Solar panels and battery - any real world reccomendations?

[Zeeflyboy]

Why pay 10p of gas when I get free hot water from solar? Or have I missed something?

Because that is a kWh of electricity you could have exported at 24p or 36p in peak.

You are “giving up” 14-26p by using that electricity instead of the gas, because it’s now a kWh you won’t be exporting.

Put another way that kWh of electricity is worth 24-36p to you. It isn’t free as such, the opportunity cost of using it is whatever it is worth to sell. So using it is preventing you earning 24-36p on it in order that you “save” 10p on a unit of gas… so you are actually worse off by 14-26p by trying to avoid the gas.

 

[HungryHippos]

I'm getting serious deja vu!

 

[bigmike20vt]

But while on flux you are better off paying 10p for a kWh of gas to heat the water than using a kWh of electricity you could export for 24p (or 36p in peak)… so it renders diverting the solar to heating the water redundant.

If you have a heat pump then you’re probably looking at more like 0.25kWh of electricity which makes it cheaper to use it than the gas, but flux definitely seems to render immersion heater diverting redundant to me, at least for now.

lol I never really thought of that ....actually that is a bit of a flaw really (assuming part of the incentive to use these tariffs is going greener) because it is encouraging us to use Gas over clean electricity.

 

[Freefaller]

Because that is a kWh of electricity you could have exported at 24p or 36p in peak.

You are “giving up” 14-26p by using that electricity instead of the gas, because it’s now a kWh you won’t be exporting.

Put another way that kWh of electricity is worth 24-36p to you. It isn’t free as such, the opportunity cost of using it is whatever it is worth to sell. So using it is preventing you earning 24-36p on it in order that you “save” 10p on a unit of gas.

Yes but I still need to use electricity - the reason I got solar isn't to make money it's to minimise my use of natural resources, and be able to use electric devices without drawing from the grid. If I'm using gas regardless of the fact it's technically "cheaper" it makes less sense for me to use it as I'm using a resource I don't need to use.

I still need to use the washing machine, dishwasher etc... the best time to do that is when there's excess solar, so similarly when there's excess solar I might as well heat up my water.

Or again have I missed something?

 

[Zeeflyboy]

Yes mate, it’s really simple and you are over thinking it… whatever else electrical you are using has no effect on the equation. You can’t run your washing machine or dishwasher on gas, and using them has no effect on your hot water heater.

Regardless of whatever else you are doing, using 1kWh of electric to heat your water uses up that kWh. That unit has an opportunity cost of whatever it was worth to export, by sending it to your immersion heater it is no longer available to export which deprives you of the 24-36p you would have got for it.

If the export is worth more than the import of gas, which in this case it is, then it loses you potential earnings to use it rather than export it.

In this scenario a water diverter is actually costing you money (or more accurately costing you potential earnings).

So from a financial standpoint you are worse off doing what you are doing. If you don’t care about the money and want to minimise gas usage that’s another discussion of course. If you are more interested in preventing use of resources though, then really the main way to do that would be a heat pump which uses much less energy to achieve the same heating than either immersion or gas.

 

[Mercenary Keyboard Warrior]

The green thing with gas is neutral right now at grid level.
Eg if you use 1kwh of gas more because your exporting some elec then the elec is 1kWh that doesnt need to be gas generated at grid level.

Its going to need to get to zero gas being required at times before the real impact of using your elec rather than exporting is actually better for the environment.
Some years off yet

The thing you guys are referring to is opportunity cost. Its the value of the best alternate usage for something in very simple terms.

 

[Welshman]

Why pay 10p of gas when I get free hot water from solar? Or have I missed something?

i guess what hes getting at, is if you use 1kwh gas to heat the water you pay 10p , then you can export the kwh of electric you would have used from solar and gain 22p……so in essence 12p in profit.

If you use a kwh of solar which you say is free, but its costing you a kwh of export now instead. Which is 22p loss

 

[Mercenary Keyboard Warrior]

Should bear in mind that gas isn't 100% efficient like elec though, boiler efficiency, you need to pump the water, heat loss in pipes etc means you should probably only work on around 85% conversion efficiency best case in the real world, unless you have a much old boiler that can be significantly lower.
Its not a game changer but its closer than simply taking elec export - gas price.

 

[Freefaller]

Yes but the point is I don't want to use gas if I don't have to? I'm not bothered about earning an extra 24p if I can avoid using gas. Excess solar for me is to be used as much as possible, i.e. it's there might as well use it to power stuff, heat stuff, clean stuff etc...

The hot water heats up a lot quicker with solar than with gas too.

Heat pumps at the moment I'm still not sold on - however, when we do our 50sqm extension it will have underfloor heating so the ASHP does seem to make sense for that, and explore if it could be good enough to heat the house - but at the moment they don't seem that efficient.

I've paid for the diverter I might as well use it - we use a LOT of hot water (2 kids, and a wife that loves a shower).

I'm clearly being thick Don't worry I'm probably wrong - I'm not trying to say I'm right - but it just feels instinctively that using excess solar is the best way of heating up water for me.

 

[HungryHippos]

As MKW said though, you don't export that kWh of electric, which means the grid is likely using gas elsewhere to generate the kWh of electric you don't export, for someone else to use.

The main person being disadvantaged is you, because you don't get the export payments, so your cost to heat the hot water is higher than if you just used the gas, and the grid isn't really any more or less green no matter what you do.

Removing gas supply entirely and using a heat pump would be the way to really use that electric you generate more efficiently.

 

[Freefaller]

As MKW said though, you don't export that kWh of electric, which means the grid is likely using gas elsewhere to generate the kWh of electric you don't export, for someone else to use.

The main person being disadvantaged is you, because you don't get the export payments, so your cost to heat the hot water is higher than if you just used the gas, and the grid isn't really any more or less green no matter what you do.

Removing gas supply entirely and using a heat pump would be the way to really use that electric you generate more efficiently.

Yeah I guess that makes sense - I mean the problem is we're not exploring an ASHP until we do the works on the house.

But if the grid uses gas then it makes no difference if I use it or not

 

[b0rn2sk8]

Heat pumps at the moment I'm still not sold on - however, when we do our 50sqm extension it will have underfloor heating so the ASHP does seem to make sense for that, and explore if it could be good enough to heat the house - but at the moment they don't seem that efficient.

there is nothing inefficient about a heat pump. A heat pump can heat any house, well insulated or not using 1/4 the energy of gas.

The issue is what you are connecting it to. If the heat exchangers (radiators) are too small (because they are sized for a boiler rather than a heat pump), you’ll get rubbish performance. That is all there is to it.

The economics of replacing loads of rads is a different question altogether.

 

[HungryHippos]

Yeah I guess that makes sense - I mean the problem is we're not exploring an ASHP until we do the works on the house.

But if the grid uses gas then it makes no difference if I use it or not

Yeah that's why it's really up to you, you're being a net exporter is helping the grid out and satisfying the green credentials by itself.

So people wouldn't judge you for using gas when needed, you would be doing your bit on the other hand by sending those kWhs to the grid for others to use.

 

[Freefaller]

there is nothing inefficient about a heat pump. A heat pump can heat any house, well insulated or not using 1/4 the energy of gas.

The issue is what you are connecting it to. If the heat exchangers (radiators) are too small (because they are sized for a boiler rather than a heat pump), you’ll get rubbish performance. That is all there is to it.

The economics of replacing loads of rads is a different question altogether.

I've read a lot of +ves and -ves about heat pumps at the moment especially in winter... but we have a log burner that's coupled to the central heating network so we've been using that quite a bit.

I mean we're definitely exploring it as for underfloor heating for 50sqm is a no brainer - I may need to spend more to over-spec it so that it can cope with the size of the house.

 

[Freefaller]

Yeah that's why it's really up to you, you're being a net exporter is helping the grid out and satisfying the green credentials by itself.

So people wouldn't judge you for using gas when needed, you would be doing your bit on the other hand by sending those kWhs to the grid for others to use.

Yeah this year so far I've imported 796kWh and exported 602kWh... I reckon by the end of the year I'll be fairly neutral if not export than import which to me is more than good enough.

Dammit - I really want to do my extension now!

 

[bigmike20vt]

Yeah I guess that makes sense - I mean the problem is we're not exploring an ASHP until we do the works on the house.

But if the grid uses gas then it makes no difference if I use it or not

actually I think what you are doing is still right if you want to be as green as you can. yes I would love it if our grid electricity was 100% green. it isn't BUT I expect generating electricity from gas turbines is probably (I am not certain) better than piping it to your home and burning it. good on you for not caring about profit and only your carbon footprint

 

[HungryHippos]

actually I think what you are doing is still right if you want to be as green as you can. yes I would love it if our grid electricity was 100% green. it isn't BUT I expect generating electricity from gas turbines is probably (I am not certain) better than piping it to your home and burning it. good on you for not caring about profit and only your carbon footprint

Point is though it's much of a muchness, you effectively gain credit when you export, and spend them when you import.

 

[b0rn2sk8]

I've read a lot of +ves and -ves about heat pumps at the moment especially in winter... but we have a log burner that's coupled to the central heating network so we've been using that quite a bit.

I mean we're definitely exploring it as for underfloor heating for 50sqm is a no brainer - I may need to spend more to over-spec it so that it can cope with the size of the house.

Defo do the underfloor thing on the extension. Gas or not, rads are pretty ugly and rooms just work so much better when you don’t have to consider furniture placement around them. No one’s ever thought ‘oh that’s a really nice radiator, it really adds something to the room’.

When they put it in, just make sure they don’t skimp on the runs so it can run at a really low flow temperature. Gas or heat pump, the lower the flow temp it can run at (E.g. sub 40c), the better the performance you can get out of it.

 

[SoliD]

Because that is a kWh of electricity you could have exported at 24p or 36p in peak.

You are “giving up” 14-26p by using that electricity instead of the gas, because it’s now a kWh you won’t be exporting.

Put another way that kWh of electricity is worth 24-36p to you. It isn’t free as such, the opportunity cost of using it is whatever it is worth to sell. So using it is preventing you earning 24-36p on it in order that you “save” 10p on a unit of gas… so you are actually worse off by 14-26p by trying to avoid the gas.

But you'd burn more units of gas than electric to get the same heat input to the water.

 

[HungryHippos]

But you'd burn more units of gas than electric to get the same heat input to the water.

A little but only based on the efficiency loss that MKW mentioned, where gas isn't 100% efficient.

Forgot to mention @Freefaller but even if you decide to carry on heating the hot water, I would disable it in the Flux peak, your exported kWh is more valuable to the grid at that time, you can almost heat hot water whenever but the grid will be using more fossil fuels in the 16:00 - 19:00 window.