Solar diverter impact
I'd like a sanity check.
I have an iBoost driving the top electric element of a water tank that is also on the gas central heating. When I compare the four years prior to installing the solar panels+diverter to the 3 years following, gas consumption fell ~2700 kWh. The difference is very clear with the pre- and post- annual consumption figures to be tightly clustered. Nor am I aware of any change in household behaviour. But my estimates of the annual amount diverted is something around 1000-1300 kWh.
Evidently, I'd expect direct heating through an element to be more efficient than indirect heating via CH but I have hitherto assumed the difference would be minor. Could heat losses from my condensing boiler and pipework to water tank be so extreme? Is it just a summer thing? Or have I just made a mistake somewhere. If true, this radically changes my valuation of diverted electricity that I had previously just assumed it just 1:1 offset gas consumption.
Posted by: @ronin92I'd like a sanity check.
I have an iBoost driving the top electric element of a water tank that is also on the gas central heating. When I compare the four years prior to installing the solar panels+diverter to the 3 years following, gas consumption fell ~2700 kWh. The difference is very clear with the pre- and post- annual consumption figures to be tightly clustered. Nor am I aware of any change in household behaviour. But my estimates of the annual amount diverted is something around 1000-1300 kWh.
Evidently, I'd expect direct heating through an element to be more efficient than indirect heating via CH but I have hitherto assumed the difference would be minor. Could heat losses from my condensing boiler and pipework to water tank be so extreme? Is it just a summer thing? Or have I just made a mistake somewhere. If true, this radically changes my valuation of diverted electricity that I had previously just assumed it just 1:1 offset gas consumption.
It would never be a 1:1 ratio because your gas boiler is not 100% efficient. It could also be that your estimate of the amount of energy diverted is not that accurate. Dependent upon the size of your tank, the level of insulation and the temperature to which the water is being heated, there may be a slight difference in heat loss.
You should take comfort from the fact that you are not burning gas and are getting free energy from the Sun.
I've done a bit more investigating.
The diversion data comes from the iBoost. I don't think it can be too far out, certainly not to the extent that makes my summer gas use look reasonable.
I think the situation being compared is continuous DHW-only heating by the boiler during summer vs diverted electricity-heated DHW generation during daylight hours only. So what is known about gas boilers making DHW in summer? A Carbon Trust report that actually examined this in homes indicated that perhaps only 40% energy consumed in boilers actually makes it into DHW delivered to the users (i.e. leaving HW cylinder). Although 80% of fuel to the boiler actually makes it into the primary pipework, losses in primary pipework and hot water tank are a large chunk of this. Since diverted electricity heats only the top of my tank and that water is used soon after, unlike the boiler maintaining a hot cylinder continuously, it may explain why my summer DHW production is so inefficient.
This episode also forced me to look deeper into my boiler. When my last one died, the heating engineer fitted a Vokera Mynute 25HE, a 25 kW condensing boiler. From smart meter records, the boiler did not output more than 6kW average over an hour even in deepest winter. I just tested it on DHW duties and it heated the tank from cold in 20 minutes and switched off. The spec sheet says min heat output at default conditions is 6kW or so. I think I have an very overspecified boiler and I really doubt it is operating in condensing mode in summer. Unfortunately, I have been unable to measure the return temp accurately with my IR thermometer to confirm this.
Anyway, it does appear that using electricity to heat water in my cylinder in summer is more efficient than using the boiler and this brings the cost of using either rather closer together than I had hitherto believed. I should therefore value diverted electricity at some multiple (2x?) of the gas price when working out the economics of my panels.
- 24 Forums
- 1,413 Topics
- 29.7 K Posts
- 32 Online
- 1,198 Members
Join Us!
Latest Posts
-
RE: ASHP Advice: High Temperature vs. Low Temperature Heat Pump For Microbore
@jamespa I fully agree with James that a HT heat pump...
By Derek M , 48 mins ago
-
RE: Installing your own ASHP - DIY
@tomasmcguinness Have you been able to perform any sani...
By IanMK13 , 4 hours ago
-
All heat pumps will hit the point where their minimum o...
By HarriUp , 5 hours ago
-
-
RE: Viessmann Vitocal 250-A in the UK
For reference, I have a 10 kWh Viessmann 151-A installe...
By GC61 , 7 hours ago
-
RE: Vaillant Arotherm Settings for New Installation
@drew-pa Ah thanks. Good to know I dont have a misconce...
By bontwoody , 7 hours ago
-
RE: Aira Heat Pump: Stylish Scandinavian Heating
On the whole marketing claims vs reality on performance...
By GunboatDiplomat , 7 hours ago
-
RE: Gas Combi to ASHP - Making sense of survey results and proposal.
@harriup If the radiators need to be twice the size t...
By IRMartini , 8 hours ago
-
RE: Microbore Central Heating Plumbing, will it be a barrier / pain?
@mattc All the existing (designed for T50) radiators ar...
By IanMK13 , 22 hours ago
-
The temporary fix has reconnected about 60% of users, a...
By Abernyte , 24 hours ago
-
RE: What is Wrong with our Heat Pump Installation?
Having to run the heat pump during the summer for DHW s...
By Toodles , 1 day ago
-
Issues with Vaillant connectivity via the MyCONNECT gateway
I'm sensing a variety of issues with Vaillant connectiv...
By dr_dongle , 1 day ago
-
Interesting heat pumps installations
Thought it would be cool to share photos of interesting...
By Mars , 1 day ago
-
RE: Say hello and introduce yourself
@Toodles That's very interesting to hear, thanks. I ha...
By dr_dongle , 1 day ago
-
RE: Massive Electricity Cost for Running My Air Source Heat Pump
@allyfish In fairness installer has replied stra...
By Holts , 1 day ago
-
-
RE: Are Solar Diverters Necessary for Homes with ASHPs and Solar PV?
@zzxap19 that's a fair point. With the eddi, is it poss...
By Mars , 2 days ago
-
RE: Delivering a smart and secure electricity system: government consultation
"I don't think I'll need to refer to past iterations of...
By eggnchips , 3 days ago
-
RE: Error on Immersun – Error 8 Load Short Circuit
@julesmp8 fingers crossed. I have to say our Immersu...
By Mars , 3 days ago
-
Latest Topics
-
Interesting heat pumps installations
By Mars 1 day ago
-
What is Wrong with our Heat Pump Installation?
By Mars 2 days ago
-
Fossil Fuel Fired Heating v Heat Pump?
By Toodles 2 days ago
-
Viessmann Vitocal 250-A in the UK
By treehugger 4 days ago
-
By HUBB84 6 days ago
-
By jswhite 6 days ago