During the Praha Zari festival in Prague, Czech Republic, we will give you daily energy updates from the GEM-Tower, starting on Tuesday the 15th of September.

Solar canvasses @ Praha Zari festival

Daily Update – Sunday, September 20th 

How it works – Solar Canvas

Not physically connected, but a very important element of the renewable power generation of the GEM Tower are the Solar canvasses. There are 12 canvasses with on each canvas 6 flexible solar panels. In the current set-up, the canvasses are mounted on aluminium frames, which allows us to easily position them in the optimal position towards the sun on every festival location.

The difference in solar energy for the various set-ups is registered by energy loggers. All these input will be used to develop the ultimate application for the solar canvasses; a Solar carpet.

The solar carpet can be used as a tent roof for a stage or small (lounge) area on events.

Making smart and useful combinations of the various energy sources makes the GEM Tower not only an iconic energy supplier, but also the heart of the renewable energy supply on your event.


GEM Battery Storage

Daily Update – Saturday, September 19th 

How it works Battery Storage

The total energy system of the GEM Tower is consisting of renewable energy solar and wind. There is always a dependency on the actual weather conditions.

The power demand of an event does not take account of weather conditions. If there is a need for power, there should be enough available.

The base of the GEM Tower needs to be heavy, in order to stabilise the tower.

In order to have always sufficient power available, the GEM Tower is equipped with a large battery system. There are various battery types available, but for the GEM Tower there is chosen for an industry quality battery type called VLRA (Valve Regulated Lead Acid). The advantages of this type of battery is that these have the highest reliability, even in non-optimal conditions and are maintenance free. A downside of VLRA batteries is the relative high weight, but that’s just what there is needed for stabilization of the tower.

If there is a surplus of renewable energy generation from wind- or solar energy, this energy will be used to charge the battery. When the energy demand of the event is larger then the actual renewable energy generation, the missing energy will automatically filled up by the stored energy from the battery. The battery management system will keep all systems in balance.

If the state of charge of the battery will come below 30%, then the battery management system can even automatically start a charging procedure from a grid connection (if available) or start a generator running on bio-diesel. So with all these different systems in place and the battery with the battery management system as a central energy point of the GEM Tower, we not only guarantee the stabilisation of the tower but also guarantee a constant and reliable energy supply to your event.


Figure by Maja Gajic RMIT University | RMIT · School of Engineering

Daily Update – Friday, September 18th 

How it works LCS panels

The eye catching colored panels in the GEM-tower are Luminescent Solar Concentrators (LSC). LSC panels are colored solar panels which catch the light and change the wavelength of the light. Reflection is used to transport the light to the edges where the light is converted into electrical energy by small strips with PV cells. These LSC’s do not need direct sunlight and therefor the panels can be placed in any direction.

The LSC panels are used with micro converters, which convert the solar energy direct into AC. If there is an energy demand from the festival, the solar energy of the LSC panels will be used directly.

Only if there is no energy consumption at all, the energy from the LSC panels will be stored in the battery which is also part of the GEM Tower.

Daily Update – Thursday, September 17th 

How it works – the Energy Generation Calculation of GEM-Tower

One of the main elements of the GEM-Tower is the wind turbine, located on top of the tower. The wind turbine converts wind energy into electrical energy. The more wind there is, the more electrical energy the wind turbine generates.

However, a minimum wind speed is required for the wind turbine to start generating electrical energy. The turbine starts generating energy with the wind speed 5 m/s (3 Beaufort). At the speed of 13 m/s (7 Beaufort), the turbine automatically stops in order to prevent damage due to over speed. The maximum electrical output of the wind turbine is 3.000 Watts.

When we are preparing for an event with the GEM team, we always look at the weather forecast and the predicted wind speeds at the specific location during that time of the year. In the overall energy generation calculation of GEM, we use the predicted energy consumption as one of our sources.

During the event itself, we log the energy generation of many different components of the tower. This summer, we added a wind speed tracker on to the tower to get relevant data. The data is then compared to the predictions to increase the reliability of the power from the GEM-Tower.

Daily Update – Wednesday, September 16th 

How it works – the GEM-Tower 

The 22-meter tall GEM-Tower exist of a vertical wind turbine on top of the tower (wind energy). There are colored LSC-panels mounted in the triangles of the tower itself (solar energy). Also, there is a large battery storage in the base of the GEM Tower (energy storage). On the roof of a transformer station in the festival area, there are put a lot of Solar canvasses. On these canvasses, flexible solar panels are mounted (solar energy).

All these renewable energy sources will supply the power to the energy users on the festival area. If there is a surplus on energy generation, this will be stored in the battery. If the energy consumption in the festival area is more than the energy generation, the missing energy will be delivered by the battery storage. If the energy consumption is that high that the battery will be almost empty (discharged) than a grid connection will be opened, and the battery will be recharged from the grid.

 GEM-Tower is an Interreg innovation project by Eindhoven Technical University, Off Grid Energy, IBIS Power, Pukkelpop, Double 2 Mediaproducties, Democrazy, Eurosonic Noorderslag, Flexotels, Zap Concepts, and RPS Concervation Services.

GEM-Tower @ Praha zari festival before the official opening. Photo: Paul Schurink

Daily Update – Tuesday, September 15th 

After the arrival of the GEM-Tower on Monday, September 7th, the construction of the tower was started on Tuesday and finished on Wednesday the 9th. During the construction phase, the GEM team was using a grid connection to partly charge the battery to make sure there was enough power for the construction, and for the first show.

Energy Monitoring Systems
From Wednesday to Friday, the battery was charged up to 100% by solar energy – there was nearly any wind on-site, so the windmill on top of the GEM-Tower was not able to produce any power yet. After the construction, the GEM-Tower was then connected to the power grid of the Letni Poloha Area. This area has plenty of energy monitoring systems to track the energy performance. This part of the festival has a big festival tent with a stage, which fits approximately 50-seated guests. It also has a backstage area, a bar, and a toilet facility.

On Friday, September 11th, there were two shows booked in the Letni Poloha area:

  • 18:00 – 20:00 Groove Production uvádí – Bluesman ZDARMA
  • 20:00 – 21:00 Marcus Jurkovič – Koncert ZDARMA

Letni Poloha capacity
The maximum power demand of the Letni Poloha area was 27,5% of the maximum capacity of the GEM-Tower. The total solar power that was generated by the GEM-Tower on September 11thwas enough of 17% of the power consumption of the Letni Poloha area during the day including both shows. Because the GEM-Tower contains large battery storage, there was plenty of energy available to power both of the shows.

If the program of the Letni Poloha area were a weekly show, the GEM-Tower would be able to fully power the area. It would take six days to fully recharge the battery by renewable energy.
In the next few days, we will explain to you how the different energy systems combined in the GEM-Tower work together for a fully renewable and reliable energy supply.