Love the idea...I've basically gone a different direction at this point, but I've been looking for a configuration like this and picked it up anyway.

I do have 2 "issues" with it.

What should I be getting for performance? All by itself I was able to get it to what I assume is its full temperature (300 degrees...didn't get any hotter) in a day. Thought that was a bit slow, but I understand taking time to get to temperature. I now have 11 segments of heat pipe connecting it to 2 heat boilers and I'm at day 3 and I'm still not up to temp. It might hit temp on day 4, but I think it is going to be day 5. Is this normal?

Also, I'd make the suggestion that instead of whatever multiplier you used to get to 57.4/s for the water consumption and steam production, changing it to the standard 30/s base (or in this case it would be 60/s) that the game uses. (Edit: This seems to be normal for the heat exchangers...I missed that the base exchanger does 103/s not 90/s. However, setting it to the other side of 60/s (change your multiplier to 1.6 from 1.5) still makes sense in my opinion so it will run a Steam Turbine (albeit at 1/2 power due to the 250 degree steam) or 2 steam engines.)

Balancing this heat stuff appears to be difficult...

The main decision was, that the steam produced with solar thermal plants is hotter than the steam produced by boilers but lower than the steam produced with a nuclear setup. So the desired temperature for the steam boilers was set to 250 degrees. Steam on that temperature contains about 1.5 times the energy of 165°-boiler steam and 0.5 times the energy of nuclear 500°-steam.

The solar panel's maximum tempereature is 300 degrees. This value is arbitrary, but higher than the temperature used by the heat boiler, so there will be no need of a heat accumulator.

A single solar thermal plant needs some days to reach the operational temperature, but the time gets drastically higher, the more heat pipes are in your setup. When you build a single solar thermal plant, you can watch the temperature go up, but when you place a single heat pipe next to it, you can see the heat pipe taking halve the temperature of the plant. Your setup start working, as soon as every entity in it has reached the desired temperature, but a large setup need many days to heat up.

What you can do about it: Use as few heat pipes as possible. My setup consists of four thermal plants next to each other and directly connected to a single heat boiler.

What I can do about it: I will try to experiment with some values of the heat inside the solar thermal plant. Currently it treated like a single heat pipe, but there could be a way to make it behave more like about 25 heat pipes considering the stored energy.

About the water consumption / steam production rates: they are just copied from vanilla, but I will take a look into it. Thank you for the suggestion.

I don't know what it does to any of the math (specifically to "Produces 420KW during the day") and it arguably still needs some tweaking (I was shooting for 2 heat boilers from a single array but when I moved from a test game to my main game I suddenly got at least 5 running at full capacity...doing more testing now) but I made the following tweaks and got something I felt was a more reasonable balance in my opinion.

300° for a maximum output temp seems perfectly fine to me and while I contemplated it, ultimately I didn't change this. I just hadn't (and haven't) seen anything stating what max temp of the solar array should be and was curious.

The easy one is I hardcoded the energy consumption on line 4 in heat_exchanger.lua to 2.84 instead of the formula. This seemed to result in the maximum throughput I was looking for around 60/s (60.4/s to be exact) and since I personally wasn't looking for a number relative to another value it didn't make sense to have the system doing the math.

Right now, on line 98 in solar_thermal.lua, I've changed the specific heat from 1MJ to 10MJ. No real math or anything behind this...I was reading some of the wiki articles on the heat pipes, heat exchanger, and to some degree the nuclear reactor, and between that and trial and error, that seemed to be a good number. Might actually be a little too large for my ultimate target.

In control.lua on line 3 I changed the temperature factor to 1. This seemed to speed up the rate at which the array got up to temperature but not too much and allow it to keep up with the boilers better.

As you say, as if the opinion side wasn't hard enough, heat and fluid are hard to balance in the first place. In this case the numbers I changed, on further testing, seem not to have maxed out where I thought they did but rather, for the specific configuration at the specific point in game time I did the testing, that was what the array could handle. It seems over time, the array was allowed to get hotter and was able to support more units. The numbers also keep changing. I changed some things in my setup and instead of maxing out at the desired 2+ boilers of my initial testing or the 5 (or perhaps more) boilers I got when I looked earlier in writing this, I'm sitting at 3.5 boilers (and 10 heat pipes connecting them all) right now and the solar array maxing out at 263 degrees. I'm going to let it run, try some more configurations, and see what happens. For one thing, when I had 5 boilers running I realized I had pulled off a second tap on the solar array...want to look into that aspect more.

Thanks for the work. Despite my opinions on the balance, I really like it and am having fun with it. (That might actually be WHY I'm having fun with it...seeing how I can change it to fit my personal game play style.)

Well, since I had this "empty" post already, I'll just update it instead of a new one...

I think getting above 3.5 heat boilers with those numbers was a fluke associated with the rate at which I was using the steam it produced. I had over produced and production had slowed, which allowed the solar arrays to get hotter. Once the backup was cleared, they produced till the temperature fell to equilibrium and I was at 3.5 boilers again.

Definitely need that 50degree headroom and glad I didn't change the max temp. Each heat pipe has 1 degree of insertion loss (I believe by design to create the "flow") and each heat boiler uses a degree as well, so it effectively means the boiler can be up to 48 or so pipes away depending on how many are on the line giving some flexibility in design.

I was pleased to find that the solar arrays will "pass through"...I could connect 2 arrays together and put more boilers on a heat pipe line without the second array being directly connected to the heat pipes. I was also pleased to see it didn't have the neighbor bonus reactors do. Don't know if any of that was intentional or not, but I for one approve.

In the end, my changes are all opinion I've made for my game play. If you decide to use them or some variation, great. If not, I know how to change it. Personally I still might try to either reduce the maximum count from 3.5 boilers to the 2 or so I was initially shooting for, or go the other way and try to get it to 4 (or one per side/connection), but I like what I've done and couldn't have done it without your mod to work off of, so thanks! I look forward to seeing what you decide to do with it officially.