Hi

I am looking at micro generation for a number of reasons -

1) Cost savings
2) Potential to go "off grid" for electricity
3) Environmental benefits
4) Energy security
5) Understanding the viability of technologies

After some research it appears that wind power is really not a credible option. We currently consume around 17kwh per day and live in the grim East Midlands.

I read in another post that Keith estimated the cost of PV at around £6,000. I am in a fortunate position that I can get hold of a leading suppliers panels at reseller cost prices so in theory the payback could be low if I did the work myself, although I would need a kind person to design it for me.

The main issue is that I dont know the size of system I would need. Could I manage to get 17kwh per day out of a PV?

My house is 10 years old, south facing with a roof width of 8 metres. The south facing pitch is around 3.5 metres high.

The panels I am looking at has the following performance.

Open Circuit Voltage (Voc)* 36.3 V
Maximum Power Voltage (Vpm)* 28.71 V
Short Circuit Current (Isc) 8.35 A
Maximum Power Current (Ipm) 7.53 A
Rated Power (Pmax)* 216 W (+10% / -5%)
Module Efficiency Maximum Power (hm) 13.3%
Maximum System Voltage 600 VDC
Series Fuse Rating 15 A
Type of Output Terminal Lead Wire with MC Connector

I really don't know how to work viability out and would really appreciate your assistance.

Posted By: (GBP) Keith17 kWh is a big ask Simon. Can you not work to get that consumption down? What are you running, is it an office?

A fixed array is only going to give you about 980kWh a year per m2 installed.

For offgrid with PV only setup and a REALLY BIG battery bank, at a rough guess you would need to install about 6kW.

Thanks for the reply. I realise its a big ask. Since the beginning of the year we have been working hard to reduce our consumption. As we are downshifting we are using our home for the office. Even so we have reduced our electricity use by over 20%. I can't think how else I can effectively reduce it further. The washing machine takes a battering because we have three children. Lights are rarely used. All other electrical items are either switched off when not in use or are timer switches - eg the server (thin linux box) router etc. The only item that I am looking at changing is the oven - currently electric and going to be changed for gas. Any suggestions would be gratefully recieved though.

If the fixed array produces about 980kwh per m2 is the problem more storage rather than adding panels or have I missed something?

Thanks again

While I was on this chain of thought, I did some searching for reasonably priced efficient fridges. The MIELE K2319S fridge, is A++ rated and claims only 84 kWh/year, and can be found for around £300. And you can get A+ rated one for £200 with 117 kWh/year.

guyc: fridge --- best way is to measure for few days a scale to 365. Use something like a Kill-a-watt to measure (quick google will find, I know that UK has similar products to Kill-a-watt).

Off grid: Too expensive, too much trouble with batteries, environmentally very bad.
If you want backup electricity and are in UK, then use Micro CHP (combined heat and power), I think that you can run CHP units on natural gas or propane.

Most CHP that I know of are configured for anti-islanding so if grid goes down they will shutdown (to avoid energizing a cable while utility worker is repairing), but you may be able to reconfigure or override some it you promise to physically disconnect from utility in power outage.

Posted By: SimonG

If the fixed array produces about 980kwh per m2 is the problem more storage rather than adding panels or have I missed something?

Thanks again

The problem is the generation Simon. there will be many days when even a 6kWp array will barely generate 6kWh.

To be successful offgrid you should plan a battery bank to hold about three days of energy. That is three time 17kWh! x 2 (so you don't drain the batteries lower than 50%). Impossibly large I think.

Therefore, if you are wanting to be offgrid then you really need to consider some form of hybrid system and get your consumption down to about half what it is. Have you tried monitoring where this energy is going. We run three computers, cooker, all the normal conveniences of modern living here and only average between 4.5 and 7.5 (we vary our consumption to suit available energy).

Posted By: guycSorry to hijack this thread, and bore you all with fridge talk, but I wonder if anybody has real world usage figures for a pretty standard older fridge.

I have a pretty ratty 20 year old fridge/freezer. Haven't replaced it yet mainly because I haven't decided in the context of future plans whether to have a single fridge/freezer or separate fridge and freezer. Anyway, measurements:

2005-11-06 12:05 to 2005-12-06 12:05 (720 hours) took 81.84 kWh. So that's an average of 114 W, 2.7 kWh/day, 996 kWh/year. That's £114 per year at my marginal electricity price. Gulp.

If the published figures on new fridges are even close to true then the payback for replacement on-grid would be five or six years. Off PV, payback would be many times over and immediate, obviously.

I should do some measurements in summer (if that ever happens). Meter is currently in use for something else but I will do soon.