Solar panels but increased energy usage?

Martyn1981

I'm running the house (atm) on two A2A heat pumps, instead of using the GCH.

So yes, my leccy consumption has gone up quite a bit.
But my gas consumption (for central heating) has dropped massively (actually, at zero).

It's a game of two halves ....... not sure that saying works, but it will have to do!

Solarchaser

I think it's mostly been covered by other users, but just to say your £40 / month for your oil burner, it's perhaps useful to say that since you like 16c, it's extremely unlikely your oil burner was burning any oil in the billing period of April to October, and so your £40/ month is really more like £0 / month for the 6 brighter months of the year, and £80/ month for the 6 darker months of the year.
And as heedtheadvice helpfully pointed out, although your electricity use has increased, it has increased at significantly less than £80 / month, so you are definitely saving money.

Apologies if this is rude, but only because you mentioned a brain injury may impare your understanding. 

Simply you didn't used to heat with electricity,  you used to heat with oil, and so you are saving £480 over the year, not buying oil.
Between October and March you will use more electricity than before for 2 reasons.
1. You now heat using electricity. 
2  the solar you have bought to reduce your electricity usage works to produce much more electricity when it is bright outside.

So to sum up, you should use less electricity in the brighter months (start of April to end of September) and more electricity in the duller months (start of October to the end of March), but the whole year you are not using any oil,  so you are saving the £40 a month, which is £480 for the whole year

Tiger_greeneyes

Newbie_John said:

Tiger_greeneyes said:

Exiled_Tyke said:

As others have said at this time of year solar panel production starts to decline massively as we head towards winter.  My production at the low of winter is about a tenth of what it is for the best early summer months.  On top of that the last couple of weeks have been incredibly dull for most of us. I've had next to zero production. 

On the heating side my ASHP is using around 500 kWh (or units) each month at the moment . But that has saved me a substantially higher amount of gas compared to last year.   If you are only 70 units up I think you are doing pretty well   

500 units per month seems very high considering they're meant to be so much more energy efficient. Our old boiler was 97% efficient but it was 15 years old and we got the chance to upgrade. Looking back over the old bills, it must have cost peanuts to run, just the price of the kerosene.

Heat pump is 400% efficient - so 4x times better (efficiency wise).

Thank you, that's exactly what I understood.

Tiger_greeneyes

Heedtheadvice said:

Trying to keep things simple....

Forget solar for the moment. As has been writ above very low generation this time of year so just ignore for the moment.

You paid, for an average of £40 per month kerosene, that is £480 per annum.

You do not have  an average yet for the electricity consumed by the heat pump but lets assume your Nov bill is typical and is your average. The extra the Heat pump  has used (again an assumption) is 328 - 257 =71 units (this Nov minus last Nov consumption shown on your bills).

71 units will cost you a nominal £0.30 per unit ( in very round figures.) So that is £21 per month or £255 for a year.

So lots of assumptions in there and not enough information to do a full comparison but if the assumptions are in the correct ball park it could be costing you £200 less a year....?

As written earlier electricity ( currenty!) Is more expensive than both oil and gas by about 4 times but if Air Source Heat Pump was running efficiently it would consume less power and therefore cost a similar amount.

As the weather has been different to last October (November's billing period) and you are not heating to a high temperature much and having  windows open a lot it is difficult at the moment to do a comparison but your current running costs di not seem excessive compared with last year.

Best thing is to do a comparison after  lengthy period say over the year.

However I would add having a small house , well insulated, will not save you much if you heat whilst having the windows open!! Ventilation is essential but it is a good idea to close up before heat just goes out the window!

Thank you, that's all really helpful. I don't have the windows open at the same time as the heating is on, not unless I'm getting a hot flush of course! Because my living room is south facing and my windows are floor to ceiling, the sun heats this room up very quickly so heating generally doesn't need to go on until around 3pm if it's sunny or if we're out. Once the house is warm, the heating either stays on 16c or is turned off.

Tiger_greeneyes

Spies said:

Tiger_greeneyes said:

Spies said:

My advice is realise that a ASHP uses electricity and we have had very little to no solar so far this month...

We've had a good number of bright days where I am, the ASHP isn't on every day and when it is on, it's set to 16c which means it doesn't come on all that much. It's a small, well insulated house. Looking back, we didn't have the heating on on the bright days as our living room faces south and has big windows. We've had the windows open pretty much daily, if anything.

What was the point of getting a heatpump of you're going to run at such a low internal temperature?

They design the systems around MCS guidance which is heating the living areas to 21c, bedrooms to 18-19c and bathroom to 22c.

Its probably cycling loads trying to maintain such a low flow temperature.

It's a steep learning curve. So I need the heating higher to stop it from cycling so much? Our rooms are very small - living room 10ft by 11ft - so 21c in here means setting the thermostat, which is in the hallway where it's colder, on around 19c. I think in the depths of winter we will be doing that. It's just a bit too warm for us as we like a cooler house. We will get there, I'm sure. This is all very new to me!

Reed_Richards

Surely your old oil boiler would have been cycling a lot at this time of year?  Unless it was unusually sophisticated, it would only ever have been full-on or off and probably much more powerful than your modest heating demand required.  Cycling of itself is not much of an issue provided the cycles are not very short and very frequent.  My heating controller limits the number of cycles per hour to 3 for both a heat pump and an oil boiler.  So that gives me fewer longer cycles.  

Tiger_greeneyes

Reed_Richards said:

Surely your old oil boiler would have been cycling a lot at this time of year?  Unless it was unusually sophisticated, it would only ever have been full-on or off and probably much more powerful than your modest heating demand required.  Cycling of itself is not much of an issue provided the cycles are not very short and very frequent.  My heating controller limits the number of cycles per hour to 3 for both a heat pump and an oil boiler.  So that gives me fewer longer cycles.  

Our thermostat with our other boiler was placed in a warmer room which makes a difference, our new thermostat is located in the hall which is much colder, being placed by a borrowed light window and the floor being slate. We've been really frugal with our electricity, the June before covid struck we were paying £35 a month. It went up to £150 a month after that so we switched the boiler off in late April and back on again in November. That's why we were only paying £40 a month in kerosene. I've just had the November period bill in and it was £13 higher than it usually is - so it works out that it's cheaper to run the AHSP than pay kerosene when we run the heating modestly.

thevilla

This may be difficult for you to work out but have you considered changing to a heat pump electricity tariff like Octopus Cosy? It's ok using more electricity if the price is lower.

If you're in the north of Scotland (the only bright spot last week I think) you're also using the greenest supply.

Tiger_greeneyes

thevilla said:

This may be difficult for you to work out but have you considered changing to a heat pump electricity tariff like Octopus Cosy? It's ok using more electricity if the price is lower.

If you're in the north of Scotland (the only bright spot last week I think) you're also using the greenest supply.

Thank you, I'll look into it!

Nick_Dr1

We also recently moved from oil to heat pump so are still learning how to best run it.

However, on quick calculations (details later) it should be the same or slightly cheaper overall to run a heatpump when compared with oil, but could be much cheaper. The actual savings (or not) will depend on the cost of oil and the cost of electricity, which obviously vary and change regularly.

With a heat pump you are taking heat from the outside and squashing (pumping) it into your house. This takes energy and so uses electricity. For every 1kW of electricity you will get 3 to 4kW of heat squashed into your house.

This heat would previously have come from the oil burner.
1 litre of oil contains about 10kW of heat (round numbers being used)

If a litre of oil costs 50p then the cost per kW of heat is 50p/10kW = 5p per kilowatt.

If a kw of electricity costs 25p (about the cap) and your heatpump gives (pumps) 4kw heat per kW of electricity then each kW of heat costs 25p/4 = 6.25p

But as pointed out, switching to a different tariff for electricity will change the balance. Lets say you go onto Octopus Cosy and manage to get your whole use into the cheaper periods so it only costs 12p per unit of electricity (unlikely but again lets use round numbers). Then the heatpump calculation looks a bit different. Now its 12p/4=3p per kW of heat.
Now, at 3p per unit, it is much cheaper to run than the oil boiler, which was 5p per kilowatt. Oil would have to drop to 30p a litre to compare.

As you have solar, your average price per unit of electricity could be cheaper still. For example, if you manage to generate all the electricity you use on a day, then your cost to use you heatpump becomes zero. Similarly if you manage to only generate half the electricity you use, then the cost to use the heatpump that day would be halved. So if the normal electricity price was 12p unit (so heat was 3p unit as above) your effective price per unit of heat drops to 3p/2 = 1.5p unit of heat. Oil would still be 5p unit for comparison. 

All this is grossly simplified (it assumes no other use of electricity  for example , and that a COP of 4 is achievable, and 100 % efficiency of the boiler amongst other things), but bottom line is the cost to run the heatpump should be the same or better than a boiler and because it driven by electricity, there are options with tariffs and solar panels to get the AVERAGE cost right down.

I hope that helps. I find its easier work these things out if you keep it simple and go step by step!

PS A heatpump doesn't operate like a gas or oil boiler. It won't heat your house rapidly. It heats it slowly and then tries to keep it at that temperature by slowly dribbling heat in to replace that which leaks out. If you get a 1 degree rise in temperature in an hour then you are doing quite well!