HowardH
Member
Hi guys,
I am building a new house and in the future i am planning to install solar panels with a home battery (between 2-5 years when the price is right), just wondering what type of instantaneous hot water system should i go for in preparation for it, gas or electricity?
I am leaning towards electric, the upside is that it will be free once the battery is installed, the downside is that its more expensive to run compared with gas.
thanks
These days Gas isn't cheap.
If I was building again I would be going for a heat pump rather than a gas system as it's much cheaper to run.
With an induction hob and reverse cycle air conditioning you don't need gas, and straight away are saving the gas standing charge + the connection charge.
As far as the solar goes getting solar panels now and running the heat pump during the day means that hot water is going to cost you little from day 1.
With current prices of solar panels and electricity rates there is no point waiting to put the panels on the roof. You can always add a battery in a couple of years.
Benny
Member
Go electric but not instantaneous. They consume heaps of power for short time periods - e.g. 13kW and mean you have to oversize your inverter capability. Get a storage electric system and spread the heating out over a longer time - just resistive if you have heaps of panels/generation or heat pump if you don't have much generation to spare.
Heat pumps are expensive but if you can save having a gas connection you can pay the difference off pretty quickly.
They are also very efficient, typically providing 3 kw of heat for each kw of power in. If that kw is solar then you will be saving a lot.
Johnnojack
Member
Some maths to look at. Heat pump costs $2500 plus installation. If it's a 5kw output it will need about 2 kW of solar panels to run it. Spending the $2500 on extra solar panels gets you about 3kw of panels which added to the 2 kW makes 5kw (rated not actual) to use for hot water, so the same result with no moving parts or noise. My figures may be out a little so feel free to correct them. While a heat pump can be run at any time to make hot water, solar power can be used for other stuff and credits from FIT.
Benny
Member
You'll find a lot of debate about whats better - heat pump or resistive heater - but its really up to you and your budget. Heat pump overall is more efficient (4 times better than a resistive heater) but of course you pay a few thousand dollars to get that efficiency. If you can fit/afford a big PV system - say 5kW with 6.5kW of panels, you'll probably have plenty of energy available to heat your hot water resistively - depending of course on how much hot water you use! 5kW should give you 15kWh per day in winter - worst case (apart from cloudy days of course!). 1kWh will supply 20L of hot water at 60C.
So you need to evaluate it for your particular case. How much hot water will you use and how much energy to heat it. How many PV panels do you plan to buy and how much "spare" energy will you have to heat water. If a lot then get resistive. If not much you need a heat pump to boost the efficiency.
Lance
Key Master
Ben, that's true, but bear in mind that resistive element water heaters are a lot more reliable than heat pumps and a lot simpler to fix, and also require a great deal less energy to make, having a simple element instead of a complex heat pump system.
I have no idea what the embodied energy of a heat pump is though, is bound to be considerably less than the energy needed to run a resistive unit over 10-15 years, so they probably come out in front, assuming they last for a decent amount of time. Unfortunately, with some models, that most definitely hasn't been the case, although a unit like the Sanden is most likely going to be quite reliable.
Johnnojack
Member
If it's a Sanden Heat pump then the refrigerant which escapes is CO2 which will not have a major impact, considering the amount.
