Home Solar Batteries: 2.2a Demand - Annual / Quarterly

Home Solar Batteries - Modelling Performance

Introduction

This post specifically addresses the charging of domestic battery systems using solar PV and forms part of a series of entries looking to establish a reasonable view as to how the combination of solar PV and battery storage system should be modelled to ensure that information available to consumers should be considered accurate enough to establish a reasonable justification for investment in storage technologies.

If this is the first time you've accessed this information it is recommended that all of the relevant posts are considered in order through accessing the 'relevant posts' links

Demand Modelling

Firstly, it is important to note that the more accurate the household energy demand data that is available, the more likely an accurate assessment of the amount of spare solar PV self generated energy which is available for export or diversion to domestic battery storage can be.

Annual

Energy suppliers within the UK are mandated to provide their customers with information relating to annual consumption for both gas & electricity within each bill as per the example highlighted here.

Using annualised demand figures to model the performance of a battery provides for basic assumptions to be used to estimate excess energy available for either export or diversion to batteries.

Unlike the estimation of solar PV generation discussed in section 2.1, the pattern of energy usage is to a large extent controllable by the household and normally has relatively little variability on a day-to-day or even week-to-week basis, however, in circumstances where electricity contributes towards space heating there will be a marked asymmetry between winter and summer usage.

Home Solar Battery - Annual Performance Model

The Annual model chart shown here illustrates the effect of applying annual solar PV generation to annual consumption.

In this case the PV generation marginally exceeds the demand, therefore an unscrupulous argument could be made to claim that such a household wouldn't need to import any energy if a domestic battery of sufficient capabilities was provided, however, as the thought process develops, we'll find that the logic employed in such an assumption totally unravels.

Quarterly

As briefly touched upon above, when compared to the variability in generation inherent in solar PV systems, demand tends to display relatively little difference on an averaged basis, but where there is a seasonal difference in electricity usage this can be modelled by utilising quarterly usage.

As energy efficiency technologies such as LED lighting and TVs permeate further into the domestic market many households will likely notice a significant reduction in any seasonal energy usage imbalance. The effect should be more apparent in households that either currently have, or plan to install, solar PV systems without batteries, this resulting from the differential in daylight hours and the affect this has on self consumption of the home's own generation.

Summary

Obviously, both of these methods should be considered as nothing other than a basic reality check to test information being provided related to battery performance claims.

As previously mentioned when considering the various generation model candidates, there have been numerous reports of potential suppliers justifying home battery costs based on payback figures which look to have been calculated using such basic information.