How to best use my solar panels? Warm Blown air heating and emersion heater for water.

[Robbrosky]

Hi all,

 

I live the the very North West of England (on the Scottish border)

 

I have a 3 bedroom house with 12 solar panels on the roof (there when I bought the house so no idea of capacity). What I know about solar you could write in only a few words so any info would be very helpful. House has good levels of insulation.

 

I have been toying with the idea of getting a storage battery and running my warm air heating from that all year round (topping battery up overnight on cheaper rate in the winter when solar panels do not provide enough umph). Off set slightly by small feed in £ through the summer months.

 

I need to replace the Warm air 'boiler/heater' anyway so was going to remove the existing gas one and install an electric one. Not much difference in cost to purchase the 'boiler' if I go Gas or Electric. Currently VERY old gas one installed.

 

Now my question is, Is this the best way of doing it?

 

I know gas is cheaper per KWH than electricity even on night rate electricity but I will have a good few months (Oct, Feb, March, April) where I will need the heating on and can run off free solar stored energy from the battery and/or direct from the panels (as the solar panel should provide enough to keep the battery full). I will also run the emersion for hot water so again similar to the heating but obviously I will need HW all year round.

 

I could just install another gas one and use gas for heating and battery for all other electricity needs (hot water through emersion heater, washing machine, shower etc etc etc) but I wondered if anyone has a similar set up for have any information on anything really  . 

 

Is it worth it and will it actually pay back the cost of the battery (battery around £5k)? I obviously don't have to buy the panels etc so will have shorter payback than if starting from scratch and have to buy everything.

 

From internet searches the life span of batteries is about 10 years.

 

Any advice as to options I may not have considered would be gratefully received!

 

Thank you!

 

 

[Robbrosky]

Additional thought.

 

My old electricity usage on my previous house was £1800/ year (gas boiler so just normal electricity items used).

 

If I was to get a battery say £6K including installation etc and run everything but the heating (get another gas warm blown air unit to replace existing one).

 

Is my maths below missing anything vital?

 

Assuming I have to buy some off peak elec during the mid winter months to keep the battery with enough juice to run electrical house items (maybe £80/ month for 4 months = £320/year) minus small gain back from feed in rate over the summer. I could potentially save around £1500/ year on my elec bill.

 

Battery cost 6K with installation would give me a payback time of 4 years for the battery then large yearly saving after that.

 

Does this sound correct?

 

Thanks again

[ProDave]

34 minutes ago, Robbrosky said:

My old electricity usage on my previous house was £1800/ year (gas boiler so just normal electricity items used).

Just what are you using?

 

We spend £1200 pa on electricity including all heating and hot water (ASHP)

 

I assume your house had the panels fitted under the old FIT scheme, so you should be getting a quarterly payment for that, if not ask your solicitor about it and why not?

 

Best way to self use it is a diverter to put surplus power to the immersion heater (assuming you have a hot water tank not just a combi) and to use all the big appliances like washing machine etc in the middle of the day.

[SteamyTea]

2 hours ago, Robbrosky said:

12 solar panels on the roof (there when I bought the house so no idea of capacity)

Going to take a guess it is around 3 kW_p capacity.

Go to PVGIS here and see what sort of output you can expect.

You should get something similar to this.

 

As for best usage, that is probably best to divert excess to a heat pump and store some as hot water.

That would probably cost about the same as some batteries.

It all really depends on how and where you use your energy most, DHW, Space Heating, General Usage i.e. cooking, clothes washing, lighting, entertainment systems.

[Robbrosky]

1 hour ago, SteamyTea said:

Going to take a guess it is around 3 kW_p capacity.

Go to PVGIS here and see what sort of output you can expect.

You should get something similar to this.

 

As for best usage, that is probably best to divert excess to a heat pump and store some as hot water.

That would probably cost about the same as some batteries.

It all really depends on how and where you use your energy most, DHW, Space Heating, General Usage i.e. cooking, clothes washing, lighting, entertainment systems.

 

Thanks SteamyTea,

 

I went to the link but could not make heads nor tails of it and could not get anything like your image from it....sorry!

 

I intend to try to use the existing solar panels to run as much (thinking as close to all as possible) of the General Electricity usage in the house (hot water via emersion, Cooking, washing clothes, electric showers etc) when connected to battery storage for evenings (not home really during the day so 80% would be evening use with some morning showers etc)

 

Is this even feasible without having to have a massive KwH battery storage and therefore making it completely not viable from a financial point of view.

 

I thought/think I'm in a good position as the PV part of the system is already there so my expense is on battery storage and installation etc. I was hoping to be able to run all electric side of the house (not heating) from battery storage (taken from solar panels when they can and cheaper rate KwH over night for use next day)

 

Am I being too simplistic and its not really financially viable? Yes, I love our planet too but my wallet also like £ notes in it each month  

 

I dont mind a pay back period of 8 years or so. I have the money for a battery system now (which I probably will not have in the future) so my thinking is that I use it for battery storage and then will save around £80/£100 per month off my bills going forward.

 

One other thought that just came to me....maybe better to pay the £7000K off my mortgage instead?  

 

Bloody mine field....not even got into how big a battery I need debate.....Ahhh.  

[SteamyTea]

18 minutes ago, Robbrosky said:

could not make heads nor tails of it and could not get anything like your image from it

Get yourself on a laptop or desktop and try this link.  Mobile phones are useless on their site.

https://re.jrc.ec.europa.eu/pvg_tools/en/

 

You should get a screen like this.

 

Zoom in on the map and put a click/pin where you live, choose any of the solar radiation databases, they are all similar (at this stage).

Change any angles if you need to, as well as the size of the system.  Then click on Visualise Results.

 

24 minutes ago, Robbrosky said:

I was hoping to be able to run all electric side of the house (not heating) from battery storage (taken from solar panels when they can and cheaper rate KwH over night for use next day)

While this seems like a simple solution, the devil is in the detail.  When your system cannot supply enough energy, you may be drawing from the grid at a much higher financial rate.  Also these Time of Use tariffs are, generally, being trialled by suppliers, and may be withdrawn, which makes medium term decisions hard.  Our electrical energy market is basically in turmoil and different political parties are using it to attract voters.  So be wary.

[Robbrosky]

This is what I get when I change the output to 3.5KwH.

 

Is that OK?

 

What does it actually mean in terms of my thoughts as it just looks like a lot of pretty blue bars to me?

 

Ive 'fag packet' calculated my average KwH usage is around 16 Kwh. This is just the mean average so obviously a lot more in the winter than summer.....although to be fair the monthly electricity bills range from £188 in Dec to £136 in September so not a HUGE difference.

 

[JohnMo]

Simple way to think of solar and heating - they do not align well. Solar output when there is a heating demand is very low.  A battery can be charged by solar, or filled via the grid ideally on cheap rate. Most of the winter it will be filled via the grid.

 

Your heating - a direct electric heating system is likely to bankrupt you, will cost at least 2x gas more likely 4x without a huge battery. Either stay with gas or do a heat pump hot air system (no grants) or dump the hot air system altogether and go wet ASHP (grants available) or replace whole system with A2A heat pump and even storage heaters will be better.

[SteamyTea]

2 hours ago, Robbrosky said:

This is what I get when I change the output to 3.5KwH.

 

Is that OK?

 

What does it actually mean in terms of my thoughts as it just looks like a lot of pretty blue bars to me?

Right, the important times are October, November, December, January, February and March, with the really problematic months being December and January.

So October you will get a mean generation, the kWh (not Kwh), of 191 kWh, November 126 kWh, December (the worst month) 85 kWh, January 98 kWh, February 162 kWh and finally March 274 kWh.

Starting with heating hot water, it takes 4.2 kJ (kilojoules) or 0.00117 kWh, to heat 1 litre of water by 1 K (kelvin, which uses the capital K).  One kelvin (uses lowercase first letter when used in science, except at the start of a sentence) is, in this case, the same as 1 °C.

So in October, you have enough energy from the PV, on average, to heat up 4310 litres of water from 12 °C to 50 °C, which is 139 litres a day.   Quite a useful amount.

November would be 95 litres/day, December 62 litres/day (not much), January 71 litres/day, February 131 litres/day and March 199/day litres.

Now I have no idea how much hot water you use, you will have to work this out (a measuring jug, thermometer and a stop watch).

This does assume that all your PV production goes solely to heating hot water.  In reality, with a diverter, you may only get 2/3^rd diverted (depends what else is going on in the house at the time).

If you diverted to a heat pump, when it is running, you may, with careful timing i.e. run it from 10 AM to 2 PM utilise half your production, but you will get about 3 times that electrical energy converted to thermal energy.

So October you will get 208 litres/day, November 142 litres/day, December 93 litres/day, January 107 litres/day, February 196 litres/day and March 299 litres/day.

Now as you will be importing energy at the day rate from your supplier, you may find that during these months there is not much difference in running costs, but from about mid March to Mid October, you will be saving, but you will have to have bought a heat pump and possibly a domestic hot water cylinder depending on what you have installed already.

 

Now let us consider battery storage.  There are energy losses during the charge/discharge cycle.  These vary depending on the rate of charging and the amount of charge that is already in the battery.  The fuller they are, the harder it is to charge them the final bit.

10% losses would be a reasonable starting point.

So rather than look at what can be done heating water, we will look at how much PV energy can be stored and extracted per day.

October 5.5 kWh/day, November 3.8 kWh/day, December 2.5 kWh/day, January 2.8 kWh/day, February 5.2 kWh/day and March 8  kWh/day.

Now it should be possible to store most of your PV production into the batteries with some clever diversion, though it may be more sensible to work on 80% utilisation.

So October 4.4 kWh/day, November 3 kWh/day, December 2 kWh/day, January 2.3 kWh/day, February 4.2  kWh/day and March 6.4 kWh/day.

If we convert that to amounts of hot water.

October 100 litres/day, November 68 litres/day, December 45 litres/day, January 51 litres/day, February 94 litres/day and March 144 litres/day.

So less energy is directly put into the hot water than heating directly from the PV.

Any shortfalls will need to be made up by imported energy at whatever rate you pay.  But remember that if you fully charge your batteries during a cheap period, there may not be any spare capacity to store excess PV generation.

 

You may find that doing some simple and cheap improvements to the fabric of your house will give a better saving overall.  There are also behavioural changes that can make a huge difference (why half the time my house uses no energy at all).

The biggest change you could probably make is to change your car, and use it less.  In the last decade I have gone from a car that does 53 MPG to one that does 65 MPG on average.  That is a 22% reduction, considering I drive 35k miles a year, that is 1050 kWh/year.  With my house using about 3,000 kWh/year (down from 11,000 kWh/year when I moved in) I am now hard pushed to make any great savings without spending a fair bit of cash.

 

Edited Saturday at 18:52 by SteamyTea