# Influence of Hydrogen-Based Storage Systems on Self-Consumption and Self-Sufficiency of Residential Photovoltaic Systems

^{*}

## Abstract

**:**

## 1. Introduction

_{p}was installed in Germany [5], corresponding to a share of 5.7% of the annual gross electricity production in 2014 [3].

_{p}[5]. As a consequence of the reduced profitability, only a few PV systems were installed in 2014.

## 2. Modelling

#### 2.1. Input Data

_{p}, which accords well with the average potential of 8.7 kW

_{p}in suburban areas [44]. The roof inclination is 45° and no shading occurs.

^{2}, a generator temperature increase of 27 K relative to the ambient temperature is expected. Consequently, the power output decreases with −0.45%/K compared to the standard test temperature of 25 °C. Additionally, a generator field efficiency of 96.5% (due to losses in diodes, power mismatch, dirt, etc.) and a constant inverter efficiency of 97.6% are taken into account [45]. Power degradation is ignored.

^{2}·a), corresponding to a radiation onto the inclined PV generator of 1382 kWh/(m

^{2}·a), the following annual yields are achieved: 1103 kWh/kW

_{p}(2011); 1,077 kWh/kW

_{p}(2012); 977 kWh/kW

_{p}(2013) (Table 1). Validation of the simulation with a commercial design program [45] in consideration of additional loss factors (data sheet tolerances, cabling, diodes, inverter design, etc.) shows deviations in annual yields lower than 3.5% and accordance with the generated electricity during the whole period under review.

Solar potential | Unit | Value |
---|---|---|

Average sum of global radiation on horizontal surface | kWh/(m^{2}·a) | 1160 |

Average sum of global radiation on inclined surface (45°, south) | kWh/(m^{2}·a) | 1382 |

PV production | ||

Installed PV power | kW_{p} | 8.64 |

Average annual PV yield | kWh/(kW_{p}·a) | 1052 |

Consumption | ||

Annual electricity demand | kWh/a | 4752 |

**Figure 2.**(

**a**) Daily load profiles characterized by day and season type; (

**b**) Fitting function to take into account seasonal variations.

#### 2.2. Direct Consumption

_{res}results from the difference between load demand P

_{load}and PV power P

_{PV}and describes the energy exchange with the grid:

_{p}, power peaks are almost always lower than 6 kW. About 30% of all load demands have a power smaller than 1 kW. The rest is nearly evenly distributed to the power range between 1 and 5.5 kW.

**Figure 4.**(

**a**) Cumulative frequency distribution of demand power; (

**b**) Cumulative frequency distribution of feed-in power.

#### 2.3. PV Storage System

_{use}as well as by maximum filling P

_{in,max}and withdrawal P

_{out,max}rates (Figure 1).

_{st,in}of 60% is conservatively assumed (literature gives values up to 70% for water electrolysis [53]). A fuel cell reconverts hydrogen into electricity with an efficiency ƞ

_{st,out}of 50% [53,54]. No further losses like ageing or self-discharge are taken into account. Neglecting the influence of power level and temperature, storage efficiencies are regarded as constant. An unlimited dynamic behavior according to response time and to changes in performance is assumed due to the lack of knowledge concerning dynamic properties of hydrogen-based storage systems. The influence of this assumption is investigated in Chapter 3.2.

_{st}results from trying to compensate the residual load. Ideally, no power is fed into the grid or taken from it (P

_{grid}= 0).

**Figure 5.**Storage behavior of a PV storage system on three days in April 2011 (PV 8.6 kW

_{p}, storage 8 kWh, demand 4752 kWh/a).

#### 2.4. Assessment Criteria

_{dir}or taken from the storage E

_{out}and the whole energy demand of the household E

_{load}. It describes the part of energy purchased from the grid E

_{grid}that is substituted by on-site generated energy:

_{dir}and for filling the storage E

_{in}and the energy generated by the PV system E

_{PV}. Another possibility of calculating Ω takes into account the energy which is fed into the grid E

_{feed-in}:

_{fc}. It can be determined by the ratio of energy taken from the storage and the usable storage capacity.

## 3. Results and Discussion

#### 3.1. Direct Consumption System

_{p}is about 54%, along with a proportion of consumption Ω of 8.1%. Further simulations are based on the described PV system with 8.6 kW

_{p}.

#### 3.2. Short-Time Storage

**Figure 8.**Degree of self-sufficiency and proportion of consumption in dependence of usable storage capacity.

_{use,opt}is shown in Figure 10. A storage capacity of 50 kWh is determined as a maximum storage size. As described above, a target achievement of 80% obtained by installing a storage system compared to a PV consumption system is selected as a decisive criterion (Equation (11)).

**Figure 11.**Evaluation dependent on storage efficiencies. (

**a**) Degree of self-sufficiency; (

**b**) Proportion of consumption.

#### 3.3. Seasonal Storage

**Figure 12.**Degree of self-sufficiency and proportion of consumption dependent on usable storage capacity.

#### 3.4. Scenarios to Achieve Self-Sufficiency

_{p}PV system, the limitation of the filling rate is raised to 9 kW, just a small increase in the degree of self-sufficiency from 96.4% to 97.2% has an effect, thereby requiring a usable storage capacity of 1.8 MWh instead of 1.6 MWh. As it is shown in Figure 15, a very huge PV system (scenario 2 c) also does not achieve full self-sufficiency. This is caused by a minimal storage level at the start of the considered period, corresponding to a commissioning of the storage system in autumn or winter. The power of the PV system is insufficient for direct consumption and simultaneous storage filling until spring. A minimum initial level is implemented in simulation because not each storage system can be transported and installed in the filled state. Furthermore, different initial levels influence simulation results. Thus, devoid of an initial level, the comparison of simulation results of both short-time and seasonal storage systems is enabled.

_{p}) is necessary to gain a full and sustainable self-sufficiency. In this scenario, the initial level is also outnumbered by the final storage level. Consequently, a low energy surplus is achieved in spite of a bad solar year in 2013 at the end of the considered period. However, the usable storage capacity has to be raised by 58%.

^{3}compressed hydrogen (120 bar) [59].Thereby, a very high proportion of consumption is achieved, which is induced by the high losses at conversion of electricity into hydrogen and vice versa.

## 4. Conclusions and Outlook

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**MDPI and ACS Style**

Pötzinger, C.; Preißinger, M.; Brüggemann, D.
Influence of Hydrogen-Based Storage Systems on Self-Consumption and Self-Sufficiency of Residential Photovoltaic Systems. *Energies* **2015**, *8*, 8887-8907.
https://doi.org/10.3390/en8088887

**AMA Style**

Pötzinger C, Preißinger M, Brüggemann D.
Influence of Hydrogen-Based Storage Systems on Self-Consumption and Self-Sufficiency of Residential Photovoltaic Systems. *Energies*. 2015; 8(8):8887-8907.
https://doi.org/10.3390/en8088887

**Chicago/Turabian Style**

Pötzinger, Christian, Markus Preißinger, and Dieter Brüggemann.
2015. "Influence of Hydrogen-Based Storage Systems on Self-Consumption and Self-Sufficiency of Residential Photovoltaic Systems" *Energies* 8, no. 8: 8887-8907.
https://doi.org/10.3390/en8088887