What is a micro-grid?

I would just like to briefly explain about a micro-grid before going in more detail about the full “plan”.

 It is a locally sourced electricity “system” which is capable of operating independently or along with the main (traditional) grid. This is similar to the vision of  local electricity generation by Thomas Edison. However this has the added benefit that the local DC grid is able to operate either in parallel with the surrounding AC grid or in isolation from it.

This sort of DC micro-grids also have much smaller footprints, avoid most transmissions and distribution losses.

For this project, we will only be looking to generate electricity using renewable sources. At this stage, we are hoping to source from solar, wind and hydro power. This will all be done in small scale.

showing overall system in a renewable grid [credit: www.pitt.edu]

The idea about the micro-grid is that is can be used as either a backup to the main grid or it can also be used as a sole provider of the electricity in remote areas disconnected from the main grid.

I have also posted the following video from Texas university that explains it more visibly.

Initial thoughts and ideas

So, currently we are thinking of using three different types of renewable sources for our grid: solar, wind and hydro. These will all be a miniature version obviously! However, at this stage we think that trying to manage a water flow for a small hydro powered system might be a bit more challenging.

Sam was also kind to lend me one of this PV(photo-voltaic) array (1Watts) and water turbine to be used in a project. I will be using those to get ideas about the maximum power that can be generated.

Regarding the configuration, we have decided as following:

Full system configuration (with arrows representing switches)

The job of the regulator is to maintain a fixed output voltage (grid voltage) which we have decided to have as 12V. Its input can have a range of voltage depending upon the sources’ “ability”.

One point to note is that the battery shown in figure only charges, if there is more power available from the source after supplying the loads (the ones that are turned ON). It also discharges/supply the power to the loads if there is no/less power from the sources.

The further decision on the type of linear regulator and the battery, will be decided upon testing the power generation from the sources.

We will also be ordering components gradually to test our design and will update the further developments later in this blog.

UPDATEss

After, testing the solar array, I found that the maximum voltage that can be generated was 18V (on a bright day) with the average of around 5.5 V in normal brightness. This meant we had to order a regulator that has the input voltage range between those figures. However, if you were wondering about the efficiency it was around 12%, so I may have to replace it with “better” panels at the later stages of this project.

After looking at different types, we have decided to order an isolated DC/DC converter with input range between 4.5 to 18V. It has an output voltage of 12V (as it is our grid voltage).

Isolated regulator from Tracopower

Supercapacitors vs Battery

The power from PV array, wind turbines are intermittent in nature, therefore to make it more reliable an efficient way of energy storage is necessary. This is indeed a main reason why the sustainable energy systems are taking a while to become a primary source of electricity.

Currently, batteries remain the “go to” energy storage system. Although they have higher energy density, their ability to retain energy degrades overtime due to charging/discharging cycle.

The new system that has got engineers going is to use supercapacitor as a storage mechanism. Here, the energy is stored electrostatically and does not involve chemical reactions. Therefore, it can undergo “million” charge/discharge cycle without losing its energy storing capability. It has a very high power density but its energy density is low. However, recent advances have made it possible to be used in commercial applications like electric cars.

Now for this project, I will be using supercapacitor to illustrate the energy storage. This is because while doing short demonstration later, I can quickly show that the grid stores energy during excess power and provides when power is low.

The capacitor I will be using is: Panasonic electric double layer capacitor SG of 1 Farads.

From sun to the grid!!!

So, today I finished implementing the full string for solar energy i.e. test the power from PV cells to grid to charging and discharging the capacitor. The schematic for this circuit is shown below.
                                                 

Schematic showing for solar string

Testing the schematic

Here for testing purposes, I have used 10,000 micro farads capacitor rated at 16V. (waiting for the capacitor).

The voltage across variable resistor was 11.8 V (grid voltage =12V).

Then the solar power was also tested to charge the capacitor. As shown in schematic, the capacitor gets charged thorough the schottky diode to around 15V. Diode is necessary to prevent the capacitor discharging during charging cycle momentarily. As capacitor discharges, another converter was used to have constant 12V (grid voltage).

Wind power!!!

As mentioned in earlier post, our another renewable source will be from wind.

To let you know, according to BBC, UK is one of the best places (top in Europe) in the world for wind power. Although, still not comparable to the other hydrocarbon sources, it contributed around 11% of the total electricity generated in 2015. The future certainly looks bright for this cheapest source of electricity.

At start, I had the DC generator that converts the rotation of the shaft into a DC power supply. The speed of the rotation is proportional to the angular speed of the shaft. The propeller which is connected to shaft is itself rotated because of the wind energy (well, hair dryer in our case)

Therefore, initially I bought 3 different types of propeller:

         Propeller 3 Blade 210mm
         Propeller 3 Blade 125mm

          Propellor 5 Blade 60mm

After testing all those blades, I found that the 60mm blades can generate the maximum voltage. This is because it has the least weight means more rotation which in turn means more voltage (EMF). Using 2.2KW hairdryer the voltage generated was around 7volts. The voltage generated from other blades were lower as the length increases.

Although, 60 mm blades would generate the voltage in the region we wanted, we figured that it would not be as visibly demonstrative, the idea of wind turbine.

The other idea we tried was to use gear system, which meant we could get large voltage with small angular speed.

More of this in the next post.

Power from water!!!

As discussed in the beginning, our third and final source (until we can find others!). Similarly, to wind farming, large scale hydropower is normally suited (cheaper) for the areas which have naturally occurring springs or rivers or is mountainous. However, its not to say, it cant be done in other places for example in Bristol university. And to find out more about small scale project called Pico hydro project, then the best thing to do is to contact Dr Sam Williamson. You could also consider reading some of his publications on Low head Pico Hyro-power, although it is quite advanced and specific, it can be of great benefit for someone who have keen interest.

(http://www.bris.ac.uk/engineering/departments/aerospace/people/sam-j-williamson/publications.html)

For this project, I initially started with making turbine for the generator. My first attempt in making is shown below:

However, upon testing, it was realized that the above shown turbine did not provide sufficient power. This was because to generate enough voltage---more rpm required---which in return meant large flow rate/increased height.

Then the second option was to create smaller turbine as shown below: