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Planning & combining solar thermal and pv

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  • 01-05-2018 8:39pm
    #1
    H.E. Pennypacker
    Closed Accounts Posts: 844 ✭✭✭


    Does the 12 m2 planning exemption cap apply to pv and thermal separately or combined? Any references to the cap that I've found refer to either pv or thermal but not a combination of them. The original legislation just refers to solar panels so no clarity there either?

    Can I put near enough 12 m2 solar pv on my roof and then have a thermal panel as well without running into planning issues?


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    #2
    Gumbo
    Moderators, Society & Culture Moderators Posts: 38,437 Mod ✭✭✭✭Gumbo


    H.E. Pennypacker wrote: »
    Does the 12 m2 planning exemption cap apply to pv and thermal separately or combined? Any references to the cap that I've found refer to either pv or thermal but not a combination of them. The original legislation just refers to solar panels so no clarity there either?

    Can I put near enough 12 m2 solar pv on my roof and then have a thermal panel as well without running into planning issues?

    Total area combined. Also, don’t forget the 50% area of roof too.


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    #3
    H.E. Pennypacker
    Closed Accounts Posts: 844 ✭✭✭H.E. Pennypacker


    kceire wrote: »
    Total area combined. Also, don’t forget the 50% area of roof too.

    Grand - thanks. I'm safe enough on the roof area but was thinking of 6 pv panels and either a 20 or 30 tube thermal panel. Back to the drawing board....


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    #4
    quentingargan
    Registered Users Posts: 1,627 ✭✭✭quentingargan


    H.E. Pennypacker wrote: »
    Grand - thanks. I'm safe enough on the roof area but was thinking of 6 pv panels and either a 20 or 30 tube thermal panel. Back to the drawing board....
    If you are putting up PV, adding a few panels and a hot water diversion unit will not add much to the cost, and would be a lot cheaper than adding a separate hot water system.

    The diverter measures your electricity export and as soon as you start exporting, it turns up a dimmer switch on your immersion to ensure you use all your own power.

    I would also think about applying for planning permission unless you think there would be objections or the house is in a visually sensitive area.


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    #5
    H.E. Pennypacker
    Closed Accounts Posts: 844 ✭✭✭H.E. Pennypacker


    quentingargan wrote: »
    If you are putting up PV, adding a few panels and a hot water diversion unit will not add much to the cost, and would be a lot cheaper than adding a separate hot water system.

    The diverter measures your electricity export and as soon as you start exporting, it turns up a dimmer switch on your immersion to ensure you use all your own power.

    I would also think about applying for planning permission unless you think there would be objections or the house is in a visually sensitive area.

    Thanks. The reason that I was thinking about solar thermal alongside pv is that pv & immersion won't heat the entire tank whereas thermal will, given that the thermal coil is at the bottom of the tank and the immersion element only goes down maybe two thirds. That's my understanding and I'm open to correction. We tend to use a lot of hot water and while I'm planning to get a bigger cylinder, I think that 250 litres is as big as I can fit. I'd like to heat as much of it as possible. Currently, with our 120 litre tank, the oil boiler heats about enough of it to keep us going whereas the immersion on its own can't. Our hot water demand is likely to grow as the kids get bigger.

    I don't really want to go for planning at the moment.


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    #6
    quentingargan
    Registered Users Posts: 1,627 ✭✭✭quentingargan


    If you go for 7x300W panels, that would produce slightly more total energy per year than a 4 sqm solar thermal system, but you would use some of this total energy to power devices during the day.

    You will need to top this up on dull days with either system. One advantage of the immersion diverter is that there are two outlets. You can get a cylinder with two immersions - one at the bottom of the tank and one in the middle. Heat the top first so you have hot water available and then heat the second one at the bottom.

    The main advantage of PV over thermal is lack of maintenance required. With thermal you are looking at the cost of changing glycol and also there are pumps and expansion vessels that can cause problems down the line. By comparison, PV is quite maintenance free.

    On the shoulders of the season, you could use your top immersion off-peak to heat the top of the cylinder, leaving the sunshine do the rest during the day.


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    #7
    H.E. Pennypacker
    Closed Accounts Posts: 844 ✭✭✭H.E. Pennypacker


    The cylinder with two immersions sounds like it'd work well.

    You've persuaded me :)

    Thanks for your help


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    #8
    rolion
    Closed Accounts Posts: 3,362 ✭✭✭rolion


    I have and use every day the dual system. Is a beauty...
    I can show graphs that the 5KW PV installed power cannot beat the 40 tubes solar tubes !!!
    There are days when PVs will barely generate to keep minimum load while the solar tubes were heating up the cylinder.

    The logical reason(s) someone will say that PVs are better than tubes ..well, that I just cant understand and I'm waiting to be proven that I'm wrong... one single basic query is how you manage the PV and immersion on those days when people at home and keep using the electricity, taking all the generated power off PVs, leaving almost nothing to be diverted to immersion unit or switching on and off !? How can we measure the efficiency of a well designed solar coil versus a single 40cm long immersion stick against a mighty water thermodynamics in a 300l cylinder !?

    Have fun...


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    #9
    unkel
    Registered Users Posts: 64,773 ✭✭✭✭unkel


    rolion wrote: »
    The logical reason(s) someone will say that PVs are better than tubes ..well, that I just cant understand and I'm waiting to be proven that I'm wrong

    You're not wrong. PV to heat water is very inefficient and the cost / benefit is terrible (as you have to value 1 kWh generated by PV at about €0.04 because that is the cost to apply 1 kWh of gas to heat the water

    And there is a substantial subsidy on tubes, there's none on PV and there is no FIT.

    That said, PV is now considerably cheaper than it was a few years ago when you and I installed tubes. It is well possible that it will be so cheap in a few years time that people just plaster their roofs with it and use it for quite a bit of their DHW and space heating even in winter (and of course charging their cars, home attached batteries, etc.)


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    #10
    H.E. Pennypacker
    Closed Accounts Posts: 844 ✭✭✭H.E. Pennypacker


    Thanks for your posts - plenty to think about there!

    @Rolion - would you mind posting a graph that shows good solar thermal heating and poor pv panel output and the weather conditions that day?

    @Unkel - I live in a rural area so there's no cheap gas. I've a kerosene boiler and electricity as hot water options. In terms of costs, they're neck and neck. Night rate electricity is €0.0976 per kWh less 28% so costing me €0.07 per kWh including vat. According to the SEAI, kerosene costs €0.0665 per kWh in terms of delivered energy but there's a little problem. That's assuming 100% efficiency. My boiler is rated at 95% efficient but when you heat hot water on its own, the boiler can't condense as the return temperature is too high. A non-condensing boiler is around 60% efficient so we're looking at 25% loading on the kerosene option. That brings my kerosene price to €0.088/kWh so its cheaper to use night rate electricity to heat my hot water cylinder. Daytime heating obviously favours kerosene.

    In terms of costs, I've been quoted €3800 including vat and immersion diverter for a 1.89 kWh pv system. AEI are quoting €5480 for a 2kWh system and Electric Ireland are €4490 for a 1.8 kWh system including diverter.

    Solar thermal is €4586 from AEI and €4175 from Glenergy for equivalent Kingspan setups (Including grant and vat)

    Base load on the house is 240 watts per hour. We use approx 17 kWh per day with 8 to 10 of those being at night. As our daytime load is low, my plan was to get pv instead of thermal because I can be reasonably sure that daytime immersion diversion will ensure that I don't export much if anything to the grid.

    I haven't factored a solar cylinder into the pv price so the lowest thermal and pv prices are probably equivalent. PV has less maintenance costs and it can do many things whereas thermal can only do one. The question is - can thermal efficiency compensate sufficiently for its lack of versatility?


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    #11
    unkel
    Registered Users Posts: 64,773 ✭✭✭✭unkel


    PV excess not having to compete with cheap gas makes a huge difference alright.
    H.E. Pennypacker wrote: »
    Solar thermal is €4586 from AEI and €4175 from Glenergy for equivalent Kingspan setups (Including grant and vat)

    You don't say what kind of system you are talking about (30 tube Kingspan? and a 300l cylinder?) and you don't mention details about your household and how much hot water you use. From doing some basic sums, solar thermal only really works well (financially) if you use a lot of hot water. In my case, there's 5 of us, with 4 women, with all my daughters coming into their teenage years now or soon enough. They all like massive showers and huge baths all the time. The hot water in my 360l cylinder was completely gone by late last night and by mid day today, all of it was heated to 60C by the sun.

    A very simple rule of thumb (but please do your own research and spreadsheets) is that unless you use lots and lots of hot water, you better go PV only. PV panels are very cheap these days.


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    #12
    rolion
    Closed Accounts Posts: 3,362 ✭✭✭rolion


    There are two aproaches here: cost based and efficiency...

    Cost based,PVs ar winning due to lower installation cost,even with the grant included
    Efficiency:well,PVs are for electricity and tubes are for water,nothing beats them in their own designed solution,

    I cant go back and argue one versus other,i advise go for both.I am not selling anything and i have no plans to change the system soon,either.
    I spent at least one year checking angles,Sun position,location and testing the ground, all at the same time observing how other systems are performing live.

    H E R E is my PV system.
    H E R E is my solar tubes.
    H E R E is the PVs system of all people installed across Ireland.Ho "home" and search for country "Ireland"

    A quick Q:when the sun goes less intensity,the PVs just stops producing anything. The tubes will continue to heat the water for a longer perio of time due to collector higher temprature,water flowing and exchangin heat and ... the air is warmer.
    And..the beauty with PVs is you need to use it "now" and cannot be stored for later.

    Yesterday,i made a tea with the 80 degrees water off the kitchen taps...two baths full with same cylinder.But,thats only a day,so far.

    Take your time,do your home work and enjoy every step...


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    #13
    H.E. Pennypacker
    Closed Accounts Posts: 844 ✭✭✭H.E. Pennypacker


    @Unkel - a bit of detail about our household - two adults and two 18 month old toddlers. On average, we'd do two washing machine loads a night, two matching drier loads as well, although that's starting to come down as the weather has improved. We also do one dishwasher load per night. The immersion runs on timer for two and a half hours a night as well so we consume between 8 and 10 kWh of night rate electricity, depending on the washing machine cycle temperature. We have a pumped shower which delivers between 60 and 90 litres of water per shower. That's a mix of hot and cold but the bottom line is that our 120 litre hot water cylinder will be lukewarm to cold after one shower if its not being heated while the shower is running. The toddlers have baths which probably use around 50 litres of water a go. To complicate things a little, I shower in work three days a week because I cycle (I work from home two days a week).

    At a wild guess, our daily hot water consumption is probably 200 litres on average but is not consistent on a daily basis.

    In terms of electricity, we use approx 7 kWh during the day with a base load of approx 240w rising to approx 450w when I'm working from home. Most of our consumption is early morning and evening with midday being just base load. The oven and kettle are astonishingly heavy on electricity.

    In terms of thermal, I was pricing a 30 tube Kingspan panel and 300 litre tank. In terms of pv, I was looking at a six or seven panel setup so max 2100 kW (less 20% I guess).

    As my daytime electricity consumption is low, I thought that pv would only make sense if I heated enough water to prevent export to the grid. Having washing machines, driers and dishwashers running at night is a small hassle in terms of coordination so it'd be nice to be able to kick them off during the day at weekends etc provided that pv could fully power them which is by no means a given.

    My daily hot water consumption is inconsistent so thermal panels will either provide too much hot water some days or will not provide enough if I undersize the system and go for a 20 tube/200l tank setup. A thermal installation gets me a bigger tank whereas that's an extra expense with pv.

    On the face of it, I don't have a clear case for either option as I think as each option has a compromise involved. I like the idea of renewable energy and doing something to reduce my environmental footprint is more important to me than payback (within reason).

    @Rolion - thanks for the graphs and info. I agree with you that a combination is a good approach but its expensive to do both and I don't have time at the moment to self-source components and track down a willing installer. I also don't have time to chase both parties if there are any issues and sort out the mutual blame game. An undersized 20 tube thermal system alongside pv would tick a lot of boxes though.

    A 20 tube Kingspan panel and 6 pv panels would be in and around 12 m2 which is the planning limit. Too much of a compromise though?


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    #14
    conor_mc
    Registered Users Posts: 649 ✭✭✭conor_mc


    Just re tumble dryer, if you have the space you could switch to a dehumidifier plus a couple of clothes horses. Not only much more energy efficient, but also a flatter load curve to align better with PV.

    Don’t have solar, but recommend dehumidifier over dryer regardless!


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    #15
    unkel
    Registered Users Posts: 64,773 ✭✭✭✭unkel


    H.E. Pennypacker wrote: »
    On the face of it, I don't have a clear case for either option as I think as each option has a compromise involved. I like the idea of renewable energy and doing something to reduce my environmental footprint is more important to me than payback (within reason).

    This is it. For your situation, you'll enjoy having your pumped showers (nice, aren't they? :)) knowing that most of your water cam from renewable energy. And in general, doing your thing for the environment. By the start of today, we had used up all of our 360l of hot water and by sunset, we had 360l of 60C water again today from the sun.

    For your family a €4k 30 tube / 300l thermal system would have a payback of about 15-20 years I'd say. PV is probably a good bit longer than that, more like 30 years (without FIT). The inevitable switch over to electric cars and / or the future availability of cheap house attached battery storage might shorten this.


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    #16
    rolion
    Closed Accounts Posts: 3,362 ✭✭✭rolion


    A compromise is the worst case scenario... not enough from each system to enjoy the outputs or to satisfy the needs whenyou need it the most.I "learned" to design my system for when i need it the most and when i don't need it either...when it has the minimum and when it reaches the maximum.Is one system for winter (both PVs and tubes) and another for summer sunny days,both in relation to inputs/demand and to outputs/expectations.

    Get one done properly while staying in the budget and start working/saving on the second,one being efficient ,other upgrading along... your call !
    Either way,enjoy it...

    LE

    Sorry for late edit.
    Below,is my immersion today reports,powered at full 3000w designed capacity of the element...
    I wonder what kind of PV system is that you will need to reach the 3Kw power so that the immersion element will heat the 300l cylinder for a decent usage !?
    Also,the spikes up and down will be shorther and lower directly related to people living in the house and turning the electrical appliances on and off
    You will get a warm-up solution that will assist/help the gas or oil boiler but not the one that can make you tea out of the tap...a compromise yes,but not efficient in any way on any of them !

    450267.jpg


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    #17
    H.E. Pennypacker
    Closed Accounts Posts: 844 ✭✭✭H.E. Pennypacker


    @Rolion - what energy monitor are you using? It looks very useful


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    #18
    air
    Registered Users Posts: 2,822 ✭✭✭air


    What use are the SEAI, other than running BS grant schemes to create jobs for themselves they don't seem to achieve a whole lot.

    Why aren't they advising the government to remove this nonsensical restriction and bring us into line with the UK and most other European countries? What is the downside to having more than 12m2 of PV on any roof?

    Similarly on EVs, instead of running a charge point grant scheme, why don't they lobby to put in place legislation to allow people in apartments install charge points there or within shared street spaces etc.
    Another pointless quango.


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    #19
    robp
    Banned (with Prison Access) Posts: 1,934 ✭✭✭robp


    I have a very basic question and sorry if it is a bit obvious. If the water in your solar thermal is not used it cools, does this cooling provide a background home heating?


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    #20
    unkel
    Registered Users Posts: 64,773 ✭✭✭✭unkel


    Yes. The law of conservation of energy applies. So if you don't use the hot water, it is a heat store, gradually giving off heat to its surroundings. Don't overestimate the impact of this though. My own hot water cylinder in my hot press is so well insulated that the water only drops 1C per 24h in it. Since it was installed, our hot press is no longer hot :p


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    #21
    H.E. Pennypacker
    Closed Accounts Posts: 844 ✭✭✭H.E. Pennypacker


    If you’re looking to use the energy gained from solar thermal beyond hot water then you need to start thinking about a thermal store - like a hot water cylinder but different....


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