Uploaded September 2026 | Updated September 2026, 2 hours ago
How much electricity will your solar panels actually generate each year?
Solar installers, PVGIS and other solar calculators can all give you an estimate, but they don’t necessarily agree.
In this video, I use my free Solar Annual Generation Estimator to compare three different approaches:
☀️ NASA POWER climate and solar data
☀️ PVGIS from the European Commission’s Joint Research Centre
☀️ A UK MCS-style planning benchmark
Rather than relying on a single number, the Considered tool shows the different estimates and produces a blended planning figure.
I then put it to the test using my own 5.16 kWp solar installation and compare the predictions with what my panels actually generated during a complete year.
We also look at how roof direction, pitch, mounting, shading, multiple solar arrays, inverter sizing and clipping can affect predicted generation, and how you can use the tool to sense-check an installer’s solar forecast before spending thousands of pounds.
🔗 Try the Solar Annual Generation Estimator free:
considered.uk/tools/solar-generation-estimator
No login. No account. No paywall.
💚 Support Considered / become a member:
considered.uk/go/patreon
The estimator is intended as an independent planning and comparison tool. It isn’t a replacement for a professional site survey or installer assessment, and actual solar generation will vary with weather and site conditions.
If you already have solar and a complete year’s generation data, try your system in the calculator and let me know in the comments: which model came closest to your actual generation, NASA POWER, PVGIS or the MCS-style benchmark?
PVGIS — European Commission Joint Research Centre:
pvgis.com/en
Gary Does Solar:
garydoessolar.com
❤️ SUPPORT THE CHANNEL
If you find the content useful and want to support the channel, you can join here: patreon.com/c/Considered
🐙 SAVE MONEY ON YOUR ENERGY BILL
£50 Credit to both our Octopus Energy Accounts when you SWITCH to Octopus Energy here:
http://share.octopus.energy/noble-bloom-324
🎧 MUSIC
All music is from Epidemic Sound:
epidemicsound.com/referral/tq2vsf
💬 COMMUNITY
Join the Discord: discord.gg/uj3YSQx
📩 BUSINESS ENQUIRIES
For collaborations or sponsorship opportunities:
partnerships@considered.uk
Timecodes
0:00 - Intro
1:47 - Why another solar calculator
3:43 - My existing array
4:53 - Adding another array
6:37 - Inverter and system
8:07 - Electricity use and installer estimate
9:21 - Three different estimates
11:21 - The considered estimate
12:10 - Support Considered
12:34 - Installer vs the models
15:31 - The monthly picture
16:17 - Use it to sense check a quote
17:40 - My Solar
18:52 - Free tools at Considered
How much electricity will your solar panels actually generate each year?
Solar installers, PVGIS and other solar calculators can all give you an estimate, but they don’t necessarily agree.
In this video, I use my free Solar Annual Generation Estimator to compare three different approaches:
☀️ NASA POWER climate and solar data
☀️ PVGIS from the European Commission’s Joint Research Centre
☀️ A UK MCS-style planning benchmark
Rather than relying on a single number, the Considered tool shows the different estimates and produces a blended planning figure.
I then put it to the test using my own 5.16 kWp solar installation and compare the predictions with what my panels actually generated during a complete year.
We also look at how roof direction, pitch, mounting, shading, multiple solar arrays, inverter sizing and clipping can affect predicted generation, and how you can use the tool to sense-check an installer’s solar forecast before spending thousands of pounds.
🔗 Try the Solar Annual Generation Estimator free:
considered.uk/tools/solar-generation-estimator
No login. No account. No paywall.
💚 Support Considered / become a member:
considered.uk/go/patreon
The estimator is intended as an independent planning and comparison tool. It isn’t a replacement for a professional site survey or installer assessment, and actual solar generation will vary with weather and site conditions.
If you already have solar and a complete year’s generation data, try your system in the calculator and let me know in the comments: which model came closest to your actual generation, NASA POWER, PVGIS or the MCS-style benchmark?
PVGIS — European Commission Joint Research Centre:
pvgis.com/en
Gary Does Solar:
garydoessolar.com
❤️ SUPPORT THE CHANNEL
If you find the content useful and want to support the channel, you can join here: patreon.com/c/Considered
🐙 SAVE MONEY ON YOUR ENERGY BILL
£50 Credit to both our Octopus Energy Accounts when you SWITCH to Octopus Energy here:
http://share.octopus.energy/noble-bloom-324
🎧 MUSIC
All music is from Epidemic Sound:
epidemicsound.com/referral/tq2vsf
💬 COMMUNITY
Join the Discord: discord.gg/uj3YSQx
📩 BUSINESS ENQUIRIES
For collaborations or sponsorship opportunities:
partnerships@considered.uk
Timecodes
0:00 - Intro
1:47 - Why another solar calculator
3:43 - My existing array
4:53 - Adding another array
6:37 - Inverter and system
8:07 - Electricity use and installer estimate
9:21 - Three different estimates
11:21 - The considered estimate
12:10 - Support Considered
12:34 - Installer vs the models
15:31 - The monthly picture
16:17 - Use it to sense check a quote
17:40 - My Solar
18:52 - Free tools at Considered
