Free solar panel discussion

grahamc2003

ed1178 wrote: »

Sorry Zeupater, clearly having a blonde moment, it is Friday after all. I was confusing your discussion of Rent a roof with Owned. It appears we do agree on returns for owned systems, and your logic suggests the same is true of rent a roof. Again very roughly to save £100 a year you would have to produce AND consume approx 3kwh a day - not as easy as it sounds when remembering that this production / consumption must be perfectly balanced. Perhaps the answer to greatest savings would be to dump the excess generated as heat into the DHW or CH - If only Rent a Roof technology allowed for this - however I can't see them encouraging anything that would lower thier returns!

Not sure what you mean by balancing the consumption and generation. As Z said, they are decoupled. You generate according to many variables, including the sun's intensity, and you consume indepednently of all those factors even though you may attempt to 'match' the generation). Hence, you always consume less of your solar power than you generate.

You may consume typically 60% of a small array, and 40% of a large array, both being around £100s worth, give or take. There is a bit of a problem in using the spare capacity - say by having electronics which switch in you immersion heater when there's a certain level of surplus power.

Firstly, the value of the eledctricity used to heat the water isn't them your day electricity price. It is the marginal cost of water heating, which for many with gas ch will be about 1/3rd of the elecricity price (i.e. 1/3rd of the value you'd get by running your dishwasher for example). So if you divert about 50% which is currently exported, you'll gain about £33pa.

Secondly, setting the level at which the immersion is switched on is also tricky. If you have 2kw being exported, and you switch in a 3k imersion, and if you have gas ch, then you'll gain nothing, with the imported electricity cost equalling the marginal cost of water heating. So there are no gains to be made unless you are exporting at least 2kw (with a 3kw immersion).

Obvioulsy, you could fit a 2kw immewrsion, but the same logic still applies - there'd then be no gain unless the export was at least 1.6kw (i.e. all surplus generation below 1.6kw would still be wasted to you as a consumer).

One thing I'm not sure of, and perhaps some electronics bod could answer - is there a way just to feed say 500w into a standard 3kw immersion heater? If so, then all the excess could be used to heat water, and there'd be an extra £33 saving.

zeupater

Cardew wrote: »

...... The problem is that some people having got Rent a Roof systems make silly over-estimates of how much they will save - probably they need to convince themselves the gains are higher than they will actually achieve. See the other thread that is currently running.

The problem is that these over-estimates cannot be challenged in that thread and so will give a totally false impression of likely savings.

Hi

I've just been through the thread referenced and there are actually quite a few posts which I agree with which seem to have what I would classify as being genuine descriptions of savings .....

Of course, there are also some extravagant savings claims from some ..... love to see the basis & some figures to justify the values posted

Z

ed1178

grahamc2003 wrote: »

Not sure what you mean by balancing the consumption and generation. As Z said, they are decoupled. You generate according to many variables, including the sun's intensity, and you consume indepednently of all those factors even though you may attempt to 'match' the generation). Hence, you always consume less of your solar power than you generate.

You may consume typically 60% of a small array, and 40% of a large array, both being around £100s worth, give or take. There is a bit of a problem in using the spare capacity - say by having electronics which switch in you immersion heater when there's a certain level of surplus power.

Firstly, the value of the eledctricity used to heat the water isn't them your day electricity price. It is the marginal cost of water heating, which for many with gas ch will be about 1/3rd of the elecricity price (i.e. 1/3rd of the value you'd get by running your dishwasher for example). So if you divert about 50% which is currently exported, you'll gain about £33pa.

Secondly, setting the level at which the immersion is switched on is also tricky. If you have 2kw being exported, and you switch in a 3k imersion, and if you have gas ch, then you'll gain nothing, with the imported electricity cost equalling the marginal cost of water heating. So there are no gains to be made unless you are exporting at least 2kw (with a 3kw immersion).

Obvioulsy, you could fit a 2kw immewrsion, but the same logic still applies - there'd then be no gain unless the export was at least 1.6kw (i.e. all surplus generation below 1.6kw would still be wasted to you as a consumer).

One thing I'm not sure of, and perhaps some electronics bod could answer - is there a way just to feed say 500w into a standard 3kw immersion heater? If so, then all the excess could be used to heat water, and there'd be an extra £33 saving.

To take your points / questions in turn:

By balancing generation and consumption I ment that in order to achieve the greatest saving one must use as much of the produced electricity as possible, by attempting to carefully manage consumption to ensure it is generally around the level being generated at any given time. I agree that one will never manage to consume all electricity generated, unless your consumption was continuously higher than the maximum output of the panels.

In your first point I assume you are refering to the cost benefit of heating water using gas rather than electricity which per kwh is approx 3 times more expensive. You are correct in saying that water heating costs are marginal for a typical household using a gas boiler, the majority of our gas bills are for running the central heating. However the point I was trying to make is that there is still a saving to be made using surpless electricity to heat water. 1kwh or surpless electricity used to heat your tank is 1kwh of gas no longer required. So the saving would be the equivalent price of one unit of gas. Since there is no payment made under rent a roof for exported electricity then why not use as much as possible.

Under the same point I'm afraid I didn't understand your mention of a dishwasher? I think you mean that savings would be greater if exported electricity were used to power electrically operated items rather than as a substitute for gas in heating - in which case I agree - why use a unit of electricity to replace 3p worth of gas, when you could use it instead of 12p worth or imported electricity!

On your second point I don't quite see the logic, perhaps you could clarify a little? Any electricity used in place of gas represents a saving. The size of the immersion has nothing to do with it, although it is worth remembering that a 3kw immersion will not function if drastically undersupplied. To repeat my point any electricity used in heating in place of gas represents a saving of the cost of gas that would otherwise have been consumed.

On your question of using 500w in a 3kw immersion, unfortunately this would not work. You might get away with about 80% of its rated output but at very low levels the heating effect of 500w or approx 2 amps through an appliance rated at 3kw or 13 amps would be negligable if not non existent. There is no way to alter the resistance of a heating appliance such as in immersion heater which is what would be required to generate heat. However small, low output immersions are now available which can be inserted through ordinary pipe fittings into cylnders. It should be possible to use a small array of these, each with an output of say 200w, and clever electronics to switch one, two or three etc on depending on the surpless power available at any given moment. The cost of this is likely to far outweigh the benefit however!

One thing is for sure, this thread is likely to rumble on for some time yet! I do have to say that I agree that savings have probably been exaggerated by those promoting this technology, and are only likely to be achieved in ideal conditions almost impossible to replicate in the real world. With so many factors to consider the only way to find out for sure is to try the technology ourselves. I am still undecided if I can be bothered with the hassle as there are far easier ways to save such small amounts of money. Having said that I don't think anyone can question the green credentials of a well sited and installed system, and in the end perhaps it is the future of the planet that should concern us more than annual cash savings that won't even buy us a half decent meal out!

casey17_2

I have recently used a company called Mark Group apparently nationawide who have installed my panels fro free, I have as yet to receive a bill but looking at the meter during the day I am certainly using less electricity. They have offered me the opportunity to buy back the panels at anytime witin the 25 years on a reducing balance, if it looks like I am generating enough power I may well take up this option and take the feed in tariff I have 14 panels my roof is just slightly east of south, installers were excellent and the assessor gave me almost to much info, very helpful

ronlizpatsimon

casey17 wrote: »

I have recently used a company called Mark Group apparently nationawide who have installed my panels fro free, I have as yet to receive a bill but looking at the meter during the day I am certainly using less electricity. They have offered me the opportunity to buy back the panels at anytime witin the 25 years on a reducing balance, if it looks like I am generating enough power I may well take up this option and take the feed in tariff I have 14 panels my roof is just slightly east of south, installers were excellent and the assessor gave me almost to much info, very helpful

I shall have to Google your supplier as I have never heard of them and your report reads rather like an advertisment! If I am over suspicious, I,m sorry. Please supply more details such as any survey fees etc. any maintenance charges. What would it cost you to buy back the system after 1 year. I found that "Thinkgreen earth" would install for free (but will try to extract a survey fee of £375 and if you wanted to buy back the system from "Homesun" after 1 year, it would cost you £23K

jackieblack

casey17 wrote: »

I have recently used a company called Mark Group

ronlizpatsimon wrote: »

I shall have to Google your supplier as I have never heard of them

Mark Group are the installers used by several of the big companies selling PV systems.
I bought mine from E-On and they were installed by Mark Group. When their 'surveyor' came he told me alot of the companies they installed for (I can only remember Tesco & M&S off the top of my head) this enabled me to get several quotes from different companies as a result of this one 'survey'.

ronlizpatsimon

jackieblack wrote: »

Mark Group are the installers used by several of the big companies selling PV systems.
I bought mine from E-On and they were installed by Mark Group. When their 'surveyor' came he told me alot of the companies they installed for (I can only remember Tesco & M&S off the top of my head) this enabled me to get several quotes from different companies as a result of this one 'survey'.

Thanks for that Jackie. However; you omitted to answer the questions about set up costs and maintenance and also the buy back cost.

jackieblack

ronlizpatsimon wrote: »

Thanks for that Jackie. However; you omitted to answer the questions about set up costs and maintenance and also the buy back cost.

I didn't answer that part because I don't know. I just know who Mark Group are.
This is a thread about Free Solar Panel Systems, I bought mine last year so my costs were different.


Hopefully casey17 may be able to answer the questions about set up costs, maintenance and also the buy back cost.

grahamc2003

ed1178 wrote: »

In your first point I assume you are refering to the cost benefit of heating water using gas rather than electricity which per kwh is approx 3 times more expensive. You are correct in saying that water heating costs are marginal for a typical household using a gas boiler, the majority of our gas bills are for running the central heating. However the point I was trying to make is that there is still a saving to be made using surpless electricity to heat water. 1kwh or surpless electricity used to heat your tank is 1kwh of gas no longer required. So the saving would be the equivalent price of one unit of gas. Since there is no payment made under rent a roof for exported electricity then why not use as much as possible.

!

Of course if you supply 1kwh of solar energy to your hot water tank, it'll mean you save 1kwh of gas heating.

But if you have spare (exported) generation of just 1kw at any time, and then you turn on you 3kw immersion to use it, then you'll import 2kw of electricity which will cost more than the saving on the gas.

ed1178 wrote: »

On your second point I don't quite see the logic, perhaps you could clarify a little? Any electricity used in place of gas represents a saving. The size of the immersion has nothing to do with it, although it is worth remembering that a 3kw immersion will not function if drastically undersupplied. To repeat my point any electricity used in heating in place of gas represents a saving of the cost of gas that would otherwise have been consumed.

!

This is the ame point as made above. The size of the immersion heater does matter!

Let's add some numbers to the explanation above

While generating sufficient to export 1kw (for which there's no benefit to the homeower with free panels), you turn on your 3kw immersion to use up the spare 1kw. The value is 3p/hr (being the typical cost of 1kwh of gas) However, you'll also be importing 2kw at day rate electricity prices, which will cost you 22p/hr. So you'll be losing out 19p/hr using that strategy (which is often the strategy put forward on these boards) under those conditions.

If you had a 1kw immersion, then you'd neitherlose nor gain under the above conditions.

If you had a 2kw heater, then you'd lose out 8p/hr undre those conditions.

If you had a 500w immersion, then you'd gain 1.5p/hr under the same conditions.

So the size of the immersion does matter.

(Note the above is simplified, as the output from the panels will vary constantly, and the 'background' demand in the home will also vary as things like fridges an irons reach their thermostat threshold).

ed1178 wrote: »

To take your points / questions in turn:

On your question of using 500w in a 3kw immersion, unfortunately this would not work. You might get away with about 80% of its rated output but at very low levels the heating effect of 500w or approx 2 amps through an appliance rated at 3kw or 13 amps would be negligable if not non existent. There is no way to alter the resistance of a heating appliance such as in immersion heater which is what would be required to generate heat. However small, low output immersions are now available which can be inserted through ordinary pipe fittings into cylnders. It should be possible to use a small array of these, each with an output of say 200w, and clever electronics to switch one, two or three etc on depending on the surpless power available at any given moment. The cost of this is likely to far outweigh the benefit however!

!

One thing's for sure - if you could arrange to feed only 500w through a 3kw immersion, it would warm the water at exactly the same rate as a purposely designed 500w immersion heater!

I'm sure it must be possible (but maybe not feasible) to design electronics to work with the impedence of an 3kw immersion to get it to act like a 500w immersion - by varying the frequency parameters for example, or feeding it DC. But even if you could feed into the immersion the varyiing instanteaneous spare solar generation, the extra saving would only be around £33, and that's before any ineffiencies of the electronics were taken into account.

grahamc2003

casey17 wrote: »

I have recently used a company called Mark Group apparently nationawide who have installed my panels fro free, I have as yet to receive a bill but looking at the meter during the day I am certainly using less electricity. They have offered me the opportunity to buy back the panels at anytime witin the 25 years on a reducing balance, if it looks like I am generating enough power I may well take up this option and take the feed in tariff I have 14 panels my roof is just slightly east of south, installers were excellent and the assessor gave me almost to much info, very helpful

Whenever anyone has posted that they have the option to buy the panels in the future, I have always replied asking them the costs of doing so, and I've yet to receive a reply, indicating that the person with the option may not know.

So do you know the costs of buying out yor contract at say 1year, 5 years, 10 years, 20 years?

If you could reproduce the bit of your contract detailing the buyout clause and the buyout cost, it would be very enlightening to many of us.

In fact, imv, it's reasonable for the company to require payment of the current value of the panels, plus the outstanding fits (maybe with a discount representing the early receipt) since if that isn't the case, the company doesnt seem to have a viable business. Of course, this makes any buyout quite expensive if it is the case. Awelocme clausethough since it means thatin the future, if a buyer of your property doesn't want to take on the contract, you can still sell to him after buying out the contract. If there isn't that option, you simply can't sell to any buyer not wanting the panels.