Current state of affairs

 Been a while since the last blog post, but progress hasn't stopped. If anything it has been in a bit of a frenzy of late. The current state: caravan still not 100% finished, but I don't think it never will be. It'll be continual tinkering.

The painting is finished. Pin striping is on. The original tape didn't stick. I vastly underestimated how long spraying the stripes on would take. Though, it wasn't the spraying as the masking that took so long.

Pin stripes done

Electrical panel was wired up and installed. Solar panels mounted and connected.

I've been sleeping in it since 19th December. That day was a 40°C. The house (brick and timber) heated up and retained the heat. The caravan heated up with air temperature, but as it has zero thermal mass, as the sun went down and the air temp dropped, the caravan cooled. The house was much slower. It was cooler in the van. I do have a ventilation fan on one window, but just having the windows open was enough breeze to feel cool sleeping.

By sleeping inside it each night, I've opening/closing the door a lot. Some of the discoveries from this:

1. Three wheels would have been a better choice. Anything I can't reach from the open door, that needs me to step inside needs the back legs down. If I need anything from the front, the front legs need to go down too. Even for just putting them down once, there is an amount of fussing. I added a bubble level to help with leveling.
2. Two locks on the door got old fast. Two locks on the outside and two catches on the inside. The door needs it, but one would be much more user friendly.
3. The door opening upwards seemed a good idea. It does double as an awning when it showers. The door doesn't have support struts, but I do have some supports I can put under it to hold it up was an awning. But that doesn't happen as often as it is get in/get out, or open and get something in/out and close it again. I lift it enough to slip in/out from the side. Or if I need to get rummage a bit, it rests on my back as I do so. In the future I may redo the door to a barn door configuration with one lock.
4. I made the van a little too short. 30cm more would have been a bit cramped getting in and closing the door without being on the bed.
5. I thought I'd sleep with my head at the door end, but ended up liking the other way around. This meant the shelf that my feet were to go underneath was too low. I banged my head on it a few times. It was the first change next day: cut the shelf out and the repaint the wall. I've come to thinking that the shelving I have would be better as soft bags or nets hanging on the walls.
6. The bed is 630mm wide, but with the wheel wells and shelving beside it, there is no room to push off the sleeping bag to the side. The bed is effectively in a well. The sleeping bag is either stuffed to a side, pressing against my back or pushing over my legs/front, or, pushed to the end of the bed. Lately I found that stuffing it in a bag is better. Keeps it bundled up taking up less room even if its down where my legs are.
7. The electrical panel has a surprising amount of lights: blue, orange, green and red. So bright, I haven't needed an inside light. New to me the first night was that some of them flash. All night. I'd never noticed in the day, but at night, it's very noticeable. I'm still using the temporary fix of hanging a shirt over it each night. One day I'll make a better cover.
8. It seemed a good idea to have the electrical panel face the bed. Sit in bed, turn the switches on/off, see the voltage/current/power meters and plug in devices to the USB and cigarette lighter socket. Reality is that I don't need the switches very often. Most things have another switch closer to the business end, or it doesn't matter if they are turned on/off. eg. the ventilation fans, USB devices. I leave the fans on 24x7. The meters, I looked at often on the first few days, but rarely look at them now. The battery drain is so low, and I've so much solar, that even on overcast and rainy days, under the trees, the battery fully recharges. The UBS/cigarette access was a major pain point. I couldn't leave anything plugged in over night as the plugs in stuck into be bed space. Turning over could catch the lead or plug and break it. Anything plugged in really wanted to be on the bed. I still use the sockets when I'm awake, but I installed a cigarette lighter socket and USB plugs on the forward and backward sides of the panel for when I want to leave things plugged in over night. There is shelf space in front and behind to leave devices, rather than on the bed and the cables are out of the bed.
9. The roof was extremely loud in the rain. Light rain was okay, but heavier showers, it was unbearable. I'm parked underneath some trees and larger water drops drop from the branches. They manage to make a loud cracking sound. The raised solar panels are okay, so it was only the strip around them that was the problem. With testing, a piece of fabric is enough to break up the drops to deaden the noise. I wanted green velvet but type I got was too thin. I found a piece of cream corduroy. It works to deaden the noise, but I'm not sure if it will remain. I'll leave it on for now and monitor how the water drains and if it drys enough to not become mouldy.
10. The bed! So many problem with the bed. It was terrible for storage underneath. When I cut the original height down, I thought I was clever by making it 110mm high - the height of a tin of beans. I was thinking that tinned food could be also be the bed top supports. But too many things are taller than 110mm. So I had a storage problem for stuff I had planned on going under the bed. The bed creaked a lot. I laminated it with paper rather than fabric like the rest of the caravan foam. But the paper with glue/paint become very stiff and hard. No give at all. The polycarbonate bed top and floor creaked when it rubbed on them. I could have fixed this, but I made the base a tight fit between the wheel wells and shelving. More creaking points. and as the fit was so tight, no space to put anything to stop the rubbing. New bed base fixes all these and more.

New bed base under construction

Cheap Solar panels

When I planned the caravan, I took a quick look about on online for solar panels. I saw that a 100W panel was about 1m long. The next size up was about 1.5 or 1.6m long. That was the basis for the caravan. If I'm committed to 1.6m, when my tent is 1.9m long, why not sleep under the solar panel?

A few months ago I looked quickly on Ebay and saw 300W and 400W panels. Small sizes too. Wow. This is great. Cheap too! I could get 4 panels on the roof. That's an amazing 1200 watts! I'll be swimming in power. Solar must have improved a lot. I was happy for weeks.

Then I went to order. 

Money on the line, so I really dug into the details and specs to compare panels.  A huge face palm moment. How did I not notice earlier!

I won't put a link here, but search Ebay and you'll find a lot of examples for cheap solar panels.  I'm looking at flexible panels, but this also applies to rigid panels.

Taking one example on Ebay, advertised as 400W for $136.99.  Looking through the nice pictures, lots of claims of high efficiency. High conversion rate. Panel size is 960x670mm. Nice and small. The seller has a lot of sales. High ratings and good reviews.

Scrolling down to "Item specifics" to get more details is the first hint of something not quite right. 

Power: 201-300W  Charging Mode: PWM (Pulse Width Modulation)
Connector Type: MC4   Wattage: 300-399W 

Power versus Wattage? What's this about?  Both given as a range, but it is advertised as 400W.  What would I really get out of it?

The panel is using monocrystalline cells. 

Solar Technology: Monocrystalline

Googling, the top result: Monocrystalline cells are rated at 15%–24% efficiency. Looking at other results, 15%-20%, 15%-23%.   Note this is for the cell. After you encapsulate it in plastic the rating will drop. But then searching for solar panel efficiencies, I also find 15%–24%.  Cheap Ebay panels are unlikely to be 24%.

How to compare solar panels: using Standard Test Conditions. 

Standard Test Conditions (STC) are the industry standard conditions under which all solar PV panels are tested to determine their rated power and other characteristics. When a panel is advertised as having a capacity of 350W for example, this is the power it is expected to produce under STC. 

It tests a cell at:

Cell temperature: 25°C
Irradiance: 1000 W/m²
Air mass: 1.5

This is the cell, there are other measurements that give a more real world data for a panel. 

But taking STC, and using the 1000W/m² and a low and high efficiency value, we have:

The panel size is:  0.960x0.670m = 0.64m²
Panel Wattage = Solar Irradiance x Area x Efficiency

Low efficiency: 15% 
            =  1000 W/m² x 0.64m² x 15%
            = 96 W

High efficiency: 24%
            =  1000 W/m² x 0.64m² x 24%
            =  154 W

96-154W is a long way from the advertised 400W. Not even close to the 201W power rating either.

But I might not get even that. That was at 1000 W/m².  Using the solar radiation in Sydney. On the day I was doing the calculations, the maximum was 961W/m² at midday. The average of 10am to 3pm was 833W/m². The day average was 569W/m².

Running the numbers again this time using 15, 17, 20 and 24% efficiency for the hours of the day. How many watts at the different hours at an efficiency.

October 28
----------	------------
Sunrise	06:00
Sunset	19:18
Total	7398 wh/m²
Panel m²	0.64
		Watts
Time	W/m²	15%	17%	20%	24%
07:00	144	14	16	18	22
08:00	376	36	41	48	58
09:00	594	57	65	76	91
10:00	777	75	85	99	119
11:00	901	86	98	115	138
12:00	961	92	105	123	148
13:00	826	79	90	106	127
14:00	771	74	84	99	118
15:00	763	73	83	98	117
16:00	612	59	67	78	94
17:00	445	43	48	57	68
18:00	213	20	23	27	33
19:00	15	1	2	2	2

What time you test and the efficiency of the panel matters. In the real world, that 400W panel is only going to give a maximum of 148W on that day if (and that's a bit if) it is 24% efficient and the temperature of the panel is 25C.  Spoiler: It won't be 25C in the sun and it isn't 24% efficient.

All the high quality brand name panels I checked had Monocrystalline efficiencies of 17%, so using that, the 400W panel might give 105W at midday at most. Real world will be less.  Flexible panels also  degrade faster than rigid panels.

But all is not lost.  

I created a spreadsheet of all the solar panels I was looking at. On and off Ebay.  The off Ebay panels were by Renogy, Sunman and ATEM. Their specifications as advertised.  Price, size, advertised watts, panel type, Voc and Vmp. I then calculated the watts at STC for all panels based on its size. No surprise, most Ebay panels were way less than advertised. But not all. All the non Ebay panels I included were better than advertised at STC. 

I also calculated $/watt at STC for all panels. If area wasn't a concern this would be one deciding metric, but panel size was also important to me. I only have so much space on the roof. How could I get the maximum use of it?

With the different panel sizes, I could get between 1 and 4 panels.  In the end, I decided on three Ebay panels advertised at 400W, but by my calculations are more likely to be 90W each.  I got lucky that the seller was having a sale, so each panel ended up costing $70 delivered.  There was a Sunman panel I really liked with watt output only slightly lower than the combined three I panels I ordered. But I could only get one on the roof and it's price was significantly higher.  Annoyingly a couple of weeks later, they had a 60% off sale. At that price I would have purchased it. But too late by then. 

I'm happy with the three I did order. All the reviews of flexible panels show they don't last as long as rigid panels. Flexing cracks the cells, lowering output. Over heating is a problem if they don't have an air gap underneath. As my caravan is insulating foam, I intend to mount them raised. So having cheap panels for a first go suits me. I think of it as an experiment to test the mounting system. When they fail, I'll know more about my usage and the mounting system. Then I might look at a more expensive options.