Is it practical to change oil fired heating and water boiler for a similar electric system?

KevinBattle

Hi, just wanted advice as to whether it's a sensible consideration.
We're now having a 15.5 kwH solar panel system installed with storage batteries.
We have an efficient oil fired boiler for heat and water.
With solar, would it be practical for us to swap out the gas boiler, tank etc with an electric system using our solar and batteries?
It seems wasteful to use oil if we can save money heating the house and water from our panels.
I just don't know what the pros and cons would be.
Any helpful advice appreciated

QrizB

Welcome to the forum.

Practical? Yes.

Sensible? Unlikely. You need heat in the winter but the sun shines in the summer.

A moderatley-sized house might need 40-60kWh of heat on a typical winter's day and your solar panels are unlikely to produce even a quarter of that.

If you really want to give up oil in favour of electricity you'd be better with a heat pump. You'll still need to buy electricity (just ask @Reed_Richards ) but you'll only be buying 1/3rd as much. And it might just about break even with oil.

doodling

Hi,

KevinBattle said:

Hi, just wanted advice as to whether it's a sensible consideration.
We're now having a 15.5 kwH solar panel system installed with storage batteries.
We have an efficient oil fired boiler for heat and water.
With solar, would it be practical for us to swap out the gas boiler, tank etc with an electric system using our solar and batteries?
It seems wasteful to use oil if we can save money heating the house and water from our panels.
I just don't know what the pros and cons would be.
Any helpful advice appreciated

It is not clear how big your solar system is as you quote a figure in kWh which is a measure of the amount of energy you might store or consume, not kW which is the instantaneous power of the system.

If you have a 15.5kW solar array then that is a big array (most domestic installations are around 4kW), I suspect that you are quoting the size of the battery, but even an array of that size is still not big enough for what you need.

On an overcast day (e.g. many winter days), a solar array will probably deliver around 5% of its peak rating.  If you heat your house with a heat pump, and making a very big guess, you will need at least 3kW electrical power (which a heat pump will magically turn into a ~10kW heat output) on average during a cold day.

That means, just to run your heating when it is light outside but overcast, you need a 60kW solar array.  Unfortunately people often want heating when it is dark and in winter it can be dark for 3/5s of the day (~15 hours).  In order to generate enough energy to heat your home (and assuming magical 100% efficient batteries) you therefore need a 60/3*5=100kW solar array.  [ Edited to correct this, it is of course 60/2*5=150kW. Its light for 2/5 of the day, dark for 3/5. ] You also need enough battery storage for each night which assuming just a 3kW load would be 45kWh.  I've not thought about what happens if your panels are covered in snow - that probably means bigger batteries.

I don't recommend getting rid of the oil boiler in favour of a purely solar system unless you have a substantial field you are willing to fill with solar panels and space for a literal shed-load of batteries.  Also note that in summer such a system would be grossly oversized for your needs and you'd need an industrial grid connection to export the power.

There are however things that you can do to reduce oil usage.  In general you don't get paid very much for supplying solar energy back to the grid so it is better to use it at home.  You can buy devices which detect when you are returning power back to the grid and they will divert that power into an immersion heater for you.  By doing this, assuming a reasonably sized set of solar panels, you will probably avoid having to run the oil boiler at all for hot water during the summer which is probably the best you can hope for.

There is a more or less completely separate calculation which you might choose to do to see if it is cheaper to heat your house using an electrically driven heat pump than to use an oil boiler.  Before the recent electricity price increases electric heat pumps were a cheaper source of heat than oil, but the economics might not look so good now.  Arguably heat pumps are the greener solution so you might be willing to pay more for that.

KevinBattle

Thanks for highlighting my error, it's 15 PANELS for 5.75kw - silly error, not previewing text!
Certainly exporting doesn't seem sensible at current prices (see what I did there?) BUT.... even the government could work out that with many (many, many) houses switching to solar panels, there would immediately be a lessening of demand so less need to import power from France or tankers or wherever. They're building more and more offshore wind turbines, so the principle of many small energy sources feeding into the Grid is established, but the payback is derisory, so no incentive but to use it myself.
Just toying with the aspect of going all electric so as not need heating oil, and whether an electric system would make economical sense. 
I'll leave it till we need to replace the boiler, not very old so should have a good few years left.
Next on the shopping list will be an EV car, next year!

ProDave

A 5.75kW solar PV system is not much above "average"  In summer, with the batteries, it should be pretty easy to self use all that it generates, particularly as well as charging the batteries you divert some of the surplus to heating the water in your hot water tank via the immersion heater.

In winter when you need your heating, solar PV output will be very low.  You will be able to self use it all easily without looking for a heating system to use it up.

So stick with your oil boiler.

matelodave

We've got a heatpump in a 140m2 reasonably well insulated bungalow and last week our leccy consumption was around 300kwh which is an average of 42kwh a day.(over £10 a day on the capped tariff from EoN)

Sometimes it ramps up to 60kwh a day when its really cold (although we've had a couple of days below freezing this week and haven't seen the sun for three days either)

My summer daily average for leccy is around 8-9 9kwh a day so I can guesstimate that leccy for heating with the heatpump this week was around 30-35kwh/day.. Multiply that by 2.5-30  to convert that to heat from a leccy boiler or panel heaters and you'd be using around 90-100kwh a day which isn't practical with solar especially if the sun doesn't shine much

lohr500

As a comparison to matelotdave's data, in the current cold spell we are getting through +/- 15 litres of kerosene a day at a current cost of £8.50 per day to heat our large and energy inefficient 5 bedroomed converted Yorkshire farmhouse.

The house is in an exposed location and we have the heating on all day. The boiler is also heating the water. Our ancient Myson boiler was replaced in Spring last year with a brand new modern condensing Grant 36kw boiler, re-jetted to give a 30kW output. 

In the summer, when heating the water alone, the boiler is using less than 2 litres a day at a current cost of about £1.

I am able to monitor our oil consumption quite accurately as I have an low volume flow meter in the fuel line between the tank and the boiler. I know it is accurate, based on dipping the tank and comparing the level after a known delivery volume
My conclusion from all of this is that an efficient oil boiler is still more cost effective to run than a heat pump (and as an aside at a lower capital outlay). 

Granted oil might not be as eco friendly as an all electric system.

Your solar panels and battery array will help to reduce your electricity costs, but sadly I don't see small scale PV generation as viable strategy to replace your oil boiler  

  

Ectophile

As an indication of how hopeless solar panels can be in the wrong weather, I checked my solar output at lunchtime today - a grey overcast winter day.

My 3.4kWp installation was putting out about 160W.  Which coincidentally was what I was using at the time working on the computer.  So no power at all to charge the battery for later.

Whereas, in spring and summer I tend to have more electricity that I know what to do with.  The battery is fully charged by mid-morning, and the rest goes out to the grid.

Reed_Richards

Just ask yourself "Why is it cold in winter and hot in summer"?  Of course the answer is that we get so much less energy from the sun in winter and so your solar panels will generate very much less electricity.  Solar panels are a great match to an air conditioning system that cools your house in summer and a terrible match to any system that heats your house in winter. 

KevinBattle

Thanks to you all for your responses.
To be fair, our garden and also the roof, is a suntrap, directly south and no shading.
We did think of PV panels when we moved here some 10 years ago but then the government scrapped the beneficial Feed In Tariffs so it didn't seem worthwhile.
But with electricity prices going through the roof, we thought we might as well use our roof!
We also want to get an electric car, but the models so far don't fit what we want particularly well.
Hybrids don't seem logical to have 2 propulsion systems and thus weight to reduce available range and reduce boot space for our two labradors.
So we thought "Go solar this year and see what that does, and then think of an EV next year".

I just don't like supinely accepting that we simply have to pay more and more for electricity, oil and petrol IF we can do something ECONOMICALLY worthwhile. B*gger saving the planet, look after ourselves first.

Your answers have been helpful but PV isn't going to be the absolute answer.
However, we are close to the site specifically chosen for the Greenwich Observatory to move to for "dark skies" (just not CLEAR skies) on a hill which helps split cloud formations either side of us.

tim_p

Huge missed opportunity 10 years ago! The FIT back then would now be bringing a couple of grand a year on a typical 4 kWp system.