East & West-facing PV panels are more profitable.

East & West-facing PV panels are more profitable.

 1.   Introduction

Have you thought about the best direction to install your solar panels? Panels facing East and West might be better than North. They could help you get your money back faster.

Panel orientations are important. This article will help you decide what’s best for you. It can help with buildings, fields, and lakes. It also applies to existing rooftops and to get the most energy from a limited space.

South Africans use most of our electricity in the morning and early evening. Our high demand for power at these hours makes Eskom use costly power stations. So, commercial customers pay more at peak times.

Your solar power replaces Eskom’s energy whenever the sun shines. During Eskom's peak times your solar energy is more valuable. Getting more from your solar plant then can boost your Return on Investment. A modest increase in your cost can lead to better returns.

Panels facing East and West have an advantage compared to North-facing. They will produce more energy in the first half of the morning and late afternoon. These hours align with Eskom's costly peak demand times. Thus East-West panels could be a better choice than the popular North-facing panels.

The financial value of energy from East and West-facing panels is usually higher. They generate more of their energy during costly times of the day. Thus their energy is more valuable even though they may generate less energy than North-facing panels.

This article addresses homes and larger projects up to 1 MW (Mega-Watt).

A solar plant is any solar installation. It can be a small residential system, or a large industrial installation.

When I say 'Noon,' I mean when the sun is at its highest, known as solar noon. We measure power in watts or kilowatts (kW).

Energy is measured in watt-hours or kilowatt-hours (kWh). We commonly refer to kWh as Eskom electricity ”units.”

1.   How does the position of an array affect its output?

When designing a solar plant, we want to know how much power and energy it will generate. Installers use simulation software to calculate this.

Panels may not produce as rated. This could be due to air temperature, light, or sun angle. The environment and seasons may also affect the generation level.

Orientation refers to the direction the panel faces and its tilt (or slope). We note the direction in compass degrees and the tilt in angular degrees.

A panel's orientation will set its highest possible power output at any moment. These power levels translate to an average hourly power level. The yearly energy production is the sum of the average power levels generated each hour of the year.

Figure 1: Generation Curves. The curves show how different solar plants’ power levels rise and fall during the day.

Figure 1, shows how solar power increases in the morning and decreases in the afternoon. Both curves are on the same day and for the same place. The PV plant sizes are identical for both curves {PV= PhotoVoltaic}. However, the plants’ panels face different directions.

The solid line shows the curve for North-facing panels. The dotted line is for a combination of East and West-facing panels.

The area under the curves represents the energy generated on the day. You will notice that the area under each curve is similar. Although the dotted line lies lower, it has energy bulges in the morning and afternoon. Compare it to the North-facing panels' output at noon.

Figure 1, point 1 shows the maximum power generated by North-facing panels. Point 2 shows the maximum power generated by equal arrays of East and West-facing panels.

The output of East or West panels will differ from those facing North. Each array's orientation affects its generation curve. A site may have various array sizes, orientations, and generation curves. All the arrays together create the site's generation curve.

Figure 2: Solar panels facing East and West on a roof with 30° slopes.

For example, consider panels facing due East and West on a roof with a 30° slope. Under ideal conditions, they can generate up to ±95% of their rated power. A North- facing panel would generate its whole rated power level, i.e., 100%.

The East and West-facing panels’ total energy produced in a year would be ±85% compared to the same panel facing North.

This shows East and West panels are also good energy generation options!

Figure 3: A solar array on a North-facing roof.

 North-facing solar panels work best in winter. They will outperform East or West-facing panels. Your latitude will affect the required tilt. In turn, this will affect the power output.

 1.a.   The power generation curves of panels facing East, North, and West.

 East-facing panels catch the morning sun. Thus, they have an early power ramp. They'll hit their highest power level before noon. In summer, their highest level is around 11

a.m. They then tail off to 5 p.m.

Westerly panels generate nothing for the first two hours of the day. Then, they gradually ramp up to about 2 p.m. In summer, they stay at a high power level until about 4 p.m., when they tail off.

The following generation graphs use actual data from a project in Bergvliet, Cape Town. They show how much power solar panels generate during a sunny summer day. Power levels change moment by moment. The panels' orientation sets the ceiling for power output at any moment.

The two charts below (Figures 4 and 5) compare the power from 10kWp panels. They faced East, West, and North, or an equal mix of East and West.

Figure 4 shows the power generated by 10kWp panels facing North, East, or West. The graph shows power on the left side in Watts and the time on the bottom, starting at 5

a.m. and ending at 8 p.m.

Figure 4: Generation Curves – East, North & West facing panels – Equal array sizes (10 kWp)

 In Figure 4, power levels reach their maximums at different times (zoom in for details). The East and West arrays reach their maximum of 8800W three hours apart. When one is highest, the other produces less.

Neither East nor West is fully powered at noon (they are both at 8000W). At noon, the Easterly panels are down from their highest level of 8800W. Meanwhile, the Westerly panels are still ramping up to that level.

The North-facing array reaches its maximum power level of 9300W at noon.

1.b.   The generation curves of 10kWp panels facing North vs. a mix of panels: 5kWp facing East and 5kWp West.

In Figure 5, 10 kWp panels are evenly split between East and West-facing. The 10 kWp of panels in the other array all face Northwards.

Figure 5: Generation Curves – ½East + ½West vs. North facing panels - Equal sizes (10 kWp)

 We compared the North-facing panels to the mix of East and West ones. You can see the differences as "bulges" on the left and right sides of the chart:

• East-facing panels are better in the They produce more power, then;
• West-facing panels are best in the late afternoon;
• At noon, the North-facing panels are better than the East-West

 Let's review the charts above. Fig. 4 shows three orientations for a 10kWp solar panel: East, West, and North. Note the time difference between the East and West maximums. Also, there is a difference in power levels as we progress through the day.

In Fig. 5, we compare the 10kWp North-facing array with two 5kWp arrays: East and West. Note the noon power yield of the North-facing array. It's interesting. The 5kWp East and 5kWp West arrays together can’t reach that power level.

The charts show that the direction the panels face is key to power generation. Panels facing East and West generate more power during Eskom’s peak demand times. Thus, they may be a better fit than North-facing panels.

1.c.   How do panels added to the East and West affect the generation pattern?

In the following graph, I've added one kWp of panels each to face East and West. Now, six kWp of panels face East as well as West. Thus, a total of 12 kWp is divided equally between East and West. The East and West-facing arrays use 20% more panels than the North-facing array. See Figure 6.

Figure 6: Generation Curves – 6 kWp East + 6 kWp West vs. 10 kWp North-facing panels.

Note the combined power generation (kW) at noon. The 12 kWp East-West mix barely exceeds the maximum power level of the 10 kWp North-facing panels.

Let's consider the energy generation of the 12 kWp system. In summer, the East-West arrays generate more energy than the North-facing array. The extra energy comes mainly in the early morning and late afternoon. Yet in winter, the 10 kWp North- oriented array will win.

Annually, a 12 kWp East-West solar plant will generate about the same energy as a 10 kWp, North-facing system.

The solar arrays’ power output governs the sizing of wiring and the inverter(s). Thus, you could use the same inverter model for either plant. In this example, the only extra cost of an East-West plant vs. North-facing is installing extra solar panels.

 1.d.   The benefits of East and West-facing arrays observed at this site:

 We first gathered and used the premises' consumption data to design the panel layout. The layout aimed to optimise generation to match daily use.

The optimisation was vital to maximise the usable instant energy. Thus, we lowered battery use, which will prolong the battery's life.

The careful optimisation reduces low-value excess energy.

East and West panels often do better than North-facing ones on cloudy days. You might have a bright morning, a gloomy afternoon, or vice versa. But North-facing panels only get a chance around noon.

East-West layouts allow for more hours of high energy generation. They also provide smoother, more consistent output. This is partly due to dispersed light on the opposite array.

 2.   Incorporating costing into your energy value

The cheapest way to use your solar plant is immediately using the energy. Another option is to draw from batteries, which adds a cycle cost, or to use the grid. Depending on the grid might force you to draw electricity during peak times.

Your battery ages slightly each time you send energy through it. This ageing costs about R0.80 for every kWh cycled through the battery (pricing in 2024).

It's best to optimise your panel orientations. Their power generation should match your consumption.

East-facing panels are best for morning energy. Their power is cheaper than with the extra cost of battery capacity. Without these panels, you'll have a greater need to buy from the grid or use batteries. Alternatively, you can use your battery capacity for more pressing needs.

In the afternoon, West-facing panels can supply energy. Thus you’ll have a lesser need for battery energy. Instead, you can save it for nighttime, avoiding grid fees.

 2.a.   The generation-capacity cost

The efficiency of solar panels, in watts per square meter, has improved. Also, solar panel sizes have increased. They're now longer and wider, thus having a greater generation capacity.

We measure the capacity in Watt-peak (Wp). A panel's Wp rating is its peak power capacity, which is the power it can yield under ideal conditions.

The cost of generation capacity has gone down a lot. In the last decades, the cost of generation capacity has shrunk by an average of 12% per year. You can buy new generation capacity at a lower cost every year. This makes many new uses feasible.

The solar industry benchmarks panel prices in US Dollars. Therefore the international price is noted in USD/Wp ($/Wp).

Despite their greater efficiency and size, solar panels are now much cheaper in US Dollars. The Rand to USD exchange rate affects solar panel costs in South Africa.

 2.b.   How PV panel costs relate to the total project investment

I assume the only variable in this discussion is the panel costs. All other costs remain similar. PV panels are the only part of an installation that can generate power. In this sense, all other components are auxiliary equipment.

The auxiliary equipment is costly but required. Also, it's costly to get an installation team on-site.

Think about a project and its goal. It has fixed costs that stay mostly the same with output. These costs include planning, site preparation, labour, housing, and transport. The fixed costs will stay similar when changing the layout from North-facing to East- West. Even though you might add half or double the panels, the fixed costs remain similar.

PV projects always have solar panels, but batteries are an option. Without batteries, it would be a PV-only project. The panels and their installation are about 40% of the cost of a PV-only project. Then, doubling the number of panels would increase the project cost by ±40%.

Assume the initial budget was R200 000. Doubling the panels would raise the budget to R280 000. Yet your annual energy production would increase by 40% to 60% (for 40% more cost). An increased energy production is a win for your investment.

Moreover, the value of your energy would increase by much more.

If your project includes batteries, it would nearly double your budget. Compared to our previous example, the budgeted cost is now ±R400 000. However, the number of panels has stayed the same. Thus, the panels are now about 20% of the cost.

In this case, doubling the panels would add ±20% to the project cost, to a total of

±R480 000. Likewise, your annual energy yield increases by 40% to 60% (for 20% more cost).

 2.c.   Electricity pricing

 Large consumers are buying more energy on the open market. Yet, most residential grid energy users don't know that. Eventually, residential users will trade energy in the grid's open market.

You've heard of peak tariffs, a type of variable pricing for grid energy. Eskom’s peak tariffs apply at times of very high electricity demand.

The peak demand is in the morning and evening and will likely remain at that time. Electricity costs more during peak hours. It's usually two to three times the standard rate. Thus, your solar plant's energy is worth two to three times as much during that time.

Buying a solar plant is an example of open-market pricing. You prepay for kWhs, which you'll receive over the plant's lifetime.

You enter a supply-and-demand market when you get paid for the electricity you send to the grid. Solar plants nearly always generate too much energy at noon. Nobody will want your noon energy when 'everybody' has a solar plant. It will have no monetary value. Even hundreds of kWhs at zero price are worth almost nothing. Their time of generation makes them almost worthless. But your excess energy in the evening, night, and morning will be valuable.

In time, energy's value will depend on market prices—supply and demand. It may take some years before you can access open market prices. Open markets usually switch to 5-minute pricing.

 3.   Do you want to generate as much energy as possible from a restricted space?

You might have a flat roof, a piece of land, or a lake. Here’s how to generate as much energy as possible within a limited space:

We did a Helioscope simulation for a 40m x 40m field in Johannesburg. We compared 30°-tilted North-facing arrays with 30°-tilted East and West.

We tried to fit as many panels as possible into the space. Both designs allowed space for maintenance and shading. We used 500W panels.

With the North-facing design, we managed to fit in 378 modules (module is another word for panel). For the East-West design, we managed 646 modules. So, the East-West layout had 70% more modules.

The resulting layouts had 189 kWp of North-facing and 323 kWp of East-West panels (378*500W=189kWp; 646*500W=323kWp).

The simulation showed:

• You can fit more panels facing East-West than North;
• More panels lead to more energy;
• East-West arrays had a 20% drop in performance vs North-facing;
• Nevertheless, East-West panels generated more energy
• The East-West design produces 38% more energy than the North-facing

Article Credit to AREP