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General Renewable Topics => General Discussion => Topic started by: martinwinlow on January 11, 2021, 05:28:38 PM



Title: PV, Powerwalls and Local Microgrids...
Post by: martinwinlow on January 11, 2021, 05:28:38 PM
Hi,

I'd be interested in input from experienced renewable generators re our community's plans to install ~20kW of PV on the unshaded, south-facing village hall roof along with installing 2 x PW2s.

Initially, the intention is to just make use of what little sunshine we get to reduce electricity bills (I do appreciate there will be a fairly long paypack period) but also and fairly critically, provide community resilience in the event of mains outage; a fairly common winter issue here.

In time, we hope to go onto a much more 'enlightened' tariff and then take advantage of load shifting (ie charging the battery with cheap night-time power - especially if the forecast is pants the next day), too, and (importantly) exporting any excess PV to the adjacent village shop to help run its refrigeration - ideal in summer when PV and fridges will be making/using the most energy (respectively).

One issue is that the hall has a 3 phase supply and *all* its heating is electric-resistive...  Again, in time it would be nice to think that the heating could be upgraded to heat pump but that would most likely be a long time off due to the cost.

Any input gratefully received.

Regards, Martin.


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: pdf27 on January 11, 2021, 06:20:59 PM
  • How much are you trying to back up with the Powerwalls - just the village hall, the shop as well, something bigger?
  • Are the village hall and the shop on the same meter? That would help a lot since your self-consumption would be a lot higher. The bigger the network the PV is behind the meter for, the better the payback.
  • If you've got frequent issues with power cuts then the grid might be a bit shaky and so the DNO might have issues with 20kW of PV - have you checked with them yet?
  • Don't worry too much about a heat pump - if usage is intermittent, total energy usage might be better from heating on demand with resistance heating rather than over a much longer period with a heat pump. That requires a big & expensive heat pump but if the place is mostly empty & thus not heated savings might be quite low.
  • PV won't support much resistance heating in winter - with Powerwalls it'll keep the lights on but you won't have any heating.
  • Have you got room for ground mount instead? That's probably cheaper and since the panels will be cooler it should give you a little bit more generation.


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: billi on January 12, 2021, 12:11:09 AM
Quote
PV won't support much resistance heating in winter - with Powerwalls it'll keep the lights on but you won't have any heating.
funny enough , that i  still saw people in August to buy coal and firewood in Ireland ....  must be  permafrost  whistle  , but i agree in deep December  , forget PV for heating ,
most of the year a perfect match  for "(c)old buildings"

But 20 kW of PV is quite substantial  idea ,  to as well think about heating in October  or March  via a heatpump , 2x  tesla 2 idea for storage ?   is that 13 kWh storage each  ?   Just   was  in my pole  position , get at least 50 kWh  capacity ......


Better  go now its dark ....


Anyway sounds like a intresting project


Billi


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: gnarly on January 12, 2021, 07:26:45 AM
Can you find out the annual electricity usage in kWh?  If all electric then thatís the total amount of heat supplied


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: brackwell on January 12, 2021, 09:14:20 AM
If the hall is intermittently occupied my suggestion would be infrared overhead heaters


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: Fintray on January 12, 2021, 01:16:24 PM
Martin

As you are thinking about installing Powerwalls it might be worth getting a smart meter fitted to the hall (if there isn't one in already) and considering the Octopus Energy Tesla Energy Plan Lite. This gives you a rate of 11p/kWh for both export and import with no standing charge. Also with the Tesla back-up gateway this will allow you to set a lower limit on the discharge side to allow you to have some in spare in case of a power cut.

If your DNO wants to limit your export you can get inverters that can be programmed to limit the export so you could still fit the 20kW of PV. If you should move to Octopus Energy using the code share.octopus.energy/red-tiger-267 (http://share.octopus.energy/red-tiger-267) will get us both £50 of free electricity  ;D.


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: martinwinlow on January 12, 2021, 02:16:40 PM
Hi Everyone, thanks for all the useful comments.

Firstly, you have all confirmed a lot of info which I had already heard but it is nice to hear it all again coming from users rather than retailers...

My understanding is that the hall already has a smart meter (installed only a few months back along with a very expensive-looking GSM antenna) but I have been unable to ascertain exactly what the score is there.  I can hear you all saying "What?! Surely you should know already!?" and you are right but it is such a nebulous set up that it has proved difficult to pin anyone with good info down... I guess a good start would be to find out what meter it is and go from there...

Interesting re overhead IR heaters as that's exactly what it has... 10 (inc. upstairs?) x 1500W (wall heaters) + 7 x 3kW hot water tank immersion heaters in 2 tanks + 6kW cookers etc.  And I completely take your point about the IR space heaters potentially being more appropriate/efficient overall than a heatpump if used intermittently, which the hall absolutely is, of course...  Interesting...

There is a 'service point' at one end of the hall which will be a lot easier to export electricity to (same building) but still has its own meter...  That's manned during office hours by 1-4 part-time staff whereas the hall sees most of its use in the evenings in normal circs.  Maybe we could do something with the service point first as an experiment and expand to the shop (50m away) in due course?

Already thinking about Octopus (at home, too, where I plan a similar system but already have about 30kWh of re-purposed early lithium batteries - Valence U27-12XPs from the Sainsburys/Smiths EVs Transit conversion fiasco).  Although Octopus have said they can supply power to us, as our location is particularly remote (an island, in fact - but with SSE undersea interconector) I have yet to test that by actually signing up.  I shall do so shortly and see what happens.

Going on from that, I was aware of the wonderful tariffs that Octopus offer as well as the Tesla Energy Plan with its 11p/kWh both ways tie-up.  It would be a huge step forward to be able to take advantage of that for hall and home alike (I have 6 hungry EVs!).

Unfortunately the hall and shop have separate meters but early indications are that some sort of very local microgrid might be feasible, possibly even outside of the existing local grid.

Annual energy use for the hall alone is ~12MWh but that's historical so I'm not sure how accurate it is.

Tesla PW2s are 13.5kWh a piece with a 5kW continuous output (each).  One of the burning Q's is how to connect them for best effect given that the hall has a 3 phase system with loads shared across phases in the usual way but with the limitation of PWs that only a phase with a PW can continue to generate from the PV array in a grid failure scenario... and I think only one phase can have a PW.  So, they'd both have to be on the one phase...?  Or not?

Ideally we'd like to use stored power across the whole microgrid.  So, hall needs first (with a hierarchy of demand eg, lights, sockets, hot water storage, cooking facilities (all electric), heating), then the service point and then the shop.  There are a couple of business units nearby, too, but I doubt there would be much left over from the others even in max sunlight... but one of them *is* a brewery...

Discussions with DNO are being handled by one of the other team members so I don't know what progress has been made there.  I was hoping that the inclusion of storage would make the application more likely to succeed than without...?

No ground-mount PV facility and the roof is next to perfect so seems a shame not to use it!

Thanks again for the input...  MW


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: Fintray on January 12, 2021, 03:27:14 PM
Keep us all updated with the project with pictures if possible as good the hear of greater roll-out of renewables and decentralisation of generation.


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: billi on January 12, 2021, 03:54:47 PM
Hi again ,  can 2     Tesla PW2s for aground 8000 GBP   each , deal with 3 phase ?


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: pdf27 on January 12, 2021, 09:08:40 PM
Going on from that, I was aware of the wonderful tariffs that Octopus offer as well as the Tesla Energy Plan with its 11p/kWh both ways tie-up.  It would be a huge step forward to be able to take advantage of that for hall and home alike (I have 6 hungry EVs!).

Unfortunately the hall and shop have separate meters but early indications are that some sort of very local microgrid might be feasible, possibly even outside of the existing local grid.
Actually, that's got me wondering. Is there any possibility of a small amount of PV on the shop as well? If so then you could put 1x Powerwall on the shop (providing backup to the refrigeration units), and sign both up for the Tesla Energy Plan. Assuming the same organisation pays the bills for both, you're essentially tying the two together without needing to do any complex wiring or fiddling about with electricity meters. It's a bit of a risk since it isn't guaranteed to be around in the long term, but generally I think splitting the PV and batteries might be a better option anyway - particularly if there is refrigeration and a dodgy grid.

Annual energy use for the hall alone is ~12MWh but that's historical so I'm not sure how accurate it is.
Is this the place you're talking about? (https://www.google.com/maps/@56.0702079,-6.1878522,3a,75y,326.13h,89.36t/data=!3m7!1e1!3m5!1sRVqTUy_7ai2oOxfApYfihA!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DRVqTUy_7ai2oOxfApYfihA%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D190.307%26pitch%3D0%26thumbfov%3D100!7i13312!8i6656)
PVGIS says you should get 17 MWh per year from a 20kW system - not a lot in winter though, maybe 10kWh/day. Enough to keep the lights on in winter, but not a lot more.

Tesla PW2s are 13.5kWh a piece with a 5kW continuous output (each).  One of the burning Q's is how to connect them for best effect given that the hall has a 3 phase system with loads shared across phases in the usual way but with the limitation of PWs that only a phase with a PW can continue to generate from the PV array in a grid failure scenario... and I think only one phase can have a PW.  So, they'd both have to be on the one phase...?  Or not?
You're not likely to be allowed to stick 20kW of PV on a single phase (it unbalances the grid), so that either means a 3-phase inverter or three single-phase inverters. Three single phase inverters makes more sense if you're only looking to have enough batteries to back up part of it - then it's essentially three single-phase systems behind a common meter.

Ideally we'd like to use stored power across the whole microgrid.  So, hall needs first (with a hierarchy of demand eg, lights, sockets, hot water storage, cooking facilities (all electric), heating), then the service point and then the shop.  There are a couple of business units nearby, too, but I doubt there would be much left over from the others even in max sunlight... but one of them *is* a brewery...
Remember that electricity isn't worth a whole lot per kWh, and wiring infrastructure like you're talking about costs money and adds a lot of complexity (fully segregated circuits to avoid creating loops between the two grids, etc.). Unless you're talking about taking over the whole local grid yourselves and putting a whole community behind a single meter (which opens up a new can of worms with regard to billing, etc. but has been done before - http://www.communitypower.scot/case-studies/projects/eigg-electric/ ) then it's a lot of investment and headaches for very little added value.
It's also worth pointing out that if using the battery as a grid backup you need to decide what the hierarchy is well in advance - anything on that circuit will be provided with power, everything else won't be. Assuming you want year-round backup then a 20kW array will give you something like 10kWh/day - split 3 ways (3 phases) then each Powerwall would get maybe 3kWh on an average December day. Unless you've got multi-day power-cuts as a threat then the Powerwall is going to be almost purely in grid backup mode at that time of year, although things will obviously improve as the days get longer - in May you'll average 8x as much. At a guess you can probably back up lighting and sockets, and cooking if it's gas rather than electric. Hot water and heating would drain the batteries in no time.

Discussions with DNO are being handled by one of the other team members so I don't know what progress has been made there.  I was hoping that the inclusion of storage would make the application more likely to succeed than without...?
Basically the power companies care about the amount of power being taken from or injected into their grid, the power quality (how close to a perfect sine wave it is, and what the power factor is), and how well balanced it is across the three phases. Depending on how you drive a battery it can make things better (supporting the grid when it's under strain) or worse (stopping charging just as the solar hits it's peak causing rapid change in demand). At a guess if you had one Powerwall per phase on all 3 phases it would support the application, two might not actually help very much.

No ground-mount PV facility and the roof is next to perfect so seems a shame not to use it!
Generally ground-mount is cheaper and performs a bit better - no need for scaffolding on installation, no risk of a leaking roof and better ventilation plus better alignment to the sun means slightly more power produced. Most people don't have anywhere to put it though.


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: martinwinlow on January 15, 2021, 02:54:13 PM
Thanks, pdf27 - Just the sort of useful insight I was hoping for.

All the respective buildings' power are paid for separately so I don't think that Eigg-like plan would work.  If we all had Powerwalls, then that might be a different matter...  Trenching etc to install a Hall to shop power link would be free but I take your point about payback times.  Can you expand on what sort of electrics would be needed (or indeed if it is practically-speaking possible) to power the shops fridges with excess PV?  I imagined a connection which essentially isolated the fridges in question from the shop supply (and meter) and connected them to the Hall's PV output only when it was advantageous to the Hall to do so...

We had a project meeting since my last post and as far as the 20kW of PV was concerned, the DNO has no objection...

MW


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: martinwinlow on January 15, 2021, 02:55:59 PM
Oh, and as a matter of interest, I have heard that Powerwalls are in very short supply at the moment... MW


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: pdf27 on January 15, 2021, 04:31:39 PM
All the respective buildings' power are paid for separately so I don't think that Eigg-like plan would work.  If we all had Powerwalls, then that might be a different matter...
Grids are a really, really good way of sharing power. Duplicating it really makes no sense at all - so either take over the whole island (like Eigg) or don't export power past where the meter is at the moment.

Trenching etc to install a Hall to shop power link would be free but I take your point about payback times.  Can you expand on what sort of electrics would be needed (or indeed if it is practically-speaking possible) to power the shops fridges with excess PV?  I imagined a connection which essentially isolated the fridges in question from the shop supply (and meter) and connected them to the Hall's PV output only when it was advantageous to the Hall to do so...
Essentially you need a transfer switch (https://www.justgenerators.co.uk/power-transfer-switches.html), pretty much like the ones you use for backup generators only triggered from an external sensor rather than whenever the grid drops out. The circuit for the fridges gets isolated completely isolated from the mains and goes onto the backup supply (in this case from the Hall). Not massively expensive, but does add complexity and you're going to cut the power whenever you transfer to and fro. Not sure if that would have any impact on the fridge reliability - probably not but worth checking with the manufacturer maybe.
And there is always a cost - even if you've got a mate with a digger who said they'll do it, they're giving up their time and diesel and will want paying back in future even if it's in free ice creams. You also need the armoured cable, transfer switch and the wiring modifications in the shop and hall.

If you really want to use PV in the shop, I'd look at disconnecting it from the grid and running it off a spur from the hall. That gives it access to the backup, means that PV will be used fully on it and avoids a standing charge - just run a 3-phase cable from the hall to the shop and connect it up where the current supply for the shop goes in. If necessary (depending on how the shop budget compares to the hall one) fit your own meter and pay for electricity used at an agreed rate. Probably cheaper overall - no standing charge and max PV self-consumption - but it's something that needs to be locked in over the longer term to justify the works.


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: martinwinlow on January 23, 2021, 01:26:06 PM
Hi pdf27,  It is looking like COVID is going to delay this project - mainly due to the problem of getting the instal company up for a site survey.  But that probably wont matter much in the scheme of things.

The shop reports about 1.1MWh annual electricity use.  In theory about 5% of the hall but we have no accurate data for the hall for some inexplicable reason.  I'll try to pin that number down a bit more...  Not being directly involved in its day-to-day running is making things a bit tricky.

The generally idea is appealing but whether the interested parties will agree is another matter.

Martin.


Title: Re: PV, Powerwalls and Local Microgrids...
Post by: billi on January 23, 2021, 05:41:43 PM
Well , why not get ONE battery  and three clever Inverters for each phase ?