Written by Nani Pradeepan, P.Eng.

 

Depending on the type of property and where it is located a specific type of solar electric system that best suits for the needs. Depending on where a property is located – in the heart of a city, in the suburbs or in the woods an appropriate type of solar electric system installation must be implemented.

Location is the key characteristic as grid availability and distance from the grid will be determinant in choosing the type of system best for a given property.

There are basically three types of Solar Electric Systems:

Grid Tied Solar Systems, Grid Tied Solar System with a Battery Back-up or Hybrid Power Generator, and the Off-Grid Solar Power System.

Grid Tie Solar System:

This is a very common type of installation for cities and suburbs with close proximity to the electric grid. In this system, the PV installation is connected to the grid and two meters or one two-way meter may be installed to measure the flow of electricity to and from the grid.

In Ontario residents participates in Micro FIT program need to have two meters to measure the flow of electricity and the Ontarians participates in Net metering program need to have one two-way meter to measure the flow of electricity.

The advantage with Grid Tied Solar System is that the PV installation need not necessarily be seized to meet all the needs of a property. If demand surpasses supply at any one time especially in peak hours, electricity is simply pulled from the grid to make up. This situation is reversed when the capacity of the installed Grid Tied Solar System is high enough and produces more than needed electricity. The extra electric power is pushed or back-fed into the grid which produces credits the consumer can then use at periods of low production such as at night to offset their power consumption.

Grid Tie Solar System with Back-up or Hybrid Power system:

Grid Tie Solar System with Back-up system differs from the above described in that it has a battery or power generator to provide power during grid outage. Grid Tie Solar System with Back-up best suits areas without a reliable power grid. Our solar engineer design the system to store some of the electricity produced when production exceeds demand for use when the grid goes down. This type of system can also incorporate an electric generator for the same function.

Off-Grid Solar Power System:

Off-Grid Solar Power System is for locations without traditional electric grid. It best suits for properties located in the woods, mountains or remote areas of the developing world with no electric grid.

Off-Grid Solar Power System also incorporates the battery and the power generator in its design. Instead of using a battery or generator as a back-up as in the previously described system, it is used as a necessary component.

The battery is used to save electricity produced during the day time to use in nights and during rainy/cloudy days. A generator is provided in this case when the battery drains out due to continuous use and in days with no low power production from solar.

Use of these systems depends on location and it is important to note that in each design, convenience and efficiency will vary significantly depending on the use and location.

Now you know more about solar electric system types–which of these would best suite your needs depending on your location? We can help you pick the best solution for your need and location; do not hesitate to contact us with any questions you may have.

Written by Nani Pradeepan, P.Eng.

Inverter

We know that solar panels produce direct current (DC) electricity and our utility grid is powered by alternating current electricity (AC). Inverter used in solar power system converts solar DC electricity to AC electricity we all use at homes and other buildings.

As solar panels are rated at standard test conditions and not all installation locations and situations come close to these test conditions. Hence it often makes sense to oversize a solar array relative to inverter rating. This enable for greater AC electricity harvest when production is below the inverter’s rating, which is typically for most of the day and also can results in clipping.

Inverter clipping

Every inverter has a maximum rated power and it will generally never output more than their max-rated AC power. This is very important as the component ratings of the power electronics in the inverter are designed with a specific power and voltage range and the grid connection points in the buildings are designed with a specific max power limits.

When the DC solar array is generating the most amount of energy that is greater than the inverter’s power rating, the “extra” power generated by the array is “clipped” by the inverter to ensure it is operating within its capabilities. This leads to a flat line in the green curve in the figure below, and capping the power at the inverter’s nameplate power rating during peak production hours and known as inverter clipping.

The purple line in the figure shows a typical bell curve of AC output power peaking at noon, just below the rating of the inverter indicated by the dashed line. If we increase the size of the solar array by adding more panels, which increase the DC-to-AC ratio of the system (as illustrated by the green curve), we can harvest more energy throughout the day. The area between the green and purple curves is the energy that is gained by increasing the DC-to-AC ratio.

Standard test condition temperature is 25ºC but solar panels are hotter than 25ºC when the array is receiving maximum sunlight. Higher than rated temperature of 25ºC results in loss of power production when solar panel receive maximum sunlight. In other words the solar array produces less than the rated power when solar array receive maximum sunlight, this reduce the losses due to clipping of inverter.

Written by Nani Pradeepan, P.Eng.

As the cost of a solar installation come down people are looking for choices for their solar systems. One of the choices people look for is a solar PV system with minimal deviation to the appearance of their house.

Solar roof shingles are one way to turn a traditional shingle roof into an energy producer. Solar roof shingles are a new green roofing product of the past few years. Solar shingles like traditional solar panels use the sun light to create electricity. Each of the solar shingles is comprised of photovoltaic cells and each shingle is a small PV module that has to be connected electrically in series to reach the DC voltage needed by the inverter which converts the DC electricity to commonly used AC electricity.

The typical DC input voltage for inverters is 350 to 500 VDC. That means many shingles need to be wired in series. This requires long strings of module to module connections wires that are all hidden beneath the finished roof and difficult to access.

When one module or its connection fails, all the modules in the string go out just like in Christmas tree lights. A service tech has no easy way of knowing which shingle is defective. A big portion of the roof often needs to be taken apart, and all components tested. Then, if matching replacement solar shingles are available, the array may be able to be reassembled.

PV shingles have been nailed or screwed into place as the PV shingles marketers wanted to entice roofers to be installers. However, roofers do not have the understanding or the necessary training to install solar-electric systems. If there is an electrical arc caused by a faulty shingle-to-shingle connection, it could start a fire in combustible tarpaper and wood roof sheathing.

Solar shingles are less efficient than traditional solar panels meaning need more roof surface than the traditional solar panels. Rated output of solar shingles is about 12 watts per square foot; whereas today’s best crystalline modules offer about 20 watts per square foot. Since solar shingles are installed on the roof deck there is no back-surface convective airflow, the all-black solar shingles run hotter than conventional solar panels, meaning further lower efficiency and possibly shorter product life.

PV shingles have been a transitory product. How long will companies selling this product keep producing them? For example, after five years, Dow ceased manufacturing and distributing solar shingles. There is no long-term experience with solar shingles products and they may or may not last. Will the warranty be supported over twenty five years as with traditional solar panels?

Even if the company and product is still available, will it be in the same form and electrical configuration to allow replacement? With all these uncertainties at present solar shingles are not prudent options for a green roof.

Currently, there’s no mass produced solar PV shingle solution for retrofit. If your house has a black roof, using conventional black-on-black modules installed flush with the roof may offer the best acceptable solution. Standard framed PV modules have been proven, reliable and productive, and we know how to install them well for the long term. For many people, the solution is to accept the beauty of a product that will produce clean electricity reliably for 40+ years.