Solar Electric Question & Answers

This basic question and answer page is designed to help anyone understand the sequences of events for purchasing and contracting to install a solar electric system. If you consult with a licensed solar electric contractor, this will help guide you in your decision making process.

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A.) WHAT IS THE NORMAL SEQUENCE OF EVENTS IN PURCHASING SOLAR ELECTRIC EQUIPMENT OR SOLAR ELECTRICAL CONTRACTING?

1.) Read the Solar Electric Design Guide and the articles on "sizing your load." Review the ECS Solar Products Catalogs or similar product catalogs. 2.) Make an appointment for an initial consultation with a licensed solar contractor and/or take the one day, 3 hour Solar Electric Design Course at Santa Fe Community College. The classes are offered 3 times a year by ECS.

B.) WHEN MAKING A PURCHASE, WHAT ARE MY MAJOR CONSIDERATIONS AND HOW DO I KNOW IF I HAVE A GOOD SOLAR SITE?

1.) A solar site analysis can be used to determine a roof or ground location that is not shaded from 9am to 3pm in the winter and 9am to 4pm in the summer. Most licensed solar contractors have a solar site shading analysis tool for finding the best location. 2.) Decide whether or not you want to purchase equipment and plan to install the system yourself or if you want a licensed local solar contractor or a licensed electrical contractor and roofer to install the system. There are differences in cost based on the services provided. Equipment that is installed by a contractor and purchased from a local contractor assures you of more responsibility from your contractor than a "real deal" from a solar catalog supplier that is halfway across the country. 3.) Purchase your system based on your budget, your present needs, and future expansion potential for more solar electric power and/or batteries. This is where a licensed solar contractor can benefit you the most on matching the proper components (wiring size, charge controller, etc.) for future expansion.

C.) DO I NEED TO GET A LICENSED ELECTRICIAN INVOLVED?

A CVC state licensed solar contractor can contract to install the solar electric (PV) modules, the batteries, and the inverter or power panel (balance of systems). A CVC state licensed solar contractor is also uniquely licensed and insured to make penetrations in a roof in order to attach solar collectors to the home. The solar contractor is not, however, licensed to make electrical hookups to the AC circuit breaker box. A licensed electrician must make all AC connections between the following:

1. Connecting AC power from the inverter to provide power to the circuit you choose to solar power in your home. For Example:

A. You need to have an electrician hook up a sub-panel circuit breaker box and transfer switch near the main circuit breaker box to put in those circuits you wish to be solar powered each day.

B. You may have the electrical contractor install a transfer switch that will allow power to the other circuit breakers during an emergency (i.e. hurricane or utility power outages)

2. You need to provide AC utility grid power to the inverter's battery charger to back up the battery bank during periods of low sun conditions. You can use the utility company to back up your system and "maintain the batteries" during cloudy weather. This is a great way to take advantage of utility power. In summary, you will need a licensed electrician to wire AC utility power to the battery charger in the inverter and to provide a connection from the inverter to the AC circuits in the home. Also, county or city permits are required for most solar applications.

D.) WHAT ARE THE MAIN COMPONENTS OF SOLAR ELECTRIC SYSTEMS?

Modules generate electricity from sunlight. An inverter changes low voltage DC power to high. A Controller regulates power to and from batteries. Inverters' battery charger converts AC electricity (from generator or utility power) to DC power. Fusing/Breakers and Disconnects are the overcurrent protection. Fixed mounts or Tracking Mounts support and aim modules toward the sun. The combiner box encloses the batteries for paralleling module output, and stores DC electricity. It is not necessary on grid connected systems. Monitors and meters report system status and power flows, both instantaneously and cumulatively. The Power Center combines controllers, overcurrents, disconnects, lightning protection, and monitors in one enclosure.

E.) WHAT ABOUT RUNNING DC FANS. LIGHTS, OR APPLIANCES?

DC systems are usually very small, using only 300 watts or less of solar panels. AC wiring in conventional homes and AC wall switches are not appropriate for DC power. Usually, DC systems are for lighting up outdoor signs, billboards, etc and for water pumping systems for cattle. Often, a homeowner will power a ceiling or porch fan directly by DC power. Some remote homes have small DC lighting systems. Most conventional homes use an inverter to change DC power to conventional AC (like the utility company) for normal, everyday appliances in the home.

F.) WHAT ABOUT INVERTERS?

Trace makes the most popular inverters which also come with built in battery chargers. The SW Trace series of inverters makes a pure sine wave equal to utility grid power. Also, a DR series, available from Trace, makes a modified sine wave which is acceptable for most appliances in the home. It is suggested that you review the Trace literature or talk to a CVC solar contractor to see what inverter will meet your needs. The inverter should be sized for all the loads or circuits that it will power to all be on at the same time, plus the ability to handle starting surge power from well pumps or other motors. You can link to Trace’s web site from ours at www.ecs-solar.com.

G.) WHAT ABOUT WATER OR WELL PUMPING?

There are typically two types of solar wells or water pumping systems. DC Solar Direct and AC pumps that use inverters and batteries. DC Solar Direct systems cost less and are now more reliable and economical than wind mills or hand pitcher pumps. This is a natural for providing unpressurized water for cattle or other livestock. Its hookup is simply two wires attached directly from the solar panels to the pump - whenever the sun shines, it pumps water into a water trough. THE MAIN QUESTION TO ADDRESS IS WHETHER OR NOT, YOU NEED PRESSURIZED WATER FOR YOUR HOME. You typically need a cistern or water tower (like the wind mills) to produce pressurized water with DC well pumps. Some DC well pumps can produce pressurized water with a large battery bank. Usually, it is much more cost effective to use a conventional AC well pump, commonly available and easily serviced from well drillers, powered by the properly chosen sinewave inverter to produce pressurized water for the home.

H.) HOW SHOULD I PLAN MY HOME FOR SOLAR POWER AND WHAT IS PRACTICABLE TO POWER WITH SOLAR ENERGY?

1) Make sure you have a solar hot water heater to pre-feed a backup LP gas or electric water heater. Try to avoid using electric water heaters only. 2) Spending $1.00 on energy efficient fluorescent lights, appliances, etc will save $4.00 on the cost of solar electric equipment (panels, batteries, etc) to power energy inefficient loads. For example, a 25 watt fluorescent bulb will give the same amount of light as a 100 watt incandescent that uses 4 times the solar power. Send $4.00 to American Council for an Energy Efficient Economy (1001 Connecticut Ave NW suite 801; Washington DC 20036-5504) to get the current list of energy efficient appliance ratings on all types of appliances. (See SIZING YOUR SOLAR POWER SYSTEM) 3) In remote homes, use as much LP gas for refrigerators, stoves, water heater back-up, clothes dryers, home heating, etc as possible. A super efficient modern refrigerator (preferably non-frost free) is also recommended. Do not plan to run air conditioning with solar power in remote homes unless you have a heavy duty generator backup. 4) In a grid connected home, start by putting some of the AC circuits on with an inverter with a battery charged power backup from grid power during bad weather.

I.) DOES IT MAKE A DIFFERENCE IF I MAKE MY SYSTEM 12 . 24 OR 48 VOLT?

Usually, only small DC lighting systems are 12 volt. Most household systems will use a DC to AC inverter with solar panels and batteries arranged at 24 or 48 volts to be converted to 120 and/or 240 volt AC electricity. In most cases, a lot of money will be saved on 48 volt systems due to a simple fact that all the DC wiring, for solar panels, batteries, etc must be larger and therefore more expensive for 24 volt systems. We suggest 48 volts system for grid connected systems.

J.) WHAT TYPE OF BATTERIES ARE BEST?

Do not use car batteries or marine batteries; use the heavy duty deep cycle Trojan 6 volt batteries, or the heavy duty deep cycle 2 volt commercial batteries. Typically, 6 volt 220 amp hour golf cart or 395 amp hr deep cycle L-16 's are put together in series for 12, 24, or 48 volt strings and in parallel strings to increase amperage. Water Miser safety vents are recommended on these batteries as water recyclers. Batteries must be in a secure locked location that is well vented. Battery Monitors are recommended

K.) WHAT ABOUT USING GRID CONNECTED POWER AND/OR A GENERATOR TO BACKUP THE BATTERIES DURING BAD WEATHER OR FOR HEAVY LOADS?

The most popular remote or utility backup home power systems are hybrid systems, where a gas or diesel generator or utility power or both are operated only occasionally to run high power consumption tools, etc. and/or to provide backup power during bad weather and/or to maintain and increase the life of the battery bank.

The most efficient inverters have-high powered programmable battery chargers built right in. This makes running a generator extremely cost effective since the power that the load doesn't use is not wasted, but is being stored in the battery bank. (See GENERATORS AND SOLAR GENERATOR HYBRIDS). The inverter powers the load and acts as an energy recovery device for the generator or uses utility power as a battery maintainer. Most importantly the "photo-gen" or hybrid system can reduce the cost of a solar electric system by as much as three quarters. Only a minimum of run time is needed each week to provide abundant A.C. and D.C. electricity. Solar electric power can be added as the budget permits, until the generator or utility grid power is relegated to minor backup status or eliminated.

Your first step is to size your solar power station by determining Your daily power needs or your load (See SIZING YOUR SOLAR POWER SYSTEM). Once you have arrived at your daily load requirements, then you can determine the size of your battery bank, the proper inverter, and the size of the solar array. Until you arrive at your needs by calculating your daily electrical load, you cannot make an intelligent purchase decision or plan for future expansion on your system.

Once you have calculated your load, the next step is to determine your autonomy based on year round weather conditions at your site. The most cost effective method is to base your requirements on the AVERAGE DAY of the year, using a generator or utility power for infrequent large loads during bad weather. More storage means a deep-cycle battery bank of greater capacity; a larger daily load means a greater photovoltaic array. There are three paths to energy independence: conserving to reduce power consumption (you can do this in any case), purchasing a solar array capable of providing power storage during extended bad weather (we do systems on this scale), or augmenting with a small generator or utility power. The combination backup method can extend, even triple, the life of your battery bank by preventing it from being cycled too deep too often. Choosing a generator should be based on your local requirements, the chosen inverter and pump or motor surges. If utility power is available to back up the battery bank, its probably best to get a inexpensive gas AC generator for emergencies from hurricanes, tornados, etc.

If you live in a remote home and need backup during bad weather or for short periods of heavy daily loads, I recommend a high quality DC Direct permanent ceramic magnet diesel generator -like Fischer Panda - or a high quality industrial type diesel AC generator that can be locally serviced and is designed for heavy use. Some options to look for are continuous duty rating and full wattage output on each generator circuit, voltage regulation to match your load, and surge power delivery for starting induction motors such as well pumps.

L.) CAN I SELL POWER BACK TO THE UTILITY COMPANY?

You can sell electricity from the sun directly back to your utility. If the utility lines go down after a hurricane, however, you will not have power at night unless you include a few batteries in your system.

Connecting your PV system to the utility grid will require you to enter into an interconnection agreement and a purchase and sale agreement. Federal law perhaps your state's public utility commission regulations require utilities to supply you with an interconnection agreement. A few utilities have developed simplified, standardized interconnection agreements for small-scale PV systems.

The interconnection agreement specifies the terms and conditions under which your system will be connected to the utility grid. Shell Solar has perfected EarthSafe Systems that meet all interconnection requirements and have the battery option.

Solar Electric Q&A | Solar Products Store | Free Estimate | Why ECS?