Help with solar pv

[ProDave]

The key to self usage, is use the big appliances (Washing machine, dishwasher, tumble dryer) near to the middle of the day, one appliance at a time.  If you are out at work, set them on a timer.

 

I time our ASHP to do the DHW heating starting at 11AM so PV generation should be reasonable by then.

 

And the PV dump controller sends excess that would otherwise be exported to the immersion heater automatically.  The only electricity that I export is when the PV generates more than the immersion can absorb or when we are away and the HW tank has maxed out at full temperature.  About 1/3 of what we generate goes to the immersion heater.

 

 

[A_L]

4 minutes ago, Mike_scotland said:

so you dont think i would get the 3600 kwh free to run electrical items in my house?

 

You will generate about that amount but to make a saving you will have to use it to substitute for electricity from the grid. If you have a 9 to 5 lifestyle you may only use 20-30% with the rest going out to the grid.

[ProDave]

1 minute ago, Mike_scotland said:

 

 

awwwww i get you now, its such a hard decision, part of me wants to buy a battery and charge it at night with cheap elecy from octopus go (4p)

In the present climate I doubt that will be available much longer. I just paused from switching to it as I suspect it won't be around much longer.

[SteamyTea]

2 minutes ago, Mike_scotland said:

from octopus go (4p)

That offer will vanish, relying on an energy supplier to off a cheap deal for years is not going to happen.

 

[Mike_scotland]

1 minute ago, A_L said:

 

You will generate about that amount but to make a saving you will have to use it to substitute for electricity from the grid. If you have a 9 to 5 lifestyle you may only use 20-30% with the rest going out to the grid.

 

i currently work away from home for 2/3 weeks at a time and my wife works 9-5. (but she may be working from home shortly)

 

i get it im selling it to the grid during the day for5p yet when i need it at night im buying it for 25p its a false economy at times, is a battery not worth it in the long run dont you think?

battery fills during the day and gets used at night? and im hoping to use my ASHP and UFH to go on at night with a cheaper tarrif.

[Mike_scotland]

2 minutes ago, ProDave said:

In the present climate I doubt that will be available much longer. I just paused from switching to it as I suspect it won't be around much longer.

yes i did think that also, i also seen they dont offer the buy electricity from you scheme if your on the octopus go. so its one of the other they will either buy elecy from you or you can get 4 hours cheap elecy.  but like you said it will likely disappear

[Nickfromwales]

2 hours ago, pdf27 said:

Since 5.5p/kWh is more than the cost of gas, then assuming you go for an MCS installation then it **may** be worth exporting to the grid rather than feeding to an immersion heater.

How so? If you then need to top up later via the boiler, you're then labouring the boiler, heating up all of the connective pipework and suffering all the relative losses from that process. Immersion will be close to 99% efficient vs gas boilers which sit in the early 90th percentile at best, ( considering the losses after the heated water leaves the boiler and more ) and that makes for a poor / uneconomical choice IMHO.

During summer the boiler should moth-ball and the extended longevity of the boiler and heating components ( motorised valves not moving multiple times every day etc ) needs to added to the equation.

[Nickfromwales]

5 hours ago, Mike_scotland said:

Are you recommending the solar thermal?

Heck no. Solar PV all the way AFAIC as ST is a one-trick pony. All summer you'll just have wasted excess energy that just mimics you boiling the kettle but not taking your finger off the button that makes it boil. ?

[Mike_scotland]

1 minute ago, Nickfromwales said:

Heck no. Solar PV all the way AFAIC as ST is a one-trick pony. All summer you'll just have wasted excess energy that just mimics you boiling the kettle but not taking your finger off the button that makes it boil. ?

ok mate, i will look into the solar PV as my first choice then, i have a ashp i want it to help run haha!

[Nickfromwales]

6 minutes ago, Mike_scotland said:

ok mate, i will look into the solar PV as my first choice then, i have a ashp i want it to help run haha!

Even worse an economical decision because of the duress you have to put the ASHP under to produce high temps for DHW, and the huge costs in replacing the ASHP vs a boiler. 100% wrong train of thought here  Excess electricity into the immersion ONLY.

Winter time, absolutely forget the PV adding to the ASHP running costs ( for heating ) as the PV will be at 25% or much less, or zero. The base loads for the house will consume everything you produce in the winter time so there will be extremely little or no excess to have to divert. 

Edited September 27, 2021 by Nickfromwales

[SteamyTea]

16 minutes ago, Mike_scotland said:

i get it im selling it to the grid during the day for5p yet when i need it at night im buying it for 25p its a false economy at times, is a battery not worth it in the long run dont you think?

Have you ever logged your actual energy usage by the hour, then seen what you can shift to the times that PV will most likely be producing.

Something like this:

[Mike_scotland]

3 minutes ago, Nickfromwales said:

Even worse an economical decision because of the duress you have to put the ASHP under to produce high temps for DHW, and the huge costs in replacing the ASHP vs a boiler. 100% wrong train of thought here  Excess electricity into the immersion ONLY.

Winter time, absolutely forget the PV adding to the ASHP running costs as the PV will be at 25% or much less, or zero. The base loads for the house will consume everything you produce in the winter time so there will be extremely little or no excess to have to divert. 

 

so what exactly is a divert? is that equipment that will divery elecy to a pre set electrical device?

so what are you thinking? ashp works away itself for heating... but excess elecy is pumped into immersion to heat HW? but in the winter it might give a little but not much.

[Mike_scotland]

2 minutes ago, SteamyTea said:

Have you ever logged your actual energy usage by the hour, then seen what you can shift to the times that PV will most likely be producing.

Something like this:

 

i have not mate my house is in the process of being built currently, currently i have a Ashp with plenty insulation and nothing else renewable but with rising elecy prices im thinking solar panels

[SteamyTea]

1 minute ago, Mike_scotland said:

so what are you thinking? ashp works away itself for heating... but excess elecy is pumped into immersion to heat HW? but in the winter it might give a little but not much.

That is Nick's view.

The way I see it is that if the ASHP is set up right, it is going to produce around 2.5 times the input energy, even for DHW (this is not true for a badly set up system).

So say your PV is producing 500W for an hour, or even a 100W, you can multiply that by 2.5.  So 1,200W or 250W.  You can take that energy input away from any imports.

So say your ASHP needs 1500W of energy, and your PV is delivering 500W, you are only importing 1000W.

That is better than using all of it for the DHW, and paying full price to run the ASHP, even of the CoP goes up a little.

 

Having said that, I do think that there may be benefits in having 2 ASHPs, one for space heating and another for DHW, but the installation costs are too high.

[SteamyTea]

6 minutes ago, Mike_scotland said:

 

i have not mate my house is in the process of being built currently, currently i have a Ashp with plenty insulation and nothing else renewable but with rising elecy prices im thinking solar panels

Just fit them, roof intergraded systems cost about the same as tiling a roof.  

Once fitted, you can play with the wiring later.  Much harder to play with pipes later.

Edited September 27, 2021 by SteamyTea

[Mike_scotland]

2 minutes ago, SteamyTea said:

That is Nick's view.

The way I see it is that if the ASHP is set up right, it is going to produce around 2.5 times the input energy, even for DHW (this is not true for a badly set up system).

So say your PV is producing 500W for an hour, or even a 100W, you can multiply that by 2.5.  So 1,200W or 250W.  You can take that energy input away from any imports.

So say your ASHP needs 1500W of energy, and your PV is delivering 500W, you are only importing 1000W.

That is better than using all of it for the DHW, and paying full price to run the ASHP, even of the CoP goes up a little.

 

Having said that, I do think that there may be benefits in having 2 ASHPs, one for space heating and another for DHW, but the installation costs are too high.

 

yeah i get you, it is a valid point thought if the ashp needs to work extra extra hard to produce hw, so the ASHP will produce HW upto a certain temp then a immersion tops it up x amound of temp? 

[SteamyTea]

Just now, Mike_scotland said:

 

yeah i get you, it is a valid point thought if the ashp needs to work extra extra hard to produce hw, so the ASHP will produce HW upto a certain temp then a immersion tops it up x amound of temp? 

How hot do you think stored water needs to be?

Here are my temperatures, and I don't run out.

[Mike_scotland]

2 minutes ago, SteamyTea said:

How hot do you think stored water needs to be?

Here are my temperatures, and I don't run out.

so you keep a steady 45-48 degrees? 

[SteamyTea]

4 minutes ago, Mike_scotland said:

so you keep a steady 45-48 degrees? 

Yes.  That is the top of the tank temperature, the median temperature is lower, but I can take a shower with 35°C water quite happily.

[Mike_scotland]

3 minutes ago, SteamyTea said:

Yes.  That is the top of the tank temperature, the median temperature is lower, but I can take a shower with 35°C water quite happily.

and these temps are all from your ASHP producing the HW?

 

i take it most systems will have a immersion for safety incase they require more heat?

[ProDave]

1 minute ago, Mike_scotland said:

and these temps are all from your ASHP producing the HW?

 

i take it most systems will have a immersion for safety incase they require more heat?

I, and a few others on here, heat our DHW to 48 degrees with the ASHP.  that is plenty hot enough and within the capabilities of an ASHP.

 

I don't heat it deliberately with the immersion heater, someone else concluded that with an unvented hot water cylinder and treated mains water, there really is no risk of legionairs.

 

The immersion heater will heat it above the 48 degrees when the sun shines using excess solar PV.

[Mike_scotland]

1 minute ago, ProDave said:

I, and a few others on here, heat our DHW to 48 degrees with the ASHP.  that is plenty hot enough and within the capabilities of an ASHP.

 

I don't heat it deliberately with the immersion heater, someone else concluded that with an unvented hot water cylinder and treated mains water, there really is no risk of legionairs.

 

The immersion heater will heat it above the 48 degrees when the sun shines using excess solar PV.

so you can have it set to that in your system? so in the cloudy/bad weather months the ASHP will heat to X pre set temp and in the good days the immersion will heat more ( hopefully at a free or heavily reduced cost?)

[SteamyTea]

7 minutes ago, Mike_scotland said:

and these temps are all from your ASHP producing the HW?

No, I am on E7.  So resistance heating.

The grey columns shows my usage (two charts up), but if I had an ASHP, the heating time could easily be shifted by 10 hours.

[ProDave]

Just now, Mike_scotland said:

so you can have it set to that in your system? so in the cloudy/bad weather months the ASHP will heat to X pre set temp and in the good days the immersion will heat more ( hopefully at a free or heavily reduced cost?)

Yes exactly that.  the ASHP is set to start heating DHW at 11AM (to ensure there should be reasonable PV generation by then) and shuts off when it gets to 48 degrees.  Any surplus PV after that, and the immersion heater soaks up the excess heating the water hotter.

 

In the summer, often there is enough just from the immersion heater that the ASHP does not turn on because by 11AM it is already up to 48 degrees.

[SteamyTea]

4 minutes ago, Mike_scotland said:

so you can have it set to that in your system? so in the cloudy/bad weather months the ASHP will heat to X pre set temp and in the good days the immersion will heat more ( hopefully at a free or heavily reduced cost?)

You got it.