Green Building Forum - Solar PV with accumulator tank Tue, 19 Dec 2023 06:26:53 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296717#Comment_296717 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296717#Comment_296717 Wed, 06 Jul 2022 23:37:15 +0100 Followthemoney
Not permitted to put solar thermal on roof or anywhere near house. Solar PV is only practical generation we can install in a field about 80m from the house.

We have 'twin phase' electricity supply (two single phase mains through two separate meters, two consumer units) use average 16kWh/day of electricity. In winter around 18L/day oil and in summer 7L/day on domestic hot water (300L cylinder) and keeping the under-floor slab ticking over.

A neighbour has 17kW PV (the max permitted 1ph grid tie) and in Nov / Dec / Jan it delivers average 10kWh/day. Not much, but enough to run the dishwasher and supplement the hot water. May / Jun / Jul / Aug it's 60 to 70+kWh/day.

My take-away from these figures is go large because PV is relatively inexpensive and aim to export nothing we don't have to. I think we might get permission to grid-tie 8kW to each incoming main, and this is about the max size of domestic 1ph inverters.

So, proposal is 24kW PV array, 3 x 8kW 1ph inverters, two of which hooked into our existing consumer units. 1500L accumulator tank fitted with 9x 2kW immersions. Set up the demand management to favour any domestic load, followed by the lower immersion in the domestic hot water tank. Any additional energy (in 2kW increments, as available) from the two grid-tied inverters to the accumulator, plus all the energy from the third inverter.

On average mid-winter day we should get a chunk of our domestic demand covered, plus most of our hot water. For the other 9 months, and particularly Apr to end Sept there should be 75 to 100kWh/day (on average) Knock 30kWh off for domestic use and hot water and that leaves 45 to 70kWh for the accumulator, saving maybe 4.5 to 7L of oil we'd burn otherwise. The 1500L accumulator should store around 70kWh if the mass of water is heated from 45C to 85C, then extracted to a heat exchanger on the central heating circuit.

No PV installer is much interested in this plan, too much plumbing and a bit left-field, but what does the community think?

P.S. I've considered batteries and calculated that they are no friend of the environment or my wallet, even with electricity at 35p/unit. One of the problems Is that we would need two batteries and charge controllers for each 'phase' of our supply, doubling the cost.]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296718#Comment_296718 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296718#Comment_296718 Thu, 07 Jul 2022 10:16:37 +0100 philedge
A few things that spring to mind-
Hows the 3rd non grid tied system going to work without batteries?

You may be able to find 1ph inverters that can have 12kw of panels connected so youd only need 2 x grid tied systems. Solaredge inverters can have more than 150% PV connected over their rated value.

Youll need quite an array of PV diverters/CTs to drive 9 x immersions

Probably worth speaking to your DNO about adding generation. If youve got neighbours with substantial PV already connected, assuming DNO approved, then it lowers the chance of others connecting substantial generation without network upgrades being needed and having to be paid for. You may already have a robust local grid but worth enquiring as cost of upgrades can be substantial!]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296719#Comment_296719 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296719#Comment_296719 Thu, 07 Jul 2022 11:16:07 +0100 WillInAberdeen
Where are you located? There are practical and regulatory and economic issues with that scale of PV, but maybe works in other places?

In the UK, oil is about 12p/kWh and solar can be exported for 15-20p/kWh, so it actually costs you money to use PV yourself to displace oil, is better value to export it. But to reduce carbon emissions, it is good to electrify your heating, ideally with a heat pump to vastly reduce the electricity consumption. Then investing in a matching amount of generation/storage would be a way to buffer against price rises or falls.

Something staggering has happened with commercial PV in the UK in the last year as solar farms have broken grid parity and there is now an explosion of utility scale schemes in development (10s of GW) including community-led schemes. These can install many more kW per £ than individuals can domestically, you might be interested to participate in one of those?]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296726#Comment_296726 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296726#Comment_296726 Fri, 08 Jul 2022 08:35:16 +0100 tony Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296735#Comment_296735 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296735#Comment_296735 Fri, 08 Jul 2022 16:36:25 +0100 Followthemoney There’s no doubt the system is complex. Contactors go wrong, fail to contact and you don’t notice unless you’re monitoring endlessly. We’re based in Berwickshire, sunny side of Scottish Borders.
If we really could get 20p/kWh for export that would be a game-changer. Far better to take the money and buy oil. At least from an economic point of view. I thought the domestic export tariff was only 4 or 5p/unit? Where do I investigate other avenues to sell power to the grid?
The EPC objective would be met with a small domestic installation; we won’t get a better assessment for a bigger PV generation capacity.
It probably would be more grown-up (strictly logical) to install ground source, but our bathrooms would never be properly warm again… We have two ground source systems in other houses, one 240kW (a mad size dictated by RHI) and a domestic 12kW system. These heat at around 40C and stay on 24/7. Cop is around 3.5, so directly comparable cost to oil at £1/L]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296741#Comment_296741 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296741#Comment_296741 Fri, 08 Jul 2022 19:51:31 +0100 WillInAberdeen Posted By: FollowthemoneyIf we really could get 20p/kWh for export that would be a game-changer. Far better to take the money and buy oil. At least from an economic point of view. I thought the domestic export tariff was only 4 or 5p/unit? Where do I investigate other avenues to sell power to the grid?The one I was considering before price rises was Octopus Outgoing tariff, IDK if they are taking new customers or if there are alternatives. Their prices are logged by https://www.energy-stats.uk/octopus-agile-outgoing-export-southern-scotland/ graph attached

Solar panels are a multi year payback so be prepared for the price to change up/down from present levels (maybe the price of oil/gas would also change in parallel). I haven't made the figures work out yet!]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296748#Comment_296748 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296748#Comment_296748 Sat, 09 Jul 2022 15:29:24 +0100 revor
Posted By: Followthemoneyone 240kW (a mad size dictated by RHI)

?? 24Kw?]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296750#Comment_296750 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296750#Comment_296750 Sat, 09 Jul 2022 21:29:37 +0100 Followthemoney The 240kW gshp is a 4x60kW cascade on a 16kM / 3 acre ground loop. It was a massive gamble, but it ticks away heating a small hotel. It works very well, if only at 40 to 47C, displacing about 35000L of oil. The economics will go to bits when our electricity rises from 14p to 33p/kWh early next year…]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296772#Comment_296772 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296772#Comment_296772 Wed, 13 Jul 2022 13:31:01 +0100 andrew_rigamonti Thanks]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296773#Comment_296773 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296773#Comment_296773 Wed, 13 Jul 2022 15:50:17 +0100 djh Posted By: andrew_rigamontiCan you now install more PV than the maximum 4kw as long as the inverter is limited to 13A? If so do you have not notify in advance as the gov site implies its still limited by the array sizeMaybe if you point to the documents you're using, since I don't recognize either of those numbers?]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296774#Comment_296774 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296774#Comment_296774 Wed, 13 Jul 2022 16:48:17 +0100 Pile-o-Stone Posted By: andrew_rigamontiSorry a bit off topic. Can you now install more PV than the maximum 4kw as long as the inverter is limited to 13A? If so do you have not notify in advance as the gov site implies its still limited by the array size Sorry to raise newbie query, finally going to look at doing this as we have a huge south facing roof in devon to use.
Thanks

You are allowed to install 10Kw on a single phase electricity supply (30kw on three phase). However you will need to get the consent of the DNO if you install over 4kw. This may or may not be easy to do and may depend on how modern the electrical grid is near you and how many other people have solar in your area. We wanted to increase our solar from 5.5kw and the DNO said that we would have to pay a charge to 'upgrade the system' to cope with it. The charge was quite expensive and would make the ROI on the solar untenable.

An alternative would be to install equipment to limit the export to the grid. Details in the link:

https://www.sma-uk.com/solar-systems/export-limitation.html]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296775#Comment_296775 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296775#Comment_296775 Wed, 13 Jul 2022 18:50:21 +0100 philedge Posted By: andrew_rigamontiSorry a bit off topic. Can you now install more PV than the maximum 4kw as long as the inverter is limited to 13A? If so do you have not notify in advance as the gov site implies its still limited by the array size

You can install as much generation as you want, but without prior approval, you cant export more than 16amps to the grid. How much you install will likely be limited by the inverters DC input from your panels. As an example, a Solaredge SE3680H is rated at 3.68kw and limited to 16A output but it can have up to 5.7kw of DC input from a PV array. Such a system is governed by the DNOs G98 specification, so a G98 compliant inverter is what youd use if wanting to export no more than 16A per phase.
If you want to export more than 16A you need to apply in advance and get approval via the G99 application process]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296776#Comment_296776 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296776#Comment_296776 Wed, 13 Jul 2022 19:42:01 +0100 revor Posted By: philedgeIf you want to export more than 16A you need to apply in advance and get approval via the G99 application process

My application was G99/ g100 for a 6kw inverter but restricted to 3.68 export presumably because inverter was capable of exporting more. Included in the application was the manufacturers statement of how the export limitation would be achieved. My inverter is done via software and password protected. In April this year applied for information as how to go about getting permission to export more and was informed that I could go to 5Kw at not cost but to get to 6 would cost £750 to apply and subject to a witness test whatever one of those is. No brainer settled for 5Kw made a big difference to how much I am exporting. All DNO's have different situations it seems .]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296780#Comment_296780 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296780#Comment_296780 Wed, 13 Jul 2022 22:58:23 +0100 Followthemoney https://www.spenergynetworks.co.uk/pages/application_forms_and_guides.aspx
It may be a factor that the dwelling has a c.500kVA grid transformer in the garden that only supplies a few other small consumption meter points. Obviously this is a pretty rare situation, but in rural areas it wouldn't be unusual to have individual properties on 20 or 25kVA 1ph transformers. Exporting 15kW through one of these should not raise technical concerns. But I'm not the DNO...]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296781#Comment_296781 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296781#Comment_296781 Thu, 14 Jul 2022 07:45:02 +0100 revor Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296783#Comment_296783 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296783#Comment_296783 Thu, 14 Jul 2022 08:50:37 +0100 philedge Posted By: revorIn April this year applied for information as how to go about getting permission to export more and was informed that I could go to 5Kw at not cost but to get to 6 would cost £750 to apply and subject to a witness test whatever one of those is. No brainer settled for 5Kw made a big difference to how much I am exporting. All DNO's have different situations it seems .

That £750 charge is about what SPEN charge for a G99/G100 application and site witness test if export limitation is required. Application is £250+vat and witness test is £350+vat. I beleive the witness test is for you to prove to them that your system does actually limit export and that the limitation is fixed in such a way that the user cant increase. Ie engineer/manufacturer password protected, or other "secure" means.]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296784#Comment_296784 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296784#Comment_296784 Thu, 14 Jul 2022 10:07:50 +0100 revor Posted By: philedgeThat £750 charge is about what SPEN charge for a G99/G100 application and site witness test if export limitation is required. Application is £250+vat and witness test is £350+vat. I beleive the witness test is for you to prove to them that your system does actually limit export and that the limitation is fixed in such a way that the user cant increase. Ie engineer/manufacturer password protected, or other "secure" means.

Thanks for the explanation. Looks like I was fortunate I was not charged only mention of payment if I wanted to go over 5kw then £750+ . got the impression that 5Kw was now standard here but could be just my line. We were "rewired" from the transformer and onward about 3 years ago the 5 wires (3P) to the property were replaced with a twisted set so now no wires for me to enjoy the migrating swallows that used to congregate on them in their masses.]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296785#Comment_296785 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296785#Comment_296785 Thu, 14 Jul 2022 10:14:09 +0100 WillInAberdeen
Anyone know what happens if you subsequently need to replace your inverter with a new model without changing the peak export kW? Or add a battery or V2G that exports at a different time of day, no extra kW export? Do you have to reapply for a new G99 based on the new make/model - what risk is there that gets declined because neighbours have upped capacity in the meantime?]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296790#Comment_296790 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296790#Comment_296790 Thu, 14 Jul 2022 11:42:51 +0100 philedge If theres no or limited spare export capacity in your section of the grid then you may end up having to pay for grid upgrades after your neighbours have used up spare capacity. If youre putting in a G99 application it may well be worth considering any changes youll make in the nearish future and apply for that future capacity now??]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296792#Comment_296792 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296792#Comment_296792 Thu, 14 Jul 2022 13:05:56 +0100 WillInAberdeen
If after a few years the PV inverter fails and I want to replace it with a different make/model, I would have to reapply for the G99, and risk having it declined?]]> Solar PV with accumulator tank http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296793#Comment_296793 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17509&Focus=296793#Comment_296793 Thu, 14 Jul 2022 15:41:36 +0100 philedge
If the inverter fails after a few years and you change it for a different make and model, then I belive you have to notify them. If its not functionally the same then likely a new application or maybe just another witness test to see that the limitation has been set correctly.]]>