ASHP and Solar PV calculator

ryanemery

http stuff::/web.me.com/emeryryan/calc.xls

See attached link for solar / ASHP (i.e. 14kw ecodan) calculator - need to up our radiator size anyway

I like the idea of this as I become a lot less dependent on energy companies (and the inevitable ensuing inflation)

I would have liked a larger Solar PV system but don't have the roof space (two tiered roof).

ASHP RHI tarriff scheme is not confirmed yet - hence you need to change the figure in the formula in year 1 to what you think it will be and then copy the fomula down... anyone know when to expect this to be confirmed?
Im generally being told for my house (1990s 4 bed detached) it will be £1500 + some savings on current bill (crappy old gas combi)

If the figures end up being anything like this then it means I can be mortgage free in c12+ years (when ill be 42)

I thought about using a shade greener for the solar, but havent convinced myself yet that there wont be future problems when we want to sell house & move.

Lastly im told 14kw will be enough for our house.. our combi is 27kw.. judging by our bills we dont use a great deal of gas.

Any comments? - I know cardew / noncom will have some good pointers

p.s. i know I need to factor in a new inverter (£1k) and a bit of maintenance but dont see this as being too much in comparison to what we are already paying for gas / boiler inspections.

noncom_2

A few comments, on the Solar PV side only, as I know next to nothing about ASHP....

1) You are assuming 850kWh/kW peak pa from the panels, which is at the upper end of what you could expect (I don't know where you live, but the fact you considered A Shade Greener suggests North England, in which case 850 may be too optimistic). As your table states, 750-850 is expected. I personally would have estimated lower, not because I know what you will produce but because I would always rather know the "worst reasonable case" and if that adds up for me, I'd go for it and maybe be pleasantly surprised.

2) Also, you have assumed that the panels will produce as much electricity in year 25 as in year 1. The panels will come with some sort of performance guarantee, that they should produce at least 80% of their rated ouput after a certain period, usually either 20 or 25 years. Personally, when I made a similar spreadsheet, I factored this in as a % decline in the output each year. Again, hopefully they will not decline so quickly and I will do better than predicted.

3) 50% is probably correct for the export amount for now, as I believe most energy Co.s will assume that, rather than fit an export meter. This may change in future. However, if you actually use less than 50%, then this will affect the "savings" column. I think I may have to work quite hard to use 50% - because we are out at work during daytime, much of our consumption is in evenings for lights, TV, computers etc. We will try to use timers for the washing machine, dryer, laptop chargers etc to maximise the daily use, but I don't know what proportion we'll end up getting "free".

4) 12p per unit is quite high at the moment, unless you are on a Standard tariff (for which there is no excuse!) or a Green supplier (Ecotricity is who I will be using, and they match the Standard tariff of the regional supplier - I know I could beat that easily, but it is a price I am prepared to pay for increasing the Green mix in the nation's supply). If you are someone who will simply go with the cheapest available tariff, I would suggest maybe 10p per unit is more realistic.

5) 4% electricity inflation rate is probably reasonable, and I believe the Energy Saving Trust thinks 5% is quite possible. I did my calculations twice, once using 3% and once using 5%.

5) 4% general RPI seems a little on the high side. I used 2.5%, again to give me a "worst case", as that may well prove too low.

6) The 3p export rate is also subject to RPI, I believe, although that hasn't been done here. It makes little difference however as the amount is so small.

7) I don't really understand "present value" tbh. What I did in my final column was to calculate my financial position each year if I took the cost of the Solar PV system and instead paid it off my mortgage. So for each year, I could produce a figure for how much worse or better the Solar Panels would be as an investment compared to reducing my mortgage, and work out the point at which the Panels "overtake" the lower mortgage.

8) You say you can't get a bigger system because your roof is two-tiered. If they both face the same way, that's not necessarily a problem. My own roof (although the house is possibly a little larger) is split between a main roof at a 50deg pitch and a lower extension roof at 30deg. My system will have panels on both, feeding into a single inverter with two inputs (two Maximum Power Point Trackers, which as I understand it will maximise the generation from such a combination). Perhaps you could consider this?

9) Are you ditching your Gas Boiler altogether? If not, then obviously any maintenance costs for the new systems will have to be ADDED to those for your existing one. FWIW, I "guestimated" £75 per year repairs throughout for my Solar setup, even though it will have a 5-yr warranty at the beginning.

geordie_joe

noncom wrote: »

4) 12p per unit is quite high at the moment, unless you are on a Standard tariff (for which there is no excuse!)

Sorry but that is complete rubbish.

I am on a standard tariff, I pay 11.5p per unit and use around 1000 units per year. I don't pay any standing charge.

11.5 x 1000 = £115 per year.

A few days ago I checked the prices, as I had read a Cardew post saying most companies are offering electricity at around 7p per unit. But when I checked, I found I could get it at 7.5p per unit, but would have to pay an £80 per year standing charge.

7.5 x 1000 = £75 + £80 = £155

So if I changed to the lower tariff I would pay £155 per year for my 1000 units, instead of the £115 per year I am paying now.

I consider paying £40 per year less a VERY GOOD reason for being on a standard tariff.

I think only looking at the price per unit is a very poor way to do things, you have to take into account the total amount you will be paying.

And if you are generating your own electricity then you have to take into account that you will be buying less from the electricity company, so you should choose your tariff based on what you will be buying, not what you will be using.

A tariff aimed at low volume users may be better for you than one aimed at higher volume users.

noncom_2

Thanks for that correction. I'm no expert in electricity tariffs, and what you say makes sense, although 1000 units per year is less than half the average household consumption, so it may be only a small proportion of people for whom it would apply.

Is there not a "tier 1" and "tier 2" price on your tariff? I thought most (if not all) No Standing Charge tariffs apply a more expensive rate to the first xxx units per year, which effectively acts as a hidden standing charge (unless you use less than xxx per year). Having said that, the amount seems to add up to less than £40 per year.

Your point that micro-generators will buy in less electricity from their Power Co. and therefore are more likely to benefit from a tariff which benefits lower consumption is perfectly valid though.

Thanks
Andy

ryanemery

Thanks noncom, some really good poits for thought there.

noncom wrote: »

A few comments, on the Solar PV side only, as I know next to nothing about ASHP....

1) You are assuming 850kWh/kW peak pa from the panels, which is at the upper end of what you could expect (I don't know where you live, but the fact you considered A Shade Greener suggests North England, in which case 850 may be too optimistic). As your table states, 750-850 is expected. I personally would have estimated lower, not because I know what you will produce but because I would always rather know the "worst reasonable case" and if that adds up for me, I'd go for it and maybe be pleasantly surprised.

The 850 is where i had left the calculation when i saved it... Im still happy with the 750 result

2) Also, you have assumed that the panels will produce as much electricity in year 25 as in year 1. The panels will come with some sort of performance guarantee, that they should produce at least 80% of their rated ouput after a certain period, usually either 20 or 25 years. Personally, when I made a similar spreadsheet, I factored this in as a % decline in the output each year. Again, hopefully they will not decline so quickly and I will do better than predicted.

Good point, ill add it to the spreadsheet, however Im looking at a 13 ish year time horizon and dont expect it to make too much of a difference.

3) 50% is probably correct for the export amount for now, as I believe most energy Co.s will assume that, rather than fit an export meter. This may change in future. However, if you actually use less than 50%, then this will affect the "savings" column. I think I may have to work quite hard to use 50% - because we are out at work during daytime, much of our consumption is in evenings for lights, TV, computers etc. We will try to use timers for the washing machine, dryer, laptop chargers etc to maximise the daily use, but I don't know what proportion we'll end up getting "free".

4) 12p per unit is quite high at the moment, unless you are on a Standard tariff (for which there is no excuse!) or a Green supplier (Ecotricity is who I will be using, and they match the Standard tariff of the regional supplier - I know I could beat that easily, but it is a price I am prepared to pay for increasing the Green mix in the nation's supply). If you are someone who will simply go with the cheapest available tariff, I would suggest maybe 10p per unit is more realistic.

Ive used EON fix online 6 - works out at 21p for 900kwh then 10p with a 26% discount. - personally i think electricity proces will be going up quite a lot along with general inflation. - (if you look at current inflation its careering above government targets, will go up with the VAT increase and is much higher if you look at the RPI measure instead of the distorted CPI)

5) 4% electricity inflation rate is probably reasonable, and I believe the Energy Saving Trust thinks 5% is quite possible. I did my calculations twice, once using 3% and once using 5%.

Agreed

5) 4% general RPI seems a little on the high side. I used 2.5%, again to give me a "worst case", as that may well prove too low.

I strongly recommend in anything you do you consider the fact that inflation is going to be a lot higher.

6) The 3p export rate is also subject to RPI, I believe, although that hasn't been done here. It makes little difference however as the amount is so small.

I think potentially (and very soon) you can opt for a market value for your export. but agree its probably a small element

7) I don't really understand "present value" tbh. What I did in my final column was to calculate my financial position each year if I took the cost of the Solar PV system and instead paid it off my mortgage. So for each year, I could produce a figure for how much worse or better the Solar Panels would be as an investment compared to reducing my mortgage, and work out the point at which the Panels "overtake" the lower mortgage.

Yes that is an alternative, prosent value is a similar concept in some ways - I think of all of this as more like an annuity (but with a bit of costs / maintenace / uncertainty)

8) You say you can't get a bigger system because your roof is two-tiered. If they both face the same way, that's not necessarily a problem. My own roof (although the house is possibly a little larger) is split between a main roof at a 50deg pitch and a lower extension roof at 30deg. My system will have panels on both, feeding into a single inverter with two inputs (two Maximum Power Point Trackers, which as I understand it will maximise the generation from such a combination). Perhaps you could consider this?

Will look at it, and is a good thought.. shading may be a limiting factor

9) Are you ditching your Gas Boiler altogether? If not, then obviously any maintenance costs for the new systems will have to be ADDED to those for your existing one. FWIW, I "guestimated" £75 per year repairs throughout for my Solar setup, even though it will have a 5-yr warranty at the beginning.

Yes gas boiler is going.

noncom_2

Well of course the higher inflation is, the better a bet my Solar PV system will have turned out to be, so again I'm quite happy to err on the "low" side. But you may well be right about it being 4% or more in the next few years.

Andy

geordie_joe

noncom wrote: »

Thanks for that correction.

I've just read the first line of my last post, I hope you didn't take it as an insult. It wasn't meant as one, just my first thought to the notion that cheaper units means you pay less for your electricity.

noncom wrote: »

I'm no expert in electricity tariffs, and what you say makes sense, although 1000 units per year is less than half the average household consumption, so it may be only a small proportion of people for whom it would apply.

You could be right, I live on my own and spend a fair bit of time at someone elses house, so don't actually use a lot.

Having said that, I've just done a quick calculation. If I used 2000 units per year then I would pay the same with either tariff.

noncom wrote: »

Is there not a "tier 1" and "tier 2" price on your tariff? I thought most (if not all) No Standing Charge tariffs apply a more expensive rate to the first xxx units per year, which effectively acts as a hidden standing charge (unless you use less than xxx per year). Having said that, the amount seems to add up to less than £40 per year.

My tariff does have a 2 tier system. I get charged at the higher rate for the first 364 units per quarter, then the lower rate. The thing is, I don't remember ever being charged the lower rate.

noncom wrote: »

Your point that micro-generators will buy in less electricity from their Power Co. and therefore are more likely to benefit from a tariff which benefits lower consumption is perfectly valid though.

Yes, as long as your kit actually generates what it is supposed too. I've had a tough enough time, the last couple of days, trying to find the best tariff for me (if I switch supplier). I would hate to have to do it taking into account whatever electricity a solar panel, or wind turbine might or might not generate!

noncom_2

Don't worry, no offence taken. If I talk rubbish, I'm perfectly happy for people to say so! Your comments have made me consider something which I hadn't before in terms of my future consumption of electricity once my panels are up and running.

Cheers
Andy

Cardew

geordie_joe wrote: »

Sorry but that is complete rubbish.

I am on a standard tariff, I pay 11.5p per unit and use around 1000 units per year. I don't pay any standing charge.

11.5 x 1000 = £115 per year.

A few days ago I checked the prices, as I had read a Cardew post saying most companies are offering electricity at around 7p per unit. But when I checked, I found I could get it at 7.5p per unit, but would have to pay an £80 per year standing charge.

7.5 x 1000 = £75 + £80 = £155

.

Geordie,

The average electricity consumption in UK is 3,300kWh.

You presumably use Ebico which makes sense for very low users.

However on my post(that you are quoting) the person was using, in Yorkshire, some 1500kWh during daylight hours so he was obviously not a low user and 7p/kWh for tier 2 is reasonable.

In the case of someone exploring the possibility of using an ASHP in a 4 bed detached then you are going to be talking about at least 10,000kWh pa so the only price to use is the lowest Tier 2 price available.

Cardew

Ryanemery,

Been away and just read this thread.

Noncom has come up with most points, however I would stress the issue of the price you use for saved electricity.

The price of Tier 1 electricity is irrelevant to any calculations; with an ASHP you will exceed that 900kWh quota by a vast margin, even with gas heating you will almost certainly exceed it in a 4 bed detached.

So if you pay 10p/kWh(less 26% for discounts) for Tier 2 to EON then you should use 7.5p/kWh as the start point in all your calculations. Ofgem recently produced a report where their best 'guess' was that electricity prices would rise by 14% to 25% above inflation by 2020.

Not sure I agree with Noncom about 850kWh/kW peak pa being too high. A Shade Greener only fit 3.3kWp systems in Yorkshire and monitor their installations. If output drops to 2,800kWh they inspect as they think their might be a problem. This suggests that they expect a minimum of 848kWh/kW peak pa.

This is not perhaps the thread to get involved with ASHP sizing. The only point I would make is that you are unlikely with a 14kW Ecodan to cope with all winter conditions up North in a 1990's 4 bed detached. That said - so what! If it copes for 90% of weather conditions, it isn't a financial disaster to have to use a cheap electrical heater for a short while.

noncom_2

Well, I hope you're right Cardew! The more my imminent Solar PV installation exceeds 850kWh/kWp, the happier I will be!