Plain words
Solar in plain English
This is a trade with a lot of its own words, and none of them help you judge a quote. So every term we use anywhere on this site is written out here in ordinary English, with an example from an ordinary Irish home.
The size of the system (kWp)
kWp is the size of the system, meaning how much your panels can produce at their best. A 3-bed semi usually takes about 3.5 kWp, which is around eight panels on the roof. We model every kWp as producing 900 units of electricity a year, a typical Irish yield, and the SEAI grant is worked out per kWp as well. How we calculate this
A unit of electricity (kWh)
A kWh is a unit of electricity, the thing your bill counts. A home on about €200 a month buys roughly 6,900 units a year, and we model those at 35c each. A kettle boiled a few times a day is a fraction of one unit; an immersion heater is a couple of units an hour. How we calculate this
How fast it can deliver electricity (kW)
kW is how fast something can deliver electricity, rather than how much it delivers in total. A 7kW home car charger puts in about 7 units an hour, so an overnight charge adds most of a typical battery. The same idea applies to the inverter: its kW figure is the most it can pass through to the house at any moment.
The box that turns what your panels make into the electricity your house runs on (the inverter)
The inverter is the box that turns what your panels make into the electricity your house runs on. It usually goes on a wall in the utility room, the garage or the attic, about the size of a small briefcase. Everything your panels produce passes through it on the way to your sockets.
Where your daytime electricity waits until you need it (the battery)
A home battery holds the electricity your panels made during the day so you can use it in the evening. Most of what a roof produces arrives around the middle of the day, and most of what a family uses happens between 4pm and 9pm. A 10 kWh battery on a 3-bed semi covers that evening block, which is why storage is in every system we design.
A heavier electricity supply some larger homes have (three-phase)
Three-phase is a heavier electricity supply that some larger homes have, and most Irish homes are single-phase. You can tell from the meter box, and your quote confirms it either way. It matters because it changes which inverter and which car charger suit the house.
Solar panels, the panels on your roof (PV)
PV, short for photovoltaic, means solar panels, the panels on your roof. You will also see them called an array or a string, which are both just words for the set of panels working together. They run on daylight rather than direct sunshine, so an overcast Irish day still produces, at a lower output.
The electricity you use yourself instead of buying (self-consumption)
Self-consumption is the electricity you use yourself instead of buying. Every unit you use from your own roof is a unit you do not pay 35c for, which is where the saving comes from. A battery raises it sharply, because the washing machine at 7pm can run on what the roof made at 1pm.
What you're paid for the electricity you send back to the grid (export)
Export, paid through the Clean Export Guarantee, is what you are paid for the electricity you send back to the grid. It happens on a bright day when your panels are producing more than the house is using and the battery is already full. Your supplier pays it as a credit on your bill, at a lower rate than the price you buy at, which is the reason a battery is worth more than exporting.
How much less the panels make as they get older (degradation)
Degradation is how much less the panels make as they get older. It is slow and steady rather than sudden, and panels carry a long performance warranty for exactly that reason. A roof fitted today is still producing the large majority of its first-year output well into its second decade.
How much of the battery you can actually use (usable capacity)
Usable capacity, sometimes called depth of discharge, is how much of the battery you can actually use. A battery keeps a small reserve rather than running to empty, because that is what makes it last. So a 10 kWh battery is quoted on what you can draw from it, and that is the figure we use in the calculator.
Making your own electricity (microgeneration)
Microgeneration is making your own electricity at home, on a household scale. It is the word the rules and the paperwork use for a house with panels on the roof. Registering it is part of the job, and it is what lets your supplier pay you for what you export.
Your meter's number, printed on your bill (MPRN)
The MPRN, or Meter Point Registration Number, is your meter's number, printed on your bill. It identifies your house to the grid, so it follows the property rather than you. The SEAI grant is one per MPRN, so a home that has already claimed for panels cannot claim again. How we calculate this
Using stored electricity at the hours when buying it costs most (load-shifting)
Load-shifting is using stored electricity at the hours when buying it costs most. In a house on a day and night rate, that means the battery covers the evening peak and refills when electricity is cheapest. The dishwasher runs whenever suits you; the battery decides where the electricity comes from.
How long before it pays for itself (the payback period)
The payback period is how long before the system pays for itself, taking the cost after the grant and dividing it by the yearly saving. For a 3-bed semi with 3.5 kWp of panels on a south-facing roof, a 10 kWh battery and a €200-a-month bill at 35c a unit, we'd expect about 6.2 years. After that the system keeps producing electricity you don't have to buy. How we calculate this
Money off your panels from the state (the SEAI Solar Electricity Grant)
The SEAI Solar Electricity Grant is money off the cost of your panels, paid by the state. It is €700 per kWp for the first 2 kWp, then €200 per kWp from 2 to 4 kWp, capped at €1,800, so a 3.5 kWp system attracts €1,700. It covers the panels only, not the battery, and the home needs to have been built and occupied before 31 December 2020. How we calculate this
Which way your roof faces (orientation)
Orientation is simply which way your roof faces, and it is one of the biggest things behind any figure we give you. South produces the most over a year. An east or west roof produces less in total but spreads it across the morning and the evening, which can suit a house that is empty in the middle of the day. How we calculate this
Whether the cable is fixed to the charger (tethered or untethered)
Tethered means the cable is fixed to the charger; untethered means you plug your own cable in. Tethered is quicker on a wet evening because the cable is always there on the wall. Untethered keeps the wall clear and lets a future car with a different plug use the same charger.
The charger slows down when the house is using a lot (load balancing)
Load balancing means the charger slows down when the house is using a lot, so it never trips the supply. If the oven, the immersion and the car charger all want electricity at 6pm, the car simply takes less for a while. You would not notice it happening; the car is still full in the morning.
Anything here you'd still like explained, ask us and we'll write it into your quote.
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