We have spoken much about solar panel inverters over recent weeks. Partly because of their importance, and partly because they can be complicated. Specifying a solar power system is relatively straightforward. You calculate the peak load of the property, add a percentage, then choose enough panels of the type suitable for your location.

The panels have a specific wattage, batteries have a specific capacity, and the overall system is pretty straightforward. Things aren’t so simple with a solar panel inverter though. Should it be grid-tied or not? Sine wave or modified sine wave?

Today we’re going to discuss the sine wave. It’s a term that not everyone will be familiar with, yet is important to know when choosing a solar panel inverter.

A sine wave is the alternation of electrical current that makes up AC power. Think of a pendulum, that ticks back and forth in a constant, predictable fashion. That’s how electricity flows through the grid into your home.

The electricity is fed to an alternator which ticks back and forth creating the wave. It rotates at 60Hz and as it ticks, spilling forth electricity, the sine wave is created. The more exact the wave, the more efficient the appliance that uses it.

These waves have been found to be the ideal transport mechanism for electricity. The wave travels distance very efficiently, and with minimal loss, which is why our grid uses AC power. In reality, most of our appliances actually use DC power. Each contains a small inverter to convert AC to DC internally in the appliance.

A solar power system generates DC current. The panels collect the energy and directs it through a system of channels, which is how direct current is generated. That power is fed to the batteries, which also use DC power.

The job of the inverter is to take that power from the batteries and transform it into AC which our homes can use. That’s where the complications begin. We mentioned the two types of sine wave, true and modified. A true sine wave is a much cleaner signal and is more efficient than a modified wave.

Solar panel inverters that generate true sine waves are more expensive than modified ones. If you use a modified sine wave inverter, you many notice your appliances are slightly noisier than they were before. That’s a by-product of a “dirtier” wave. It just means the wave isn’t quite as exact as a true one, so makes more electrical noise, which is transmitted through the appliance.

Anyone with computers, servers, sound recording equipment and other sensitive electrical devices will need to use a true sine wave solar panel inverter. The modified sine wave inverter isn’t clean enough to reliably power these kinds of devices. It has been known for them to damage sensitive gear.

For the rest of the household appliances, a modified sine wave inverter is fine. The devices will be slightly louder, and slightly less efficient, but not as much as you would notice.

Choosing a solar panel inverter is about getting the right device for the application. Not everyone is going to need to spend the extra money on a true sine wave inverter, but those with the devices mentioned above should. It’s possible to use both kinds in a system, as long as the feeds from each go to the right places.

We covered inverters in a previous post, but I’ll run over it quickly first, so this post can stand on its own.

Solar panel inverters are necessary to change stored current from the solar panels from Direct Current (DC) to Alternating Current (AC). This is necessary because the solar power system generates DC current, and our appliances need AC.

Our appliances don’t actually use AC current, they convert it back again to DC internally. The nature of current PV technology means the way electricity is channeled in a solar cell, comes out as DC.

While this is the most efficient way of powering electrical items, it isn’t the most efficient way to transport electricity. The nature of DC current means it can lose up to 25 percent of the electricity in transit, which is why we use AC.

The AC sine wave is much more efficient at traveling long distances, which it would over the grid. A solar panel inverter sits between the batteries of a solar panel array and the grid or mains. It’s job is to control power flow back and forth into the system, and change DC power into AC, ready for use.

In a traditional setup, there is a single inverter to control the entire system. This is an efficient way of doing it, but presents a single point of failure for the system. A solar power array is a fairly low-maintenance piece of kit, but if any trouble occurs, it’s almost always the inverter at fault.

A micro inverter is a smaller version that sits behind each solar panel. Each panel has its own micro inverter pumping AC current directly into the batteries, or straight to the house. While there is more equipment involved, it’s a much more efficient way of working.

We mentioned that DC is far from lossless, and can lose quite a bit of current in transit. We know AC can travel further while losing less, so it makes sense to have AC moving around the system. That way we get to use more of the power we generate. So by using micro inverters instead of standard solar panel inverters, we save a potential 25 percent of the energy we generate.

Add to that the physical benefits and you have quite a compelling case. Micro inverters are of course smaller, and they cost less individually than a standard inverter. If one fails, it’s cheaper to repair or replace. It also doesn’t bring the whole system down, just the panel it’s connected to. So in the event of hardware failure, you’re still generating power.

Micro inverters also add scalability to a solar energy project. If you find you need more power at a later date, it’s simply a matter of bolting on another solar panel and micro inverter and connecting them up. It’s a much simpler exercise than the traditional setup.

Both solar panel inverters and their micro cousins have distinct advantages. However, in the pursuit of efficiency and convenience, micro inverters win every time.

Solar panel inverters are devices that transform direct current (DC) produced by a solar panel array into alternative current (AC) which powers our homes. Most solar power systems, and other renewable energy sources provide DC power, which isn’t much good in that form. Inverters are the necessary last link in the chain to turn that power into usable energy.

There are three types of solar panel inverters, Standalone, Grid-tie and Battery backup. Each differs slightly in operation and adds something to a solar power system.

Standalone inverters stand between the solar array and the mains. It draws DC power from the solar system, then converts it into AC. It can draw that power directly from the batteries, and also charge those batteries from mains power if necessary.

These systems vary in size and capability, from 100 watts to 8000 watts. Each will lend itself to different projects and will need to be specified in accordance with the system. This can be calculated by determining the maximum wattage required at any one time by measuring each appliances wattage requirements.

It’s also important to have surge-protection on an inverter. This protects other appliances and the solar power system from power surges from appliances.

Grid-tie inverters are also referred to as synchronous inverters, and are used when the solar power system is connected to the grid to enable the sale of excess power. They also have a safety cut-off in case mains power is shut off for any reason. These types of inverter cannot provide backup power during these outages.

The grid-tie inverter balances the power requirements of the system. If you use less power than anticipated, it feeds it into the grid and makes you money. If you need more than you produce, it allows the grid to supply you. While more expensive than a standalone inverter, it offers much more flexibility.

Battery backup inverters do exactly what their name suggests. They manage the batteries connected to the solar array. They draw from, control, and charge the batteries as required.

Some solar panel inverters convert a direct current to an alternating current through a delicate electrical switching process. This process makes an inverter function as a synthesized alternator. These are typically used to produce AC current by creating a smooth alternation, like a pendulum.

This alternation takes the form of a sine wave, which is the ideal wave pattern for transmitting AC power. Sine waves are also used by power companies, which is why the two can meet through an inverter.

There is no “best” type of solar power inverter to buy for any type of solar power system. Each has its own advantages and capabilities, and offers something to each type of installation.

When buying solar power inverters, you will need to know peak power demands and the intended use of the system. If you’re planning to sell excess power to the grid then a grid-tie will be your best bet. If the system is merely to power outside lights or a water pump then a standalone would be ideal.