Overview


There are several recurring questions posed by people interested in setting up a photovoltaic (solar) electric system to provide them with either 12 volt DC or 110 volt AC power for a remote site. This brochure addresses the most common of those questions.

1)What is a photovoltaic (PV) or "solar" system?

Photovoltiacs is the process of converting sunlight into electricity. This is accomplished with a photovoltaic (or solar) panel that, when placed in sunlight, converts energy from the sunlight into useable electrical current. Since most applications will often have either periods of time when the electrical demand exceeds the panel output or periods of darkness when there is no electrical output from the panel, a storage reservoir is also needed for the energy. It is helpful to think of this in terms of a water reservoir for a city. The rain falls in the mountains and drains into the reservoir where it is stored until needed by the city. In the PV system, the energy reservoir is the battery. The electrical power flows into the battery from the solar panel where it is stored for future use. In this context, then, you can think of the PV (solar) panel as a "solar battery charger" filling the battery reservoir with energy. The PV (solar) panel and the battery are the major components of the PV system.

2) Is a PV system practical in Alaska?

Contrary to common belief, there are actually more annual sun-hours in Alaska than many other areas of the country. The obstacle to overcome in Alaska is the distribution of the sun-hours over the year. From the period of November 1 to February 1, it is best to expect very little solar panel output, which means that an alternative method of keeping the battery "reservoir" filled must be utilized. Usually this is accomplished with the use of a portable gas generator or wind generator. In areas with reasonable sun exposure, PV systems will work very well from February 1 to November 1.

3) Is a PV system cost effective?

The results of several studies and cost analyses indicate that photovoltaic power is not cost effective if compared to public utility power. The exception to this is when the cost of connecting to the utility grid (I.E. line extensions, etc.) is excessively high, as it is in many rural areas of Alaska. Solar power is normally very cost effective if compared to a gas or diesel generator, although initial setup costs will usually be higher. The pay-back period when compared to the gas or diesel generator will vary with the specific application and the size of the system (which affects its initial cost).

4) Can I use the PV system to power my whole house?

Yes, it is possible to power the whole house but you will find it better to use an alternate energy source for any application designed to generate heat, such as stoves, heaters, hot water heaters, coffee pots, etc. The size of the PV system necessary to produce enough electricity to generate heat would be such that you would have a huge initial investment with a resulting substantial period of time required for the pay-back.

5) Will one solar (PV) panel run my TV?

In one form or another, this is a very frequent question and it requires an understanding of the makeup of the solar system to answer. The first question to address is whether the television is capable of operating on 12 volts DC. If not, the answer is NO unless you have what is called an "inverter". The inverter changes the 12 volt DC coming off your PV system into 110 volt AC (normal household current). Please refer to the section "INVERTERS" for more detailed information on these electronic wonders.

OK, so let's assume that the TV is 12 volt DC. The normal PV panel used for home power applications produces a maximum of approximately 50 watts of power. In looking at the electrical information tag on the back of the TV, you discover that the TV requires 100 watts of power to operate. Bad News! Your solar panel does not produce enough power to operate the TV. But, all is not lost! Please refer to the description of a photovoltaic (PV) system above. This is where the battery comes into play. The battery is the "electrical reservoir" that supplies the additional 50 watts of power needed by your TV to operate. After the TV is shut off, the solar panel continues producing it's 50 watts of power, recharging the battery.

From this, then , you can see that the question is not IS the solar panel will run the TV but HOW LONG the TV will run on the PV system (which consists of the solar panel and the battery). How long it will run is determined by the wattage output of the solar panel, the wattage demand of the TV and the amount of wattage stored in the battery "reservoir".

6) How big a solar system do I need to do what I want to do?

I have saved the best for last. This question is posed quite frequently and is impossible to answer without more detailed information. It is relatively easy to calculate what size solar system you would need and outline what options are available once we know what your needs are. And that is the point I want to stress in answering this question. IT ALL BEGINS WITH AN INVENTORY OF YOUR ELECTRICAL NEEDS. This requires some work and forethought and, yes, a little speculation on your part. But you will find it well worth the time invested when what results is a solar system that does what you want it to do.

The Electrical Needs inventory is not as complicated as it sounds. Every electrical item has a wattage (power) or amperage (current) rating. This is the amount of energy required for the item to operate. A 100 watt light bulb, for example, uses 100 watts of power. An 800 watt microwave oven requires 800 watts of power. A 7 amp circular saw requires 7 amps of current to operate properly.

Make a list of all the electrical items you will be using and record their wattage or amperage requirements. Many appliances have this information recorded on a small tag found next to where the power cord comes out of the appliance. Once the list is complete, sit down with your thinking cap on and speculate as to, on the average, how many hours per day each item will be used. I recognize that, in many situations, this is pure speculation. It is extremely beneficial, though, to follow these steps in arriving at a beginning point, even when it will undoubtedly be modified later.

Once the Electrical Needs inventory is complete, we can assist you in determining the best type and size of power generating method to use, what type and size battery bank would be best, whether to use an inverter and what types of options would be beneficial.


HOME POWER (SOLAR) SYSTEMS

Generating your own electricity by tapping into sunlight can be an exciting and rewarding experience. Designing the system properly, however, can be quite confusing to many people. This section is designed to explain in basic terms what a home power system consists of, how it works, and what the approximate cost will be. Remember that this information only covers the basics and that there are many design alternatives and a multitude of optional accessories that are available. Contact the home power system consultants at SOLAR ALASKA for more detailed application information.

THE HOME POWER SYSTEM:

This is the home power system in its most basic form. It consists of a solar (photovoltaic) panel which converts sunlight into electricity, a battery that stores the electricity and an electric light bulb (or other electrical device) that uses electricity. Even the largest and most sophisticated home power systems are merely expansions of this basic concept.

HOME POWER SYSTEM COSTS

A basic system (as shown above) consisting of one 3 amp solar panel, one deep cycle 12 volt battery and one 12 volt DC light fixture will cost approximately $450.00 to set up. Larger systems, consisting of multiple solar panels and batteries and other optional electronic equipment and accessories, can require an initial investment of $2000 to $8,000. One of the advantages of home power systems, though, is that they are modular. You can start very small and expand as budget and need dictate.


HOME POWER BATTERIES

THE BATTERY IN THE HOME POWER SYSTEM

The battery bank in a home power system serves two purposes. It acts as a voltage stabilizer for the system, moderating the high voltages that can occur during battery charging and minimizing the low voltages common in high demand situations. It also acts as a power reservoir, supplying the power needed when the load demand exceeds the capabilities of the power (charging) source. For instance, if you have a solar panel that produces 51 watts of power and want it to power a light bulb that requires 100 watts, the additional 49 watts of power required by the light bulb will be supplied by the battery. The power used by the battery is then replaced when the light bulb is not in use.

RV/MARINE BATTERIES

RV and marine batteries are available in a variety of sizes to 100 amp hour and are normally 12 volt. They may be of the standard, serviceable type or the sealed, "maintenance-free" style. They are common in small home power and portable power systems.

GOLF CART BATTERIES

These batteries are available in 220 to 300 amp hour capacities and are normally 6 volts per battery. They are a good choice for small to medium home systems.

INDUSTRIAL/STATIONARY BATTERIES

These batteries, which are normally manufactured as individual 2 volt units, are available in a broad range of capacities to 3000 amp hours. Six 2 volt units are connected in series for 12 volt systems. They are an excellent low-cost choice for medium to large capacity home power systems.

NICKEL CADMIUM/NICKEL IRON BATTERIES

The batteries previously discussed are called "lead-acid" batteries in that they consist of lead plates in a sulfuric acid solution and are the most common batteries utilized in home power applications. Nickel cadmium and nickel iron batteries consist of nickel alloy plates in an alkaline solution which dramatically alters the operating characteristics of the battery. These batteries are also good choices for home power systems but involve special considerations.

Advantages:
Disadvantages:


INVERTERS

Inverters are electronic devices that change battery voltage (normally 12 volt DC but it can be any low voltage direct current) into regular household current (110 volt AC) for operating tools, appliances and other common electrical equipment. Inverters are of three basic types: sine wave, modified sine wave and square wave. This distinction refers to the quality of the electrical output of the inverter and the types of electrical devices the inverter can successfully operate. Electricity that you can receive from your local electrical utility company is sine wave and is the best form of electricity. Good sine wave inverters are starting to show up on the market now but are fairly expensive. If you are operating sensitive electronic equipment such as televisions, radios or computers and want top quality performance, sine wave inverters are the way to go. If you can tolerate the possibility of minor distortions there are several excellent modified sine wave inverters on the market. The prices on modified sine wave inverters are very competitive. Consequently, they are presently the best choice for the majority of applications. Square wave inverters are still available and are inexpensive but they will not operate certain types of equipment, such as induction motors, and will create noticeable distortion and interference. The prices on modified sine wave inverters are now low enough that square wave inverters are becoming a thing of the past.

WHICH INVERTER IS BEST FOR ME?

If your requirements are very specialized, sophisticated or sensitive (such as computers, laser printers, test equipment, radio equipment, audio recording equipment or motors with SCR speed controls), sine wave inverters are the best choice. If your requirements are simple and you are willing to put up with limitations and potential distortion, square wave inverters are a very inexpensive way to get started. For most applications the modified sine wave inverter is the best choice. It has eliminated most of the limitations of the square wave inverter, it can provide you with a variety of options to enhance the performance of your electrical system and the prices are very competitive.

Review the options available for the inverter. Many inverters are available with features such as corrosion resistance, overvoltage protection, overheating protection, low voltage protection, battery charging capability, 240 volt capability, voltage and amperage monitoring, and automatic load sensing. If what you need is portable power for occasional use on shop truck, these options may not be beneficial, but if your inverter is to be part of a home power or marine system they can be invaluable. The qualified technicians at SOLAR ALASKA can discuss the various styles and options with you in more detail and assist you in the selection of the best type of inverter for your needs.

HOW DO I SELECT THE PROPER SIZE?

Inverters are normally sized by output wattage capability. Understanding a couple of simple concepts will enable you to select the proper size for your needs. First, the inverter will normally have two ratings with respect to output capacity. The first is the wattage that it can sustain on a prolonged basis. This is normally the published rating. For most inverters it is the wattage that the inverter will support on a continuos basis, but not always, so check the specifications to verify. (The Trace 812 inverter, for instance, is rated at 800 watts but this is the wattage it will sustain for 1/2 hour. Its continuos rating is 675 watts.) The second wattage rating is that which the inverter can support on a short term basis for momentary surges in demand and is called the surge capacity. All electrical devices require more electrical current to start than to run. For some devices, such as fans or computers, this additional starting wattage is minimal. For other equipment, such as water pumps and refrigerators, the starting wattage requirements can be three times the operating wattage requirements. Check the surge capacity rating to ensure that the inverter will operate and start your electrical devices.

The second concept to consider is the conversion efficiency of the inverter. This refers to the amount of electrical loss that is incurred in converting the electricity and can be extremely important if battery power is expensive or difficult to replace. The amount of loss is influenced by the quality and type of inverter and by the percentage of the inverter capacity being utilized. All inverters have an optimal efficiency range and most good inverters will have a conversion efficiency of 95% or better in their optimal range. It is important that the inverter be sized so that it is normally operating in its optimal efficiency range. A 95% efficiency means that 5% of the power is being lost in the conversion process.

In comparing the output capability of the inverter to your electrical requirements, remember that, at 110 volts AC, one amp equals 110 watts. If you have a skilsaw that uses 7 amps to operate and 15 amps to start you will need 770 watts and 1650 watts of inverter power respectively. The qualified technicians at SOLAR ALASKA can assist you in assessing your electrical load requirements and properly sizing your inverter.


LOW VOLTAGE LIGHTING

Lighting is a very popular and practical application for photovoltaic (PV) systems, as it provides a high degree of benefit for the amount of energy used. There are many options available in lighting type, size, voltage and placement, however, so selection can be somewhat confusing.

VOLTAGE

The first question to address is whether to use 12 volt DC lighting directly from the battery bank or to use standard 110 volt AC lighting by including an inverter in the system. In a small home, the 12 volt DC lighting is usually the best choice. DC wiring runs can be kept short, allowing the use of fairly small gauge wire, the system cost is lower as an inverter is not required, low voltage bulbs are more efficient than AC types, and standard fixtures can usually be easily converted to 12 volt. If the house is larger and wiring runs are long (35 ft or more), or if the system is already utilizing an inverter for other purposes, AC lighting should be considered as the wiring costs and the bulb and the fixture costs will probably be less. If the home is being constructed, a combination of 12 volt DC and 110 volt AC circuits is often quite feasible.

TYPES

A broad variety of lighting is readily available for standard 110 volt AC circuits and will not be addressed here except to say that many of the efficient AC fluorescents will not work well on an inverter. On the low voltage side, though, the options are not as well known and will be addressed. For indoor applications, the normal options are incandescent, fluorescent and halogen. There is a high degree of integration as 12 volt DC incandescent and halogen bulbs will fit in most standard 110 volt AC fixtures and standard 110 volt AC fluorescent bulbs are used in most 12 volt DC fixtures.

Incandescent bulbs are the least expensive to purchase but are also the least efficient of the three. (12 volt DC bulbs are 30 % more efficient than 110 volt AC bulbs, however.) Wattages from 5 to 100 watts are readily available.

Halogen bulbs fit most incandescent applications, either directly or through the use of adapters. They are approximately 30% more efficient than the incandescent bulbs but seem much brighter because they emit a much broader spectrum of light. Halogen is also generally a longer lasting bulb than the incandescent but the initial purchase cost can be four to five times as high. Available wattages generally parallel incandescent.

Fluorescent is the most efficient (up to 4 times) but the selection is somewhat limited as fixtures utilizing 12 volt DC ballasts are required. Several styles are available for a variety of indoor area or spot lighting requirements. Standard 110 volt AC fluorescent fixtures can also be converted to 12 volt DC by replacing the ballast.


SYSTEM DESIGN

While this brochure has given a basic overview of home power systems, it is recommended that the home power system consultants at SOLAR ALASKA (or other qualified individuals) be consulted for specific application design suggestions to ensure that your energy needs are met.


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