PV "top up" systems

[lulubel]

I hope this is the right place to post this. Apologies to mods if not.

My partner and I live in a place with lots of sunlight, so it makes sense to use it. I'm playing around with the idea of using PV panels to top up our electric supply and to provide us with at least a minimum supply in the case of power cuts, but I have a few questions.

How mobile can a PV array be? We don't plan to move home in a hurry, but we would like the option to take it with us if we did move.

I don't envision we would ever generate more than we use (condsidering we have aircon/heating), but if we did, what are our options? Would the excess have to be put back into the grid? Do we have to make arrangements with our supplier to do this? Could the excess be stored by us for use at times when there's no sunlight?

Is it viable to start with a small array and add to it as funds allow?

Are there any good DIY guides (either print or online)? It would be fun to set it up ourselves if we could.

Am I taking an overly simplistic approach to this?

The idea would be to not put them on the roof, but on a 2nd floor south facing terrace that doesn't get used much because it's usually too hot if the sun's out, and there are plenty of other places to go if it's cloudy. It might not make much of a contribution to our overall usage at first, but if we could add to it over time, it would build up. Plus, we'd be able to run fridges, laptops and a few other essentials if the power went off.

[Madpaddy]

Hi lulubel,
There are hundreds of posts on this site dealing with the type if questions you are asking. As a starting point for your own info, I would subscribe to Homepower magazine which is choc a bloc full of case studies outlining how to set up a PV system for your home. You basically have two choices, to have an off grid system or a grid connected system. The former is more expensive as you need to have a battery bank that is charged by the array and you then use an inverter to convert the dc current to ac current that your appliances can run off. You can also buy dc run appliances but these are generally more expensive. If you go grid connected your utility company can either have a reverse metering system where your meter effectively runs backwards when you are producing electricity or they can put on a separate meter and pay you for what you produce. Sometimes the utility company will pay you much more for the electricity you produce than what they charge you for what you consume. This varies widely from country to country or state to state.

Going grid connected means you will not have an independent electricity supply that will run your home in the event of a power cut etc.

Hope this helps a bit.

[Hawkcreek]

Homepower.com -- would be a good place to start.
You can make a system portable, but you should maybe consider that type of system to be mainly for laptops, radios, and a few lights. Forget air conditioning and heating completely. A fan would be ok, though.

[Mesuge]

The first question one should ever ask, how many hours of sunshine can I count on in my geo loc throughout the year? Given the provided place of residence Malaga, Spain, you are clear to discuss the second and upper levels of PV cookbook..

[pstarr]

How mobile can a PV array be? We don't plan to move home in a hurry, but we would like the option to take it with us if we did move.

You can a buy a small portable PV "Generator" with a solar panel, charge controller, batter, and inverter and run a radio (and in bright sunlight maybe a toaster) with it. The one Alex Jones sells is probably junk.

In the real world, serious photovoltaic panels are heavy and generate little electricity, relative to the demands of a modern home. Each of the twelve panels on my roof generate, on average (the sun moves clouds pass etc.), about enough electricity to power one light bulb--100 watts. Each panel is twelve square feet, weights 70 lbs. and requires a equally heavy metal mounting frame to prevent if from flying off the roof in high winds. I need most of those panels (an associated bank of eight heavy batteries) just to pump water for my house.

No. PV, relative to its functionality, is not mobile.

I don't envision we would ever generate more than we use (condsidering we have aircon/heating), but if we did, what are our options? Would the excess have to be put back into the grid? Do we have to make arrangements with our supplier to do this? Could the excess be stored by us for use at times when there's no sunlight?

I have never heard of a PV generating heat and air conditioning. I doubt a roof would be big enough. It makes more sense to design a house properly for passive heating/cooling using sunrooms, insulation, and thermal mass in the structure.

Is it viable to start with a small array and add to it as funds allow?

Only within reason. I have 12 panels and will grow to 16. You could not start with 1 and move up to 16 without replacing equipment at great cost in labor. The roof rack, wiring, charge controllers, inverters, battery bank, etc. must be sized and matched specifically to the power (the panels) and load (use).

Are there any good DIY guides (either print or online)? It would be fun to set it up ourselves if we could.

Am I taking an overly simplistic approach to this?

It is not "fun." PV is expensive, heavy, roofs are steep and slippery and the entire experience, especially 24 or 48 volts, is very dangerous,

The idea would be to not put them on the roof, but on a 2nd floor south facing terrace that doesn't get used much because it's usually too hot if the sun's out, and there are plenty of other places to go if it's cloudy. It might not make much of a contribution to our overall usage at first, but if we could add to it over time, it would build up. Plus, we'd be able to run fridges, laptops and a few other essentials if the power went off.

Direct solar contact is critical and you want to have the sun hit the entire array of panels for 5 hours during the day. Remember, depending where you live, the summer sun actually passes north of overhead during a large part of the day.

[lulubel]

Going grid connected means you will not have an independent electricity supply that will run your home in the event of a power cut etc.

That sentence alone is a fantastic help. Thanks.

We definitely want it available for "emergencies", so it's looking like we need all the critical stuff separated from the main circuitry in the house. Then we run that on the PV array permanently, and everything else on the mains. That sounds straightforward enough.

pstarr, I won't quote you because I'd probably end up quoting everything you said, but thanks so much for that really informative reply.

No, we didn't envision running the aircon on PV. I just wanted to use it as an example of why we wouldn't be putting anything back in the grid! Our main priority is to keep critical things like our laptops (and therefore our business) running in case of prolonged power cuts, along with fridges, freezers and at least a bit of light. The aircon is a luxury not a necessity. We do have a wood stove in the living room, but after the last year we've had, being able to warm the place up by pressing a button is a luxury we can't resist.

I think "fun" was probably the wrong word to use, although setting up our own array (and maybe hiring strong men to do the heavy lifting) would still be fun in my mind. I like to know exactly how things work, so I can fix them myself if they go wrong, and the best way to do that is to build it yourself. I've learnt most of my DIY skills by watching various tradesmen we've used and asking irritating questions like, "Why are you doing that?" and "How does that work?"

I totally agree about the importance of house design. Unfortunately, the spanish construction industry doesn't. To insulate the roof space, we'd have to take the entire roof off and redesign it. Our most viable option would be to dry line the upstairs ceilings, and for that we'd have to redesign the ducting for the aircon. Spanish houses are designed to keep cool, and they do that very well in the winter - you often don't realise how warm it is until you go outside! They're not good at keeping warm because of all the heat lost through the roof. I'd really like to build my own low energy house, but I can't see that happening in the foreseeable future.

We'd get at least 5 hours of sun a day all year round by putting the panels on the front terrace. It gets about 7 at this time of year, and probably 9 or 10 in mid-summer. I've been looking at some of the commercial arrays around and they all seem to be angled slightly south, but actually not far off horizontal. I assume when you say each panel generates around 100 watts, you mean during the time the sun is actually on them (ie 5 hours = 500 watts in total throughout the day) and not an average of 100 watts per hour across the whole day.

What happens if your array generates more (in the summer) than you have capacity to store? Is it just lost, or are you in danger of overloading your system?

[pstarr]

I assume when you say each panel generates around 100 watts, you mean during the time the sun is actually on them (ie 5 hours = 500 watts in total throughout the day) and not an average of 100 watts per hour across the whole day.

yes. You get 500 "watt hours" or 1/2 "kilowatt hours"

What happens if your array generates more (in the summer) than you have capacity to store? Is it just lost, or are you in danger of overloading your system?

You store it in batteries, or sell it back to the grid (or both as my system allows). Otherwise it is lost as heat off the panels, the charger, and the inverter.

[Madpaddy]

Lulubel you may find that there are grants available in Spain for some of the capital cost of your PV array. In my ideal system I would have a large capacity battery bank and inverter running the entire electrical ring main in my house. The battery bank is charged by my PV array and is also topped up by the grid during off peak hours when the tariff is lower. During the days that you are producing more than you are using or you are on holidays and the battery bank is full, you reverse meter or sell back to the grid for a subsidised rate. Win win situation. Where I work (a Naval Base) we use a generator to act as emergency back up and to run the base when the electrical tariff is highest (5-7pm). We also sell excess back to the grid at this time which hugely cuts our energy costs. Using your PV and battery bank as outlined above may have a similar benefit for you.

[papa moose]

Not quite on topic but just wondering:
The way i understand it most of the PV units that you see now days dotted on the roofs (rooves?) of suburbia are grid-linked, therefore in a situation where the grid is permenatly out they become "useless".
So what i'm thinking about is a DIY/MacGyver style solution to turn a street's worth of "useless" PV panels into at least a system that, even if it can't store power, could feed useful equipment during the day.
I'm not suggesting for a second doing something like this in anything other than a complete break down of society, even then probably wait quite a while to make sure the mains dont come back on.
I understand that PV output is DC but std household stuff runs on AC, unless i'm missing something that means the powerlines running up and down the street carry AC? That would mean "typical" PV units have an inbuilt inverter so they can feed back into the grid?
I guess my point with this line of thinking is that while PVs cant provide the western worlds base load power in a post-bottleneck/isolated survivor scenario scavenging power from existing infrastructure would be an enormous boon.

[edit:typos]

[lulubel]

We don't have variable tariffs here. I'm not sure if it depends on where you are in Spain, but here the tariff is the same 24/7. It leaves you with the option to either generate your own electricity or not. And, as I've said before, there's no way we'd be putting anything back because the aircon would just eat it all up and more.

We're leaning towards the idea of having a non-grid connected system that uses batteries for storage and powers one circuit for the 2 fridge freezers, a few lights, the router and sockets for charging laptops (and the TV and satellite box if my partner has anything to do with it!)

It isn't so much about protecting us from price increases as providing an emergency supply in case of long power cuts. It's only in very recent years that Spain has started to get serious about providing a reliable supply. It probably wouldn't take much to make things slip back. (We were left without water for 3 days in the summer because of a faulty pump.) Our biggest problem would be losing the aircon, but it's bearable in summer, and you can use shutters to keep the worst of the heat out. We've got an enclosed fireplace in the living room that would heat that one room in winter if we had no aircon, so we're going to get an inflatable camping bed for emergency sleeping arrangements!

[Pops]

It isn't so much about protecting us from price increases as providing an emergency supply in case of long power cuts.

If this is primarily an emergency backup plan, the most portable, easiest to operate and most reliable - not to mention much cheaper than PV solution is a small generator.

The can be had in diesel, gasoline, propane, gas/natural gas, gas/natural gas/propane flavors in whatever capacity you need. Small enough to keep on the veranda and run a few lights and the laptop/cell charged would run US $500 - whatever that works out to nowadays.

[Ludi]

The safest thing is to make sure you can survive even without power. For instance, I think it is a good idea to have an emergency water supply from rainwater.

Redundancy is a survival strategy.

[lulubel]

We can survive without power until the money runs out.

All our income is via the internet, and without power we lose that as soon as the laptops run out of charge.