UKC

Starting to give serious thought to getting some home solar panels installed - partly as my wife's company has changed their car policy and we're about to order an electric car.

We've got a large, south-facing roof with no obstructions like trees or other buildings in the way, so would get a full day of exposure all year round.

Assume I don't know anything about them and go from there, please!

Don't get me started on why they weren't installed as standard on a new-build!

I have had solar panels for 8 years or so and have had a electric car for a year and half. So with 3.4 kW max panels I can generate 14kW on a clear summers day. So 3 such days charges the car fully.now PV is much cheaper than it was last decade. My friend has just had a quote of 13k GBP for 8kWmax (inc battery). You'll need to get at least three quotes to drive the price down as the installers do take the piss if not pushed. The energy saving trust has a calculator that tells you how quickly your panels will pay for themselves but in short any south facing, east or west facing roof. That isn't overshadowed will pay for itself so get as many panels as you can afford. Consider installing a zappi charger from myenergi.com as it will sync with the sun and only charge your car when there is solar energy available. Many people install a battery too but that is very expensive. You have a massive battery in the car and when you are out and about you could use the spare capacity to heat water using an eddi. In my view that makes a battery unnecessary but you can make your own decision based on the capacity of the array and how often your car will be connected. 

Sorry no help to you but a further question.

What is typical payback time both with and without an electric car?

I am in my 50s so a 25yr payback would be a huge turn off. 

https://energysavingtrust.org.uk/tool/solar-energy-calculator/

Depends on latitude, roof angle from south and inclination and over shadowing. 

Any idea if the car battery can be used in two directions? Charge the car in the day but then draw power from the car overnight when needed, obviously with a minimum car battery charge state programmed in to prevent it going below 75% for example. 

I'm no expert so I might get all this wrong 

We got a battery with ours, a 5.6 KW I think. It was about 2 grand. I think the house runs on about 1KWh when the air source heating is off and no washing machines etc running. When it's sunny the battery is full and we can run any high power appliance without using it. So once the sun sets I think we get about 5 more hours of free power.  

Cheers for the link. Assuming all goes well and you stay in the same house for 25 years there appears to be a modest benefit.

I’m not sure there are large enough benefits for me currently*
*the definition of ‘static’ electricity prices could have a significant influence. If it means stay at June 22 rates then the lifetime benefit would likely be significant.

I have solar panels, an electric car and a zappi.  During the summer months I can largely run my car directly on energy harvested from the roof of my house.

Have very recently got an Eddi, which diverts any unused solar energy into my water-tank, cutting out most of the need to use oil to heat the water.

Unfortunately I don’t have any payback figures as I’ve had my panels for about 10 years, the zappi and electric car for just short of four and only very recently got the Eddi.

Ha, according to that it would cost me an additional £1,200 over the lifetime of the PV panels to install them - and I would imagine that they base there figures on generous payback rates etc 

The energy price cap is due to go up again in October, currently expected to be around another 40% hike on the current cap.

The smart grid is going to do that I. The future so expect payments or discounts on your fuel bill if you let the grid use your car battery.

But in terms of energy usage air heating is first and water heating is second so using the eddi will likely consume every last watt for your own benefit. Running the telly in he evening is trivial.

OK, in simple terms how does that work in terms of metering?

Does the house run off battery and them metering kicks in when power from the grid is fed to battery/house?

You would want to check the number of cycles the car battery can handle before doing that and work out your electrical energy money saving Vs the battery depreciation.

I'd have assumed that due to the weight requirements of a car battery it would be an expensive way of doing things compared to a house battery.

You can get microgrid control hubs which will organise all this for you. I spoke with a chap who had PV, electric car, house battery and big water tank. The hub would then use the PV to preferentially charge the car, charge the house, heat the thermal store and then finally export to the grid.

What was the delivery time for the kit?

I am looking into it. I have an old house and my energy bills are pretty large. I have a paddock and would like to install the panels there. I have had a company around and long story short, they predict their system will halve my electricity bill a year (or provide at least 50% of my electricity)

Unfortunately for me, it seems the council will have an issue with installing the panels  in my paddock as that land is designated "agricultural" and the panels are for home use (I don't live on a farm) Ridiculous as far as I am concerned and I am hoping they will allow it

Reply to NottsRich:

Theoretically yes, but in practice not yet.

ROI for indivual projects will depend massively on indivial circumstances and how the home is used, though for many people out of the house 8-6 you'll need battery storage to get the most out of panels..

Worth shopping around to see what types of tariffs people like Octopus can offer for eV charging, export payments, grid balancing etc etc

You should be able to pick up a 4kWp system for 7kish now, plus a few grand on batteries. Costs are likely to fall with batteries, and second life used EV batteries will be fine for home applications 

What's your motivation here?

If this is purely to get cheap car charging, then honestly it'll be lots easier just to switch to a tariff like Octopus Go to get their super cheap off-peak pricing.  I think they're currently offering 7.5p/kWh overnight (I'm still on a fix at 5p). Although I have PV, most of my car charging is done overnight as it's convenient and reliable.  In the daytime, you need to be thinking about whether the sun is actually shining...

If you're doing it for environmental reasons, then yes, getting as many panels as you can is a great move.  They become carbon neutral in year 3.  Lots of calculators (like the one linked above) assume 25 year lifespans but in reality there's no real reason they won't keep going for rather longer, just with their performance gradually tailing off.

I am unconvinced by the arguments for home batteries yet - you're better just exporting the power and letting someone else use it.  As long as the UK grid still have gas fired stations as part of the mix, then exporting your PV is always a good thing to do.  And I suspect we aren't far from cars being able to run both ways and power the home when the sun isn't shining.  I'm holding off for now.

As for the Eddi type diverters - if your hot water tank is gas heated, then they are actively carbon increasing and should never have been introduced.  If you are on oil then there's an argument for using one.

As a useful guide, if your roof is south facing, around 40 degrees, and absolutely unshaded, you will generate approximately as many kWh in a year as your peak output in Watts.  But it's heavily seasonal.  This year my June average (from a 5.7kW system) was 22kWh a day, but December was 3.7kWh (and that was boosted by three very sunny days - the rest of the month averaged about 2kWh/day).

Historically, the best thing to do was to install just enough panel capacity to satisfy your baseload daytime demand (Fridge + things on standby).  This was because the cost of panels was so high and the payment for export was so low (relatively) you only profited by not using peak rate grid power - the value of any of the excess kWs you sent to the grid was less than the cost of the panel capacity to provide them.

Today, things are different - cost of panels has plummeted, value of export units has risen. Thus it almost certainly makes sense to install as much capacity as possible as the value of exported units outweighs the panel cost.  We had a quote a couple of years ago for an 8kWp system on a 'perfect' roof which would have paid back in 12 years. That was ~£12k for marine-grade panels with 25yr guarantee, expensive labour rates for the install, 8.3p/kW feed-in tariff, and minimal domestic usage.  Battery storage (Tesla powerwall etc.) is not so clear-cut - I think a lot depends on your household consumption and when you consume.  For us it wasn't worth it as we had gas heating & hot water.  What you need is quotes, and testimonies.

Jamie's 'annual kWs = kWp installed capacity' rule of thumb is about right, case studies from LGEC demonstrate this. Interestingly, although Scotland is far north, apparently panels on the eastern (sunny) side can produce as much per year as panels in the south of England as the days are longer in summer.  If you live in Scotland I believe you can get up to £10k interest free loan from government for panels / heat pumps etc.

You also need to consider the roof - If your roof is likely to need work before the panels' life expectancy expires, then the extra costs due to panels could outweigh the benefits.  Also, although it's not fashionable, solar thermal is more efficient than PV and should be considered.

Not *yet*. Sigh.

My wife's first job, post PhD, was directly tackling this problem. Then here company got a bollocksing by the parent corporation for having too many green-fields projects, costs got cut under COVID mitigation measures, people changed and the whole thing went up in flames.

So she got another job in another company working on similar problems and applications, this time with grant money, but they've gone full "silicone valley start-up", C-level has tasted moneys and turned maximally rabid, everyone with a brain has consequently jumped ship, the empty desks have been filled with uneducated newbies, and she's now looking for another position, again.

How so?

When getting quotes, ask each installer what the lead time is for the inverter.  Make sure you get an actual lead time, not an off-the-cuff estimate.  Then you can consider the quoted price vs when they might actually be able to make the system work.

Things are not looking great in the supply chain for power conversion electronics right now.

I think it bypasses so the house runs off the battery until it's out then switches to the supply. I might be wrong about that though. 

I'm shortly moving into a new house with solar panels and an air source heat pump with under floor heating.  I was told that during the summer months, with careful use of things like washing machines, the electricity provider will be paying me but another friend has advised that the repayments are so small these days that it is better to install batteries and store the electric for your own use.  What experience do others have?

It depends on your supplier, some pay as little as a £0.01/kW, others up to £0.06/kW. Google smart export guarantee scheme comparison 

But yes, the business case for bettery storage gets better and better, especially given another price hike in the autumn

https://www.kaluza.com/flexibility-platform/

Kaluza Flex (OVO Energy) does exactly this. Source: I work there

Edit: https://www.kaluza.com/vehicle-to-grid-v2g/ is the product

This is what we were told, I'm not sure what rate we get. Our bills are low in summer compared to winter but still 80 quid or so. We've got solar thermal too which heats the water in summer.

Have you considered batteries?  Have you any idea how much they cost?

It makes a considerable difference if you have a tariff (eg Octopus Outgoing) that allows you to export back to the grid at peak times (usually when the sun is not shining) - hypothetically allowing you to make more from exporting than you actually pay for the electricity you use.

Of more practical concern is the actual availability of components, which currently suffer from the same supply chain issues as electric vehicles.

The Octopus Outgoing tariff is considerably more than this. It varies throughout the day but at time of writing is around 28p/kWh. 

Last month I made around £20 in export from my 2.2Kw array.

All solar PV exported can be considered as displacing the most responsive non-renewable source of electricity, which is gas (CCGT).

So, you either displace gas (heating water) or gas (CCGT electricity).  The efficiency of heating with gas is much better than of electricity generation and distribution, so exporting is the way to go from a CO2 perspective.

Through the same statistical lens, what batteries do is load shift the time of gas CCGT generation, reducing efficiency through round trip battery losses in the process.

Batteries are not intrinsically green, but if they provide a financial McGuffin that gets someone installing solar PV, it’s not all bad…

All this changes in the future as the supply mix changes.

Yes, but that's a dedicated battery storage export tariff and not covered by what's usually thought of/covered by the OFGEM regulated Smart Export Guarantee scheme, which only applies to microgeneration.

I.e  anybody with solar can receive approx 0.01 -0.06/kWh but to access your rates you need battery storage, and an Octopus contract

It is not. I don't have a battery.

Is that commercially available? Also, is that available to SMEs or just domestic premises?

Alternatively, after a good look into the costs and payoffs, you could start idly browsing for clean energy funds, or specific solar energy funds, and after a bit of thought decide to put your £12k in those instead. That way you've paid to put solar panels somewhere known to generate plenty of power, buying and installing them at industry prices, not retail. Decent chance you'll get your payoff much quicker, not least because you can sell when you like. Environmental win and financial win.

I stand corrected

Incidentally, Octopus really show up the rest of the market!

The Eddi arrived in about a week - it was the only one we could find in stock.  Most stockists had run out, so I suspect there might be a problem with demand outstripping supply atm.

The panels and Zappi have been installed for years.

The amount of FiT you receive for your energy depends on when you (or whoever installed the panels) signed up.  As I understand it, the FiT pay-in tariff is attached to the property and not the person who initially signed up.

So, if your property was signed into FiTs when the payment was generous, you will now be the recipient.

Wildcard option.

Take your cash and invest it in utility scale battery storage.

These guys can take advantage of daily wholesale electricity market fluctuations to profit from arbitrage and sell frequently response services to the grid.

Currently paying dividends with a yield of 7% and up 4%. The only good investment I've made in the last few years.

Anyone with battery storage and a suitable tariff can do that, as wholesale prices for the next day are available publicly.

We've got a battery, it was quite cheap but I don't know how much or what rating it is. This is a family home I renovated for my mam and sister so I don't have the details. The battery seems quite good to me but will have to look into these energy suppliers because we seem to be getting quite a bad deal!

Quick illustration for the benefit of the phantom disliker:

Octopus Go tariff gives five hours of electricity at 7.5p/kWh

Average export tariff during peak period the next day is 21p/kWh

Export 5kwh back to the grid (say 50% of 10Kwh battery capacity) the following day during peak period gives total profit 67.5p leaving 5kwh for domestic consumption.

Do they give you separate meters, or it it a single one run backwards? If it's separate ones then surely you simply want to join them together with a fat wire and diode..........?

That calculator is well out on installation costs - estimated £5k for me, I had a few quotes last year, nothing under £8.5k, which does eat somewhat into the 5k lifetime profit... Any tips for finding someone who will do me a 4kwp setup for around £5k in Yorkshire would be gratefully received if there are any tricks beyond ringing several and trying to quote-war them

£8.5k for 4kWp PV alone, no battery?  That's steep.  I got 5.7kWp for almost exactly £10k, five years ago (prices have dropped since then), in Oxford.

That did include a 1k battery to be fair. Prices are going up here not down, definitely - my mother paid significantly less a few years ago.

Just looked, I have an email from 2018 advertising a 4k setup for £4,150, and a look on their site shows the same now for £6295, going up past 10k if you want a battery with it. Even if they ain't the cheapest available, I'd bet the % increase isn't unusual
https://contact-solar.co.uk/

Apparently there is a shortage of batteries and inverters and a huge demand because of the high energy prices. In time that will settle down but the best way I have found is to know what you are willing to pay (and what is reasonable) and have the money ready. Then you can honestly say to the supplier that if they match that price and have stock then they can have the business. 

Any idea if I can access the octopus export tariff alongside my FIT payments? On 2p / kWh is the deemed export which I would willingly forgo for aa 21p/kWh payment.

I've just had a few quotes from various installers for a 4kW array and also looked into self installing using an unaccredited electrician - so wouldn't be eligible for the smart export guarantee.  They're slightly different systems, so not 100% comparable, but the cost of a kit for self installing was £6.3k (micro-inverters + immersion controller with ground mount kit). I would have to also persuade a friendly electrician to do the final connection to the CU and all the groundworks and panel set up myself.

Two quotes from installers (string inverters, no immersion controller) were £6.7k and £7.8k. No battery included in any of these. I'm in north Scotland.

As someone else has pointed out, prices are rising rather than falling.

I don't know much about FIT as that scheme had expired before my installation was done. As far as I am aware the Octopus Outgoing tariff is available to anyone with a smart meter.

Yes this will be the sticking point for many I think. It's the same issue with EVs and the reason why the second hand car market is so buoyant.

May be worth noting for people in England that this falls outside of the permitted development rights in a conservation area. The install has to be MCS approved for those.  (No idea of the rules in Scotland where you are.)

Bimble Solar often have great deals on used solar panels; get some of a popular size for new panels and you can re-power the array in a decades time when prices are hopefully under control.

Pro tip - if you're doing DC cabling to an inverter yourself, don't use cheap MC4 crimp connectors from a common online marketplace; get quality ones from somewhere like wind and sun.  Don't forget to budget for the cost of the appropriate crimping tools (!), again I would buy known quality over cheap; you don't want poor contacts leading to a fire an MC4  It may be that use of micro-inverters avoids any custom DC cabling.

Hah... well it's not quite so simple as the arbitrage opportunities are only available at certain times of day so you need software to decide when to charge the battery and when to export.

There are two metering points (MPAN codes), one for export and one for import - but only one hardware device as far as I can tell.

This is not possible because Octopus will not allow Go customers on to a decent export tariff. The best you can get is 3-4p/kWh. I've looked in to it. Of course Go is still a great deal if you have an EV...but if you have panels too, you do not get the 'too good to be true' option.

But not to anyone on Octopus Go, or I believe Octopus Intelligent (just to reiterate my other post). Unfortunately there are no other competitive EV (is cheap off-peak) tariffs at the moment.

It's called a grid-tie inverter. It coverts the DC from the, usually 48V, battery to mains AC but syncs up the 50Hz grid frequency so both power sources can put energy into your house wiring at the same time. The inverter will have a slightly higher voltage than the grid so that is used first but only up to the limit of it's power capacity. So if you have a 5kW inverter and turn a 3kW kettle and 3kW hob on, then you'd pull 1kW from the grid.

The battery/inverter system will have a connection to a separate meter after the utility meter to know how much power to put back into the house to try to keep the export to the grid as close to zero as much as possible. If your house is only using 200W then, ideally, that's what the inverter will be producing.

I've got about 1.2kW of solar between the couple of second hand panels in my garden and the panels on my campervan roof but there's a 7kWh battery in the van with a 3kW inverter/charger. I'm using a scheduled charge on Octopus Go's 5p/kWh night rate (currently 7.5p for new customers) for the van battery and powering the house in the day from that. My last monthly electricity bill was £19.80. I worked out it would be over £60 without the van system. I still use gas for hot water btw.

The battery and inverter will have paid for itself in around 3 years I think. Batteries make a lot of sense even if you don't have solar. My panels will be hardly getting any energy in winter but the battery will still be offsetting my usage to the cheap rate at night.

I can see a time coming when there is no cheap night rate though as the demand for EV night charging means it'll no longer be off-peak.

If you're going DIY ground mount solar, it may be worth giving these guys a call https://www.solar-frames.co.uk/

Being able to seasonally adjust the panel angle should be a big bonus in Scotland.

I've been monitoring PV cost:benefit for a few years now an have never felt the returns on a £10k investment were justified. I agree that recent installation costs are climbing fast. As a tangent I've shied away from installing air conditioning in the house due to unethical use of energy. However a recent trip to Norway showed commonplace use of air to air heat pumps to heat in winter and cool in summer. Running these off a PV array might prove cost effective. Anyone got experience of air to air in the UK? Online sources seem very vague.

Aren't most commercial HVAC systems air to air?

This is what is used in most small office buildings that have been built in the UK over the last decade. This typically is referred to as a VRF split system.

People don't typically use them in the UK domestic setting due to the indoor units using fans to drive convection over the heating/cooling coils. This can cause noise.

You can get high efficiency and output out of them however so they are much more suitable for high heat loss existing housing than an air to water heat pump reliant on radiators or underfloor heating.

Large building tend to still use wet systems with an air to water heat pump heating/cooling water to then be circulated round the building to provide local heating and cooling. There are limitations in the lengths of refrigeration runs possible with VRF systems for this application.

The only all air heating systems tend to be used in spaces with enormous volumes such as sports stadium, airport terminal etc. These all would traditionally had wet systems attached to boilers.

We are looing to replace a cheap, very reliable inline electric boiler (no servicing required at all in 9 years) with some form of air source heating. We've got quotes for various air-to-water systems and will likely go down this route, but we have also got a single quote for an air-to-air system. Both heating systems are for a modern extension but not for the older part of the house, which is heated separately. Its largely open plan, so well suited to air to air and the header unit inside would have a very short run of ducting to the outside unit. Install costs are much lower: £2-3k compared with £8-10k for air to water. However, air to air systems won't heat the DHW tank and are not eligible for grant funding. To counter that, they do have a claimed Coefficient of Performance factor (i.e. higher efficiency) than air-to-water - close to 4 compared with 3 on a good day (scotland in winter) for air-to water.

I don't know what's available in England, but in Scotland we can currently claim for a 75% grant for the air to water system, making the two systems very similar costs to ourselves. So a fairly easy decision for us, but maybe not everybody. It does also mean that you have to actually get hold of Home Energy Scotland and get yourself in the queue for grant funding (and be eligible) - which is definitely not trivial right now!

I think you're right that current deals will no longer exist in the same form, but something will be very necessary, otherwise a lot of people will get home from work at 5-6pm and plug in at peak time. I suspect that we'll either end up with something that is actively managed remotely like Octopus Intelligent where you just set a deadline and the electric company then decides, via the now-mandated smart charger, when to charge the car for you for a slightly cheaper rate, or else we'll retain cheap rates but they will be over a variety of time periods and not quite so cheap. But who knows really.

I bought a small air-to-water heat pump intended for small, metal framed above ground swimming pools.  With the help of some insulated pipe runs going through a baffle in the cat fap, and inflatable paddling pool and a wee little galvanically isolated DC pump we can cool the house and have hot garden baths instead of using the fossil boiler in the summer.  

Heck of a kludge and you can’t use the door with the cat flap, but there’s no reason houses with a thermal store couldn’t have an internal air > water system to cool the house and heat the water.  You’d probably need to have baths rather than showers to make it worthwhile…?

The problem with our house is that it’s temperature ratchets up day-by-day over several sunny days.   The energy efficient answer to cooling I think is to reset the interior temperature each night with housewide positive input ventilation of cool night air.

That's unfortunate, but makes sense from Octopus' perspective. It may be possible to do this kind of thing with the Octopus Agile tariff (which I believe *is* available with Outgoing) but at the moment that is not cost effective due to high wholesale prices. Anyone on Agile at the moment will be regularly paying 35p/kWh for their electricity, compared to about 3p/kWh at various points a couple of years ago (plus the occasional negative rate when you get paid for putting your tumble drier on...).