How do hybrid solar and wind electric power systems work?

Published: 13 May 2018

Are hybrid power systems the answer for harnessing the power of more than one resource to deliver non-intermittent electric power?

To this day, the expectation of supplying electrical needs without the use of fossil fuel has increased substantially, but amongst all the clean and renewable options, sun, wind and water are the most appealing energy sources because they are options not just for industrial and country-sized solutions, but also for residential and commercial cases. The solution? Hybrid power systems? Let’s see.

One of the main problems of this goal is the difficulty of relying entirely on one single source of energy, all day long, taking total advantage of all the available landscape (rooftops, plains and open high grounds). 

Therefore, these options must be integrated to between them have the ability to supply high demands and particularly with energy storage solutions, to save excess energy  and supply it when the sources are not producing as expected.

These integrated systems are called Hybrid Power Systems or Hybrid Systems, and seeing them as residential solutions (for a simpler and better comprehension), they may be classified as off-grid (not connected to the utility grid) or grid-tied (connected to the utility grid).

The difference between residential and industrial solutions is mainly the magnitude of the electrical variables used, and therefore the size and or quantity of devices that are integrated in the system.

Here is a simplified diagram to exemplify Hybrid Power Systems topology:

Archivo:Hybrid Power System.gif

Hybrid Power Systems Topology

Let’s give a more detailed approach to the Hybrid Power System topology.

1. Generation Units

  • Photovoltaic (PV) Modules Array 

The interconnection of PV panel strings (PV modules series connection) that produce electric power using solar radiation as its energy source. Generating DC power.

  • Wind Turbine(s)

A wind turbine or the interconnection of several, that produce electric power using the wind speed as its energy source. Generates DC power.  

As a curious design fact, for small wind systems for direct water pumping in remote areas, average wind speeds as low as 3-4 could be found acceptable. But for larger systems, average wind speeds less than 6-7 m/s might not be economically feasible.

  • AC Generator: This could be one or a group of generators that act as an AC energy source. Samples could be a power plant fossil fueled, the utility grid and/or a mini-hydraulic generator, among other possibilities.

2. Energy Storage System

Also known as ESS, these units are able to store all the excess energy originally produced to supply the load. 

Instead of losing that excess energy, these units can save it until the system demands more power than the renewable energy sources can provide. 

It may seem obvious, but such battery packs must be capable of reliably discharging and being recharged up to a safe percentage of their capacity in repeated cycles (when talking about lead batteries these are called deep cycle batteries).

3. Energy Converter

An inverter device is often used to turn the DC power produced by PV modules and wind turbines into the AC needed by most of the loads in the system, and send the DC Power excess to the ESS when needed. 

When the system also has an AC generation plant, it must be able to supply the load and turn this AC power into the DC power that can charge the ESS when needed.

The inverters are often the “brain” of these systems, and as the investigation and research departments technology keeps getting better, so does the reaction time of the switching between energy sources, energy management systems and the voltage or frequency ranges to give the best possible compatibility and performance when being connected to the grid.

There are different models for each application, depending on whether you want a solar system, a wind system, a grid-tie or one of the many others. 

They shouldn’t be mixed up for the optimal use of each generator, as each model has a different behaviour that a different converter would not be able to follow  as intended.

4. Charge Controller

This is the device that must control the charging levels of the ESS. The charge controller must protect the ESS from overloading and must also be able to safely control the sudden changes between the charge and discharge rates, ensuring that everything occurs at the required voltage levels.

There must be a solar charge controller and a separate wind charge controller to safely control the speed of the turbine and the state of the battery as well.

5. Energy Management System

This refers to the device in charge of deciding where the energy will be directed. This decision will be based according to the system’s energy production. 

It could be found in the converter unit, in the charge regulator or as an independent device.

6. Loads

For hybrid systems, loads may be either a residential or commercial type, with AC or DC powered devices. 

These can be classified as DC or AC loads, where some of them can be backed up with the battery bank.

When there is a grid tied system, remember to consider which loads are going to be connected directly to the utility grid.

Here’s an example of an Off-Grid Hybrid Solar and Wind System diagram.

https://2.bp.blogspot.com/-nzjPAaCOhMY/WACX8MxNJeI/AAAAAAAABLo/P9pa8mJZQgY-Af3QeXy7gPMKJsdXg1jAQCLcB/s1600/Solar-Wind-Hybrid-Power-System-Block-Diagram.jpg

Conclusion

With the incoming future so close, and increasing marketing on the distributed generation solution, understanding these systems is getting easier every day. 

Luckily, to use these types of systems you do not require specialized knowledge since they are intended to be user-friendly for those who have opted for a simple fossil free solution. 

Hybrid power systems offer an advantage that a single renewable energy source solution cannot provide, that is, reliability. 

The sun resource is only available during the day, but it can be easily predicted. 

However, the wind resource is available across the day and night, but presents constant intermittency and is harder to predict. 

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