Solar PV system with not tied into the grid?

[Jean de Florette]

I know that ordinarily a solar PV system would be tied into the grid, and feeding-in to the grid when not used. But I do not want to feed into the grid, and neither do I wish to go completely 'off grid'. I want to use the solar array to run a 3KW immersion heater fitted to a 300Ltr indirect cylinder. When the water reaches temperature, the PV are then charging the battery system. When the weather is too dull to meet the immersion heater demand, then the battery system runs, via the inverter, to supply immersion demand. This proposed system would be earthed separately from the grid system using suitably located earth rods, hence the S/S tank would be earthed to the ground rods, and all associated domestic hot water pipes would be in plastic - including the CW rising main into the HW tank. Obviously, the generation of the grid supply means that there can never be any link between grid supplied earth and the 'floating' PV array derived 240V AC supply to the HW immersion heater.
Does anyone see any valid technical or regulatory reason why this could not be done?

 

[binky]

I know that ordinarily a solar PV system would be tied into the grid, and feeding-in to the grid when not used. But I do not want to feed into the grid, and neither do I wish to go completely 'off grid'. I want to use the solar array to run a 3KW immersion heater fitted to a 300Ltr indirect cylinder. When the water reaches temperature, the PV are then charging the battery system. When the weather is too dull to meet the immersion heater demand, then the battery system runs, via the inverter, to supply immersion demand. This proposed system would be earthed separately from the grid system using suitably located earth rods, hence the S/S tank would be earthed to the ground rods, and all associated domestic hot water pipes would be in plastic - including the CW rising main into the HW tank. Obviously, the generation of the grid supply means that there can never be any link between grid supplied earth and the 'floating' PV array derived 240V AC supply to the HW immersion heater.
Does anyone see any valid technical or regulatory reason why this could not be done?

nothing to stop you doing that, but grid tied is easier, and of course, reliable in winter. Climate change seems to be giving us long spells of dark, gloomy, overcast winter weather here in Devon. Your area might be faring better, but getting all yuo need from an off-grid system tends to be difficult. You might actually be better off with Solar Thermal for what you propose.

 

[Jean de Florette]

nothing to stop you doing that, but grid tied is easier, and of course, reliable in winter. Climate change seems to be giving us long spells of dark, gloomy, overcast winter weather here in Devon. Your area might be faring better, but getting all yuo need from an off-grid system tends to be difficult. You might actually be better off with Solar Thermal for what you propose.

Thanks binky

I see your point about the winter sun factor limitations, but a system that uses solar thermal as well looks like a good idea until I get to the bit where evacuated tube arrays are so efficient that come summer I have to use a heat dump! The idea of having to use an air blast cooler in order to take-out excess heating leaves me wondering if it would be such a good idea? According to what I have read, evacuated tubes give the best thermal efficiency - summer/winter, but can be damaged when excess heat is not diverted to a heat dump. This is the reason why I havn't gone down the route of a total solar thermal array.

 

[fourtytwo]

I have had a PV water heating system such as you describe since 2015. I am intrigued by your description of a 240V AC supply for the immersion heater as this would cause it to absorb its maximum rated power (perhaps 2.4 or 3Kw) that may be far in excess of the power produced by the panels. In my case I have a converter between the panels and the heater that runs an MPPT algorithm and generates a variable output voltage to ensure the heater only absorbs as much as the panels can generate.

I cannot see any reason for not using the grid earth (are you overhead or underground supply ?), this is likely to be a lot more solid than a few rods banged into the ground. This could certainly be used for earthing the HWcyl itself and as the PV array & heater are floating then there is no reason to not earth one of those poles too, in fact it maybe advisable to prevent breakdown of the heaters insulation that is only intended to withstand normal grid power with a loosely grounded neutral.

I too looked at direct solar water heating but was put off by the plumbing, new cylinder, weight on the roof, pumps, anti-freeze etc etc

 

[binky]

I have had a PV water heating system such as you describe since 2015. I am intrigued by your description of a 240V AC supply for the immersion heater as this would cause it to absorb its maximum rated power (perhaps 2.4 or 3Kw) that may be far in excess of the power produced by the panels. In my case I have a converter between the panels and the heater that runs an MPPT algorithm and generates a variable output voltage to ensure the heater only absorbs as much as the panels can generate.

I'm a little intrigued as to what your gadget is? I fit Solic 200 for such things.

 

[johnb2713]

I know that ordinarily a solar PV system would be tied into the grid, and feeding-in to the grid when not used. But I do not want to feed into the grid, and neither do I wish to go completely 'off grid'. I want to use the solar array to run a 3KW immersion heater fitted to a 300Ltr indirect cylinder. When the water reaches temperature, the PV are then charging the battery system. When the weather is too dull to meet the immersion heater demand, then the battery system runs, via the inverter, to supply immersion demand. This proposed system would be earthed separately from the grid system using suitably located earth rods, hence the S/S tank would be earthed to the ground rods, and all associated domestic hot water pipes would be in plastic - including the CW rising main into the HW tank. Obviously, the generation of the grid supply means that there can never be any link between grid supplied earth and the 'floating' PV array derived 240V AC supply to the HW immersion heater.
Does anyone see any valid technical or regulatory reason why this could not be done?

Why not grid tie it with zero export? You can then at least use your power generated anywhere and use excess to heat the water.

 

[Jean de Florette]

Why not grid tie it with zero export? You can then at least use your power generated anywhere and use excess to heat the water.

'Grid tie with zero export' sounds good, but that would infer that I can configure my system not to export. Also, I take it that grid tied would still require phase and amplitude alignment - even if I didn't ever export. Can you expand a little further, as your initial suggestion sounds worthy of further investigation.

 

[fourtytwo]

I'm a little intrigued as to what your gadget is? I fit Solic 200 for such things.

It was originally a DIY designed SEPIC converter, it is now a DIY designed full bridge converter, in both cases they convert power directly from PV to immersion without any grid connection that I gather was the OP's original question. I think the Solic 200 is designed for use with an existing GTI system that is grid tied ?

 

[johnb2713]

'Grid tie with zero export' sounds good, but that would infer that I can configure my system not to export. Also, I take it that grid tied would still require phase and amplitude alignment - even if I didn't ever export. Can you expand a little further, as your initial suggestion sounds worthy of further investigation.

On my Growatt inverter I can set the maximum export rate to 0, it then just does it's job supplying my house in preference to the grid power while it has solar or battery energy to feed it. If a large demand comes on line or the solar / battery supply is depleted the grid continues feeding the house uninterrupted. The grid tied inverters simply increase their voltage out in sync with the grid supply so the load on the grid is zero as much as possible. It works amazingly well.

 

[stuboy]

I'm just writing a new thread on Solic200, don't buy one there is no support if it breaks!

 

[binky]

I'm just writing a new thread on Solic200, don't buy one there is no support if it breaks!

Never had one break, but they've always done a 'return to base' warranty, which is annoying.

 

[Gian]

I'm just writing a new thread on Solic200, don't buy one there is no support if it breaks!

I can second Goodwe support as a no go . You will wait months unless your installer changes the unit. If the installer goes through warranty support you will wait a long long time. Infact I waited months for a Tranergy inverter replacement. It would be good to hear other people talk about good support

 

[binky]

I can second Goodwe support as a no go . You will wait months unless your installer changes the unit. If the installer goes through warranty support you will wait a long long time. Infact I waited months for a Tranergy inverter replacement. It would be good to hear other people talk about good support

Solis have generally been good, although I think they are struggling to keep up with calls at the moment.

 

[stuboy]

Solis have generally been good, although I think they are struggling to keep up with calls at the moment.

They keep apologizing, they still haven't fixed the BST offset on the Solis Cloud i reported many months ago, surly a British Summer Time tick box is not rocket science for a programmer these days??????
Luckily no drop off in product quality so far ;-)

 

[Jean de Florette]

On my Growatt inverter I can set the maximum export rate to 0, it then just does it's job supplying my house in preference to the grid power while it has solar or battery energy to feed it. If a large demand comes on line or the solar / battery supply is depleted the grid continues feeding the house uninterrupted. The grid tied inverters simply increase their voltage out in sync with the grid supply so the load on the grid is zero as much as possible. It works amazingly well.

Thanks johnb2713.

Just to get this right; I can have a solar array - suitably sized for the primary intension of just running my hot water tank immersion heater, but the reality is that with the water up to temperature, the system will also run anything else on my domestic system up to the point where domestic load exceeds PV array capacity. By using a grid tied invertor (with grid earth tie) set to zero export rate, I can use my PV panel array up to the point where a large domestic demand can no longer be supported by the solar/battery array, at which point the grid supply takes over to support domestic load demand.

 

[Jean de Florette]

Series and parallel panel connection? As each panel is effectively a power supply in its own right, it follows that there has to be an optimized form of panel connection. So what is the best configuration of panel connection based on a 14 panel array? I know it will all come down to panel type and output voltage, but there seem to be so many variables, so what is the best panel type and output voltage for my suggested 14 panels?

 

[Ucatchmydrift]

If you dont want grid tie, you can use a pass through hybrid inverter like im doing. Seperate system to the grid. When pv and batteries run out, it takes the feed from the grid, but is unable to feed back to the grid, hence why it is a good diy solution.

 

[Jean de Florette]

If you dont want grid tie, you can use a pass through hybrid inverter like im doing. Seperate system to the grid. When pv and batteries run out, it takes the feed from the grid, but is unable to feed back to the grid, hence why it is a good diy solution.

Ok, thanks for the feedback. Can you give me more details about the pass-through hybrid invertor you have used: product name, power capacity, where you got your unit from etc etc. Many thanks

 

[Ucatchmydrift]

Hi, i bought it from bimble solar (for £550): (click on download to get access to the manual and datasheet etc)

https://www.bimblesolar.com/epever-upower-24v-3000w-100a-lithium-all-in-one(their picture is incorrect- it shows the old version)

One on ebay here: bit pricy for a second hand unit, but shows the correct picture:

https://www.ebay.co.uk/itm/29509001...sv1MPSPSK-&var=&widget_ver=artemis&media=COPY
They do a 5000w version too for a bit more money that supports 48v battery banks.

https://www.bimblesolar.com/index.php?route=product/product&product_id=2451
Ive literally only just started using mine yesterday without battery storage, yet.
Fans are quite noisy, but go off below about 20 degrees c.

 

[binky]

Series and parallel panel connection? As each panel is effectively a power supply in its own right, it follows that there has to be an optimized form of panel connection. So what is the best configuration of panel connection based on a 14 panel array? I know it will all come down to panel type and output voltage, but there seem to be so many variables, so what is the best panel type and output voltage for my suggested 14 panels?

I would wire that as 2strings of 7 panels, the MPPTs are highly unlikely to take the ampage of the panels wired in parallel, plus that would involve a lot more cabling.