Solar Home Back-up

175 watts times 5.5 hours is 962 w-hr and you use 2000 w-hr. so slightly less than 50% of you energy ON THE AVERAGE.

If you wanted to store all the power at 24 volts, then 962 watt-hr / 24 is 40.1 amp-hrs of storage, so a 50 amp-hour battery(ies) would be required.

You can buy a 2kW inverter with a battery charger build in.

I think with 24V solar panel it will not be able to full charge a 24Volt 50 Ah battery ie two 12Volt batteries in series.Battery needs little higher voltage for charging say about 32 Volt.

Secondly , to maximise use of the Soalr Energy , the battery will have to get drained daily. This will severely reduce capacity of Lead acid battery after some time.

So it is better to be on little higher size battery may be twice the size recomended. a 12 Volt 200 Ah battery may be better with cut off at 50% discharge and going to Utility power if Solar is not available. This will give you longer life and capacity of battery.

What if I use 48Vdc as a system voltage, and do I need to increase my solar panel?

Yes 4 in series ie giving you approx 84v dc open circuit load at 1kw/m2 sun radiation. Check with the panel manufacturer and get a data sheet on the PVC (photo voltaic cell) The higher voltage will allow you to drop your cable diameter too. Personally i would use 4 200 Ah deep cycle batteries in series connected to a charger to the solar panels. Depending on your sun intensity target for about 10% solar ampere to battery ampere. e.g 240 watt panel at charging 12v dc gives you 20A a nice trickle charge for a 200Ah battery. You can always up the panel wattage if the recharge cycle is too slow(sun dependant and weather). Try to have a intelligent charger that shuts down the battery load when each battery has dropped to about 10.5 volts, and stop charging at 14.5 volts. The whole set up is quite a capital investment so it would pay to do it right for the long run. Remember the solar panel average life span is about 15 to 20 years(good ones) and batteries around 4 to 5 years if looked after. I would be very interested to know what kind of prices you are paying for batteries and panels. Here in south Africa its about R100($12.50)/watt for the panel and R 1700.00($212.50) for a 105Ah battery. I think I'm getting ripped off. Let me know if you need any more info if the above guided you.

Dear Friend

Some clarification, before anything can be commented upon.

Please introduce yourself, whether u r a professional or want to put a system at your home. From which country you belong to etc. I donot see any reason why you should hide your identity.

Average sun is 5.5 - Is it the time duration for which sunlight is available or solar insolation? Both have impact on pv sizing.

Your proposal to use 175 W solar panel at 24 V is based on what sizing/design?

Thanks and regards

Ashok Toshniwal, Bangalore, India

Thank you for the info

- 5.5 is solar insolation

- 175w x 2 pcs in series.

Hi

I have only solar power in my house (apart from a petrol generator for lifting water from 180m underground and for the relatively few cloudy days we get here in southern Spain.

I have 4 x 175w panels and run 12 batteries in series (24v).

On totally cloudy days (I am at an altitude of 850m and occasionally can be in thick cloud all day) the system can produce nothing.

On a good day I can produce 4.4 kWh.

An normal day averages out at around 3.0-3.4 kWh.

REMEMBER I AM IN SOUTHERN SPAIN.

I can give you all the information on the makes and models of my installation if it would help, but you might find what you are looking for here. Or, at least, it will give you a start.

Solar power works wonderfully for me and I would heartily recommend that you experiment.

Word of warning, though: initial costs can run away with you. Do your research and calculations very carefully unless you have money to burn. With careful choosing you should be able to get a system up and running to achieve your 2kWh per day requirement (depending, of course, on the average insolation m² in your location.

Let me know if you need a little or a lot more information.

Best wishes

Joe

What is your each 2V battery Ah (capacity) ?

You don't want to run the batteries past 50% Depth of Discharge(DOD) as that will diminish their useful life so size the batteries accordingly. 48V is better than 24V because the wire can be smaller.

Choose a charge controller that matches with the PV modules for voltage and current. Most 24V solar modules actually run around 28V so they are matched for 24V battery systems.

A U.S. company that makes battery-based systems is Outback Power Systems http://www.outbackpower.com/ their web site has lots of info that you should read.

Do OutbackPower have an inverter/charger that the utility do not charge directly to battery rather it provide only a backup power to loads instead ,during the inverter/charger at the heavy load state and in low battery mode and it switch back automatically to direct solar mode when its output become within the power range and charge the battery as well.

cpl, in what country do you live? If you are in the USA, then I suggest you look here, http://www.epa.gov/chp/, and here, http://www.eere.energy.gov/, for help. Other nations have similar sites, too, but since I live in the USA, I know of this one as teh major source of information for what you want. We are spinning our wheels if we keep trying to reinvent the wheel.

If you live in Southern California, check out www.aerosunelectric.com for information--two things to consider 1)How much do you pay for electricity now? 2)How long do you plan to live where you are? Both these effect whether it makes economic sense to do this--also, if you live in the US, states vary as to rebates/incentives offered for adding solar electric, and most offer nothing if a system is not grid-tied. As of yet, it is difficult for most property appraisers to figure what a solar-power system adds to a property, and almost assuredly it will not be what you paid to install one.

The cheapest way may be to use a reflector to make steam to run a steam-powered generator and have the whole unit follow the sun, then return to face east at sunset. It may last longer than photovoltaic panels. Of course when the sun goes down or it is cloudy you will have to get power from the grid. To ensure you have power at those times you could use a steam boiler to power the steam engine and fuel it with an inexpensive fuel. Batteries are expensive, so you want to use as few as possible. You can still use the grid as backup too.