Solar PV and Gas Bolier

[Kustom]

Hello all, 

 

First time post. 

Weve just downside and bought a small 1960's bungalow, which is currently heated by a gas combi boiler. There are only two of us most of the time, so a 5 bed house was deemed unnecessary in the current climate. 

 

Were due to have Solar PV and a battery storage installed (Currently on hold due to part availability)

We would like to dump any excess solar into a hot water tank. 

As there is currently a combi boiler fitted there is no hot water tank but we have a space for one in an airing cupboard. 

 

Plan 1 was to install ASHP but the house plumbing is the wonderful microbore system so would require re plumbing throughout to achieve the require flow rates plus potentially bigger radiators so that idea was parked. 

 

Plan 2 was to get a Mixergy cylinder, but this would only help with the DHW and a couple of plumbers have said that its not really suitable for being fed by a combi. 

 

Plan 3 Was to use excess solar to heat the tank to pre-heat water before going into the boiler, I like this idea but unfortunately the old combi (2006ish British gas / Worcester) is not able to accept pre-heated water. 

 

So after some reading around on this forum I think I need some advice on a plan 4. 

New gas boiler (combi or system?)
New tank (Two immersions, two coils, does it need a buffer tank)
Eddi to deal with the diversion

Any help would be greatly appreciated. 

 

Edited November 16, 2022 by Kustom

[TonyT]

I would live in the house for a while and insulate the place as much as possible then do a heat loss calculation.

 

Then stick the PV in with a hybrid inverter to allow for battery storage.

 

 

[JohnMo]

A schematic of my system.  Have a simple combi thermal store (160L) upstream of the combi (with additional insulation to limit heat loss).  Immersion heater connected to PV diverter.  You need a diverting valve and thermostatic limiting valve on the output of the thermal store DHW coil.  This will reduce gas usage and stop un-necessary boiler firing when the cylinder is above about 45 degrees.

 

The cylinder is also being used as the central heating buffer.

 

 

 

[Kustom]

@TonyT Thank you for the reply, we will be having a hybrid inverter and battery fitted when givenergy gen 2 inverters are available. 

@JohnMo Thank you for your schematic, I think I understand what's going on but I have a couple of questions 

 

What is AVV is short for? some kind of relief valve?

 

Also what the the circular/dot connections on the tank in the Heating diagram?

 

Is the buffer built into the tank like this Telford one? or separate. Would you mind telling me where your tank came from?

 

 

Thank you 

 

[JohnMo]

AVV - automatic vent valve

Dot connectors are the connections on the thermal store - these tap in the inhibited fluid in the cylinder.

 

Its just a 160L vented thermal store, with a indirect heating coil (supplemented with a large plate heat exchanger) and DHW coil.  DHW water does not enter cylinder directly goes through a coil.

[SteamyTea]

Welcome.

 

4 hours ago, Kustom said:

Were due to have Solar PV and a battery storage installed (Currently on hold due to part availability)

We would like to dump any excess solar into a hot water tank

Why bother with a battery when for a large slice of the year a cylinder of water will use all/most of the PV generation.

[Kustom]

45 minutes ago, SteamyTea said:

Welcome.

 

Why bother with a battery when for a large slice of the year a cylinder of water will use all/most of the PV generation.

Because my wife wanted to have the house "protected" against power cuts. 

[SteamyTea]

1 minute ago, Kustom said:

Because my wife wanted to have the house "protected" against power cuts. 

Is it an 'islanding' system with automatic grid connection?

Edited November 17, 2022 by SteamyTea

[JohnMo]

PV inverters switch off when the mains supply goes off. A generator does not enable the inverter.

 

So unless the battery will run in island mode and not export a live load when the mains is off, you may be being sold a pup.  Well worth checking before you hand over the cash.

[SteamyTea]

3 hours ago, JohnMo said:

Well worth checking before you hand over the cash.

And before it is needed.  Last thing you want to do it start poking about in the dark with a screwdriver.

[Kustom]

18 hours ago, SteamyTea said:

Is it an 'islanding' system with automatic grid connection?

We've asked for a manual switch over so we know to isolate any high draw items to avoid damaging the inverter. 

[JohnMo]

You should also have a switch similar to a generator/mains switch.  So when mains power is off, and battery is on you cannot electrocute anyone working on the mains cables down the street.

[SteamyTea]

32 minutes ago, Kustom said:

We've asked for a manual switch over so we know to isolate any high draw items to avoid damaging the inverter. 

But is the inverter capable of running independently if the grid?

What model are you getting?

[Kustom]

49 minutes ago, SteamyTea said:

But is the inverter capable of running independently if the grid?

What model are you getting?

Givenergy Gen 2 5kw Hybrid inverter. 

[JohnMo]

Just had a quick look at the inverter and noticed its G98 approved, which would suggest that once the grid connection is removed, so is the functionality of the inverter.  So its/could be an expensive paperweight in a power cut.  Looking at the cost of circa 4-5k with battery, you need to get it right.

 

Hope I'm wrong - but please double, triple check you are getting what you want/need from this, or one p*ssed off wife may be the outcome.

[billt]

I don't think G98 certification disallows island operation; presumably the inverter must be wired in such a way that the grid is disconnected in the event of a fault, but can still operate in island mode.

[SteamyTea]

I had a quick look and some claim to island.

https://www.givenergy.co.uk/products#giv-hy-5-0-gen-2

 

Keep checking and make sure the installer knows what they are doing. Too easy to set it up on defaults and walk away.

[TonyT]

You will need your own earth too, as you cannot be sure that the fault hasn’t taken out the network earth.

[Kustom]

22 minutes ago, TonyT said:

You will need your own earth too, as you cannot be sure that the fault hasn’t taken out the network earth.

 Yes we were aware of this. It's being installed outside in an insulated shed so access to put in an earth spike shouldn't be an issue. 

Microsoft Word - EPS configuration (givenergy.cloud)

The link above gives some detail about the Givenergy inverter in island / EPS mode. We have chosen method 3 which is the manual switch over of the entire consumer unit. 

Taking the advice from @TonyT above perhaps I should wait on the hot water diverter until I have a better picture of exactly how much surplus we will have.

I was mainly pushing ahead with the tank as im having some plumbing done to convert one room to a bathroom and replacing the power hungry electric shower with a traditional mixer so thought I could kill two birds with one stone whilst ive got the plumber in. 

[Iceverge]

A ten minute electric shower might use 1.5kWh. A conventional mixer would use about double once you take into account the boiler inefficiencies, storage and transmission losses and higher flow rate. A much nicer experience however. 

 

@Marvin has a nice priority list for improving energy use and very importantly comfort. AIM APE

 

Airtightness.

Insulation.

Mechanic ventilation with heat recovery.

 

Air Source heat pump.

PV solar

EV. 

 

You seem to be starting at the end. If you get the first 3 sorted you'll be shocked how little of difference the last 3 make. 

 

 

 

 

 

 

 

 

 

 

 

[Marvin]

 

Hi @Kustom

 

@Iceverge is spot on with the assumptions on what saves most in the long run. Also - and often overlooked is that the Airtightness and Insulation should require no maintenance over many years and use no energy, and our MVHR running all year for 100m2 floor area home consumes about 260kWh a year. 

 

M