I’m looking for a solution that will allow a continuous electricity backup if the electricity supply grid goes down but without relying on a backup generator but instead using a solar PV array. The electricity generated needs to be stored (obvious choice would be a battery array using deep cycle maritime batteries).
The solar PV array would be constantly in use providing a reduction in electricity drawn from the grid with the consequent energy and financial savings.

After doing some calculations the PV array would need to be about 1.2 to 1.5 KW. This was calculated after carrying out an online solar energy calculator, which will provide an average over the year of 5.5-6KW/hrs per day. Saving $11/week or $572/year. (This would cut current electricity bills by about 30-40%)

By using energy efficient lighting using a combination of modern CF and LED lighting the total lighting load (upstairs and downstairs ring mains) for an average 3 bedroom house would be around 250-300 Watts peak and the normal continuous load would be around 60 Watts say for 6-8 hrs/day i.e 0.48 KW/hrs

Refrigeration load would be a continuous 200W i.e 4.8 KW/hrs per day

Communications and entertainment (Low powered PC with Digital Satellite card, Digital TV card, cable router and amplifier/speakers) would account for 130-150 Watts again for 6-8 hrs/day. i.e 1.2 KW/hrs per day

There would be no other appliances except for possibly a microwave oven i.e 600 Watts for 30 min maximum/day i.e 0.3 KW/hrs per day.

A generator around 2KW would be used as a backup to top up the battery array if solar conditions were poor during an emergency grid outage.

Therefore peak power usage would be no more than 1.25 KW at any one time. Typical power would average 250W over 24 hrs

Therefore over a continuous 24hr period of operation the battery array would need to be around 800-900 AH

There is a product called the Xantrex Powerhub 1800 which is essentially a powerful UPS but has additional inputs from solar arrays, wind turbine and generators etc but can only support a 420 AH battery array.

Costs for the setup would be around approx $6000 for the PV array, approx $1400 for the Powerhub, approx Deep Cycle Batteries $1500 and modern lighting CF and LED $800 and cabling $250 and approx $1500 for the generator.

Total Project cost would be approx $12,000

Time to recover initial project cost approx 20 years.

Would this be a worthwhile project?

I've been running a bunch of solar panels for a while. I have about 120 watts of generation so far, a motley assortment of batteries, and assorted cheap inverters. I run battery chargers, cell chargers, laptop computers, LED lights, etc. from this rig on an intermittent basis.

A few things I've learned, FWIW:

1. Start small, test and learn. You will make mistakes -- can't be helped. Better to write off $500 than $12,000.

2. Solar power is much more expensive per watt than grid power. If your only goal is to save money, forget it.

3. Be aware that this market is in enormous flux. Better and less expensive products are coming out every few months.

4. Wean yourself off the grid slowly. Choose some things that will run off solar, and use grid power as a backup only. Cell phones, battery chargers, laptop, LED lanterns, etc. (I think I said that already.)

5. Once you have a modest amount of generation, shape your consumption to match it. This is where you will really save money. Adjust your lifesyle; and buy efficiency, not generation.

6. Be aware that modified-sine-wave inverters are not compatible with some items, and may accelerate wear on the power supplies of others. Shavers, MAC computers, most stereos and TVs, and many computer printers do not play nicely ...

7. Full-sine-wave inverters are on the horizon, at a modest cost. Stay tuned. (Hint: computer UPS units are full-sine-wave converters, and most use an internal 12VDC battery. Perfect item for penny-wise scroungers and recyclers. Or if you're going to be caught in a high-rise during an outage ...)

8. Don't let nay-sayers dampen your enthusiasm. It's a grand and practical hobby, with preparedness and environmental responsibility as bonuses. Nothing sweeter than saying "my office is off-grid." Even die-hard coal-fired cowboys will be curious.

Luck!

Are wind generators/turbines a reasonable option in your area? In reading about solar and wind power it seems that turbines can produce more power under certain conditions.

Hi frostbite

Wind turbines are a reasonable alternative in the area but not for me as the location of the house is in a sheltered spot away from the wind. Generally to get the best return from a wind turbine they have to be quite large.



Although it hasn't stopped others from putting up some wind turbines in the area.

Hi dougwalkabout,

Thats some great advice. Perhaps I'll start quite small. A garden shed project to begin with using a 80 W solar panel etc and take it from there.

I would love one of those!!

Learn to live with less electricity usage.

Keep us posted. Sounds interesting.