What Is The Grid-Tied Solar System? How Does Grid-Tie Work?

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What is a grid-tied solar power system and how does it work?

It’s no secret the world is turning green.

People are gravitating toward renewable energy sources, such as solar panels, which are part of the green revolution.  This is because green energy is environmentally friendly, saves money and becoming relatively cheap.

Other than that, installing a grid-tied solar system will increase your property value while eliminating some or all of your utility bills.

The most common renewable energy option for the homeowner is the grid-tied solar power system.

The grid-tied solar system is a type of solar system permanently connected to the electrical power grid. Grid-tie does not require batteries, as in the case of off-grid solar systems. Grid-tie solar systems allow the home to use solar energy when available, or to channel excess power back into the grid.

Video – How grid-tie Solar Systems Work

 

How does grid tied solar work?

Before delving into the working mechanism of grid tie, it is essential to mention that the system is linked to an electrical grid and cannot function in its absence. Thus, for the system to work, the grid should be working as well.

The grid-tie solar system is composed basically of an energy (net) meter, one or multiple inverters, and solar panels.

Solar panels, usually installed on a rooftop or open space, convert rays from the sun into direct current electricity through the photovoltaic process. For the conversion of produced electricity into alternating current, the grid-tied system needs an inverter.

The inverter is an instrumental part of the whole system as it changes DC electricity from the panels into the power grid frequency, which is either 50 or 60Hz, depending on the continent.

DC electricity from solar panels goes into the inverter that is in turn connected to the distribution board.

This is quite different from the off-grid system, where DC electricity is stored in batteries directly, before being fed to the inverter. In this case, electricity gets fed straight into the grid.

Components of a grid-tie solar system

Diagram – The basic components of a grid-tied solar power system

Connection diagram for grid-tied solar system

The basic elements of a grid-tied solar power system (grid connected.)

What does a solar inverter do?

Solar panels generate direct current or DC. Direct current is not ideal for home use as it is susceptible to power loss and attracts high maintenance costs. Of course, modern appliances use only AC, so conversion is required.

However, solar panels are not able to convert the DC to AC on their own. This is where the solar inverter comes in.

Older solar systems had just one central inverter and later converted to the more efficient string-inverter.

A string-inverter converts the voltage from several solar panels connected in a single array, and there may be several of these in a large installation.

A big problem with central and to some extent string inverters, are shading losses. When one or more panels are shaded, the output of the rest of the system is severely reduced.

Micro-inverter protection against shading losses

This problem is largely overcome by the installation of micro-inverters. Micro-inverters convert DC to AC at the panel level and are connected to the back of individual panels. Some micro-inverters can accommodate several panels.

Solar Panels

Solar panels feature photovoltaic (PV) cells that are silicon-based. The PV cells are capable of converting irradiance from the sun into DC electricity.

Cells within the panel interconnect to one another through tiny cables. For efficiency, solar panels are connected together to create a solar array known as a string. A system may have several strings.

The potential amount of electricity every array can produce is subject to losses linked to shading, tilt angle, orientation, and the efficiency of individual panels.

Infographic: 10 Solar PV System Losses

Energy losses for UK home grid-tie solar power system

Infographic with percentage losses for home grid-tied solar system

A good quality solar panel will produce electricity when it is sunny and also be productive during overcast or cloudy weather. This will depend on the height or thickness of clouds.

Another crucial attribute that impacts the power output of a solar panel is the sun’s irradiance. Irradiance is the amount of light energy falling on the panel mesured in kWh/m2/day or year, also known as Peak Sun Hours(PSH).

Solar panels use the sun’s irradiance to produce electricity and not its heat.

How does net-metering work in a grid-tied solar system?

To enjoy net metering services courtesy of the grid-tied solar system, you need a power meter. It also goes by the name net meter or the two-way meter, owing to its ability to account for power going in both directions.

Solar panels generate DC power

All solar panels operate under the photovoltaic principle producing DC current

What is the difference between a grid-tied and off-grid solar system?

The grid-tied system refers to a system that is connected to the local utility grid. The utility grid acts as as a huge energy reservoir, which saves buying costly batteries to back up excess solar energy production.

If the solar panel produces excess energy, the extra power is fed to the grid of your power company.

The excess solar energy allows you to build credit against future electricity use. Net metering is the name used to the equipment that controls this process.

On grid solar is connected to power grid

Batteries are essential for an off grid system – grid-tie is connected to the power grid

An off-grid solar system operates independently of the utility company or grid power system. It is an autonomous option that gives you total control over your energy consumption and production.

The system is perfect for use in remote areas with no access to the utility grid, or for people who don’t want to depend on external power.

The biggest drawback of off-grid is that you must by backup batteries. Apart from being environmentally unfriendly, batteries are bulky and expensive.

How many solar batteries are needed to power a house?

You will need 10 LiFeP04 3.8kWh batteries to run a home with daily energy consumption of 30kWh (the U.S. daily average.) The number of solar batteries necessary to power a house depends on several factors:

            • round-trip efficiency
            • depth of discharge (DoD)
            • power rating
            • household energy used

Table – Calculate batteries needed for 30kWh/day home

Backup For 24 Hours

Rating

Measurement Units

Total load for 24 hours backup

30000 

Watt-hours (Wh)

Battery bank voltage

48

volts

Total amp-hour rating

30000/48=625

amp-hours (Ah)

Required Batteries (60% DOD) Lead-Acid

583/0.6 = 1041

Ah

Number of lead-acid batteries @250Ah each

4

Required Batteries (80% DOD) Lithium Iron Phosphate

583/0.8 = 729

Ah

Number of Lithium batteries batteries @250Ah each

3


What is round trip efficiency of battery?

It indicates the amount of energy a battery can supply as a percentage the amount it was charged with. You will lose less energy for a battery-operated with high round-trip efficiency. A typical value is about 80% for lead-acid batteries.

What is battery depth of discharge?

It shows the amount of power that can be drawn from the battery without causing damage.

For solar energy storage, two basic types of battery are used:

          1. Deep-cycle lead-acid batteries
          2. Lithium iron phosphate batteries (LiFeP04)

Deep-cycle lead-acid batteries can be discharged up to 80% but 50% is normally advised to preserve the longest life.

LioFeP04 batteries can be discharge up to 95%, so this DoD represents a greater value for money.

What happens when solar batteries are full?

Most solar-focused batteries take less than a day to get to a full charge. When the battery is 100% charged, it ceases taking current from the solar system.

A lot of folks tend to worry about safety in the event of such an occurrence. That used to be a concern with the traditional lead-acid batteries, which produce hydrogen gas when overcharged.

Hydrogen gas is highly flammable, and a battery operated in this state could explode if not correctly installed.

Modern-day batteries incorporating lithium, are very safe. They do not emit any hydrogen gas, plus they get equipped with an in-built battery management system (BMS) to control charge and discharge values.

Which is better, on-grid or off-grid?

Being on-grid comes with some benefits compared off-grid. To begin with, you can save a lot on your utility bills with the net metering option.

Net metering allows you to save up excess solar energy and sell it back to your utility company without the need to invest in costly backup batteries.

The utility grid acts as a virtual battery, a battery which is maintained and operated by someone else.

The off-grid solar system stores chemical energy in batteries, which attracts severe losses. When batteries are fully charged they stop taking power from solar, so solar generation is wasted if not being used in the home.

Excess solar energy from an on-grid solar system gets utilized in the utility company grid, so the homeowner is always credited for solar production over and above his needs.

Grid-tie is a more environmentally friendly option, as batteries are a potential environmental pollutant. They are also represent a heavy capital outlay for the homeowner.

Which solar power system is more expensive, off-grid or on-grid?

The off-grid solar system is much more expensive than the on-grid alternative as it demands costly backup batteries.

You will also need to spend more on installation and maintenance. For the on-grid solar system, the utility company running the grid will do the entire power backup on your behalf.

What is the difference between off-grid and hybrid solar systems?

While the system can operate independently of the utility grid, the hybrid solar system blends both the off-grid and on-grid solar stems.

It has batteries to backup any excess power and the ability to feed electricity to the utility grid. In terms of financial feasibility, it is cheaper.

Diagram – Hybrid Solar system, combination of off-grid and grid-tie solar systems

Off grid and grid tie hybrid schematic

A hybrid solar system is permanently connected to the power grid but also uses bartteries

Solar energy should be about saving money and living greener. A model solar system should be efficient and finically feasible. While the off-grid solar system seems to allow for flexibility and self-sustainability, it is way more expensive.

On top of that, it is not reliable on cloudy days or at night. The ultimate solution is to go for the grid-tied solar system.

You will not have to purchase backup batteries or struggle with financially straining maintenance costs. It is the go-to solar system if you are after predictability and security.

Grid-tied solar panel sizing calculator

Use the calcualtor below to calculate how many solar panels you might need for your home:

          1. Enter you home’s average daily energy usage from your utility bill
          2. Use the site GlobalSolarAtlas to find your location irradiance
          3. Enter the size of solar panel you intend to use (300 watts entered as 0.3)

Posts relating to home solar systems:

Off grid and grid-tie compared

Solar Energy Storage

What is an inverter and how does it work?

Solar panels FAQ


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