Gas combi v electric combi = 3.75kw solar being instaled

Pincher

The most recent power outage was one or two year ago. Only four houses affected. Transco came with mechanical digger and worked throughout the night. Dug up the pavement, and we got our power back some time over night. It wasn't cold.

I just like to have backups. Obviouly I already have candles and lighter. Battery lights. Gas heater with two Calorgas bottles (always sold out when I need it). Electric heaters are for boiler failure.

So which inverter is good with which batteries?
Off grid use, of course.

rogerblack

energysavingexp wrote: »

if it is a grid connected inverter then if you are producing 1kwh with an 3kw heater then you will be using 2kwh from the grid.
it cannot be grid connected and off grid at the same time

In principle it can be, but it'd need an extra bit of kit.
This would be a 'dimmer' that the immersion heater is plugged into, which then has a sensor in the meter cupboard, to turn it up if there is any energy going into the grid.

energysavingexp

rogerblack wrote: »

In principle it can be, but it'd need an extra bit of kit.
This would be a 'dimmer' that the immersion heater is plugged into, which then has a sensor in the meter cupboard, to turn it up if there is any energy going into the grid.

please explain the dimmer controler/sensor in the meter cupboard
and how this knows when there is any energy going into the grid
how will this work?

as for the inverter please tell me how it can be both off grid and on grid at the same time

if the dimmer system works why whould you need to go off grid

im very intrested to know more about it

energysavingexp

Pincher wrote: »

So which inverter is good with which batteries?
Off grid use, of course.

you can buy any leasure batterys mine are 2x 80amp
my inverter bought from maplin is just a standard 240v 1kwh

inverter
http://www.maplin.co.uk/merlin-m-power-sine-wave-dc-ac-inverters-511237?ordercode=N13JT
battery
http://www.amazon.co.uk/dp/B003U3Z5ZE/ref=asc_df_B003U3Z5ZE5099732?smid=A32RCGBURXVV39&!!!!!googlecouk06-21&linkCode=asn&creative=22218&creativeASIN=B003U3Z5ZE

hope this helps

chris1973

An 140 litre Electric Boiler, the type with CH demand is rated at anything upto 14KW, to be honest even at full power a 3.75KW Solar panel isn't going to make much of a dent, considering the 10KW difference would be costing you at least 80P an hour on E10 rates (8p KW/H) or £1.30 (13p KW/H) an hour on a decent standard tariff- in order to take advantage of the solar input inevitably you'd be using the boiler during the day, with daytime / peak electricity rates making up the difference.

I'm not even sure how you'd split up the load safely, a typical boiler has an element array consuming the full 14KW load, its not like it has two elements - one rated at 3.75KW and another at 10KW to easily enable one to be connected to the solar panel and one to the mains, its the the full 14KW load or nothing.

you can buy any leasure batterys mine are 2x 80amp

The usefulness of this depends on what load you are drawing off it. A 3KW load through an invertor running from a 12v battery pack will draw 250 Amps of load from the batteries, probably slightly more as an inverter is not 100% efficient at turning input voltage into output voltage, so losses from heat and control circuitry / fans will also apply (even on a SMPS design). 250 Amps, to put into prospective, is around the current draw of a petrol engined car starter motor cranking on a cold morning.

Now if you've ever had a car which has failed to start, you'll know how soon the battery will go flat from costantly turning over the engine, even in intermittant bursts at getting it to start. How long do you think two leisure batteries will supply 250 Amps for before they drop low enough to trigger the low voltage cut-off on an invertor?, lets work it out

Your example of 160AH (2x 80AH) of available capacity will be flat in a few minutes with a connected 3KW immersion element, certainly not enough to heat a tank of hot water and probably just enough to boil a 2.4KW kettle.

Even with a larger (more expensive) battery pack capacity its touch and go for how long large connected loads will run for. Lets assume that you are using a battery pack rated at 300AH, running a 3KW load through an Inverter will flatten the batteries in around 0.5 hours - in other words 30 minutes, before the batteries require a full charge.

A 2KW load run from the same 300AH supply will flatten in around 0.75 hours - or 45 minutes.

30 - 45 minutes might be enough to heat a useful amount of water in a small well insulated tank, I find my 80 litre tank heats to around 55c using a 3KW element in just over 1 hour before the water reaches the shut off temperature. To get 1 hours worth of Free Electricity from a battery / Inverter combination charged from Solar - you'd need supply batteries of at least 600AH of capacity - for example - (9 x) 12v 70AH deep cycle batteries. I'd also advise a decent brand of deep cycle battery for this type of application, certainly with large loads being drawn off in relatively short periods of time, so budget £80 - £100 per battery. So there is upto £900 outlay just on batteries alone, to produce the 600AH required to run a 3KW immersion in the given example.

You can check the math by using this handy calculator located on the link below, where you can enter in the intended AH capability of your supply pack, the load of the connected appliance(s) and it will output how long it will reasonably power the appliance for, before the batteries are flat and they require a full recharge - in other words, its useful life 'per charge'

http://www.donrowe.com/inverters/inverter_faq.html#how_long

This all sounds reasonable so far until you put it into some prospective. The same £900 (which you would spend on the example battery pack) buys you 18,000 Economy 7 units when sold at 5p per KW/H which will equal 6000 days worth of hot water, if you only run the 3KW immersion for the same 1 hour period every morning on an E7 tariff to heat the tank- 6000 days is effectively 16 years - how many £900 battery packs would you have replaced in that time?.

And dont forget you have to factor in the cost of the Inverter as well, which for 3KW would cost £489 - equal to another 9780x E7 Electricity Units

http://www.sunshinesolar.co.uk/khxc/gbu0-prodshow/VP3000.html?gclid=CMuZ0NLXnawCFQEd4Qodkj9F_w



These figures also assume a good quality supply made up of healthy batteries with cells in peak condition, and as most people have found with mobile phones etc, batteries do age and their capacity does reduce noticably with that aging process, and where loads are high even a medium amount of aging, may reduce the load time noticeably.

Yes, charging batteries from "Free" Energy sources and then using Inverters to power domestic appliances off them during the Evening etc, is a good idea and yes potentially it will save money. However even thinking of running heating loads off it, certainly above 2kw - 3kw , is pretty much a non starter, unless you only want heat for a very short time, obviously these batteries are not cheap and outlay to get started is pretty significant and so should be factored in against effectively the 30 - 45 minutes of 'free' heat saving compared to buying it from the mains, which at 13p / KWH tariff would cost effectively 26p per hour with a 2KW load, or 10p an hour on a decent E7 Tariff.

energysavingexp

chris1973 wrote: »

An 140 litre Electric Boiler, the type with CH demand is rated at anything upto 14KW, to be honest even at full power a 3.75KW Solar panel isn't going to make much of a dent, considering the 10KW difference would be costing you at least 80P an hour on E10 rates (8p KW/H) or £1.30 (13p KW/H) an hour on a decent standard tariff- in order to take advantage of the solar input inevitably you'd be using the boiler during the day, with daytime / peak electricity rates making up the difference.

I'm not even sure how you'd split up the load safely, a typical boiler has an element array consuming the full 14KW load, its not like it has two elements - one rated at 3.75KW and another at 10KW to easily enable one to be connected to the solar panel and one to the mains, its the the full 14KW load or nothing.

The usefulness of this depends on what load you are drawing off it. A 3KW load through an invertor running from a 12v battery pack will draw 250 Amps of load from the batteries, probably slightly more as an inverter is not 100% efficient at turning input voltage into output voltage, so losses from heat and control circuitry / fans will also apply (even on a SMPS design). 250 Amps, to put into prospective, is around the current draw of a petrol engined car starter motor cranking on a cold morning.

Now if you've ever had a car which has failed to start, you'll know how soon the battery will go flat from costantly turning over the engine, even in intermittant bursts at getting it to start. How long do you think two leisure batteries will supply 250 Amps for before they drop low enough to trigger the low voltage cut-off on an invertor?, lets work it out

Your example of 160AH (2x 80AH) of available capacity will be flat in a few minutes with a connected 3KW immersion element, certainly not enough to heat a tank of hot water and probably just enough to boil a 2.4KW kettle.

Even with a larger (more expensive) battery pack capacity its touch and go for how long large connected loads will run for. Lets assume that you are using a battery pack rated at 300AH, running a 3KW load through an Inverter will flatten the batteries in around 0.5 hours - in other words 30 minutes, before the batteries require a full charge.

A 2KW load run from the same 300AH supply will flatten in around 0.75 hours - or 45 minutes.

30 - 45 minutes might be enough to heat a useful amount of water in a small well insulated tank, I find my 80 litre tank heats to around 55c using a 3KW element in just over 1 hour before the water reaches the shut off temperature. To get 1 hours worth of Free Electricity from a battery / Inverter combination charged from Solar - you'd need supply batteries of at least 600AH of capacity - for example - (9 x) 12v 70AH deep cycle batteries. I'd also advise a decent brand of deep cycle battery for this type of application, certainly with large loads being drawn off in relatively short periods of time, so budget £80 - £100 per battery. So there is upto £900 outlay just on batteries alone, to produce the 600AH required to run a 3KW immersion in the given example.

You can check the math by using this handy calculator located on the link below, where you can enter in the intended AH capability of your supply pack, the load of the connected appliance(s) and it will output how long it will reasonably power the appliance for, before the batteries are flat and they require a full recharge - in other words, its useful life 'per charge'

http://www.donrowe.com/inverters/inverter_faq.html#how_long

This all sounds reasonable so far until you put it into some prospective. The same £900 (which you would spend on the example battery pack) buys you 18,000 Economy 7 units when sold at 5p per KW/H which will equal 6000 days worth of hot water, if you only run the 3KW immersion for the same 1 hour period every morning on an E7 tariff to heat the tank- 6000 days is effectively 16 years - how many £900 battery packs would you have replaced in that time?.

And dont forget you have to factor in the cost of the Inverter as well, which for 3KW would cost £489 - equal to another 9780x E7 Electricity Units

http://www.sunshinesolar.co.uk/khxc/gbu0-prodshow/VP3000.html?gclid=CMuZ0NLXnawCFQEd4Qodkj9F_w



These figures also assume a good quality supply made up of healthy batteries with cells in peak condition, and as most people have found with mobile phones etc, batteries do age and their capacity does reduce noticably with that aging process, and where loads are high even a medium amount of aging, may reduce the load time noticeably.

Yes, charging batteries from "Free" Energy sources and then using Inverters to power domestic appliances off them during the Evening etc, is a good idea and yes potentially it will save money. However even thinking of running heating loads off it, certainly above 2kw - 3kw , is pretty much a non starter, unless you only want heat for a very short time, obviously these batteries are not cheap and outlay to get started is pretty significant and so should be factored in against effectively the 30 - 45 minutes of 'free' heat saving compared to buying it from the mains, which at 13p / KWH tariff would cost effectively 26p per hour with a 2KW load, or 10p an hour on a decent E7 Tariff.

i think you missunderstand my point.

i was sugesting using batterys and inverter to run the electrics on a gas boiler this amount of electric is only a small amount less than 300watts to run the pump gas valve and circuit board

chris1973

i was sugesting using batterys and inverter to run the electrics on a gas boiler this amount of electric is only a small amount less than 300watts to run the pump gas valve and circuit board

Its much less than 300W. A Fan in a combi boiler uses around 22 Watts, a CH Pump uses around 80W and the Ignitor uses 5W

Non of these run continuously either, the CH pump is controlled by the wall stat, so that it only circulates water to the radiators when the temperature drops, in most boilers the fan runs when the jets are lit and the ignitor operates for milli-seconds to light the jets.

Taking the 80W CH circulation pump, you can run this for more than 10 hours continuously for 1 unit of Electricity (13p), and like i've said once the rooms are warm it wont be running continuously it will be running on 'demand' for short periods as determined by the room stat.

In other words, the £100+ outlay on leisure batteries, a similar amount on an inverter, is going to take quite a while to claw back in Electricity savings from a Gas Combi boiler. So my original 'false economy' point still has similar validity.

energysavingexp

chris1973 wrote: »

Its much less than 300W. A Fan in a combi boiler uses around 22 Watts, a CH Pump uses around 80W and the Ignitor uses 5W

Non of these run continuously either, the CH pump is controlled by the wall stat, so that it only circulates water to the radiators when the temperature drops, in most boilers the fan runs when the jets are lit and the ignitor operates for milli-seconds to light the jets.

Taking the 80W CH circulation pump, you can run this for more than 10 hours continuously for 1 unit of Electricity (13p), and like i've said once the rooms are warm it wont be running continuously it will be running on 'demand' for short periods as determined by the room stat.

In other words, the £100+ outlay on leisure batteries, a similar amount on an inverter, is going to take quite a while to claw back in Electricity savings from a Gas Combi boiler. So my original 'false economy' point still has similar validity.

no you still missunderstand my point. its not about saving money its about running a gas boiler in a power cut to keep warm

as for the batterys i had them lying around i did not buy them for this purpose same with the inverter also with an inverter this size you can run some low energy lighting
as you say the boiler uses less than 300 watts this was to point out that you can run your heating for a long time off 2 x 80amp batteries
then when your power comes back on you can charge the batteies from your solar

Pincher

It's just for a backup scenario.

Why huddle in one room with a Calorgas heater when I can have a whole house nice and warm by having an inverter and a battery. If the leisure battery will keep the central heating going for a day, then that's pretty good. I assume I can charge it up from the car alternator on day two.

It's a winter scenario, so solar PV charging the battery is moot.

£500 for an inverter? Surely that's a rip-off price?

A dynamo driven by a 12V DC motor, plus some feedback control to maintain 50Hz. Two complementary power transistors to maintain 230V. Chunky heat sink. The rest should be cheap stuff. The syncing to grid stuff might be tricky, but I don't need it.

energysavingexp

Pincher wrote: »

It's just for a backup scenario.

Why huddle in one room with a Calorgas heater when I can have a whole house nice and warm by having an inverter and a battery. If the leisure battery will keep the central heating going for a day, then that's pretty good. I assume I can charge it up from the car alternator on day two.

It's a winter scenario, so solar PV charging the battery is moot.

£500 for an inverter? Surely that's a rip-off price?

A dynamo driven by a 12V DC motor, plus some feedback control to maintain 50Hz. Two complementary power transistors to maintain 230V. Chunky heat sink. The rest should be cheap stuff. The syncing to grid stuff might be tricky, but I don't need it.

you dont need to pay £500 for an inverter you can get them for as little as £80 yes the batteries will last for a long time just running the boiler how long are you expecting the power cut to last

like i say last time i had a power cut i used the generator but the batteries and inverter work just aswell