The present energy production of Reykjavik is 73% renewable (mostly geothermal energy) and 27% fossil fuels. I changed this to 50% geothermal energy, and 50% coal. I changed this because of the new technology I am using for the building material. It is a cement that absorbs CO2, and produces calcite with it. With this technology, energy can be produced efficiently, and it would not affect the environment negatively. Energy will also be produced through solar panels, but there is very little hours of sunlight in Reykjavik, so it will only produce a very small, and almost insignificant, amount of energy. It could only be used for back up electricity for elevators. Every building in the city will have solar panels on the roofs. Some other sources of energy are the dynamos in the bicycles, and the energy producing tiles on the roads, but they too, produce very small amounts of electricity.
The way the electricity will be produced is very similar and both include heating water. There are multiple ways electricity is produced with geothermal energy. The technique that will be used in Reykjavik is called the Binary Cycle Power plant. The hot water from the geothermal energy is cycled through the ground and up to the power plant. In the power plant, a heat exchanger transfers the heat to another cycle of water which is heated and evaporated to steam. That steam is then used to spin a turbine and power a generator. That steam then condenses, and in liquid state, it is ready to be heated and evaporated again to go through the same cycles. Here is a diagram explaining this:
Electricity from coal is produced very similarly, but the only difference is that the coal is burnt to heat water, which is then turned to steam. The coal also gives of CO2 as a byproduct, and leaves ash as waste as well. Here is a diagram explaining this:
Although coal does negatively affect the environment, it is controlled through the peridotite. I increased the use of fossil fuels from 27% to 50% so that the accumulation of calcite on the peridotite buildings would be more significant in a few centuries rather than around a millennium. The limitation to using coal would be the money spent on importing it from another place as Reykjavik has no coal or fossil fuel production of itself. The limitation to geothermal energy would be to manage the power plant because if there is a problem in the generator, turbine, or heat exchanger, this could negatively affect the whole city because only the industrial zone is powered with coal. So if the energy production fails at some point, the city will only have solar panels bicycle dynamos to produce electricity, and as mentioned above, it would not be sufficient.