ETIP Photovoltaics

Roadmap 2

Improved efficiencies by integration of PV-systems in DC-networks

Rationale for Support

The presence of DC grid is becoming evident as more and more sources and systems in the integrated grid are DC reliant. PV generation is DC based but primarily it is trans- formed to AC for storing or use even though applications to a great extent are DC operated. This reality is generating the obvious question as to why generated energy is con- verted to AC for use. This approach is generating transfor- mation losses that can be avoided if energy is directly used in the physical form that is initially generated i.e. DC.


The AC grid is still currently a highly interconnected system dependent on centrally generated energy away from load centres, that is either directly generated or transformed to AC to achieve long distance transmission to reach econom- ically the end users. However, distributed DC generation is rapidly growing and is used on our roofs, yards or other premises that are nearby load centres. Moreover, battery systems, electric vehicles, heat pumps and others are di- rectly DC operated or they are more efficient when they are operated in DC. Direct use of the DC energy generated is an obvious choice, thereby avoiding costly conversions.

Targets, Type of Activity and TRL

The objectives of this roadmap include developing systems and solutions for which PV as the energy source is directly connected to DC driven systems to achieve improved effi- ciencies. The following targets are anticipated:

Combining batteries with PV for minimizing inverter costs and improving overall system efficiencies. This requires optimal sizing of systems for lowest cost both in capital investments and operational costs. Sizing of storage systems will be quantified in rela- tion to the wider needs of the interconnected sys- tem leading to low-cost aggregated systems for the DSO, energy communities and end users. Based on vehicle to grid technologies, EV batteries as well as stationary batteries can be used to support flexibil- ity and grid management. This exercise will lead to defining optimum battery /PV capacity depending on demand for households, energy communities or large-scale systems etc.
Combined systems using DC where possible to the highest degree of integration (ex: PV+ heat pumps + EV charging + electrolysers etc) including DC to DC EV charging where it is economically viable adding power when required for faster charging and flexi- bility to the system for optimal use of resources for the benefit of the integrated grid. The integration of PV plants with HP and storage systems including thermal storage where optimal solutions favour such options, can increase the share of self-con- sumption of energy produced with minimum im- pact on the electrical AC grid. However, sizing is a wider issue and this calls for a system approach that energy communities, aggregators and wider service providers will optimise for the benefit of all inter- connected users.

Planned activities for developing the required DC or hybrid AC / DC system solutions based on PV as the source of en- ergy are the following:

  • Action 1: Technical development of DC systems for providing heating, cooling, hot water and DC appli- ances in buildings using PV as the resource moving TRL from 6 to 8 by 2025
  • Action 2: Commercial development of DC systems for providing heating, cooling, hot water of build- ings using PV as the resource moving TRL from 6 to 8 by 2027.
  • Action 3: Technical and commercial development of DC or AC/DC hybrid systems to meet the needs of energy communities for providing heating, cooling, hot water, DC appliances and e-mobility using PV as the resource moving TRL from 6 to 8 by 2027.


Possible KPIs that can be utilised for capturing progress in the above identified R&I fields are:
KPITarget Value
Systems to be commercially available for pro-
viding heating, cooling and hot water directly
from DC powered systems relying on PV as the
source of energy

By 2025: efficiencies surpassing 20 % com-
pared to AC alternatives

The hybrid AC / DC systems in buildings based
on PV as the energy resource.

By 2027: to be the norm in new buildings with
DC covering the needs for heating, cooling,
hot water and e-Mobility

The hybrid AC / DC energy community systems
resourced primarily from PV systems.
By 2030: achieve 30 % improved efficiencies
using DC as the prime source for heating,
cooling, hot water, DC appliances and e-Mo-