[
{"url":"/_holding/pump-controller","title":"Solar Pump Controller","summary":"Variable-speed solar pump controller with automated siphon management for drainback systems.","text":" Solar Pump Controller A daughterboard module for the RP2350 Motherboard(/motherboard) that manages variable-speed pumps in drainback solar thermal systems. The controller automatically fills collectors, establishes siphon, modulates flow based on temperature differential, and shuts down safely when conditions require it. How it works The controller continuously reads panel and tank temperatures from the RS485 network. When the panel is hotter than the tank by more than a configurable threshold (default 5.0 C), the pump starts. Speed ramps linearly from the minimum (30%) to maximum (85%) as the temperature differential increases. An optical bubble sensor on the pump discharge line monitors flow. When air is detected, the controller purges at full speed until water is confirmed, with temperature-compensated run-on times to ensure dispersed air is cleared before it can coalesce into siphon-breaking Taylor bubbles. State machine The pump operates through seven states: State Speed Description --------------------------- Off 0% Waiting for sufficient temperature differential and sunlight Filling 100% Filling pipes and establishing siphon at full speed Modulating 30-85% Normal operation, speed proportional to temperature differential Full speed 100% Temperature differential exceeds ramp range Purging 100% Clearing air bubbles detected by bubble sensor Calibrating Variable Automated minimum-speed calibration sequence Safety shutdown 0% Stopped due to overtemperature, freeze risk, or sensor fault Drainback hydraulics The controller design is informed by research into two-phase flow in drainback solar systems. During filling, flow transitions through annular flow (thin water film around an air core), slug flow (large air bubbles), and finally single-phase choking where the siphon establishes. The choking flow velocity is calculated from pipe diameter and type, with adjustments for corrugated pipes and horizontal sections. Once the siphon is established, the weight of the wat"},
{"url":"/blog/2024-03-05-new-modules-testing","title":"New Modules - Testing","date":"2024-03-05","summary":"Initial board tests yielded promising results with only a minor ESD protection issue.","text":" New Modules - Testing Initial board tests yielded promising results. The dual voltage regulators, EEPROM, oscillator, test points, programming, and USB components all work. Regulation was stable up to 18V DC. RS-485 testing We conducted exhaustive RS-485 connection testing, processing close to a million messages with no significant problems. We intentionally induced errors to verify detection systems worked correctly. Signal integrity regarding shape and slew rate performed well. Minor issue A small design flaw was identified — a hiccup involving tracing to an ESD protection diode array. The next revision will address this along with USB-C in vertical orientation and Schottky diode updates. Manufacturing The boards were fabricated by JLCPCB. Shipping was fast, components were perfectly placed, and there were no visible defects. !Main board detail(main-board.jpg)"},
{"url":"/blog/2022-07-02-tilt-angle","title":"Tilt Angle","date":"2022-07-02","summary":"Optimal solar collector positioning depends on latitude and season.","text":" Tilt Angle Solar collectors and panels have to be correctly aligned to get the best performance; these angles can affect the amount of energy collected and are based on two factors: latitude and the season. Solar collectors will capture the most energy when most of the solar radiation falling on them is perpendicular to the collectors. Because axis tracking systems are prohibitively expensive and complex, we'll ignore those, and assume the collectors are to be mounted in a fixed manner. Fixed-mount guidelines The general rule of thumb for fixed-mount solar collectors is to subtract 15 degrees from the latitude of your location during summer and add 15 degrees to your latitude during winter. Collectors should point towards the equator wherever possible. Practical considerations In practice, it's rather more complex. People want most heat during the winter and less during the summer. A fixed-size collector array that can easily produce their domestic hot water needs to be large enough to do so in the winter and angled appropriately for that season. During the summer that large array will not be best aligned, but it will be adequate to manage their hot water needs, given the longer hours of sunlight available. Choosing the location The best is a roof facing the equator with a pitch that is close to your latitude + up to 15 degrees, and that is not shaded by surrounding trees or buildings etc. Be aware that winter sun is much lower in the sky, so objects that appear to not shade or obstruct the collectors during the summer might well do so during the winter. If you are mounting collectors on a flat roof, make sure that they do not shade each other when the sun is low in the sky."},
{"url":"/blog/2022-08-19-insulated-tank","title":"Insulated Tank","date":"2022-08-19","summary":"Insulating a 1000-litre IBC tank with 100mm mineral wool and tarpaulin.","text":" Insulated Tank We finally insulated the 1,000-litre tank this morning with 100mm mineral wool plus a tarpaulin cover. Before this, the tank was un-insulated, which benefited us as it cooled overnight and allowed us to perform repetitive tests. It will be interesting to see how well the tank performs, and heat accumulates. !1000 litre IBC(insulated-tank.png?w=600) The tank is a 1 cubic metre IBC. It's outside, at the bottom of a scaffold tower with two test panels at the top."},
{"url":"/blog/2022-08-02-test-array","title":"Test Array","date":"2022-08-02","summary":"Repositioning from 80 to 55 degrees produced significant performance improvement.","text":" Test Array After setting inclination to 55 degrees Up until today (02 August 2022), our test array was inclined at nearly 80 degrees from horizontal. That gave degraded performance. We set it this morning to 55 degrees and saw a large difference. You can see this in the graphs(https://privateersystems.com/docs/solardata/index.html). We'll set it to about 35 degrees in the next few days. !After — 55 degree angle(array-55.png?w=600) !Before — 80 degree angle(array-80.png?w=600) We noticed that a typical sustained measurement of heat harvested was in the region of 630 W/m2. That compares favourably with the maximum possible from just over 1000 W/m2 we measured with an irradiance meter. Changing the inclination of the array to 35 degrees and increasing the temperature delta should allow us to exceed 700 W/m2."},
{"url":"/blog/2022-08-03-inclination","title":"Inclination","date":"2022-08-03","summary":"Adjusting test panels to 35 degrees and exceeding 700 W per square metre target.","text":" Inclination Today, 03 August 2022, we finally adjusted the panels of the test array to 35 degree inclination. The morning was clear and fairly bright; a hot day with air temperatures in the region of 30 C. And we easily reached our target of over 700 watts per square metre output. In fact, we got peaks of up to 750 W/m2 with water at 30 C inlet temperature! You can see this in the graphs(https://privateersystems.com/docs/solardata/index.html). Choose Aug 03 and press the graph button."},
{"url":"/blog/2022-08-19-digital-sensors","title":"Digital Sensors","date":"2022-08-19","summary":"DS18B20 temperature sensors and the counterfeit problem in the market.","text":" Digital Sensors We're using external temperature sensors, always insulated from the outside. The Analog Devices / Maxim / Dallas Semiconductor DS18B20 is perfect for this, but the problem is that most DS18B20 sensors on the market are fakes — clones marked as the real thing. These work well for the most part, but they are susceptible to issues. Working around issues from these clone / fake sensors has been a major headache. Our software tries to detect them, and we allow the user to enter a bias offset in case they read high or low. !DS18B20 temperature sensor(ds18b20.png?w=400) It's always best to buy genuine items from DigiKey, RS, Farnell, Mouser, etc. but we know that many people will not. Sealed probes The DS18B20 does not have a sealed package and cannot be submerged in water. If you need to submerge the DS18B20 in a liquid, several third parties manufacture sealed temperature probes that use the DS18B20. Maxim does not endorse any particular manufacturer of these probes nor maintain a list of these probe manufacturers. Most probes that we found do not have genuine chips in them. Lots of information here(https://github.com/cpetrich/counterfeitDS18B20)."},
{"url":"/blog/2025-11-20-copper-collectors","title":"Why Copper Collectors","date":"2025-11-20","summary":"Why we use copper exclusively in our collector designs.","text":" Why Copper Collectors Aluminium is cheaper. Stainless steel is stronger. So why copper? Copper has the second-highest thermal conductivity of any metal at 401 W/mK. Silver beats it at 429 W/mK, but nobody is building solar collectors from silver. Aluminium manages 237 W/mK. Stainless steel limps in at 16 W/mK. For a solar thermal collector, where the entire job is to move heat from the absorber surface to the fluid in the risers, conductivity is everything. A copper riser conducts heat to the water roughly 25 times faster than a stainless steel one. !Solar pump controller(solar-pumps.png?w=600) Copper also forms a protective patina that resists further corrosion. An all-copper system running plain water has a service life measured in decades."},
{"url":"/blog/","title":"Blog","summary":"News and updates from Privateer Systems.","text":" Latest posts from Privateer Systems."},
{"url":"/blog/2025-01-03-carters-solar-system","title":"Carter's Solar System","date":"2025-01-03","summary":"President Jimmy Carter's 1979 White House solar thermal installation and its legacy.","text":" Carter's Solar System In June 1979, President Jimmy Carter made a bold statement about renewable energy by installing 32 solar thermal panels on the roof of the White House. This event was not just a practical move to heat water for the White House but also a powerful symbol of the United States' commitment to harnessing solar energy during an era marked by an energy crisis. The installation of these panels represented a significant shift in public perception regarding renewable energy, encouraging many to consider solar thermal systems as viable alternatives to traditional fossil fuels. The impact of Carter's solar panels Carter's installation was projected to supply nearly 75% of the hot water needed for the White House kitchen and laundry. The flat plate collectors worked by absorbing sunlight, which heated water circulating behind them. This innovative approach showcased how solar energy could be utilised effectively in everyday applications. Carter famously stated that in the year 2000, these solar water heaters would still be supplying \"cheap, efficient energy,\" highlighting his vision for a sustainable future. The installation cost around $28,000 at the time, which translates to approximately $100,000 to $120,000 today when adjusted for inflation. This investment laid the groundwork for future advancements in solar technology and inspired both individuals and businesses to explore solar solutions. A shift in perception and costs Since the late 1970s, the costs associated with solar technology have dramatically changed. The price of solar panels has decreased significantly due to advancements in technology and increased manufacturing efficiency. What once was considered a high-cost investment is now much more accessible for homeowners and businesses alike. At Privateer Systems, our small group specialises in developing solar drainback systems, which are designed to maximise efficiency and minimise risks associated with freezing temperatures. Our systems utili"},
{"url":"/blog/2026-02-15-winter-performance","title":"Winter Performance Update","date":"2026-02-15","summary":"How our drainback system performed through the 2025-26 winter.","text":" Winter Performance Update The 2025-26 winter tested our prototype installation thoroughly. The coldest panel reading was -14.8 C on 21 January 2026, with outside air at -23.2 C. The panel can sit a few degrees above ambient at night if there is any residual radiation, or drop below ambient due to black-body radiation to a clear sky. The drainback system handled all of this without intervention. On cold nights, the collector stood empty and dry. No freeze risk whatsoever. On clear winter days, even with ambient temperatures well below zero, the system ran and contributed useful heat. !Roof-mounted sensor unit(roof-sensors.png?thumb) Data from the test rig All figures drawn from the RS485 sensor logs on the test rig near Prague, from 18.5 m2 of collector aperture. Data runs from 1 December 2025 to 14 March 2026 (102 days). Month kWh collected ---------------------- December 2025 269 January 2026 257 February 2026 333 March 2026 (to 14th) 473 Total 1,332 The pump ran on 51 of the 102 days. The highest tank temperature reached was 56.2 C. That gives 72 kWh per m2 of collector over the winter period, with March already showing strong spring gains. View live data from the test rig(https://privateersystems.com/docs/solardata/index.html)"},
{"url":"/blog/2022-08-18-stagnation-testing","title":"Stagnation Testing","date":"2022-08-18","summary":"Dry panel stagnation test reaching 92.88 C with 28.81 C ambient — a 64 C differential.","text":" Stagnation Testing We ran the test rig today, 18/08/2022, without the pump. The panel was dry. The panel temperature reached 92.88 C. The ambient temperature at that time was 28.81 C. So it's possible to have the panel innards 64 C hotter than the surrounding air, even in central Europe."},
{"url":"/blog/2022-08-13-smoother-running","title":"Smoother Running","date":"2022-08-13","summary":"Reducing operational cycles through improved control logic and ambient light detection.","text":" Smoother Running In an effort to smooth out the troughs, when the delta between the panel and tank is just a bit too small to run, we're trying an additional technique of using the light level to determine whether to keep the panel filled, even when we might lose a little heat from the tank. Keeping the semi-syphon system filled, but not flowing, requires quite a delicate balance. Overshoot and lose heat, undershoot and drain back. By using irradiation data, the panel can operate sooner after sunrise, reducing latency in sensor detection and eliminating waiting periods for adequate temperature differential conditions. The test system will be on and off over the next few days during testing, and there will likely be some strange results showing up in the logs and graphs(https://privateersystems.com/docs/solardata/index.html)."},
{"url":"/blog/2022-10-18-new-test-system","title":"New Test System","date":"2022-10-18","summary":"From two-collector test rig to a ten-collector system with improved winter inclination.","text":" New Test System !Solar master controller(solar-master.png?w=600) After running a test rig with two collectors for several months (on a scaffold tower next to the office!), we're building a ten-collector system in a more permanent location. The new installation will feature a more appropriate inclination for winter of about 60 degrees. Results so far We're very pleased with the performance so far during the summer. There are logging data online for August and September this year for this small test system. Once we've installed the bigger system, we'll start the online data logging(https://privateersystems.com/docs/solardata/index.html) again."},
{"url":"/blog/2022-10-05-differential-controller","title":"Differential Controller","date":"2022-10-05","summary":"A three-channel controller that prioritises heating domestic hot water from the lowest cost source.","text":" Differential Controller Our three channel differential controller prioritises heating of domestic hot water from the lowest cost source and conserves heat in the domestic hot water tank when the input medium temperature is too low. !Privateer's three channel differential controller(diffcontrol-front.png?w=600) Three input sources - Solar accumulation tank - Solid fuel boiler (such as wood gasification) - Electric resistive heater (immersion heater) If the domestic hot water temperature is below a preset limit, the controller will check to see if an input source temperature is above a preset delta. If so, the source is used to heat the domestic hot water. Inputs are prioritised in the list order above. More here...(/controller)"},
{"url":"/blog/2024-02-05-new-modules","title":"New Modules","date":"2024-02-05","summary":"A modular system with modules connected on a 2-wire data bus.","text":" New Modules We have designed a modular system with modules connected on a 2-wire data bus, with an additional 2 wires for power. Previously, we used premade PCBs connected to our own boards, but we needed a more professional approach. Design goals - Increased memory capacity beyond the limited kilobytes previously available - Text-based menu configuration accessible via terminal emulator on any device - No client software needed for configuration — what works now will work in 10, 20, 30 years - Built-in RS485 communications - Dual voltage support (3.3V and 5V) - Comprehensive power conditioning and ESD protection - Field-upgradeable firmware - Robust and cost-effective design Accordingly, we developed the following new module: !New module board(new-module-board.png?w=600) Architecture The new module simplifies child module development. Each specialised module requires only the specific circuitry for its function. Temperature sensors can be simple NTC sensors with a resistor divider and some ESD protection. Pump control follows a similar approach. Status The new board has been fabricated and is undergoing testing. Following successful validation, we will redesign each solar system component with dedicated daughterboards and appropriate code adjustments, followed by comprehensive system testing and improvement iterations."},
{"url":"/blog/2023-09-05-new-installation","title":"New Installation","date":"2023-09-05","summary":"Building a 10-collector array on welded scaffolding after successful prototype testing.","text":" New Installation The testing conducted earlier proved valuable. We had successfully developed a functional prototype featuring a couple of collectors. Recognising this was insufficient, we constructed a 10-collector array mounted on welded scaffolding. The building is historic and listed, making roof installation impractical. Consequently, the collectors were positioned approximately 30 metres away from the house. Despite this distance, system performance remains strong. The setup includes 2,000 litres of clear water storage in insulated tanks. Hot water for the house flows through a simple stainless corrugated heat exchanger. !10-collector array installation(collector-panels.jpg?w=600) The installation will undergo rigorous testing throughout winter. Daily performance graphs are available for monitoring."},
{"url":"/blog/2022-10-25-first-truly-global-energy-crisis","title":"First Truly Global Energy Crisis","date":"2022-10-25","summary":"The IEA characterised the situation as the first truly global energy crisis.","text":" First Truly Global Energy Crisis Tightening markets for liquefied natural gas (LNG) worldwide and major oil producers cutting supply have put the world in the middle of \"the first truly global energy crisis,\" Dr Fatih Birol, Executive Director of the International Energy Agency (IEA), said on Tuesday 25 October 2022. In March 2022, the IEA released a 10-point plan to reduce the European Union's reliance on Russian natural gas. Of the 10 points, Action 4 is to accelerate the deployment of new wind and solar projects. !Electric prices(electric-prices.png?w=600) Heating demand The main use of energy by households in the EU in 2020 was for heating their homes (62.8% of final energy consumption in the residential sector), with renewables accounting for more than a quarter (26.8%) of EU households' space heating consumption. Done in a simple and cost-effective way, solar thermal can significantly reduce the need for other heat sources — thereby reducing electricity grid loading and gas use. And solar thermal can use the cheapest battery available: water. Solar thermal opportunity > Solar energy systems have long been a low-cost and reliable solution for > heating in many European countries but overall solar heat accounts for just > around 1.5% of heating needs. To reach the EU 2030 targets, energy demand > covered by solar heat and geothermal should at least triple. > Rooftops have been the place for most of the solar energy deployment so far, > but huge untapped potential remains. It is a low-hanging fruit and the EU and > its Member States must join forces to exploit it rapidly as much as possible, > given multiple benefits for consumers."},
{"url":"/blog/2022-07-02-why","title":"Why?","date":"2022-07-01","summary":"Planetary stewardship and the case for solar thermal energy.","text":" Why? !Pale Blue Dot — NASA/JPL-Caltech(pale-blue-dot.png?w=600) In 1990, Voyager 1 took a photograph of Earth from 6 billion kilometres away. Carl Sagan reflected: > That's here. That's home. That's us. On it everyone you love, everyone you > know, everyone you ever heard of, every human being who ever was, lived out > their lives ... on a mote of dust suspended in a sunbeam. > In our obscurity, in all this vastness, there is no hint that help will come > from elsewhere to save us from ourselves. The case for solar thermal Half of the world's energy consumption is related to heat. Among renewable technologies, solar collectors represent the most efficient environmentally-friendly method for harvesting heat energy. We are developing direct solar-to-heat collection methods that are simple, inexpensive, and reliable. No intermediary conversion steps. No complex electronics. Just sunlight heating water."},
{"url":"/motherboard","title":"RP2350 Motherboard","summary":"Our modular RP2350-based controller platform for solar thermal systems.","text":" RP2350 Motherboard Our next-generation controller platform, built around the Raspberry Pi RP2354B (dual-core Cortex-M33 at 150 MHz). This single board serves as the base for all current and future Privateer Systems products. !New motherboard(RP2350-80-motherboard.jpg) Modular daughterboard architecture The motherboard provides power regulation, RS485 networking, and display output. Stackable daughterboard connectors expose all 48 GPIO pins, allowing specialised modules to be added without modifying the base board. All handler modules are compiled into one firmware image. Users enable or disable modules via USB serial menu — no hardware straps or separate firmware builds required. Current modules - NTC temperature monitor — eight-channel NTC thermistor sensing via Wheatstone bridge and ADS1115 16-bit ADC with analogue multiplexing. Cascaded median and moving average filtering (64 samples per reading) delivers sub-degree accuracy - Solar pump controller — variable-speed PWM pump control with temperature-compensated flow and safety interlocks (overtemperature lockout, freeze protection, sensor fault detection) RS485 network Nodes communicate over a multi-master RS485 bus using CSMA/CA collision avoidance with CRC32 error detection. Any node can read sensor data from any other node on the network. The dual-core architecture dedicates one core entirely to RS485 I/O for deterministic timing. Technical specifications Parameter Value ------------------ Processor RP2354B dual-core Cortex-M33 @ 150 MHz Memory 520 KB SRAM, 2 MB QSPI flash ADC 12-bit, 8 channels (RP2350 internal) Network RS485 half-duplex, selectable baud (19200 default), CRC32 Power input 24V DC with four-stage regulation (24V/12V/5V/3.3V) Display Auto-detected TM1637 7-segment or HD44780 LCD Configuration USB serial menu, hot-plug supported Protection ESD, TVS clamping, polyfuse input protection > --- >"},
{"url":"/about","title":"About","summary":"About Privateer Systems — solar thermal engineering from central Europe.","text":" About Privateer Systems We are a small engineering group based in central Europe, focused on making solar thermal heating practical, affordable, and independent of subsidies. What we do We design and build drainback solar thermal systems — the hardware, the firmware, and the control software. Everything from the copper collectors on the roof to the RS485 network protocol that ties the system together is our own work. Our goal is a solar heating system that pays for itself within three years, runs autonomously without internet connectivity, and lasts decades with minimal maintenance. How we work We write all our own embedded code in C++. Our boards run bare-metal firmware on RP2350 microcontrollers — no operating system, no cloud dependency, no subscription. Configuration is via USB serial terminal. The hardware is designed in KiCad and fabricated in small batches. We use all-copper collectors for maximum thermal conductivity and long service life. This website This site is built with MarqueDown(/marquedown), our own lightweight site engine. Content is authored in Markdown, stored in a git repository, and served from memory via FastCGI. There is no database, no CMS, and no JavaScript framework."},
{"url":"/contact","title":"Contact","summary":"Get in touch with Privateer Systems.","text":" Contact For enquiries about our solar thermal systems, please email us at . We are based in central Europe and typically respond within a few working days. (function() { var u = 'systemsprivateer'; var d = 'gmail.com'; var e = document.getElementById('email'); var a = document.createElement('a'); a.href = 'mailto:' + u + '@' + d; a.textContent = u + '@' + d; e.appendChild(a); })();"},
{"url":"/controller","title":"Differential Controller","summary":"Three-channel differential temperature controller for domestic hot water.","text":" Differential Controller Ver 3.x Our original three-channel temperature controller that prioritises heating of domestic hot water from the lowest cost source. This design uses an Atmel 328 microcontroller with Dallas DS18B20 digital temperature sensors. This product is being superseded by the RP2350 Motherboard(/motherboard) platform, which uses NTC thermistor sensing via Wheatstone bridge and offers modular daughterboard expansion. Overview The controller manages three input sources: 1. Solar accumulation tank 2. Solid fuel boiler (wood gasification) 3. Electric resistive heater (immersion) If the domestic hot water temperature is below a preset limit, the controller checks whether an input source temperature is above a preset delta. Sources are tried in the order listed above, always preferring the cheapest option. Basic function The controller conserves the domestic hot water temperature and prevents it from dropping as output from solar systems or boilers cools. It transfers heat through tank heat exchangers while maintaining DHW temperature integrity. !Controller front view(diffcontrol-front.png?w=600) Mode of operation !LED status indicators(diffcontrol-leds.png) Four LED indicators show system status: - STORE — solar heating DHW - IMMERSION — electric heating - BOILER — solid fuel heating - POWER — device operational Configurable parameters - Preferred DHW temperature (60-90 C) - Delta (temperature differential threshold) - Hysteresis (prevents valve cycling) - Minimum operating temperature - Clamping temperature - Maximum DHW temperature (hard limit: 90 C) - Valve exercising (every 28 days of non-operation) Installation Electrical connections !Power connections(diffcontrol-power.png?w=400) - 220VAC mains power - Thermo actuator valve connections - Immersion heater relay - Thermal store pump relay - Dallas DS18B20 temperature sensors (3-wire, 5VDC) !Dallas sensor connections(diffcontrol-dallas.png?w=400) Sensor placement !DS18B20 temperature sensor(ds18b20.pn"},
{"url":"/","title":"Home","summary":"Drainback solar thermal systems and renewable energy engineering.","text":" > > Water-based solar thermal collectors outperform photovoltaic panels by approximately three times in energy yield per square metre, at lower cost. Two-thirds of a home's energy use is normally for heating. Let's use the sun whenever we can. Drainback solar The Privateer solar system re-invents drain-back solar collectors. We reduce cost, increase performance, improve reliability, reduce maintenance, remove mechanical complexity, lengthen product life, and speed up payback. Our system has one moving part: the pump impeller. It uses water, not antifreeze. Because the collector's default state is dry, it cannot freeze or boil. It needs no expensive pressure vessel and requires almost no maintenance. !Collector panels on roof(collector-panels.jpg) Our approach We combine our design of hardware and software with novel engineering and OEM smart pumps. We simplify the mechanics but increase performance. We couple this with all-copper collectors for high performance and long life. > Keep it simple The overall goal is to reduce the cost of the system so that it pays for itself without the need for government subsidies. Simple design reduces cost, reduces failure modes, and increases longevity. Security and independence > All embedded code is ours. There is nothing to hack, nothing to subscribe to, and nothing that stops working when a company folds or decides to change their terms of service."},
{"url":"/products/live-data","title":"Live Data","summary":"Live performance data from the test rig near Prague.","text":" Live data Data from the test rig near Prague(https://privateersystems.com/docs/solardata/index.html) The above page is best viewed on a PC, or device with a larger screen, not mobile. Test rig specifications The installation uses: - 1 cubic metre water capacity tank - 18.5 m2 total collector aperture area - External tank location (overnight heat loss) - Panels pitched for winter collection Graph explanation The graph plots seven channels logged every minute: Colour Channel Description ------------------------------ Orange Panel Collector panel temperature (C) Blue Tank Tank bottom temperature (C) Green Out Outside air temperature (C) Black Flow Pump flow rate Purple kWh/m2 Cumulative energy per m2 of aperture Red kWh Cumulative energy (kW) White Day (ldr) Light level from LDR sensor The initial \"teeth\" in the panel trace show the collector catching morning sunlight, with modulating pump speeds to prevent short-cycling. Location The test rig is near Prague: - Large trees to the immediate east - 1,670 hours annual sunlight average - Summer temperatures approaching 40 C - Winter temperatures reaching -20 C Data collection Sensor data transmits via RS485 protocol. Logging occurs about every minute with CSV uploads to the server for browser-based graphing."},
{"url":"/products/ntc-daughterboard","title":"NTC Temperature Daughterboard","summary":"Eight-channel NTC thermistor daughterboard with Wheatstone bridge sensing, designed for reliable remote temperature measurement in solar thermal systems.","text":" NTC Temperature Daughterboard The NTC temperature daughterboard is a stackable module for the RP2350 motherboard(/motherboard). It provides eight channels of precision temperature measurement using NTC thermistors(/resources/ntc-calculator) in Wheatstone bridge(/resources/wheatstone) configurations, connected via standard Cat5 cabling. !Cat5 cable(cat5.jpg) Solar thermal systems need reliable temperature readings from sensors mounted in hostile environments — on rooftops, inside hot water tanks, on collector panels, and alongside inverters and pump motors. The sensors must work continuously for years without maintenance, survive temperature extremes, tolerate electrical noise, and cope with long cable runs. Getting this wrong means false readings, wasted energy, or equipment damage. Why NTC thermistors? There are three common approaches to electronic temperature measurement: one-wire digital sensors, platinum RTDs, and NTC thermistors. We evaluated all three and chose NTC for good reasons. Problems with one-wire digital sensors One-wire sensors like the DS18B20 are popular in hobbyist projects. They are cheap, easy to wire, and give a direct digital temperature reading with no analog circuitry. But they have serious limitations for solar thermal use. Maximum temperature The DS18B20 is rated to 125 C. Solar collector stagnation temperatures can exceed 200 C, and even normal operating temperatures regularly reach 90-100 C in summer. Running a semiconductor device near its maximum rating for sustained periods accelerates ageing and drift. NTC thermistors are passive devices — glass-encapsulated types are rated to 300 C and do not degrade with sustained heat exposure. Glitches and data integrity One-wire sensors communicate digitally over the same wire that powers them. The protocol is timing-sensitive, and the sensor contains an on-board ADC, digital logic, and a ROM. Any of these can glitch. In practice, DS18B20 sensors are known to occasionally return readings of ex"},
{"url":"/products","title":"Drainback Solar System","summary":"Our drain-back solar thermal collector system with RS485 network.","text":" Drainback Solar System The system operates on an industrial RS485 network with modular components powered through the cabling. - No collector to tank heat exchanger - No glycol, 15% higher efficiency - No freeze problems - Almost maintenance free > !Master control unit(solar-master.png) Master control unit The master unit manages up to four separate collector arrays, variable speed pumps, and accumulation tanks (typically 1,000+ litres each). It reads remote temperature data and continuously adjusts pump speeds for optimal efficiency based on collector orientation and sun exposure. Pumps Custom OEM pumps transmit real-time flow rate data via RS485 network modules. The system operates in semi-syphon mode to reduce pump energy consumption, achieving approximately 70:1 coefficient of performance. !Solar pump controller(solar-pumps.png?w=600) Collectors > We recommend a maximum of four collectors per bank width. Snow detection capability allows pre-heating to shed morning snow accumulation. Temperature sensing NTC thermistors in Wheatstone bridge configurations provide high-resolution temperature measurement across the system. An ADS1115 16-bit ADC with analogue multiplexing reads up to eight channels per node. Cascaded median and moving average filtering delivers stable, accurate readings. This replaces the Dallas DS18B20 digital sensors used in earlier prototypes, which suffered from widespread counterfeit parts on the market. !Roof-mounted sensor unit(roof-sensors.png?w=600) Tanks Non-pressurised thermal storage tanks (typically 1,000+ litres capacity) store heated water. Measured evaporation is approximately 100cc daily from 1,000-litre test systems using plain water. Logging A Windows/Linux daemon (runs on Raspberry Pi) collects RS485 network data, exports to CSV files, and uploads via FTP. A JavaScript HTML interface displays performance graphs. View live data from our test rig(https://privateersystems.com/docs/solardata/index.html) Connectivity Single array modu"},
{"url":"/resources/wheatstone","title":"Wheatstone Bridge Calculator","summary":"Calculate Wheatstone bridge output voltage for precision resistance measurement.","text":" Wheatstone Bridge Calculator A Wheatstone Bridge is essentially two voltage dividers connected in parallel, with their outputs compared to determine a difference. This configuration is used for precise resistance measurement and sensing applications like temperature or strain measurement. How it works The bridge consists of four resistors in a diamond arrangement: - Static divider: R1 (top-left) and R3 (bottom-left) - Variable divider: R2 (top-right) and R4 (bottom-right) The output voltage is the difference between the two divider midpoints: Vout = Vvariable - Vstatic Where: - Vstatic = Vin x R3 / (R1 + R3) - Vvariable = Vin x R4 / (R2 + R4) When R1/R3 = R2/R4, the bridge is balanced and Vout is zero. Any change in one resistor (for example an NTC thermistor responding to temperature) creates a measurable differential voltage. Applications - Temperature measurement using NTC or platinum RTD sensors - Strain gauge measurement - Pressure sensing - Any application requiring precise detection of small resistance changes Worked example A bridge with R1 = R2 = R3 = 10,000 ohms and an NTC thermistor as R4, powered by 3.3V. As the thermistor temperature changes, the bridge output shifts: Temperature (C) R4 (ohms) Vout (mV) ---------------------------------------- 0 32,650 +880 20 12,490 +183 25 10,000 0 40 5,325 -258 60 2,488 -558 80 1,256 -764 100 677 -879 The output is non-linear but provides good sensitivity across the working range. An ADC with 12-bit resolution on a 3.3V reference gives approximately 0.8 mV per count, well within the range needed for sub-degree accuracy in solar thermal monitoring."},
{"url":"/resources/sizing","title":"Sizing Calculator","summary":"System sizing in metric — DHW load, collector area, tank volume, with an annual-yield projection from the same multi-day simulation used by the tilt optimizer.","text":" Solar thermal system sizing This calculator turns a heating load (DHW + optional space heating) into a collector-area and tank-volume sizing recommendation, then runs the same multi-day simulation the /resources/tilt-optimizer(/resources/tilt-optimizer) uses to confirm the system actually delivers the targeted solar fraction. Inputs and outputs are metric throughout. The methodology follows F-Chart (Klein, Beckman & Duffie 1976; canonical reference Duffie & Beckman, Solar Engineering of Thermal Processes, Photovoltaics and Wind, 5th ed. 2020) and the industry-standard DHW load rules of thumb from the ASHRAE Handbook — HVAC Applications (Service Water Heating chapter, current edition). For the η₀ → annual-delivered cascade behind the efficiency inputs, see /resources/collector-efficiency(/resources/collector-efficiency). Worked example — typical UK household (click to expand) For a 4-person UK home, DHW only, here's how the inputs flow through the calculator: 1. §1 Site & climate: pick London from the location preset. That sets lat ≈ 51.5°, lon ≈ −0.1°, cloudiness 50 % (UK maritime — cloudier than central-Europe average). Leave cold-water supply at 10 °C. 2. §2 Domestic hot water: occupancy 4, hot-water 90 L/p/d (residential default), heater setpoint 60 °C. The readout shows ~360 L/day and ~7625 kWh/year DHW load. 3. §3 Space heating: leave at 0 for a DHW-only install. 4. §4 Collector array: target SF 50 %, specific yield 400 kWh/m²/yr (UK climate sits at the lower end of the European 400–600 band), seasonal effective η 0.45, drainback water. The sizing-rule estimate gives ~9.5 m² of collector — typically 2–3 flat-plate panels. 5. §5 Storage tank: click \"Use 55 L/m² ≈ XXX L\" → tank auto-fills to ~520 L. Pick \"Good\" insulation. 6. §6 Annual yield projection: the simulation runs at tilt = latitude (~52°), south-facing, and reports delivered ≈ 3500 kWh/yr at ~46 % achieved SF. Per-m² yield ≈ 365 kWh/m²/yr — the lower end of the typical mid-latitude band ref"},
{"url":"/resources/collector-efficiency","title":"Collector Efficiency Reference","summary":"How a solar thermal collector's headline \"efficiency\" turns into the much smaller fraction that actually arrives at the tank, with the Hottel–Whillier–Bliss equation and a worked example.","text":" Collector efficiency reference A solar thermal collector's datasheet headline number — the peak optical efficiency η₀, typically quoted at 0.70–0.82 for a good flat-plate panel — is the maximum possible fraction of incident sunlight converted to useful heat at one favourable instant: sun normal to the glazing, fluid entering at ambient temperature. The annual delivered fraction — useful heat at the tank, divided by sunlight incident on the panel over a whole year — is much lower because of a cascade of physical losses, each modest on its own, that compound through the year. This page lays the cascade out explicitly, shows the Hottel–Whillier–Bliss equation that drives the biggest term, and lists published references that bracket the real-world range. If you're trying to size a collector array, this page is the \"what fraction of the sun do I actually get?\" input to the /resources/sizing(/resources/sizing) calculator. If you're trying to orient an existing array, head to the /resources/tilt-optimizer(/resources/tilt-optimizer). From peak η₀ to annual delivered: the cascade Typical residential drainback flat-plate, mid-latitude site StageFactorRunning Peak η₀ (SRCC / Solar Keymark nameplate, ΔT = 0, normal incidence)0.7878 % × Temperature derate (collector hotter than ambient — Hottel–Whillier–Bliss)0.8566 % × Cosine-of-incidence averaged across the day (sun isn't normal except at one moment)0.8556 % × Pump / control losses + morning warm-up of cold pipe0.9353 % × Stagnation periods (tank full, collector idle, no useful collection)0.9550 % × Pipe loss to surroundings (worse for long outdoor runs)0.9347 % × Soiling, dust, partial shading over the year0.9745 % A reasonable starting point for seasonal-average delivered efficiency in the /resources/tilt-optimizer(/resources/tilt-optimizer) or /resources/sizing(/resources/sizing) calculators: - 0.40–0.45 — typical residential drainback flat-plate - 0.50–0.55 — well-designed short-pipe / l"},
{"url":"/resources/ntc-calculator","title":"NTC Thermistor Calculator","summary":"Calculate NTC thermistor resistance at any temperature using the Beta equation.","text":" NTC Thermistor Calculator An NTC (Negative Temperature Coefficient) thermistor is a type of resistor whose resistance decreases as its temperature increases. These semiconductor devices are highly temperature-sensitive and find applications in thermostats, temperature sensors, and protection systems. The Beta equation The resistance at a given temperature is calculated using the Beta equation: R(T) = R0 x exp(B x (1/T - 1/T0)) Where: - R0 — reference resistance in ohms (typically at 25 C) - T0 — reference temperature in Kelvin - B (Beta) — characteristic constant of the thermistor - T — target temperature in Kelvin The formula works by comparing the inverse of the absolute (Kelvin) temperatures of the target and reference points. The Beta constant amplifies the differences for precise modelling. Parameters - Reference resistance (R0): the nominal resistance at the reference temperature, typically 10k ohms at 25 C - Reference temperature (T0): usually 25 C (298.15 K) - Beta constant (B): provided in the thermistor datasheet, typically 3000-4000 for common NTC devices - Target temperature (T): the temperature at which you want to know the resistance Worked example For a typical 10k NTC thermistor (B = 3950, R0 = 10,000 ohms at 25 C): Temperature (C) Temperature (K) Resistance (ohms) -------------------------------------------------------- 0 273.15 32,650 10 283.15 19,900 20 293.15 12,490 25 298.15 10,000 30 303.15 8,055 40 313.15 5,325 50 323.15 3,600 60 333.15 2,488 70 343.15 1,752 80 353.15 1,256 90 363.15 915 100 373.15 677 Resistance (ohms) Temperature (°C) 0 5k 10k 15k 20k 25k 30k 35k 5.1px per °C --> 0 10 20 30 40 50 60 70 80 90 100 330px / 35000 = 0.009429 px/ohm --> 32,650 19,900 12,490 10,000 3,600 677 The steep resistance curve at lower temperatures gives excellent resolution for solar thermal monitoring, where tank temperatures of 20-80 C are typical. Steinhart-Hart equation The Beta equation assumes a simplified two-point model of the thermistor's resista"},
{"url":"/resources/","title":"Resources","summary":"Technical resources, calculators, and guides for solar thermal systems.","text":" Resources Technical resources for solar thermal system design and maintenance. - Sizing Calculator(/resources/sizing) — DHW load + collector area + tank volume, with an annual-yield projection - Collector Tilt Optimizer(/resources/tilt-optimizer) — pick collector tilt for minimum unmet demand, not maximum yield - Collector Efficiency Reference(/resources/collector-efficiency) — how a datasheet η₀ becomes the much smaller annual delivered fraction - NTC Thermistor Calculator(/resources/ntc-calculator) — calculate thermistor resistance at any temperature - Wheatstone Bridge Calculator(/resources/wheatstone) — model bridge circuits for precision sensing - Corrosion Inhibition(/resources/corrosion) — protect your thermal store with sodium silicate and sodium sulfite"},
{"url":"/resources/corrosion","title":"Corrosion Inhibition","summary":"Using sodium silicate and sodium sulfite to prevent corrosion in thermal storage systems.","text":" Corrosion Inhibition Instructions for using sodium silicate and sodium sulfite to prevent corrosion in thermal storage systems. Sodium silicate (corrosion inhibitor) Sodium silicate forms a thin, protective silica film on metal surfaces such as copper, brass, and steel. This reduces maintenance costs by minimising corrosion-related damage. Dosage: 400 grams per cubic metre of water. Sodium sulfite (oxygen scavenger) Sodium sulfite chemically reacts with dissolved oxygen in the water, eliminating it and thus reducing corrosion risk. This is particularly important where air ingress occurs. Dosage: 30 grams per cubic metre of water. Application process 1. Safety preparation — wear protective equipment (gloves, eye protection) 2. Dissolve and add chemicals to the thermal store 3. Circulate — run pumps for a minimum of 1 hour per cubic metre for thorough mixing 4. Monitor pH levels (target 9.0-10.5) and sulfite concentration (target 20-40 mg/L) 5. Top up chemicals when water is added or levels drop Maintenance Test every three months: - pH level (maintain 9.0-10.5) - Sulfite concentration (maintain 20-40 mg/L) - Visual inspection for corrosion - Water clarity Additional considerations - Minimise air ingress to reduce oxygen scavenger consumption - Use softened or demineralised water where possible - Store chemicals in cool, dry conditions away from direct sunlight - Both chemicals are registered under the REACH Regulation (EC) No 1907/2006"},
{"url":"/resources/tilt-optimizer","title":"Collector Tilt Optimizer","summary":"Pick the right collector tilt for your solar thermal install based on array size and heat demand — not just latitude.","text":" Collector tilt optimizer The textbook \"tilt = latitude\" rule maximises annual yield — which is the wrong objective when the collector array is oversized for the heat demand. This tool models hour-by-hour clear-sky irradiance through the year, caps daily collection at what the tank can absorb, and picks the tilt that minimises unmet demand. For an oversized system, the answer comes out steeper than the textbook value — pushing more of the yield into shoulder months where it isn't wasted as bypass-dump. Site Latitude (°) Longitude (°) Defaults are the centre of Prague. Enter your own coordinates — positive latitude = north of the equator, positive longitude = east of Greenwich. System Collector area (m²) Collector efficiency Annual heat demand (kWh) Tank size (litres) Max tank temp (°C) Cold-water supply (°C) Tank insulation Excellent (100 mm+ PUR) Good (50–80 mm PUR / 8 cm reference rig) Average (30–50 mm rockwool) Poor (under 30 mm or aged) System / fluid Drainback, pure water Closed, ~40 % propylene glycol mix Collector efficiency: effective seasonal-average fraction of incident sunlight delivered as useful heat — NOT the peak optical efficiency you see on a collector datasheet (typically η₀ ≈ 0.75–0.82 for flat-plate, 0.70–0.78 for evacuated-tube). That peak number is the maximum possible at a single moment, with the sun normal to the collector and the tank cold; seasonal-average delivered is much lower because of a cascade of physical losses (temperature derate, cosine of incidence, control / pipe / stagnation losses, soiling). Conservative starting point: 0.40–0.45 for typical residential drainback flat-plate; up to ~0.50–0.55 for a well-designed short-pipe / low-temperature-delivery install; ~0.45–0.55 for evacuated tube in high-ΔT applications. The full cascade table and the Hottel–Whillier–Bliss equation behind these numbers live on the collector-efficiency reference page. Tank inputs (size, max temp, supply temp, insulation): the model tracks tank state day"},
{"url":"/marquedown","title":"MarqueDown","summary":"About the MarqueDown engine that powers this website.","text":" MarqueDown This website is powered by MarqueDown, a lightweight site engine written in C++17 by Privateer Systems. The name is a play on Markdown (MD) (which is a lightweight plain-text formatting language that uses simple symbols to structure text—such as headings, lists, links, and emphasis - so it can be easily converted into formatted documents like HTML), our dynamic version which is assembled at the webserver, and letters of Marque which were Privateering licences. How it works Content is authored in Markdown and stored in a git repository. MarqueDown polls the repository, rebuilds when it detects new commits, and renders pages through HTML templates (typically in under a millisecond per page) into an in-memory cache. Requests are served directly from cache via FastCGI — the serve path is a hash table lookup returning a pointer to the pre-rendered HTML, typically completing in under a microsecond. There is no database, no CMS, and no JavaScript framework. Pages are pre-rendered at build time and served instantly from memory. Features - Markdown with includes — pages can pull in shared text blocks, reducing repetition across the site - Template inheritance — a base layout is extended by specialised templates for blog posts, listings, and other page types - Navigation menus — defined in a simple text file with nested includes; the current page is automatically highlighted - Blog listings — a directory of Markdown files becomes a date-sorted blog with thumbnail images, summaries, and RSS feed - Image pipeline — source images are automatically resized into multiple widths with responsive srcset attributes - Git integration — the engine polls a remote repository and rebuilds the cache when new commits are detected - Live preview — a built-in development server watches for file changes and refreshes the browser automatically and a VSCode Extension makes life easy Performance MarqueDown is single-threaded by design. Git checks happen between requests, never mid-rend"}
]