All About PV Solar Panels Last Updated: 24th June 2022

Introduction

If you're looking for ways to reduce your electricity bills and carbon footprint, or would like to get a better understanding of solar panels in general - this page will guide you through all you need to know, as well as the benefits of solar panels and how they work.

What are PV Solar panels?

PV Solar panels, also know as PhotoVoltaic solar panel or electric solar panels, are the type of solar panels that produce electricity. When daylight hits the panels, they will begin to start producing electricity.

There is another, older type called thermal solar panels. These make hot water directly, and are the type that were most commonly fitted 10-years old. They are much less popular in Ireland now due to the huge price drop in PV solar panels and their lower maintenance. The electricity generated from PV panels can be used to produce hot water as well as using the electricity directly, giving you the best of both. Follow this link for a Solar PV vs Solar Thermal comparison.

How much electricity do solar panels produce in Ireland?

Peak production (in kWp, or kilowatts)

Most PV solar panel systems are quoted in kW peak (or kWp). If someone talks about a 3.5kW system, that's the peak production their solar panel could generate in perfect lab conditions. Realistically in Ireland, your solar panels might top out at about 90%-95% of this in the middle of a perfect summer's day.

Annual Production

Most of us are more concerned with the total number of units of electricity produced over a year though.

1kWp of solar panels in Ireland will generate about 860 units (kWh) of electricity per year. This is for a typical Irish house somewhere in the middle of Ireland.

Here's how that works for average house sizes:

Typical Two Bed Mid-Terrace House

• Solar Array Size: 3.48kWp
• Roof Area Covered: 16.9m²
• Annual Generation: 3,080kWh (units of electricity)

Typical Three Bed Semi-Detached House

• Solar Array Size: 4.35kWp
• Roof Area Covered: 21.2m²
• Annual Generation: 3,850kWh (units of electricity)

Typical Four Bed Stand-Alone House

• Solar Array Size: 5.22kWp
• Roof Area Covered: 25.4m²
• Annual Generation: 4,620kWh (units of electricity)

Typical Six Bed Stand-Alone House

• Solar Array Size: 6.96kWp
• Roof Area Covered: 33.8m²
• Annual Generation: 6,160kWh (units of electricity)

The above are numbers for a typical house with a south-facing roof somewhere in the middle of Ireland. If your roof faces south-east or south-west, then production will be about 5% lower, and for east / west facing roofs about 20% lower.

Please note these are back of envelope numbers to give you a rough guide. In any quote we'll give you more accurate numbers for your home.

Which direction is best for solar - East / South / West?

Due South: most power output

A south-facing roof will produce the most electricity. Being a bit off directly south though has minimal impact on production. Anywhere between south-east and south-west will be very similar.

South East / South West: ~5% Lower

If your roof faces south-east, or south-west, then your production will be around ~5% lower on a typical 30° sloped roof. The timing of your electricity production will change too. South east produces more in the morning, and south west more in the afternoon / evening, which makes it a bit more useful for most households.

East / West: ~20% Lower per panel, but double the roof area

If your roof faces due east, or due west, the production will be about 20% lower than a south-facing roof on a typical 30° sloped roof.

One big advantage though of an East & West facing roof is you can fill the whole roof with solar panels, giving you twice the area to work with compared to a North / South roof, where you can only use the south facing half.

There's a another benefit to east / west facing solar arrays too, as they produce the most electricity when you need it most. Homes use their largest amount of electricity in the morning (when east facing panels are producing), and late/afternoon evening (when west facing panels are producing).

There's a good argument for east / west facing arrays as it means less need for battery storage as you can use the power directly.

Northerly: not worthwhile in Ireland

As you move to pointing north the production from solar panels rapidly drops off, and we would not recommend it as a good financial or carbon-footprint reducing investment. The only except here is shallower pitched roofs, that suffer much less with the Northerly drop-off compared to steeper roofs.

Do solar panels work on cloudy days?

Yes is the short answer. Solar panels will produce electricity in all weather conditions including on cloudy or rainy days.

Their production is impacted though by heavy clouds. Light hazy clouds have a small impact. Days that have those thick black clouds that keep the whole day dark can have a significant impact though, significantly reducing electricity output from the panels on the worst days compared to a perfect blue-sky day.

Here is a graph of a month's production from a domestic solar installation in Cork (that's May 2022, which had fairly changeable weather). You can see here that during the month there were three days of particularly bad weather with significant drops in output from the solar panels due to heavy black clouds. On the other days you can see a small variance due to normal weather patterns with lighter clouds.

We also have our solar PV case studies that feature live production data. These update every day with daily electricity production from various solar installations we've done, so you've real unbiased data to help you make your own plans on solar. They are great for seeing how daily weather can affect solar output.

How do solar PV panels work?

When daylight strikes the solar panels, there is a movement of electrons within the cell. This activity creates an electrical voltage. This voltage is collected by conductors (those tiny wires you can see like a grid on a solar cell), and then connected to output cables. (If you want to get really nerdy and understand the science behind how solar panels work, you can read our article here. )

The electricity generated is a DC (direct current). The voltage depends on the number of panels connected together and how sunny it is, though it can be up to 500v or more on a larger string of panels. This voltage then travels through solar PV cables, into an inverter which is normally in the attic. The inverter changes DC electricity into AC (alternating current) electricity and adjusts the voltage to 240v so it matches your house's needs.

What are the benefits of solar PV Panels?

Below is some information on the benefits of installing solar PV panels.

• Reduces Electricity Bills - Solar PV is a proven technology, and will result in a lowering of your electricity bills.

• Government incentives - At the moment there are grants of up to €2,100 for installing solar PV panels.

• Make money from excess electricity - You get paid by your utility company for any excess electricity you generate and export back to the grid.

• Low Maintenance - Solar PV panels have no moving parts. Therefore there is very little maintenance required except cleaning them the rare time the rain doesn't clear off any debris.

• Locking in Electricity Prices - Solar PV is a way of protecting yourself against rising electricity prices. You are locking in the cost of your solar electricity, but those panels will be generating for the next ~25 year or so, when it's fair to assume that general electricity costs will be a lot higher yet your solar costs will not have changed.

What are the disadvantages of solar PV panels?

Solar isn't for everyone and isn't suited to all homes, check out below, some disadvantages.

• Upfront Cost - While the cost of owning a solar PV system has come down substantially over the past number of years, the initial upfront investment is considerable.

  You are effectively paying for your electricity all in one go at the start. Unfortunately, for energy-poor households, that would benefit substantially from solar energy, this can be a stretch too far economically.

• Weather - Although solar energy can perform during cloudy and rainy days, the efficiency of the solar system drops.

• Battery storage is expensive - Electricity generated from solar energy needs to be used straight away, or it will be lost back to the grid. A way of ensuring you maximise the full usage of your solar panels is by storing the surplus energy in batteries.

• Space - Solar PV panels require a lot of space, and some roofs don't have enough. The more electricity you want to harness, the more solar PV panels are required to collect as much solar energy as possible.

What are the costs of installing solar PV panels?

The cost of solar panels is dependent on your electricity usage, in terms of how much you are spending on electricity monthly. Your roof space also determines how many solar panels you can install. This in turn will determine the cost of your solar panels.

Also, the costs of solar panels are also determined by the installer. It is always a good idea to get a minimum of three quotes from different installers.

For more information we have a full guide to solar panel prices in Ireland which includes prices, payback, electricity production forecasts and carbon-footprint reduction numbers.

Are solar panels environmentally friendly?

Yes indeed they are. Solar energy is one of the cleanest forms of energy on earth. Solar PV doesn't use water to operate or release any harmful chemicals or substances.

The carbon footprint of an average solar photovoltaic (PV) system is between 14-73 grams of carbon dioxide equivalent (CO2e) per kilowatt-hour (kWh).

Although this sounds like a lot for a renewable energy source, it's relatively low compared to the average emissions of burning oil - 742g of CO2e per kWh.

How long do solar panels last?

Solar panels are designed to last up to 25 years. Many solar manufacturers have warranties that are up to 30 years. The 25-30 year warranty does not mean that they will give up after this period. It means the manufacturer will guarantee their output for this time.

It's more than likely that the solar panels will still produce energy after 30 years. But, with possible degradation of generation output.