There are four major components to solar electric systems; Solar Panels, Charge Controllers, Batteries and Inverters. All of these components are necessary to have a functioning Solar Electric (PV) system. The solar panel is the basic building block of the system. This is your battery charger. If you have several solar modules wired together you have created a solar array. The size of the solar array determines the amount of power or energy that will be produced. Your location is also a factor in the amount of energy produced. If you live in Florida, Southern California, or Texas you will produce more than if you live in Oregon, Maine or Maryland. In general the closer to the equator you live your system will produce a larger amount of energy. Do you want to know how much power can be produced in you area. Check out our FAQ question "How much power will a solar module produce at my location?" Charge controllers come in many different sizes and types. They all basically do the same thing. The charge controller prevents the solar panel or array from overcharging your battery. Batteries are the energy storage for your system. Without batteries there is no way to store the energy your solar panels produce during the day. Typically loads receive their power from batteries instead of directly from the output of a solar panel. A solar panel produces a high voltage that will damage electronics if loads are powered directly. A common application for solar panels directly powering a load is water pumping. Instead of storing energy you store water. This way you can pump during the day and have water all night. Batteries will provide you with the energy you need at night. The last major component is the Inverter. The inverter converts the DC energy stored in your batteries and turns it into the AC power you use in your home. Inverters are rated by wattage and the quality of their output. You can use a 50 watt inverter that plugs into your car 12 volt outlet to power a computer, or you could have a 4000 to 11,000 watt inverter system that powers your home. These major components can be put together in many different ways. Minor components like wire, disconnects, circuit breakers, and fuses are also needed for a complete system. Now that you know what the major components are, let me introduce you to you how these different components are used in systems...

Stand Alone or "Cabin" Systems

Solar/ Charge Controller/ Battery/ Inverter/ AC Loads

or

Solar/ Charge Controller/ Battery/ DC Loads

A Stand Alone solar system is just as it sounds. It is not connected to the utility or other types of charging sources. This type of system is used when utility power is not present and is to costly to bring in from the nearest pole. If you have a shed set off from the house, a cabin in the mountains, or a summer home by the lake that is without power this type of system can often be very cost effective. When compared to bring in the power lines the initial cost can be less. Some of the pros of this type of system are: The lack off reliance on the utility. Potential cost savings. Some of the cons of this type of system are: Even thought there maybe a cost savings over running utility line, there can be a high initial cost. You have to know your loads and have the system designed correctly since you don't have utility power for backup.

Utility Tied System

Solar/ Inverter/ Utility

This system is the newest addition to our site. The system utilizes an inverter that does not require batteries. During the day, the power generated is fed back into the utility. If you are producing more power then you are using your meter can even spin backwards. Due to the simplicity of the system, it has the lowest cost per watt. The downfall of this system is that when the utility grid fails the system will shut down.

Battery Backup System

Utility/ Battery Charger/ Batteries/ Inverter/ AC Loads

This is a system that does not involve solar power. This system utilizing an inverter that has a built in battery charger. It will charges batteries and hold them at 100% waiting for a power outage or a brownout. Your critical loads will never see the power outage. Computers, home health equipment, and lights will continue to operate when the utility grid fails. This is a system that is great for areas where power is lost for short periods of time. The limit on this system is the amount of battery capacity that you have. The larger the batteries the longer your run time will be.

Utility Tied Battery Backup System with Solar

This system operates on the same principal as the Battery Backup System. The difference is the addition of solar. The solar is used to charge your battery bank. When the batteries are full the excess power is fed back into the grid. In the event of an outage, your critical loads are powered by the system, and the solar panels continue to charge the batteries. The benefit of this system is that you have the ability to sell power back and have the piece of mind that you critical loads will continue to operate. The drawback is the cost per watt is higher then a Utility Tied System.

More Technical Terms....

Solar energy systems fall into two categories:

1. Solar Electric

Also called photovoltaic (PV) systems, these convert sunlight to electricity. PV systems can provide all the electricity needed by a home or business, or they can be used as backup or to supplement energy needs.

Photovoltaic (PV), often called solar cells, are semiconductor devices that convert sunlight into direct current (DC) electricity. Groups of PV cells are electrically configured into modules and arrays, which can be used to charge batteries, operate motors, and to power any number of electrical loads. With the appropriate power conversion equipment, PV systems can produce alternating current (AC) compatible with any conventional appliances, and operate in parallel with and interconnected to the utility grid.

History of Photovoltaic

The first conventional photovoltaic cells were produced in the late 1950s, and throughout the 1960s were principally used to provide electrical power for earth-orbiting satellites. In the 1970s, improvements in manufacturing, performance and quality of PV modules helped to reduce costs and opened up a number of opportunities for powering remote terrestrial applications, including battery charging for navigational aids, signals, telecommunications equipment and other critical, low power needs.

In the 1980s, photovoltaic became a popular power source for consumer electronic devices, including calculators, watches, radios, lanterns and other small battery charging applications. Following the energy crises of the 1970s, significant efforts also began to develop PV power systems for residential and commercial uses both for stand-alone, remote power as well as for utility-connected applications. During the same period, international applications for PV systems to power rural health clinics, refrigeration, water pumping, telecommunications, and off-grid households increased dramatically, and remain a major portion of the present world market for PV products. Today, the industry's production of PV modules is growing at approximately 25 percent annually, and major programs in the U.S., Japan and Europe are rapidly accelerating the implementation of PV systems on buildings and interconnection to utility networks.
 

How PV Cells Work

A typical silicon PV cell is composed of a thin wafer consisting of an ultra-thin layer of phosphorus-doped (N-type) silicon on top of a thicker layer of boron-doped (P-type) silicon. An electrical field is created near the top surface of the cell where these two materials are in contact, called the P-N junction. When sunlight strikes the surface of a PV cell, this electrical field provides momentum and direction to light-stimulated electrons, resulting in a flow of current when the solar cell is connected to an electrical load.

Regardless of size, a typical silicon PV cell produces about 0.5 - 0.6 volt DC under open-circuit, no-load conditions. The current (and power) output of a PV cell depends on its efficiency and size (surface area), and is proportional the intensity of sunlight striking the surface of the cell. For example, under peak sunlight conditions a typical commercial PV cell with a surface area of 160 cm2 (~25 in2) will produce about 2 watts peak power. If the sunlight intensity were 40 percent of peak, this cell would produce about 0.8 watts.

PV Cells, Modules & Arrays

Batteries

One of the most misunderstood parts of a solar power system is the battery or battery bank, and that is where our class begins. Some solar battery banks use wet cells, like golf cart batteries, while others use sealed or gel cell batteries, and each have different temperature, mounting, and ventilation requirements.

Every battery is designed for a specific type of charge and discharge cycle. Car batteries have thin plates to keep their weight down and are designed for a heavy discharge lasting a few seconds, followed by a long period of slow re-charge. A 6-volt golf cart battery (size T-105) is the minimum battery I recommend for a residential solar application. You will need to buy these in "pairs" to make 12 volts. Golf cart batteries have very thick plates and are designed for hours of heavy discharge each day, followed by a fast recharge in only a few hours each night. This is similar to the duty cycle of a residential solar application, only in reverse. A solar battery must be able to provide long periods of deep discharge each evening and night, followed by a full recharge in only a few hours of sunlight each afternoon. Very few batteries can take a deep discharge-recharge cycle every day, and the 6-volt golf cart battery is the least expensive and easiest to find locally that can.

For some reason, everyone wants to use a sealed marine battery for their homegrown solar system. I strongly recommend that you do not. Included is a photo showing a sealed marine battery that "exploded" after being connected to a small solar charger for several months.

Even though this was a small 12-volt DC 5-amp solar charge controller powered from a single 50-watt solar photovoltaic module, this was enough energy to gradually overcharge the battery and evaporate all of the electrolyte even though this battery was "sealed." A low electrolyte level can expose the plates which will gradually warp or "grow" in thickness as they oxidize. This can cause an internal short circuit and ignition of the hydrogen gas.

Plate damage can also occur when there is a large buildup of sediment after the upper plate areas become exposed from reduced water levels and begin to "flake" off. Most liquid acid batteries do not vent gasses while discharging. However, near the end of a typical charging cycle, when the battery is almost "full," the sulfuric acid and water electrolyte will begin to break down into hydrogen and oxygen-a very explosive combination.

When ignited by a nearby spark or flame, an "explosion" can result, but this flash lasts only a fraction of a second, which is usually too fast to ignite nearby walls. However, this is still a very explosive reaction, with plastic battery parts becoming acid-covered shrapnel. While using a hand grinder one day in a shop, I accidentally directed the sparks towards several car batteries being charged about 30 feet away. There was a very loud explosive sound with acid and plastic hitting every wall of the large shop, yet I did not see a flame and there was no fire. Regardless, it was not a pleasant experience.

Always wear eye protection and acid proof gloves when working around batteries, and have lots of water and baking soda nearby. This will neutralize any acid spills from battery refilling and prevent further corrosive damage.

A typical 6-volt golf cart battery will store about 1 kilowatt-hour of useful energy (6 volt X 220 amp-hr X 80% discharge = 1056 watt-hours). Since this would only power two 50-watt incandescent lamps for 10 hours (2 X 50 X 10 = 1000 watt-hours), your alternative energy system will most likely require wiring several batteries together to create a battery bank. Since each golf cart battery weighs almost 65 pounds, there are weight considerations as well as battery gas venting issues to think about.

An area of a garage or storage building having a concrete floor is the most common location for a battery bank, although some large systems have their own specially designed battery room. I am going to assume you are installing a much smaller system and will only require four to eight batteries.

If you need more than the 220 amp-hr capacity contained in each golf cart battery, I suggest switching to the larger "L-16" size traction battery, having a 350 amp-hour rating, which may allow using fewer batteries. This battery is the same length and width as a golf cart battery, but is much taller and twice as heavy. This is an excellent battery for solar applications and can take very heavy charge-discharge cycling. This industrial rated battery may be more difficult to find, as it is only available from battery wholesale distributors.

Batteries can lose over half of their charge when exposed to extreme temperature swings, so be sure your proposed battery location stays in a 50° to 80° F range, or you will need to insulate the battery box. Since liquid batteries require refilling and battery terminal cleaning to remove corrosion several times each year, the floor area selected should be able to take an occasional acid spill and water wash down.

Battery venting is very important as discussed earlier, and if you build an enclosure around your batteries, it should be designed to direct all vented gasses to the outside. A 2-inch PVC pipe makes a good vent, but be sure it is located at the highest point in your battery enclosure where the lighter hydrogen gas will accumulate. Be sure it also includes a screened vent cap to keep out rain and insects. Do not locate your battery bank near a gas water heater or other open flame appliance that could ignite any accidental hydrogen accumulation.

A battery box can be built using standard 2 x 4 framing construction, with pressure treated plywood lining the interior surfaces. A hinged top door is needed for periodic battery maintenance, and should include a gasket to prevent gases from entering the room. Note how the top of the site-built battery box shown in these photos slopes up to a high rear area where two PVC vent pipes are located. The interior plywood surfaces of this wood frame construction were painted with several coats of fire and acid resistant paint. Since batteries lose capacity with lower temperatures, your batteries should not rest directly on a cold un-insulated concrete floor.

Pressure treated 2 x 4s on edge, spaced every 6 inches and covered by a fiberglass laminated concrete board, makes an excellent base for your battery box. This heavy sheet material is sold in most building supply outlets as a backing behind ceramic tile work in wet shower stalls, and is usually available in smaller 2-foot by 4-foot sizes. By careful planning, you may be able to use the entire sheet without cutting or splicing.

If you can afford to invest in the more expensive gel or absorbed glass matte (AGM) batteries, you will have more flexibility in locating your battery bank, since these batteries do not need to be refilled and do not normally generate explosive gasses. The photo shows a large battery bank with the batteries mounted close together in a vertical steel rack. You do not need a vapor proof enclosure or vent pipe when using these batteries, however they cost almost 30 percent more without providing any additional life or storage capacity.