Solar install recently (boiler replacement options)

arms

We’ve recently had solar and storage installed. 5.2kw Panels and 9.6kwh batteries.
We have a Baxi back boiler now needs replacement. The boiler has bitten the bullet and the whole system is very old and woefully underperformed.
I had planned to swap out our electric shower to use the hot water tank to use the spare solar for heating water for showers. Seeing the load go above what the battery can output kills me. 4hrs at 1kwh is better than 30mins at 8kw.
But now I’m wondering if a combi would be a better bet and take the 4.1p SEG. 

As a family of 5, what heating system would people suggest?
We exported 160kwh last month. I’ve also got a 24kw Nissan Leaf so I could add V2H into the mix. 

Reed_Richards

Well gas is now about 7p per kWh and the price is likely to rise.  The gas boiler is likely to be 90% efficient at best for hot water.  A hot water cylinder will lose heat over time and both a cylinder and a combi will leave hot water trapped in the feed pipes when you run a tap, which will waste energy.  You'll pay a premium for a combi over a regular boiler.  As you already have a hot water cylinder then heating it with spare solar electricity should work out cheapest, unless it is very badly insulated and you waste a lot of energy keeping it at temperature.  

arms

Reed_Richards said:

As you already have a hot water cylinder then heating it with spare solar electricity should work out cheapest, unless it is very badly insulated and you waste a lot of energy keeping it at temperature.  

Cylinder is in wrong place ( miles away from demand) and isn’t best insulated so would need a new cylinder too. Thinking both in loft above the only bathroom which is over kitchen.

Reed_Richards

A cylinder of water is extremely heavy.  If it is in the loft it probably needs to be positioned above a load-bearing wall.

Another alternative you could use with a combi boiler is to use a smaller tank with an immersion heater to pre-heat the cold water feed to the combi.  But some combis have a low maximum input water temperature so you would need to check.  I have read about those phase-change Sunamp thermal stores being used for the same purpose, but those were really expensive last time I checked.   

70sbudgie

Have you looked into heat pumps? I am in two minds about them, but whether they are really suitable is dependent on your overall circumstances.

We had to replace our combi boiler about 5 years ago. Although we replaced it because it failed, it was also woefully undersized. Imho, combi boilers aren't a great idea if you have more than one bathroom. Because the total water pressure is dependent on the infeed pipe to your property, you really notice if one of the children goes to the toilet while you are in the shower! We went for a condensing system boiler (high efficiency but with a hot water tank). Although there was an airing cupboard where the predecessor to the combi boiler's hot water tank had lived, the new hot water tank is sufficiently well insulated that we were able to put it in the garage next to the boiler. 

I didn't go for a diverter when the PV panels went in, but having now had them for a year, it is something I am looking to do. I believe that our PV generates enough to heat between 2/3 and 3/4 of our hot water. 

(I have also fitted EcoCamel showerheads. They use air to reduce the water flow, but feel almost like a power shower.)

Screwdriva

Sounds like a similar journey to the one we just went through:

1) Here's a video of our solution. We decided against a Heat Pump as the incremental cost for a HP was £6K and the supply of Vaillant pumps are running on a 3 month backlog. Instead, we went with a Viessmann 200-W System Boiler. Efficiency is yet to be bested by any other gas boiler on the market. We haven't measured savings on heating but we're currently using substantially less gas to heat our hot water cylinder. More on this soon.

2) On average, our rooftop solar powers our immersion heater entirely for ~30 days per annum entirely. Said another way, 1 month of free hot water via our Megaflo unvented cylinder per annum. You'd be giving that up if you went with a Combi.

3) Your SEG expectations are quite conservative. Octopus outgoing Agile is paying .>25p per kWh currently. 

4) While we may have passed on a Air to Water Heat Pump, we are still considering an Air to Air heat pump for heating and cooling the living spaces. More on that soon...

Reed_Richards

Screwdriva said:

3) Your SEG expectations are quite conservative. Octopus outgoing Agile is paying .>25p per kWh currently. 

I'd say "realistic" rather than "conservative".  Octopus offer far and away the best SEG rates available so if they go the way of so many other electricity companies or revise their policies then your economics are out the window.  You need to be an Octopus customer for your incoming electricity, with a smart meter.

Outgoing Octopus comes in two flavours – Fixed or Agile. Outgoing Fixed guarantees 7.5p per kWh for every unit you export. Outgoing Agile matches your half-hourly prices with day-ahead wholesale rates, helping you make the most of the energy you generate. 

2nd_time_buyer

Reed_Richards said:

Screwdriva said:

3) Your SEG expectations are quite conservative. Octopus outgoing Agile is paying .>25p per kWh currently. 

I'd say "realistic" rather than "conservative".  Octopus offer far and away the best SEG rates available so if they go the way of so many other electricity companies or revise their policies then your economics are out the window.  You need to be an Octopus customer for your incoming electricity, with a smart meter.

Outgoing Octopus comes in two flavours – Fixed or Agile. Outgoing Fixed guarantees 7.5p per kWh for every unit you export. Outgoing Agile matches your half-hourly prices with day-ahead wholesale rates, helping you make the most of the energy you generate. 

I was wondering about how profitable the Agile Export is for Octopus. However, whilst it has been much higher than other fixed SEG rates out there. I think it has still generally been lower than the market rate that they would otherwise be paying. And of course, it is only a small minority of their solar customers who will be on Agile Export as most will be on a fixed export rate that below the market rate. So by cornering the market on domestic solar, it may have helped Octopus to be more profitable as they are buying energy cheaper than they would on the open market.

Reed_Richards

Surely this is doublethink?  If only a small minority of their solar customers are on agile export and, presumably, only a small minority of their total customer base has solar, then Agile Export will not make Octopus significantly more profitable.

Are they even allowed to offset their metered imported solar electricity against the cost of their exported electricity?    

2nd_time_buyer

Reed_Richards said:

Surely this is doublethink?  If only a small minority of their solar customers are on agile export and, presumably, only a small minority of their total customer base has solar, then Agile Export will not make Octopus significantly more profitable.

Are they even allowed to offset their metered imported solar electricity against the cost of their exported electricity?    

Yes, good point. I meant that they are probably not losing much if any on Agile export. But by cornering the market in Solar generally they are probably improving profitability.

In contrast, apparently the Octopus Go tariffs are run at a loss, according to a reply from Octopus on the Facebook Octopus smart tariffs page: 

"Both Go and Intelligent off set the lower rate by charging slightly more during the daytime, which allows us to offer these reduce rates. Currently these tariffs are run at a loss, theses Tariff are also part of our initiative to encourage more EV use and reduce the reliance in fossil fuels.

The Agile tariff was much more dynamic in its price when first introduced but with the current energy crisis it rarely drops below its peak,

Battery storage only tariff are something we are looking to develop and we have worked in partnership with Tesla and their Powerwall. The current technology for battery storage and their charge controls is less standardised than EV chargers and is proving more difficult to offer a purely battery storage tariff"

shibli

Would definitely consider a hot water cylinder in the loft, thats where we have ours, and where our system boiler is fitted. We also have an iboost which helps heat the water, its early days for us and not every day will heat the water as we also have a battery to charge.