Hi

Iv enot been on here in a good while. I finally got our house up and running with an oil boiler heating my thermal store

I know theres a lot of variables but could it be possible to generate enough electric from Pv panels to run an airsource heat pump here on Isle of Man? Im sure theres some experts out there that would know the figures?

I am tempted to buy solar thermal panels to connect to my store but id like to keep my options open

Thanks

There are two ways to answer this.
Do you want to run the ASHP directly of the PV. Then the answer is no (except with a very large module array).
The other way is to off set the electrical usage of the ASHP with electricity generated by the PV, then yes (assuming the sized are reasonable).

You can use PVGIS to get a production estimate for your location. It does show average energy production and not power though.

It is worth remembering that when the PV is generating, current it produces will go to the nearest load (by some magic). So if an ASHP was running and the modules were producing a bit of current, that current would be used by the ASHP and your imports would be reduced.
So one trick is to only allow the ASHP to run during hours of daylight if you can.

On start up heat pumps have very high power demands

Sorry to bump this old thread but I have a similar question:

I am in Portugal and am planning to have an extra PV array to run an ASHP during sunny days in winter. I also have a 10kW to water WBS that heats a 300L buffer tank each evening (direct connection) that provides radiators (aluminium 45C flow temp) during the night and lasts until 9-10am in the depths of winter (drops to around 0-5C at night). The house has huge thermal mass (rammed earth) and is well insulated with lots of passive solar heat gain (large west facing windows with electric shutters).

I would like to heat this tank using something like a Valiant Arotherm high temp ASHP (75C max, R290 gas) during the day using PV when air-temps are around 18C. The ASHP is 3.5 kW so I am estimating around 3 hours to heat the tank. The radiator pump shuts off at 45C so the ASHP is looking to heat the tank from 45-75C each afternoon.

I am trying to avoid changing any of the existing equipment and keeping the WBS connected for really cold days or cloudy days. I have no space for a larger TS. The aim is to reduce my wood use.

Can anyone shoot any holes in my idea or come up with a better idea ?

Heat pumps and high start up currents and PV won’t cope with that

It will run it but output needs to be guaranteed to be above run demand power which is unlikely

If connected to the grid it will be ok

For heating poor as max demand at point of minimum solar insulation

Posted By: DamonHDhttp://www.earth.org.uk/note-on-solar-DHW-for-16WW-UniQ-and-PV-diversion.html#Simple

The council is determined to pull our place down in a few years, for redevelopment.

Oops! That seems like a new thread, right there.

How much of what you have installed in the house will you be able to take with you and reuse?

What are your plans for a new place?

Thanks for your reply Ed. The main issue I have is that the PV generates during a narrow band of time at close to its design power, and also I have a small TS/buffer so to store enough for the morning the buffer temp. needs to be high.

To answer your second point, we already heat with passive solar on the west side and the house gets almost uncomfortably hot late afternoon while a bit parky early morning. The aim is to add a little thermal "momentum" early in the morning. The existing system normally shuts down between 12am and 2am.

I am erring on the side of a 3kW immersion heater for simplicity and low cost; PV is so cheap now and my roof is pretty big.

When I have left the house unheated over winter it stabilises around 13C.

My thought process would be as follows;

- you have grid power, so running a HP is possible
- you want it ideally to only run when the sun is out (ie. not behind a cloud)
- you shouldn't control a HP to cut in/out to match the solar insolation
- not sure how your Rpi device works, but a regular solar excess energy diverting device will feed down to say 200W of excess PV elect to your chosen device, so it's not a case of 3hrs @ 3kW, it's 8 hours varying from 200W up to 3kW and back down again
- if you run the HP, sometimes you'll have sufficient PV to cover all the running power, but sometimes you'll be importing, and you won't really have control over that.

If the above is along the right lines, I would go for a good number of PV panels, and feed the excess PV via the immersion. My own system, and various clients, use this approach (with LBS and therm store), and it is so simple. As I think Ed said above, go for a more vertical PV inclination if you can, to increase the winter capture.

GreenPaddy,Y
Your conclusion is similar to mine, an immersion heater. I would be unable to control the inverter in the ASHP as you suggest, I can just turn loads on and off. However I am able to mimic the curve of the PV generation by turning various loads on and off during the day, saving the largest loads for the middle of the day; this immersion would probably be the largest load. Perhaps I could fit a 1kW immersion & a 2kW, there is no fitting for this but there is an access panel at the bottom of the tank I could have drilled and threaded.

Peter,
I do feed in however due to Portuguese bureaucracy I receive nothing for this so I try to consume as much as I can. An outdoor TS wouldn't be a preferred option. I am trying to reduce dependence on wood as I spend quite a lot of money on it and although I burn fast and hot, combustion isn't the best for the environment. I'd also like to have a labour free option and probably more so when I get older ! I am pretty sure eventually , with enough PV I could reduce my wood consumption significantly.

Thanks all for your comments, very helpful to be able to mull these things over with like minded people, Mrs daserra generally glazes over

My main array for house electricity is at 45' for exactly this reason, to maximise winter gain and flatten my yield curve, however I have noted I don't meet demand in the early evening so I am planning another array pointing due west, which although it won't be operating in a way that maximises the electricity it produced, will minimise the amount of electricity I have to buy. I do have a long term aim to be off-grid, not just for environmental financial reasons, but the battery payback time is 17 years or so, I think I'll wait 5 years when I hope we will see a decent drop in prices as lithium/iron and flow battery technologies evolve and become cheaper.

Hi again Ed.

The old core of the house is rammed earth (50cm, unknown u-value), the add-on extensions at either end are a 50cm thick masonry walls (hollow clay pot blocks) with 10cm of compressed cork in the middle. The south facing wall has outer masonry in 20cm Ytong (AAC). The u values of those walls are about 0.35.

A 1m wide strip of floor is insulated with 4cm XPS around the perimeter, the centre left uninsulated to use the earth as a thermal store (following the Passivhaus guidelines for properties in Portugal). The roof is mainly 9-10cm XPS (u-value of the entire sandwich is about 0.35) although the original rammed earth section roof is only 3cm XPS. For Portugal these are very good levels of insulation.

I built the place in stages over 20 years and was learning as I went along. We also have built to deal with the hot (40-50C) and extremely sunny dry summers so optimising for heat gain or cooling has been tricky.

It gets uncomfortably hot in winter because of the west facing glass with direct sunshine and air-temps around 18C, 2/3 of the west facing walls are glass. This is by design in the winter, there are electric shutters for shading when required, I was aiming at 100% passive solar heating but fell short.

It cools down quickly as our night time temps in the interior of the country are quite low, 0- 5 C , sometimes as low as -5C. The house isn't particularly airtight as we suffer from condensation due to the large day night swing in temps with high humidity, so I am happy with sacrificing some heat to alleviate this. At this point it would be impossible to have an airtight envelope.

When I say "parky", I am a bit of a softy since my blood has thinned living here, it's usually 18C in of a Dec/Jan morning, 20C in the evening with the WBS running; the house has a pretty even temperature throughout.

In the last 24 hours it went from 11c to 38C outside, inside from 21 - 24C, so in Summer it's pretty stable. All windows are open at night of course.

Posted By: daserraHowever I am able to mimic the curve of the PV generation by turning various loads on and off during the day, saving the largest loads for the middle of the day; this immersion would probably be the largest load. Perhaps I could fit a 1kW immersion & a 2kW, there is no fitting for this but there is an access panel at the bottom of the tank I could have drilled and threaded.

This sounds unduly complicated. A single 3 kW immersion is capable of absorbing anything from 0 to 3 kW. There's no need for any additional heaters or other devices. The diverter device automatically measures how much power you are generating and sends just that much to the immersion.

Looking at the high price of the Immersun I think I'd rather build something else connected to the pi, something like a high power transistr driven by a Zwave dimmer unit. Then I could integrate it myself.

Posted By: daserraLooking at the high price of the Immersun I think I'd rather build something else connected to the pi, something like a high power transistr driven by a Zwave dimmer unit. Then I could integrate it myself.

The most efficient unit I have come across for driving an immersion heater using excess PV is the one by Robin Emley:
https://mk2pvrouter.co.uk/about.html
There are extensive descriptions for the DIY enthusiast on his website, and the cost is very, very low.