Solar panels

[Itsallaguess]

And I'm assuming a 4kw system is still the maximum permitted for a domestic installation?

I don't think that's ever actually been the case, although there are reasons why it's commonly misunderstood for domestic Solar PV installations -

You can have more than 4kWp -

It’s a very common misconception that domestic Solar PV systems are limited to 4kWp. This myth was driven by two factors. Firstly the tariff used to reduce for installations above 4kWp, not so any more, it’s the same between 0-10kWp and actually goes up for installations over 10kWp. The other is the paperwork when registering installations with the local DNO, they’re the people who maintain the wires that supply your electric. If you’re installing 4kWp or less then it’s a ‘fit and inform’ process. If you want to install more than 4kWp then a pre-application is necessary. The pre-application process involves a lot more work for the installer so many installers have been in the habit of putting customers off the idea of having a larger system.

https://nakedsolar.co.uk/how-much-pv/

Cheers,

Itsallaguess

[Mike4]

And I'm assuming a 4kw system is still the maximum permitted for a domestic installation?

I don't think that's ever actually been the case, although there are reasons why it's commonly misunderstood for domestic Solar PV installations -

You can have more than 4kWp -

It’s a very common misconception that domestic Solar PV systems are limited to 4kWp. This myth was driven by two factors. Firstly the tariff used to reduce for installations above 4kWp, not so any more, it’s the same between 0-10kWp and actually goes up for installations over 10kWp. The other is the paperwork when registering installations with the local DNO, they’re the people who maintain the wires that supply your electric. If you’re installing 4kWp or less then it’s a ‘fit and inform’ process. If you want to install more than 4kWp then a pre-application is necessary. The pre-application process involves a lot more work for the installer so many installers have been in the habit of putting customers off the idea of having a larger system.

https://nakedsolar.co.uk/how-much-pv/

Cheers,

Itsallaguess

For fans here of dimensional analysis puzzled by the introduction of "kWp" as a unit of power, reading the link reveals it is a construct of the solar panel industry. It means kW peak. So it is the same as kW.

It is probably used as consumers might otherwise assume their panel array gives a constant and fixed output all the time. In reality output of solar panels vary widely with daylight, weather conditions and time of day (or night!)

There is a lot of hyperbole about solar panels in the world of boating. The most amusing is the one where owners claim their panels are so 'efficient', they even produce electricity when bathed in moonlight.

[88V8]

..... output of solar panels vary widely with daylight, weather conditions and time of day (or night!)

KWp... a sneaky way of 'notifying' customers that they won't usually get 4KW.

Some years ago the company for which I worked was producing a small pump for wet solar panels... remember those.... and the pump was powered by a solar cell, the idea being that the brighter the light the faster it pumped.

Some tests of the solar cell showed that even the thinnest veil of cloud plumetted the output.
I dare say things have moved on somewhat.

Brief overview here of solar output/light
The standard formula for rating solar panels looks at the amount of power the unit produces in full sunlight at 77F. However, many homeowners in northern latitudes might only reach that optimal standard for solar collection a few days per year.
https://www.ehow.co.uk/list_5783187_solar-panels-low-light_.html

V8

[scrumpyjack]

I had an idle few moments last night so decided to revisit the cost of a rooftop 4kw solar panel array. The first ad that came up = £3900 for a 4kw fully installed and certificated Solar panels and battery systems.

From memory, this is a huge reduction on the cost of a similar installation, say, 10 years ago (and I'm sure there's better than £3900 out there). I'm assuming most of the customer friendly government incentives / tariffs have disappeared though. I'm not looking for anyone to do the research for me, but at first glance, it would seem that solar panels are a better deal now than in the past?

A quick question or 2 though, I take they still buy the excess electricity from you and i it possible for the panels to charge storage heaters or an electric immersion water tank? And I'm assuming a 4kw system is still the maximum permitted for a domestic installation?

Cheers

That is incredibly cheap. Mine cost £11,221 in Nov 2011. I can't complain though as I've more than had the total cost back and carry on getting about £2,400 a year RPI'd until 2036. It was a crazy scheme which simply meant UK consumers were subsidising the build up of the Chinese solar panel manufacturing industry.

[PhaseThree]

I'm currently looking at the same thing, however to reduce costs even further I'm looking to self install.
The price of a 4Kw roof array plus all required fitting etc is around £2500 ex VAT. for all black panels (cheaper for less aesthetic versions)

https://midsummerwholesale.co.uk/
https://easy-pv.co.uk/home

Installation in my case should be relatively easy - I have an easily accessed south facing garage roof, with full electric supply.

[csearle]

There is a lot of hyperbole about solar panels in the world of boating. The most amusing is the one where owners claim their panels are so 'efficient', they even produce electricity when bathed in moonlight.

I take it that electricity would be at the night rate. C.

[servodude]

're the batteries. Are they necessary? I don't have a garage to put them in. Unless they are talking a tesla power wall thing that Ive seen on the sides of houses.

It is that kind of thing they mean nowadays

The batteries not "necessary"

They can help in a few ways from a tech perspective but mainly they are for storing your solar power for later (so you can use it over night or if there was a power outage)

But depending on who your supplier (or regulating body is) is they can also affect any "feed-in" tariff you might get as some schemes want to discourage people feeding-in power from anywhere other than purely solar panels.

The quick over view of a solar with battery scheme would be
The solar panels provide DC electricity (at a very variable output) to charge the battery which provides a more "stable" DC output for an inverter that converts the DC to AC for use in the house or feed-in to the grid

-sd

[scrumpyjack]

I would very much doubt that batteries are economic. The last time I looked at the Tesla Powerwall figures (storing a max of 13.5kw), it was utterly uneconomic in the UK. Cost is 8.5 to 10.5k and lifespan maybe 10 years, so it costs getting on for £1,000 pa. Can't remotely see how you can get that back unless virtually all your panel output would be wasted unless you had a battery system?

[Nocton]

From memory, this is a huge reduction on the cost of a similar installation, say, 10 years ago (and I'm sure there's better than £3900 out there). I'm assuming most of the customer friendly government incentives / tariffs have disappeared though. I'm not looking for anyone to do the research for me, but at first glance, it would seem that solar panels are a better deal now than in the past?

No I don't think that "solar PV panels are a better deal than in the past". We installed ours in 2010 (at a cost of £13,000) and received a FIT payment of 41.3p, now risen to 55.36p in 2020. The IRR is 7.9% depreciating to zero value over 25 years. A better benefit for the environment is to install solar thermal/hot water panels, which we did before the solar PV panels. They transfer about 75% of the sun's energy to the hot water, far more efficient than PV panels. Our two panels can easily heat our 225L tank to 75C in a few hours of decent sunshine at temperatures up to 80C. Of course, we do not get a generous subsidy like the FIT payments.

However, now that the benefit from solar PV panels is much less, I should think that solar thermal panels are financially sensible too.

We installed a 4.5kwh battery last year at a cost of £5,000. It is correct that as a financial investment it is not great, although better than money sitting in a simple bank/BS deposit account.

One cost to think about, especially if you plan to do it yourself, is the cost of the scaffolding to access the roof. Some of the prices quoted below seem to me to be only relevant when fitting to a new house. And remember also, a professional electrician will still be needed to certify the system and get it registered to allow export to the grid, which they may be reluctant to do if they have not installed the system.

[Mike4]

I would very much doubt that batteries are economic. The last time I looked at the Tesla Powerwall figures (storing a max of 13.5kw), it was utterly uneconomic in the UK. Cost is 8.5 to 10.5k and lifespan maybe 10 years, so it costs getting on for £1,000 pa. Can't remotely see how you can get that back unless virtually all your panel output would be wasted unless you had a battery system?

I think it has to be like that, or demand for the Powerwall would go through the roof and threaten the electric car 'revolution'. The lithium needed to make the LiFePO4 batteries is, AIUI, a precious and limited resource most effectively used for reducing carbon emissions from fossil fuels burned in cars.

If Powerwalls soaked up a big proportion of our lithium mining production, they would partly be replacing electricity already generated by wind and solar.

[swill453]

I would very much doubt that batteries are economic. The last time I looked at the Tesla Powerwall figures (storing a max of 13.5kw), it was utterly uneconomic in the UK. Cost is 8.5 to 10.5k and lifespan maybe 10 years, so it costs getting on for £1,000 pa. Can't remotely see how you can get that back unless virtually all your panel output would be wasted unless you had a battery system?

I think it has to be like that, or demand for the Powerwall would go through the roof and threaten the electric car 'revolution'. The lithium needed to make the LiFePO4 batteries is, AIUI, a precious and limited resource most effectively used for reducing carbon emissions from fossil fuels burned in cars.

If Powerwalls soaked up a big proportion of our lithium mining production, they would partly be replacing electricity already generated by wind and solar.

The way I see it, if PV solar panels and batteries made economic sense at a household level, then economies of scale would mean it would make even more sense for the power companies to build massive installations of them.

The fact that in general they don't (on a countrywide scale), tells me there's a lot of smoke and mirrors around, and without subsidies we wouldn't be doing any of it.

Scott.

[Mike4]

I would very much doubt that batteries are economic. The last time I looked at the Tesla Powerwall figures (storing a max of 13.5kw), it was utterly uneconomic in the UK. Cost is 8.5 to 10.5k and lifespan maybe 10 years, so it costs getting on for £1,000 pa. Can't remotely see how you can get that back unless virtually all your panel output would be wasted unless you had a battery system?

I think it has to be like that, or demand for the Powerwall would go through the roof and threaten the electric car 'revolution'. The lithium needed to make the LiFePO4 batteries is, AIUI, a precious and limited resource most effectively used for reducing carbon emissions from fossil fuels burned in cars.

If Powerwalls soaked up a big proportion of our lithium mining production, they would partly be replacing electricity already generated by wind and solar.

The way I see it, if PV solar panels and batteries made economic sense at a household level, then economies of scale would mean it would make even more sense for the power companies to build massive installations of them.

The fact that in general they don't (on a countrywide scale), tells me there's a lot of smoke and mirrors around, and without subsidies we wouldn't be doing any of it.

Scott.

It's a shame the way money clouds the issue. No we would not be doing any of it without subsidies, but the reason for the subsidies is to reduce carbon emissions, not save people money.

Lithium is also AIUI, a limited resource and even if it cost peanuts to mine, there just isn't that much of it in the ground so we need to use what we can get out, wisely.

[88V8]

I would very much doubt that batteries are economic. The last time I looked at the Tesla Powerwall figures (storing a max of 13.5kw), it was utterly uneconomic in the UK. Cost is 8.5 to 10.5k and lifespan maybe 10 years, so it costs getting on for £1,000 pa.

It might make sense if one is off-grid. But money-wise, it's worse than that:
The £8.5/10.5k can be invested at, say, 5% so one is foregoing an income of c£500 pa, which has to be recovered before one can talk about 'saving money'.

It's a basic principle that capital expenditure for the purpose of 'saving money' has to take into account the foregone income aka the Opportunity Cost.
A basic principle that salesmen don't want one to think about

V8

[PhaseThree]

One cost to think about, especially if you plan to do it yourself, is the cost of the scaffolding to access the roof. Some of the prices quoted below seem to me to be only relevant when fitting to a new house. And remember also, a professional electrician will still be needed to certify the system and get it registered to allow export to the grid, which they may be reluctant to do if they have not installed the system.

For a single story roof the hire cost for a suitable scaffold tower is around £80/day. You shouldn't need it for any longer.
The prices I quoted above are for a full fitting kit for an existing roof (panels, inverter, mounting components, isolators etc).

The certification requirements will depend on where in the UK you live and what type of connection you require.
Certified MCS installation is only required if you want to be paid for export via the SEG export tariff (~£80/yr) but will up your installation costs by ~£1500 - £2000.

There is no Part-P electrical regulation in Scotland or Northern Ireland. There is no form of export tariff in Northern Ireland.
Living in Northern Ireland the only way PV is cost effective is via self install. I would suggest the same is true in the rest of the UK given that a realistic fault free lifetime of a PV system is 10-15 years (most inverters seem to fail around this point).

[servodude]

I think it has to be like that, or demand for the Powerwall would go through the roof and threaten the electric car 'revolution'. The lithium needed to make the LiFePO4 batteries is, AIUI, a precious and limited resource most effectively used for reducing carbon emissions from fossil fuels burned in cars.

If Powerwalls soaked up a big proportion of our lithium mining production, they would partly be replacing electricity already generated by wind and solar.

The way I see it, if PV solar panels and batteries made economic sense at a household level, then economies of scale would mean it would make even more sense for the power companies to build massive installations of them.

The fact that in general they don't (on a countrywide scale), tells me there's a lot of smoke and mirrors around, and without subsidies we wouldn't be doing any of it.

Scott.

It's a shame the way money clouds the issue. No we would not be doing any of it without subsidies, but the reason for the subsidies is to reduce carbon emissions, not save people money.

Lithium is also AIUI, a limited resource and even if it cost peanuts to mine, there just isn't that much of it in the ground so we need to use what we can get out, wisely.

Funny how this stuff changes based on how the markets are controlled (or skewed or not)!

From an engineering perspective having local storage makes a lot of sense
- it's like putting bucket caps at heavy output points of your electrical circuit; they smooth the load on your supply (or more correctly distribute it)
- if everyone had a wall battery there's no "EastEnders surge" in the grid, and no risk it causes a problem
- that surge handing is an inconvenience in the UK and a major problem in some other places in the world

Reducing the instantaneous load and increasing the robustness of the delivery grid benefits EVERYONE (even if you're off grid your emergency services aren't!)
- but as we can see from the figures put about there's a real disincentive for people to join in


-sd

[PhaseThree]

Funny how this stuff changes based on how the markets are controlled (or skewed or not)!

From an engineering perspective having local storage makes a lot of sense
- it's like putting bucket caps at heavy output points of your electrical circuit; they smooth the load on your supply (or more correctly distribute it)
- if everyone had a wall battery there's no "EastEnders surge" in the grid, and no risk it causes a problem
- that surge handing is an inconvenience in the UK and a major problem in some other places in the world

Reducing the instantaneous load and increasing the robustness of the delivery grid benefits EVERYONE (even if you're off grid your emergency services aren't!)
- but as we can see from the figures put about there's a real disincentive for people to join in
-sd

Five years ago there was a big push in the automotive industry to enable the the batteries in electric cars to be used as buffer batteries for the electricity supply. The argument being that having a (big) battery in you car that was sat doing nothing while you charged and discharged a separate battery for you home supply made little sense. This would have required the Electricity operator to "borrow" the energy when needed (Usually at EastEnder's time) and replace it overnight when there was spare capacity.
This idea seems to have hit the "too hard to deal with" barrier as well as concerns about consumer acceptance, but it's time may yet come.

[servodude]

This idea seems to have hit the "too hard to deal with" barrier as well as concerns about consumer acceptance, but it's time may yet come.

I can see why there would be push back as it makes charging off a normal supply tricky (which would be a big impediment to uptake)

Throughout the world there's a lot of sparse distribution networks for power that were put in a long time ago and only just capable of delivering peak (or close to peak) load
- just look at how much has been thrown at "automated demand response" in places like California as a result (huge subsidies for allowing your power to be cut when needed!)
Changing/expanding infrastructure to cope with the inevitable demands isn't a vote winner (because it works on much longer time scales) and ultimately you can only make the wires so thick!
So I do expect home storage to end up being widely subsidized in areas that can't upgrade the supply network to places as quickly as they can build houses (with electric heating and AC demands) in them - even without on site generation.

-sd

[9873210]

The quick over view of a solar with battery scheme would be
The solar panels provide DC electricity (at a very variable output) to charge the battery which provides a more "stable" DC output for an inverter that converts the DC to AC for use in the house or feed-in to the grid

-sd

While it can be done that way I think on most installation the PV would have a dedicated inverter that produces a stable AC mains voltage and the battery would have a dedicated inverter/rectifier connected to the AC mains and charging/discharging the battery.

Using a single DC-DC converter between PV and the batteries requires that inverter to "know" the properties of both the PV and the batteries. Using AC mains as an intermediate allows for greater modularity, such as mixing brands, changing to a different battery chemistry / configuration, or adding a generator for emergency emergency backup.

The configuration you suggest is slightly more efficient using stored solar power while having the systems separate is more efficient using solar power at the time of production. Which is more important depends on usage patterns and is hard to predict (particularly as this depends on choices of the user such as when they run the dishwasher, water heater, etc. which in turn can depend on the type of system installed.)
.

[servodude]

The quick over view of a solar with battery scheme would be
The solar panels provide DC electricity (at a very variable output) to charge the battery which provides a more "stable" DC output for an inverter that converts the DC to AC for use in the house or feed-in to the grid

-sd

While it can be done that way I think on most installation the PV would have a dedicated inverter that produces a stable AC mains voltage and the battery would have a dedicated inverter/rectifier connected to the AC mains and charging/discharging the battery.

Using a single DC-DC converter between PV and the batteries requires that inverter to "know" the properties of both the PV and the batteries. Using AC mains as an intermediate allows for greater modularity, such as mixing brands, changing to a different battery chemistry / configuration, or adding a generator for emergency emergency backup.

The configuration you suggest is slightly more efficient using stored solar power while having the systems separate is more efficient using solar power at the time of production. Which is more important depends on usage patterns and is hard to predict (particularly as this depends on choices of the user such as when they run the dishwasher, water heater, etc. which in turn can depend on the type of system installed.)
.

Indeed! ....but I didn't want to confuse the guy who was asking if he needed a battery

[roger4]

The only advantage of having batteries is to ensure continuity of supply. If you live in an area where the mains power supply is variable or unreliable, batteries mean you can continue your life style. The big drawback is their inefficiency. Over time, batteries become less efficient. The type of battery also has a bearing. For example lead acid type batteries can only be used down to 30% of capacity whereas Lithium-ion batteries can be used down to 5% of capacity. (Round numbers only)

Roger