#1 April 8, 2015 15:42:05

morrisok
From: Sussex
Registered: 2011-11-09
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Solar Thermal and Iboost

My inlaws have just has solar thermal and an Iboost system installed, they already had the solar PV. This seems to me a complete waste money as the solar thermal is soo much more efficient than the spare electricity that comes from the Iboost.

Just wondered if I was wrong or if others have done the same. They were recommended this by their installer.

Kevin



Kevin

URN 131, 3.92KWp 12x 327W E20 SunPower panels Sunnyboy 4000 inverter, facing ~south, no shading issues. Location: Sussex, http://pvoutput.org/list.jsp?userid=12216

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#2 April 9, 2015 08:32:38

bhommels
Registered: 2011-10-03
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Solar Thermal and Iboost

I would think that despite the low efficiency the PV/Iboost meets hot water demand easily in the summer months. In that case, no matter its efficiency, Solar Thermal could be considered a waste of money. If hot water demand is high, or PV capacity is low, or both, an additional thermal system is justified, provided there is sufficient south facing roof/wall space available.

According to data gathered so far on PV yield and PV power diverted to the immersion heater, our 2.88kWp system would only just cope with hot water demand if our current electric shower is converted to use solar hot water, even when taking the planned installation of a large hot water tank this summer into account. Therefore I am looking to add solar thermal on our south facing wall to avoid having a cold shower in March/October. With the RHI available for domestic solar thermal, it does not look too unattractive at the moment.

Edited bhommels (April 10, 2015 07:09:15)

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#3 April 9, 2015 10:49:29

rogerhoward
From: Southend
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Solar Thermal and Iboost

Hi Kevin.

I have both solar thermals and solar PV (without immersion switching), with 2.5kW PV on my East roof plus 1.5kW PV and the solar thermals on my West roof (to build the hot water temperature over the afternoon period). When wanting a bath or shower on spring or autumn evenings we do additionally switch on the immersion to give a final brief boost to the water temperature (having had the solar thermals for 10 years, the water pressure has dropped off and is long due a servicing!).

What I have difficulty imagining is how your in-laws solar thermals and PV immersion switching interact over the course of a sunny day. But are the new thermals perchance on a different roof to the PV, to achieve a complementary hot water solution?

Of course whereas solar thermals - like a gas boiler - heat the whole of the hot water cylinder, immersion rods only heat the top ??inches of it (e.g. 18 inches is the modest length of our immersion rods). So with our 2 methods of water heating occuring at different times of the day/evening, we do find our methods being complementary and certainly more energy-saving than switching on the gas boiler to boost the water temperature of the entire cylinder top to bottom.

Given that immersion switching is relatively low-cost, I'd be looking at the degree to which the immersion-switching complements, or not, the solar thermals for the particular lifestyle/schedule of your in-laws.

Excuse my ignorance of solar thermals RHI payments, but are they based on a simple estimate, or calculated from actual recorded kWh saved? Your in-laws wouldn't want their RHI payments compromised by the effect of the immersion-switching on the solar thermals saved kWh - which I believe could indeed occur depending on the setup.



Economy 10 tariff provides 6.9p/kWh off-peak import between 12am-5am, 1pm-4pm and 8pm-10pm; http://www.pvoutput.org/aggregate.jsp?id=21047&sid=18934&v=2&t=m on approx. 63% off-peak usage, 22% solar usage, and 15% peak-rate usage.
1,900kWh annually is exported, mostly in summer, on approx. 3,200kWh generation. Approx. 4,500kWh/year is imported, mostly for (a) winter and springtime off-peak Storage Heaters, and (b) off-peak hot water Immersion heating (which is “dumb”, i.e. not linked to the solar PV).
PV array is split East-West. Income is from Phase II 21p/kWh Feed-in-Tariff plus smart metered 3.2p/kWh Export Tariff.

Edited rogerhoward (April 9, 2015 12:44:43)

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#4 April 9, 2015 12:45:49

morrisok
From: Sussex
Registered: 2011-11-09
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Solar Thermal and Iboost

Hi Guys,

Thanks for the responses.

They have a big tank with 3 elements in it at different positions in the tank.
1. Immersion
2. Iboost PV
3. Solar Thermal

Both panels are on the same south / south east orientation.

The IBoost cuts off if the water is up to temp.

They were mainly after the solar thermal but the installer suggested they get the IBoost as well.

They have an eco-eye monitor so hopefully I will be able to see how much is actually diverted over this nice sunny week.



Kevin

URN 131, 3.92KWp 12x 327W E20 SunPower panels Sunnyboy 4000 inverter, facing ~south, no shading issues. Location: Sussex, http://pvoutput.org/list.jsp?userid=12216

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#5 April 10, 2015 09:38:35

bhommels
Registered: 2011-10-03
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Solar Thermal and Iboost

Hi Roger,
As far as I could see, RHI for domestic solar thermal is estimated from a SAP with the panel technology, and orientation as input. It lasts for 7 years, and is inflation linked, just like PV FiT. Eligible systems should provide domestic hot water only, no space heating. Given the current pricing it should more than compensate for the price of a solar thermal panel, but not a suitable solar hot water tank, or installation cost however.
Bart

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#6 Aug. 5, 2015 08:19:58

weijing3333
Registered: 2015-07-23
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Solar Thermal and Iboost

morrisok
My inlaws have just has solar thermal and an Iboost system installed, they already had the solar PV. This seems to me a complete waste money as the solar thermal is soo much more efficient than the spare electricity that comes from the Iboost.Just wondered if I was wrong or if others have done the same. They were recommended this by their installer.Kevin

The solar thermal is soo much more efficient than the spare electricity that comes from the Iboost.I agree with you.

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#7 Aug. 5, 2015 10:25:38

Capetown
From: The Banks Of The River Mole
Registered: 2014-03-22
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Solar Thermal and Iboost

I just ran a few figures through this https://renewable-heat-calculator.service.gov.uk/Default.aspx and it worked out that I'd receive about £1500 in total over the 7 years of the Domestic RHI.



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