Simple PV->DHW system

[Crofter]

I've got a small house used as a (mostly) summer holiday let. It has a direct UVC currently heated by an overnight immersion on E7, with a higher level boost immersion that is manually switched as needed.

The tank is 170l and the house is one bedroom.

 

Can I install say a couple of panels on the E/W facing roof slopes, a grid tie inverter, and then start feeding the immersion from that?

I'm starting to get to grips with the basics of domestic PV but I think there's still a lot don't know. E.g. I'd only want to be heating the tank during the day when I have output from the PV- the rest of the time it would revert to E7, not sure if the inverter is clever enough to do that.

 

Apart from the panels and inverter, what other gadgets would I need for this system?

And roughly what kind of sized system would make sense? I'm quite far north in Scotland so don't have the best weather- but we do get really long days in summer, which is when the demand is.

[JohnMo]

I am near Elgin (NE Scotland), just fired 12x 285W panels, apart from a brief spell when the sun came out they are generating about 500W on a generally cloudy day.  So it can be hit or miss, so I wouldn't rely on it.

 

My-PV do a DC immersion which can also take an AC input, it comes with mppt controller built in. Bimble solar do kits with panels

 

https://www.bimblesolar.com/elwa-PV-water-heater

[JamesPa]

1 hour ago, Crofter said:

I've got a small house used as a (mostly) summer holiday let. It has a direct UVC currently heated by an overnight immersion on E7, with a higher level boost immersion that is manually switched as needed.

The tank is 170l and the house is one bedroom.

 

Can I install say a couple of panels on the E/W facing roof slopes, a grid tie inverter, and then start feeding the immersion from that?

I'm starting to get to grips with the basics of domestic PV but I think there's still a lot don't know. E.g. I'd only want to be heating the tank during the day when I have output from the PV- the rest of the time it would revert to E7, not sure if the inverter is clever enough to do that.

 

Apart from the panels and inverter, what other gadgets would I need for this system?

And roughly what kind of sized system would make sense? I'm quite far north in Scotland so don't have the best weather- but we do get really long days in summer, which is when the demand is.

I have PV with a grid tied inverter, a solar diverter feeding the immersion and currently a gas boiler.  I set it up so the boiler dhw cycle is at night.  Furthermore the immersion is set to a higher temp than the boiler dhw thermostat.

 

Thus if there is sufficient PV, all the dhw heating is by PV.  If there isn't then the boiler tops it up.  Works perfectly.

 

I have 4kWp so I can turn the gas boiler off entirely from April to September.  However the same principle should work in your case.

[JamesPa]

2 hours ago, JamesPa said:

I have PV with a grid tied inverter, a solar diverter feeding the immersion and currently a gas boiler.  I set it up so the boiler dhw cycle is at night.  Furthermore the immersion is set to a higher temp than the boiler dhw thermostat.

 

Thus if there is sufficient PV, all the dhw heating is by PV.  If there isn't then the boiler tops it up.  Works perfectly.

 

I have 4kWp so I can turn the gas boiler off entirely from April to September.  However the same principle should work in your case.

Ps

 

To clarify the prime function of the diverter is to match the load to the available PV.  Immersion heaters are typically 3kW and your PV will generate less than this most of the time.  The diverter modulates the immersion down to match.

[Crofter]

The Solic seems to be coming up as a reasonable budget option for diverting PV to DHW- but without the ability to use the same immersion element for a timed/scheduled boost from the grid.

I could use the Solic for the upper element and crank the thermostat right up, but it seems a shame not to be able to heat the whole tank.

Presumably clever things can be done using relays, to allow a single immersion to be switched and powered from different controls and sources?

[JohnMo]

I had a solic and it lasted less than 18 months.

 

Just purchased a cool energy one instead, it can do two immersions sequentially and tells you what it is doing in figures (kW and kWh). Way better and was a similar price.

 

It also has an in built timer so you can ask it to boost during cheap rate times if you want.

[Crofter]

1 hour ago, JohnMo said:

 

Just spotted that on another thread. Looks like a good bet.

 

So a basic system is looking like panels, grid tie inverter, diverter. Job done?

[JohnMo]

Couple of isolation switches, one DC the other AC.

 

Look on Facebook market place and gumtree.  That's where I got all my panels and inverter from.

[JohnMo]

The diverter is cheapest on eBay from their outlet store

[dpmiller]

or cheaper still direct from China

[JamesPa]

Just tell clarify the diverter will feed power to the immersion after other power demands in the house have been satisfied.  It's basically a mechanism to use up 'spare' electricity generated by PV.  The idea  do works a treat, I can't comment on specific models as the one I have (which has worked for 10years) is no longer made.

[Conor]

9 hours ago, JohnMo said:

I had a solic and it lasted less than 18 months.

 

Slightly over a year here. Fails to sync and detect load. The boost button fell off at the very start. Not rated at all.

[JohnMo]

22 minutes ago, Conor said:

Slightly over a year here. Fails to sync and detect load. The boost button fell off at the very start. Not rated at all.

My boost worked for the first week then did nothing, but the unit failed just like yours. Ended up with random lights flashing, but nothing else.

 

Solic units have no active cooling and that could be the issue, they just fry themselves.

[JohnMo]

Good point by @JamesPa, if you just want water heating, the grid tied inverter and diverter and a few panels may give you what you want.

 

 

[ProDave]

5 minutes ago, JohnMo said:

Solic units have no active cooling and that could be the issue, they just fry themselves.

I would bet electrolytic capacitors, well worth trying a repair.

[JamesPa]

Of course you could wire the panels into the same circuit as the immersion, then put the CT for the diverter upstream of both.  This will, I think, cause the diverter to feed the dhw in preference to the rest of the house, if that was the effect you desired (not sure why this is desirable though).

[JohnMo]

2 hours ago, ProDave said:

I would bet electrolytic capacitors, well worth trying a repair.

Was skipped

[Crofter]

1 hour ago, JamesPa said:

Of course you could wire the panels into the same circuit as the immersion, then put the CT for the diverter upstream of both.  This will, I think, cause the diverter to feed the dhw in preference to the rest of the house, if that was the effect you desired (not sure why this is desirable though).

On E7, it makes sense to feed the house first, because I'm replacing 40p/kwhr electricity during the day. If I don't get the tank heated up, it will just boost overnight at 16p/kwhr.

[Crofter]

Another question:

If I get my panels, inverter, and diverter, what regs, rules, notifications etc are involved?

I understand that without going MCS I can't get paid for export? And I believe on systems larger than 4kw you have to notify the DNO?

But assuming I don't go down the MCS route, what else do I need to do? BCO sign off? Qualified electrician to connect grid tie inverter?

[JohnMo]

You need to do a G98 notification to DNO.  You will need a qualified electrician to sign off the certificate.  All this us done after the event.

 

As long as you not in a listed building or conservation area, it should be permitted development, so no BCO involvement I believe.

[Crofter]

29 minutes ago, JohnMo said:

You need to do a G98 notification to DNO.  You will need a qualified electrician to sign off the certificate.  All this us done after the event.

 

As long as you not in a listed building or conservation area, it should be permitted development, so no BCO involvement I believe.

 

You say after the event... what happens if you 'forget'? Would it just come up when you came to sell the house?

[Dillsue]

42 minutes ago, Crofter said:

Another question:

If I get my panels, inverter, and diverter, what regs, rules, notifications etc are involved?

I understand that without going MCS I can't get paid for export? And I believe on systems larger than 4kw you have to notify the DNO?

But assuming I don't go down the MCS route, what else do I need to do? BCO sign off? Qualified electrician to connect grid tie inverter?

Anything able to push more than 16amps(3.68 kw) needs permission from your DNO via a G99 application. Anyhing 16amp or less just notify the DNO via a G98 notification. All LV electrical work should be done by a qualified spark, but often isnt! Planning as stated above is usually permitted development. Your adding load to the structure so technically you should get building control approval but I dont think many people do!

[Dillsue]

3 minutes ago, Crofter said:

 

You say after the event... what happens if you 'forget'? Would it just come up when you came to sell the house?

Why would you want to forget? Do it within 30 days of connecting to the grid. It's technically a legal requirement to notify your DNO of any generating equipment being connected. Unlikely to be an issue when selling your house as I dont beleive anyone consults the DNO at the time of sale. 

 

No reason not to notify your DNO and it helps them manage the grid

[JohnMo]

Or do what I said in the first post and it's off grid, so no-one cares

[Crofter]

14 minutes ago, Dillsue said:

Anything able to push more than 16amps(3.68 kw) needs permission from your DNO via a G99 application. Anyhing 16amp or less just notify the DNO via a G98 notification. All LV electrical work should be done by a qualified spark, but often isnt! Planning as stated above is usually permitted development. Your adding load to the structure so technically you should get building control approval but I dont think many people do!

I'm playing around with various ideas just now.

Full picture:

We have two properties, either side if the road from each other. Both on electric for everything, no mains gas here. The older one is a 3 bed bungalow, with ample space behind it for a ground mounted array, and E/W roof. The roof is made from some delicate looking felt type tiles, and I really don't want to mess around with it. The other house is the one on my profile pic, 1 bed built under the 'portable building' exemption so no building warrant (it does have PP). Also has E/W roof. It's corrugated steel on battens and I'd be quite happy to mess around up there and add panels- I did design and build it, after all.

 

At the moment both are used as holiday lets, because we're living on our boat (how's that for off grid 🤣). We're likely to move back in to the bigger house for a while and then, hopefully, go back to boat life again in the future- for the summers at least. So anything I install should be idiot proof and need no manual intervention. The primary aim is to get the bills down. I also think it would be a good selling point to be able to offer free EV charging, although I'm not convinced the ROI adds up there.

 

At the moment I'm thinking about a ground mounted array on the bigger house, and roof mount on the other one. Both designed to feed a 16A diverter which would offset daytime loads and use the immersion heaters as a dump.