So now I have a solar PV system how do I make the most of it???

zeupater

Martyn1981 wrote: »

Hiya Zeup, I've been bouncing those numbers around in my head, since a lot of these companies' claims are more than a little optimistic. However, I'm not convinced that the 1,100 units you suggest is unreasonable. Considering generation from a 4kWp system:

May to Aug should provide 5 to 6 excess units most days. A lot of the days, excess will be higher, but I assume(?) the system and household won't be able to make use of all summer excess. So that's around 600.

Mch, Apr, Sept should provide 2 to 3 a day, with excess days being usable, so that's another 270.

Oct to Feb, conservative estimate of 1 per day, (higher still if the roof has a steep pitch) but again some zero's, but high use of good days, so another 150+. In fact, I'd be willing to bet that over those 5 months you'd see at least 50 days with 3 usable excess units on their own.

So that's around 1,000 units, which I think is a reasonable estimate (not too high or low). Certainly not 'wildly optimistic' as you were misquoted.

I remain concerned at pricing these PV units at nil (rather than 3.2p export), but I suppose it's unlikely we'll see export/smart meters in the next 5 years.

In Hobbo's case (and particular circumstances) I think a suck it and see approach is probably a good bet. But those are particular circumstances that most of us would not gain from.

Mart.

Hi Mart

I don't think that the figures are wildly optimistic, but would still consider them to be optimistic for most unless the H/W capacity is increased.

I've just crunched my own generation for the past 12 months to date on a very simplistic (& optimistic) basis. Let's assume that you could divert the full 6kWh to H/W on days where total production is >12kWh and that you would likely need a 6kWh day to be able to divert any reasonable amount of power, this assumption would likely reflect the removal of early/late hours where generation is low and allow for background usage, but for fairness remember that other high load appliances such as cookers, washing machines, dishwashers, kettles etc have been ignored for this exercise .... crunch my figures for a 4kWp system and I get a potential maximum of 1056kWh, not far from the 1100kWh claim, but the switching/management process on the automated unit would need to be almost perfect to achieve this and this is where the crux lies ... how good is the switching and how accurate is the measurement of generation vs consumption on a minute-by-minute basis ?

Personally, I think that around £500 for a simple power management system is a rediculous amount and that around a fifth of that is a more realistic figure with the high price simply being set to bolster customer expectations rather than reflect the reasonable cost of manufacturing & supply. As we know, on a DIY basis using off-the-shelf components from a source which is well known to be expensive, some members have developed usable solutions for a fraction of £500 and will therefore see a much better return even if the switching logic is massively less efficient.

HTH
Z

sly_dog_jonah

The point is the immersun can divert even small amounts of otherwise exported power to the immersion heater, and my understanding is that it does this in real-time rather than periodic sampling.

I've done some basic estimations of our export based on our pre-installation electricity usage, our post-installation import and generation. These calculations assume that our total electricity consumption is the same this year as last. In Q1 this year we most likely exported around 45% of generation, Q2 76% and Q3* 70%. In that period the total export is around 1900kWh, so the annual figure is probably around 2200kWh, or average 6kWh/day.

While there's certainly no guarantee that export will be eliminated (due to finite energy capacity of the tank) it would certainly be beneficial to only export when you have a fully heated tank. Export can be minimised by setting the immersion thermostat higher (subject to scaling and scalding risk).

* extrapolated based on Q3 readings to date.

zeupater

Cardew wrote: »

Hi zeupater,

Agree with your 'maths' but the fact that you have solar thermal(and solar PV) makes your situation atypical!

There seems to be an assumption that a HW tank has infinite capacity to absorb 'surplus' electricity, and to ignore the fact that on many days there will be no surplus electricity.

Also with the present metering system, combined with FIT, you still get an assumed 50% export payment regardless of the consumption of your generated electricity.

When smart metering comes in over the next ??years the situation will change and there will be the ability to calculate exactly how much electricity is exported. Every kWh diverted to the immersion heater will reduce the export payment by ??pence. For those with gas CH I suspect the 'savings' will be marginal.

Essentially I am suggesting that the savings from these devices need to be looked at realistically.

EDIT - hadn't read Martyn's post above re smart metering - with which I concur!

Hi Cardew

Agree on the requirement of having pv to power the thermal system, but the saving isn't that significant.... The majority of our H/W is provided at just below 1kW.t of ET input (currently supplying ~1.8kW.t) and the system is run by an electric pump so you need to ensure that you have a suitable low power pump unit which would typically draw around/below 20W, not the 60W to 120W of a typical domestic central heating pump unit.

At the moment the return of heat for electrical input (COP) is showing as 90x (~1800W/~20W), which seems to be a little better than most forms of heatpump, so I wouldn't consider that a bad return if we were paying for the electricity.

HTH
Z

Hobbo2006

zeupater wrote: »

Hi Mart

I don't think that the figures are wildly optimistic, but would still consider them to be optimistic for most unless the H/W capacity is increased.

I've just crunched my own generation for the past 12 months to date on a very simplistic (& optimistic) basis. Let's assume that you could divert the full 6kWh to H/W on days where total production is >12kWh and that you would likely need a 6kWh day to be able to divert any reasonable amount of power, this assumption would likely reflect the removal of early/late hours where generation is low and allow for background usage, but for fairness remember that other high load appliances such as cookers, washing machines, dishwashers, kettles etc have been ignored for this exercise .... crunch my figures for a 4kWp system and I get a potential maximum of 1056kWh, not far from the 1100kWh claim, but the switching/management process on the automated unit would need to be almost perfect to achieve this and this is where the crux lies ... how good is the switching and how accurate is the measurement of generation vs consumption on a minute-by-minute basis ?

Personally, I think that around £500 for a simple power management system is a rediculous amount and that around a fifth of that is a more realistic figure with the high price simply being set to bolster customer expectations rather than reflect the reasonable cost of manufacturing & supply. As we know, on a DIY basis using off-the-shelf components from a source which is well known to be expensive, some members have developed usable solutions for a fraction of £500 and will therefore see a much better return even if the switching logic is massively less efficient.

HTH
Z

If you're in the know then then DIY route does save money but I have doubts about it.

1. No intelligence about what power is being used in the home.
2. A DIY device is untested and has no creditation and I just didn't want to potentially put the family at risk because I wanted to save money.
3. Don't want to mess about with the HW tank/Element.

With a bit of ringing about and getting a few like minded people to club together I think you can get the cost to under £400 and let's face it the Immersun will pay for itself before the Solar PV does.

Doc_N

Hobbo2006 wrote: »

With a bit of ringing about and getting a few like minded people to club together I think you can get the cost to under £400 and let's face it the Immersun will pay for itself before the Solar PV does.

I think the jury's still out on that one.

I'm waiting for a quote from a local installer, and I'll be going through his projections with a fine tooth comb. There's another issue, of course, and that's the longevity of the manufacturer, 4eco Ltd.

zeupater

Hobbo2006 wrote: »

If you're in the know then then DIY route does save money but I have doubts about it.

1. No intelligence about what power is being used in the home.
2. A DIY device is untested and has no creditation and I just didn't want to potentially put the family at risk because I wanted to save money.
3. Don't want to mess about with the HW tank/Element.

With a bit of ringing about and getting a few like minded people to club together I think you can get the cost to under £400 and let's face it the Immersun will pay for itself before the Solar PV does.

Hi

Agree, if you have no idea what you're doing with the circuitry then leave it alone. What I was actually attemping to convey is that it's possible to purchase all of the components to build a system which could achieve a similar result from a very expensive source and still assemble a solution for a fraction of £500, therefore the cost of the components to a manufacturer must be incredibly low, resulting in extremely high margins ...... margins which could only be justified if the potential savings make the investment look good ....

If it was me and the only form of water heating was an electric immersion heater I'd simply go for E7 and heat the water overnight, summer, winter, spring, rainy days & dull days ... save on the cost of running the fridge & freezer overnight and be quids in overall and still have my £500 in the bank .... If gas was available, I'd use that in preference to the immersion and wouldn't consider the E7 option and still leave the £500 in the bank ....

If you have already made the decision spend the money regardless then that's fine and I, along with others, will be interested to follow your experiences if you would care to share them with us .....

HTH
Z

Cardew

zeupater wrote: »

If it was me and I the only form of water heating was an electric immersion heater I'd simply go for E7 and heat the water overnight, summer, winter, spring, rainy days & dull days ... save on the cost of running the fridge & freezer overnight and be quids in overall and still have my £500 in the bank .... If gas was available, I'd use that in preference to the immersion and wouldn't consider the E7 option and still leave the £500 in the bank ....


HTH
Z

That was the point I was making above:

Indeed I am surprised that you don't have an Economy 7 tariff and heat your
water at around 5p/kWh. On some tariffs the 'break even' percentage for using E7
is below 20% on cheap rate. That 20% can be achieved without any water heating.

Some people with oil or LPG central heating go on Economy 7 and heat water on cheap rate as around 5p/kWh it is cheaper.

Hobbo2006

Cardew wrote: »

That was the point I was making above:



Some people with oil or LPG central heating go on Economy 7 and heat water on cheap rate as around 5p/kWh it is cheaper.

I'll check out Economy 7. I need to find out if my meter supports it first. Then do some comparisons on uswitch. Apparently the day rate of electricity is usually higher so that may not be great with a family at home during the day, though shouldn't be a problem in summer with the panels etc.

Cardew

Hobbo2006 wrote: »

I'll check out Economy 7. I need to find out if my meter supports it first. Then do some comparisons on uswitch. Apparently the day rate of electricity is usually higher so that may not be great with a family at home during the day, though shouldn't be a problem in summer with the panels etc.

I have an Economy 7 meter, although for years the readings were added together and treated as a single total.

I found that without any attempt to maximise use during the 7 hours cheap rate period, I used about 20% in that period. Don't forget that, depending where you live and when you get up in the morning, activity can be using cheap rate electricity - showers, cooker, etc.

With water heating and timed use of washing machine/dryer/dishwasher it would be easy for me to raise that percentage to 30% - 35%.

sly_dog_jonah

Cardew wrote: »

I have an Economy 7 meter, although for years the readings were added together and treated as a single total.

I found that without any attempt to maximise use during the 7 hours cheap rate period, I used about 20% in that period.

Since 7hrs/day is 29% of the day, that implies that your nightime electricity consumption rate is only 31% less than the daily average. Sounds like you may have some inefficient fridge/freezers running overnight?

Unless people are early risers, it's unlikely they will be able use the cheap rate when cooking etc, although as you say it varies by region and time of year.