Solar Water Heater Savings

Solar water heater savings

A solar thermal collector takes over 60-80% of the electricity an electric shower would otherwise burn, while a gas or electric backup picks up the slack on cloudy days. A 200-litre reservoir is usually enough for a family of 4. The monthly saving works out to savings = people × min_shower × kWh_per_min × 30 × tariff × replacement_fraction. A 5.5 kW shower pulls about 0.092 kWh per minute, so for 4 people × 8 min × 0.092 × 30 you land at 88 kWh/month. At R$0.75/kWh that is R$66/month, and a solar heater can shave roughly R$45-55 off of it. Installation runs from R$3,000 to R$8,000 once you add up collector, tank and boiler, which puts the payback at 3-5 years against a 20-year useful life.

Applications

Middle-income homes, the Minha Casa Minha Vida housing programme with its solar thermal credits, Procel Edifica energy efficiency labelling, hotels and gyms that go through a lot of hot water, off-grid rural houses, and the swap-out of electric showers in older buildings.

FAQ

Does it work in cold or cloudy regions? It does. The collector still captures diffuse radiation, you just lean on the backup more often. In southern Brazil and at high altitude the replacement fraction tends to drop to around 50-60%.

Solar thermal or photovoltaic? If your goal is hot water, thermal wins easily, since it is 3-4× more efficient per square metre. PV earns its keep when you want to offset your whole electricity bill, not just the shower.

How long does the equipment last? Figure on 20-25 years for the collectors, 15-20 for the reservoirs and 5-10 for the electric backup resistance. The yearly maintenance is mostly just cleaning the glass cover.