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