Just like in life, off grid systems are all about finding the right balance. Here are some of the common imbalances that we regularly see.
Batteries too small for the inverter
Using poor quality batteries that are too small is the easiest way save money in stand alone power. These are often small 12V batteries, connected in many parallel strings. It works great out of the box, but leads to all sorts of imbalances that shorten the life of the battery bank. In the worst case, it can lead to fires if the battery strings are not correctly fused.
This sleight of design can be glossed over in system marketing by emphasising a big inverter. But the truth is that if the batteries aren't big enough, they won't be able to provide enough current to get the full potential out of the inverter and may even do damage.
Inverter is too big for system voltage
This is another symptom of the previous problem. Some less reputable manufactures will inflate the claims of their inverters, so you might be lulled into thinking that you only need a 12V system to run a 3000W inverter. This is a very bad idea, it will not comply with Australian Standards and will typically come along with incorrect wire sizes and fusing for the 300A that this would require. Remember Watts / Volts = Amps.
Inverter is too large for loads
It can be tempting to get the biggest you can afford, but if your actual requirements are small then you are usually better off getting an appropriately sized inverter.
Inverters are not very efficient when they are running at a small fraction of their potential. If you get an inverter that is too large, it may end up being the biggest energy consumer in your entire system. We have seen some cheaper, oversized inverters consume as much electricity per day as a refrigerator!
The inverter size should be matched to the loads, better is more important than bigger. A well designed system will meet your needs without unnecessary waste.
Low quality batteries
Even low quality batteries can last several years. And by the time they fail, support may have disappeared.
Be careful of using batteries that are designed for cars or trucks in stand alone systems. These batteries are designed to crank out a lot of amps to start a vehicle, but perform poorly when the lights are left on.
Stand alone power systems are expensive upfront, but if they are built right they should last a very long time. It's important to think about the total cost over the lifetime of the system. This includes not just the financial cost, but also the inconvenience of an unreliable power supply and the environmental impact.
Solar array is too large for batteries
Big numbers sound better. A lot of customers are sold on how many kW their system is. But the truth is the solar array is one of the cheaper parts of the system, and the most easily upgraded.
Getting the system fundamentals right in the first place is a much better investment for something as long lasting as a stand alone power system. This means time spent on the load design, layout, as well as electronics and good quality batteries.
If you would like help balancing up all the options in solar power systems, give Rainbow Power a call on 02 6689 1430, or come in to see us at our showroom workshop at 1 Alternative Way in Nimbin.