Showing posts with label micro grids. Show all posts
Showing posts with label micro grids. Show all posts

Sunday, September 9, 2018

Isolated Micro grids and Hybrid micro grids and tie with utility, assessment




Isolated Micro grids and Hybrid micro grids and tie with utility, assessment
Introduction
Rooftop system uses very less space and is also cost effective. The major issue behind utility scale solar PV project is availability of land. It takes around 5 acres of land for installing 1MW of solar PV plant at times the land utilized for sola is productive kand , needed for  growing food grains to support the growing population. Agricultural land conversion for solar project does not seem a viable option. Another issue is the availability of grid in developing countries significant number of people are still unconnected to the grid , electricity generation is usually a costly affairs with fuels that are imported , which can cause balance of payments issues. .Decreasing solar costs have opened opportunities for solar panels to be installed on roof tops to feed domestic demand. There are various options some of which are briefly discussed in this presentation .What are the benefits of grid-connected solar panels vs. living off the grid? Deciding whether or not to grid-tie your solar panels is usually pretty straightforward – the clear-cut benefits of being grid-tied   are, however, some people that choose to live off the grid.
Rooftop Solar PV system: How it works?

Solar PV rooftop system is basically a small power plant at your rooftop. The Grid interactive Roof Top Solar Photo Voltaic (PV) mainly consists of three major components. These are the solar PV modules, mounting structure for the modules and the inverter or power conditioning units. Solar PV modules form an array and it requires a mounting structure to hold PV modules at the required angle for maximized generation. The solar panels convert solar energy in the form of light into electricity in DC form (Direct Current). The DC electrical energy is converted to AC (Alternate Current) power by the inverter/power conditioning unit which is connected to the power grid through AC distribution board. The AC power output can be measured through metering panel connected to it. The 415 V AC output of the system can be synchronized with the grid and the electricity can be exported to the grid depending upon solar power generation and local consumption.

Grid-Tied Solar Systems
Grid-tied, on-grid, utility-interactive, grid intertie and grid back feeding are all terms used to describe the same concept – a solar system that is connected to the utility power grid.


Advantages of Grid-Tied Systems
1. Save more money with net metering
A grid-connection will allow you to save more money with solar panels through better efficiency rates, net metering, plus lower equipment and installation costs: Batteries, and other stand-alone equipment, are required for a fully functional off-grid solar system and add to costs as well as maintenance. Grid-tied solar systems are therefore generally cheaper and simpler to install.
Power generated from the rooftop solar system during the daytime can be utilized fully by powering the building loads and feeding excess power to the grid as long as grid is available. Whenever, solar power is not available due to shadow or a cloudy day, the building loads can be served by drawing power from the grid or DG sets. Smart inverters automatically understand the power situation and always give preference to power generated from solar modules.
Your solar panels will often generate more electricity than what you are capable of consuming. With net metering, homeowners can put this excess electricity onto the utility grid instead of storing it themselves with batteries. Net metering (or feed-in tariff schemes in some countries) plays an important role in how solar power is incentivized. Without it, residential solar systems would be much less feasible from a financial point of view. Many utility companies are committed to buying electricity from homeowners at the same rate as they sell it themselves.

2. The utility grid is a virtual battery
Electricity has to be spent in real time. However, it can be temporarily stored as other forms of energy (e.g. chemical energy in batteries). Energy storage typically comes with significant losses. The electric power grid is in many ways also a battery, without the need for maintenance or replacements, and with much better efficiency rates. In other words, more electricity (and more money) goes to waste with conventional battery systems. Lead-acid batteries, which are commonly used with solar panels, are only 80-90% efficient at storing energy, and their performance degrades with time. Additional perks of being grid-tied include access to backup power from the utility grid (in case your solar system stop generating electricity for one reason or another). At the same time you help to mitigate the utility company`s peak load. As a result, the efficiency of our electrical system as a whole goes up.

Equipment for Grid-Tied Solar Systems
There are a few key differences between the equipment needed for grid-tied, off-grid and hybrid solar systems. Standard grid-tied solar systems rely on the following components:
  • Grid-Tie Inverter (GTI) or Micro-Inverters
  • Power Meter

Grid-Tie Inverter (GTI)
The solar regulates the voltage and current received from your solar panels. Direct current (DC) from your solar panels is converted into alternating current (AC), which is the type of current that is utilized by the majority of electrical appliances. In addition to this, grid-tie inverters, also known as grid-interactive or synchronous inverters, synchronize the phase and frequency of the current to fit the utility grid. The output voltage is also adjusted slightly higher than the grid voltage in order for excess electricity to flow outwards to the grid.

Electrical inverters convert direct current generated from solar PV modules to alternating current. Therefore, solar modules need to be connected to inverters. Nowadays we have smart Grid-interactive inverters. These inverters can produce AC power that matches voltage and frequency of the grid and the power line it connects to. There is another requirement of adding an isolation transformer. For safety purposes, isolation transformer is used to transfer electrical power from inverter to the connected load while isolating the load from the power source. In addition, the injection of DC power into the grid can be avoided by using an isolation transformer at the output of the inverter.

Micro-Inverters
Micro-inverters go on the back of each solar panel, as opposed to one central inverter that typically takes on the entire solar array. There has recently been a lot of debate on whether micro-inverters are better than central (string) inverters. Micro-inverters are certainly more expensive, but in many cases yield higher efficiency rates. Homeowners who are suspect to shading issues should definitely look into if micro-inverters are better in their situation.

Power Meter
Most homeowners will need to replace their current power meter with one that is compatible with net metering. This device, often called a net meter or a two-way meter, is capable of measuring power going in both directions, from the grid to your house and vice versa. You should consult with your local utility company and see what net metering options you have. In some places, the utility company issues a power meter for free and pay full price for the electricity you generate; however, this is not always the case.
Off-Grid Solar Systems
An off-grid solar system (off-the-grid, stand alone) is the obvious alternative to one that is grid-tied. For homeowners that have access to the grid, off-grid solar systems are usually out of question. To ensure access to electricity at all times, off-grid solar systems require battery storage and a backup generator (if you live off-the-grid). On top of this, a battery bank typically needs to be replaced after 10 years. Batteries are complicated, expensive and decrease overall system efficiency.

Key facts about rooftop solar systems;
1.      The solar panels should be south facing to maximize the production. The angle of panel should be 25-30 degrees with respect to the land surface, both facing and angle will vary from country to country.( Solar panels should always face true south if you are in the northern hemisphere, or true north if you are in the southern hemisphere. True north is not the same as magnetic north. If you are using a compass to orient your panels, you need to correct for the difference, which varies from place to place. Search the web for “magnetic declination” to find the correction for your location. The angle from horizontal should the panels be tilted should be equal to your latitude, plus 15 degrees in winter, or minus 15 degrees in summer. It turns out that you can do better than this - about 4% better. It is simplest to mount your solar panels at a fixed tilt and just leave them there. But because the sun is higher in the summer and lowers in the winter, you can capture more energy during the whole year by adjusting the tilt of the panels according to the season, adjusting the tilt twice a year gives you a meaningful boost in energy. Adjusting four times a year produces only a little more)
2.      The weight exerted by the Solar Panels and the structure is around 10 kg per square meter.
3.      The solar installation requires about 100-150 square feet of area per Kilowatt.
4.      No frequent maintenance is required for the solar system except regular cleaning of surface of the panels.
5.      There are two types of rooftop solar installations. First is for captive use and second is for feed in tariff based grid connected system. In captive use, rooftop solar system installer himself consumes all electricity generated by the system. However, in second type i.e. feed in tariff based grid connected system, installer can also feed/sale excess power to the grid.
6.      In captive rooftop solar systems, there are two types. The first one is standalone systems and other is grid connected system.
 Net metering schematic
Benefits of Rooftop Solar PV systems
1.      Cost of electricity is increasing. Electricity utility companies are bound to increase the cost per unit of electricity due to increase in cost of fuel.
2.      Many regions in the country are facing severe power cuts extending to 12 -14 hours in a day.
3.      Grid tied solar PV systems are the most common systems for captive power generation. It is technologically feasible to have hybrid systems such as Solar PV +Grid or Solar PV +Diesel Generator
4.      It cost about US $. 3000/kW with battery storage and US $ 2200/kW without battery storage. It seems high as compared to conventional diesel power generators. However, operational cost for diesel generator is very high. Considering the replacement cost of power generation from diesel generators, solar PV systems provide attractive returns.

Advantages of Off-Grid Solar Systems
1. No access to the utility grid
Off-grid solar systems can be cheaper than extending power lines in certain remote areas. The economics will vary from place to place.

2. Become energy self-sufficient
Living off the grid and being self-sufficient feels good. For some people, this feeling is worth more than saving money. Energy self-sufficiency is also a form of security. Power failures on the utility grid do not affect off-grid solar systems. On the flip side, batteries can only store a certain amount of energy, and during cloudy times, being connected to the grid is actually where the security is. You should install a backup generator to be prepared for these kinds of situations.

Equipment for Off-Grid Solar Systems
Typical off-grid solar systems require the following extra components:
  • Solar Charge Controller
  • Battery Bank
  • DC Disconnect (additional)
  • Off-Grid Inverter
  • Backup Generator (optional)
                                                        
Solar Charge Controller
Solar charge controllers are also known as charge regulators or just battery regulators. The last term is probably the best to describe what this device actually does: Solar battery chargers limit the rate of current being delivered to the battery bank and protect the batteries from overcharging. Good charge controllers are crucial for keeping the batteries healthy, which ensures the lifetime of a battery bank is maximized. If you have a battery-based inverter, chances are that the charge controller is integrated.

Battery Bank
Without a battery bank (or a generator) it’ll be lights out by sunset. A battery bank is essentially a group of batteries wired together.

DC Disconnect Switch
AC and DC safety disconnects are required for all solar systems. For off-grid solar systems, one additional DC disconnect is installed between the battery bank and the off-grid inverter. It is used to switch off the current flowing between these components. This is important for maintenance, troubleshooting and protection against electrical fires.

Off-Grid Inverter
There`s no need for an inverter if you`re only setting up solar panels for your boat, your RV, or something else that runs on DC current. You will need an inverter to convert DC to AC for all other electrical appliances. Off-grid inverters do not have to match phase with the utility sine wave as opposed to grid-tie inverters. Electrical current flows from the solar panels through the solar charge controller and the bank battery bank before it is finally converted into AC by the off-grid-inverter.

Backup Generator
It takes a lot of money and big batteries to prepare for several consecutive days without the sun shining (or access to the grid). In most cases, installing a backup generator that runs on diesel is a better choice than investing in an oversized battery bank that seldom gets to operate at its full potential. Generators can run on propane, petroleum, gasoline and many other fuel types. Backup generators typically output AC, which can be sent through the inverter for direct use, or it can be converted into DC for battery storage.

Hybrid Solar Systems
Hybrid solar systems combine the best from grid-tied and off-grid solar systems. These systems can either be described as off-grid solar with utility backup power, or grid-tied solar with extra battery storage. If you own a grid-tied solar system and drive a vehicle that runs on electricity, you already kind of have a hybrid setup. The electrical vehicle is really just a battery with wheels.


Advantages of Hybrid Solar Systems
1. Less expensive than off-gird solar systems
Hybrid solar systems are less expensive than off-grid solar systems. You don`t really need a backup generator, and the capacity of your battery bank can be downsized. Off-peak electricity from the utility company is cheaper than diesel.   The introduction of hybrid solar systems has opened up for many interesting innovations.New inverters let homeowners take advantage of changes in the utility electricity rates throughout the day. Solar panels happen to output the most electrical power at noon – not long before the price of electricity peaks. Your home and electrical vehicle can be programmed to consume power during off-peak hours (or from your solar panels). Consequently, you can temporarily store whatever excess electricity your solar panels in batteries, and put it on the utility grid when you are paid the most for every kWh. Smart solar holds a lot of promise. The concept will become increasingly important as we transition towards the smart grid in the coming years.

Equipment for Hybrid Solar Systems
Typical hybrid solar systems are based on the following additional components:
  • Charge Controller
  • Battery Bank
  • DC Disconnect (additional)
  • Battery-Based Grid-Tie Inverter
  • Power Meter

Battery-Based Grid-Tie Inverter
Hybrid solar systems utilize batter-based grid-tie inverters. These devices combine can draw electrical power to and from battery banks, as well as synchronize with the utility grid. for the vast majority of homeowners, tapping the utility grid for electricity and energy storage is significantly cheaper and more practical than using battery banks and/or backup generators.

Solar, renewable energy, climate change, global warming, off grid energy, hybrids, domestic power consumption options, batteries, storages, two way metering, buy back tariffs.