We recently moved into our new house and the current hot water system is an LPG storage unit which uses a lot of gas. At $1.60 a litre (how does Origin get away with that?), it's costing us around $5 a day, so the crappy water heater has got to go.
My thoughts are either:
1) Instantaneous 6 or 7 star unit, such as a Rinnai Infinity 16
2) Close coupled evac tube system mounted on the roof immediately over the current water heater position (closest point to the current pipework)
3) New off-peak electric unit with a remote solar collector
4) New off-peak electric unit with 1.2kW of PVs running the bottom element
5) Sanden heat pump (the only one with reasonable efficiency in cold Tassie that I can find).
So, thoughts?
My own thoughts are that:
Heat pumps are overly complex, expensive and prone to failure, so they are low on my list. Not sure about the Sandens, but most other brands have many available horror stories about owners waking up to no hot water.
The instantaneous option would probably halve our gas use by increasing efficiency and removing the pilot burner, but it's still expensive bottled gas which is only going to get more expensive.
Close coupled evac tube systems are pretty cheap now, at least the open vented direct imports are. My main issue is that it would add another 3 metres to the hot water pipe run. Not a train smash, but would be nice to avoid.
The electric/remote coupled option I would do with an evac tube collector and a simple DC circulation pump running off a small PV panel, probably controlled via a simple thermostat that runs the pump when the tubes are above a certain temp.
The electric/PV option is probably my preferred as it is the simplest and easiest to implement of any system with a solar component. As we use most of our hot water at night, the boosting would most likely be manually controlled, at least until I have a chance to make a smart controller.
The other thought was that we just go with a standard off-peak electric with no solar input and install a 3kW GI PV array. This way we heat water with off-peak priced elec (about 13c/kWh) and get paid full peak prices for energy generated (27c/kWh).
But, the big fly in the ointment with that option is that the grid voltage here is already excessively high, around 250V most of the time. Adding 3kW of PV pushing into the grid is going to push that higher, possibly over 255V, which is too high and will result in dead electronics. Within a few days of moving in here we had several failures of devices that had been ok elsewhere. The high grid voltage combined with voltage spikes from the Davey bore pump (not my choice, it was already here, when it dies a solar unit goes in instead) are the most likely cause. I am in the process of adding powerline filters to the important stuff like the PCs and entertainment setup, and will also build a couple of voltage reducers to drop it down to 230 or so.
So, unless I can get Aurora to fix the grid voltage here (not likely, looks like the pole transformer is a fixed tapping unit, not adjustable, so would have to be replaced) then GI is a problem. We also want to take the house off grid eventually, power supplies are pretty variable here.
So, thoughts on the best option would be appreciated by all, thanks!
Luckily our daily temps are high this time of year so no hot water isn't a big deal.