Solar-Electric Panels
AKA: solar-electric modules, photovoltaic (PV) panels

PV panels are a solar-electric system’s defining component, where sunlight is used to make direct current (DC) electricity. Behind a PV panel’s shimmering facade, wafers of semiconductor material work their magic, using light (photons) to generate electricity—what’s known as the photovoltaic effect. Other components in your system enable the electricity from your solar-electric panels to safely power your electric loads like lights, computers, and refrigerators.

PV panels are assigned a rating in watts based on the maximum power they can produce under ideal sun and temperature conditions. You can use the rated output to help determine how many panels you’ll need to meet your electrical needs. Multiple modules combined together are called an array.

Although rigid panels are the most common form of solar electricity collector, PV technology also has been integrated into roofing shingles and tiles, and even peel-and-stick laminates (for metal standing-seam roofs).

PV modules are very durable and long lasting—most carry 25-year warranties. They can withstand severe weather, including extreme heat, cold, and hail stones.

Battery Bank
AKA: storage battery

Your PV panels will produce electricity whenever the sun shines on them. If your system is off-grid, you’ll need a battery bank—a group of batteries wired together—to store energy so you can have electricity at night or on cloudy days. For off-grid systems, battery banks are typically sized to keep household electricity running for one to five cloudy days. Grid intertied systems also can include battery banks to provide emergency backup power during blackouts—perfect for keeping critical electric loads operating until grid power is restored.

Although similar to ordinary car batteries, the batteries used in solar-electric systems are specialized for the type of charging and discharging they’ll need to endure. Lead-acid batteries are the most common battery used in solar-electric systems. Flooded lead acid batteries are usually the least expensive, but require adding distilled water occasionally to replenish water lost during the normal charging process. Sealed absorbent glass mat (AGM) batteries are maintenance free and designed for grid-tied systems where the batteries are typically kept at a full state of charge. Gel-cell batteries can be a good choice to use in unheated spaces due to their freeze-resistant qualities.

Inverters transform the DC electricity produced by your PV modules into the alternating current (AC) electricity commonly used in most homes for powering lights, appliances, and other gadgets. Grid tied inverters synchronize the electricity they produce with the grid’s utility grade AC electricity, allowing the system to feed solar-made electricity to the utility grid.

Most grid-tie inverters are designed to operate without batteries, but battery-based models also are available. Battery-based inverters for off-grid or grid-tie use often include a battery charger, which is capable of charging a battery bank from either the grid or a backup generator during cloudy weather.

Most grid-intertie inverters can be installed outdoors (ideally, in the shade). Most off-grid inverters are not weatherproof and should be mounted indoors, close to the battery bank.

Many factors will influence the extent of your solar system. You may wish to generate enough power to cover all your needs but find that certain constraints limit your ambitions.

When designing a system, the first things a professional designer will consider will be the sunlight levels for your area (insolation) and your total power requirement. The optimum performance of a photovoltaic panel is obtained when it’s correctly aligned to the sun when the sun is directly overhead. This usually equates, as a fixed mounting, to an alignment of around latitude + or – 15 degrees. Even though it may be visible all day, there may only be around five hours of full sun, due to reflection off your panel and the amount of atmosphere the light has to pass through. This will naturally be least when the sun is directly overhead, called solar noon.

A good rule of thumb to remember when selecting the site for your panels or array is to try and find a spot that is unshaded between the hours of 10 A.M. to 2 P.M. on your hemisphere’s shortest day. Most PV panel manufacturers now incorporate bypass diodes. These diodes are usually placed in the PV panel junction box. In a solar PV array, the panels are usually connected in series strings to increase voltage. These strings are then parallel connected to increase current (amps). The bypass diodes are designed to allow the flow of amps through the series connection with minimal current loss when one or more panels in the array are partially or fully shaded. Don’t forget that even the seemingly inconsequential shading from a tree branch can still cause a substantial reduction in generated power.

To offset the effects of low insolation, you may be able to install additional panels, larger panels with a higher output or panels designed to track the sun’s passage across the sky, thereby maximizing correct orientation (although the depth of the atmosphere cannot be overcome). Concentrator panels, with a lens arrangement designed to better concentrate weak sunlight onto the cells are another alternative option. Unfortunately these options introduce one of the biggest constraints on a system’s size: that of your budget.

Solar panels are not cheap although the cost is steadily decreasing. Many countries have compensation schemes and grants available designed to encourage solar power generation and the enthusiastic uptake in certain countries, particularly Germany and Japan, has caused a panel supply shortage. As the market increases and supply improves, prices should come down. For more information on the Ontario Government rebates and incentives, go to: http://www.rev.gov.on.ca

Solar panel output is measured in watts and is usually supplied at a nominal 12 or 24 volts although this may well be up to 17 or 36 volts effective output. Panels can be wired in series (+-+-) to increase voltage, parallel (++--) to increase amperage. Series/parallel wiring, where sets of panels already wired together in series are wired together in parallel. This serves to increase both voltage and amperage.

Be aware also of the distance between the various components of your system when choosing the nominal DC voltage. The greater the distance, the greater the voltage drop and a higher voltage will travel further than a low one around the same cabling. 24 or 48v nominal systems will avoid having to use more efficient cabling, especially if your batteries are a considerable distance from the solar panels.

The easiest way to calculate the total amount of electrical load you currently use is to check your electricity bill, where the amount you’ve used over your billing period will be expressed in kWh (Kilowatt Hour). Alternatively, you will have to laboriously list the loading of all your electrical equipment using either the data given in the user manual or on the labels usually affixed to the back or underside of the appliance. If your appliance is rated in amps, find the wattage by multiplying the voltage by the amps. You may wish to consider reducing the total load by investing in low wattage energy saving equipment. Reasonably priced meters are available if you are in any doubt. Most hydro electric utility companies have an appliance wattage rating chart on their websites. Waterloo North Hydro has this chart on their website: http://www.wnhydro.com/savingenergy/SavingEnergy.pdf

Batteries are rated by the amount of current they can supply over a period of hours i.e. in amp hours (ah). E.g. a 300 ah battery will be able to supply 15 amps for 20 hours or 30 amps for 10 hours. Don’t forget to consider the drain of a 120 or 240 volt AC system on a low voltage DC battery bank. For example, to calculate the drain on a nominal 24 volt DC system using an inverter to supply an appliance with a load of 4 amps at 120 volts AC for 3 hours per day, use the following calculation: divide the voltage of the load (120v) by the battery nominal voltage (24v). This gives 5. Multiply this by the 120v AC amp hour load (4 amps for 3 hours = 12ah), 5 x 12, to give a total drain on your nominal 24 volt DC system of 60 amp hours. Try to ensure you design in enough amp-hour capacity to take account of any involving bad weather periods. An additional one-fifth capacity is thought to be sufficient to cover this eventuality.

It is possible to run a completely DC system although not entirely practical as although many appliances now come with DC alternatives, they may be difficult to obtain and priced at a premuim. DC lighting is readily obtainable though. If you have alternative power for high load appliances, a smaller system solely for DC components may be an option. Otherwise you are going to need an inverter to convert the DC supply to your chosen 120 or 240v AC supply. Your inverter should be capable of coping with the power surges caused when starting certain appliances, especially those incorporating high-powered motors. The minimum surge rating will be roughly twice that of the continual wattage your system is calculated at. It's also advisable to have a DC powered light in the room where the inverter and batteries are located in case the system is down for maintenance or repair.

Finally, if you are able to produce more energy than you require, it may be possible to export the excess back to your local utility company. Many utility companies have or are exploring the practicalities of localised generation of “green” power and have put in place the mechanisms by which they can buy back surplus. They will be able to advise you on what equipment and metering arrangements will need to be installed. For more information on the Ontario Net Metering Program and the Standard Offer Contract Program (RESOP), please go to our Informational Links page and click on the appropriate link.

Designing and installing a solar powered system does involve a considerable amount of expertise and should not be undertaken without first researching the subject and preferably taking professional advice. Mistakes can be very costly to rectify.