On-site energy matching indices for buildings with energy conversion, storage and hybrid grid connections

• Six indices are defined to aid the matching analysis of the on-site energy system.
• These indices cover electrical, heating, and cooling energy forms.
• The conversions between different energy forms can be illustrated and evaluated.
• Impact of single or hybrid storages on matching can be analysed by these indices.
• On-site energy system with bi-directionally connected hybrid grids can be analysed.

In order to meet EU objective of nearly zero-energy building, mismatch problem is an inevitable side effect, which requires suitable criteria to quantitatively evaluate the problem. There are two commonly used basic indices for matching analysis: on-site energy fraction (OEF) and on-site energy matching (OEM). OEF indicates the proportion of the load covered by the on-site generated energy, while OEM indicates the proportion of the on-site generated energy that is used in the load rather than being dumped or exported. However, with rapid development of energy technology, matching problems become more complicated when a system involves different energy forms, energy conversions, storages, and hybrid grid connections. In order to meet these challenges, six matching indices are defined based on the extension of the two basic indices. Four examples at one time-step are presented for the usage of these extended indices’ equations. Furthermore, in order to evaluate the applicability of these extended indices in a dynamic simulation process, the hourly and daily matching situations of one Finnish single-family house with hybrid grid connections are simulated for one summer's day. It shows that the extended matching indices are powerful tools for assessing the matching situation of increasingly complicated on-site energy systems.