When purchasing or upgrading a solar power system for the home or business, things can get confusing with all the various components. A grid connect system typically includes solar panels, an inverter(s), mounting and cabling. Below is an elaboration of the components. Let's start with the most important one.
Solar Photovoltaic (PV) Panels
Solar panels convert sunlight into electricity via the photovoltaic effect. The photovoltaic effect is the creation of voltage (or electrical currents) upon the panel's exposure to sunlight.
Dozens of crystalline silicon cells compose the solar panel, known as photovoltaic cells.
Typically, there are two types of solar panels: monocrystalline and polycrystalline.
Monocrystalline PV cells have been regarded as a superior technology in the past, however polycrystalline PV cells are now closely comparable to monocrystalline PV cells. Read about the differences in PV panels: click here>
Learn how to read a solar panel data sheet here>
Solar Panel Prices
There will be some small discrepancies when analysing solar panel prices. Comparing the price of a 300W panel with a different brand of 300W panel is one way to accurately assess prices. A 350W panel offers 16% more power than a 300W panel, therefore a price comparison with a 300W vs a 350W panel would be inaccurate.
Power aside, there are other factors that can impact price variations; brand, country of origin/manufacture, quality of materials, conversion efficiency and length of the warranty. Therefore, picking up a solar panel solely based on price is not recommended.
Solar Panel Conversion Efficiency
Efficiency percentages are allocated to every solar panel model. Percentages range from 18% to 22%, with most solar panels on the market tested under standard temperature and conditions (STC). View the efficiency ratings of solar panels on the New Zealand market here.
Conversion efficiency refers to the portion of sunlight that hits the solar panels, which is then converted into electricity via the photovoltaic effect.
Highly efficient solar panels are ideal for rooftops with limited space, however, they can be expensive. With ample rooftop space, a regular solar panel/s with lower conversion efficiency could be the cost-efficient route to take.
Longevity and Warranties
Solar panels deteriorate gradually over time. For this reason, reputable solar panel manufacturers guarantee a 25-year performance warranty. Manufacturers offer a declining performance warranty rate that covers 25 years as seen in the graph below.
The performance warranty by 0.8% on average per year; by the end of the 25-year period the panels will be producing no less than 80% of the energy they were expected to produce following the first year of installation. If a solar panel/s perform below 80%, replacements are readily available.
Example 2 of the declining warranty structure: If a solar panels efficiency performs below 90% after 15 years since the date of installation (see graph below), then the owner can, and should, claim their warranty.
Although this is the typical warranty structure offered by the majority of solar panel manufacturers, please allow for variations, and always check the fine print.
What else does a solar power system warranty offer customers?
If a company offers a 25-year performance warranty then 25 years is the minimum life expectancy of the solar panels on offer.
Grid-Connected Solar Power Inverters
String Inverter
A string inverter is comprised of a box that is connected to solar panels and is usually placed on a wall in the garage, or outside the garage, with close proximity to the meter box. Cables run through to the inverter to reach the solar panels. The string inverter takes direct current (DC) transforming it into alternating current (AC). The power produced from solar panels is now ready to be used by standard household and commercial appliances.
String solar inverter specifications to consider prior to purchase:
Keep an eye out for the maximum efficiency rating (normal range lies between 94% and 98%). Enquire to see if the inverter has maximum power-point trackers (MPPTs), these help convert the maximum amount of power from solar panels.
String Inverter Warranty
String solar inverters generally have 5 to 10 year warranties with an option to extend the warranty at a cost.
Micro Inverters
Micro inverters are much smaller than string inverters. Typically, one micro-inverter is connected to the back of one panel; in this setup there is one micro-inverter for each solar panel. They perform the same function as a string inverter in that they convert DC electricity from just one panel into AC. An AC cable connects all the panels and sends the electricity through to the switchboard, where power is distributed into the home or to the grid.
Some of the benefits of installing a micro inverter solar system include;
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Each solar panel has a designated maximum power-point tracker (MPPT), this allows each panel to perform at its best without being dragged down by panels with a lower performance.
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Micro inverters usually have a warranty period of 10 to 25 years, depending on the manufacturer. Micro inverters tend to last longer because these types of inverters aren't exposed to high heat loads that are borne by string inverters.
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Expanding the size of a system is easy should the user decide to add more solar panels at a later date. A micro-inverter system allows a user to add more panels whenever they please.
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Using a web-based monitoring system allows users to check the performance of each solar panel. A panels performance can be affected from shade created by trees etc. It's a good idea to check every so often for light obstruction to a panel, to ensure maximum power generation.
Solar Mounting
Solar mounting consists of aluminium rails which are bolted to a roof allowing solar panels to be clamped onto them. The mounting is designed to ensure the solar array can withstand strong winds, and other harsh environmental elements common to New Zealand's climate.
Solar panel mounting frames are usually fixed flush to a roof with a 15-45 degree angle. Also available is titled frames that allow panels to be orientated to the ideal angle for solar gain (as advised by your solar installer).
Ground Mounting
At an extra cost, a structure for solar panels can be built on the ground - should the user decide that it's better than placing solar panels on a roof. Solar installers will give exact specifications for a ground mount frame should the customer decide to have one built. Galvanised steel readymade frames work well for ground mounting panels. In the case of ground-mounted solar panels, a trench in the ground will be required to feed the cable from the solar array to the main switchboard.
Solar Cable
Solar cable is the wiring between solar panels, inverter and the switchboard. This cable is specifically designed to be UV and weather-resistant and to allow maximum permissible DC voltage.
Let The Solar Power Companies Pick The Best Components
Solar installation companies have a range of solar power component brands/models selected that they feel are best suited for their customers. Generally, customers are not required to select the components themselves. Reputable solar power installers have components that are the right balance between quality and price. Experienced solar installers will not select sub-par components. Sub-par components are likely to fail, and infer costly replacements.
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