If you have a new account but are having problems posting or verifying your account, please email us on [email protected] for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact [email protected]

Solar for Dummies.

  • 12-12-2021 11:30am
    Registered Users Posts: 12,556 ✭✭✭✭

    Hello. I've been reading through the PV threads here and there's alot of information. Some a little confusing if you're not familiar with the units and terms

    1kwh is 1 unit of electricity, 1 payable unit of electricity and what a 1kw heater would use in 1 hour of use?

    A 5kwh PV system is what that system theoretically can produce in 1 hour of sunlight depending on panel efficiencies and actual sunlight?

    I've no idea about batteries however other than I know they're costly and probably not worth the payback?

    I'm not familiar with measurable terms, but what size batteries would be needed to store average daily excess? Or is it more cost effective to leave it out and use night tariff



  • Registered Users Posts: 2,340 ✭✭✭bullit_dodger

    You pretty much have 90% of the answer yourself Ackwell (love the name btw).

    So batteries are measured in "Kilo-Watt-Hours" or "kWhr" for short. You can basically think of it as "units" of electricity. To use your example, your 1Kw heater would use "1Kw in 1 hr".....which is "1kWhr". So a battery which is rated for 8kWhr capacity would be able to run that heater for 8 hrs. Or if the heater was 2Kw, then it could run that for 4 hrs, etc.

    There are two sides to the argument about batteries and payback. I'm firmly in the camp that batteries do have a positive payback, but (and this is important) it very much depends on your "usage profile". How many units do you use per year, when in the day do you use those units, etc. No sense in buying a huge battery as it will never pay for itself , or take 20 years .....unless you consume a lot (more than 4000-5000 units / year). Conversely super small batteries tend to have a longer payback too as the capacity per €€€ that you get isn't as favourable.

    There is a sweet spot I believe somewhere about 5Kwhr capacity for batteries that 80% of people will see them payback in 10 years or so, assuming you qualify for the €600 grant. Again, depending on your usage others will see payback as short as 7-8 years, while others will be 11-12 years.

    Aside: Your question about the "night tarrif" is a good one. Many people, including myself charge the battery up using the night rate in winter, and then during the day use the battery to power things when the electricity is more expensive.

  • Registered Users Posts: 12,556 ✭✭✭✭AckwelFoley

    Thanks. I need to go and see what we actually use per year.

    Are these systems easily tinkered with.

    For example, Is it relatively straight forward to add additional panels and batteries if usage patterns change?

  • Registered Users Posts: 2,340 ✭✭✭bullit_dodger

    Everything can be upgraded, barring the "inverter" (the device which converts the DC from the panels to AC which your house uses). So if you do plan on expanding your system down the road , you should ensure that you get a biggish inverter from the get go. Something around 5Kw-6Kw will see you right.

    That said, adding additional panels after initial installation is typically more expensive. When you think about it, having 2x guys come out and install 10 panels is a fixed fee, and to put on 12 panels instead of 10 probably would be 400-500 extra..... but to get them to come out a year later and add 2 more.... you end up paying that fixed "call out charge" so ....maybe this would cost €800-900 (I'm guessing) to get those 2x panels on later.

    So it's probably best to try and "overspec" the panels from the get go. If you can avoid people going onto your roof you'll be better for it.

    Batteries/adding hot water diverters are all easily added later, but again, it's a little complicated as there are grants to get gained and normally (normally) it's cheaper to do it right from the start. I appreciate that not everyone has all the money in one year to put in the system they'd like - so sometimes it's necessary to split

  • Registered Users Posts: 12,556 ✭✭✭✭AckwelFoley

    Yea. What inmean by change in consumption would be 6 or 8 years down the line. Elec car or more use of electricity on other devices...not now buy potentially down the line

  • Registered Users Posts: 2,340 ✭✭✭bullit_dodger

    Gotcha. Yeah, you can add years later down the road, although many installers won't touch another installers work. Some of it with good reason, as if the original installers were "cowboys" then they may inherit a problem someone else made years ago. Then you are looking to the new installer thinking that they did something bad, but really it was the original guys.. Then again, sometimes ..... they are just being dicks :-)

    Really though whatever about batteries, EDDI, Harvi's, Zappi's (for the car), I'd max your panels as much as you can from the get go. Panels change, and ideally you want to get the same panels as you have already got up there. Couple of years later, and they simply may not be making the same panels anymore as technology has moved on. It's not a complete crap show if you can't get the same of course, but ideally they work better when all the resistenaces are the same and if you have different makes/models it can make a difference.

  • Advertisement
  • Registered Users Posts: 12,556 ✭✭✭✭AckwelFoley

    I'm one to mostly over spec with lots of things but I'm seeing that if I over produce kwh I'm just increasing the payback length because of the extra cost of the system that I'm effectively not using

  • Registered Users Posts: 2,340 ✭✭✭bullit_dodger

    Yup - sound logic there too. However, if you can go for 5Kwp of panels and 5Kwhr of a battery, that system should see you right for the foreseeable furture . Yeah, you can add to it later, but it's a solid good spec that will do most of what you need. IN about the €7-8K mark (assuming you qualify for a grant)

  • Registered Users Posts: 12,556 ✭✭✭✭AckwelFoley

    Our consumption last 12 months is 5400kwh

    Would the 5kw system be considered a good size for this usage?

    How many kw of this would the solar be expected to cover? Assuming normal no large night consumption

  • Registered Users Posts: 1,677 ✭✭✭Deagol

    Don't overlook that a 5kw system (i.e. with 5kw of panels) will only produce that power on a bright sunshiny day, with the sun hitting the panels at a good angle and in the spring / summer / autumn.

    Many of us have many more panels than that installed so that you get maximum allowed (by size of the inverter) in less than ideal conditions. For instance, I have a 5kw inverter but 6.1kw of panels. So on a great summers day I'm maxed out at 5kw (actually a little more than that as the inverters are not precise) but on a cloudier day in the summer I can still hit 5kw and in early spring and late autumn I'm still pushing 5kw even when the sun is lower in the sky etc.

    The general advise here would be to put up as many panels as you can fit / inverter will take (i.e. my inverter will take around 24 panels total on 2x strings).

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,036 Mod ✭✭✭✭Jonathan

    This site will give you a reasonably accurate estimate of what the system will produce based on your size, location, aspect etc.

  • Advertisement
  • Registered Users Posts: 12,556 ✭✭✭✭AckwelFoley

    If the system generates more than is required during the day, the surplus will go to the hot water and then to the battery and then to the grid? Can that order be changed?

    If the household requirements during the day does the system pull power from the battery before it pulls from the grid? Or is the battery only for night use?

  • Registered Users Posts: 1,677 ✭✭✭Deagol

    No. Usually surplus will go to battery, then hot water. Yes, it is possible to change things around a bit - there are quite a lot of settings on both the inverter and diverters that allow you to customize what you want to happen.

    The battery will be pulled from before the grid generally. If you think of the grid as a giant reservoir, and the battery like a small pond between your house and the grid.

    If you are pulling less power from the solar system than you need then the pond will fill up first, once that's full it will start to try and fill the reservoir.

    If you need more power than the solar system can provide (ie. you turn on the cooker for the lunch) then the first thing that will empty is the pond (the battery) and then once that's gone you will start pulling from the reservoir (the grid).

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,036 Mod ✭✭✭✭Jonathan

    Good analogy. Once thing to add is that the Inverter (and the battery if you get one) have a maximum power output, so even if you have a full battery, you might still end up pulling from the grid if you use more power than the inverter and battery can provide.

  • Moderators, Home & Garden Moderators Posts: 5,508 Mod ✭✭✭✭graememk

    The pipes/pumps can only supply so much.. gotta keep with the analogy

  • Registered Users Posts: 12,556 ✭✭✭✭AckwelFoley

    Hello. Yes. That's a good point. What is the usual limitations to the battery. Are they only usually for lights and low demand applications. The cooker and dryer will require the grid?

  • Registered Users Posts: 1,677 ✭✭✭Deagol

    No- the batteries can supply up to 3kw (at least mine can - depends on the inverter and battery model) - I believe some can do 5kw.

    So theortically if you have a 6kw inverter, a very sunny day and a full battery you can do 9-11kw for a limited time. (I think?? - is the limit still 6kw due to the inverter?? - maybe someone else can answer that?)

    Bear in mind, if you were pulling 5kw from a 5kw battery you will only get this for a short time (perhaps 45 minutes).

  • Moderators, Home & Garden Moderators Posts: 5,508 Mod ✭✭✭✭graememk

    Hybrids (combined solar and battery) inverter are limited to 6kw max (or whatever their rating is) even if they can do from the battery. Most likely due to internal limits on the inverter.

    I have separate solar inverter (6kw)and storage inverter(3kw) so could be a max of 9 kw at midday in a good may/June day.

    Generally 3,kw from storage covers the house quite well, but if I had the kettle and oven on, I'd have to pull from the grid (assuming there is charge in the batteries)

  • Registered Users Posts: 1,500 ✭✭✭Manion


    Not to hijack this thread but I was wondering what are the add on secondary features people should consider when getting solar? I've seen people talk about

    * Being able to charge a batter on Solar or Night rate

    * Being able to use Solar for EV charging

    * Being able sell excess power back to the grid

    * Being able to heat water with excess power

    * Monitoring of solar power generation and battery usage

    Is there any other secondary features people should keep in mind when looking into Solar. Some of the above I hadn't thought about until I started reading this forum and others I hadn't thought too deeply above. For instance I've an EV charger but it's wired into the ESB Meter box as opposed to the main consumer unit, I guess that means I cannot use Solar to power an EV? 

  • Registered Users Posts: 1,871 ✭✭✭garo

    Meter vs consumer unit has nothing to do with ability to use solar. You need an EV charger that can detect the amount of excess solar going to the grid and modulate the power it is consuming.

    Post edited by garo on

  • Registered Users Posts: 1,500 ✭✭✭Manion

    OK, I have a Andersen charger with that capability. There's something I'm missing though, how does the solar power get returned to the grid? My main concern is that the meter box is at the front of the house and the consumer unit is in the middle of the house. I don't want power cables running all over the place.

  • Advertisement
  • Registered Users Posts: 1,677 ✭✭✭Deagol

    Power flows in both directions through cables. To have solar panels you need an inverter. The inverter is connected to your house power - your house power is (presumably) connected to the national grid.

    Your house already has power cables running all over the place :)

  • Registered Users Posts: 12,556 ✭✭✭✭AckwelFoley

    You're not hijacking the thread. More than welcome to add queries

  • Registered Users Posts: 12,556 ✭✭✭✭AckwelFoley

    I've been furnished with the following.

    I gave them my consumption as per this thread and request around a 5kw

    How do these prices stack up

  • Registered Users Posts: 1,677 ✭✭✭Deagol

    The 'budget' one is overpriced by about 2k in my opinion. Wouldn't even comment on the 'premium' and 'elite' stuff.

    10x panels cost c.€1500.

    Battery about 2k

    Inverter 1.5k

    Eddi 500.

    Other mounting and electrical 1k at most.

    So you would be getting 6500k of hardware plus a days labour for 2-3 people for €11,200. I'll leave it up to you to decide if that's a fair margin.

  • Registered Users Posts: 1,500 ✭✭✭Manion

    Ah right, so it's just the net of neutral over live. Maybe I've the wrong idea about Solar, if I want to power say the kettle in the kitchen, how does the power from the solar get to the kettle without going through the consumer unit?

  • Registered Users Posts: 2,340 ✭✭✭bullit_dodger

    Good questions. It's kinda hard to explain without diagrams, but in a nutshell a device will take its "power" from whatever has the highest voltage.

    Very simply, the grid nominally puts power into your house at 230 volts. (Technically there's a variance of +/- 10% on that, but let's say 230volts) Your inverter is connected (usually) to the main busbar on your fusebox and detects what the grid voltage is that day, and then outputs at a higher voltage, say 245V.

    So then when you turn on your kettle it will pull from the 245v source over the grid 230v, that works while the sun is shining on the panels or you have power in your battery. Once you've no sun or battery the inverter will no longer be able to supply 245v and then of course your devices (kettles, tv) will take from the 230v that the grid supplies. Of course, there's a bit more behind the scenes such as "aligning the power sine wave" etc, but that's the simple explanation.

  • Registered Users Posts: 1,500 ✭✭✭Manion

    OK so the invertor will have to run directly back to the consumer unit, and this is where I get a little unsure as my EV charger doesn't come off that consumer unit. For me this is more than academic as I wonder if someone with an EV really needs a battery.

  • Registered Users Posts: 1,677 ✭✭✭Deagol

    You're over thinking this. Your inverter has is it's own MCB at the consumer unit, but that is connected back to the grid anyway. Your car charger won't care where it is connected. Once the solar system is producing surplus it will be fed into the electrical system and back to the grid. Your car charger will just use whatever power it has available. If that power is coming from the solar system then your electricity meter won't be running 'forward' so you won't pay for it.

  • Registered Users Posts: 2,340 ✭✭✭bullit_dodger

    The question of "Do I need a battery if I have an EV?" has come up a few times too.

    I'm not sure there's a right/wrong answer here. Depends on a number of factors, which you'll have to answer yourself and then draw your own conclusions.

    For example, will the car be in the driveway when it's sunny? With working from home, this is normal for many of us, but if your using the EV to drive into the office, obviously you'll be exporting a lot when it's sunny outside and the car is in the company car park and not at home.

    Similarly, even if the car is at home....great you'll be able to soak up the excess. EV's get (roughly) 5Km for every 1Kwhr, but if you fill the battery on Monday and it's also sunny on Tuesday.....will you have driven 50Km or so to "free up" 10Kwhr or so capacity from the battery.

    Depends on the circumstances. My own gut feeling is that most people with an EV do need a moderate sized battery (5Kwhr) or there abouts, but that's just my own opinion.

  • Advertisement
  • Registered Users Posts: 6,768 ✭✭✭Alkers

    I don't like this crowd at all in that they try and make their website look like a comparison website but in reality it's just one company installing difference products. Also they're prices are not competitive at all, they're not the most expensive but certainly up there.