A guided STEM (Science, Technology, Engineering Mathematics) activity session

Suitable for Key Stage 2 (ages 7 to 10)

Skills: Measurements, Counting, Addition, Multiplication, Division, Averages, Directions and Angles.

This is a practical STEM (Science, Technology, Engineering and Mathematics) activity that is easily tailored to a specific age group. The purpose is the same: understanding solar panel installations.

Click here for a session designed for ages 11 to 13

Click here for a session designed for ages 14 to 16

Click here for advanced learners

To make the most out of a site visit it is recommended to bring a long sports field tape measure, a large protractor (which could be made in class, especially by slightly older children), a spirit level, a compass and a large scale map (or use Google Maps or equivalent).

The organiser of a site visit would be well advised to conduct a risk assessment. This session is expected to be conducted under adult supervision.

There are some activities in boxes that could be prepared prior to the main activity.

Starting Discussion

It is good to start the session off by thinking about what solar power is. This leads quickly on to discussing the position of the Sun in the sky and how facing the Sun gives us the maximum power. It is quite useful to think about how we perceive the Sun’s trajectory across the day. Here it is useful to have a model house and something like a tennis ball to hold above the house during the discussion. Talk about sunrise in the East and sunset in the West. Think about the highest point of the Sun in the sky. Here in the UK we don’t see the Sun ever directly above us at midday. In mid summer the Sun rises in the North East and appears to follow a circular path to its highest point due South before descending towards the point it sets in the North West. In the winter the Sun rises in the South East and again appears to follow a circular arc in the sky getting to its highest point due South at midday (which is much lower than in summer) and then setting in the South West.

The purpose of this discussion is to get the children to think about where the Sun appears to be in the sky so that we understand what to measure: what we are really after is the angle between the panels and the sun throughout the day.

To collect as much solar energy as possible we want to face the Sun.

But the roof is fixed.

The amount of solar energy we collect depends on

  • The angle between the panel and the Sun
  • Whether there are objects blocking the Sun (shading)
  • How cloudy it is

This discussion allows us to introduce the “Solar Recipe” we will be using in this STEM activity

Solar Recipe

Here is our Solar Recipe to allow us to work out how much solar power we can get from our roof

  1. Find the Latitude of the Building
  2. Find the facing direction of the roof (South, East, West)
  3. Measure the pitch angle of the roof (0° is flat, many houses are around 30-35°)
  4. Measure the roof area: how many panels can we fit? Typically panels are 1.6m x 1.0m and have peak power ratings of between 250W and 400W
  5. Look at shading: scan round the building noting direction of blockage (S, E, W), angle of top of blockage from roof (we may need height and distance of blockage)
  6. Put the numbers in the calculator…

Step 1: Find the Latitude of the Building

How do we find out how far North of the equator we are?

For this we need the help of a map. We can interpret grid references from a map or in the UK we can use the grid reference finder tool on the internet with our postcode.


Step 2. Find the facing direction of the roof

Ask how do we know where North is? Can anyone point to North? What can we use to find North?

Once we know where North is, how do we measure the angle between North and our building?

We can either use a compass or use a map of the site if that has North indicated. Then we will need a protractor to measure the angle between North and the building.

Step 3. Measure the pitch angle of the roof

Ask how can we measure the angle of the roof. Some children will have been introduced to a protractor at school. It is very useful to be able to find a level. This is because we need to measure the angle from the horizontal. Ask if any of the children know how we find a level. A spirit level is the most useful device but we could also measure to a plumb line as an alternative.

STEM preparation: making and using a large protractor

The small protractor in most school geometry sets is quite tricky to use for this. Much better to create a large protractor with a hinged view arm as shown. We attach a spirit level to the bottom arm and rotate the upper arm upwards until we align it with the roof line. A large angle scale is then used to read off the angle. We found this to be a two person activity, with one person concentrating on keeping the bottom arm level and the other concentrating on keeping the upper arm aligned with the roof.

To make this we used two straight pieces of wood hinged at one end and suitably sanded down to remove sharp edges and splinters. The spirit level is simply taped under the lower arm. A cardboard protractor is placed next to the upper rotating arm so we can easily read off the angle.

To make the cardboard protractor we will need a large piece of cardboard, a large compass for scribing a circle, a pen and some scissors. Cut a quarter circle so it looks like a quarter of a cake. To mark the degrees on we will need a large school protractor or we can use a fabric tape measure wrapped around the circular arc and then divide 0, 5, 10, 15, … by 90 and multiply by the tape length to give us the distance around the arc for 0, 5, 10, 15 degrees. Older children or the teacher can instead use trigonometry to mark out the angles with a calculator and ruler. See version 2 for this.

STEM alternative: counting bricks

If your building has walls which are visibly made of regular bricks or blocks then we can measure and count bricks. If we draw what we see on a scale drawing then we can measure the angle on the scale drawing instead. This task will require some guidance for the youngest learners. Unfortunately we can’t use this technique with every roof – we need to be able to count bricks along and up at a gable end.

Using averages to make brick counting more accurate:

It is recommended to measure five bricks across a number of times on the building in question to get an average brick width (taking into account the mortar thickness) for this building. Repeat this with ten bricks up to get an average brick height for the building. Now when you count bricks you are also measuring lengths and heights! Just don’t forget to multiply your brick count by the brick length or height.

Back to the pitch angle task

Double check: we are looking for an angle measured from the horizontal – so a flat roof is 0°, a shallow roof may be around 20° and a steeper roof could be above 45°.

Step 4. Measure the roof area

For this it is best simply to measure the building area (plan view) using the exterior walls as a guide. Can the children sketch out the plan of the building? Then work around the building measuring each wall length.

Maybe one side is longer than our tape measure? Then we will need to add up distances and keep track on where we are measuring to.

On the sketch identify what the roof looks like. We could check our sketch using Google Maps.

For each roof in turn, what is the plan width and length of the roof. Now that we know the pitch angle of the roof we also know what the roof area is.

Fitting panels

Using a scale drawing of the plan of the roof we can cut panels out and arrange them or stick them on our plan.

Let’s say our plan is scaled so that 1cm on our drawing represents 1m on our building. This is a 1:100 scale.

If we want to represent the panels on our plan view, we need to be careful of the roof pitch because the slope makes that dimension appear shorter. See Box below.

It may be a good idea to have sheets of panels already printed that can be cut out by the children.

What size are panels viewed on a plan?

Let’s assume our panels are 1.675m x 1m.

For fitting panels vertically, this is what our apparent plan-view panel size is

Roof Pitch (°)Panel size along slope (m)Panel size along level (m)
Longer length of panel on slope of roof

For fitting panels horizontally, this is what our apparent plan-view panel size is

Roof Pitch (°)Panel size along slope (m)Panel size along level (m)
51.001.68 (rounded)
Shorter length of panel on slope of roof

Older children or the teacher can work these dimensions out using trigonometry. See version 2 for this.

Remember to scale the panel size for your drawing scale. For 1:100 scale we can interpret the numbers in the tables as cm instead of m.

Step 5. Look at shading

If you have time you can look at shading. While on site we can walk around the building and ask what objects might create shade? Children may point out buildings, trees and so on. We’ve had some quite creative answers too: aircraft, clouds and the Moon. The clouds are taken account of with most solar calculators but shading is more specific to a building. Don’t forget about the landscape (hills and mountains).

STEM preparation: making a large compass rose

For noting shading it is handy to have a large circular disc with the cardinal directions of North, East, South and West marked on it along with ordinal directions (NE, SE, SW and NW) and secondary intercardinal directions (NNE, ENE, ESE, SSE, SSW, WSW, WNW, NNW). The greater the number of directions marked out, the better the resolution of shading for the building. With 16 directions, we have 360°/16 = 22.5°. A very fine shading resolution could be 7.5° (48 directions, or split each of our 22.5° sectors into three).

With the North of the large compass rose aligned with true North, look at each of the directions and note the object that is blocking light in that direction. How far away is that object and how tall is it? If it is a tree, is it deciduous or evergreen?

Really we want to assess the shading as though we were at the roof height. So anything lower down we can ignore.

There is also the shading from objects on the roof itself – most notably chimneys.

Step 6: Calculating the Solar Power potential

Take each roof in turn and describe where the Sun rises in relation to the roof and what its perceived trajectory through the sky is and where the Sun sets. On that path you talk about the shading that is present. You can do this for the longest summer day and the shortest winter day. For this we can use our tennis ball again, this time over a plan of our building. We can see that shading in winter can be quite significant because the angle of the Sun in the sky is fairly low so that other buildings can produce quite a lot of shadow especially at sunrise and sunset.

Note: If you have access to a solar power calculator or online tool then that could be a bonus. However it is better to get the children to think about the discussion points above.