Hi Yatchsman,

Welcome to the forum.

We have had a 4kW solar PV system for approximately 10 years, and it produces about 3000kWh of electrical energy each year. That is the good news. The not so good news is that most of the generation is from Spring through to Autumn. At the time it cost £10.5k for the panels, inverter and installation, but prices have fallen since then when the Feed in Tariff was reduced, and then stopped altogether.

Our system consists of 16 x 250W panels, on an East facing roof with a slope of 24 degrees. As an example, today, which was a typical grey November day, the total generation was 1.48kWh, so not enough to charge your car.

If you are planning to totally remove gas from the equation and install a heat pump, then you will no doubt required a hot water tank, which would allow the use of an immersion heater.

Let me explain how we use our solar PV system, to minimise the energy we draw from the grid. Once the panels start generating as the Sun rises, the output is initially used by what I call the base load, frig, freezer, router etc. Installed in my system is a unit called a power diverter, which can divert up to 3kW of electrical energy to a selected load. The advantage is that it only diverts the excess generation, which would normally be exported back to the grid. The diverter unit initially supplies power to the immersion heater in the hot water tank. From Spring through to Autumn, virtually the whole of our hot water is produced from solar energy.

One very important thing to check is that there isn't any form of shading to any of your roof space, as this will reduce the generation from your panels.

I don't have a battery system installed, but there are forum members who should be able to advise you about the pros and cons.

As far as anticipated output is concerned, I seem to remember someone posted details on the forum of a calculator that will give an assessment of what you can expect.

I have 8.4kw of solar, 14.2kwh of batteries and an ASHP (I'm also on Go). Will it run our house just from that? No. In the winter there is just no chance. We only made 6kw of power today total.

However can you make use of the low power and offset costs, certainly. You've opted for a very expensive, but very good battery. In total my total system including install cost me about £11k. However I sourced the panels myself and I decided on the battery/inverter for it. Powerwalls are good, I do like the UPS feature and it contains the inverter as well. But they are very expensive. If you want more storage for less money (and you're prepared to do some work) you might want to consider modular Lifepo4 batteries and building your own.

As an FYI you can just estimate your own solar production using this website. It's very straightforward and from my experience pretty accurate. My personal rule of thumb (down south) is 1000x your array. So for you, I would expect around 4.5MW

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

My panels are based around the roof (West, South and East) and produce all day. However you will get slightly less production than all South. However you'll find for a battery this is better as it smooths the peaks in and provides the maximum sunlight hours you can use.

I can't say i know how accurate this is or how flexible. 

Loop takes actual electricity readings from your electric smart meter every 30 minutes (assuming you have a smart meter) and can simulate the use of solar pv and batteries in your home. Like your energy provider, 30min is the limit they can get the data from the meter over the smart meter network which isn't great but would give you an idea. 

It is an app that you install on your phone.

https://loop.homes/

Might be interesting to see what it says for your home if nothing else. 

@batalto Hello and thank you for your comments and suggestions. I’m not really into diy of this kind and would prefer to leave it to the experts, obviously I pay for their expertise.

I didn’t specify the Tesla battery & do understand there are cheaper alternatives. I think the supplier said if I have a Tesla battery and Tesla car I would be eligible for the Tesla energy tariff, currently 8p/kWh flat rate through 24hrs. & therefore not limited to the 4 hours (although cheaper) octopus go tariff.

Are you able to top up the battery during the night on only the 4 hrs GO tariff during winter months or is 4 hours insufficient when solar is very limited.

@yachtsman I top up my battery fully using that 4hrs, but it's mostly gone by the end of the morning due to the ASHP grinding it up. But that time 12-8am is the heaviest heating use time

@derek-m thank you Derek that’s very interesting. Initially my plan is to install PV with battery storage and add an immersion heater for hot water, keeping the gas boiler, with a view to replacing it with a ASHP sometime later.

I want the solar to feed the battery which will then be topped up from the grid using one of the low cost nighttime tariffs. However if that’s not possible during winter months due to lack of solar and limited low cost hours (4hrs for GO) I would switch to the Tesla energy tariff presently 8p/kWh through 24hrs.

My questions to the forum are;

1. is the proposal good value for what is included ignoring ROI.

2. Can I achieve my goal with the proposed system and the likely generation or it it just a pipe dream

I didn’t mention in my original post that I have approx 10 pages of calcs, charts & graphs from the proposer to show their workings.

There is very little shading only marginal at the extremities of the suns arc where one roof falls out of exposure & another becomes exposed.

@yachtsman if you don't care about the ROI, then you cant really judge the value. The Tesla battery alone is the hands down the most expensive element at maybe £7k including install. I'm a little confused why you need the inverter, as the powerwall has an inbuilt one. £15k does seem punchy.

For example you can buy pre-built kits and install for much less and just get some bigger batteries - https://www.ebay.co.uk/itm/224443287556?hash=item3441dcc804:g:IikAAOSw3FBbKqt8

that said, you need a powerwall to get the Tesla tariff. So you could down the line of panels only - https://www.ebay.co.uk/itm/222853930371?hash=item33e3211d83:g:jrUAAOSwm8NbKqOM  

and then get the Powerwall2 afterwards. It would save you a few £k on the bill 

Posted by: @yachtsman

@batalto Hello and thank you for your comments and suggestions. I’m not really into diy of this kind and would prefer to leave it to the experts, obviously I pay for their expertise.

I didn’t specify the Tesla battery & do understand there are cheaper alternatives. I think the supplier said if I have a Tesla battery and Tesla car I would be eligible for the Tesla energy tariff, currently 8p/kWh flat rate through 24hrs. & therefore not limited to the 4 hours (although cheaper) octopus go tariff.

Are you able to top up the battery during the night on only the 4 hrs GO tariff during winter months or is 4 hours insufficient when solar is very limited.

Last time i looked the Tesla rate was 10 to 12p depending on location. 

https://octopus.energy/tesla-energy-plan-faq/

Is it this plan or another one? 

@jeff Hello Jeff, I’m not sure the 8p was quoted by both potential suppliers I contacted so they may have been quoting the rate prior the recent price hikes, maybe to make it look attractive.

Posted by: @yachtsman

@derek-m thank you Derek that’s very interesting. Initially my plan is to install PV with battery storage and add an immersion heater for hot water, keeping the gas boiler, with a view to replacing it with a ASHP sometime later.

I want the solar to feed the battery which will then be topped up from the grid using one of the low cost nighttime tariffs. However if that’s not possible during winter months due to lack of solar and limited low cost hours (4hrs for GO) I would switch to the Tesla energy tariff presently 8p/kWh through 24hrs.

My questions to the forum are;

1. is the proposal good value for what is included ignoring ROI.

2. Can I achieve my goal with the proposed system and the likely generation or it it just a pipe dream

I didn’t mention in my original post that I have approx 10 pages of calcs, charts & graphs from the proposer to show their workings.

There is very little shading only marginal at the extremities of the suns arc where one roof falls out of exposure & another becomes exposed.

Hi Yatchsman,

If you have a breakdown of the cost of the individual component parts and installation, you should be able to make a better assessment.

You can always Google the individual component parts and see the actual price at which they can be purchased by a customer. Your installer may get a discount from the distributor.

As I stated before, our 4kW solar PV system cost £10.5k, but prices have fallen since then and I think that you could expect to pay in the region of £6-7k for a 4.5kW system, which includes installation.

Obviously, you should get more generation from the SE and SW facing panels than the NE, and the peak generation of the whole system will be lower, but spread over a longer period of daylight hours. I assume that your installer has specified the Solar Edge P401 Optimisers is to help ensure maximum generation from the overall system as panels become shaded. The other thing to remember is that the degree of shading will probably vary throughout the year, since in June the Sun peaks at an angle of 60 degrees, as against December when then peak angle is only 13 degrees.

What size Tesla Powerwall are they proposing? The energy required, and time to fully charge, will be dependent on its capacity. I don't yet have battery storage, but Batalto seems to have no problem charging his batteries within a 4 hour period.

From the point of view of charging your EV, battery storage and possibly running an ASHP at the same time, you would need to confirm with the local grid that your electricity supply is adequate to meet the full load.

Yes Jeff that will be the plan.