MCS Savings
How savings from a solar PV system or a solar PV system with battery storage are calculated with the MCS Document MGD003 v2 guidelines.
This document refers to twenty-seven table and they are listed from 7 -1 to 7-27
Information we need to complete the saving forms for you.
Your consumption per year in KWh
Do you class yourselves, Home all day, out all day, home half the day.
What solar generation in kWh would you like to generate from a solar PV system per year.
Solar generation is determined by several different factors.
Location.
We use different table for different locations around the UK, Lincolnshire falls under zone 11.
Direction.
Facing south at a pitch of thirty five degrees and no shading issues will yield the greatest return per kWh installed.
Facing East or West will be about twenty percent less than south and panels installed on a north facing roof would be fifty percent less than south facing one. These would also have mound growing on them year on year and solar generation would be reduced. I wouldn’t recommend installing any solar panels on a North facing roof.
Pitch of Roof.
The pitch of roof affects the solar generation with thirty five degrees being the best angle.
Shading issues.
Chimneys and trees cause shading issues on solar panels and reduce solar generation.
See tab for shading issues videos from you tube for more information.
The best meter to check for shading issues is a Seaward PV150 meter.
Available size of roof space for installation.
I will go over one of the examples from the MCS document in more details below.
Please print off page 19 and page 24 for reference to this example.
Information we have to hand.
- Customer is classed as home all day
- They use 3879 kWh per year before solar PV is installed.
- The solar PV system they are looking to be installed should generate 4059 kWh per year.
- The usable battery capacity is 7.5 kWh.
Step 1
Find the correct table to use.
Home all day and consumption of 3879 kWh
The table we require is Table 7-5 on page 24.
Step 2
Expected solar generation per year 4059 kWh
As stated above the expected solar generation depends on several factors.
To generate 4059 kWh in Lincolnshire zone 11 you would need at least 4.5kWp of solar panels installed on a south facing roof with a pitch of thirty degrees and no shading issues.
Or 5 kWp of solar panels on an East or West facing roof with the same pitch and taking some shading issues in from the very roof its mounted on.
In the left hand side column find the expected solar generation of 4059 and this will be between 3900 kWh and 4199 kWh.
Step 3
Savings with solar PV only
Move to the right and the second column along with a heading of PV only.
You’ll see a percentage of 29%
This percentage is what you’ll save with just installing a solar PV system that would generate 4059 kWh per year.
29% of the solar generation 4059 kWh is 1177 kWh.
If no other devices are installed like power diverters to heat your water or charging a EV car all the remaining solar energy will be exported to the National Grid.
Step 4
Adding battery storage can greatly increase the usage of the solar generation within your home.
The example gives a usable battery capacity of 7.5KWh therefore this battery used is greater in capacity but when it discharges it doesn’t discharge to zero , it always keeps some back as reserve.
We call this DOD Depth of Discharge and you’ll find it can vary from 80% to 95%.
The example uses column greater than 7.1 kWh and below 8.1 kWh and percentage of 69%.
Again the percentage refers to the solar generation and not your consumption per year.
69% of 4059 kWh is 2801 kWh would be saved from your electric bill per year.
We don’t use prices in the formulars as these prices are always changing.
But if your paying say £0.29 per kWh you total saving would be
2801 kWh @£0.29 equals £812.29 saving.
Step 5
Grid independence without battery storage is 30% (1177/3879kWh)
Step 6
Grid independence with battery storage is 72% (2801/3979 kWh)
All MCS installers should give you the an example as per page 19 of this document with your quotation.
Please note the following:
If you think your going to save twice as much if you double up on battery size take a look at the last column on the right.
Battery usable capacity greater than 14 kWh to less than 15.1 kWh. The percentage only rises from 69% of solar generation used to 71% solar generation used.
The cost of the extra battery doesn’t warrant the extra saving made.
Saying this its possible to charge batteries on cheap rate electric and discharge when prices are high in winter months. Some EV tariffs are as low as £0.07 per kWh and some export payments for SEG (Smart Export Guarantee) could be £0.16 at time of writing this article.