Is your solar hot water really so green?

Showering in solar hot water, it feels good outside and in. But what if your decision to shower in solar was, in part, misguided and is propping up the gas industry?

Well that's the case with most of Australia's existing solar hot water, backed by perverse government subsidies which favour domestic solar boosted by fossil gas.

Now, if you've reading this and you've got a gas-boosted solar hot water heater already, don't get me wrong, you did the right thing at the right time.

But times have changed and the now climate solution is renewables boosting renewables. Edson, an Australian hot water services manufacturer, has released their Heat Pump boosted solar hot water heater – or, as they put it, their Solar boosted heat pump.

Edson are combining the two most abundant renewable resources available to Australians: renewable ambient heat, which is the biggest source of domestic renewable resource, combined with direct solar through a set of evacuated tube collectors, which is our second biggest renewable resource.

In the past, my own gas-boosted solar hot water heater (even I had one once) was boosted over 35 per cent of the year by an instantaneous gas booster. This gas booster used a huge amount of gas and electricity (yes, electricity as well) in order to perform its task of delivering me up to 60°C hot water.

Now, with a stand-alone heat pump, or heat-pump boosted solar hot water, we can get 85-90 per cent solar or stored solar contribution in Victoria, and more in other states, of our annual hot water directly from the sun using evacuated tube collectors on our roof and from the delayed solar energy that is stored in the environment using a heat pump.

If you're not sure what a heat pump is, think of your refrigerator.

Turn it around so the cold inside part is facing outdoors and the hot area at the back is heating up your hot water. That's one of the most efficient ways you can heat water.  Of course you can do the same with your spaces eliminating gas heating in favour of reverse cycle air conditioning, equally important but that's another story.

With a heat pump boosted solar hot water unit, you can expect about 65 per cent of your hot water to be from the sun via the solar collectors and around 25 per cent from the stored solar heat in the outside environment.

Edson Australia's unit goes a step further, utilising a very quiet, climate-friendly, high-end Japanese CO2 heat pump. CO2 in a small volume with an insignificant global warming potential should be mandated for all heat pumps in Australia. In fact we must commence phasing in CO2 for refrigerators, for hot water heat pumps and for reverse cycle air conditioners. In an Australian first, Edson is offering a CO2 heat pump for hot water.

Now that the right product has hit the market, In order to encourage uptake and a trend in bringing more high quality units to market, the federal government should be offering additional incentives to get people to specifically purchase heat pumps based on CO2 refrigerant. And in the near future, solar installations boosted by gas should not receive renewable energy certificates, and should be phased out in favour of straight heat pumps and heat pump-boosted solar.

In addition, households with existing gas-boosted solar hot water systems should be offered a rebate to either upgrade to a new heat pump-boosted solar, or to retrofit in a heat pump storage system to eliminate gas and make them truly renewable and clean.

For those wondering why you shouldn't just use a cheaper resistive electric kettle style booster rather than going for a more expensive high quality heat pump, then consider that it can cost a few thousand dollars to provision each 1000W of capacity on the grid.

With a CO2 heat-pump boosted solar hot water service in most locations the worst C.O.P would be just under three, meaning that instead of provisioning 3600W for an electric kettle-based resistive element heater, the grid only needs to provision 1000W for a heat pump unit, which is the case with the CO2 Edson model. This is important when costing the entire system.

And for those wondering about problems with heat pumps in the past, units that include a resistive element should be banned, and COP performance at 7°C shouldn't be below 3 while 0°C COP performance should be well above 1.

A switch to gas will likely produce four times the emissions than an orderly phase-out in favour of renewables. Coal and gas, equally, must be phased out and no new installations should add to the problem. A shift to heat pumps for our hot water and heat pump-boosted solar solves this problem. The products are commercial and available on the market. And if you're just waiting for economies of scale to get the prices down, appropriately directed government incentives can make this shift happen in a very short period.