Net Zero Energy Solar Buildings – The German Approach

Bergische Universität WuppertalDepartment ArchitectureBuilding Physics and Technical Services Prof. Karsten Voss, Eike Musall M.Sc.arch.

Net Zero Energy Solar Buildings –The German ApproachDanish Net ZEB Conference, Aalborg, 25th August 2010

Prof. Karsten Voss, Eike MusallUniversity Wuppertal, Department Architecture, Building Physics and Technical Services, Germany


Content Introduction

The German Building Energy Code –On-Site Renewable Power Options

Net ZEB Settlement –A Mixed Source Example

The Solar Decathlon -An All Electric Solution Set

Outlook & Definition(s)


Wuppertallatitude 51° n

longitude 6° e

380.000 inhabitants,city of the suspension

railway, built 1901 and still the major public transport in

town

Wuppertal


The Net ZEB Data Base currently registers about 300 Projects


state 1

city 9

resort 8

settlement 14

appartment building 23

single residential building 69

special typology 41

office building 52

factory 5

high rise building 6

educational building 25

experimental building 17

polar 3

snow 47

warm temperate 190

equatorial 11

arid 12

unknown 21

The Net ZEB Data Base currently registers about 300 Projects

Building Types Climate

Outlook: A Net ZEB section will be part of the US DOE high performance building data base


The Focus of the IEA ActivityNet zero energy / emissions in the building sector might be based on

energy efficient buildings in combination with grids 100% based on renewables, or on-site Net ZEB solutions

credits exceed energy demand(“plus energy“)

energy demand exceeds credits

energy demand

energy credits forelectricity generation

demand reduction

credits


„If a building uses power from renewables, the generated electricity can be subtracted from the monthly electricity needs, if

power is generated on-site andpower is mainly used on-site and only excess electricity is fed into the utility grid.

Only that amount of electricity is counted, that covers the needs on the monthly bases. “

All calculations within the national building energy code consider energy demand of service technology only. As feed-in electricity is taken as part of the grid, seasonal balancing of winter needs by summer excess electricity is not taken into consideration. The PV yield is considered only to reduce the monthly electricity needs. Other demands such as fossil fuel for space heating can not be balanced.

PV as Part of Building Energy Concepts2009 German Building Energy Code


A simple Example:1,000 m², 3 storey office building, central heating by condensing gas boilerpartly air conditioned6 zone energy modelling (+ car park)south oriented PV generator, 35 ° inclined on the roof Source: M. Lichtmeß


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Aufteilung Primärenergiebedarf

Lüften Beleuchten Heizen Kühlen

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Primärenergiebezug in kWh/(m²a)

Netto‐Null‐Primärenergiebilanz

Netto‐NullenergiegebäudeReferenzgebäudeOrginalgebäudeOriginalgebäude mit PV (30,9KW)Zielwert über Teilkennwerte

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Aufteilung Primärenergiebedarf mit PV

Restbedarf Nullenergie Ertrag über PVLüften BeleuchtenHeizen Kühlen

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Strombilanz und PV‐Anlage (30,9 kWp)normativ nicht anrechenbarer Ertrag PVanrechenbarer Ertrag PV (88%)Gebäudestrombedarf

Example Calculation for a 1,000 m² Office Building

Primary Energy Demandwith 30.9 kWp PV

Primary Energy Demand


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Primary Energy Demand 30,9 kWp PV, 230 m²


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37 kWp

300 m² PV


Proposal for the 2020 Standard of the Energy Code Reference Building


Findings Balance BoundaryElectricity for appliances and miscellaneous loads are not taken into consideration. In high performance buildings like Passive Houses a major part of the electric load is not addressed. Load matching is not correctly estimated.

Fuel Switching and Seasonal BalancingThe building code does not credit feed-in electricity to balance seasonal electricity mismatch and/or the use of fossil fuels. Net ZEB options almost not exist within this framework. Feed-in electricity is taken as part of the grid, thereby reducing its primary energy factor.

PV alone is not sufficient in Multi-Storey BuildingsDu to limited roof space per energy consuming floor area additional options become relevant, specially in building renovation and building types with high energy needs. Decentral CHP is the most relevant technology.

ZEB practise in Germany differs from the building code perspective!


Solvis Zero Carbon Factory, BraunschweigArchitecture: Banz & Rieks, Bochum Energy Concept: solares bauen, Freiburg

8,000 m² factory and office building, 600 m² PV roof generators,

rape oil CHP unit

Fuel Switching Example: Net Zero Carbon Factory


Freiburg Solar Settlement, Architecture & concept: Rolf Disch 11.000 m² estate with 59 timer built terrace houses, 3.150 m² PV roof generators,

district heating partly wood ships basedFuel Switching Example: Solar Settlement


basis: source energy, non renewable (0.9, 2.7)

net zero energy

“plus energy”

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0 50 100 150 200total source energy consuption in kWh/m2a

total source energy credits in kWh/m2a

Monitoring Results

total source energy consumption in kWh/m²a


A build according national building code 2007

B energy efficient appliances

C Passive HouseD local heating grid partly

based on renewablesE feed-in credits

ABCD

E

Road to Sucess

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Primärenergiegutschriften in kWh/m2a

total source energy consumption in kWh/m²a

total source energy credits in kWh/m²a


Net Zero Energy but Different PerformanceAlthough having an equalized annual energy balance Net ZEBs might differ in

load matchingthe temporal match of the energy generation on site with the building load grid interaction the temporal match of the energy transferred to a grid with the needs of a gridfuel switching the match between the type of energy imported and exported.

Some energy concept may intensify stress on the local grid for example on the seasonal level, thereby worsening its energy or emission performance. The temporal match/mismatch occurs on the daily level - e.g. excess solar power generation during daytime with electricity needs from the grid during night - as well as on the seasonal level (in most climates). Local power grid stress is maximised in concepts based on off-site options to compensate for on-site demands or on-site power generation offsetting fossil fuel utilization for space heating/DHW.


On-Site use of On-Site generated power avoids transportation and storage of electricity within the utility grid.

On the other hand, benefits from levellingout the mismatches between individual buildings and the „economy of scale“ may not be utilized thereby increasing Net ZEB investment costs.

On-Site versus Off-Site Options


All Electric Net ZEBMany of the known Net ZEBs are all electric buildings. Beside feeding the appliances and plug loads electricity is used for space heating, DHW and cooling by heat pumps. An increasing number of low energy, non domestic buildings apply ground coupled, reversible heat pumps for all year space conditioning. The heat pump application increases the seasonal mismatch by adding a load in times with low PV yield. Team Wuppertal Solar Decathlon Home 2010, Madrid. Photo: P. Keil


Load Matching in an All Electric Home

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8 power in kW feed in power grid supply PV yield load

18.6. 19.6. 20.6. 21.6. 22.6. 23.6. 24.6. 25.6.

Monitoring results for the competition week of the Team Wuppertal Solar Decathlon Home 2010, Madrid. Photo: A. Garridio


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Load Matching in an All Electric HomeEven though the wording “Net Zero Energy Building” focuses on the annual energy balance, large differences occur between solution sets in the amount of grid interaction needed to reach the goal.

Simulation results for the Team Wuppertal Solar Decathlon Home 2010 with a scaled PV generated able to match 100% of the annual load. The cumulative graph (left) describes the seasonal mismatch between demand and supply of electricity. Depending on the balancing interval the load match index strongly varies. Net metering lead to typically 30 to 40% load match in a residential building in Mid European climate.


=~ grid

0120

sub meteringinverter batteryPVgenerator

0005

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=~

AC/DC converter

reducing peak loads and mismatch

lightingappliances

0125

metering

HVAC back-upDHW back-up

electric loadsIntelligent energy management

Improved Load Matching by Small Electric StorageLoad matching can be improved by adding small electric storage. This strategy is favourable only in a network with smart metering and time-variable electricity costs. The load and storage capacity of electric transport are options in future scenarios.


Outlook Zero Energy/Carbon Energy InfrastructureIncreasing the fraction of renewables in the energy infrastructure improves the options for cost effective Net ZEBs for new and existing buildings.

Integrated Thermal and Electricity ManagementNet ZEBs create the need for an integrated power and thermal energy management to optimize load matching and grid interaction. Smart metering, small batteries in the building and electric vehicles are future options for the integrated energy management.

CHPBuilding integrated CHP operated with biomass is an important option for existing and multi storey buildings.

Life Cycle AssessmentAll Net ZEB solution sets must be analysed on life-cycle energy/carbon and cost level to judge about future perspectives.


DefinitionsZEBA ZEB is non grid connected building fully matching its annual energy needs/consumption by on-site generation fully based on renewables.

Net ZEBA Net ZEB is a grid connected, energy efficient building that balances its total annual operating energy needs /consumption and associated carbon emissions by on-site feed-in credits. Focus of the on-site generation is matching the on-site load.

Net ZE ClusterA Net ZE cluster is a network of buildings fulfilling the Net ZE definition not on the level of each building, but a cluster of buildings using the identical energy infrastructure. The clusters uses benefits from the economy of scale and levelling out the load and generation profiles of each building.



TechnologiesSolar Power

PV 1 kWhelectricity supply

1 kWp PV (= 8 m²) delivers 900 kWh/y in Wuppertal. Scaling is no Problem, but roof space is limited in high buildings. Output relates to climate and orientation and varies with solar availability.

Co Generation (CHP)

CHPfossil

4 kWh

1 kWh

0.4 kWh

2.6 kWh

thermallosses

heatsupply

source energy

electricity supply

By generating 1 kWh electricity 2.6 kWh heat is produced and must be utilized. Downscaling and biomass feasibility of CHP units with high efficiency still is a technological challenge.


Energy Supply System


A major communication advantage of the Net ZEB concept is the absence of energy performance indicators such as kWh/m², removing the need to define benchmarks and reference areas. The focus is the balance. This simplicity is the background for the high political and public acceptance of the concept. It has become part of the current EU as well as the US energy policies. In the 2010 recast of the EU Directive on Energy Performance of Buildings it is specified that by the end of 2020 all new buildings shall be “nearly zero energy buildings”.

Net ZEB Policy

Net Zero Energy Solar Buildings – The German Approach

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