Welcome to the forum and I am pleased to hear that you are very pleased with your Nibe heat pump.

It is always difficult giving definitive advice, just as it is often difficult knowing if you are making the correct decision. Here are some ideas for consideration.

Even with a 500L hot water cylinder, 10kW of solar PV should be able to provide most, if not all, of your hot water requirement from Spring through to Autumn, unless you use vast amounts of hot water. Electrical Diverter units are limited to 3kW, but it may be possible to install two diverter units and two immersion heaters to speed up the process and utilise more of your solar PV generation. I am assuming that you have received the necessary permission from your local Distribution Network Operator for a 10kW Solar PV system. The beauty of power diverters is that they reduce or stop drawing power when those pesky clouds appear, which reduces the amount of solar PV generation. In this way the diverter does not draw power from the grid, but of course may not be heating the water during this period. We have a 4kW solar PV system which provides virtually all our hot water needs from Spring through to Autumn. It also provides much of our heating and cooling during the same period thanks to our Air to Air heat pump. My next project will probably be battery storage.

Alternatively you could run your GSHP to produce hot water, but power it from your solar PV. In this case, if the clouds appear, you may be importing power from the grid.

During the colder months you could consider heating your hot water using your GSHP around the peak solar PV generation period, since hot water production normally requires a higher water flow temperature, and hence the heat pump is less efficient.

To reduce your electricity import, have you considered also installing battery storage? If done at the same time as solar PV, I do believe that it also qualifies for the reduction in VAT. Excess solar could then be stored in your batteries to help power your home and heat pump after the Sun has gone down. Obviously it all comes at a cost, but the payback period is now much shorter because of the more expensive prices we now have to pay for energy.

If you have any further questions then please feel free to ask.

Derek M - thanks for this really helpful.  Your point about the variable input due to clouds makes a lot of sense - and therefore does make sense to just use the power diverter to input variable power into the water system rather than risk running the pump.  I'll see the options about a second immersion.  re. the permissions i'm reliably told (?) by the solar power installer that they will sort out MCS and DNO - note it's a 3 phase system.

  I'm trying to be a bit forward thinking here by installing as much solar as i can as plan to acquire electric car when the diesel (yes I'm sorry!) eventually shuffles off - within a year or so.  So i'm not contemplating battery option at the moment because when the EV comes i'm assuming i can use this intelligently as storage.   There seems a vast amount of options - all involving a lot of electricians help in planning the correct priorities between hot water and EV charging.   I'm a bit baffled why this seems so DIY rather than off the shelf.

@bob-grumble

We still have a diesel, though don't do a vast amount of mileage.

I haven't researched it, but I think that you will be okay with 10kW of solar on a 3-phase supply. If my knowledge is correct the limitation on single phase is exporting up to 3.6kW. This is to limit possible phase imbalance, which obviously will not be the case on a 3-phase supply.

At the height of Summer our 4kW PV system can occasionally produce 25kWh, though most sunny days it is in the 15kWh to 20kWh range, so you could possibly expect 2.5 times that amount. Unless you use a great deal of hot water and do a great deal of mileage in an EV, you will find it difficult to utilise all your PV generation.

Of course, when you need it in the Winter time the solar PV generation is much lower, but can still help mitigate some of your energy demand. You could also consider one of the cheap overnight tariffs, to charge the car battery for use during the peak periods during the day.

After battery storage I am seriously considering a battery lawnmower, which makes obvious sense since our grass seems to insist on growing in the sunnier months. Being a Yorkshireman and an Engineer, our present petrol mower will have to be pronounced totally dead by at least three doctors, before I take the plunge.

@bob-grumble

You made a very good decission purchasing the Nibe unit and this will make you even happier. There are 2 different modules that fit in to the heat pump that connect to the solar inverter or line. If you purchase an inverter that has compatable MODBUS communication, connect it with a 3 core cabe to the unit and it will do verything for you. It will utalise as much of the solar as possibe preventing it going back to the grid. It will raise temperatures above the desired just to use the free energy. This unit is the better option, but if your inverter does not have compatable MODBUS, the second unit is just a CT on the main incommer and it prevents electricity going back to the grid, not as good as the first but much better than an I boost or similar as you are multiplying the free electricity. I have installed both than they work very well. Your installer should be able to help.

@bob-grumble A few thoughts to add to the mix.

We have 2 9kW Kensa Evo GSHPs, 4kW solar panels, 4kWh battery storage plus a 77kWh battery EV.  More by luck than good management we have found a very efficient electricity usage strategy.

The key to it is, oddly, the EV, which gives you access to Octopus Go Faster.  This tariff is currently 8.25p for five hours at night, 41p at other times.  It is has been temporarily closed to new applicants due to the Government's Energy Subsidy conditions, but hopefully will reopen soon.

We charge the car, fill the 400 litre HW tank, run dishwasher, washing machine overnight.  We charge the batteries to a level which, with solar, makes sure we can get through the whole of the following day without using the grid.

During the winter:

• Normally our GSHPs are set to kick out 45C heat for the radiators. However during the off peak hours we run both heat pumps at 55C.  (Worse Coffeccient of Performance, but way cheaper overall.)  This means we wake up to a toasty warm house, but also the fabric of the building soaks up the heat and gradually releases it during the day.  This means that the CH seldom comes on before dusk, often much later.
• We charge the house batteries during the OP to 100% as well which means that even when the CH comes on, we can delay using Peak electricity for an hour or more.

The house batteries are also handy in other ways:

• They are configured to be an Uninterruptible Power Supply, so that when we lose grid (as we more than occasionally do in deepest darkest Cornwall) the lights stay on.
• When your BEV isn't there or is full they can store excess juice.
• If you do buy a BEV, they make efficient charging from your panels on the roof much simpler. BEVs like a nice stable current, whereas panels' output is very variable due to clouds etc.  We can set to charge the car at 2kW or 1kW depending on the weather and let the house batteries cope with the variable output of the panels.  When there is full sun, the house batteries charge.  When a cloud comes over, they top up the panels' output.

Our annual electricity usage is 8,800 kWh, but 80% of it is at 8.25p/kWh.  Even at current electricity prices, I doubt that we will spend £1,500 in total on electricity in a year.  And that includes 6,000 of the car's annual mileage.

One final thought: adding solar doesn't really make that much of an impact on winter GSHP costs, especially without house batteries.  You want to run the CH when the sun tends not to be out. Even when the sun is out, in winter the extra panels won't make much of an impact compared to the total juice used.

Hope that this is of some use.

I've got the same question as bob grumble, but about my Stiebel GSHP.

I've got the Stiebel Eltron WPF13S GSHP. And I recently got a solar installation based on a SolarEdge HD Wave 5kW inverter.

I would love it if my heat pump and solar installation could integrate so that the heat pump makes use of my excess solar generation. I'm well aware that I could fit an iBoost... but that would give me a CoP of 1, whereas, if I could integrate my GSHP and solar, then I could get a CoP of 4.

Integrating heat pumps and solar isn't easy, because solar is quite intermittent (cloud drifting across the sun) and heat pumps don't like short cycling... they run better for longer periods. So any integration system will have to be fairly intelligent... cleverer than an iBoost, anyway. 

The other day, I discovered that Stiebel does have a just such a solution on the market. It is called Energy Management Interface and it is built around the SMA Home Manager. Energy Management Interface (EMI) (stiebel-eltron.co.uk)

When I contacted Stiebel, however, they said that it wasn't worth it for me, because you need 4kW of excess solar to start the heat pump.

That answer doesn't make sense to me at all. After all, I've got a grid-tied system like 99% of solar pv installations, and I could just draw part of the wattage from my excess solar, and part of it from from the grid. Even though my heating won't be totally free, it would still be worth it to me because it would allow me to drive part of my heating bill from solar (thereby at least reducing my heating bill). 

Does anyone here have experience with Stiebel? Or even with the SMA Home Manager?

Posted by: @benguela

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I've got the same question as bob grumble, but about my Stiebel GSHP.

I've got the Stiebel Eltron WPF13S GSHP. And I recently got a solar installation based on a SolarEdge HD Wave 5kW inverter.

I would love it if my heat pump and solar installation could integrate so that the heat pump makes use of my excess solar generation. I'm well aware that I could fit an iBoost... but that would give me a CoP of 1, whereas, if I could integrate my GSHP and solar, then I could get a CoP of 4.

Integrating heat pumps and solar isn't easy, because solar is quite intermittent (cloud drifting across the sun) and heat pumps don't like short cycling... they run better for longer periods. So any integration system will have to be fairly intelligent... cleverer than an iBoost, anyway. 

The other day, I discovered that Stiebel does have a just such a solution on the market. It is called Energy Management Interface and it is built around the SMA Home Manager. Energy Management Interface (EMI) (stiebel-eltron.co.uk)

When I contacted Stiebel, however, they said that it wasn't worth it for me, because you need 4kW of excess solar to start the heat pump.

That answer doesn't make sense to me at all. After all, I've got a grid-tied system like 99% of solar pv installations, and I could just draw part of the wattage from my excess solar, and part of it from from the grid. Even though my heating won't be totally free, it would still be worth it to me because it would allow me to drive part of my heating bill from solar (thereby at least reducing my heating bill). 

Does anyone here have experience with Stiebel? Or even with the SMA Home Manager?

I am not certain what you mean by 'integrate my GSHP and solar'. I assume that your solar PV is connected in at your consumer unit, therefore any solar generation will supply your home's internal demand, and any excess generation will be exported to the grid. If you switch your heat pump on for CH or DHW then any excess generation will be used by the heat pump. If there is insufficient generation to fully supply the heat pump, then it will draw the remainder from the grid. To smooth out any dips in solar generation when clouds appear, you could consider installing some battery storage.

@derek-m The Nibe unit actively monitors the electricity going back to the grid and will raise the water temperature first and then the house temperature slightly to prevent electricity going back to the grid. It works very well, the new units (S Series) actually connect to the inverter through MODBUS and decides how to use excess electricity in the best possible way.

Hi Derek M, Brendon Uys (above) explains what I mean and am hoping for from my Stiebel. 

'Integrate' is the technical term that I heard someone use for what Brendon describes... maybe there's a better word. But what I want is to enable my heat pump and solar inverter to 'talk' to one another and control the heat pump so that it works harder when there is excess solar (and works less hard when there is no excess solar).

Brendon, I'm a bit curious about how the Nibe unit does it and three questions tickle me in particular:

1. How much excess solar does the Nibe unit want before it switches on?

2. Once it switches on, is there a minimum run time to avoid short cycling?

3. If, during this minimum run time, the sun disappears behind a cloud, what happens... the Nibe unit just draws power from the grid I guess?

Thanks!

Posted by: @benguela

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Hi Derek M, Brendon Uys (above) explains what I mean and am hoping for from my Stiebel. 

'Integrate' is the technical term that I heard someone use for what Brendon describes... maybe there's a better word. But what I want is to enable my heat pump and solar inverter to 'talk' to one another and control the heat pump so that it works harder when there is excess solar (and works less hard when there is no excess solar).

Brendon, I'm a bit curious about how the Nibe unit does it and three questions tickle me in particular:

1. How much excess solar does the Nibe unit want before it switches on?

2. Once it switches on, is there a minimum run time to avoid short cycling?

3. If, during this minimum run time, the sun disappears behind a cloud, what happens... the Nibe unit just draws power from the grid I guess?

Thanks!

If my memory serves me correctly, the SMA Home Energy Manager is based around a battery storage system, which is one of the options I would suggest. It does not necessarily have to be the SMA system, any battery storage system should achieve the objective. It is a pity that you did not consider battery storage when you had the solar PV installed, as I think you could have saved the VAT.

I'm not an expert on battery storage systems, there are other forum members who are much more knowledgeable. The idea is quite simple, excess solar generation is used to charge the battery storage and also supply your heat pump when it is running. If there is insufficient solar generation to fully supply the heat pump, then the deficit is provided from the battery storage. When the heat pump is not running, the excess solar generation is used to recharge the battery storage. In this way when clouds appear, the heat pump will still continue to run without drawing power from the grid, until the battery storage is discharged.

A further way to improve overall efficiency would be to warm your home by 1C or 2C during the warmer afternoon period, which then reduces the need for your heat pump to operate during the peak evening period.

In the Summer period, when CH is often not required, it may be preferable to produce hot water using a power diverter, thereby giving your heat pump a rest.

Dependent upon the capacity of a battery storage system, it could also be beneficial to charge the batteries using a cheaper overnight tariff, and then use this energy to power the heat pump during the peak evening period, and hence reduce the demand on the grid, which should help keep down the cost for everyone.

Posted by: @derek-m

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Posted by: @benguela

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Hi Derek M, Brendon Uys (above) explains what I mean and am hoping for from my Stiebel. 

'Integrate' is the technical term that I heard someone use for what Brendon describes... maybe there's a better word. But what I want is to enable my heat pump and solar inverter to 'talk' to one another and control the heat pump so that it works harder when there is excess solar (and works less hard when there is no excess solar).

Brendon, I'm a bit curious about how the Nibe unit does it and three questions tickle me in particular:

1. How much excess solar does the Nibe unit want before it switches on?

2. Once it switches on, is there a minimum run time to avoid short cycling?

3. If, during this minimum run time, the sun disappears behind a cloud, what happens... the Nibe unit just draws power from the grid I guess?

Thanks!

In the Summer period, when CH is often not required, it may be preferable to produce hot water using a power diverter, thereby giving your heat pump a rest.

Unless you have vast amounts of excess solar available, enough to give you ample hot water, this would be very inefficient because you are only getting 1kWh of heat per kWh generated, not the 3-5 kWhs generated via the heat pump.  The heat pump will be having a quiet time of it in the summer anyway.