Run house off batteries during the day, no solar.

[colin247]

Get your units right first and that might help.

Energy is measured in Joules (becomes relevant later). One Watt (capital because it was named after someone) is defined as one Joule per second (again capital for the same reason). Kilowatt (kW) means 1000 Watts or 1000 Joules per second.

This only tells you the rate at which you are using energy not how much you have used. To know that you need a time frame. Hence kWh (kilo Watts per hour).

An example, it takes 330kJ of energy to boil one litre of water. Therefore if you had a 330kW kettle you could boil 1 litre in a second. Realistically you don't so a kettle is say 2kW. This would then take 330/2 or 165 seconds to boil the water, 2 minutes 45.

Now to work out how much electricity you've used in conventional units you need to convert them to the same units. We've used 2kW for 2m45 so that's 2x(2.75/60) = ~0.1kWh (note we have to divide runtime in minutes by 60 to get it to hours).

Battery capacity tends to be quoted in either kWh or Ah. So a 30kWh battery can supply 30kW for one hour or equivalent. So 15kW for 2 hours and so on. Note depending on the design of the battery it might not be able to deliver 30kW, it might be limited to a maximum output of say 2kW in which case you can max it out for 15h.

Using your example of a 30kWh battery over 24h then it would be capable of delivering a continuous 1.25kW for 24h. If you only had 100W load for part of the day then you can draw more at other periods.
If you think of it in terms of a graph with kW on the y axis and time on the x axis then the area under the graph can't exceed 30kWh.

If the battery capacity in Ah then you need to know the nominal voltage because Voltage x Current = Power (V x A = W) to get the capacity.

Bear in mind that an inverter won't be 100% efficient so you lose some power there.

When you get into the nitty gritty you need to start looking at graphs rather than "figures" as the capacity isn't linear with voltage etc., so to get a more accurate picture you have to start working it out for different profiles etc (adding areas under graphs or integrating).

Very interesting, thanks for posting.

 

[Milkybars]

@Gareth J Given his usage during the day as outlined its futile to go MCS, there is no spare capacity to be sold to grid !!

Any over generation can go to the battery to be used as when required

 

[gaz1]

now roger can insulate between the windows and lift the whole lot from the floor

using a mix of tech

light guage steel truss

with stage truss lifting ability

 

[Gareth J]

@Gareth J Given his usage during the day as outlined its futile to go MCS, there is no spare capacity to be sold to grid !!

Any over generation can go to the battery to be used as when required

If you can get an export tariff, potentially without MCS via octopus, it more or less makes batteries futile. That's why I'm mentioning it.

Regarding over generation, it's always the way with PV, there's always over generation.

 

[GRW]

Get your units right first and that might help.

Energy is measured in Joules (becomes relevant later). One Watt (capital because it was named after someone) is defined as one Joule per second (again capital for the same reason). Kilowatt (kW) means 1000 Watts or 1000 Joules per second.

This only tells you the rate at which you are using energy not how much you have used. To know that you need a time frame. Hence kWh (kilo Watts per hour).

An example, it takes 330kJ of energy to boil one litre of water. Therefore if you had a 330kW kettle you could boil 1 litre in a second. Realistically you don't so a kettle is say 2kW. This would then take 330/2 or 165 seconds to boil the water, 2 minutes 45.

Now to work out how much electricity you've used in conventional units you need to convert them to the same units. We've used 2kW for 2m45 so that's 2x(2.75/60) = ~0.1kWh (note we have to divide runtime in minutes by 60 to get it to hours).

Battery capacity tends to be quoted in either kWh or Ah. So a 30kWh battery can supply 30kW for one hour or equivalent. So 15kW for 2 hours and so on. Note depending on the design of the battery it might not be able to deliver 30kW, it might be limited to a maximum output of say 2kW in which case you can max it out for 15h.

Using your example of a 30kWh battery over 24h then it would be capable of delivering a continuous 1.25kW for 24h. If you only had 100W load for part of the day then you can draw more at other periods.
If you think of it in terms of a graph with kW on the y axis and time on the x axis then the area under the graph can't exceed 30kWh.

If the battery capacity in Ah then you need to know the nominal voltage because Voltage x Current = Power (V x A = W) to get the capacity.

Bear in mind that an inverter won't be 100% efficient so you lose some power there.

When you get into the nitty gritty you need to start looking at graphs rather than "figures" as the capacity isn't linear with voltage etc., so to get a more accurate picture you have to start working it out for different profiles etc (adding areas under graphs or integrating).

There's also the DoD (Depth of Discharge) batteries can stand (they like to state their 100% to Nil capacity as it sounds good, but in reality isn't usable unless you want to kill them asap).
60% is about the maximum (for lead-acid for sure, while I don't think Lithium is much different).
Then there's the manner in which they established the capacity rating.... e.g. a C20 battery was measured over a 20-hour discharge, where a C5 battery over 5-hours. Given that a battery is able to sustain smaller loads over longer periods far better than vice-versa, then a C5 battery is actually more powerful than a C20 unit (despite the same nominal AH rating).
To be on the safe side, then whatever capacity in AH you work out that you need.... you need to double that to actually a battery pack to deliver it.

The way that sellers are able to state output & capacity ratings that are nowhere near real-world conditions or capability is IMO highly misleading, and very confusing to the lay-person.

 

[RaceDiagnostics]

Doesn't seem to make much sense for me. Last year I used 2000kwh of electricity. Lets say that cost me £500, at 25p per kWh.

If I could run off of batteries charged at 7p and an overall efficiency of 80%, it would cost 2000*0.07/.8 = £175.

Most of our electric is used for cooking using an induction hob and ovens so I'd need a battery/inverter capable of a high peak load say 7kw, that means expensive, say £10k (that's a bit of a guess, if anyone knows better let me know a link).

So a saving of £325 per year would take 30 years to pay back, and the battery would never last that long.

Seems pointless, have I got that wrong? Even if the electric was free it wouldn't make sense.

 

[drjim]

We use nearly 8000Kwh, even the small scale shed solar I have set up is worth it. Plus excess solar heats the water tank so we hardly use any gas in the summer if the sun shines.

I'm looking to get the biggest inverter I can and at least 6Kw of panels in the next month or two.

 

[Gareth J]

I'm looking to get the biggest inverter I can and at least 6Kw of panels in the next month or two.

You can have multiple inverters on the same phase/s if you exceed the size of standard inverters. Although they do come pretty big nowadays, certainly exceeding 6kw single phase and loads more 3phase.

 

[drjim]

I am planning to get the panels on the roof myself, then get an installed battery package from ITS. The loss of VAT on the price offsets the cost of the electrical work, plus it gets an MCS ticket. If I can buy the panels from ITS all as zero VAT then that's good, or city plumbing are still almost unbeatable on price for kit if you aren't in zero vat MCS install scenarios. I think 6Kw of panels with mounts came to 1200 plus VAT or really nothing in the overall scheme of things.

Compare to the quote I got from a reputable company of £8k to install panels and string inverter plus £10k to add battery. Yes they were pushing solaredge and optimisers but if you pay next to nothing, a slightly decreased performance means nothing. I am aiming at around 6k all in for inverter 10Kwh battery and a 5 or 8kW inverter.

I also have a Scout hut that I was quoted £27000 to put 12Kw panels and a three phase inverter on - again solaredge. That is about £4.5k of kit if you omit solaredge and the installers Range Rover finance payments. Easy single story access and new 3 phase box with a big empty wall to mount kit on. As long as I can get an MCS sparky to install it should make £1k per year profit and thus pay for itself in 5 years.

 

[jmp49]

Actually coming up with a "system", in detail, i think is my biggest stumbling block. I just cant my head around it. The principles are fine, its just coming up with what components and how to tie them together. Im also not keen on lots of complicated electronics. I understand simple domestic electrics. I dont understand electronics. These will only go wrong at some point, so need to be kept to a minimum. Jmp49, comments were extremely useful, but when it got to the monitoring side, that lost me completely. Absolutely no idea what most of that meant. Im sure its very clever, but unless i understand it, i wont install it. Whatever gets done, i need to be able to understand it and fix it when it fails. Getting anyone specialist & competent to come out here is borderline impossible. Ive been trying to get someone to come and quote for some roof repairs for over a year with no success!

You dont need the monitoring side if your not planning on doing anything fancy like using the realtime generation numbers to align the panels, or automatically switch loads on to consume the excess when its present automatically. The whole automation side has become a bit of a hobby in itself for me rather than a turn key solution that I dont need to understand but until we got all the metering and automatic switching in place, my mrs used to just look at the amount of sun, then check the quantity of power either being drawn from the grid or a -ve number if it fed back in the electricity metering thing (shelly pro3-em) we installed at point of entry, and start the washing machine etc up manually.

Also hoymiles offer to feed the panel monitoring data into their own cloud software if you buy a extra box to let the inverters talk to the internet, and then you browse it in their cloud with a web browser, but I value my privacy vs a chinese black box device so I went the local network only diy route (which is why it seems so complicated, but also why I can make it do more complex stuff).

 

[Roger440]

Doesn't seem to make much sense for me. Last year I used 2000kwh of electricity. Lets say that cost me £500, at 25p per kWh.

If I could run off of batteries charged at 7p and an overall efficiency of 80%, it would cost 2000*0.07/.8 = £175.

Most of our electric is used for cooking using an induction hob and ovens so I'd need a battery/inverter capable of a high peak load say 7kw, that means expensive, say £10k (that's a bit of a guess, if anyone knows better let me know a link).

So a saving of £325 per year would take 30 years to pay back, and the battery would never last that long.

Seems pointless, have I got that wrong? Even if the electric was free it wouldn't make sense.

No. not wrong. But im using 6 times more energy than you, likly to be 8 times soon. Changes the numbers.

 

[jmp49]

Here's the box (DTU, aka a data terminal unit) to let the panel inverters talk wireless radio out to the internet (I dont have this, I made my own with arduino's...) https://www.hoymiles.com/us/product/dtu-w100-g100/

Once you have their dtu, you can use hoymiles cloud software. I've never used it to comment more, but it claims to be easy to use and setup.

S-Miles Cloud - Hoymiles Power Electronics Inc.

global.hoymiles.com

I get all the same info wtihout sending it off my local lan and use it to make decisions in realtime, that's the extra bit of capability I have.
I think most micro inverter manufacturers will have a analog of this in their line up, they dont expect customers to be soldering arduino's up and making complex configurations like I did.

 

[Roger440]

If you can get an export tariff, potentially without MCS via octopus, it more or less makes batteries futile. That's why I'm mentioning it.

Regarding over generation, it's always the way with PV, there's always over generation.

This is an interesting take on it. Maybe not futuile, but it would certainly massively extend the payback period though.

My understanding at the moment is that its not currently available. Cleary the MCS union is pushing hard to prevent the break up of their cash printing monopoly. Id like to think their stranglehold will be broken, but i cant wait forever, and at some point need to make a decision.

 

[Roger440]

Here's the box (DTU, aka a data terminal unit) to let the panel inverters talk wireless radio out to the internet (I dont have this, I made my own with arduino's...) https://www.hoymiles.com/us/product/dtu-w100-g100/

Once you have their dtu, you can use hoymiles cloud software. I've never used it to comment more, but it claims to be easy to use and setup.

S-Miles Cloud - Hoymiles Power Electronics Inc.

global.hoymiles.com

I get all the same info wtihout sending it off my local lan and use it to make decisions in realtime, that's the extra bit of capability I have.
I think most micro inverter manufacturers will have a analog of this in their line up, they dont expect customers to be soldering arduino's up and making complex configurations like I did.

I appreciate you posts, but this is straight over my head.

The first link says:

Hoymiles gateway DTU- W100/G100 is a data transfer unit which collects information and data of PV microinverter using 2.4G wireless solution and sends them to S-Miles Cloud, Hoymiles
Monitoring Platform via Wi-Fi or GPRS communication.
This model is small and easy to install, a suitable option for residential PV systems. Users can easily read module-level data and alarm, realize remote operation and maintenance of PV
system at anytime from anywhere on S-Miles Cloud.

It might as well be written in chinese, sadly. This is my struggle with some of it.

 

[drjim]

The whole MCS thing is a massive scam really. My electrician has done the courses but isn't keen on paying the annual fees unless he has loads of work lined up to pay for it.

 

[Roger440]

Look into the requirements Octopus are currently saying they need to get non MCS installation allowed. They were advertising that they were going to/do accept but I don't know if it got off the ground or if it's realistically doable. But if you can get paid to export, it makes the investment to earn from every kWh you produce much easier.

3x dehumidifiers.... Really? Is your workshop a hanger? Maybe a few cans of expanding foam to seal some gaps could let you cut down on the dehumidifier habit...?

What Gaz1 posted!

Ive sealed it all up. I guess it could be classed as "big".

Unless i insulate the roof and the roller door, de-humidifiers are unavoidable. I wont live long enough to break even on the roof from saved energy.

 

[Roger440]

The whole MCS thing is a massive scam really. My electrician has done the courses but isn't keen on paying the annual fees unless he has loads of work lined up to pay for it.

Exactly that. One huge scam. Theres a small number of people getting very rich at everone elses expense. Bit of thread drift though.........

 

[drjim]

Roger you can just buy something like this...

Multiple 6.0Kw Pv Pack - 14X Longi 430W + Sunsynk 5.32Kwh Storage + Fastensol Mounting PVK023

Complete Solar PV pack comprising 14 x LR5-54HTB-430M Longi 430W panels, Sunsynk 5K-SG01LP1 Hybrid inverter with 5.32Kwh battery storage. Fastensol mounting system with mounting rails, Pantile roof hooks, universal mid / end clamps and bird guard. Electrical accessory pack with AC and DC...

www.cityplumbing.co.uk

Install yourself do a G99 application yourself, and it all just works. Use manufacturers monitoring and you are done. I have 2400w panels on a shed with a Growatt 2Kw inverter from ebay which has done 1050Kwh so far for a cost of about £500 including buying lots of electrical bits to connect up. Then I have 2Kw of second hand panels I got for £100 with a £60 new old stoick inverter for £60. Mounted using wood on the roof of pent sheds in valley between houses, that's done 450Kwh since I built it last spring/summer. It has basically paid for itself in electric. Gas savings from a Solic 200 cheap as chips immersion diverter means I am probably ahead of costs already.

 

[drjim]

And although I have noformal qualifications either I'd be happy to help you with it, the electrics are very simple once you have it figured.

 

[jmp49]

As DrJim says, jfdi and use the manufacturers monitoring that goes with your inverter. I have done it the complex diy way, you dont have to take this route.
The 3Kw kit I put in has yielded 1500Kwh to date in about a year according to my logs. Thats 1500Kwh I didnt have to buy as I auto (self) consumed 98% of it so at 22p Kw/h that's 300 quid saved in one year. So 3 years with a bit more tweaking it will have paid for itself outright. Thats better return than putting the money in the bank and then its all profit.