A pre-feasibility assessment in under a minute. Drop the pin on your building, describe it in five clicks, and see the size, cost, returns and occupier savings a solar PV system could deliver.
The site
Couldn't find that address. Drag the pin onto the building instead.
Drag the pin onto the target building. Location sets the generation region automatically.
The building
Units follow the pin: sq ft · UK. Tap m² or sq ft to choose yourself.
Not sure? Measure it on the map above: tap Measure roof, then click the roof corners.
Roof lights reduce the usable roof area for panels.
0%Slide to resize the system80%
Calculated from the roof type and roof lights.
Energy
Optional: if you have the building's real figure, enter it to override the selection above.
How many days a week the building uses power. Continuous operations should choose 7.
Operating model
The landlord invests and either sells the power to the occupier or gives it away as an incentive.
If the landlord controls the roof, a licence or lease variation is needed before the tenant can install.
These two shape the recharge arrangement available, and set the default PPA rate.
The rate the occupier pays for each unit of solar power.
What the occupier pays the grid today. Adjust if you know the actual rate.
If the lease has under ten years to run, the report gains a lease-aware second page.
If provided, the occupier's saving is also expressed against the rent.
Report extras
A point is added to your yield for prudence, and acquisition costs are allowed for.
Specialist asset finance via Syzygy's panel. Arrangement costs of 5% are included.
Capacity
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Project cost
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Net revenue · year one
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Yield on cost
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25-year IRR
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Gross revenue / yr
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Generation, year one ·
Energy
Power demand / yr
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This is an estimated figure
Potential capacity
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Generation / yr
0
Year one
Consumed on site
0%
Decarbonisation
0%
Generation vs power demand
CO₂ avoided / yr
0 t
Grid displacement
Commercial
Payback
-
Simple, on net revenue
Occupier savings / yr
£0
Their reason to say yes
Opex / yr
£0
Maintenance + asset mgmt
Illustrative valuation
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Financed over 10 yrs
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Capacity
0
Power demand / yr
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Occupier savings · year one
£0
Year 1
£0
5 years
£0
10 years
£0
15 years
£0
Savings vs buying the same power from the grid
Capacity
0
Indicative, pre-survey
Generation / yr
0
Year one
Consumed on site
0%
Power demand / yr
0
This is an estimated figure
Decarbonisation
0%
Generation vs power demand
Export revenue / yr
£0
Surplus sold to the grid
Opex / yr
£0
Maintenance + asset mgmt
The two models, side by side
Sell power
Free power
Project funded by
Landlord
Landlord
Landlord net revenue · yr 1
-
-
Yield on cost
-
-
Occupier benefit · yr 1
-
-
Running costs paid by
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One system, two ways to run it: earn from it, or deploy it as a letting and retention incentive.
Pre-feasibility indication only, produced from rules of thumb and the assumptions stated on the report. A Syzygy feasibility study replaces every number here with your building's real half-hourly demand data, grid position, roof condition and structural capacity.
The basics
Three parts, one system
A rooftop solar PV system comes down to three working parts. Together, they supply power behind the meter, which is where the savings come from.
The panels
The panels collect daylight and are installed directly on the roof. Their output varies with the amount of daylight, but they keep generating whether it is sunny or not. With 25-year warranties and very slow degradation, they are the most reliable of the three components.
The inverter
The inverter converts the direct current (DC) produced by the panels into alternating current (AC), which the building can use and the grid can accept. This makes it a crucial part of the system. It is also the most complex component and the most common point of failure, which is why monitoring it matters so much.
The connection
The system is wired in on the building's side of the electricity meter (behind the meter). The electricity it generates is used on site first, reducing the amount imported from the grid and lowering the energy bill. The grid tops up any remaining demand, and any surplus solar electricity is exported.
The two units worth being precise about
kWp is the size of the engine. kWh is the miles driven.
kWp (kilowatt peak) describes the size of the system: what the panels could produce in ideal conditions. kWh (kilowatt hours) is the volume of energy actually produced (what appears on bills, what gets sold and what generates savings). Almost every misunderstanding in solar traces back to muddling these two.
Rule of thumb: a well-designed UK rooftop system produces approximately 900 kWh per year for every kWp installed (c. 850 kWh/kWp in the north and c. 950 kWh/kWp in the south).
Key figures
c. 900 kWh
Per kWp, per year
UK average, well-designed system
25+ yrs
Panel warranties
Performance guaranteed long term
350
A 1.5 MWp system's annual output
Equivalent to 350 homes' yearly demand
Commercial mechanics
Where the money comes from, and how it flows
Every kWh the solar PV system generates goes one of two ways, and the two are worth very different amounts. That single fact shapes the whole project commercially.
On-site consumption · the valuable bit
Power consumed in the building displaces electricity the occupier would otherwise buy from the grid at full retail rates. The occupier buys it from you at a discount, typically in the range of 14p to 17p/kWh. They save money and you earn revenue, while the building's carbon footprint falls. Everyone is better off.
Export to grid · the leftover
Whatever the building does not use at the moment it is generated flows out to the grid and is sold under an export agreement, typically at c. 7p/kWh. This is worth having, but the commercial impact is less significant.
Because on-site power is worth more than twice the exported power, returns depend less on how big the system is and more on how well its output matches the building's demand. The aim is a system sized so that most of its output is used on site. This is also why our recommendation is based on size relative to demand, and why the feasibility study works from real consumption data rather than assumptions.
The operating models
Four different types of project structure
Who buys the power, and under what document, depends on the lease structure and how the building is supplied. Pick a model to see how the power and the money flow.
Worked example: a 1 MWp system (c. 60,000 sq ft of panels) generating 1,020,000 kWh a year, with 75% consumed on site. All rates are indicative.
Power
Rooftop solar PV1 MWp · landlord's asset
75% used on site 765,000 kWh
The buildingthe occupier's demand
grid top-up
The gridimport and export
25% exported to the grid · 255,000 kWh
Money
Occupierpays for solar used
£115,000 a year 15p/kWh
Landlord£133,000 gross a year
£17,900 a year 7p/kWh
Utilityexport PPA
£133,000
Gross income a year
£68,900
Occupier saving a year
37.5%
Below the 24p market price
Occupiers are billed at their agreed rate
The structure
Revenue and costs
How the money flows
The system meters what each occupier uses
Billing-grade metering records every unit of solar power supplied to each unit, and every unit exported.
Occupiers are billed at their agreed rate
Under a PPA or lease variation, or through the service charge on multi-let assets. Recharge statements are issued monthly or quarterly, evidenced by the meter data.
Surplus is exported and paid for
An energy company buys the exported power under an export PPA. The rate is reviewed against the market so each system keeps earning its full potential.
Income lands with the owner
Operating costs (monitoring, maintenance, insurance) are deducted, and the balance is the return the business case promised.
How Syzygy reports it
You see the same numbers we do
Every system we manage sits on pvlab®, our asset management platform. Each quarter you receive financial and technical reporting: generation against forecast, revenue and savings, operating costs and carbon. We issue the recharge statements to occupiers on your behalf, review export rates against the market, and feed data straight to your valuers and environmental, social and governance (ESG) advisers. No spreadsheets to chase, no estimates where there should be evidence.
Key figures
14–17p
On-site rate
Typical recharge range, per kWh
c. 7p
Export rate
Indicative export PPA, per kWh
Over 2×
The value gap
Why on-site use drives returns
The project
From idea to operating asset: four stages
A solar project follows the same shape every time. Knowing where the effort really sits – in development, not installation – is half the battle.
01
Scope
About one month
During the feasibility study, real energy data is analysed, the system is sized and visualised, the grid position is checked and the operating model is presented. The result is a business case with a forecast budget, indicative returns and the sensitivities to consider. This is the decision point: a small fee buys the numbers to commit with confidence, or to rule the asset out.
02
Develop
4 to 8 months
The busiest stage, with limited involvement required from you. Grid applications, structural and roof condition surveys and, above all, occupier engagement: agreeing terms with each occupier and converting them into power purchase agreements (PPAs) or lease variations. Nothing is installed yet; this stage dictates how smoothly delivery will go.
03
Deliver
2 to 4 months
Syzygy uses its bespoke technical specification. Contractors are tendered and appointed, and works are administered to practical completion. Almost every fault that surfaces during the system's life is built in at this stage, so a quality specification and oversight of the project are paramount.
04
Manage
25 years and more
The longest stage by far. Monitoring, maintenance, billing, export rates, reporting and compliance. A solar system is an income-producing asset. Like any other, its performance is directly linked to how well it is managed.
Inside stage one
The variables we weigh before making a recommendation
Every project starts with a structured checklist, and it grows with every project we deliver. A sample of what it covers, and why each item could change the outcome:
01 · YOUR OBJECTIVES
What you are optimising for. Decarbonisation, financial return, or a weighting of the two: the same roof gives different right answers.
Your expected holding period. A five year hold and a twenty five year hold justify different systems and different operating models.
02 · THE ASSET
What it is and where it is going. Logistics, retail park, shopping centre, offices or bare land; standing asset or development. A development can bake solar into the leases from day one.
Who is in it. Occupied, part occupied or vacant; single-let or multi-let; and which occupier(s); this guides the operating model.
Who controls the roof. The single biggest delivery factor: landlord, occupier or mixed. On developments, the question is whether roof control will be retained.
What is already there. Existing solar or EV charging and who owns it (undocumented kit is a risk, documented kit is value), car parking for car ports, and land on or adjacent to the site.
03 · ENERGY
The building's real demand. Overall and per square metre, from half-hourly data where it is obtainable. We start by sizing to the roof, then make a recommendation based on size relative to demand.
Who procures the energy. Landlord, occupier or both: it determines who benefits from the power and who needs to sign what.
04 · THE GRID
Grid mapping: green, amber or red. Capacity at the local substation can make or break a project, so we check the grid position as part of the scoping stage.
Export headroom. Whether surplus power can be sold, and at what cost of connection. This plays a role in shaping the system size.
Two identical roofs can justify completely different projects. That is why every feasibility study starts with questions.
On multi-phase sites
One study, phases at their own pace
Where a site has distinct opportunities, a terrace being redeveloped and a terrace fully let, say, one feasibility study can cover both, and each phase then moves at its own speed. One aligns with the construction programme; the other can start development the day the study is approved. You are not held to the slowest-moving phase.
Occupier engagement
The part that decides the project
Installing the panels is the straightforward part. The occupiers are the customer: they either buy the power, or pay for the system through their rent. Their agreement is what turns a design into an income stream. This workstream deserves more care than any other.
What the occupier is actually being offered
Cheaper power
Solar at a clear discount to their grid rate, with savings from day one and some protection from volatile energy prices.
Greener power
On-site renewable generation counts towards their own net zero and environmental, social and governance (ESG) commitments, which most national occupiers now have.
No capital outlay
Under a power purchase agreement (PPA), you fund, insure and maintain the system. The occupier simply buys the power, with nothing to build, run or repair. Under a rentalised system or lease regear, you still fund and insure the system, while the occupier operates and maintains it, unless you choose to keep that responsibility.
Put plainly, occupiers are being asked to pay less for better power. The offer is not the hard part.
Why it still takes time
Many voices. The site manager, the head office energy team, the property director and the lawyers may all have a view, and national occupiers start with standard positions.
Legal documents. Agreement is recorded as a PPA or a lease variation. Simple in substance, but anything that touches a lease moves at legal pace.
Competing priorities. Energy is rarely the occupier's day job. Without someone driving the process, engagement drifts, and this is one of the biggest killers of projects.
How to run it well
Momentum, persistence and patience, in that order
One simple proposal per occupier. Their solar rate against their grid rate, and their annual saving, on one page.
Standard documents for everyone. The same Heads of Terms, the same PPA.
A defined timeline, actively driven. Occupiers respond to a process with dates in it. Someone must own the chase; that's what we do.
Plan for the critical-mass point. Not everyone signs at once, and not everyone is easily won over. Once the anchor occupiers commit, the rest tend to follow, so the order of approach is a strategic decision.
Use the relationships. Your managing agent's occupier relationships open the doors. Syzygy drives and manages the process alongside them.
The roof rights conversation
Sometimes engagement buys more than a PPA
Where occupiers hold rights over their roofs, engagement can also include agreeing a surrender of roof control. That unlocks significant delivery savings: one design, one contractor, one programme, instead of unit-by-unit installations. And where new leases are being granted, on a redevelopment for instance, roof control and supply arrangements can be built into the leases from day one, which is worth far more than negotiating them later.
Key figures
1 Page
Per occupier proposal
Rate and saving
HoTs → PPA
The paper trail
Heads of Terms, then the agreement
Anchors first
Order of approach
Critical mass brings the rest
Safety & compliance
Safe, compliant, insurable
A rooftop solar system is a small power station on your building. Treat it that way from the first design decision and safety stops being a burden: it is what keeps the system insurable, the asset lettable and the income flowing in.
Fire
PV fires are rare, and the causes are almost always man-made: poor direct current (DC) connections, cheap components, careless cable routing. So fire risk is designed out, not inspected out. The insurer-backed guidance (RC62) shapes the specification: non-combustible roof build-ups where feasible, disciplined cable management, separation from roof edges and compartment walls, and clear access routes across the roof.
Structure
Panels, mountings and ballast add weight, typically 10 to 25 kg per square metre on a flat roof. A structural appraisal is a fixed early step in every project: it confirms what the roof can carry, shapes the layout, and is the document your insurer and any future buyer will ask to see.
People
Installing and maintaining a system on an occupied building is construction work, with legal duties under the Construction (Design and Management) Regulations 2015 (CDM 2015) for the client as well as the contractors. Proper appointments, method statements, edge protection and safe access are not paperwork for the sake of paperwork: they are what lets work happen above trading occupiers without incident.
The one technical risk worth understanding
DC does not switch off
While there is daylight, the cables between the panels and the inverter are live, whatever any switch says. That is why DC work is specialist work, why isolation points and labelling are specified carefully, and why the fire service is given a clear means of isolating the system. None of this is difficult; all of it depends on the competence of whoever designs and builds the system, which is why specification and oversight during delivery matter more than any certificate issued afterwards.
The framework
Seven documents that do the work
The document
What it covers
RC62
Insurer-backed recommendations for fire safety with rooftop PV, published by RISCAuthority with the Microgeneration Certification Scheme (MCS) and Solar Energy UK. The benchmark insurers assess against.
BS 7671
The Wiring Regulations: the electrical baseline for any installation in the UK.
BS EN 62446-1
Commissioning, inspection and documentation for grid-connected PV. The handover pack and every periodic inspection are built on it.
IEC 61215 / 61730
Panel performance and safety type approvals: the floor beneath any panel worth specifying.
G99
The Engineering Recommendation governing connection to the grid. The local distribution network operator's (DNO's) permission to connect and export runs through it.
CDM 2015
Construction (Design and Management) Regulations: the legal duties on client, designers and contractors during the works.
Building Regulations
Structural (Part A) and fire (Part B) requirements for works to an existing building.
You do not need to read any of these. You need to be able to ask whether your project complies with them and to see the evidence. That is what independent oversight is for.
Insurance
Tell the insurer early, and give them evidence
Insurers do not object to rooftop solar; they object to surprises. Tell them early, give them the right evidence, and cover is routine. What they want to see is who designed and built the system, what the roof build-up is, the commissioning certificates, and a maintenance and inspection regime with records behind it. A compliant, documented system is an easy conversation. An undocumented one, discovered mid-claim, is not.
Key figures
RC62
The fire benchmark
What insurers assess against
62446-1
The paper trail
Commissioning & inspection records
CDM 2015
The site duties
Yours as client, not just the builder's
Maintenance, monitoring & management
Not fit and forget
A common misconception about solar PV is that once a system is installed, it needs little further attention. In reality, solar installations are long-term energy assets that need ongoing management and maintenance. There are three key reasons why this matters:
Faults can go unnoticed
If an inverter fails or a system trips, there is often no obvious sign that anything is wrong. Without effective monitoring, a system could run below capacity or stop generating altogether for weeks or even months, resulting in lost revenue. With monitoring, a fault is flagged within hours and can be addressed quickly, minimising downtime.
Insurers require evidence
Insurers across the UK and Europe are placing greater emphasis on regular inspections and documented maintenance. Keeping accurate records helps demonstrate that a system has been properly maintained, and can support insurance claims should something go wrong.
Warranties have expiry dates
Solar panels, inverters and installation works typically come with warranties covering specific periods. Identifying defects early allows owners to pursue repairs or replacements while the relevant warranties remain valid. Once they expire, the cost of repairs may fall on the system owner.
A true story
The inverter fire nobody noticed
On a UK retail park we were later appointed to, an inverter caught fire on a roof. It went unnoticed for over two weeks, and was only discovered when water started coming through the hole the fire had burned in the roof. The system was eight years old and had never been serviced or monitored. Properly monitored, the fault would have been flagged almost immediately. Fires involving solar PV systems are rare, and the risk can be reduced further through good system design, quality installation, regular inspections and ongoing maintenance.
The budget point
The money to run the system properly usually already exists
If the system was built as a standalone investment rather than under the main construction contract, there was a business case behind it, and that business case will almost certainly have budgeted operating costs. In many cases, the budget for proper monitoring and maintenance has already been accounted for, but is not being used as intended.
The greater concern is often with systems installed as part of a wider building development, particularly where solar PV was required to meet planning conditions. These installations may have been delivered through several tiers of subcontractors, with little consideration given to their long-term operation once the building is handed over.
The result can be a system with no dedicated maintenance budget, no monitoring arrangements and no clear responsibility for its upkeep. For landlords with solar PV installations in this category, reviewing their condition and performance is a sensible starting point.
How Syzygy manages solar PV
Four service areas, one accountable team
01 · COMMERCIAL
Power purchase agreement (PPA) and recharge management, occupier billing statements, export rates reviewed against the market, quarterly financial reporting.
02 · TECHNICAL
Daily performance monitoring, fault ticketing, maintenance regime management, warranty claims pursued while the window is open.
03 · COMPLIANCE
Insurance and standards compliance (BS EN 62446-1 and local equivalents), a claim-ready document library, data flow to your advisers.
04 · EXIT
Data room populated and managed, purchaser queries handled, value protected when you sell. More under 'Selling the asset'.
Service levels (PremiumPV, EssentialPV, Data Only) are matched to system size so small systems are not over-serviced and large ones are not under-protected. Quarterly reporting comes with every package, and a sensible regime costs a small fraction of the revenue it protects.
The data
Why data accuracy matters
Reliable data is essential for managing a solar PV system effectively. From occupier billing and insurance to environmental, social and governance (ESG) reporting, asset valuations and exits, landlords need accurate records of how their systems are performing. There are four main sources for this information.
Inverters & optimisers
Inverters provide regular data on electricity generation and system performance. Where panel-level optimisers are installed, performance can also be monitored at individual panel level. This helps identify faults early, track underperforming equipment and compare actual generation against expected output based on weather conditions.
Generation meters
Generation meters record the total electricity produced by the solar PV system. Where suitable revenue-grade metering is installed, this data can be used to support occupier billing and verify the amount of solar electricity generated, rather than relying on estimated figures.
Export meters
Export meters measure how much electricity is sent back to the grid. This data supports export payments and helps landlords understand how much solar generation is being used on site. Monitoring export volumes alongside generation and consumption also helps identify opportunities to increase self-consumption.
Half-hourly electricity data
Half-hourly electricity data provides a detailed picture of a building's energy demand throughout the day. It is particularly useful when assessing the feasibility of solar PV, allowing systems to be sized to actual consumption patterns rather than annual estimates alone.
One platform
pvlab® · every system, one view
All of this information is brought together through our in-house asset management platform, which currently oversees more than 260 solar PV installations.
The platform allows us to monitor performance daily, identify and manage faults, and produce quarterly reports comparing actual generation against expected output. It also supports occupier recharge statements, stores key documentation including certificates and warranties, and provides reliable data for ESG reporting and asset valuations.
This gives landlords a clear picture of how their solar assets are performing, with verified generation and carbon savings data to support their reporting.
Key figures
Hours
Fault detection
Not weeks. Not months.
260+
Systems on pvlab®
Developed in-house, 2021
GRESB
ESG data feeds
Straight to your advisers
Asset exit
When you sell the asset
When a property with rooftop solar PV is sold, prospective buyers will want to understand the system's condition, performance and commercial arrangements. Having accurate and accessible records can make a significant difference to the due diligence process. There are four key areas buyers will typically review.
Q1
What is installed? Details of the system capacity, equipment specifications, installation dates, contractors and as-built drawings.
Q2
How is the system performing? Historical generation data, monitoring records and comparisons between actual and forecast electricity generation.
Q3
Is it safe, compliant and insured? Inspection records, maintenance history, certificates, insurer sign-off.
Q4
Is the income contracted? Signed power purchase agreements (PPAs) and lease documents, export agreements, billing records.
A well-maintained solar PV system with documented performance and contracted income can contribute positively to an asset's valuation. Conversely, missing records, unresolved maintenance issues or unclear contractual arrangements can raise concerns during due diligence and potentially affect negotiations.
Maintaining accurate records throughout the system's life is considerably easier than trying to compile them during a transaction.
How Syzygy supports asset exit
The data room is already built
For managed systems, exit support is part of the service: we populate and manage the data room, validate the numbers the buyer's advisers will test, support your valuers, and handle purchaser queries directly. The generation history, contracts, compliance records and warranties are already in one place, because they have been kept there all along. The point of good management is that selling well is a by-product.
Before marketing: ask for the solar document pack early. Gaps found in month one are fixable; gaps found in exclusivity are expensive.
Warranties transfer: make sure panel, inverter and workmanship warranties are assigned to the buyer. They carry real value.
Keep the data flowing: a live monitoring feed through completion reassures buyers in a way a spreadsheet never will.
Case studies
Working roofs, not theory
A selection from more than 1,500 delivered projects across the UK and Europe: shopping centres, airports, offices and logistics, each taken from feasibility through to a managed, income-producing asset.
455 kWp
Leicester · Logistics
DPD, Optimus Point
Leicester · Logistics
DPD, Optimus Point
455 kWp
System size
DPD
Occupier
Rooftop solar on a modern logistics unit, sold to the occupier under a lease variation: terms that work on an FRI lease.
Sale to occupier · lease variation · Client: Aberdeen
550 kWp
Cambridge · Offices
CPC, Cambridge
Cambridge · Offices
CPC, Cambridge
550 kWp
Car ports
250
Spaces covered
Solar car ports with 32 EV charging points, connected to the landlord's supply to the offices: generation with no roof to use.
PPA to service charge · Client: Nuveen
1.0 MWp
Leeds · Shopping centre
White Rose
Leeds · Shopping centre
White Rose
1.0 MWp
System size
~£200k
Saved per annum
Rooftop solar connected to the common parts supply, cutting the centre's grid dependency.
Service charge savings · Client: Landsec
1.38 MWp
Birmingham · Retail park
The Fort
Birmingham · Retail park
The Fort
16.4%
Yield on cost
£183k
Income, 20 months
Rooftop solar powering national retail brands, with a 20 bay ultra rapid EV hub. 55% of site electricity offset.
Rooftop solar · ultra rapid EV charging
1.0 MWp
Sheffield · Shopping centre
Meadowhall
Sheffield · Shopping centre
Meadowhall
1.0 MWp
System size
2019
Delivered
The largest solar PV installation at a UK retail site when delivered, feeding centre demand behind the meter.
Feasibility through to asset management
1.6 MWp
Gateshead · Shopping centre
Metrocentre
Gateshead · Shopping centre
Metrocentre
1.6 MWp
Total solar
80
EV bays
Solar car ports (1 MWp) and rooftop solar (0.6 MWp) with large scale EV charging, delivered in a fully trading environment.
ERDF funded · feasibility through to asset management
2.5 MWp
Essex · Aviation
London Southend Airport
Essex · Aviation
London Southend Airport
2.5 MWp
System size
2015
Delivered
At the time, the largest on-site solar PV project in Europe, supplying the main terminal and commercial space.
Client funded · behind the meter
2.5 MWp
Oss, Netherlands · Logistics
GLP Oss
Oss, Netherlands · Logistics
GLP Oss
2.5 MWp
System size
2022
Delivered
End to end delivery of a system agreed with the incoming occupier as part of the letting incentive: solar as a leasing tool.
Client: GLP
16.2 MWp
Zevenaar, Netherlands · Logistics
Zevenaar
Zevenaar, Netherlands · Logistics
Zevenaar
16.2 MWp
System size
2023
Delivered
The third largest PV installation on a logistics building in the Netherlands, and one of the twenty largest in Europe.
Client: GLP
1,500+
Projects completed
UK and Europe
260+
Systems managed
On pvlab® today
2010
Founded
The longest-established independent
FAQs
The questions everyone asks
Answers to some of the most common questions we receive from landlords considering rooftop solar PV.
Do we need planning permission?
Usually not. In England, most non-domestic rooftop systems are permitted development, and the previous 1 megawatt cap was removed in December 2023.
Conditions apply: panels sit at least a metre from the roof edge, protrusion is limited, and some sites need prior approval from the local authority. Listed buildings and scheduled monuments are the exception, and conservation areas need more care. The feasibility study confirms the position for your specific building.
Will it damage the roof, or void the roof guarantee?
A properly designed and installed system should not compromise the roof or its guarantee, provided the relevant requirements are met.
On flat roofs, solar panels can often be installed using ballasted mounting systems, avoiding penetrations through the waterproofing. Metal roofs typically use clamps or specialist fixings, depending on the roof construction.
We assess the roof's condition and consult the roofing manufacturer or guarantee provider before finalising the design. This helps ensure the proposed installation is compatible with the existing roof and its guarantee requirements.
What if the roof needs replacing before the panels do?
We assess this before recommending an installation.
Solar PV systems generally have an operational life of 25 years or more, so the remaining life of the roof is an important consideration. If significant roof works are expected in the near future, it may be more cost-effective to complete these before installing solar.
Although panels can be removed and reinstalled to accommodate roof repairs, doing so adds cost and disruption. Planning for this early helps avoid unnecessary expenditure later.
How disruptive is the installation?
For most commercial properties, installation can be carried out with minimal disruption to occupiers.
The majority of the work takes place at roof level. Activities such as equipment deliveries, crane lifts and electrical connections require more careful coordination, particularly on operational retail and logistics sites.
We work with landlords, occupiers and installation contractors to plan these activities to fit in with the building's operations. Where temporary interruptions are unavoidable, these are identified and agreed in advance.
What happens if an occupier leaves?
The power their unit was buying is exported to the grid until the unit is re-let, so income dips rather than stops, and sensible vacancy assumptions are built into the business case from the start. Cheaper, greener power also does the re-letting no harm at all.
Can occupiers be made to buy the power?
Not under an existing lease, which is why occupier engagement is a workstream in its own right. In practice the offer is cheaper, greener power with nothing to fund or maintain, and most occupiers say yes. Where new leases are being granted, supply arrangements can be built in from day one, which is worth far more than negotiating them later.
Should we wait for batteries?
No. Behind-the-meter solar stands on its own economics today, and a battery can be added later if and when the case for one emerges. Waiting costs a year of savings for every year waited, and the roof, the grid connection and the occupier agreements you put in place now are exactly what a future battery would plug into.
What return should we expect?
Returns vary depending on how well the system's output matches the building's demand, which is why our recommendation is based on size relative to demand. Well-matched systems typically show a yield on cost in the high single digits to low teens, against an asset life of 25 years or more. The Your building calculator gives a first indication; the feasibility study replaces it with your building's real numbers.
Who insures the system?
Usually the building insurer, with the system added to the existing policy. The premium impact is modest when the insurer is brought in early and given proper evidence: the specification, the commissioning certificates and the maintenance regime. See 'Safety & compliance' for what insurers ask to see.
What happens at the end of the system's life?
After 25 to 30 years the choice is to repower, replacing the panels while reusing the mounting, cabling and connection (often the strongest business case of all), or to remove the system, for which panels are increasingly recycled in the UK. Either way, the grid connection itself remains a valuable asset.
Jargon buster
Eighteen terms that cover most conversations
Explained as they apply to behind-the-meter rooftop solar on commercial property.
The term
What it actually means
Solar PV
Photovoltaics. Panels that turn daylight into electricity. Not solar thermal, which heats water.
kWp
Kilowatt peak. The size of the system, its output in ideal conditions. A label on the machine, not a promise of production.
kWh
Kilowatt hour. A unit of energy, the thing bills and savings are measured in.
Behind the meter
The system connects on the building's side of the meter, so its power is used on site before anything is bought from the grid.
Inverter
Converts the panels' DC into the AC a building uses. Hardest working component, most common failure point.
Optimiser
A small device on each panel (or pair) that maximises output and lets performance be monitored panel by panel.
DNO
Distribution Network Operator: the regional company running the local grid. Its permission is needed to connect and to export.
Export
Power the building does not use at the moment of generation. Sold to the grid at a much lower rate than on-site power.
PPA
Power Purchase Agreement: a contract to sell electricity at an agreed rate, to an occupier on site or to an energy company for export.
Recharge
Billing occupiers for the solar power they use, usually below their grid rate, so both sides benefit.
HoTs
Heads of Terms: the short, non-binding summary of a deal agreed before lawyers draft the full documents.
Roof rights
Who, under the lease, controls the roof. The single biggest factor in how easily a project can be delivered.
Yield on cost
Annual net revenue divided by build cost. A simple measure of how hard the capital works.
IRR
Internal rate of return: the annualised return over the project's life, accounting for timing of costs and income.
O&M
Operation and maintenance: the ongoing regime of monitoring, inspection and servicing that keeps a system safe and earning.
RC62
The insurer-backed fire safety recommendations for rooftop PV. The benchmark insurers assess a system against.
CDM 2015
The Construction (Design and Management) Regulations: legal duties during the works that sit with the client as well as the contractors.
Practical completion
Construction finished, system commissioned and handed over. The operating life of the asset begins.
My Account
Your sites and reports
Sites you are working on save themselves as you go. Reports you export are kept here exactly as they were when you exported them.
Portfolios
Group your sites into named folders, for example by fund or region. A site can sit in more than one portfolio.
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Sites in this portfolio
Tick the sites to include. Removing a site from a portfolio does not delete it.
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How to use this tool
Getting started
This tool gives you a pre-feasibility view of what a rooftop solar PV system could do for a specific building: how big it could be, what it might cost, what it could earn or save, and what it does for the building's carbon position. It takes about a minute.
Register once with your name and work email. Your details and use of the tool are recorded so we can respond if you send us an asset.
Find the building on the map, describe it with a few taps, and the results appear instantly on the right.
Nothing is saved on your device between visits except your registration, so note down or export anything you want to keep.
Every figure is an indication built from Syzygy's standard assumptions. A feasibility study replaces them with the building's real data.
The site & map
Site name
Anything you like. It appears on the report and in your enquiry, so a recognisable name helps.
Address or postcode
Type a UK postcode (full, like M8 8EP, or just the outward part, like M8) or a street address, then press Find. The map jumps to the location and drops the pin.
The map
The satellite view is the default so you can see the actual roof. Switch to a street map with the control in the corner.
Drag the pin onto the target building, or simply tap the building to move the pin there.
The pin's location sets the generation region (North, Mid-country, South) automatically. You can override it under Energy.
Measuring the roof
If you don't know the roof area, measure it straight off the satellite image:
Tap Measure roof. Scroll-zoom switches on so you can get in close.
Tap each corner of the roof in turn. Any shape works, with as many corners as you need. A live readout shows the area as you go.
Split roofs are no problem: after one shape, tap + Add another area and draw the next; the tool keeps a running total.
Tap Use this area (or Use total) to drop the measurement into both the Building size and Roof area boxes (in sq ft for UK sites, m² elsewhere), or Clear to start again.
Measure the whole roof. The tool makes its own allowance for the parts a system cannot use.
The building
Type of asset
Industrial, retail park or office. This shapes how the building is assumed to use energy through the day and the week.
Building size
The building's size, in m² or sq ft. This drives the estimate of the building's energy demand.
Roof area (optional)
If the roof differs from the building size, enter the roof separately or measure it on the map. Multi-storey buildings are the common case: a 5,000 m² office may sit under a 1,000 m² roof. Leave blank and the roof is taken as the same as the building size.
Roof type
Pitched, flat or barrel-vaulted. This affects how many panels fit and what the installation costs.
Days in use per week
How many days a week the building actually uses power. It defaults from the asset type (retail parks trade seven days; industrial and offices default to five) but set it yourself: a cold store, 24/7 logistics hub or data-heavy site is a seven-day building whatever its label, and this materially changes how much of the generation is used on site.
Roof lights
Roof lights substantially reduce the area available for panels, so tell the tool whether the roof has them. The question does not appear for flat roofs, where the usable share is governed by plant, walkways and edge setbacks rather than roof lights.
Usable roof area
The share of the roof a system can actually occupy. The tool calculates it from the roof type and whether there are roof lights, and the slider shows that figure. If you know the roof, move the slider and your figure drives the system capacity instead; Reset to calculated hands it back to the tool.
Energy
Generation region
How much a solar system produces varies across the UK, broadly north to south. The map sets this automatically from the pin; adjust it if you know better.
Building energy usage
For industrial and retail park assets, choose how heavily the building uses electricity, from Low to Very high; pick the nearest fit, and if unsure start with Medium. For offices, choose the fit-out category (CAT-A, CAT-B or CAT-C) instead. Your choice drives the estimated building demand shown in the outputs, so if that figure looks wrong for the building, try a different level.
Operating models
Sell power to the occupier
The landlord funds and owns the system and sells its power to the occupier at an agreed rate, the PPA rate, which you can set. The occupier pays less than they would for grid power; the landlord earns the income from those sales and from any surplus exported to the grid, and pays the operating costs.
Free power to the occupier
The landlord funds the system and gives the occupier everything: the power at no charge and the export income. The occupier covers the operating costs. The landlord takes no direct revenue; the return comes through the letting itself, which is why the outputs focus on the value delivered to the occupier.
Who controls the roof, and is there a landlord's power supply?
These two questions shape the strength of the recharge arrangement, and set the default PPA rate accordingly. Where the landlord controls the roof and also supplies the building's power, consents are simpler and power can be recharged at up to the market rate: the strongest position. Where the occupier controls the roof (a standard FRI lease), their consent is needed and a discount to the market rate is the commercial mechanism that secures it. In multi-let offices, a landlord who controls the roof usually also supplies the building's power, recharging tenants through sub-meters. You can always adjust the rate after the default is set.
Report extras: illustrative valuation
Optional, under the sell-power model. Enter the asset's current valuation yield and the report includes an illustrative value for the project: a point is added to your yield for prudence and acquisition costs are allowed for, with the potential profit on cost shown in pounds and percent. It is an illustration to frame the conversation, not a formal valuation.
Report extras: financing illustration
Optional, under the sell-power model. Choose a 10 or 15 year term and an indicative rate (specialist asset finance is available via Syzygy's panel of providers; arrangement costs are included). The report shows the annual payments, whether the project's own revenue covers them, and if not, either the annual top-up required or the up-front contribution that would let revenue carry the payments in full.
Lease expiry year
Optional. If the lease has under ten years to run, the report adds a lease-aware view: how much of the cost is expected back by expiry, what the system is worth to the next letting, and why installing now futureproofs the asset against refurbishment requirements and grid-connection risk.
Rent
Optional. If you enter the rent, the occupier's saving is also expressed as a percentage of it, in the outputs and the report. A recurring saving worth a meaningful slice of the rent is a powerful letting and retention argument, particularly under the free-power model.
PPA rate
The price per unit the occupier pays for solar power under the sell model. The default is a typical figure; adjust it to test the deal you have in mind.
Market electricity rate
What the occupier currently pays for grid power. The default is a typical commercial rate; if you know the building's actual rate, enter it. Occupier savings are measured against this figure, so it sharpens the comparison.
Outputs: landlord view
Net revenue (year one) · income from power sales and export in the first full year, after operating costs.
Project cost · the all-in indicative budget, rounded to the nearest £1,000. It includes: construction (design & build), grid connection costs, structural survey, roof condition survey, occupier agreement, legal fees, project management fee and contingency. It excludes VAT.
Yield on cost · year-one net revenue as a percentage of the project cost.
25-year IRR · the annualised return over the system's 25-year working life, taking account of when money is spent and earned.
Gross revenue · income before operating costs, with the split between occupier sales and export shown beneath. Both streams belong to the landlord under the sell model.
Capacity · the size of the system in kWp: the size of the engine, not its annual output.
Generation · the electricity the system produces in its first year.
Consumed on site · the share of generation used in the building rather than exported. On-site power is the valuable part.
Decarbonisation · the system's annual generation as a share of the building's estimated annual electricity demand.
Opex · the annual cost of keeping the system safe, compliant and earning: maintenance plus Syzygy asset management, with the service package matched to the system's size.
CO₂ avoided · the carbon saved each year by displacing grid electricity.
Outputs: occupier view
Occupier savings · what the occupier keeps compared with buying the same power from the grid, shown for year one and cumulatively over 5, 10 and 15 years. Under the free-power model this becomes the full value the occupier receives: free power plus export income, net of the operating costs they carry.
Power demand · the building's estimated annual electricity consumption, from its type, size and usage level.
Export revenue · income from surplus power sold to the grid. The label shows who receives it: the landlord under the sell model, the occupier under the free-power model.
Opex · as in the landlord view, with the label showing who pays it under the chosen model.
Report & next step
Export report
Generates a short PDF report of the assessment: the building as you described it, the system, the returns, the occupier position and a short written summary. Review it on screen, then use Print / save as PDF to keep or share it.
Send this asset to Syzygy
Sends your assessment straight to our team, and emails you a confirmation with your report attached as a PDF. A member of the team will be in touch within two working days to help you take it further. What follows is a feasibility study: about a month's work that replaces every indication here with the building's real energy data, grid position, roof condition and structural capacity, and gives you a business case you can take to a board.
Your data
Your registration details and use of the tool (assets assessed, results, date and time) are recorded so we can respond to enquiries and improve the tool.
Your account
Sites you are working on are saved to your account as drafts, so you can return to them on any device. Syzygy does not view your drafts: we only see how many you have. Once you export a report or send a site to us, we can see that report, along with the names of any portfolios you create and which of your submitted reports are in them. If you delete a report you have already exported or sent, it is removed from your account, but Syzygy keeps its copy.
We also keep basic records of how the Toolkit is used, such as which parts of the Toolkit are used and when, without the details of the sites you are working on.
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Syzygy Solar Toolkit
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