Solar electricity...........not for your house

[Someone-Else]

[chrrris]

I know I'm a bit late to this thread, but I been running an off-grid solar setup for just over a year now. I have two large panels (about 6ft by 2ft6" each), one is (nominally) 380W and the other is about 340W I think. 2kW inverter and a couple of 120A marine batteries for storage. It works fine and, although the panels are not mounted ideally,, being only 8ft off the ground so they get a limited period of full sun each, I'm currently getting about 2.5kWh a day which is plenty enough for a shed/outbuilding (TV, lights, computer, fridge, etc). Obviously it's rubbish in December though... I got a grand total of 2.68kWh during the whole of last December.

I've learned a lot from it (which was part of the point of doing it), particularly about batteries. I naively imagined my batteries would work like a water storage tank -- i.e. the sunnier it was, the quicker they'd charge up and once the "tank" was full, you could empty the batteries out either slowly or quickly and get the same total power from them. In actual fact, the batteries will only charge at the rate they charge at -- once I'm putting more than about 25.5V across them (I have a 24VDC setup) they're charging, and they basically charge at the rate they want to charge at regardless of whether it's full sun or overcast. And, with lead-acid batteries at least, the chemical process is very apparent. If I pull 1KW continuously from them, they'd be flat (i.e. down to 24V) in less than an hour. If I pull 200W from them, I'd get a good 5 or 6 hours. In other words, you get more power from the batteries if you draw the current from them slower. Also, you can let them rest and get get more current from them. And then there's the massive effect of ambient temperature on them too -- you get loads more power out of lead-acid batteries once they get warm.

Really, to get the best out of PV, you need to use as much of the power generated as possible, as it's being generated. I do now have the ability to power my entire house off-grid on sunny days with the flick of a couple of switches (I won't describe the setup to do this, as it's not regs compliant...) and it really comes into it's own with a couple of tellies, fridge freezer, computer, and maybe the microwave or toaster going in the kitchen. Up to the maximum capacity of the panels, it's typically a case of "the more you use, the more it generates". On the days when I'm out and about, and all it's doing is powering the fridge/freezer, I might get 800Wh out of it, even on a nice sunny day. The rest disappears into the ether. Wish there was an inexpensive way of storing it up for use in winter but there isn't.

[big-all]

looking at this thread i think solar only available from my say 6ftx11ft away from the stove flue on my south south west facing shed roof
now in general only advantage is the warm feeling from using the sun for energy
buuuutt thinking storage batteries expensive buuutt
i have several 18v /54v batteries able to charge at 18v [about 50ah ryobi and the same dewalt ] now assuming to work needs 230v for chargers as being the cheapest way to use the power and using the batteries to power tools and lighting iff possible to a greater level than panel outputs
now i already use powertool batts for fans lighting charging phone around the house in general
now i suppose what i am asking is it ok to have panels connected to an inverter [or other ]supplying only a 230v charging circuit only connected battery chargers to keep it simple
would it be a problem using less than imput ampage i assume not and i also assume no backfeed as in input power less than battery contains so no back feed or drain on battery ??

if i have made this complicated i apologise looking at perhaps 4-£800 for basic panels and control ??

[Someone-Else]

With any solar project you have to ask will it cost more to set up/install than you will gain, for charging power tool batteries the answer is yes, it will cost more than you will gain.
You yourself have said £800 budget, it doesn't cost that to charge your power tool batteries.

edited to add more info. (Re-posted extra info in new post)

[big-all]

i fully understand the cost payback would probably be 20 years at 800 or perhaps seven years at £300 so thats not the main idea as at 69 i will never get payback
i understand the importance off using spare capacity to bring down the pay back time dramatically or reduce the panels to the average usage to be more efficient

[Someone-Else]

If you wanted to do it for "fun" go ahead, I have done some googling and you can buy (a cheap) inverter, solar panel for less than £200. (I make no promises for the quality)

Inverter Click here

Solar panel Click here

I leave the actual choice to anyone that wishes to try, bear in mind that you will also need a support/weighted frame/fixings to stop the wind blowing any solar panel over/lifting it up.

[Someone-Else]

arco_iris, sorry to ask, any progress?

[chrrris]

If you wanted to do it for "fun" go ahead, I have done some googling and you can buy (a cheap) inverter, solar panel for less than £200. (I make no promises for the quality)

You also really need two other components to make a reliable stab at it:-
1. A solar charge controller to turn the wildly fluctuating voltage/current input from the panel(s) into a steady, usable, DC supply and (because I don't know of any solar charge controller that doesn't also need a battery)...
2. A battery. You could probably get away with using a car battery for an experimental setup, but only if you only actually use the power generated by the panel(s) as car batteries aren't meant to be discharged; you draw a small amount from them to turn the starter over in a car, then within 10 or 15 minutes they're fully charged and that's where they're supposed to stay. So if you stick to using the battery as a smoothing capacitor for the solar supply it should be okay. A "leisure" battery (also marketed as a "marine" or "deep cycle" batteries) are basically the same, but with much thicker lead plates to withstand deeper discharge cycles. Even a marine battery, you're not supposed to ever discharge below 50% capacity. So a 120Ah battery is only really usable for 12Vx60A = 720Wh or thereabouts (and that is power INTO the inverter, which is unlikely to be more than 90% efficient or so).

There are some inverters that also have built in charge controllers, but they tend to be at the higher end of the market. An MPPT charge controller is better (more efficient) than the cheaper PWM, and it will also look after the battery by putting a float charge across it when it's full, and if your battery needs it a high-voltage equalizing charges once a month.

There are also a few other bits like DC circuit breakers, cable, and an earth rod (the panels should be earthed, and depending on how your using the setup, you may want/need to tie the neutral to earth rather than leaving it floating). And I have my two panels in parallel, so that one still delivers full current when the other is slightly shaded, so I needed inline diodes to stop the current from the sunny panel ending up being pushed across the shady one. This pushes the price up a bit, as does decent cable and connectors.

It is worth doing for a shed/workshop though. And it's nice to have a reliable, off-grid, source of juice. If you choose your appliances wisely, you can even have tea/coffee making facilities with 600W kettle or coffee maker. And I regularly cook steak on my George Foreman grill powered by solar.

[Someone-Else]

You also really need two other components to make a reliable stab at it:-

What you say would be true in most situations, but not in this case.
big-all is wanting to charge his dewalt tool batteries, so he does not need another battery, or a charge controller as his project will have an inverter.

[aeromech3]

S-E what you are implying is that a solar panel can be connected to an inverter without voltage smoothing, for this you need to match the solar Vmp within the input range of the inverter and usually this will spec a more expensive inverter with a wider input range for voltages that might say vary from 18 to 32 on a 24v set up.
I know my own 12v sine wave inverter only accepts about 10.5 to 15vdc without the low/high alarm and trip actuating, hardy enough range for a solar panel

[big-all]

You also really need two other components to make a reliable stab at it:-

What you say would be true in most situations, but not in this case.
big-all is wanting to charge his dewalt tool batteries, so he does not need another battery, or a charge controller as his project will have an inverter.

yes i simply couldnt make much use off full mains as only heating would be a continuos load above 40w other tools are 5 mins max so not worth factoring in as the perhaps £400 to provide would take till i am over a ton to erode the extra cost

[chrrris]

S-E what you are implying is that a solar panel can be connected to an inverter without voltage smoothing, for this you need to match the solar Vmp within the input range of the inverter and usually this will spec a more expensive inverter with a wider input range for voltages that might say vary from 18 to 32 on a 24v set up.
I know my own 12v sine wave inverter only accepts about 10.5 to 15vdc without the low/high alarm and trip actuating, hardy enough range for a solar panel

Aye, what the solar panel produces goes all over the shop. The charge controller sorts all that out, and a battery (even a car battery will do as long as you're careful to only draw what the panel produces - i.e. only use it in full sun) will effectively act like a smoothing capacitor to allow the charge controller to provide a steady-ish input voltage.

I've seen YT vids of people just putting a 12V panel across a car battery, but it's a recipe to knacker the battery with no control of the voltage across the battery. Also, it's possible for a panel to draw current from the battery when in shade (hence the diodes in my setup), the charge controller sorts all of that out. This has been the cause of several roof fires that I've read about, including a bunch of Amazon warehouses in the US.

[chrrris]

yes i simply couldnt make much use off full mains as only heating would be a continuos load above 40w other tools are 5 mins max so not worth factoring in as the perhaps £400 to provide would take till i am over a ton to erode the extra cost

I wouldn't bother doing it for cost saving reasons. My current setup basically owes me about £1500, according to my calculations and experience so far, it's not going to generate much more than £150.00/year of electricity even at today's 36p per unit. So, in theory, it would pay for itself in 10 years, but in practice I've made loads of mistakes doing it and bought various bits of kit I no longer use (e.g. I switched from 12V to 24V which necessitated a new inverter). I've probably actually spent £2000 when you factor in all the redesigns, so that's more like 14 years to pay back. However, it's been a bit of interesting project and learning exercise, and I like the feeling of being independent from the vagaries and increasing uncertainties of our broken government and insane energy supply goals. I've lost count of the number of "impending power cut" stories I've read in the past 2 years -- if it's not Putin's fault, then it's Net Zero's fault, or Climate Change's fault. If there are power cuts in the coming years, I'll be in a better state than most...

[big-all]

saving money is never usually the point its saving the planet
about mid 80s would buy one energy saving bulb a month as they where about £20 or over 4hrs pay
then again will leds perhaps 15-20 years ago again £20 now at that price you would never get your money back but your doing your bit
my son thinks i am unusal but in a good way {i hope lol}
as an experiment bath with perhaps 50l or 10p worth off water use it to flush the toilet 7L at a time decided its easier to set the cistern to 5L and just flush solids
now off course i didnt have to do the experiment but withought added effort the saving good clean drinking water when others have to drink foul water would be fairly meaningless

[chrrris]

its saving the planet

Heh, I wouldn't want anyone to think I was one of that lot! I think the planet is absolutely fine and doesn't need saving, myself. It's worth remembering the manufacturing process for PV panels requires silicon, indium, selenium, gallium and cadmium, and that solar panel production accounts for 90% of the world silicon market (390,000 tons of silicon in 2020, forecast to rise to 807,000 tons by 2040), most of it from China apparently. I think climate change is a convenient hoax to make billionaires richer, and keep poorer people under control. Mind you, I pretended like a was a Rothschild and bought a modest amount of stock in an American Lithium mining company 6 weeks ago and it's up 8.1% already. If only I had a few million quid to invest rather than the relatively paltry amount I have actually put in!