Advice please; Augment or Replace existing failing Solar Thermal with PV?

meep

Hi Folks

Thoughts appreciated on this one….

I have a 3 panel solar thermal system in for > 12 years now, and it's been brilliant, makes piping hot water a lot of the year and has completely replaced the immersion.

However, it's developed a leak somewhere between the panels and gubbins. I've had an engineer out and it's going to cost the guts of 800 to repair.

Additionally, he mentioned that my pump (500 euro) would be due to expire in the next few years, and the panels themselves would be due to start exhibiting falloff given their age. The pump might fail sooner now that's it's been running at low pressure for a while due to leak.

Now, separately, and unknown to this engineer, I've been thinking of investing in Solar PV and have a quote for a system around 7K after grants (lets not discuss pricing on that here). I say unknown to engineer as he would not have been giving me the above bad news to incentivize me into going PV. PV is attractive as I've recently bought an EV and just got my smart meter in.

The question I'm asking here is, would I be best ripping out the solar thermal and putting my 1300 euro or so towards a PV system, or is there any merit in repairing and retaining the thermal system and augmenting it with PV?

My understanding is that the PV system would heat my water as required and if I retain the older system, I'd maybe have more issues a few years down the line?

Looking forward to what people think.

con747

https://www.boards.ie/discussion/2058347036/advice-please-augment-or-replace-existing-failing-solar-thermal-with-pv

A similar question asked here with a couple of answers.

https://www.boards.ie/discussion/2058346646/solar-tubes-best-as-i-mainly-want-hot-water

graememk

Having 3 sets of solar tubes, would deliver a lot of hot water in the summer. They are about 3x of efficient Vs PV, so you'd need to have 3x the area to match your thermal system.

It is quite the bill to keep the thermal running. My pump is hanging in there, hear odd squeal, but it's in over 15 yrs. I know the pumps are on the expensive side too.

If you did go PV, I'd possibly recommend going back to heating with the oil/gas/night rate on an immersion and selling the excess Vs heating the water with PV.

bullit_dodger

Graememk (as usual) speaks good advice there. I'd have a couple more questions for you though around your solar ambitions. More for you to have a think….

• What's your usage currently in terms of 1000's kWh per year? (Have a look at your old bills and add them up for 12 months - bearing in mind that you don't use the same all year round, so you can't just take the last one and multiple by 6 - assuming you get a bill every 2 months that is.
• Do you have a budget in mind for how much you are willing to spend? You mention €7K above, which is a low-mid sized quote.
• What's the size of your roof? Do you have enough space for both the solar thermal and a solar PV?
• How much hot water are you currently using?

I'd tend to look at everything as a combined unit. The hot water you have seems to have done you well for a decade or more. If it's a known entity (for sure) that if you spend the €800 and you are good for another 12 years, that would seem like a decent way forward. If however, the pump is going to go, there is ongoing maintenance on the solar thermal, then perhaps a break with it and going the PV route is right for you.

PV needs 2-3x times the area to heat the same water, but of course once the water is hot with the solar thermal, that's you done for the day, while solar PV will keep capturing energy which you can export and get paid for it. PV is virtually zero maintenance. Generally PV is just more flexible, but you'll need 6Kwp or more on your house if you have an EV and want to start charging that (along with heating water etc) so if you think of installing say a 4Kwp and you'll have everything you need….well you probably won't. That's not to say that it's not benifical, only that you won't cover all your needs.

Overall, 9 times out of 10 Solar PV is the way to go, but if it's a known fix and your good for another decade…..i'd be slow to get rid of your thermal.

Scoobydoobydoo101

Could you bypass the leaking panel?

2 panels should still deliver decent output....

meep

Not clear if it's a panel, or the combined feed that the leak is in. That will become clearer when the lads show up to investigate / fix

meep

Many thanks for all that sage advice.

Without going into the details, just because I don't have them to hand, I did the sums previously and based on annual usage, I should be seeing payback on the 17 Panel system within about 5 years

I've just rechecked my quote, and I'd actually misremembered my pricing - it's 11k for a 7.3 kWp system. But the basic question still stands.

My ambition. With PV is to reduce ongoing monthly electricity costs (around 300 on average), help charge an EV, help reduce spend on oil a little and possibly use FIT or, more likely, some battery storage (not included in my quote)

I have space for these to be set up. Currently looking at a ground array, but I could build a substantial shed on my property for roof mount and optimal orientation if deemed better

I've more or less decided to go for the PV system, I'm just trying to decide if it's worth spending on the existing thermal to maintain it in parallel, or redirect that cash to PV.

Thanks again for taking the time to write all that up. Very much appreciated

bullit_dodger

If your going for the PV solution and 7.3Kwp is a nice beefy system, that should see you right in terms of hot water for 8 months of the year and then for Nov→Feb, you'll get the odd bright sunshine day which will heat the tank. Sure, in the middle of December when there's a gale coming in off the Atlantic, it's not going to do much, but for those 8+ months a year it's set and forget. I've one in my own gaff and it's mint. Have to say that an Eddi isn't the best financial sense, but I do like mine all the same and would buy another.

Don't know the orientation of your roof, but plugging in 7.3kwp (South) into https://re.jrc.ec.europa.eu/pvg_tools/en/and you get about 6500kwh. At a nominal price of say €0.30 unit, that's €1950 worth of electricity produced per year. Rough mind you. You can't say that's all savings of course, as you could be charging the car at night rate, so ballpark €1500 or there abouts. Maybe 6-7 year payback which is what most of us see.

slave1

You have not mentioned your hot water cylinder, where is the immersion as PV will only heat via this?