Batteries make plug-in solar more cost-effective by time-shifting power

Plug-in solar systems alone often fail to match household energy usage, as peak solar generation occurs midday when homes are typically empty. Adding batteries allows storing solar or cheap off-peak power for use during expensive peak hours. This approach requires a time-of-use tariff with a significant rate spread to be worthwhile.

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The article highlights a fundamental timing mismatch: solar panels generate maximum power around midday, while most households consume the most electricity during morning and evening hours. Plug-in solar systems are also size-limited, with typical allowances around 800 watts in permitted regions and up to 1,920 watts in Colorado — far short of full household needs. Battery storage solves this by capturing midday solar output or inexpensive off-peak grid power for later use.

However, every charge and discharge cycle introduces efficiency losses, so the financial benefit depends entirely on the rate structure. The author's calculations indicate that time-shifting only pays off when a time-of-use tariff offers a substantial difference between peak and off-peak electricity prices. Without