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As fossil fuels become ever scarcer, the back-up systems for solar heating and cooling systems tend to employ electrical energy. This puts high peak demands on the electric utilities supplying solar heating customers, because the thermal storage of solar heating systems is likely to be empty during cold periods which coincide with the peak loads of winter peaking utilities. Oversizing thermal storage is shown not to be an efficient way of decreasing peak demands from solar heating backup systems. Solar cooling systems, on the other hand, are likely to be beneficial to electric utilities because, in general, sunny weather and periods of summer peaking utility load peaks are coincident. The thermal storage devices of solar systems can be used to reduce electric demand peaks by storing off-peak power. The use of separate storage devices for solar and off-peak electrical energy is shown to be desirable. However, the resultant increase in first cost must be weighed against cost reductions from lower peak demands.