Specification for a Solar System 6 December 2020 at 2:59PM in Green & ethical MoneySaving 56 replies 940 views

Grumpy_chap

Inspired by these two threads:
https://forums.moneysavingexpert.com/discussion/6192502/solar-pv-battery-quotes/p1
and
https://forums.moneysavingexpert.com/discussion/6215701/considering-solar-pv-installation#latest
I think I can set about solar PV as a project for 2021.  Particularly by reference to the capital indicated by these threads about £10k.

The trouble is I don't really know how to specify the system, my thoughts are:

• The maximum number of solar panels that can be installed given the roof-space available.  Assuming the large part of the cost is in having the system and then the marginal cost for additional panels reduces.
• Is there any better specification / manufacturer for the actual panels?
• Mesh to prevent birds nesting between the panels and the roof.
• Battery storage.  Presumably 20kWh would be sufficient as average daily consumption is 10kWh for the house at present.
• Is there any better specification / manufacturer for the batteries?  Is the Tesla solar wall the best?
• Ability to interface with a (future) EV.  Does that mean that larger battery array is sensible to allow energy to be stored at day and charge the car at night?
• Last place for excess energy during generation to hot water
• Finally, export to grid if energy generation exceeds consumption, storage, water heating.  I think the export has to be capped.
• Presumably I will need a new electricity meter as I currently have an old dial meter.

If the above is roughly the correct way to specify what is required, how do I go about finding a reliable company to do the supply and install?  I have asked a couple of people I know with solar and they just say the providers all went out of business so none could make any recommendations.

My thoughts are that the way to operate the solar would be in the following order:

1. Meet current consumption at time of generation
2. Battery
3. EV (when we get one)
4. Hot water
5. Export to grid

Is that correct?

What else do I need to be thinking about?

michaels

Take one large ball of gas large enough for gravitational forces to be strong enough to pull the gas molecules into a plasma supporting a fusion chain reaction.  Add some other planetary material into a gravitational disk, the more dense particles coalescing to form small solid core planets whilst the gases will form giant planets with their own moonlet and ring systems.

Hexane

You're correct about marginal cost, a large part of the cost is often the necessary scaffolding or similar to install everything. Also correct bird mesh is essential for installs on anything above a single storey building.

Panel manufacturer isn't really an issue. You should be looking to buy panels of at least 300W each.

Not sure about battery spec and manufacturer (others will know more), Tesla Powerwall is very good but expensive. You might want to look into whether the chosen battery allows modular additions at low cost, and whether it allows islanding (which I think means you can still use power from the battery in the event of a grid outage).

Obtaining sufficient home battery capacity to significantly charge an EV from the home battery may be a false economy because of the large capacity involved; some people seem to charge their home battery from their solar installation but charge their EV on a special overnight tariff.

Diverting excess generated energy to a hot water immersion heater is unlikely to be cost effective if your export payments will be based on metered (not deemed) exports as seems likely and your usual domestic water heating is by a gas boiler.

Export will need to be capped if your system is capable of generating more than about 3.7kW unless you have an agreement with the DNO to export more, which can usually be obtained for free. Most systems are limited by the inverter specification or total panel wattage not by export capping.

I'm not sure what the situation is with electric meter replacement; when my system was installed the electric meter was left as-is and it was down to the DNO or electricity supplier to makes changes if they thought it necessary (it's their problem). Metered export may change this slightly as you will need a meter capable of reliably measuring export. You still shouldn't have to pay for that (I think) but I'm not sure of the details.

Your order of using the power looks correct to me.

Grumpy_chap

Thank you Hexane - very good point about being able to use power from the battery when the grid is out ("Islanding").  I assumed that was standard, but maybe not.  It is certainly one of my drivers as grid outages seem to be on the increase, and particularly noticeable when working from home.

Solarchaser

I think Hexane has covered most points.
What I would say though is that with your use being 10kwh a day, you are really going to struggle to get especially batteries to pay you back.
I've got  just under 20kwh of batteries and use around 8000kwh a year, I also DIY 'd the batteries, and I'm still around 12 year payback 

ABrass

Why do you want this? If it's to save money, drop the batteries. If it's because you want it, crack on, looks good.

Grumpy_chap

OK - so, the Council ran a "scheme" where they get an amazing rate for "group buying" solar.  I did my enquiry and have now received my proposal, which is rather sparse on details:

Personal recommendation for solar system:  £9,889
Generate 6,287 kWh per year
Grid independence 95%
To accept this offer, please simply click "accept", pay the £150 deposit to allow us to carry out your survey.

How on earth is anyone meant to assess an offer of such great level of detail?

QrizB

Grumpy_chap said:

How on earth is anyone meant to assess an offer of such great level of detail?

It's a bit of a mystery, isn't it? And I'm not sure it's such an amazing rate either.

I don't know where you are in the UK or which way your roof faces, but in the south you would need a 6.5 to 7kWp PV system to generate that much power in a year. You should be able to buy that, fitted by a MCS-certified installer, for £6k or so. You could add £3-4k for 7.2kWh of batteries and associated electrickery (eg. three 2.4kWh Pylontechs and an inverter) which would roughly match the total price you've been quoted, but it won't make you "95% grid independent" since you'll still need grid power during the dark months (Mid-Nov to Mid-Feb).

I think you can do better without the Council, both price- and transparency-wise.

Grumpy_chap

Thanks @QrizB
Do you have any advice on how to select a solar company?
I only know one person with a system, but the company they used is no longer trading.
Doing online searches, there seems to be very little process to split the best from the worst - a slick website means little.

I assumed the "Grid independence 95%" meant really big batteries charged all summer and powering me through the whole winter except, maybe, a few days by late February when the battery is depleted

Dolor

Grumpy_chap said:

OK - so, the Council ran a "scheme" where they get an amazing rate for "group buying" solar.  I did my enquiry and have now received my proposal, which is rather sparse on details:

Personal recommendation for solar system:  £9,889
Generate 6,287 kWh per year
Grid independence 95%
To accept this offer, please simply click "accept", pay the £150 deposit to allow us to carry out your survey.

How on earth is anyone meant to assess an offer of such great level of detail?

A system that generates 6287kWhs a year would suggest a 7/7.5kWp array. However, until the installer has consulted with your DNO he will not know whether there is likely to be an export limit. The DNO’s advice doesn’t come free. I assume that a battery is included in the quote? A battery of any size is deemed to be a generator and it requires DNO approval irrespective of the size of the PV array. Unless the installer knows how much energy you will be using each year, I doubt the the 95% Grid independence claim is valid. For example, I have a 7kWp array (export limited to 5kWs) and a PW2. We consume about 4500kWhs/year of which 800kWhs is imported during the Winter months. There is no way that I will get close to 95% Grid independence.

I am happy to be told that I am wrong but I have yet to see batteries other than a PW2 that will ‘island’ the home from the Grid if the power fails. The PW2 Gateway isn’t cheap. A battery set up with a dedicated 13 amp socket is not the same as an uninterrupted supply to the whole house. A set up such as the PW2 has the additional advantage that there is no need to shut down the solar output if there is somewhere for it to go within the home or battery. Standard arrays with batteries have to shut down when there is a Grid failure to ensure that there is no export to the Grid.

FWiW, I paid just over £16k for my array with SolarEdge and in roof fitting on two separate buildings; PW2 with Gateway and a Zappi and EDDI. We have not required any Grid energy since late February. Putting to one side payback, it was the right thing for us to do and it is a great feeling knowing that the home is being powered by the sun.

PS Your original 20kWhs battery storage sounds great but with a PVGIS solar output target of 160kWhs in January, you might struggle to keep them charged with solar power, and struggle to charge them when Grid energy is cheap.

PPS A final thought. If you are looking for SEG payments from Octopus they are presently insisting that all installations have a MCS Certificate. The SEG rules allow suppliers room for manoeuvre on this. The issue is that some other installation schemes are not yet fully compliant with industry accreditations.

QrizB

Grumpy_chap said:

Thanks @QrizB
Do you have any advice on how to select a solar company?

@Dolor 's reply is more comprehensive than mine but we seem to be in broad agreement. As for choosing, this is what I did.

I've recently had a system installed (see this thread) and I did all the due dilicence I could. I made sure the company I chose was MCS certified, a member of a relevant trade organisation (HIES, in this case) and had no horror stories on this forum or elsewhere. I checked their accounts and other records at Companies House. I spoke to a MSE forum member who had used them recently and made sure he was happy with their service.

I got a detailed quote and didn't pay them anything until after they had completed their site survey and had agreed an installation date. The deposit was 25% and the remainder was only payable once the job was complete (apart for paperwork, since you need a "paid" invoice as proof of ownership in order to register for SEG payments).

I'm happy with how everything turned out!