Electricity has become such a part of our everyday lives that we simply consume it and don't give it any further thought. But what happens in the background? Is the electricity we use every day efficient at all? Everyone is talking about the energy transition. By installing more and more photovoltaic systems on our roofs, we are doing our bit in terms of ecological electricity generation, but the future doesn't stop there. Ultimately, it's about optimising the entire system! It is not only the production of electricity that needs to be changed, but also the efficiency of the energy in its application. After all, solar electricity is DC electricity - but our households are AC.
DC means "direct current" and means exactly that. This means that the strength and direction of the current do not change. We know direct current (DC) from the car as a 12-volt cigarette lighter or the 5-volt USB plug for the mobile phone.
DC grids that work with direct current are still rather rare. They are also known as DC microgrids or DC links. They are usually smaller decentralised networks within neighbourhoods, areas, commercial enterprises or energy cooperatives (ZEV).
AC means "alternating current". In this case, the strength and direction of the current change in a regular rhythm. Our entire household works with alternating current (AC): the 230 V refrigerator, the drill or the electric cooker with 400 V three-phase AC/three-phase current. The electricity from the socket that is taken for granted everywhere is 230 V single-phase alternating current.
The public electricity grid with its overhead power lines, our connection to the house or commercial enterprise and in neighbourhoods or areas is alternating current (AC).
Renewable energy systems work with direct current (DC), because the energy produced by your photovoltaic system is DC electricity. The same applies to wind turbines, biogas plants, fuel cells or other electricity producers. This energy is converted into alternating current (AC) via inverters and either consumed in households or commercial enterprises or fed into the public alternating current (AC) grid. However, we do not want to discuss the issue of expensive electricity purchases from the utility company or poor feed-in tariffs for self-produced electricity here. It is about the conversion losses due to the multiple transfer from DC to AC and vice versa. The same applies to the problems of critical grid connection power when feeding large amounts of energy into the public AC grid.
Your computer, your TV, your e-vehicle, LED lamps or electric motors of your machines work with direct current (DC) - everywhere in your household or business there are, visibly or invisibly, built-in power supplies with current transformers that have to transform the 230 V current (AC) from the socket back into direct current (DC) of a lower voltage in order to operate the devices. If the electricity from your photovoltaic system is DC electricity and many appliances also need DC electricity, then why the constant conversion from DC direct current to AC alternating current and back again? Because these conversions mean a loss of energy each time and thus impair energy efficiency. Valuable electricity is wasted "senselessly". The answer to this question of why can be found, among other things, in the history of electricity.
The energy from the roof of our photovoltaic systems is delivered as direct current (DC). Conversion losses to alternating current (AC) are a big problem and ultimately reduce our returns. What if the conversion losses could be kept lower? Let's do the math:
Conclusion: With a DC grid, conversion losses can be reduced by half.
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One of the biggest challenges regarding the future public AC grid is still ahead of us all. The addition of photovoltaics by 2050 is gigantic in order to guarantee sufficient security of supply together with all other renewable energies: 12,000 MWp of photovoltaics will still have to be installed. It is not possible to feed this energy surplus of thousands of megawatts into the public grid. The AC grid is not designed for this. The necessary grid expansion to accommodate these "energy tidal waves" costs a fortune. The consequence of this insufficient AC grid connection power is that photovoltaic systems or energy consumers are disconnected by the grid provider or PV systems that are too small to be installed. This is because the greater the power of the photovoltaic system, battery storage and charging stations, the greater the AC grid connection must be designed to allow for increased grid connection powers in order to accommodate simultaneous access. In addition, overloads due to electricity peaks and overproduction due to irregular renewable energies require increasingly complex energy and load management at the utility company. All this means either accepting a gigantic energy loss or not exploiting the PV potential.
With a DC-coupled system, the full potential of a photovoltaic system can be used because the DC electricity produced is already passed on to its consumers within the DC grid, stored and only the surplus is fed into the public grid - all with low conversion losses. Especially in the case of "oversized" solar plants, which often do not get a permit for their plants due to the low grid connection capacity or face enormous additional costs for grid expansion, a DC solution with direct sale of the produced DC electricity to the closer environment is a sensible alternative. In this case, connection permits from the utility company are no longer necessary, as you can work with the existing grid connection. This is a win-win situation for both sides: The PV system owner can fully exploit his potential and the EVU does not have to expand its AC grid and has fewer worries with its energy management. Another advantage of a DC microgrid is that no energy management is necessary, as the voltage in the DC link is automatically regulated by the participants.
In the illustration below, you can see an example of a DC microgrid in the upper part. Below the DC link, the familiar AC grid continues to exist with its previous connections. With innovenergy's DCmaxx© concept, we are making a contribution to the energy transition - through energy-efficient DC grid solutions and our ecological salimax© salt battery storage systems.