Page 94 - Zero Net Energy Case Study Homes-Volume 1

CASE STUDY NO. 4
MERITAGE PRODUCTION HOUSES
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Zero Net Energy Case Study Homes: Volume 1
Energy Production versus Energy Use: Zero Net Energy Performance
The energy production and percent-ZNE performance for each house in the ZNE Study Group are shown in the summary table and chart on page 77. The charts of Energy Production versus Energy Use for House #7 and #12 on the pages following give the monthly comparison over the one-year period of data collection.
The Cumulative New Energy Production charts shows the progression of the energy perfor- mance toward ZNE by adding each month’s net energy performance to the previous month’s total—if, at the end of the one-year period of data collection, the curve remains on the positive side of the zero axis, then the building is confirmed as ZNE. Both House #7 and House #12 can be seen to be Net-Positive.
Battery Energy Storage—Impact on Peak Demand and Load Shifting
The unique aspect of this particular case study is the main objective of the research study car- ried out with this project, namely, the inclusion of battery energy storage in nine of the houses in the ZNE Study Group. (The remaining houses had no battery storage equipment.) Each of these houses were equipped with lithium batteries with a 6.5 kWh storage capacity.
With the ability to control the use of this battery storage to modulate the energy demand placed on the utility grid and to shift the periods of peak demand, the researchers could evaluate the benefits to consumer and utility of better “harmony” with the utility-supplied power.
The EMS for the energy supply of the house could be programmed by the owner to operate in one of two ways: (1) simple prioritization to draw first directly from the energy produced by the solar PV panels, then (if the solar panels were in non-producing mode) to draw from the battery and finally (if there is no energy left in the battery) from the electric utility grid; (2) more sophis- ticated program that optimizes “time-of-use” rates to charge the battery thus minimizing utility charges. In practical terms, the latter might involve some overnight battery charging, when rates are low, in anticipation of low solar PV production early on the following day.