Does Size Really Matter?

One thing that is very important when sizing equipment for a solar system is understanding how efficient each piece of equipment is and how efficient they are in total together.

First let’s start with the Solar array, or the panels as most people call them. Solar panels at best are 20 – 22% efficient. This means that 20% of the energy from the sun that hits the panel is turned into energy. While that doesn’t sound like much, it’s a far cry from the 7% we started with back in the early days of solar panels. One thing you do need to know about panels is they don’t like the heat. Panels actually prefer it very cold; the colder it is the tighter the crystals are and the better they transfer power. So, a hot panel may lose 10% of its production. A cold panel can produce to 10% over its rated production. This is very important to understand when sizing breakers and charge controllers for your system.

Next are batteries. Batteries are tested for their output capabilities at a lab temp of 75°. Anything above or below this temperature changes their production and charging ability. A very hot battery, say sitting in the sun at 100° plus, can produce up to 110% of its rated power. However, this will diminish the quality of the battery faster than normal. And very cold batteries will reduce the production of the batteries even worse. A battery at 15° will be reduced to 90% of its capabilities, and a battery at 0° will reduce its production to 70%; and this is assuming it is 100% full. If it does not reach 100% charge, then this curve is even worse. Understanding this when sizing batteries for your system and deciding where to install the batteries is critical to the life of your batteries and the overall performance of the system.

Next let’s talk about the generator. Most generators are rated at their maximum power production. Or they may show max power or continuous power if you are working with a portable unit. Even though a generator is rated for 7,500 watts continuous power, it is not recommended that you run a unit at this level when using it to back up your house and charge your batteries. Running a unit at this level for hours on end as we do to charge batteries will reduce its life considerably. The best way to run a generator is to run it at 50 to 60% of its rated capacity and use both legs of its output power or alternate back and forth between the two legs if you are working with a 110 volt charging system. It’s also important to understand that an inverter/charger rated at 3,500 watts for instance can use much more power than that from the generator when in charge mode. When in charge mode, an inverter that is rated at 3,500 watts in inverter mode can use as much as 7,000 watts when in charge mode. This is because it can use 3,000 watts to charge the battery and then also use an additional 4,000 watts to run the house based on what is currently on in the house. This would overload a 7,500 watt generator if the house was drawing a heavy load at the same time you are charging the batteries.

To reiterate, understanding each section of your system’s components and capabilities is crucial when designing a system for longevity and proper operation of your house. If one component is too small or to large, the entire system can be compromised. Wait – how can a too large component affect a system negatively? Take a large battery system with a minimal solar panel array. This can cause two issues: 1) the batteries will not charge 100% giving the house less power than desired, and 2) the batteries will sulfate and shorten their life drastically.

If you have any questions about sizing your system or just need some help finding the proper equipment, please let us know.