How To Build A Solar-Powered Electrical System For Your Home

Introduction

If you have basic handyman skills, and a good set of tools, you can install a working solar electric system on your home; we 're assuming you already have a good reason to do this, whether it's paying a little more now to reduce your monthly utility bills, making your local community more sustainable, or some other reason. Why you're doing this is up to you; we're going to show you how. If you're a homeowner who looks at hammers with deep suspicion, we'll also give you the information needed to have a professional come and install it for you. What this book won't do is cover site and state and locale specific items, like electrical codes and wiring regulations. There's too much information there for us to fit into pieces this short, and that information changes unpredictably. You should talk to a local electrician, or your local utility company, about your requirements, though most commercially available systems are going to met the most common regulations out of the box, if they're UL or CSA approved.

See the list to the right for complete information about how to build your own solar-powered system.

Living Conservatively

Owning your own solar power system will make you aware of how much electricity you're using; solar power systems aren't a panacea; they can cut your electrical bills. Reducing your energy use in general will cut them further, and will likely cut them more. Turn things off when they aren't in use, be it radios, televisions or computers. For things that plug into wall sockets, put them on a power strip and turn that off at the source to eliminate 'vampire' consumption (a typical cell phone recharger, even when nothing is plugged in, trickle charges at a bit under a watt, other devices, like laptop chargers, do the same). While you're at it, swap out any indoor incandescent bulbs for compact fluorescents; they typically use a quarter to a fifth of the electrical power.

Something to consider down the road is replacing your appliances with more energy efficient models; energy efficient refrigerators are the top of the list, as are hot water heaters (solar thermal hoot water systems are also worthwhile expenditures). Your solar energy system isn't going to be able to power an air conditioning system, though it'll take the edge off. Swamp coolers are a low power option right now.\

See the list to the right for complete information about how to build your own solar-powered system.

System Design and Sizing

Your solar energy system is going to have a solar array (the panels that convert sunlight to electricity) and some sort of energy storage mechanism; this is, increasingly, becoming a large set of batteries, often lead-acid ones because they're cheap and in a house, the size and bulk doesn't matter. Getting your electricity from the array to the batteries will require wiring; the kind of wiring will be a function of whether the power is going by AC (Alternating Current), which requires an inverter (a source of power loss) or DC (Direct Current), which suffers transmission losses in lines of longer than 75 feet, and requires heavier wiring to begin with.

See the list to the right for complete information about how to build your own solar-powered system.

Budget

The first rule of this is that price IS an object; it's entirely possible to make a wish list for your solar energy system that causes it to cost more than the home it's attached to. So, set up your budget (including tax credits and assessment offsets for this, based on your locale) before you start. In general, the more efficient a solar panel is at converting sunlight to electricity, the more expensive it is, and the differences are nonlinear; going from a typical 17% efficient conversion to a 30% efficient conversion can cause the cost of the panels to go up by a factor of 100. (This is why NASA's solar panels are more efficient than the ones you can put on your roof; for NASA the cost of getting those solar panels into orbit dwarfs the cost of the panels themselves, so they might as well pay the extra for the greater efficiency). Other factors to think about are the cost to replace them as they wear out; long exposure to sunlight will eventually degrade solar panel performance. The expected life span of a solar panel array is about 20 to 30 years, when all is said and done.

Components

Common Components of a Home Solar Electric System:

  • Solar panels or modules - These generate 12V electricity from sunlight. Batteries - These store your electricity for future use.
  • Controller - This regulates the power to and from your batteries.
  • Inverter - This transforms low voltage direct current power to high voltage alternating current power.
  • Monitors, Gauges, Meters, etc. - These keep you aware of the status of your system and the individual components.
  • Wire - Connects the various components of the system to each other and to the loads. Fuses, Breakers, Switches, and
  • Disconnects - Gives you overload and short circuit protection, and allows you to isolate all or part of your system for safety and maintenance reasons.
  • Battery Charger - This allows you to charge you batteries from auxiliary sources.
  • Generator - This provides back up power to your system and charges your batteries when necessary; mostly for rural installations.
  • Smart metering technology – this tells you how much each appliance is using in real time, and many utility companies are providing these kits to residential customers. They're also part and parcel with net-electric metering, where you sell excess power generated back to the grid (and it shows up as a discount on your next electric bill.)

Your solar electric system is, nearly by necessity, going to be a custom job made up of these components. It will need to factor in what you need for power generation and storage, and other site specific locations (like needing a facing that gets a lot of sunlight, problems with nearby trees and more). While there are complete "off the shelf" systems, these are typically for RVs, boats and at most, small cabins; trying to tie them to your house will swamp them.

During the design process, you're going to be balancing initial purchase cost, versus your energy needs (both total volume and when it's needed), versus how much battery storage you can get, and how much you want to spend for future expandability.

 

Charge Controllers

One of the other important elements of a home photovoltaic system is a charge controller.  This device prevents your solar panels from overcharging your battery, by keeping the batteries from taking on more current when they're fully charged.  Not doing this can cause battery overloads, which, in extreme cases, can be a risk for fire or even an explosion.  Very advanced systems, in conjunction with net usage monitoring, can redirect excess power beyond the storage subsystem back to your main electrical grid, where it will be counted as a credit on your bill by your utility company.

Your solar array setup will include a recommended size for a charge controller, the two limits are how much battery capacity you have, and how much current you can expect your array to produce at peak times.  Like battery arrays, the most common charge controllers are in 12, 24 and 48 volt arrangements, with more variation in amperage, from 1 amp to 100 amps. 

Like sizing your battery array, sizing your controller for a bit overage improves safety, and saves money in the long run.  A safe metric is about 25%;if you have four 12 volt arrays rated at 4 amps, getting a 20 amp controller (4x4*1.25) is a safe margin, and gives you options to add more panels down the road.

Other than protecting your batteries from over charging, there are several other features that can be included in your controller.   These include:

  1. Reverse Current Leakage Protection - This keeps current from flowing backward from your batteries to your array.
  2. Low Voltage Disconnect - This reduces damage to your batteries by avoiding deep discharges.
  3. System Monitoring - meters, indicating lights and/or warning alarms.
  4. Temperature Compensation - The charging voltage is adjusted for the temperature if your batteries are not in a climate-controlled space.
     

Generators

In solar electric systems, generators are useful backup systems, especially in rural areas.  There may also be times when you need to run very large loads that are beyond what your energy system was designed for, such as large power tools or a clothes dryer.  Clearly, you want to use the generator as little as possible, because it costs you money for fuel, and is noisy, and emits pollution.  You'll want to try to use the generator at peak capacity for the shortest practical period, say drying a load of clothes while recharging your batteries. 

You have a lot of choices for the generator type, with diesel and propane being the most practical, and gasoline being the most convenient.  You can get generators that will automatically cut off when the batteries are full, and you'll probably want a separate enclosure for the generator. 
 

Inverters

An inverter is a central component of any alternative power system that requires alternating current power. Inverters transform low voltage 12-volt DC power to standard 120 / 240 volt AC current draws in modern appliances and tools. Inverters switch DC back and forth to make AC power, which is then filtered, and transformed and stepped up or down to match the desired waveform.  More processing makes for a cleaner output with fewer voltage spikes, but reduces the overall efficiency of the process. 

Modern inverters come in two basic types - modified sine wave and pure sine wave.  A modified sine wave is close but not identical to the waveform that comes from your public utility. Modified sine wave inverters can run most household appliances including TV's, stereos, lighting, computers, etc.  Pure sine wave inverters produce a waveform that is identical to and in some cases better than what you get from your public utility company.

Modified sine wave inverters do less processing of the power; this can cause some devices (laser printers, tools with variable speed motors, and similar items that need an abrupt pull on their power demands).  Pure side wave inverters are more expensive, but won't cause "laser printer brown outs" or "table saw brown outs" when running off them.  Because they do more processing of the power, they're less efficient overall.

When looking at inverters, of either type, they have two capacity ratings.  One is the continuous output rating, the other is the surge capacity rating.  Continuous output rating is how much power, in watts, the inverter can provide for hour after hour.  Surge capacity rating is how much power the system can deliver for a short period of time.  You'll need decent values for both – the continuous output rating limits how many devices you can have running at once; the surge limit is useful for appliances like refrigerators that need more power to start up than to keep going after they've started.  Larger inverters (up to 10,000 watt monsters, useful for running a small building) are more expensive.
 

Choosing the Right Inverter

Your inverter need will be a function of the Watts used by your current appliance mix, multiplied by a fudge factor set by the total efficiency.  You may want to oversize your inverter initially so that it can handle adding more appliances to your home, or so that you can utilize more capacity with your solar array as you add panels.  This fudge factor is generally about a 15% surcharge; take the total wattage on your home, and multiply by 1.15 to get a good value for your load calculation worksheet.

Most inverters are 120 volts alternating current, but 240-volt alternating current inverters are available if you wish to run loads that require this. There are also step-up transformers available that attach to your 120-volt inverter that allow you to produce 240 volts alternating current, if necessary. In some cases you can also "stack" two similar 120-volt inverters together to provide 240 volts.  Most inverters on the market also serve double duty as portable battery rechargers, which is a handy useful feature.

And, as with the advice on battery arrays, and solar panels, ALWAYS use the rated wiring.  Don't get cheap here; this is a piece of gear that can cause house fires if the power cabling overheats.
 

Batteries

The majority of the electricity your solar array will generate will be stored in batteries. 

Electricity as Water Pressure

Batteries are your reservoir of energy for future use.  It might help to compare this to water stored in a dam.  Both have potential that can used for various purposes. Batteries are used to even out the power that your panels generate.  They provide a constant load and give you power when the sun is down without drawing on your utility company. As mentioned earlier, your battery array will need to be hooked up to a controller, and probably an inverter if you want to use power for AC appliances.

Battery choices are fairly standardized, much the same way solar panels are. You'll want to make sure that you maintain your batteries carefully. For the most part, you're going to be using deep cycle (also known as "marine" batteries). These have lower peak yields per battery cell, but store the same amount of power. Their primary benefit is that they last longer under constant use.

You'll want as many batteries in a battery bank as you can get.  The less your battery has to work, the longer it will last, and the best way to do this (even with deep cycle batteries) is to spread the work out.

See the list to the right for complete information about how to build your own solar-powered system.

Battery Chargers

Because solar energy is variable in its input parameters (clouds, night, etc), your batteries will probably not be topped off constantly.  There are systems out there that convert 120-volt AC power to the lower voltage DC power your batteries want; this lets you bank power from your utility company for later use, and helps cut down on the wear and tear of your battery array, and can even recondition some types of batteries.  When looking at battery chargers, talk to the manufacturer of the batteries you're using for their recommendations on charging voltage. 
 

Battery Maintenance

Batteries work by moving ions across a barrier via a chemical reaction.  They need to be kept warm (roughly 10 to 25 degrees C, or broadly speaking, room temperature) and dry.  The colder the battery is, the longer it'll take to charge, just like a car battery in the dead of winter.  As with anything involving electronics, avoid extremes in temperatures; they can cause breakdowns in the chemical reactions that run your batteries.  Since you're probably building your own battery enclosure, spending the money on high quality insulation is a good idea.  Never let your batteries freeze.

You'll need to regularly monitor the storage capacity of your batteries, to know when to maintain them.  Good battery care habits can more than triple the life of your battery system.  You'll need a volt meter and hydrometer to do this; the first tells you how much voltage you're getting out of the battery, the second tells you the status of the electrolytes in the battery itself.

Your batteries are going to consume water; make sure that you fill them with distilled water to keep them running smoothly.  You'll want to keep your batteries at a 50% charge state to maximize battery life, and you should keep your batteries electrolyte levels at the indicated level.

Because batteries run off of a chemical reaction, when they're charged, they can emit hydrogen and free oxygen.  Keep your batteries in a well ventilated space, an away from open flames.  Oxygen, in particular, is a primary source for contact corrosion.  You'll want to inspect your battery contacts about once every six to eight months and clean off corrosion.  Putting a layer of grease on the contacts will keep them from corroding as quickly.

As part of your maintenance progress, you should check your batteries for signs of aging.  As they age, batteries get less efficient.  If they're hooked up in parallel, their capacity drops.  If they're hooked up in series, their voltage drops.  Roughly the same time you check the contacts for corrosion and apply a new layer of grease to them, you should be running a capacitance meter and volt meter to them to check their overall performance. 
 

Installing Your Batteries

Like your solar arrays, batteries can be wired in series to increase voltage, or in parallel to increase the storage capacity of the array.  For wiring in series, the positive terminal is connected to the negative terminal – much the same way that you put batteries in a flashlight, and for the same reason.  When hooking them up in parallel, you hook them up positive to positive and negative to negative. 

Most of your home appliances want 12-volt current, and most commercial solar battery systems run with multiple 12-volt cells.  Sometimes, for specialized needs, you'll need to run them in series for peak demand at 24 and 48 volt draws; again, knowing what your appliances need (covered earlier) is an important part of the process.  Because batteries provide DC current (until you run through an inverter) and are hooked up to transfer DC between them, it's very important that your cells and the wiring that hooks them up be of the appropriate size and capacity; doing otherwise reduces efficiency, and can run the risk of electrical fires.

While we're talking about hooking batteries up to contacts, it's important that all your contacts get tightened evenly, and that the contacts be matched appropriately. You want to avoid differences in resistance in the contacts, as this will reduce charge to one battery string and reduce battery life.  Also, put the main positive lead, and main negative lead on opposite corners of the array; this will even out any differentials in charge potential.
 

When Replacement Is Needed

These are symptoms that batteries need replacement.
1)    If the voltage rises rapidly when charging (you'll see this when the charger shuts down early), or drops rapidly under the load, this is a sign of battery wear.
2)    Cell to cell voltage variations of 0.05V to 0.1 volts.
3)    Increased water consumption.
4)    Drops in overall specific gravity in the battery; this usually means that the solute has run out.

When you replace batteries, replace entire battery banks, rather than individual cells; putting a fresh sell in series or in parallel with one that's older will cause the newer battery to degrade down to the performance of the older one, rather than boost the older one up to new.
 

Wiring and Safety

On each of the subcomponents of a power generation system, we've harped on making sure you use the proper wiring weight.  Consider those warnings repeated.  While you're at it, look up the local electrical codes, and seriously consider having a professional electrician do the installation.  It will go faster, and while you're studying the electrical contracting codes, he knows them by heart for your local area.

If your time is less valuable to you than your money is, all of the components involved are simple to install and maintain, if you follow the manufacturer's recommendations and your local codes. Any home owner who can do a moderate amount of home repair and use tools safely should be able to do this.

If you do this yourself, remember, as voltage decreases (from 120 volts alternating current to 12 volts direct current) the amperage (current) increases. Amps x Volts = Watts .  When the current increases, the size of your wire must also increase to handle the additional resistance and heat. Resistance means loss of power from the source to the load. Overheating can be very dangerous.  When in doubt, go to the next largest size of wire. The increased efficiency and safety factors are well worth the added cost.

Wire comes with varying insulation qualities, depending upon your requirements. Temperature ratings and resistance to water and sunlight are also factors to consider. Indoor and outdoor wiring are different. Let your supplier know what your application is.

Lastly, keep in mind the need for circuit breakers.   Ratings for fuses, breakers and switches are not the same for alternating current as they are for direct current. When purchasing, be sure your supplier is aware of the application.  Short circuit protection must be provided for all units connected to the battery.   Manual shutdown switches should be provided between all components and the power source. It is necessary when maintaining or replacing components to isolate them from the power source.
 

Controlling Your Electrical Needs

One of the critical changes that owning your own power generation system imposes on you is being aware of your electrical current loads.  This is where your power goes to when you're using it.  We're going to cover  the basics of load reduction here; it's not part and parcel of setting up your PV system, but it's a major chunk of it.

Lighting

Get rid of your incandescent bulbs; the difference in lighting a room with incandescents versus compact fluorescents is anywhere from a 70 to 80% reduction in total loads used…and they're now about 1.5 to 2x as expensive rather than 5x as expensive, and most are now tolerant of modified sine wave inverters.  On the horizon are LED bulbs, which are about a 90% reduction over incandescents.

If you are installing a new system, direct current lighting is much more energy efficient than alternating current lighting. Direct current wiring circuits will use larger gauge wire than alternating current circuits (See Wiring and Safety). This, depending on the number of lights and the distance of your runs, could be a significant cost factor.

Heating Hot Water

This is another major source of load, in large part because electric hot water heaters are incredibly inefficient.  Electrical hot water heaters are usually the largest single draw on power in a home.  Consider a propane hot water heater, even an 'instant on' one without a storage tank, if you're up to doing a replacement on this, or installing a secondary solar thermal hot water heater.  At the very least, put more insulation on the hot water heater you have.

Air Conditioning

The first rule of living green is that air conditioning is expensive.  If you live in a dry climate, get an evaporative cooler; these systems cool air by osmotic flow over a moist pad.  If you're not in a dry climate, cooling fans and ceiling fans are a good choice.  If neither of those are palatable, look seriously at getting an Energy Star certified air conditioning system.  And, while it's counterintuitive to most folks, improving your home's insulation can dramatically cut your cooling bills or the draw that you climate control system makes on your power system.

Refrigeration Alternatives

Refrigeration is another major consumer of electrical power. Unlike stoves or clothes dryers, which are used only sporadically, refrigerators draw power 24 hours a day.  There are energy efficient refrigerators available that use only 25% of the power of a conventional refrigerator. However, these are relatively expensive and the power they consume is still substantial.  If you're using a propane water heater, or a propane generator as part of your power system revamp, look seriously at propane refrigerators.

Computers and Other Appliances

Today there is a wide assortment of 12V appliances on the market, from kitchen counter appliances, TV's, VCR's, stereos and small vacuum cleaners. You will have to decide what your needs are and whether these 12V appliances will meet them.
While many laptop computers can be run off of 12V- direct current power, most desktop computers, printers, scanners, etc. require the use of an inverter. While most computers and accessories will run off of a modified sine wave inverter with no problems, some computers (Apple) and laser printers, as well as some photocopy machines will need a pure sine wave inverter.

Water Pumping

One of the largest draws of electricity in rural areas, especially in the Western US, is pumping water to crops, for animals or livestock, or for household use.  One of the earliest uses of solar power was to power electric pumps for just this purpose.  They're also becoming more popular in residential areas to run sprinkler systems and misting systems for lawn care.

 

Electrical Generation & Needs

To get the size of the array you need, you'll want to take the equivalent full sun hours figures, and run an average for a year (or for the period of the year you want the solar array to supplement things).  For people using solar energy in rural environments, or trying to live more 'off the grid', investing in a diesel or propane generator to help cover on peak load usage is also worth doing; for more urban residential users, electricity from the utility company is going to be cheaper than a generator.

The other half of the equation is figuring out what you're going to be using electricity for.  Your utility company can provide you with your last year's worth of electrical bills, and you can look over your appliances for more information.  (You will need to note your AC and DC usages separately.  We'll get into AC and DC a bit later).

Start by finding the number of hours each device will be on in a given day; each appliance will also list how many Watts it uses; this will be in the manual or on a tag in the rear of the device.  Devices that run off of batteries will usually have an AC to DC converter unit as part of their set up – a cell phone charger is a good example.

Now, compare the conversion efficiency of the solar arrays of your choice (typically expressed in "watts per sun hour" per panel), multiplied by the number of panels, and see how that compares to the total Watts needed to run your devices.

The output of your solar array is dependent on light intensity and the amount of exposure to the sun, not on how hot it is. On a cold, bright winter day your panels perform just as well as in summer.

Electricity Basics

Electricity is the movement of electrons through a conducting material, in our case wire. The easiest way to visualize this is to imagine that electricity is water going through a pipe; if your flow of water in a pipe is high enough, you can do useful work. The same thing applies to electricity. Electricity is measured in amperes, volts and watts. Voltage can be thought of as the pressure of the electrons going through the wire. Amperage is the overall flow rate of electricity through the wire - low voltage, high amperage could be thought of as a low pressure water main, while high voltage, low amperage could be thought of as a high pressure water hose.

Wattage is how much force you get from the system, in terms of voltage times amperage over time; you can have low amperage, high voltage system and a low voltage, high amperage system both channel the same amount of Watts. A kilowatt is 1,000 watts, and your electrical bill will be in kilowatt-hours, where an hour is broken down into seconds (3,600 seconds to the hour).

Electrical current comes in two varieties: Alternating Current (AC) and Direct Current (DC). Most everything in your home uses AC current, and that's what your electrical utility company provides; AC provides some significant efficiencies when transmitting power, and is less of a fire hazard and is generally safer. DC is more efficient over shorter distances., but requires heavier wiring and insulation.

DC power is converted to AC power through a system called an "inverter". The inverter will cause some power loss when current is cycled through it; if you've ever noticed how warm a laptop's power supply gets when it's been running, you've run into the kind of power loss we're talking about, and for most of your electrical devices, you're going to want AC power as the final input.

The trade off becomes mapping the power lost through the inverter, versus the expense of running heavier wiring to reduce resistance losses on DC power transmission, and when and where the power will be used. There is no generalized answer to this, each solution will be unique depending on your appliances, how much battery capacity you have, and your transmission distances.

See the list to the right for complete information about how to build your own solar-powered system.

Selling Electricity to the Power Company

Grid Inter-tie

Solar panels (photovoltaics) are now being used, worldwide, in homes that are already hooked up to the local power utility. This is called grid inter-tie. Many people have chosen to generate some of their own electricity through the use of a solar electric system that is tied into the power utility grid.

The cost of setting up your own power system may seem expensive at first glance, especially compared to what the local power company charges you for electricity. With your own source of electricity you get a degree of independence from your local power company, as well as the knowledge that you are producing power in a green way. Your solar electric system will also provide a back up, if you include a battery bank, in the event of a power failure.

Producing and using your own power has the immediate effect of reducing your monthly power bills. You may also be able to sell unused power you're generating to the utility company, and get a credit on your utility bills – even getting a monthly check in some months rather than a bill. 

Rules and regulations vary greatly from region to region on the use of grid inter-tie systems. In some areas the power company will buy power back from you at the same rate they sell it. In other areas, they will pay you less for your power than they charge you for theirs, even though it is identical.

In most cases, your PV site will generate power until your batteries hit capacity, then you'll sell the excess to your utility company; sometimes this will be at the same rate they charge you for it, sometimes it'll be less – it depends on your local public utility commission.
 

Shopping Around

So, you've got your parts list (see our larger articles for some recommendations), and you know where you want to put the system, and where the batteries are going to live.  It's time to comparison shop.  Comparison shopping can save you substantial amounts of money on buying a solar electric system; you can often find companies that are upgrading their systems and are willing to sell inverters and controllers at a deep discount; we've even had a few cases where they were free if we showed up on a weekend with a truck.  Make sure the parts are compatible with your overall plan, but don't be afraid to buy used; about the only systems that might be iffy if bought used are the solar arrays themselves if they're over a decade old. 
 

Siting Requirements & Insolation

After setting your budget, it's time to look at your average insolation. Insolation is a measure of how much sunlight your home gets (or your neighborhood gets) over the course of a typical day, and a typical year. It's most commonly measured in Watts/square meter for commercial applications, and for residential, in terms of "sun-hours". You find good insolation information at the weather bureau; your local city planning (or county planning) office may also have this information readily at hand, with results tailored for your local geography.

The amount of energy you get from the sun in a typical day depends on both the time the sun is over the horizon and how high up it is in the sky – the angle of sunlight matters, because low angle light goes through more of the atmosphere and heats up more air molecules (and disperses) before it reaches your solar panels. The optimal sun-hour is high noon; everything else will be measured in fractions of that; on average, most locations in the US get between five and eight sun hours each day; southern climates with fewer clouds in the sky, and fewer obstructions on the southern horizon tend to get more; lots of places in the Sonoran desert of Arizona can get up to nine sun hours per day reliably.

Another factor on insolation is how much it varies at different times of the year; think about this in conjunction with your power usage patterns; you may find that your solar panels provide you the least benefit when you need them most if you're using them in the winter time to try and power electric baseboard heaters.

Finally, be aware that shade will greatly reduce the effectiveness of solar panels; because of the way photovoltaic (solar cells) work) if one of them is reduced in output due to shading, the others will be as well; there are some premium panels that have built in diodes to prevent this, but try to avoid having anything provide shade to your solar array. You'll be happier with the outcome.

See the list to the right for complete information about how to build your own solar-powered system.

Solar Panel Wiring – Amperage and Voltage

Solar panels, when hooked together in an array can be wired in series, in parallel or both. The way you decide to wire your system together will be determined by your system's size, that is, 12 volt, 24 volt or 48 volt. When wired in series, the negative terminal of one panel is wired to the positive terminal of another panel, like batteries in your car. This increases the voltage, but has no effect on the amperage. Two 12-volt / 3.5-amp panels wired in series would produce 24 volts at 3.5 amps. Similarly, four 12-volt / 3.5 amp panels wired this way would produce 48 volts at 3.5 amps.

When wired in parallel, the terminals are wired together positive to positive and negative to negative. Wiring this way would have no effect on the voltage but does increase the amperage. Two 12-volt / 3.5-amp panels wired together in parallel would produce 12 volts at 7.0 amps, and four panels wired together in parallel would produce 12 volts at 14.0 amps.

See the list to the right for complete information about how to build your own solar-powered system.

Pre-Bundled Kits

Units called power centers are available to simplify hooking up the various components of your energy system. They can include, all in one enclosure and pre-wired: your charge controller, circuit breakers, fuses, PV array and battery disconnects, shunts and meters. A good power center will also include easy connection points for your battery, inverter and PV connection cables.  Talk to your local supplier about recommended power stations for your area, ones that have already met the local zoning requirements and electrical and building codes.
 

System Monitoring

Your utility company does total power grid monitoring for the entire area.  As you're now generating some of your own power, it falls on you to do that monitoring for your solar power system.  We covered basic monitoring gear in the "What You Need To Buy" section earlier; there are lot of choices, but the most basic meters you need are a voltage meter (which tells you how much power you've got stored in the batteries) and an amp/hour meter (preferably with an instantaneous read function), which shows how much current is coming in and how much is being pulled by your utilities.

When setting up your meters, it's important that you have them where you can see them without going out of your way; some meters can be network accessible, so you can check them on your computer screen, others are straight analog.  If you don't have a meter that can be checked remotely, we recommend putting the meter near your kitchen.  Your kitchen has the single largest electrical load in your home, and this makes it a place to get decent performance metrics under different usage patterns.
 

Understanding DC and AC

Alternating current (AC) is the sort of power the application company supplies to your house.

Solar panels produce direct current that may be stored in batteries or used to run direct current (DC) loads at once. In all power systems, electricity must be moved from one place to another. Transferring electricity is rarely a hundred percent efficient, due to resistance in the wire. In wire, the loss of electric power is an element of the resistance of the wire and the quantity of current.

High voltage AC power can be conducted over long distances with comparatively low transmission losses. When using DC power, the distance from your charging source ( solar panels ) to your battery bank becomes an element, as will the distance from your batteries to the diverse loads, due to high line loss.

Future Developments In Solar Panels

The field of solar energy is one that's constantly moving, with lots of research going on in the laboratory to improve efficiency or on the manufacturing side to make the panels easier to install, less expensive to make, or more durable – in some cases, all three.

One of the leaders in this latter development is Uni-Solar, which has brought to market Solar Shingles.  These can be retrofitted to a house (or better yet, installed as new construction) and turn the actual surface of your roof into a solar array.  They have the advantage of being less expensive, and much easier to install, while also being a bit less overt than the traditional solar cell array.  They're not quite as efficient, but their lower production cost, greater durability, and ability to cover more of the surface of your roof will make up for that difference.   They're available as shingled, rolled out roofing and bonded arrays.

Uni-Solar is also working on techniques to make them multi-layered, so that each layer of the panel reacts to a different wavelength of light, hoping to boost efficiency into the 20-21% range.  This is still being worked on as a factory process.