Grid Connected-Smart Solar Home System

Smart home is an effective way of energy management. Houses with solar generated power system is an solar power plant application concept in a small and simple scale. Its application has been applied to many houses and commercial buildings.  Usually smart homes using its own solar panels is applied in regions that is not connected to PLN’s grid, but nowadays its application has been applied to many houses in PLN’s grid because it gives so many advantages for its users. In addition, using solar generated power reduces carbon footprint for each houses.

There are two types of houses that use solar generated power, houses that still connected to PLN’s grid and houses that is independent which all its electronics appliances is powered by solar panel. The proposed system, is specifically for houses that is still connected to PLN’s grid.

While renewable energy systems are capable of powering houses and small businesses without any connection to the electricity grid, many people prefer the advantages that grid-connection offers.

A grid-connected system allows the user to power the user’s home or small business with renewable energy during those periods (daily as well as seasonally) when the sun is shining. Any excess electricity the user produce is fed back into the grid. When renewable resources are unavailable, electricity from the grid supplies the user needs, eliminating the expense of electricity storage devices like batteries.

In addition, power providers (i.e., electric utilities) in most states allow net metering, an arrangement where the excess electricity generated by grid-connected renewable energy systems "turns back" the user electricity meter as it is fed back into the grid. If the user use more electricity than the user system feeds into the grid during a given month, the user pay the user power provider only for the difference between what the user used and what the user produced.

Along research within smart grids, the current power network involves the implementation of distributed generation sources. Roof top homes have become more popular for PV solar systems. These PV systems are further connected to the local grid using many inverters and can produce many harmful impacts such as harmonics in the national grid. There is remarkable power loss due to conversion from dc solar PV to ac power at traditional grid and then back to dc for our digital devices and dc loads. Preferable source of power for most of appliances is dc due to the increasing research in electronics.

Inefficient rectifiers and power supplies are used, which add harmful impact on over all powerystem. Many devices like LED lights, Televisions, mobile chargers, personal computers, audio systems use dc supply.

A smart control priority is also defined for the system which provides extra benefit during peak hours and maximum utilization of solar PV at day time and smart battery storage during night with prediction of weather conditions and load forecasting.

Another view point is discussed in this paper, user accessibility to control load and operation of grid. With the integration of solar PV, end users are participating in the operation of that system. It is significant to give then a little bit ability to control their usage and have some influence over the grid as well.

Figure 1. Solar power system network between houses and PLN’s grid.

The network configuration needs:

1.      Photovoltaic modules

2.      Photovoltaic module connector

3.      DC cable

4.      DC switch

5.      Grid tie inverter

6.      AC cable

7.      Two ways POWER meter

Solar panels are active solar devices that convert sunlight into electricity. They come in a variety of rectangular shapes and are usually installed in combination to produce electricity.

Figure 2. Types of solar panel

Solar Cell is a Semiconductor device that converts sunlight into direct current (DC) electricity. Which is module is PV modules consist of PV cell circuits sealed in an environmentally protective laminate and are the fundamental building block of PV systems. Solar Panel includes one or more PV modules assembled as a pre-wired, field-installable unit. And an array is a PV array is the complete power-generating unit, consisting of any number of PV modules and panels. The primary component of a solar panel is the solar cells, or photovoltaic cell. This is the key component that converts sunlight into electricity.

At the present time about 80% of all solar panels are made from crystalline silicon (i.e., monocrystalline, polycrystalline, amorphous silicon, or hybrids) solar cells. Typically the solar cells are laid out in a grid pattern – with perhaps as many as 72 different solar cells.

The other 20% consist primarily of solar cells made mostly from Cadmium Telluride and a small but growing amount from CIGS. The appeal of these types of cells is their low cost resulting from the fact they can be made in large single sheets.

Array solar panels is the most efficient type of solar panel because it can generate more electricity, but the drawback is the cost of array solar panels is high. Looking forward to 2030, there will be more efficient solar panel with less cost. So the prediction is 10 years from now, solar panel cost will decrease and the efficiency will increase. 

The power that is generated by the array of solar panels flows to the inverters. Inverters take DC power and invert it to AC power so it can be fed into the electric utility company grid. The grid tie inverter (GTI) must synchronize its frequency with the grid (e.g. 50 or 60 Hz) using a local oscillator and limit the voltage to no higher than the grid voltage. A high-quality modern GTI has a fixed unity power factor, which means its output voltage and current are perfectly lined up, and its phase angle is within 1 degree of the AC power grid. The inverter has an on-board computer which senses the current AC grid waveform, and output a voltage to correspond with the grid. However, supplying reactive power to the grid might be necessary to keep the voltage in the local grid inside allowed limitations. Otherwise, in a grid segment with considerable power from renewable sources, voltage levels might rise too much at times of high production, i.e. around noon.

Grid-tie inverters are also designed to quickly disconnect from the grid if the utility grid goes down. That ensures that in the event of a blackout, the grid tie inverter will shut down to prevent the energy it transfers from harming any line workers who are sent to fix the power grid. The important thing is, in each smart homes that is connected to PLN’s grid when there’s an electrical power shuts down,  then the system must be turned off too in the same time the PV generates electricity, this is called anti islanding.  The function of anti islanding for safety precaution for the workers that are working to fix the power network during power shut down or disturbance.

Properly configured, a grid tie inverter enables a home owner to use an alternative power generation system like solar without extensive rewiring and without batteries. If the alternative power being produced is insufficient, the deficit will be sourced from the electricity grid.

When a grid-tie solar electric system generates more power than the user are using in the user home, the excess electricity is sent out into the utility grid/ PLN grid. The excess power going into the grid spins the user meter backwards, allowing the user neighbors to use clean, quiet solar power. If the user use more power than the user system is producing, the user inverter will automatically pull the needed power from the utility grid / PLN grid – and the user will never notice a thing.

This is back and forth process is called “net metering”, and it means the user are only billed for the “net” electricity purchased over the entire billing period. At the end of each billing cycle the user meter will not have spun as far forward when compared to not having solar electricity, saving the user money.  If the user produce more than the user use during a billing period, the user utility company will retain it as a credit, which will then be applied to future electric bills. Net metering provides the greatest benefit to the user as a consumer. Under this arrangement, a single, bi-directional meter is used to record both electricity the user draw from the grid and the excess electricity the user system feeds back into the grid. The meter spins forward as the user draw electricity, and it spins backward as the excess is fed into the grid. If, at the end of the month, the user have used more electricity than the user’s system has produced, the user pay retail price for that extra electricity. If the user produced more than the user used, the power provider generally pays the user for the extra electricity at its avoided cost. The real benefit of net metering is that the power provider essentially pays the user retail price for the electricity the user feed back into the grid.

Synchronization between the grid tie inverter voltage and voltage from PLN is to connect PV voltage and grid voltage in parallel, so the characteristics of both voltage must have the same frequency, amplitude, and phase. The method to synchronize both voltage is Zerro Crossing Detection, Power Network Filter, and Phase Locked Loop.  

The output of smart grid houses that is powered by solar panel can be seen from the inverter that converts DC electricity to AC, that is connected with electricity installation system at the house because the inverter’s output has been synchronized with the power from the main source / PLN. Other than that, the above system needs two ways power meter to replace the conventional power meter. Because the two ways power meter is capable to read electricity power from two ways (house and PLN / net metering).

This system allows the electricity that is generated by the PV to charge the battery for backup energy, to power the AC load without having to double the install at the system by just importing power from PLN (since PLN’s power is AC), furthermore it is able to export more power to the utilities or PLN.

Figure 3. City scheme in 2030.

 Actually there are so many ways to harvest renewable power, such as using wind and hydro. But for houses application and the condition of Indonesia’s average weather, its inefficient to apply hydro and wind turbine for houses, its most suitable for larger power plants.

In Indonesia the cities or urban regions, rarely experience heavy wind. That’s why its most efficient to place wind turbines in plateau or shores. To generate power from hydro, needs large space to build a dam to contain large amount of water. Because in hydro power plant, the higher the speed of the water spinning its turbine, the more power will be generated.

This grid connected system does not limit to only photovoltaic, but also other renewable power plants. But the power plants are directly connected to the utility grid. Hopefully in 2030, we have fully changed our non renewable sources power plants to a much greener and renewable sources power plants.

Communicating the grid and house owners using the future technology named as ‘Internet of Things’. The Internet of Things (IoT) is a system of interrelated computing devices, mechanical and digital machines, objects, animals or people that are provided with unique identifiers and the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction. In 2018, IoT has been implemented in many devices but there hasn’t been any IoT regarding Indonesia’s electrical grid. 10 years from now, every device or appliances will be connected to the internet. To support the internet of things, the system needs higher and more improved telecommunication technology to meet the demands of high data transfers. Starting from fifth generation technology (5G), and other generations to come in the future.

The power meter is able to read both power that is delivered to the home by PLN and the power generated by the PV, both of this data is connected to a communication module that is virtualized LAN (IoT).

Before the data is transmitted, the data will go through encryption process for security reason. It is important to encrypt the data, especially PLN’s data. To avoid other unauthorized parties that will mishandle PLN’s data. Therefore, the user will also not be able to see PLN’s data, other than the amount of power distributed from PLN to the user. After the data is stored to the cloud through the internet, the user can monitor the data using control application.

The control application is Mobile User Interface based. Mobile UI considers constraints and contexts, screen, input and mobility as outlines for design. The user is often the focus of interaction with their device, and the interface entails components of both hardware and software. User input allows for the users to manipulate a system, and device's output allows the system to indicate the effects of the users' manipulation. Mobile UI design constraints include limited attention and form factors, such as a mobile device's screen size for a user's hand. Mobile UI contexts signal cues from user activity, such as location and scheduling that can be shown from user interactions within a mobile application. Overall, mobile UI design's goal is primarily for an understandable, user-friendly interface.

Mobile UIs, or front-ends, rely on mobile back-ends to support access to enterprise systems. The mobile back-end facilitates data routing, security, authentication, authorization, working off-line, and service orchestration. This functionality is supported by a mix of middleware components including mobile app servers, Mobile Backend as a service (MBaaS), and SOA infrastructure.

In this case, the control application front end will be Mobile UI that is android based. The whole house self generating power system is made as one package with its control application, that will be available to be downloaded via playstore. Each user will be given a unique code based on the metering hardware, that will be inputted as an activation code. The user will be asked to change the password every single month to avoid hackers.

The back-end’s part of the application, will be the hardware from the system. Its power meter is installed with a communication module, the communication module is connected to VLAN. Its important to have stable internet connection for the module to transmit real time data.

This control application is not only to see data power, but each user can take real time actions as well.  The features of the application are;

1.      The users can monitor how much power generated by the PV. The control application has the ability to analysis whether the power that is generated is larger than the power needed to supply the home.  Using the application, the user can open / close the switch between backup battery at the home and PLN grid.

2.      See how much power that is generated by PV and fed back to the PLN grid.

3.      Monitor power usage. Power usage data is taken from net metering. Since the house is not using the conventional one way power meter, the two ways data power can be seen by exporting the data from net meter to the cloud.

4.      Shuts down the entire user home electricity. This shut down feature is very important due to anti islanding. The application will warn the user if the utility grid (PLN) shuts down, and advice the user to take immediate action to shuts down the entire electricity system in his/ her house.

5.      Billing. Since the user basically ‘sells’ the power that is generated, the user will receive payment regarding how much power he/ she fed back to the grid. The amount of payment the user receive will be automatically reduces the electrical bill the user must pay if the user still imported the electricity from PLN. The user still needs power from PLN, to support AC power appliances or the power harvested is not enough to supply the entire house. 

6.      Weather report. The control application has an analytic feature of weather data, and will warn the user if the weather is at most efficient to harvest power from the PV. 

The main purpose of  Grid Connected-Smart Solar Home System is:

1.      Power that is generated from the array of photovoltaics can be used directly by the load or home electronic appliances  without using ‘double’ installation in the smart home.

2.      When the electrical power is being consumed is smaller that the power generated by the PV, the generated power can be exported or sell to other utility or PLN.

3.      With this system, the user has an option to choose whether at that time he/she wants to user the power generated by the PV to supply the load/ export to PLN or save the power to the battery for future use at night.

4.      If the power from the photovoltaic modules is used to supply the load / export to PLN and charging the battery at the same time, it won’t efficient.

5.      The photovoltaic is portraited as an investment, it allows the user to earn extra cash by his/ her contribution in power harvesting.