Mitigating intermittent grid power supply

[clv101]

With all this talk of unreliable power supplies in the future and people turning to wind turbines and solar panels on their roofs are we missing a trick? No one is suggesting that grid electricity is going to fail permanently. The worst case scenario is unreliability, periodic blackouts, 3-day week etc. Even in Iraq and much of Africa they have an unreliable grid supply. Maybe the best way to deal with an unreliable grid supply isn?t with a wind turbine but with local battery storage. Say you want to maintain an average of 500W load for a 24 hour power outage, how realistic is mains backed battery backup? Total energy requirement is just 12kWhr.

The Rolls 4000 S-530 (deep discharge, good for years of 50% daily discharge cycles) battery has a capacity of over 3kWhr for less than $300, the four of these would be $1200 ad a couple of hundred for the inverter and charge controller and for say ~?800 you have a decent household backup supply. 12kWhr is plenty to run a fridge/freezer/lights/laptop/router/central heating pump for hours is not days. Okay the electric oven, shower and hairdryer aren?t going to work but I can?t help thinking this kind of solution is better at mitigating the problems of intermittent grid supply we could be facing in years to come.

Even if you went down the wind/solar route you would still need the battery backup above. At the individual level we aren't facing an energy shortage, we're facing the threat of intermittent supply, we don't need fancy technology to generate electricity we just need a way to store the mains electricity when it is available.

Obviously this is ignoring the very real problem of pollution, net reduction of available total available energy etc... but just thinking at an individual level maybe this kind of solution has a future.

[newmac]

If everyone did that I suspect it would cause such a surge when the power did come on that the grid would fall over.

[fishertrop]

At the individual level we aren't facing an energy shortage, we're facing the threat of intermittent supply, we don't need fancy technology to generate electricity we just need a way to store the mains electricity when it is available.

I would agree 100%.

My personal plans have been on that basis.

Beyond the most basic installation, the main issues seem not to be about the battery (either type or cost) but about selecting a mains-charger that suits the batteries you have and connecting all your key appliances both via an inverter that is suitable (see other threads for issues with cheap inverters...) and wiring that is not chaotic or indeed unsafe!

If you are prepared to do the legwork, you can pick up all sorts of used high-capcity batteries (think used fork-truck items for example) that aren't neccessarily the ideal choice but can offer huge cacpity for the money, so long as you can charge them in a way that won't ruin them in the first week...

Commercial UPS units are an option woth considering, as they include all (matched) charging and inverting equipment in one unit.

[johnhemming]

The initial suggestion from the National Grid is a reduction in mains voltage. Not an unreasonable approach to reducing power usage - up to a point.

[mobbsey]

I've got a battery back-up. It actually runs my workshop, but in the even of a mains failure I can string a cable to run low voltage lights, and an inverter keeps the central heating pump going.

HOWEVER... two points.

Firstly, the latest revision to the building regulations that came into effect 1/1/05 prohibits you installing any such system (I put the core of mine in six years ago) without first obtaining building regulations consent or hiring an 'approved' electrician to do it for you. If you don't do this, and it's not as if you can do it secretly as PV or wind installations are a big sign saying 'I've installed a home power system', then you get taken to court and fined up to 5000 quid.

Secondly, the power you can reap from the average household location isn't very dense. My 60W of PV, unlawfully installed on the roof because they won't give us planning permission, would take a month of summer sunshine to completely charge my 400 amp-hours of deep cycle battey. Likewise most of the ridge/wind charger turbines will only produce 60 to 120 watts max, and so will only trickle charge the cells -- they'r enever ever going to provide a significant source of power in comparison to the amount of power most households consume.

If you want to be really un-green, which admittedly I have the capacity to do in an emergency, you can charge the batteries from the mains to full capacity and then float the charge using PV or wind.

[fishertrop]

Firstly, the latest revision to the building regulations that came into effect 1/1/05 prohibits you installing any such system (I put the core of mine in six years ago) without first obtaining building regulations consent or hiring an 'approved' electrician to do it for you. If you don't do this, and it's not as if you can do it secretly as PV or wind installations are a big sign saying 'I've installed a home power system', then you get taken to court and fined up to 5000 quid.

A valid point, but what if you say "I installed this at the end of last year" ? It seems tough for the authorities to prove when you did something (I'm not talking about a 30ft tower mind...).

I have to say, building regs compliance is not the top of my personal priorities, tho it is something you have to be aware of.

If you want to be really un-green, which admittedly I have the capacity to do in an emergency, you can charge the batteries from the mains to full capacity and then float the charge using PV or wind.

Bingo!

That's what we're talking about here - until we all get 4kw off-grid home power ( ) we need realistic transitions.

Charging from the mains is, as you say, ungreen, but it's a viable steping stone to something else.

[jev]

Reducing voltage will not reduce overall power consumption. Power is equal to the voltage multiplied by the current. A device will require a certain amount of Power (energy) to operate correctly. That device might require 100 watts of power. Therefore theorectically (as most things won't just work off a wildly different voltage) whether the device gets it's power from 0.416 amps at 240 Volts or 2 amps at 50 volts, the overall power (energy) it requires to work correctly will be the same (100 watts).

[mikepepler]

Reducing voltage will not reduce overall power consumption. Power is equal to the voltage multiplied by the current. A device will require a certain amount of Power (energy) to operate correctly. That device might require 100 watts of power. Therefore theorectically (as most things won't just work off a wildly different voltage) whether the device gets it's power from 0.416 amps at 240 Volts or 2 amps at 50 volts, the overall power (energy) it requires to work correctly will be the same (100 watts).

Actually, that's not correct. Remember that:

• power = voltage x current

but current = voltage / resistance, so as you drop the voltage, the current drops too. So you could say:

• power = (voltage x voltage) / resistance

so reducing the voltage does reduce the power consumption.

[fishertrop]

Might it be true that reducing the voltage helps with loadings in the overall grid system, rather than "makes appliance X use less power" ?

Whilst most devices do have a range of allowed input voltages, those devices that need XX watts of power to work will either use that power or not work (or not work properly).

[mikepepler]

Might it be true that reducing the voltage helps with loadings in the overall grid system, rather than "makes appliance X use less power" ?

Whilst most devices do have a range of allowed input voltages, those devices that need XX watts of power to work will either use that power or not work (or not work properly).

I think the main thing is that it will reduce devices' consumption. Remember the bulk of electricity is used in lighting and heating, and they are not so sensitive to reductions in voltage. It would be interesting to know by what % the voltage needs reducing to help with supply problems - I wouldn't be surprised if it's not a lot.

[Bandidoz]

With all this talk of unreliable power supplies in the future and people turning to wind turbines and solar panels on their roofs are we missing a trick?

Yes - because people are getting over-excited about there being 8% loss in the National Grid, and advocating installing less efficient domestic systems which probably more than cancel the gain of being off-grid.