converting multi unit strata complex from gas to electric (with solar) hot water - Page 1
Forum section: electronics / general

author: wilfred
author_rank: Super Contributor
timestamp: March 31, 2024, 12:09:22 pm
content: In a multi unit strata complex (in Australia, Victoria) using 3 paralleled gas fired heaters for the hot water is it relatively straight forward to replace the gas heaters with electric grid powered units.I know nothing regarding strata units is ever easy. I want to propose replacing gas with electric and a small solar panel setup solely dedicated to daytime water heating with topping up/fallback to grid power.I want to avoid complexities like solar electricity distribution to units for domestic use. This is just toe in the water stuff solely to get people used to the idea and something that can be done simply and quickly with billing to units done by dividing the single common electricity meter by the portion of hot water used from the total. As it is done with gas now.Plus is there already standard off the shelf technology in common use and where is a good place to find out more about it in Australia. I think there surely must be.I think installation wise it would be simpler to send solar power down from the roof than water up and back down. There are no risers.I'm really just asking people who have some experience, good or bad, to point me at some good resources to read just to get a quick start. The politics of it is another problem entirely. Not reinventing the wheel would have to be a plus and if people can see others have done it then that will lower resistance to change Particularly if there is data on payback interval.Thanks for reading and thanks if you can point me in the right direction to hit the ground running.

author: Someone
author_rank: Super Contributor
timestamp: March 31, 2024, 10:04:48 pm
content: Problem is most solar companies just want to sell you stuff rather than use existing solutions, so you end up with uneconomic chains of single purpose boxes:https://www.solarquotes.com.au/hot-water/pv-diverters/Almost always the more cost effective solution is to use an off-the-shelf 24 hour timer to allow the heating loads power during off-peak, and the peak solar production hours (which on a ToU tariff are usually exceptionally cheap too). Some times a small gain in profit if you have tanks with multiple elements or thermostats than can be directly accessed.That's 99% normal stuff with the solar installed without regard for what it is connected to, its just the same as it would be for any residential install.There is no one size fits all analysis, it is all specific to the tariffs you have access to and betting on where the prices will lie in the future.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 31, 2024, 10:21:25 pm
content: Just install the solar with a grid tie inverter and use a contactor connected to some sort of controller to control the water heater. Consider a heat pump, that will reduce the solar required down to 1/3 to offset the consumption.

author: pgo
author_rank: Regular Contributor
timestamp: April 01, 2024, 04:37:47 am
content: Hi,We recently installed Solar and have what was originally an off-peak electrical hot water. We now have a diverter.I think it is better to install a diverter e.g.https://www.catchpower.com.au/than to simple use a timer system in this case.This makes much better use of the available electricity by spreading electrical consumption based on the available solar.For example our HW takes about ~3kW. If the array is providing more than that no problem. If it is below 3kW then it is better to reduce the power consumption of the HW system and spread it across more hours of solar rather than exceed the solar power available and use power from the mains.It also controls top-up to off peak time so you avoid heating during peak (as would a timer BUT you don't have to lose solar during peak cost times).Anyway worth considering although in a strata title the real headache is costing the actual use of the HW.However - a heat pump would be more efficient but I'm unsure how it works out in detail as I believe they can only be operated at full load?Anyway, something to consider.bye

author: David_AVD
author_rank: Super Contributor
timestamp: April 01, 2024, 05:42:45 am
content: I'm assuming that there's a body corporate in place and that there's already a separate meter for the common property electricity (exterior lighting, etc)? I don't know what the implications of putting a solar system onto the common property power is. Do solar rebates apply and if so, to what entity?As soon as I got home solar I changed from off-peak (separately metered) to a simple timer (on roughly 9am - 4pm) on the normal power buss. The change paid for itself very quickly and the HWS power used is almost always part of my self consumption (the lost export is ~ 5 times less than off-peak price).My HWS is resistive so there was no added cost there. Changing to a heat pump would use less power, but resistive is silent, simple and reliable. It would have taken a lot of use to get back the difference lost in export. I also reduced the element from 3.6kW to 1.8kW, so while it takes twice as long to heat the tank, it stays well under the solar generation curve most of the time even with other significant power consumption.

author: wilfred
author_rank: Super Contributor
timestamp: April 01, 2024, 10:21:27 am
content: Quote from: David_AVD on April 01, 2024, 05:42:45 amGood point. noted. Although in this initial plan there will be no other power consumption. Baby steps is the best way to overcome resistance I think. Deliberate punBut we do have common property lighting that can be added.

author: wilfred
author_rank: Super Contributor
timestamp: April 01, 2024, 10:23:50 am
content: Quote from: NiHaoMike on March 31, 2024, 10:21:25 pmHeat pump is a good idea but this building is not designed with convenient free space unfortunately.

author: Ian.M
author_rank: Super Contributor
timestamp: April 01, 2024, 01:05:04 pm
content: By the time you've considered code compliance, provision of accessible isolators etc. it isn't a lot easier to route wiring for photovoltaic panels vs plumbing for solar thermal panels. Both would fit in comparable volume to a typical rainwater downpipe. Solar thermal is far more efficient that photovoltaic (see:https://www.renewableenergyhub.co.uk/main/solar-panels/photovoltaic-vs-solar-thermal) so you get a lot more heat out of the same panel area. Ideally, you'd simply have enough photovoltaic panel area to run a solenoid valve (to prevent convection in the panel loop cooling the hot water tank), and the circulation pump, both of which could be low voltage DC matched to the photovoltaic panel. Due to Victoria's climate, the solar thermal loop would almost certainly need to run non-toxic antifreeze rather than plain water, to avoid freezing problems on clear winter nights.A two tank or tank + demand heater system would be preferable - solar energy would pre-heat the incoming water and hold it in a tank, which would then feed the heaters with water at least part of the way up to the required temperature.As you have ruled out heat pumps, there is no good reason to replace the gas heaters unless they are either close to end of life or gas costs are expected to be far above electricity costs for the foreseeable future. However their control systems probably need upgrading to ensure that they run as efficiently as possible, keeping as many off as is practical for the demand, avoiding short-cycling and rotating the order they are called upon weekly to avoid maintenance issues due to excessive or lack of use.

author: f4eru
author_rank: Super Contributor
timestamp: April 01, 2024, 03:09:17 pm
content: I concur, PV+heat pump is the way to go.Today, thermal solar is not economical any more against PV.

author: Someone
author_rank: Super Contributor
timestamp: April 02, 2024, 02:11:21 am
content: Quote from: f4eru on April 01, 2024, 03:09:17 pmBased on which heat pump hot water system? All the options I've seen are priced so high they cant compete economically.

author: HarryDoPECC
author_rank: Regular Contributor
timestamp: April 02, 2024, 04:56:02 am
content: Here's another way to approach it:- if going electric, you are committed to storage tanks. So make sure these are reaaally well insulated- put up as much rooftop PV as you want and connect directly to dedicated resistive heaters in tanks - you have made a battery for your panels. Not the most efficient but pretty quick, easy, cheap and maintenance free. No inverter. No grid connect so no complexity from that aspect. OK, no rebates either but the capital cost of all this is not high.- connect the regular electric heater(s) to grid with best timing/tariffs, as you usually would.Set heater thermostats so that grid only tops up when solar is insufficient. Complex controller not required.Can add more PV if desirableCan change to heat pump one day if/when the $ make sense.If you are coming from continuous gas heating then you may have political problems with users who have come to expect continuous, 24/7, "unlimited" hot water. But that will be the case with any electric option.

author: nctnico
author_rank: Super Contributor
timestamp: April 02, 2024, 09:46:58 am
content: Quote from: HarryDoPECC on April 02, 2024, 04:56:02 amSo that will be an impossible sell. People used to having 24/7 unlimited hot water won't be willing to give that up. A better system is to have a hot water storage tank which supplies the gas heaters with hot water from a storage tank. The water can be heated using thermal or PV + heatpump where thermal is the option with least moving parts. Only a pump and the thermostat/controller are needed for thermal. With this setup you get as much as possible you can get from solar energy but still have the convenience of 24/7 hot water.However, the biggest problem with installing such a system is to find an installer who does a good job and doesn't drive the price up 3 times making the system financially unviable.

author: f4eru
author_rank: Super Contributor
timestamp: April 02, 2024, 04:45:51 pm
content: Quote from: HarryDoPECC on April 02, 2024, 04:56:02 amI don't understand why ?Just dimension the size of the buffer properly for the needs, same with gas, resistive and any other buffer based heat source.Quotehttps://www.billiger.de/categories/11733/86107-warmwasser-waermepumpenSeems the LG WH20S.F5 200L buffer with heatpump can be bought for 1700 Euro. Yeah, a bit pricey, but so is a thermal system with install.Don't forget that with the PV + heat pump, you get plenty of money back over the years from reinjecting electricity when the hot water buffer is full of calories. Not so with thermal, the big summer overproduction has to be thermally managed and dumped.

author: Marco
author_rank: Super Contributor
timestamp: April 02, 2024, 05:09:42 pm
content: Going from one type of boiler to another is simple, going from tankless gas heater to boiler is not simple because some usage patterns can cause problems (family who all like rain showers).

author: Someone
author_rank: Super Contributor
timestamp: April 03, 2024, 01:44:40 am
content: Quote from: f4eru on April 02, 2024, 04:45:51 pmThanks for the example, economics are improving.grid tie PV + heat pump vs grid tie PV + resistive storage is fairly comparable, either way the excess electricity is sold off. Solar thermal or off grid solar are unlikely to be as cost effective.