Two forms of Solar Energy
Solar power can come in either of two forms: solar thermal, or solar voltaic. With solar thermal, the sun’s rays are absorbed by flat plates or tubes, which transfer the heat to a fluid (usually water), which is then collected into a tank. Often these tanks are mounted at the top of the collectors, although they can also be positioned on the ground. Hot water from the tank can then be used for the all household’s hot water needs (showers, dishwashing etc).
The downside to solar thermal is that on days when there isn’t much sun, the system may not generate enough hot water. In those cases, it’s necessary to have backup sources for heating your water, such as a boiler or electric element. Furthermore, solar thermal generates no electric power.
Solar photovoltaic power (solar PV) actually generates electrical power through the sun’s rays, using PV panels. As they absorb sunlight, the panels create their own low-voltage, direct current electricity. Since this current isn’t useful for modern appliances, it’s transferred via cables to special DC to AC “inverters” that transform it into higher-voltage AC current, which is compatible with household electric needs. The panels and inverters are the most costly part of a new solar PV system.
The installers will then wire the system to your house at your fuse box, as well as to the electric grid. (Please note: the voltages in Solar PV systems are quite high, hence very dangerous! Don’t try to disconnect any of the parts without carefully following instructions, or calling a professional).
During very sunny days, your solar PV panels may create even more energy than you need. Your solar system will include an import-export meter to export the excess power back to the grid. The electric company then buys electricity back from you, using the money to spend down your electric bill. You’ll need a new electric meter to register these changes.
Electric companies often charge you several times more for electricity than what they pay for the electricity you sell back to them. To get the maximum benefit from your solar system, it pays to look closely at how and when you’re using power in your home. This will also help you determine just how many panels and how large a Solar PV system you’ll need.
People sometimes dream of disconnecting entirely from the electric grid, completely eliminating their dependence on electric companies. But in most cases, that’s just what it is—a dream. To make your home completely grid-free, you’d have to buy a huge bank of batteries to store your excess solar power. Installing this sort of system is several times more expensive than installing systems connected to the grid. It will require much more maintenance as well, a constant investment in batteries, and you still may run out of power from time to time. Environmentally conscious consumers should also be concerned about the toxic chemicals in the batteries.
Types of Panels
There are currently three types of solar panels available. The ones that have been around the longest and are the most expensive are monocrystalline panels, made from thin slices of pure silicon. These silicon cells are laid out and crossed by wires which collect the electricity created when the sunlight hits the cell. (A bit of surface area is lost by the way they’re framed in the solar PV panel). These panels boost up to 20% efficiency. There are actually some even more high-tech panels that can produce more than 20% efficiency, but they run about 30% more in price.
Polycrystalline panels are made from a less pure form of silicon, and hence are slightly less efficient. However, their square shape eliminates the lost space between cells that occurs with monocrystalline panels, and the extra surface area compensates for the lower efficiency.
Thin film solar cells are manufactured with a different technique. Instead of slicing blocks of silicon, the solar panel is sprayed with silicon. These cells are less efficient, only about 8-10%, so you need more of them to get the same effect, and the panels are heavy.
Today, there are several dozen companies making solar panels of different grades. The cheapest ones start at about $250, and the most sophisticated, high-quality panels sell for as much as $5,600.
Panels are the single largest expense in converting to solar, but keep in mind that government incentives will help keep your costs low.
Tilting the Panels
For maximum efficiency, solar panels need to be tilted. This is because as the sun angles further down in the sky during the day, a tilted panel will catch a greater percentage of the rays than a horizontal panel.
Most roofs are constructed with a pitch (tilt). If the roof is flat, most solar installers will provide tilt frames to provide the right pitch for the panels. A tilt is essential not only to capture the maximum amount of sunlight, but to allow rainwater to run off the panels. Rainwater that remains collected on solar panels can seep through the panel seals and destroy the cells.
The rule of thumb for panel tilt is to make sure the tilt is the same number of degrees as your latitude on the globe. That’s the ideal number, but generally speaking, as long as your roof has more than 10 or 15 degrees of pitch you may not need to make further adjustments.
The direction of the panel placement is also important. In the Northeast U.S., the sun rises in the east, then heads south and west, so generally a southern placement is best. If you don’t have a south-facing roof, you can still often receive enough power depending on the placement and angle of the panels. A qualified solar installer will be able to calculate how much power your placement will give you.
Solar panels need to be connected to an inverter so that the low-voltage DC current generated by sunlight is transformed and amped up into 240-volt AC current. After the panels, the inverter is the most expensive part of a solar setup, generally about 20% of the cost. Inverters range in size depending on how large a system they’re servicing, and the company installing your system can advise you how large an inverter you need for the amount of panels you have.
You’ll want to consider one of three options in solar inverters:
Transformer type inverters: These are relatively simple to manufacture, but they’re heavy and make a humming noise some people find bothersome (one solution is to make sure it’s not placed near an area where you sleep or spend a lot of time, although all inverters should ideally be placed as near as possible to the electric meter. They should also be in the shade). Transformer-type inverters are slightly cheaper, and slightly less efficient.
Transformer-less inverters: This newer technology has no transformers, which makes it lighter and more efficient. It’s a more sophisticated technology that’s quickly becoming the most popular. Transformer-less inverters also have the advantage of being silent except for some high-frequency sounds humans can’t hear anyway.
An option many people are now choosing are MMPT (Maximum Power Point Tracker) inverters, which allows you to add new panels even if they’re not exactly the same as the original ones, or to install photovoltaic panels at different angles. The industry is also starting to produce solar panels that each have their own micro-MMPT inverter attached, which allows solar systems to integrate different sorts of panels and monitor each panel’s output separately.
Inverters typically carry displays that log the kilowatt you produce daily, the kilowatts you’ve produced since installation, and the kilowatts it’s producing currently. Most people don’t want to have to look into the meter box to access this information, but for a small investment you can set up a remote monitoring system that will send this information to your computer or smartphone.
It’s usually not wise to choose the cheapest inverter, but rather to look for good quality and a warranty. Most good inverters carry an eight to ten year guarantee. You can find reviews and stats on inverters online to help you comparison shop.
You should definitely check the inverter’s efficiency. Transformer-type inverters should be about 93% efficient in transforming solar power to electric power; transformer-less inverters run a bit higher, about 95%. Some salespeople may advise you to invest in a larger inverter than you need in case you choose to expand your solar system in the future, but before going that route you should consider whether or not your roof can handle more panels, and whether or not you’re likely to do it soon enough that you’d be buying the same type of solar panels (unless you choose an MMPT inverter).
Inverters include delicate electronic technology, and therefore need sheltering from the elements. Some are constructed to be weather-proof, but others require a cage. Adequate protection will keep your inverter functioning longer.
Government Incentives for Solar
Thanks to the Energy Policy Act of 2005, which recently extended its 2016 deadline, the U.S. government offers a 30% tax credit on the cost of solar systems. There’s no ceiling on the amount of your expenditure. People who don’t owe any taxes can roll over the credit to a future year!
The Database of State Incentives for Renewables and Efficiency, www.dsireusa.org, lists incentives offered by individual states for solar adoption. Check it out to see if there are grants, loans, individual or corporate tax credits, and/or rebates available in your area.
New York State residents have a multitude of options available to help them switch to solar. NYSERDA (New York State Energy Research and Development Authority) offers incentive programs to support solar projects for commercial and industrial companies, homes, multifamily buildings, small commercial, not-for- profit and municipal buildings. Included among them are the Affordable Solar program for low-to-moderate income residents, and the Shared Solar program to help renters and other residents who aren’t able to install solar on their own roofs. The Solarize program helps communities buy in groups to obtain the most competitive pricing.
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- Aman Bisht