Solar PV system Without batteries??

ghaxii · May 2012

hi there

i've a question. is it possible to design a solar pv system without the need of the batteries? like if some one is going to use it, he can use during the day and in the evening the grid side will turn on.

Please reply with technical details if posible

Regards,
Amer

Cariboocoot · May 2012

Re: Solar PV system Without batteries??

Welcome to the forum.

Yours is a popular question. For a strictly off-grid application the answer is "no".
However you mention using the grid at night, so I believe you're looking at a straight forward grid-tied system with sufficient capacity to offset your use during daylight hours. In that case the answer is "yes", as that type of system takes power directly from the panels and feeds the household and/or utility.

But there are limits and restrictions. No grid means no power, so it can't be used for back-up. Most importantly, such a system can not be installed without the co-operation and permission of the utility as well as meeting local electrical code.

ghaxii · May 2012

Re: Solar PV system Without batteries??

thank you for your prompt reply

actually in my locality installing a completely off grid system is not a problem. act i am a newbie with the topic and i want to know how to design solar pv systems for usage in homes and offices? any good source/book/site to get familier with the design. the request is that suggested book or site should be step by step guide.

and please help me design a 1000 watt / 1Kw system for 9-5 operation without batteries while description in details?

i will be greatly thankful.

Regards,

Cariboocoot · May 2012

Re: Solar PV system Without batteries??

Right there is the first thing to learn: off-grid means batteries. No batteries, no power. You can NOT do an off-grid system of any type without batteries to store power in. This is basically because the output from the panels never "matches" the demand of the loads.

The best way to learn about these things is to do a lot of reading.

There's a very large section of the forum here that is full of facts, links, and explanations:
http://forum.solar-electric.com/forumdisplay.php?14-Solar-FAQ-s-Links-amp-Information-Sources

Two of the most important threads there are the Glossary of Terms (so you'll know what all the words and acronyms mean):
http://forum.solar-electric.com/showthread.php?6136-Glossary

And the Working Thread for Beginners:
http://forum.solar-electric.com/showthread.php?5556-Working-Thread-for-Solar-Beginner-Post-FAQ

As for a "1000 Watt" system, do you mean 1000 Watts of panels or supplying 1000 Watt continuous load or 1000 Watt hours total power? This is one of the things people get confused about.

ghaxii · May 2012

Re: Solar PV system Without batteries??

Thank you very much for the prompt reply

first of all, i mentioned the word "off grid" by mistake in my last reply. let me tell you the complete scenario of where i live. A Customer came and demanded me to design a system with no batteries. further details are like the batteries are one of the major cost in the system. and i don't want to use the system after evening. so design a system in which the current directly comes to inverter and then to devices and no hassle of batteries. when the sun goes down, he would simply switch the main switch to local utility supply. His Requirement is to sustain a load of almost 1000 watts for 8 hours a day during day time with only help of just panels. his main concern is to harness the power of sun directly to the devices with NO BATTERIES at all

now i got the answer to the question as the panels out put never matches the load

and thank you very much for the details of the sources given. i would definitely go through it and would appreciate if you comment on the demand of my customer

Regards,

Amer

Cariboocoot · May 2012

Re: Solar PV system Without batteries??

Essentially you are talking about a straight grid-tie system. But you will not get 8 hours production out of it, as the sun doesn't really shine that long anywhere. Not as far as panels are concerned.

The upside is you can get the equivalent power in Watt hours and "store" the extra with the utility, if they allow grid-tie and will purchase the "surplus" production. In fact you could offset even more than 8 kW hours requested (1000 Watts * 8 hours).

In short form, it would consist of a grid tie inverter of at least 2kW capacity and sufficient panels to power it (slightly more than a 2kW array).

If the utility cooperates, this is fairly easily done.

jagec · May 2012

Re: Solar PV system Without batteries??

It’s time to play “good news, bad news”.
The good news is that it is fairly easy to design a grid-tied system to partially or completely offset your power usage during the day. No switch is needed…during the day, power will be produced by the panels, and any power that is not used within the household gets exported to the grid. Most utility companies (assuming that it is properly installed and an interconnection agreement is in place) will credit the homeowner for the exported power. During the night, power used within the household is completely supplied by the grid. “Switchover” is fully automatic, no user intervention is required, and thanks to net metering, you can still use your appliances during rainy days (buying power from the grid), and get full credit for sunny days where you produce more than you use (exporting to the grid).

The bad news is that you DO have to get things properly installed, permitted, and inspected, and there has to be an interconnection agreement in place with your utility to take advantage of this system. If you can’t tie to the grid, you can’t just hook solar panels directly to your loads and expect it to work (well, you can with some water pumps, but that’s a special case).

What part of the world is this in, if you don't mind answering?

ghaxii · May 2012

Re: Solar PV system Without batteries??

Thank you Guys for helping me out. yeah sure, I'm from Pakistan and here we have no concept,even a slightest one to export over-production of panels to the grid:) and switch-over means a manual switch to get the system to one side only,either panels or grid. And the Simple Answer for a system without batteries and not connected to the grid during day light is NO

i got it now. the suggested links are great. do you guys have any step by step guide which let me grasp the idea of designing?

Thanks Again:)

BB. · May 2012

Re: Solar PV system Without batteries??

Amer,

I would humbly suggest that you proceed as follows:

Measure all of your AC/DC loads (Kill-a-Watt meter or similar--230 VAC versions available too)
Look at conservation--It is almost always cheaper to replace energy hungry appliances, insulation, etc. vs generating/buying power.
Look at what you want to power with solar (if grid tied--everything is OK--does not matter). If off grid, you need to pick and choose (or build a larger system).
Decide if a) save money; b) emergency backup; c) want to be off-grid (no utility power at all)
Then look at designing system (we will help here)

Basically, it is easier to design your system if we have a good knowledge of your needs... Plus we will be less confusing if we design to your needs, not some "generic" system that may be too large, too small, or not meet your needs (or more confusing, talk about small, medium, and large AC/DC systems all at once).

In the US, a "pure" grid tied system (solar panels + GT inverter) can be pretty close to "break even" in power costs--Or even be cheaper (in expensive states like California).

For off grid system, the overall costs (solar panels + charge controller + battery bank + AC inverter + backup generator and charger) runs about 10x the cost of utility power ($$$/kWH)... So, pure off grid systems rarely save money if you have otherwise reliable and reasonably priced utility power.

There are "hybrid systems" which look like off grid systems (can supply power when the utility power has failed), but can feed back power to the utility (or at least reduce utility power usage to near zero power used)--These may be a slightly more expensive system but can be somewhat more cost effective (if your utility supports feeding power back to the utility).

Once you go through the entire process once--Everything will make much more sense.

-Bill

ghaxii · May 2012

Re: Solar PV system Without batteries??

Thank you Bill.

I will ponder the suggested points bro.

ghaxii · May 2012

Re: Solar PV system Without batteries??

See you guys after some research and reading.

Thanks Again

Regards,
Amer

BB. · May 2012

Re: Solar PV system Without batteries??

Amer,

Here is a general thread with lots of links to other Solar Power and solar related projects:

Working Thread for Solar Beginner Post/FAQ

It is a bit on the random post side--But has lots of (mostly:p) useful information.

-Bill

mejustme · May 2012

Re: Solar PV system Without batteries??

Hi

While i think what you are after is impractical, you CAN use solar power to directly power certain appliances.

It will work well given aplliances that match the panels but due to the nature of solar, running it for any length of time will be very stop start.

It would also be a problem with voltage sensitive electronics.

Where it DOES work is for things that work for a short period and are purely resistive loads.
Things like 12 volt cooking and water heating will work great from solar directly if given the right appliances/panels.

I have limited resources but just yesterday got a water to heat from solar without batteries. I have also been able to cook from 12 volts without batteries for a few months (though still needs work for it to be practical for me)...again though would work well NOW with the right gear.

Waer heating is practical NOW for me but only for emergencies or if not needing a LOT of hot water or on good days and some other situations...off course with a larger solar setup it would be easily doable.

100 watts will heat 1 litre of water 1 degree per minute...the more watts available the quicker it will be.

Best though for situations where you use solar to charge your batteries as normal and quickly have them charged so you can plug a water heating element into a panel and small amount of water and leave it to heat....you can then store in a thermos type pot.

Yes it is inefficent but if you have the panels, do not need a lot of water and the PV is going to waste, why not? 12 volt boilers cost very little....again not for everyone or everyday use but very doable.

IF the appliances where made for this or the panels made for the appliances, it will be very good for many I think.

Better for camping and RVs etc and will be better still if much more effiecient panels ever become cost effective and readily available.

Unless you can get a panel with the right voltage, you have to over rate the panels....IE work on the watts AT 12 volts rather than the "actual" panel voltage...my 200 watt panel is therefore really only about a 135 watt panle for using directly.
I suspec that small 12 volt heaters will also be somewhat useable some time from this as long as there is not a lot of electronics in the heater.

Again though, to use it for 8 hours without a battery backup would be impractical.....I would think that in years to come, someone will come up with a system that will mostly be solar direct with a battery backup that comes in and out as required.

BB. · May 2012

Re: Solar PV system Without batteries??

The other place where "Direct to Load" solar works well are those with variable power needs... Water pumping is one of those. Either let the panel+pump naturally regulate (less sun, lower motor RPM, less water pumped)--Or active control. One of the most common are Linear Current Boosters:

7 amp Linear Current Booster/Pump Driver

These devices are sort of like MPPT charge controllers, except they are designed to work with DC motors.

Motors tend to like higher current at low input voltage (and solar panels output the same current from V=0 volts to V=Vmp or so--where the current is more or less proportional to the amount of sunlight hitting the panel).

An LCB will take the higher voltage/lower current from the solar array and down convert it to the low voltage/high current that a DC motor needs to start turning/pumping water.

Note that many DC well pumps already have internal controllers that perform the MPPT/LCB type function (such as Grundfos and some other brands/models)

If you can think of other loads that can work with variable power input--Then you may be able to use a solar panel plus LCB or similar for your needs.

-Bill

Solar PV system Without batteries??

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