Hot water from PV

[Murdoch]

We are a fixed tariff that end in June.

I’ve no idea how high our DD will go after that and She’ll won’t allow me to increase our payment any higher as it says we are paying too much - but I’d rather increase it more so the July shock isn’t too much

 

[BorisJ]

Having had a new PV system installed, along with batteries and a diverter to heat water with any excess, I now question the economics of the water heating part.

Heating water with gas costs me about 5.5p a kWh. So every spare kWh I get from the solar PV only saves me that much.

The fee I've managed to get for selling my spare electricity back to the grid is also 5.5p/kWh.

So I don't actually see any advantage to heating water this way. Especially as I don't get any spare power until after the batteries are full, which can be any time of the day from say lunchtime to never, depending on how much sunshine there is and how much we self use.

Currently I'm using the boiler to top up water temperature to 50degC every morning. Then if/when there is excess power, that will take it up to 60degC. On a good day, that's enough to not need the gas boost in the morning. But I still do wonder if there's any point.

Are my sums correct or have I missed something obvious?

Your sums are similar to the figures I came to. Heating water with solar PV saves the same amount as selling excess back to the grid.

 

[binky]

Your sums are similar to the figures I came to. Heating water with solar PV saves the same amount as selling excess back to the grid.

Question is, where will gas prices be in a few years time?

 

[Berserkerboy]

As a self installer selling lecky back to the grid is not an option, so the immersion diverter is a no brainer.
It's all a bit of a gamble, as who knows where energy prices are going?
Will you still be getting a comparable payment for lecky vs cost of gas come next Autumn?
Is it even a like for like comparison gas kw vs lecky kw due to system losses burning gas?
Are you supporting Putin by burning gas?
I like the certainty of the solar immersion diverter.

 

[revor]

The fee I've managed to get for selling my spare electricity back to the grid is also 5.5p/kWh.

If you join Octopus on the flexible export you can get a lot more but you will need a smart meter. It is linked to 1/2 hour wholesale pricing. If you are interested in signing up or anyone else for that matter I can whisper you a code and we both get £50. I do not get FIT but as FIT is a generation payment and export a SEG payment you can have both. Not generally known.
Last month just gone, which was very sunny my grid usage was 0.56kWh per day average and we made £85 from the amount I sold, an average of 20p a unit. I have 6kW system battery and solar thermal with 300L open vented solar cylinder. During the month DNO allowed me to increase export to 5kW which has helped. I have a LPG gas boiler which is used from Nov to Feb and very occasionally 10 min bursts in between to top up the solar hot water. If I get a good solar summer then it more than likely for the export payments to cover my LPG costs. I sometimes think that instead of building 10 new nuclear power stations in 10 years time the money spent would be better paying for solar and insulation on all our houses and get benefit now. Back to part of the original thread my friend has a solar PV and wanted to heat his water with his export output but was advised he needed a water cylinder to store water as he is also on a combi which would be my understanding also

 

[Berserkerboy]

No to nuclear. Solar is developing at breakneck speed. Higher efficiencies and lower costs. Lets reduce burning gas to the winter months. Oh, and make it green hydrogen and biogas that we burn.

 

[Murdoch]

No to nuclear.

Problem with that strategy is we'll probably still need to import power, which I think needs to be avoided at all costs.

The UK needs energy security ASAP

 

[ProDave]

Having had a new PV system installed, along with batteries and a diverter to heat water with any excess, I now question the economics of the water heating part.

Heating water with gas costs me about 5.5p a kWh. So every spare kWh I get from the solar PV only saves me that much.

The fee I've managed to get for selling my spare electricity back to the grid is also 5.5p/kWh.

So I don't actually see any advantage to heating water this way. Especially as I don't get any spare power until after the batteries are full, which can be any time of the day from say lunchtime to never, depending on how much sunshine there is and how much we self use.

Agree. WITH BATTERIES you can use your generated PV for better uses to power stuff that you would be using anyway in the evening, saving your electricity import price, now typically 27p per kWh.

PV diversion to an immersion heater is really for people without batteries. Then you have the choice of use it or lose it (export it) And doing that and time shifting the big loads, I can self use almost all I generate.

So for me, each time I look at fitting batteries, the sums don't work, as the batteries will only enable a "better" use of the power from the PV than water heating, and for that they don't yet make economic sense.

Regarding the 5.5p export. In order to be able to claim that, you must have an MCS install, and the extra that costs to a PV system vs a DIY install would never pay for the small export payments you can claim. To put that into perspective, the small amount I have exported in the last 3 years would have earned me a massive £16.50 I won't lose sleep at the loss.

 

[Mckwhitts]

I guess it depends on the number of panels you have. Mine will be slightly larger than the standard 12 panel system but not as large as 11 Kw which I take as the maximum size without any upgrades on the grid side.

 

[ProDave]

The maximum without prior authorisation is with an inverter limited to 3.68kW output, you can have more panels than that subject to the inverter limit.

To put another perspective on whether it's best to heat DHW with an immersion heater or export it.

We have no gas here so all electric with an air source heat pump. Electricty is now 27p per kWh so assuming a best case COP of 3, it costs me 9p per kWh to heat my hot water if I import electricity to do so.

So on that basis, using surplus PV to heat DHW via the immersion heater saves me 9p per kWh sent to the immersion heater, which is a LOT better than letting it export and only getting paid 5.5p for it, even if I could.

 

[Berserkerboy]

Problem with that strategy is we'll probably still need to import power, which I think needs to be avoided at all costs.

The UK needs energy security ASAP

Yeah. I totally agree. I know I'm not gonna get my wishes. We'll have nuclear with all its attendant problems and costs.
The problem is, we've all become used to being profligate, especially with energy. Drive and fly everywhere, wear shorts and a t-shirt around the house in winter.
My experience with solar PV is that I can significantly reduce my energy requirements in a cost-effective way.
It's a shame that a DIY installation of a solar system can't be signed off in some way that doesn't cost a fortune. Then we could benefit from operators such as Octopus and maybe also from the zero VAT available at the moment. Many more people would see that the sums then add up and contribute towards UK energy security.

 

[Mckwhitts]

Seems a lot of people I've spoken to either have too much expectation of what their roof can produce or look at the equation in respect of how soon they get their money back. You don't buy a car to pay for itself, you buy it for the convenience etc. I'm viewing this in the same way, if it saves me some money I will be happy. If it keeps the lights on when the grid goes down, bonus.
I cant see why the guvt are not pushing this more than anything, surely its pretty good sense.

 

[Berserkerboy]

If you have £6k you can get maybe £60 interest a year. You'll generate a lot more than that in the way of electric from a £6k solar system. The solar system will last 20 years. What's £6k in your bank gonna be worth in 20 years with the inflation we have? Got to be one of the best investments at the moment.

 

[binky]

If you have £6k you can get maybe £60 interest a year. You'll generate a lot more than that in the way of electric from a £6k solar system. The solar system will last 20 years. What's £6k in your bank gonna be worth in 20 years with the inflation we have? Got to be one of the best investments at the moment.

Solar panels should last 30 years and more, inverters die around 15 to 20 years, unless you were sold really cheap crap.

A lot of my customers were retired and fed up with getting naff all in their ISAs or other investment/ savings pots. Many also wanted to leave the planet a better place for their grandchildren.

 

[Berserkerboy]

My Enphase micro inverters are guaranteed for 20 years. Hopefully, they will last even longer.
I also installed for environmental decisions initially. Looking like an inspired decision now..

 

[Geoff1946]

I always view long warranties like that with reservations.
Lots of technology companies don't last 20 years.
Then, actually being able to prove compliant installation, maintenance, if specified, etc, after a decade or so, and finding someone to carry out the necessary diagnosis and repairs, locating compatible components .............? Perhaps its just my sceptical outlook on life.

 

[BorisJ]

Question is, where will gas prices be in a few years time?

My crystal ball is broken, but 60 years ago electrically was twice the price of gas. In that time the difference has gradually widened to 4 times.

 

[binky]

My crystal ball is broken, but 60 years ago electrically was twice the price of gas. In that time the difference has gradually widened to 4 times.

Gas is running out along with oil. All future tech is electric. Hydrogen may offer some form of extending gas, but it's a rather inefficient system, although I personally think it's better than batteries and the like. It's hard to put a finger on what the future holds, especially with weak government policies in regards to energy security, but I just can't see gas staying cheap.

 

[Berserkerboy]

Gas is running out along with oil. All future tech is electric. Hydrogen may offer some form of extending gas, but it's a rather inefficient system, although I personally think it's better than batteries and the like. It's hard to put a finger on what the future holds, especially with weak government policies in regards to energy security, but I just can't see gas staying cheap.

It won't, along with oil. Too many people want it! People in for a big shock I'm afraid.

 

[Berserkerboy]

I always view long warranties like that with reservations.
Lots of technology companies don't last 20 years.
Then, actually being able to prove compliant installation, maintenance, if specified, etc, after a decade or so, and finding someone to carry out the necessary diagnosis and repairs, locating compatible components .............? Perhaps its just my sceptical outlook on life.

Enphase is an established American company operating for over 16 years. Hopefully, they will hang around. But you are right, companies come and go. I'm always wary of little-known entities.