The current generated by solar panels is direct current (DC) and can be used to power DC devices and batteries but must be converted to alternating current (AC) by a solar inverter. Most household devices are powered with AC from the power grid, and the power drawn from batteries or solar panels must first flow via an inverter to be changed to AC.
A solar inverter chops the direct current generated by the solar panels into lengths and inverts every alternate pulse into a square-shaped alternating current. Advanced inversion processes produce a sine-wave alternating current at a frequency of 60 Hz and 120 V commonly used in North America.
High voltage AC is the best format for power transmission over long distances from coal-fired power stations, nuclear power plants, or hydroelectric power stations via the national power grid to power users connected to the grid. Solar panels generate a DC ideal for charging batteries via charge controllers but must be converted to AC for use in most household appliances.
Inverters are commonly used to convert and smooth DC to pure sine-wave AC. The main types of inverters are:
- Grid-tied inverters
- Off-grid inverters
- Hybrid inverters
Let’s look at how and why inverters play an increasing role in blending DC to AC for transmission and back to DC for use in DC devices.
Why Do We Need Solar Inverters?
Most household appliances function with 120V 60Hz AC as this is the most commonly available format in most grid-tied houses. AC-powered devices and appliances can be run off the surplus DC generated by the solar array but require the DC to be converted to AC via a solar inverter.
Off-grid solar power systems generate DC and charge a battery bank via a charge controller. Once the battery bank is fully charged and the charge controller pinches the DC to the battery off, the surplus DC can be used to power only DC loads.
The sun’s energy packets (photons) travel to earth as wave particles. When they collide with the semiconductor crystals of the solar panel, they generate the formation of layers of positive and negative charges.
When these layers are connected via a conductor, they create an electric current that flows from an area of high potential to an area of low potential as a direct current (DC). This DC is ideal for charging a battery bank but cannot power most appliances as they require alternating current (AC).
The solar energy generated by solar panels can be used to charge batteries but need to be converted to alternating current before it can be fed into the power grid or used in AC-powered devices.
When Is A Grid-Tied Solar Inverter Needed?
Most solar systems in metro areas are grid-tied systems. Such systems do not have battery banks where the power is stored. The DC power generated by the solar array is pumped via a Grid-Tied Solar Inverter into the regional power grid during the day.
The AC fed into the AC grid power system is fed via a meter that records the net outflow and inflow of AC power from the grid to the household. The meter determines whether the household has produced more AC than it has used or vice versa.
If the household has a positive net AC power balance at the end of the month, the homeowner can earn some money from the power utility company. If the household drew more AC power from the grid than it fed in, the homeowner only has to pay for the additional power used.
Peak Power Grid Feed
The challenge that solar-generated power creates is that the most power is generated between 9 am and 3 pm during the day, but the period of highest demand is between 4 pm and 8 pm.
This mismatch between peak power generation and demand is somewhat solved by selling the surplus power to the utility company between 9 am and 3 pm at an agreed-off-peak price. Then, buying back power from the grid from 4 pm to 8 pm at peak pricing.
The power grid can only accept AC power of 120V at 60Hz, and the DC power generated by the solar panels must be inverted to AC power before it can be fed back into the power grid.
When Is An Off-Grid Solar Inverter Needed?
Off-grid solar power systems are mostly deployed on homesteads far away from the national power grid or in yachts, vans, and recreational vehicles where boondocking is commonplace.
Off-grid solar systems require a battery bank to store the power generated for use as needed. The DC from the solar panel is converted to a DC at the specified battery charge voltage. The charge controller will optimally charge the battery and protect it from overcharging and deterioration.
The surplus DC can be used to power other DC devices or converted to AC via a Solar Inverter to power AC devices such as fridges, freezers, air conditioners, and other household AC appliances.
DC can be drawn from the battery bank and converted to power AC devices via the inverter. Many AC devices require the AC to be a pure sine-wave to operate optimally.
Pure sine-wave solar inverters are expensive as they require sophisticated converters to generate pure sine-wave AC output.
What Is A Hybrid Solar Inverter?
Hybrid Inverters or Multi-Mode Inverters collect DC from the solar panels and the battery bank. Through a process of DC-coupling, it organizes the output into a single AC output current.
The hybrid inverter electronically regulates the charging and discharging of the batteries in conjunction with the surplus DC from the solar panels.
Without the use of inverters, we will not be able to use solar-generated DC to power our AC devices and appliances. AC is a better format for long-distance power transmission in a grid.
Most conventional power stations generate high voltage low amperage AC which can be transmitted via overhead transmission lines over vast distances. Most domestic and commercial appliances and electrical equipment were designed to work with AC.
The rapid growth in solar power generation and large battery storage systems has necessitated the refinements of inverter technology required to convert DC to AC.