Solar photovoltaic (PV) systems enable you to generate your own electricity using free energy from the sun. PV panels convert the sun’s rays into an electrical current through a chemical reaction within the panel and this electrical energy can then either be used directly in your house or stored in batteries for later use.
There are a large number of different types of PV systems to suit a variety of applications. Some of the more common systems are explained below.
1. Grid tied systems are connected to the main utility grid and supplement your electricity usage when the PV panels are exposed to direct sunlight. The best application of this type of systems is an environment where the bulk of your electricity usage is during daylight hours, such as an office or work environment. This system does not have a battery bank so the cost is much lower but you are still vulnerable to power failures when the sun is not shining.
Feeding power back into the grid is not yet legal in most municipal areas of South Africa as there are issues with the metering of electricity usage and safety concerns for workers working on high voltage lines. So a limiting device needs to be included in the installation to prevent grid feed in until metering and protection devices are upgraded by Eskom and municipalities. There is pressure on them to do this so we wait with bated breath. Once grid feed in is allowed, you will be able to generate electricity on your roof top during the day and feed it into the grid resulting in a negative meter reading. You then use grid power at night which registers positively on your meter. At the end of the month you only pay for power that you have used in excess of what you generated with your system.
In time, you will be able to generate more solar power than you need and be paid for the excess that you feed into the grid.
2. Grid Interactive or Hybrid PV Systems are linked to the grid but include a battery bank as a power source when the PV panels are not producing sufficient power. Grid power is only used to charge the batteries if they drop below a safe charge level.
These systems can be programmed to prioritise PV power generation as the primary power source, batteries as the second source and only if these cannot deliver enough power will grid power be brought in.
These systems are better suited to a household environment when most of your energy consumption happens at night. PV power generation during the day will be used to power daytime loads but more importantly, will be used to charge the battery bank for night time use.
This type of system offers some security benefits as you will still have power supply from the batteries during a grid power failure. It can be designed to power anything from a few key lights to your entire household.
3. Off Grid PV Systems would be used where there is no grid power available and you are entirely dependent on an alternative power source. They are essentially the same as a hybrid PV system but generally have a much larger battery bank and PV array in order to allow for a day or two of cloudy weather. A generator would normally be included to charge the battery bank in the event of extended cloudy conditions. Batteries are a costly component in these systems so a generator becomes more cost effective than a huge battery bank for the rare occasion when cloudy conditions persist for more than a day or two.
Batteries for a solar system differ from ordinary car batteries. Generally referred to as “deep cycle” batteries, they are specifically designed to deliver small amounts of power over an extended period of time. A car battery does exactly the opposite, delivering a large amount of power for a very short period of time.
There are a number of different battery technologies available, each with its own pros and cons:
Flooded Lead Acid Batteries – the cheapest batteries but with a limited lifespan and maintenance intensive. They also carry environmental risks if not disposed of safely. These will be permanently damaged if discharged beyond 50%
Gel/AGM batteries – similar in most respects to flooded lead acid but they’re maintenance free and will last longer than flooded lead acid. These are also prone to damage if discharged too far.
Lead Crystal – these have a different form of electrolyte with environmental benefits and can be discharged 100% with much less damage than the others. It will then accept a full charge thereafter. They have a significantly longer lifespan than most other battery types but cost a little more.
Lithium Ion batteries – this is the newest technology in solar power but is still prohibitively expensive. Their lifespan is double that of most others and they can be discharged fully without any permanent damage. They are much lighter weight than any lead based battery so are used extensively in the automotive and aerospace industries where weight is a major consideration. Most modern cellphones use lithium ion batteries.
There are other battery technologies but these are the most common types in the solar industry. The choice of technology will depend on the size and application of your solar system, and your budget.
Manufacturers that we like to recommend are:
Victron inverters, charge controllers, etc. Manufactured in The Netherlands, Victron is an extremely popular brand due to its rugged durability and extensive product range.
Solar Frontier PV panels. These make use of CIS technology and offer superior efficiency levels compared to poly-crystalline and mono-crystalline modules. They are manufactured in Japan.
Omnipower batteries – made in Taiwan, these are Gel/AGM batteries with a design life of 10 years but are better priced than other European, American and Canadian brands.
Deltec Lead Crystal batteries – a little more expensive but significantly better life expectancy and a number of technical advantages.
Various other brands but these are our favourites.