You have done the right thing. You have got three quotes from different solar installers. Now you need to compare them. The problem is that no two quotes look the same. One gives you a bundled price for a "4kW system". Another lists every component separately. A third includes a battery that the other two did not mention. The system sizes are different, the brands are different, and the savings projections do not match.
Here is how to make sense of it.
Start with the system size
Every quote should state the total system size in kilowatts (kW). This is the combined output of all the panels. A 4kW system means four kilowatts of peak generation capacity under standard test conditions.
But system size alone does not tell you much. A 4kW system using eight 500W panels is not the same as a 4kW system using twelve 330W panels. The first uses fewer, more efficient panels and takes up less roof space. The second uses more panels of an older, less efficient design. Both are "4kW" on paper.
What to check: the number of panels, the wattage per panel, and the panel brand. If a quote does not name the panel brand and wattage, ask for it.
Check the inverter
The inverter converts DC electricity from the panels into AC electricity your home can use. It is the most technically complex component in the system and the one most likely to need replacing within the system's lifetime.
What to check: inverter brand and model, warranty length, and whether it is a standard string inverter or a hybrid inverter (which can also manage a battery). If you might add a battery later, a hybrid inverter now saves you replacing the inverter later.
Battery: included or not?
Some quotes include a battery. Some do not. Make sure you are comparing like with like. A quote with a battery will always be more expensive than one without, but the two are solving different problems.
If a battery is included, check: brand, capacity in kWh, chemistry (LFP is generally preferred over NMC for safety and longevity), and warranty length. If the battery is optional, ask for the quote both with and without so you can compare the panel and inverter costs directly.
Itemised vs. bundled pricing
A bundled quote gives you one price for the whole system. An itemised quote breaks it down: panels, inverter, battery, scaffolding, labour, DNO application, MCS registration, and any other costs. Itemised is always better for comparison.
If a quote is bundled, you cannot tell whether the price difference between two installers comes from the equipment, the labour, or the margin. Ask any installer who gives you a bundled quote to break it down. If they will not, that tells you something.
Warranty comparison
There are three warranties to compare.
- Panel product warranty. Covers manufacturing defects. Tier-1 manufacturers typically offer 25 years. Budget brands may offer 10 to 15 years.
- Panel performance warranty. Guarantees the panels will still produce a minimum percentage of their rated output after 25 years. Look for guaranteed output of at least 80% at year 25.
- Workmanship warranty. Covers the quality of the installation itself. This is the installer's warranty, not the manufacturer's. Check how long it lasts, whether it is insured (through a scheme like IAA's IBG), and what happens if the installer goes out of business.
Savings projections
Every installer will give you a savings estimate. These are projections, not guarantees. The figure depends on your electricity usage, how much you use during daylight hours, your tariff rate, the Smart Export Guarantee rate for surplus, and future energy prices that nobody can predict.
What to check: are the savings based on your actual electricity bill, or generic national averages? Does the projection assume current energy prices, or does it assume prices will rise? If the installer is projecting future energy price increases, what rate are they using and where does that assumption come from?
Who does the installation?
Ask whether the company uses its own employed installers or subcontractors. If they subcontract, ask who the subcontractor is and whether they are separately MCS-certified. This matters for quality control, accountability, and what happens if something goes wrong after install.
The comparison table you should build
Put all three quotes side by side and fill in these rows.
- System size (kW)
- Number of panels and wattage per panel
- Panel brand and product warranty
- Inverter brand, model, and warranty
- Battery: yes or no, brand, capacity, warranty
- Total price (ex. VAT if applicable)
- Price per kW installed
- Scaffolding: included or extra?
- DNO application: included or extra?
- MCS certification: yes, and which scheme?
- Workmanship warranty: length and insured by whom?
- Own installers or subcontractors?
- Savings projection: based on your bill or generic?
Any installer who cannot or will not fill in every row on this list is not giving you a complete quote. The best quote is not always the cheapest. It is the one that gives you the clearest picture of what you are buying, who is installing it, and what happens if something goes wrong.
