit. It is the type of electricity supplied by utility companies and the type that most home appliances operate on. AC was adopted ubiquitously because with its higher voltage it can be transported over long distances without losing much of its electrical energy.

Direct current flows only in one direction and it is the type of electrical current produced by solar panels and batteries. DC cannot be transported far because of its lower voltage.

An inverter converts the DC from the panels into AC. Most home appliances run on AC. Therefore, one would not be able to use most home appliances without an inverter.

Batteries must not be allowed to discharge too deeply or be overcharged because either situation damages the batteries and reduces battery life. A charge controller prevents the batteries from charging once it reaches a fully charged state. It does this by disconnecting the panels from the battery bank. It also prevents additional energy from being taken from the batteries when a dangerously low battery level is reached by interrupting the supply of power to the loads.

Batteries: There are two battery types, flooded and sealed. Flooded batteries contain a water level that must be maintained. Once a month check each cell of every battery by opening it and dipping a measuring stick into the cell until the stick touches the battery plates inside. After withdrawing it, the stick should be wet a half inch from its tip. If not, you need to add battery water until it reaches the half inch level. Sealed batteries do not need water maintenance. However, both flooded and sealed batteries require the following maintenance:

1. Every two and half to three months, the batteries have to be “equalized”. Sulfates that build up on the battery plates reduce the battery capacity and longevity. This means batteries have to be overcharged, or equalized for a few hours in order to prevent sulfation of the battery plates. One equalizes batteries by connecting them to a generator through the inverter. The generator runs until the inverter recognizes the batteries have been fully charged.
2. Periodically, the battery terminals have to be scraped of rust or encrustations with a steel brush until the metal is shiny.

Panels: Dust or vegetation falls on the panels and can considerably reduce their capacity. Therefore, once a month they should be cleaned with a damp cloth. Also, trees branches may have to be trimmed back if they are obstructing the sunlight on the panels.

If you are going to be away for an extended period, simply turn off all loads and let charge controller “float” the batteries. This will keep the batteries from overcharging.

There are several types of PV systems
The day-use (or PV direct) system?
The simplest, least expensive PV system is that designed to be used only during the day. This system consists of PV panels wired directly to a DC appliance. When the sun shines on the panels, the electricity generated is used simultaneously. Day use systems have no electrical storage capacity, therefore, they do not have the added expense of batteries and they operate only when the sun is shining. Day use systems water pumps are up to 2.5 times more efficient than normal AC pumps.

Day use systems are an appropriate, cost effective option for loads operated only during the daytime. For example:

• Water pumping with a storage tank
• Water heating systems
• Daytime ventilation systems
• Pool pumps

A DC system with storage batteries
If a PV system is to operate when the sun is not shining, it needs a bank of batteries to store the solar energy for nighttime use or during cloudy weather. System loads can draw power from the batteries during the day or night and during clear or cloudy weather. This system’s components include panel(s) a charge controller, storage batteries, and the DC appliances that represent the system’s loads. Because this system’s loads are only DC, this system does not require an inverter to transform the DC current from the panels into the AC current required by AC loads.

A DC system powering AC loads
Most common appliances require alternating current to operate. So PV systems designed to power such appliances need an inverter to convert the direct current from the panels to the alternating current used by these appliances. Inverters provide convenience and flexibility in a PV system, but also add complexity and cost. However, AC appliances are mass produced and offer a greater number of choices at lower cost than DC appliances.

The grid-tie system
A grid-tie system is a private photovoltaic system that is tied to and generates energy for the electricity grid. Because it generates energy for a public utility, laws obligate the utility company to pay the grid-tie system owner for the energy produced. Therefore, grid-tie owners typically have considerably reduced monthly electricity bills. Grid-tie systems don’t require a battery bank because the grid provides energy at night. However, some grid-tie owners use a battery bank with their grid-tie system in order to have an uninterruptible power supply in case of grid blackouts.