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  • Writer's pictureThe Climate Coach

Rooftop solar - explained!

OK - so solar sounds like a good investment if I have the roof space and the money to invest. But where do you get started? What should I know before getting quotes?


What should I check before I get started?


If you are considering solar then it's likely you want to reduce your energy bills. So before you get started - and to make sure you don't invest more than you need, you really need to check your usage and see if you can reduce it first. E.g. if you are currently using 5000kWh per year but can easily reduce that to 3000kWh by making a few small changes - then actually the amount you would need to invest in solar will be lower and the payback could be quicker (although not always). Luckily - we've written a really handy guide on this topic exactly so check it out here.


Second, you need to know roughly how much electric you use and when you use it. If you have a smart meter - you may already know this and if you don't you can take some meter readings to work it out (or check your bill - but make sure that no estimates have been used to calculate this). This will help inform what size system would work best for you - and also whether you should include some battery storage in your system. For example, if your usage is mainly all during the daytime and hardly anything in the evenings/overnight then battery storage may not add much value to you. Whereas if you have a high "base load" (stuff that's always on) and thus have fairly high usage in the evenings/overnight then battery storage may prove a great option.


Ok, check - what next?


It's worth familiarising yourself with the key terms when it comes to solar. It's important that you see these on any quotes you receive and also understand what they mean. To help, I've listed out some of the key terms along with a description of what they mean in the table below which should be enough to give you a high level understanding of what you need to know...

Watt

Solar panels have a max. Watt rating which specifies their maximum output. Most standard size panels are between 300-400 watts. So 10 x 400 Watt panels would give you a max total output of 4kWp.

kWp

Max output of your solar panel system (e.g. 4 kWp means at max capacity, the panels are capable of generating 4 kW of power)

kWh

A unit of energy storage. (e.g. a 5kWh battery could release 1kW of power for 5 hours or if the 4kWp solar array generated at max capacity for an hour, it would generate 4kWh of energy)

​Inverter

The inverter converts energy from DC to AC- you'll need one to generate energy from your solar panels and to provide that power your house. You may also have a separate one to be used with AC coupled batteries also.

​Inverter kW rating

This is the maximum output in kW. So a 3.6kW inverter is capable of generating a maximum of 3.6kW of energy at any one time. If you had a 3.6kW inverter on your 4kWp solar panel array - even if it was in full sun and capable of generating 4kW, you'd still only generate 3.6kW because of the inverter.

Hybrid inverter

A hybrid inverter allows excess energy generation to be sent straight to battery storage without converting it to AC. In the example above when the panels could generate 4kW but are limited by the inverter to 3.6, a hybrid inverter would allow the excess 400 Watt to be directly stored in the battery or be used to power your house. Hybrid inverters have different max outputs so it's worth checking the specific model in your quote.

Microinverters

Rather than having 1 big inverter that all your panels feed into - you can have an individual inverter per panel. If one microinverter fails, you can easily replace it. You can also benefit from having individual output per panel which can be helpful if you have panels across multiple different roof aspects or have shading issues.

String

You may hear the installer talking about strings. A string will connect a group of panels to the inverter. So you may have 10 panels connected to your inverter on one string. This means that if the lowest panel output is 200W from 10 panels on the same string, all panels will be limited to 200W. Unless you have optimisers which allow panels to have different outputs. Different Inverters allow a different numbers of strings. If there is no shading and all panels are on the same roof - it's generally fine to have them all connected on the same string.

DC coupled battery

A DC coupled battery uses the same hybrid inverter as your solar panels. So this inverter controls generation from your panels, and also charge and discharge of the battery. Benefits are you don't need multiple inverters and DNO approval is generally a bit easier for this kind of solution but obviously negatives are that it's a single point of failure for your whole setup.

AC coupled battery

An AC coupled battery allows excess energy to be stored - or you can charge it from the grid and use it when you need it. It will have a separate inverter (to the one used for your solar panels) used to both charge and discharge the batteries. Additional DNO approval is usually required for this because they work of total inverter size (which would be two inverters in this case)

Optimisers

Some providers offer optimisers (SolarEdge or Tigo), which aim to improve solar panel performance where there is partial shade or split roof setups. If your installer recommends these - it's worth researching this to see whether you think it is or not. For certain types of shading - they can improve performance significantly but in others make next to no difference.

DNO

Distribution Network Operator - you'll need their approval to connect your solar panels to the grid. The installer should handle this for you but it's worth understanding the requirements so you know what to look out for.

G98/G99/G100

Various approval types required from your local DNO. Again - your installer should handle this but it's worth knowing which is required for you. For example; G99 approval is required BEFORE any work is started whereas G98 can be granted after installation. You can visit your local DNO website to see what approval type you will require, it's usually based on total inverter capacity - e.g. under 3.6kW inverter is usually G98.

​MCS

Microgeneration Certification Scheme - your installer will need to be MCS certified in order for your panels to be allowed to export energy to the grid.


Wow - surely that's it?


Well yes - with this information (your usage and the high level understanding of what a solar installation involves), you are pretty much ready to get some quotes. For any quote you get, you'll need to provide the details of your property (please note that a roof survey may be required on some older properties) and also as much detail as possible about your usage. Any quote should include details of how the proposed set up will benefit you and your usage. I would expect to see estimated total annual generation and how much you will likely use based on your usage patterns and then obviously an indication on how much you will save off your electric bills and thus an indication on ROI. You should also see within the quote exactly what equipment they will provide (what brand panels, inverters, batteries) - and I would encourage you to check out the technical specification of that equipment for reliability/warranty.


The final challenge is finding reputable installers in your area but knowing the above information can really help. For example, if you get any quotes that don't mention DNO approval (e.g. "G98 Approval") or don't have MCS registration on there - then you can either immediately discount them (because they definitely should have that) or at the very least ask why it's not on there. Also - if any of the above information is missing (e.g. your ROI, the brand of equipment), then that would be a watch out for me and definitely worth asking them about. I would also recommend checking Companies House to check how long the company has been trading and obviously read as many reviews as you can. Facebook groups can also be very helpful to find actual customers and recommendations for solar installers in your area.



What about price?


It's really difficult to compare pricing of quotes because obviously every installation is different in terms of complexity and material requirements - and the equipment itself can vary a lot too depending on what brand is used. As a simple example though, scaffolding can vary massively between two properties who are having the same panels and inverter installed. So one quote could have £0 (if you don't need any) to £1-2K (for a really complex requirement) - so in a direct comparison just looking at total price without context, the one with scaffolding would look overpriced when in fact it might not be. So if you do post in a Facebook group or similar asking for peoples opinion on whether it is a good price - ensure you include the full details in order to get decent feedback - and also bare in mind a lot of people won't know (because they are consumers and are just comparing to what they paid without taking everything into account).


What you can quite easily check though is the price of the equipment within your quote - so the cost of the panels, inverter and battery. Currently at time of writing, there is no VAT for solar installations so you should be checking the ex VAT price to what's in your quote. Your installer may even provide a breakdown outlining the cost of each part. Bear in mind though that you would expect a margin on it because obviously the installer needs to cover their costs (ordering and delivering the equipment to you) and also they have their profit on top of that. Ultimately, if it's within your budget and you can't see any excessive costs based on the above - and you've found a trusted reputable installer then you are likely good to go! You can always find things cheaper - but for me, this kind of investment isn't one you just want to go for the cheapest! You could easily find yourself with inferior equipment, shorter warranty and potential cut corners on your install - this clearly isn't always the case but the risk is definitely higher if you always go the cheapest!


All that's left to say is good luck!


If you have any thoughts, feedback or ideas you wish to contribute on this or any other topic covered by The Climate Coach - please get in touch, we'd love to hear from you.







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