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Using Your Excess Solar Power To Heat Water Can Make A Difference

In many areas the amount you are getting paid for your excess power going back into the grid has dropped substantially.

It is now becoming economically viable to store that excess energy and reduce or eliminate other utility bills

In many cases water is used instead of batteries and here’s why.

Water works

A major energy demand in any home (often around 20%) is for hot water. Most Australian homes have gas-fired, electric-resistive, or rooftop solar thermal water heaters. But gaining in popularity, given its now favorable economics and lower environmental footprint, is the hot water heat pump.

Hot water and space-heating heat pumps work like fridges and air conditioners. They use a refrigeration cycle to pump heat “uphill”, from a colder zone to a warmer one. The benefit we enjoy with fridges and air conditioners is the cooling that occurs when heat is pumped from somewhere we don’t want it (such as from our lounge room on a hot summer’s day) to somewhere else (the air outside). For hot water heat pumps, it’s the other way around – we want to gather and use the ambient heat that is always present in the air outside our homes – the way that a reverse-cycle air conditioner does when it is on heating mode.

The best hot water heat pumps can capture up to 3.5 times as much heat energy from the air outside as they use in electrical energy, meaning that the resulting tank of hot water represents a net gain of free renewable energy.

How are these economics possible? As occurred with electricity, the price of gas is going up. According to my most recent gas bill, I now pay the equivalent of 8 cents per kilowatt hour (or A$22 per gigajoule, in gas industry terms).

Gas now costs more (per equivalent unit of energy) than what electricity retailers will pay you for excess solar power. More importantly, when we consider that a gas hot water heater might only be 70% efficient at transferring the heat of the burned gas to the water, whereas a heat pump can effectively be 450% efficient when capturing renewable heat from the outside air, this easily tips the balance.

Read more about the economics of using hot water in the original article

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