Our holiday parks offer guests the luxury of a heated outdoor swimming pool at 28 °C all year round. This is an important part of our guest experience and a key differentiating feature. However, heating the pools in winter requires a great deal of electrical energy. At that time, our solar panels generate hardly any electricity. In addition, restarting pools that have been shut down is not efficient: heat pumps operate slowly in cold conditions and consume a lot of energy. **Design a technically and economically feasible sustainable heating system for the pools that: ** Can maintain 28 °C year-round. Significantly reduces electricity consumption. Makes maximum use of renewable energy. Minimises heat loss without creating operational obstacles for staff or guests. Achieves a reasonable payback period within 5 years. **Current challenges ** • High energy costs in winter: the heat pump consumes a lot of electricity at low outdoor temperatures, combined with low solar panel output. • Slow start-up of pools that have been shut down: it takes a lot of energy and time before the pool reaches the desired temperature again. • Heat loss through the surface: a thin roller cover limits heat loss, but the effect is limited. • Insulation panels tested: experiments with insulation panels on the roller cover showed measurable energy savings, but proved operationally impractical (time-consuming and inconvenient for daily use).