PV and Storage Heaters

Cardew

Kontiki wrote: »

I The figures I have been given for my system are that it should produce 2927kw per year, I should receive £1209 in FIT's & save £322 from my electricity usage (be interesting to seo see how they match up). .

Your FIT figure is correct, but how do you come to a figure of £322 saved from electricity usage? -Especially as you only use on average 2,200kWh a year.*

Few people manage to use 50% of their generated power and people with practical experience far less.

McFI5 who has had a system for over 2 years, has an export meter so knows how exactly much he uses. With a wife and young children at home all day he uses approx 500kWh per year in his house.

Personally I doubt if most people will save more than £100 a year.

* Assuming that your meter doesn't run backwards.

Kontiki

I didn't come up with the figure of £322 it was from the calculations given from the installer using some software which obviously assumes certain usage. I wouldn't expect this figure to be too accurate, the FIT's figure though is from calculations based on the orientation & size of my panels, I was told that I should get a bit better than this (but until I have the system I can't know but all the other quotes I had gave similar results)

We don't have cheap off peak electricity so that isn't a concern, I agree there is no point in going the route of unnecessarily wasting any surplus fro the panels just because I can. Possibly though some changes to how we manage the use of our electric can show some advantages.

grahamc2003

Kontiki wrote: »

I didn't come up with the figure of £322 it was from the calculations given from the installer using some software which obviously assumes certain usage. I wouldn't expect this figure to be too accurate, the FIT's figure though is from calculations based on the orientation & size of my panels, I was told that I should get a bit better than this (but until I have the system I can't know but all the other quotes I had gave similar results)

We don't have cheap off peak electricity so that isn't a concern, I agree there is no point in going the route of unnecessarily wasting any surplus fro the panels just because I can. Possibly though some changes to how we manage the use of our electric can show some advantages.

I have my quote for a 2.2kw system (£11,400, 1750kwh pa) and the estimated return consists of £718 fit and £174 for the energy generated, calculated assuming "Maximum annual savings if all solar electricity is consumed on site".

A little misleading, and not really what I'd expect from an industry trying to create an open and honest dialogue.

rhiwfield

I doubt whether I will get my net leccy use below 1,000 kwh so I will be caught with the higher supplier tariff for the first 900 units.

So my calculations are based on saving the cost of the marginal units (9p a kwh). I am assuming 50% used and 50% exported, though, as you can see from earlier post you have to work at it to achieve that 50% level and I may use a slightly lower percentage.

My first array (orientated 30W) benefitted from a grant of £2,500 and I was expecting a gross yield of c12% pa. In practice I'm getting 11.2% as generation is a bit lower than expected, primarily due to early morning shading from a tree lined ridge to the east.

My second array is orientated 60E, is higher, and is split into 4 mini strings to minimise shading impact. Here the return is expected to be 7.9% but as its recently installed I cant say this will be right.

Overall the arrays total 3.8kwp and I expect them to generate just over 3000 kwh. Overall cost was £16k (net of grant) and gross yield expected to be 9.1%.

My estimates were provided by suppliers but I checked them out with PVGIS. PVGIS has recently recalculated its data maps, in most cases increasing yield, in mine reducing

I suspect without the shading factor I would be beating estimates. I agree that suppliers should not assume 100% home usage, unrealistic in the cast majority of cases.

MisteRusty

interesting discussion (mostly). I did try to reply before the weekend, but it appears to have got lost

Still, lots of interesting contributions from others to consider since then

Here's few more interesting figures from my own setup :-

In the first 6 months my system has generated 2100kwh, of which we've used approx 500kwh. So only 25% of what we generate is used on site. Seems a bit low, but the larger the system, the harder its going to be to get close to the 50%.

During that time we used a total of 1300kwh, so we produce about 40% of what we use.

Obviously I'd like to use more of it on site, so am interested in moving the load from evening use to the daytime.

One way we use, not mentioned by anyone else, is a slow cooker. Seems to be a great way of using small amounts of power over a longer period, and also moves the period of use from evening (low production) to afternoon (higher production).

I'm still tempted by an automatic system which could soak up surplus power. The most promising system I've seen is a Ventmiser which uses a current sensor attached to one circuit to switch on another circuit. So the sensor could be on the pv circuit, switching on a storage heater when the generated pv exceeds a certain value.

When I get round to calculating the costs, I shall certainly post the results.

zeupater

MisteRusty wrote: »

One way we use, not mentioned by anyone else, is a slow cooker. Seems to be a great way of using small amounts of power over a longer period, and also moves the period of use from evening (low production) to afternoon (higher production).

Hi

Agree, the best way to utilise the generated energy without continually needing to import is to remove as many requirement spikes as possible ..... our slow cooker pulls around 181W and is ideal to soak up power as it's generated ...... next time the 3kW kettle dies I'll probably look around for one with a smaller element, around 1kW to 1.5kW, but it would still need to be big enough to fill the teapot .... there are some things that you cannot compromise on, no matter how green you try to be !!

Kontiki

Had my panels installed yesterday :T They said they always allow 2 days for an installation as sometimes there are problems/weather etc.. In my case they just got it finished in the one day & my system showed it earning 9p not much but a start. They were very professional, did a neat job, answered all my questions & made sure everything was cleaned up before they left. Scaffold should be taken down today, so just need the sun to shine, today it's pouring down & the forecast doesn't look good. 9:00am & it's only showing 9 watts but it's really dull & raining.:(

grahamc2003

Kontiki wrote: »

Had my panels installed yesterday :T They said they always allow 2 days for an installation as sometimes there are problems/weather etc.. In my case they just got it finished in the one day & my system showed it earning 9p not much but a start. They were very professional, did a neat job, answered all my questions & made sure everything was cleaned up before they left. Scaffold should be taken down today, so just need the sun to shine, today it's pouring down & the forecast doesn't look good. 9:00am & it's only showing 9 watts but it's really dull & raining.:(

Look on the brightside - at least you're using 100% of your pv output!

Does anyone know if the inverter needs a certain power in order to operate? (e.g, in the case above, are the panels likely generating 9w @240 from 10w @ 400v (or whatever) in, or is there an overhead of, say, a couple of hundered watts just to get the inverter to operate (i.e. are the panels generating 9w @240v from say 209w @ 400v (or whatever) invertor input?

Mcfi5dhc

Cardew wrote: »

Your FIT figure is correct, but how do you come to a figure of £322 saved from electricity usage? -Especially as you only use on average 2,200kWh a year.*

Few people manage to use 50% of their generated power and people with practical experience far less.

Mcfi5dhc who has had a system for over 2 years, has an export meter so knows how exactly much he uses. With a wife and young children at home all day he uses approx 500kWh per year in his house.

Personally I doubt if most people will save more than £100 a year.

* Assuming that your meter doesn't run backwards.

I agree with all the above

As my wife is at home most of the time, she'll put the washing machine on then, or maybe we'll use the delay function so it comes on in the morning.

To be honest though, besides that, we don't do a great deal of electricity-shifting. If the washing needs tumble drying, it needs tumble drying. I'm not going to wait three weeks for a sunny day!

The big sin we do, is always doing ironing at night - thats simply cos I'd rather play with the kids when they are awake, than be ironing away in a different room. No amount of sun will change that. We do do team ironing though - usually with a glass or two of beer!

I thought about using more of the energy onsite by using an EMMA - great invention though it is, its just not worth it for me.

Graham - my invertor needs 160w before it starts working. So, if I am generating 200w, only 40w is getting to the meter box. Strangely though, I can exceed 1.44kwh in an hour (my system is 1.44kwp), but not by very much, and certainly not at all in this weather.

Kontiki

Not sure how much the inverter uses but it shuts down to a standby mode when the panels stop producing. Had the system just over a week & it has generated about a tenner,not fantastic but a few of the days it just didn't get light, really dull & overcast.

We also have an E.ON energy meter which is supposed to show how much power we are using. The problem is the way the meter works it only shows the power passing through the cable, so when the panels are generating power the meter shows we are using more:huh: as you turn on more appliances the meter shows you are using less.

We can use the meter to see how we are using the power, if something gets turned on & the meter goes up we are using more than we produce, if it goes down then we still have spare capacity.
I spoke to E.ON & they said that the meter is useless for measuring our usage if we generate power & they are working on a new meter to overcome the problem.