Hybrid Solar-Wind Power Generation System Design Guide

Hybrid Solar-Wind Power

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The word ‘hybrid’ means comprising of two different types of varieties. In the case of a hybrid renewable energy system the means of generating electricity could be a combination of PV (solar panels), wind or even water turbine.

The most common hybrid power generation system is a solar-wind combination.

Why would anyone design and build such as system? In any location there is often a time when the sun doesn’t shine too often or the wind doesn’t blow.

It’s fact that the two sources of energy often don’t deliver at the same time, so combining wind and solar power makes complete sense.

In an off-grid situation, where maintaining an electricity supply is crucial, a wind turbine can supply power during the night when the sun doesn’t shine.

The extra cost of installing this may well be less expensive than adding more battery banks, which are very costly.

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What is a solar wind hybrid system?

The components in hybrid power system are not quite the same as an ordinary PV solar array installation.

Introduction To Hybrid Solar-Wind Power Generation System Design – Combing Wind and Solar Power

The sun makes us what we are. The light and heat from the sun is far more existential if we meditate deep into this. Electricity and heat generated from sun is of course solar energy, whereas wind is the natural after effect of the same “solar energy” that strikes on Earth continuously.

Again, to be precise the sun’s energy that is converted to mechanical energy and to electricity is termed as wind energy, or wind power when it rotates the turbine.

The solar energy, whether electricity or heat, is available for some period during the day and this intermittent nature of solar energy is one of its major drawbacks. Energy storage like batteries completes a solar energy system at but at additional costs.

In some installations, to complement solar energy wind energy generators are installed along side it and connected to it. As wind blows day or night but varies depending on weather and seasons, it assists solar energy in a hybrid solar-wind power generation system.

Wind turbine and solar panel combination - description (post start)

Wind turbine and solar panel combination – the best of both worlds

Hybrid solar-wind power generation system

Solar-wind hybrid system design – main points

A hybrid energy system consists of multiple electricity generation devices or systems. The term “hybrid” is a biological term which is now being used in tech to show a mix of two or more genetically unlike systems.

You might have a hybrid vehicle, where you have gas and electricity both powering the vehicle. Similarly, genetically dissimilar electricity or energy generating systems or sources like solar, wind, biomass, geothermal, ocean, hydro and diesel can be used to form a mix to generate energy.

It depends on the availability of that resource and the technical ability of the person to get it installed in the most efficient way. The economics of such a hybrid system should be well understood and should be economically profitable to claim its sustainability.

Wind turbine and solar panel combination

The components of a hybrid energy system depend on the resources used. Let us list them to see how they can contribute to building a hybrid system for a 1500 houses gated community with availability of 3 energy resources such as solar, wind and biomass.

  • Generating equipment: Solar PV panels, Wind turbine and biomass boiler
  • Energy available as: Electricity from solar PV panels, wind turbine and biomass boiler. Heat also available if combined heat and power or CHP boiler is used.
  • Transmission, rectification and regulation equipment: Wires and cables for electricity transmission, rectifiers to convert AC to DC where required, charge regulator to regulate the current to batteries, inverter to supply electricity to AC loads.
  • Heat network: Like in form of district heating for 1500 houses if CHP boiler is used.
  • Batteries and Electricity grid connection: Can be used to make a system more stable and reliable.

The difference in types of hybrid systems is the energy resource. Like geothermal can also provide heat with the use of heat pumps, or small Archimedes or any other hydro turbine in a stream of water near you can provide you hydro power.

Availability of different energy resources can easily make anyone energy independent. Use of energy storage systems like batteries or flywheels can also make the whole energy system more secure, reliable and efficient.

In large scale solar power projects, pumped hydro is a good energy storage option. During the day when sun is shining, and load is minimal, maximum energy can be stored by lifting water up a hill in a pond. At the time of high demand like at night, water from these ponds can be used to generate hydro power and make the whole solar-hydro hybrid a success.

Such hybrid installations are happening around the world where they are required and are very beneficial. Also use of such hybrid energy systems is very beneficial in the fight against climate change because dependency on fossil fuels really diminishes with use of such systems.

There are added advantages of hybrid systems but at present, their economics and lack of knowledge and will to transform is hindering such developments.

What are the advantages of hybrid renewable energy systems?

The fossil fuel driven economy from the past few centuries and its shift to a much greener one relies on non-polluting energy sources or far less polluting energy sources.

Renewable energy sources and their mix can make this transition happen with time and resources. The hybrid energy systems ensure energy security and reliability which make them the ideal way of using renewable energy sources in particular.

Some advantages of hybrid systems are:

  1. Uninterrupted power supply: The mix of two or more energy generating technologies with addition of energy storage technology never lets the consumer be short of power. If we consider a hybrid of solar and wind energy, both solar and wind can generate electricity during the day. Wind can also generate electricity at night and if energy storage is available, continuous power supply is available all the time.
  2. Increased reliability: Installation of two or more energy systems increases the reliability of the system. Like in a solar wind energy hybrid system, wind power can generate at night or sun can generate electricity when there is no wind. Similarly with energy storage, reliability increases further when both sun and wind sources are absent in solar wind hybrid system.
  3. Low life-cycle costs: Renewable energy sources in a hybrid system result in low life-cycle costs due to variability of supply to load by different energy generating systems. The maintenance and operation costs in hybrid energy system gradually decrease due to proper load synchronization between different generators.
  4. Best utilization of renewable energy sources: If any renewable energy source is available on a site for use, its utilization in best manner is done by hybrid energy system. For instance, having only solar power plant at a location with usable wind speeds is waste of wind energy on that site. In this case a hybrid of solar and wind power can very efficiently utilize both solar and wind energy.
  5. Properly managed load: Hybrid energy systems manage the connected load in a proper manner. Conventional diesel generators give a surge of power when they turn on which are not very good for the device consuming that power. In hybrid systems, control systems and batteries power devices on demand basis. This in turn also increases the life of the load or connected device.
  6. Environment friendly: Renewable energy devices in a hybrid system are environment friendly in nature as compared to fossil fueled energy generators. Efficient generation from different renewable energy sources, properly managed load and reliability of the system enhances its carbon positive nature.

How much does a hybrid solar system cost?


How much does a hybrid solar system cost

A hybrid solar system to be specific consists of:

  • solar panels
  • connected load
  • grid connection
  • battery back up to counter power outages

All these entities connected to each other by cables describes a type of hybrid energy system, as solar panels and batteries are the main generators here, with the ability to save energy in one of them. So how much will it cost to go ‘full hybrid’ solar system cost? A lot!

Let us work down the rough costs for this as an example for a hybrid 2kW grid tied with battery storage solar photovoltaic system. (In this sense ‘hybrid’ refers to a grid tie system connected to mains electricity, but also with battery storage.)

Grid tied hybrid solar system cost (materials only, not installation)

Solar panels, 2kW = 2000W

If each panel is of 200W then 10 panels are required. If panel is pretty good quality and cost approximately $300 each, solar panels for this system will cost: $3000.

Hybrid inverter, 2kW = $2000

Batteries – the energy storage size depends on the load to be tackled, so assuming: $3000

Charge controller: $400

Ancillary equipment like wires and cables: $200

Misc expenses: $100

So a the parts for a 2kW hybrid solar system can cost around $8700, it is a basic estimate as a lot of companies with different prices and specifications charge at different rates.

Now let us assume this hybrid solar system is grid connected with batteries and do a cost analysis/payback from such a system.

As per “global solar atlas”, a 1kW system in Colorado can produce 1800 kWh per year and so 2kW system will generate around 3600 kWh per year of electricity in Colorado, USA.

Assuming electricity price per unit as ₵12 per kWh or 0.12$ per kWh, then a 2kW system can generate ($0.12 x 3200) $432 worth of electricity in a year.

This means a hybrid solar system with grid connection and battery storage will take at least 20 years to cover its cost if just talk about value of electricity generated by solar panels in a year in Colorado, USA.

If we consider the costing depending on consumption of electricity by the load, the payback period shortens. Further financial assistance from the government of any kind at the time of installation or later by buying excess electricity from the solar system, further reduces the costs.

(Note: Grid electricity prices always tend to increase making solar system generate payback even faster.)

How do wind turbines work?

How do wind turbines work?

The wind turbines work with the flow of the wind. The kinetic energy of the wind rotates the turbine blades which in turn rotates the electric generator. Wind energy is a form of solar energy as differential solar heating of Earth surface causes the pressure difference in the mass of air above ground.

Simply stating, heating of Earth causes warm air from the ground to rise up as it is lighter than the colder air and this causes winds to flow. The rotation of Earth and forces acting on mass of air also decide the behavior of wind.

To understand how wind turbine works, it is necessary to know about the wind source and its behavior in any particular region throughout the year. It is good to know the flow of westerlies or trade winds in the region where wind the energy installation is being considered.

Minimum wind speed required for a wind turbine

Mostly wind turbines have cut-in speed and cut-out speed of wind in which range the wind turbines usually generate electricity. This can differ for different wind turbine types, models and manufacturers but a basic of 5 meter per second (m/s) of wind speed above ground under 100m height is the cut in speed and 25 m/s is the cut-out speed of the wind turbine.

Beyond 25m/s of wind speed the turbines stop rotating or stop generating electricity because of the high pressure and gusts which can damage the wind turbine.

The design of the wind turbine and its blade is not similar to design of a hydro (water) turbine but it is more related to wing blades of an airplane. The lift and the pressure required to rotate the turbine from the wind is all engineered and designed by experts.

The strong and persistent wind at speed above 5m/s rotates the turbine and the turbine coupled to a electric generator which generates electricity (alternating current) and is first filtered and converted to DC current to optimize the generation and frequency as per the load demand and again DC is converted back to to AC to be supplied to the grid or the load.

Wind Turbine Requirements – Is There Enough Wind?

 

How is wind energy harnessed?

To understand wind power generation and its use, it is very important to understand the wind. There are four parameters which should be analyzed, recorded or obtained to understand the potential of the wind resource. These four parameters are:

  1. Wind speed
  2. Wind direction
  3. Temperature
  4. Pressure

In these, wind speed and direction are most important, whereas temperature and pressure affect the density of the air and thus the wind energy available, so should be accounted and recorded.

The data can be recorded by specific instruments for each and an anemometer is required to record wind speed. Wind speed data of at least 1 year at the site of installation is beneficial and additional data from nearest metrological station can be used to understand the wind speed and direction of that particular location.

How is wind energy harnessed?

As the wind speed and direction changes with days, months and seasons, a comprehensive wind data is first required to understand the resource and potential of installing a wind energy turbine to generate electricity.

To get a better view about wind speed “Global Wind Atlas” is a good way to start. This shows the mean wind speed of different regions of the world. If mean wind speed is above 5m/s, the potential to install wind energy system arises. Otherwise to confirm, data from local meteorological stations and practical readings from devices like anemometers should be considered.

On sites like Lake Michigan the mean wind speed is 9.32m/s, which is really good for wind energy installation and Squaw Valley in California has mean wind speed of 3.14m/s which is not good for such installation.

How tall are residential wind turbines?

The ideal height of the turbine from the ground is 100 meters. The wind speed near to the ground is considered as zero in calculation and minimum of 60 feet height above the ground is required by a residential wind turbine. Large wind turbines are installed at maximum of 100 meters or 328 feet from the ground to get maximum use of flowing winds.

Installation of wind turbines in residential locations or urban location is rather complex. Like in case of large on-shore and off-shore wind farms, the measurement of wind speeds and direction are carefully studied which gives a detailed perspective on design and generation of electricity from wind turbines of that wind farm.

The wind flow in these locations is strong and persistent without any turbulence. The direction of the turbine rotor and blades is also synchronized with the wind flow.

In case of small installations like for a residential load or in any urban setting the wind is not that strong and persistent. Also, the turbulent nature of the wind because of various buildings and other infrastructure on the ground makes flow of wind less capable to be used as energy source.

For such cases vertical axis wind turbines are a good option. There are many examples of installation of vertical axis wind turbines in residential and urban landscape, performing satisfactorily. These turbines do not require particular direction of wind as required by the horizontal axis wind turbine and also these operate with turbulent winds of urban settings.

So, vertical axis wind turbine at height above 60 feet or 20 meter from the ground can be used in residential setting. Other options like horizontal axis wind turbine can also be considered if wind behavior of any location allows.

How does a wind turbine inverter work?


How does a wind turbine inverter work?

The blades of wind turbine rotate the rotor of the generator and these are mostly variable speed generators to synchronize with variation of wind turbine speed. The generators are synchronous and non-synchronous.

The synchronous generators are connected to the grid and are synchronized with the grid electricity. These generators produce electricity depending on the voltage and frequency of the grid electricity.

The inverter used in wind turbines is not identical to a solar inverter. It usually consists of first AC to DC rectifier with a filter. This DC is either directly stored in a battery with the help of a charge controller.

Otherwise the DC to AC converters are used to synchronize and supply it with the grid or with the load.
Power electronics equipment, filters and transformers are used to synchronize electricity generation of wind turbine with the grid and the load.

The generation and transmission of electricity from a wind turbine is managed by the inverter and other ancillary equipment along with it.

Wind turbine and solar panel combination

This combination is basically a hybrid energy system. Power generation from solar panels and wind turbines complement each other. Either of solar or wind energy cannot and does not generate electricity continuously all year round.

There is daily variation of sun depending on time of the year and weather conditions. Similarly the wind does not blow at the same continuous speed all the time.

In USA, solar and wind hybrid system is a sustainable choice as in summers the solar generates good amount of energy and in winter, when sun is seldom seen, the wind turbine generates the required energy. Also solar energy being not available at night gives wind energy an upper hand to behave as the main electricity generating technology.

This solar and wind combination can be used for on-grid installations and also can work really well for off-grid scenarios in remote places. It is just the battery storage is required for off-grid installations and without the grid connectivity solar and wind hybrid can act as the sole energy generator, with the help energy storage backup like batteries.

The basic advantages of a hybrid system:

  • uninterrupted power supply
  • increased reliability
  • low life-cycle costs
  • better utilization of renewable energy sources
  • properly managed load
  • environment friendly nature …

are all inherited in a solar and wind hybrid system.

It is just the cost of such a system which can disappoint the consumer or installer and if it is off-grid with battery storage it even gets higher. The availability of sun’s irradiation and flowing energy of wind are the most important aspects to install such a system.

Year round availability of both of these in any particular location of proposed installation should be thoroughly investigated to compute a profitable solar and wind hybrid energy system.

Best batteries for solar power storage

There are various options to store solar energy and in many forms. The solar panels generate direct current (DC) and with the help of a DC optimizer and charge controller is supplied to batteries.

In other cases the same direct current is fed to the inverter to convert it into alternating current to supply to AC loads or the grid in case of an on-grid system.

Off-grid solar systems usually have batteries to store energy generated during the day and supply during night (or when weather is cloudy with minimal sunshine) with the help of inverter to AC loads or directly to DC loads through junction box.

All energy storage systems are good for storing solar energy; it is just the viability of these options and the scope of use in any particular location which narrows down to any particular option.

Well these options are:

  • Batteries
  • Flywheels
  • Pumped Hydro
  • Super capacitors
  • Hydrogen and fuel cells
  • Compressed air
  • Heated molten salt storage

These are some of the options to store solar energy and each is suited as per the solar system design and energy consumption requirements of that installation.

Electrical energy is stored and released in form of chemical energy in a battery. For homes and small businesses at present batteries are the best options to store solar energy. There are many different types of batteries like lead-acid, lithium-ion, Nickel-Cadmium, Sodium sulphur etc.

For different applications, different batteries are used, which are dependent on energy and power capacity, operating temperature, discharge rate, depth of discharge and energy density of that battery type.

Of all the battery types, the Lithium-ion battery which is also a rechargeable battery is most suited for small scale solar installations. Long life span, fast charging, ability to handle deep discharges and compact nature of Li-ion batteries make them the best choice in a solar energy system.

Lithium Phosphate

Lead Acid

Number charge/discharge cycles

2000 (100% DOD)
5000 (80% DOD)

500 (80% DOD)

Weight

60% less than Pb

Deep cycle?

Inherently deep cycle

Special batteries

Cost comparision

$$$

$

It is just the cost of Li-ion batteries is higher than other batteries but performance of these batteries is superior to conventional battery technology.

How to connect wind turbines and solar panels?

It should be done by a professional installer to begin with. Firstly the solar energy will be available for few hours in a day and wind energy can be available anytime. This makes it bit complex for a DIYer with no or little experience of both of these technologies.

Connecting the solar wind hybrid system solely to the grid or off-grid with battery storage or both together gives various options to make this happen. The requirement of the electrical load attached is to be considered before going for any of the connecting options.

Energy generated by solar panels can shut off if no load is supplied. On the other hand wind turbine can’t be shut off in case of no load and it requires constant load. Free rotation of turbine blades causing electric generator to rotate at no load can harm the generator.

The system ahead of the solar panels and the wind turbine/generator should be designed or chosen not for solar and wind separately but for both of them to cater incoming electricity from solar panels and wind turbine in most useful and efficient manner.

The electricity from solar panels in form of direct current or DC is collected at DC junction box, from where it is supplied to DC Bus bar. The alternating current or AC generated by the wind turbine coupled generator is first converted to DC with the help of a rectifier and this wind DC is connected to the same DC bus bar with solar DC.

The combination of solar electricity and wind electricity can be done at DC Bus bar with appropriate transmission ahead.

In case of an off-grid system, the hybrid electricity from solar and wind turbine is supplied to a hybrid charge controller which is connected to battery as per design. This battery is connected to the inverter to supply AC electricity to the AC loads ahead.

In case of grid-tie system, the DC hybrid electricity is supplied from DC bus bar to hybrid inverter, which converts DC to AC and ahead to the grid or to the AC load via junction box.

This connection of all the equipment should be carefully analyzed by a professional installer to have correct values if all the attached components.

Wind turbine and solar panel combination diagram

Wind turbine and solar panel combination diagram - post

Off-Grid Hybrid Solar-Wind Power Generation System – Step By Step Design

  • Step 1: DC from solar panels via junction box and DC-DC converter to hybrid DC bus bar.
  • Step 2: AC from wind turbine generator via controller to AC-DC rectifier.
  • Step 3: DC from AC-DC rectifier of wind turbine to hybrid DC bus bar.
  • Step 4: DC electricity from DC bus bar to hybrid charge controller.
  • Step 5: DC from hybrid charge controller to battery.
  • Step 6: DC from battery to inverter to convert it to AC
  • Step 7: From inverter AC to house load.

This is the basic connection of a hybrid solar wind power generation system. Other components may be required like meters and optimizers to refine the system and its generation.

Grid-Tie Hybrid Solar-Wind Power Generation System Design

  • Step 1: DC from solar panels via junction box and DC-DC converter to hybrid DC bus bar.
  • Step 2: AC from wind turbine generator via controller to AC-DC rectifier.
  • Step 3: DC from AC-DC rectifier of wind turbine to hybrid DC bus bar.
  • Step 4: DC electricity from DC bus bar to hybrid inverter.
  • Step 5: AC from hybrid inverter to connected load and grid via point of common coupling.

In case of grid tie system the inverter should be hybrid in nature. This means the hybrid grid tied inverter should manage both solar and wind DC electricity and if possible have the MPPT function like in the solar grid tied inverter.

Resources:

How to build a small wind turbine – Home-made wind turbine plans

https://www.energy.gov/eere/next-generation-wind-technology

https://www.sciencedirect.com/topics/engineering/wind-energy-technology

https://www.bccresearch.com/market-research/energy-and-resources/wind-turbines-technologies-applications-markets-report.html


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