The economic benefit of solar PV improves as more of its energy is consumed on-site. This is possible if the onsite base electric load (minimum load) is substantial and steady relative to the peak load and not less than peak solar power generation. Except for commercial–industrial applications, steady electric loads are not the norm. Dairy farms have high variations in electric loads, especially those batch milking cows in the morning and evening. Here the peak loads morning and evening are typically ten times greater than midday loads. See load profile (blue line) in figs 1 and 2 below for typical dairy farms with these peak loads.

The conventional approach to Solar PV is to install modules on a south-facing roof to maximize the energy generated from the midday sun. But this approach is not ideal for the dairy farmer milking twice a day as peak solar power and peak farm electric loads occur at different times. Here a substantial amount of the solar energy is overspilled to the grid at little or no value. This can be overcome by diverting the surplus solar energy to battery storage and to a lesser extent, water heating and recycled later in the evening. However, lithium-ion battery technology (most popular) is expensive and has an expected service life of 8 – 10 years before performance degradation sets in. There is an alternative solar PV approach.