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Solar Irradiation

A quick solar electricity primer

Solar electricity is electricity that is created by converting the energy in sunlight to electrical energy. There are a few ways of doing this, but the most common method uses photovoltaic (PV) panels.

In this guide we will give a very brief overview of:

  • Standard solar electricity equipment
  • Installation types that can be implemented

There is a huge amount of in-depth information on solar power all over the web - this guide is intended to give a very high level overview of the solutions currently available.

 

Standard Equipment

In general, solar power systems can be grid-tie, off-grid or a hybrid thereof. We will cover each instance a little later. A typical solar system will consist of all or some of the following, depending on use case:

  • Solar panels
  • Charge Controller or regulator
  • Solar inverter
  • Batteries
  • Various connectors, cables and accessories

Photovoltaic (PV) Panels

PV panels consist of a number of silicon photovoltaic cells in the form of two separate wafers, one charged negatively and one charged positvely. When exposed to the suns rays the wafers exchange electrons and these electrons are intercepted to form a DC current when connected to a circuit. The number and size of panels used will depend on your clients requirement.


Some of our Solarworld panels

Panel Cabling

The current leaving the panel (typically via a junction box on the back of the panel) is DC and therefore the cabling used to channel this current is critcal. If it‘s too thin, too much of the current will convert to heat causing poor efficiencies and perhaps even burning the cable. Too thick and you are introducing unnecessary cost to the system and your quote may not be competitive. A cable size calculator is included in our spec system and the size will be dependent on the cable run length, current through the cable and voltage of your system.


4.0mm Solar cable

Charge Controllers

Charge controllers or regulators are only used in systems where batteries form part of the solution. The charge controller regulates the amount of current flowing into the batteries and prevent the batteries from being over charged.

A regulator can also allow you to connect the panels direclty to the electrical load, bypassing the batteries where appropriate.


Charge Controller

Solar Inverters

As you will know, an inverter converts DC current to AC current and adjusts the voltage to a domestically usable level (220-240V in many countries).

A good quality inverter is absolutely critical to the success of any solar installation. In most applications the inverter will need to produce a pure sine wave output as opposed to a modified sine wave output which is often produced by cheaper inverters. Modified sine wave outputs are no good for any equipment with any sort of inductive load (motor) and should generally be avoided.

It is also important that the inverter be able to handle the maximum current that your system can produce and to also safely shut things down should the load current be exceeded.


SMA 5KVA Inverter

Batteries

Often, there is no requirement to use the power generated by the system at that exact moment and that power then needs to be stored in batteries so that it can be used when required, typically during periods when the system is unable to function (night-time!)

The correct battery to use in a solar power system is a DEEP CYCLE battery. A Deep Cycle battery is designed to be discharged to a much lower level than a regular battery (say a car battery) and can be discharged and re-charged many more time before it fails. Another difference is that while a car battery is designed to deliver short bursts of very high current, a Deep Cycle battery will generally deliver a lower but more continous draw, much more suitable for on-going applications like running lights, etc..


Victron Battery

 

Installation Types

There are three main categories of solar power installation:

  • Grid-tie
  • Off-grid (or stand alone)
  • Hybrid

Grid-tie System

A solar grid-tie system generates electricity from the sun and feeds this directly onto the exisiting electricity mains. This has the effect of slowing, stopping or even reversing the electricity meter.

It differs from a traditional off-grid system in that it does not store any excess electricity by way of batteries, but instead diverts unused power back onto the electricity grid via the electrcity meter - effectively reversing the meter!. This allows for far greater efficiencies and less cost since every Watt produced is either used or "sold" back to the electricity provider automatically.

Off-grid System

An off-grid system is designed to operate independently of the electrical grid and therefore requires batteries to store the solar generated electricity for use at night or during prolonged cloudy periods.

Off-grid systems are deployed in areas where grid electricity is not available such as farms and remote rural areas.

Hybrid System

A hybrid system is just a system that combines elements of a gridtie system (i.e. it feeds electricity onto the grid) and a stand alone system (i.e there is a battery storage component).

Quick Fact:
Sunlight vs temperature

Click to enlarge

The sun‘s light is what is used to produce electricity NOT the heat of the sun. You get more electricity in summer simply because their are more usable sunlight hours. In fact, solar systems actually operate more efficiently on a per hour basis in winter, when the panels can operate in cooler temperature conditions.

Quick fact:
Panel positioning

Azimuth

Positioning of the panels in relation to the sun is very important. Panels should face as close to North (in the Southern hemisphere) as possible and be free from shade for the entire day. The optimum elevation for the panels will vary from season to season, but a good rule of thumb is to pitch them at an angle equal to the latitude at the installation location.

Quick fact:
MPPT

An MPPT (Maximum Power Point tracking) charge contoller is a more sophisticated controller that is able to optimise the power being produced by the panels to most efficiently charge the batteries. This need arises because of the tendency of solart panels to vary their power output under different temperature conditions. A good MPPT can increase power gains from the sytsem in winter by up to 40%!

Quick fact:
Battery Usage

Unfortunately, batteries wear out over time. Deep Cycle batteries are generally rated by how many times they can be completely discharged. The less depth it is discharged to the longer it will last. For instance, if a battery is regularly discharged to 50% of it‘s theoretical capacity, it will last twice as long than in the case where it were regulalry discharged to 80% of capacity

Typical Off-grid Setup

Typical Grid Tied Setup