In this article we try to answer some of the frequently asked questions . Of course there are too many to answer and if you need any questions answered, please contact us, we will gladly assist.
Starting with Solar
When converting to solar, the best place to start is to reduce your load by reducing inefficient loads to make your solar installation more affordable. Change your lighting from the old incandescent bulbs to the latest CFL or even better LCD bulbs. When replacing appliances such as fridges, check them for signs advertising energy efficiency.
Next step we recommend converting your electric geyser to a solar geyser. The reason for this is that a solar geyser payback period is 3 years vs a PV solar system which is 6 years. Converting the sun energy directly into heat for your geyser is much more efficient than first converting sun energy into electricity and then converting the electricity into heat. Once again the conversion of your geysers to solar geysers reduced your total load.
Once you have reduced the obvious loads, it is time to install a PV solar system. For residential installations there is the very popular Axpert solar inverter which is parallel capable. A typical installaion would be 3kW of PV solar panels (12 x 250 watt), 1 or 2 axpert solar inverters depending on peak loads and at least 4 solar batteries.
Grid Tie Solar Inverter vs Off Grid Solar Inverter
There are 3 categories of solar inverter. Off grid solar inverters, on grid solar inverters and then a combination of both solar inverter. The difference between off grid solar inverters on grid tie solar inverters is that an off grid solar inverter has batteries for storage and a grid tie solar inverter uses the grid to store energy. Which means that off grid inverters have battery backup and on grid inverters do not have battery backup. The off grid inverter is less than half the price of a grid tie inverter as it does not need such complicated construction to synchronize with the utility supply. When utility power is interupted, an off grid inverter will continue to supply power to the loads, but a grid tie will stop working. This is to prevent the grid tie inverter from being out of sync with the utility supply when the utility power is restored. This protection is called island protection.
There are many inverters in the market and none of them are the same. Each manufacturer of solar inverter uses their own technology. The simplest supermarket inverters are not suitable for residential or commercial application. They are cheaply built with minimal components and their outputs have a lot of distortion. The budget battery chargers are also too basic and waste up to 30% of the solar power generated. Budget solar inverters and chargers do have their uses such as applications supplying equipment that is not sensitive to quality such as motors. It is always best to buy a quality solar inverter for your home such as the Axpert solar inverters, Microcare solar inverters or advanced energy solar inverters. These inverters have quality outputs and some include include a quality MPPT charger. They also include an automatic changeover switch that transfers between solar, batteries and utility without interruption. These inverters provide backup from batteries and good value for money. The next type of inverter are the grid tie inverters that synchronize with the grid. The technology used in the inverter is more costly, but they do not require batteries. If no backup is required then this is the option to use. Finally there are the combination inverters that pack both technologies into one package. These are the solution if you want to be able export and have a backup. Of course these inverters are more costly due to all the technology included.
Inverter makes and models
There are many manufacturers of inverters in South Africa, to name a few Microcare, SMA, Victron, Advanced Energy, Fronius. Within each brand there are various models depending on the requirement for grid tie vs off grid, single phase vs three phase, MPPT vs PWM charger, integrated charger vs standalone charger etc
PWM stands for Pulse Width Modulating. MPPT stands for Maximum Power Point Tracking. PWM is a very basic charger which switches on and off, pulsing the battery with power and wasting up to 30% of the energy. MPPT is very efficient, typically 98% efficient. PWM is generally used on a single panel below 200 Watts where the cost of buying a bigger panel to offset the losses is not a problem. On anything larger, MPPT becomes the more cost effective solution.
Which batteries should I use
The important specification to look at when choosing solar batteries is the amount of cycles the battery can provide. An automative battery was not designed to be discharged and its purpose is to supply a large current over a short period to turn a big load. Then it spends all its time being charged by an alternator. You will not find a discharge cycle chart for this battery, because it cannot be used for this purpose. The best batteries for solar such as the lead crystal batteries can produce 3000 cycles at 50% depth of discharge. Which means if you cycle the battery every day, you will get almost a 10 year life span out of the battery