Sizing up a photovoltaic system

I have spent the day determining the power requirements of various electrical devices that I might take with me to a new home. To do that I put a power monitor between the mains socket and the plug from the device I was testing.

I am not a big electricity user so my intention is to go off-grid to avoid paying a standing charge and tax on what little I use. To do that I will need a photovoltaic panel capable of meeting my power needs.

I am not keen on wasting a lot of money on a bank of deep-cycle batteries to cover the needs of the average western lifestyle.

Instead of using electrical devices whenever I feel like it, I will use them during the day and charge up AA batteries for night time use. Lighting has a low power requirement, which can be handled with AA batteries powering LEDs. Alternatively, I can get those lights with small solar cells on them. You leave the lights outside during the day and take them indoors at night to light the house up.

Here are some results from the power monitor

Shaver - 5W
Battery Cell Charger - 1W
HP Mini Note Laptop - 22W
Mobile Phone Charger - 4W
Short Wave Radio Receiver - 6W using mains adaptor or 4 x rechargeable D cells at night
Car Battery Charger - 40W
Various CFL light bulbs ranging from 6-20W - I will probably replace them with lower power LEDs

I will need a photovoltaic panel just large enough to cover a few items being used at the same time and an inverter just big enough to convert that amount of power from DC to AC.

The shaver will only be used during the daytime and no, I won't be touching my skin with a blade. My laptop will be for day use and maybe a little war cycling to make use of an insecure corporate or governmental WiFi router. The short wave radio will allow me to pick up the World Service on Short Wave and other English language programmes on Long Wave. During the day, the radio can be powered by the sun and by batteries at night.

For communication I will just have a mobile phone to receive calls but not to make any unless there is an emergency. I will need a car battery charger to keep the car battery topped up as I intend cycling more than driving.

Of course, I will be taking large power tools with me. I won't be running them off a photovoltaic system because their power usage runs into the kW, which would require many expensive photovoltaic panels. Instead, I will cobble together a homebrew generator from a lawnmower engine to power the tools when needed.

Two household items not mentioned so far are the biggest power users of all, the fridge and the washing machine. A fridge can use well over 1kW of power during a day. My intention is to avoid having too much perishable food that requires refrigeration.

A fridge is a modern luxury that my ancestors got along without quite adequately. If needs be, I can have a small camping fridge running on 12V. In winter time a cold store would probably suffice.

Initially, I will hand wash my clothes but the washing machine is one luxury that is a necessity. Handwashing is very laborious when other things need to be done. A washing machine will have an initial peak surge of power when switched on but gets by on about 250W of power. Something that will have to powered by a generator for such intermittent use.

Of course, the best way to size up an off-grid electrical system is to do away with electricity altogether. However, there are some things (especially shaving!) which are just a whole lot easier with electricity.

If the day is particularly sunny and there is excess electricity then I have a 12V water heating element to boil water. Starting a wood fire to boil water on a hot sunny day is not pleasant.


lisa winter said...

there's this concept of an updraft cold closet that i'm looking into as a refrigerator replacement as we are building our cob house. it will be off the grid. the concept is easy, there is a hole in the ceiling and a hole at the bottom, the hot air goes out the top and pulls cool air in from below. it seems to be pretty easy to make and pretty effective.

James said...

Yes, I have seen an updraught cold closet afore.

I would even improve it with ice blocks at the top of the closet, made from a solar ice maker.

Pamela said...

James, one of the things I was able to do in Spain was to run the washing machine without heat, so it did not heat the water, which is the element that uses most of the power. Modern washing powders are perfectly capable of washing most things clean at low temperatures. Indeed, some brands (Wipp, I think), specifically say they are for use at low temperature. And the washing machine I bought in Spain only last year did have a button to turn off the heat entirely. I did this because the house I was renting had such dodgy wiring that everything would trip off if I tried to run with heat. One added bonus was making clothes last longer from less abuse and, if your water pipes are exposed and get heated up on summer afternoons, as mine did, then that's the time to take advantage to do an almost "free" hot wash!

James said...

That's a good idea. I have heard of powders that work at 15C but have not seen them yet.

I intend building another solar water heater like the one I made in Ireland.

I couldn't fit it in the van when I left so I assume the new owner binned it.

Moonwaves said...

This thread might be of some interest to you:

A few days before this thread was started I had read about a manual washing machine on someone's blog but now I can't remember whose (think it was American because it talked about purchasing from Lehmans as far as I remember). Not quite as good as an electric perhaps but still better than washing by hand. I've always maintained that a washing machine would be the last electrical item I'd want to give up!

James said...

That looks like an interesting device. My mind is running through many ideas.

For a start, the device is just a drum with a handle on a bearing. That's not difficult to fabricate with scrap.

Then again, why bother? An old washing machine at a dump thrown out because something didn't work could be used.

A damaged element is not a problem if you use the aforementioned low-temp powder.

If the motor is broken then just run a belt to the drum and another motor outside the machine.

Replicate the cleaning cycle by introducing water, powder and draining when necessary. Use a low power motor as only a high power motor is needed for spin drying, which can be handled by a mangle.

OK, automated low-power laundry is sorted. Next!

Iñigo said...

You are quite right, a fridge is good only if you have to store perishable goods, like vegetables or meat, but if you grow your own I think they are better stored in the orchad. If you raise your own poultry or cattle you can always kill it before eating.
Actually, a fridge is a townie piece of a machine, for people who cannot spend much time shopping food.
A dark room in a house with thick stone walls, kept closed, or an underground cellar can keep a good 18ºC even in summer, and thus be good to store your produce.

James said...

I call fridges townie machines too.

The fact is, a lot of townies don't need them either.

My novita's family all live within walking distance of a supermarket in Madrid.

They could all use the supermarket fridges to store their food and walk to the supermarket when they want to cook something.

It would stop them wasting food they may never eat and provide them with much needed exercise.

I am going back to Spain on Saturday. Fingers crossed. I shall say no more.