Questions on Solar/Battery Installation for Passive New Build

blobert · 05-01-2020 11:16pm #1

Hi There,

We're hoping to build a new build bungalow in the near future to passive standards. We're a family of 4 with (I would think) quite high energy usage. My wife is at home with kids and I often work from home so it's occupied all day and in the winter needs to be warm all the time.

The main part of the house will be facing pretty much fully south with minimal shading and a pretty large roof area of about 250m2, ie there is probably a lot of potential there for solar.

My plan in terms of meeting part L had been to either (1) install a ground source heat pump to heat the house in winter/provide hot water of (2) to do a solar install with batteries. I was leaning towards doing the first one as I figured I might wait a bit longer till solar/battery prices fell lower and then go to town on it hopefully getting us to a point of being able to produce nearly all our power from it. The other reason I was less keen on the solar setup was we are likely to spend a lot of the summer months away and so essentially would be wasting all these free electricity. That said I've read a feed in tariff is coming so this might help in that regard in that we could sell this energy back to ESB. Just a couple of basic questions on this:

(1) Am I right in saying I get no grants for any of this in a new build? From my reading on it it seems as though this is not that much of an issue in that the providers that are eligible for grants are often more expensive than doing it without/grant cost is factored into their pricing?

(2) Do you have to get planning permission for a solar install above X m2? If so I'm thinking it might make sense to include this in the planning application for the new house as opposed to applying for it later especially if we wanted to do a very big install.

(3) Am I right in thinking if I have a battery set up that I can charge it at night saver rates during the winter (or any times the panels are not fully charging the batteries) so I'd essentially only be using self generated or night saver electricity? Is there any downside to this, ie is there a loss in efficiency in charging the battery or somthing else? When people work out payback time do they factor this in, ie I'd imagine if all my homes energy demands can be paid for at night saver rate with batteries vs full price it will help with the payback time of the system.

(4) We have an electric car which is mostly at home during peak generating times, I'm assuming this can be charged up via solar power also, ie this would be a kind of additional storage option/we could essentially charge our car via the solar system also? We do very low mileage so in theory we might be able to run the car on all solar energy (at least in summer months) which would be nice.

(5) Is it safe to have your battery storage system inside your house as opposed to in a garage? At the moment the design of the house has the plant room inside the house, would having the batteries in there potentially be a fire issue?

(6) I'm assuming there's no issue in adding batteries over time? Ie lets say we bought 10 kwh of batteries to begin with we could add another 10kwh later as prices decreased?

(7) Am I right in saying Tesla solar roof is not an option at the moment? I was thinking as it's a new build that it might make sense to have a solar roof as opposed to roof + panels but I'm thinking this is not an option at the moment.

(8) More generally is the economics of this still a bit dubious? Ie if I spend a lot of money covering my roof in panels and have a load of batteries is it still likely to be a 10-20 year payback time? I'm kind of keen on having the new house be very energy efficient/green but at the same time it would be nice if there was some economic rationale for doing it as opposed to sinking a load of money into it just to be green. When I looked at this a couple of years ago it did not seem to add up, though this seems to be improving a bit.

(9) Finally do we have any idea what the feed in tariff will be? I'm guessing it won't be great. I'm wondering if there may be an advantage in getting this work done prior to this being announced/coming in as if it's advantageous it might = an increase in pricing for equipment or installers being busier/less available.

Any advice would be much appreciated!

Thanks

unkel · 06-01-2020 12:26pm

I'll give it a go, but I'm no expert. And these are not all facts, but also my opinions. Others correct me where I'm wrong, or add their opinions please

(1) correct, no SEAI subsidies for new builds, only for houses built before 2011

(2) correct, PP required for >12m2 of solar (PV or tubes). This is very unlikely to be enforced after a woman (with her whole road facing roof plastered with PV) won her case

(3) yes in most setups you can. The downside is that it will decrease battery life. If your battery is a lithium one and you paid current market value for it, the pros of using the cheaper night rate, don't outweigh the cons. The sums for this have been done on this forum before

(4) yes it can, but it depends on your car and on your charger. If you get a Zappi intelligent charger (some others can do the same), it can send surplus PV production directly into your car (even before it would charge your battery if you get one)

(5) no, not imho. Lithium batteries are generally quite safe, and any installed system has many safety features built in. But if a large pack goes on fire, the consequences can be catastrophic. I wouldn't be happy with the batteries in the attic, where most Irish SEAI installers install them. Tesla refuses to install their powerwall in living areas. They will only install on the outside of a building or in a garage. Having a lithium battery in a cold area (outside where there can be sub zero temps) means it can only be charged when it is heated up first. This could very well mean that over several winter months, all solar PV you produce is "undone" by having to heat up the battery

(6) no issue with most systems, most are modular. Adding batteries generally is very straight forward

(7) correct, not available yet.

(8) solar panels are very cheap these days. Probably about half the price they were a few years ago when you last looked. You have about the best possible use case with people in the house a lot of the time, and you have no other cheap source of energy like oil or gas, just electricity. And you can charge your car during the day. If I were you, I would install as many solar PV panels as physically possible on the roof of your new house while it is being built. No cheaper time than that. Payback on the panels in your case is probably in the order of 10 years (for most people in an average Irish house that is oil / gas fired and who do a retrofit install it is more like 20 years). That said, if you add a battery without the SEAI subsdidy, it will never pay for itself. Not with todays battery prices

(9) nobody knows. Some people in the know reckon it will be low, around wholesale prices. So maybe around 5c/kWh. You don't need to get any work done for this as all Irish households will get a free smart meter from some time this year and this smart meter should be able to record exported electricity

Coltrane · 06-01-2020 8:02pm

Envy you the prospect of a passive house! I’ve a period house that doesn’t wanna be passive. Ever. No matter what I try.

You may not need so much solar-PV. If you hit the PH-standard, your heating requirement will be very low. That leaves cooking (you might even use gas), lighting (LEDs are extremely low power), and other minor consumers. So a large array will (overall, across the seasons) produce a large surplus.

There’s nothing wrong with producing surplus, it’s a contribution and you’ll get paid something for it when the FIT is introduced. And if energy independence is important to you, you can now buy systems that will continue to function during power cuts.

But consider the downsides of owning PV. They have a dirty footprint of their own. They’ll potentially stress your roof. They require large ballast at lower pitches. I think people underestimate the risk of storm damage - imagine the lift a panel will generate in high winds. And storms are becoming commonplace.

PV will align nicely with you electrical heating system, but it might be worth considering alternatives to a huge PV array, like a water-harvesting system.

blobert wrote: »

Hi There,

We're hoping to build a new build bungalow in the near future to passive standards. We're a family of 4 with (I would think) quite high energy usage. My wife is at home with kids and I often work from home so it's occupied all day and in the winter needs to be warm all the time.

The main part of the house will be facing pretty much fully south with minimal shading and a pretty large roof area of about 250m2, ie there is probably a lot of potential there for solar.

My plan in terms of meeting part L had been to either (1) install a ground source heat pump to heat the house in winter/provide hot water of (2) to do a solar install with batteries. I was leaning towards doing the first one as I figured I might wait a bit longer till solar/battery prices fell lower and then go to town on it hopefully getting us to a point of being able to produce nearly all our power from it. The other reason I was less keen on the solar setup was we are likely to spend a lot of the summer months away and so essentially would be wasting all these free electricity. That said I've read a feed in tariff is coming so this might help in that regard in that we could sell this energy back to ESB. Just a couple of basic questions on this:

(1) Am I right in saying I get no grants for any of this in a new build? From my reading on it it seems as though this is not that much of an issue in that the providers that are eligible for grants are often more expensive than doing it without/grant cost is factored into their pricing?

(2) Do you have to get planning permission for a solar install above X m2? If so I'm thinking it might make sense to include this in the planning application for the new house as opposed to applying for it later especially if we wanted to do a very big install.

(3) Am I right in thinking if I have a battery set up that I can charge it at night saver rates during the winter (or any times the panels are not fully charging the batteries) so I'd essentially only be using self generated or night saver electricity? Is there any downside to this, ie is there a loss in efficiency in charging the battery or somthing else? When people work out payback time do they factor this in, ie I'd imagine if all my homes energy demands can be paid for at night saver rate with batteries vs full price it will help with the payback time of the system.

(4) We have an electric car which is mostly at home during peak generating times, I'm assuming this can be charged up via solar power also, ie this would be a kind of additional storage option/we could essentially charge our car via the solar system also? We do very low mileage so in theory we might be able to run the car on all solar energy (at least in summer months) which would be nice.

(5) Is it safe to have your battery storage system inside your house as opposed to in a garage? At the moment the design of the house has the plant room inside the house, would having the batteries in there potentially be a fire issue?

(6) I'm assuming there's no issue in adding batteries over time? Ie lets say we bought 10 kwh of batteries to begin with we could add another 10kwh later as prices decreased?

(7) Am I right in saying Tesla solar roof is not an option at the moment? I was thinking as it's a new build that it might make sense to have a solar roof as opposed to roof + panels but I'm thinking this is not an option at the moment.

(8) More generally is the economics of this still a bit dubious? Ie if I spend a lot of money covering my roof in panels and have a load of batteries is it still likely to be a 10-20 year payback time? I'm kind of keen on having the new house be very energy efficient/green but at the same time it would be nice if there was some economic rationale for doing it as opposed to sinking a load of money into it just to be green. When I looked at this a couple of years ago it did not seem to add up, though this seems to be improving a bit.

(9) Finally do we have any idea what the feed in tariff will be? I'm guessing it won't be great. I'm wondering if there may be an advantage in getting this work done prior to this being announced/coming in as if it's advantageous it might = an increase in pricing for equipment or installers being busier/less available.

Any advice would be much appreciated!

Thanks

blobert · 07-01-2020 1:05am

Thanks very much for the replies guys, I appreciate them!

@Unkel

It sounds from your suggestions like it might make sense to just have a load of panels but no battery system?

That said, if you add a battery without the SEAI subsidy, it will never pay for itself. Not with todays battery prices

Seeing as I'd not be eligible for the grant (I'm assuming as it's a new build) that might make batteries not that worthwhile?

If we were using the electricity to help power the home/heat it via heat pump/heat hot water (not sure if heat pump heating heats a tank of hot water)/charge the electric car and then sell any excess back to the grid I'm thinking that might be sufficient usage without also needing battery storage. I'm guessing we could always add it at a later time if needed/when it got cheaper.

@Coltrane

Thanks, I've been keen on the idea of a modern passive house for years, I grew up in a house built in 1800s, it was always freezing!

But consider the downsides of owning PV. They have a dirty footprint of their own. They’ll potentially stress your roof. They require large ballast at lower pitches. I think people underestimate the risk of storm damage - imagine the lift a panel will generate in high winds. And storms are becoming commonplace.

Not somthing I'd thought of, thanks for mentioning. We were planning to have a very low pitch roof covered in sheet metal, possibly somthing like this: https://catnic.com/products/ssr2-roofing-and-cladding/case-studies/graceland They have a simple clip on system to the seams for PV installation which I thought would be very simple to use/no holes in roof needed. But now you mention it, I'm thinking that might be a risk if the roof is covered in panels, they might all lift off in a storm, possibly taking the roof with them!

Questions on Solar/Battery Installation for Passive New Build

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