Observing the renewable energy transition from a European perspective

Archive for the category “thermal solar”

International Attention for Ecovat

It’s wonderful, all these new developments with photo-voltaic solar panels, wind turbines and hydrogen storage, but space heating is still the largest chunk of a national energy budget, at least in Europe. The biggest decarbonization gains can be, and will have to be made, here.

Hence, it is to be greeted that an Austrian periodical pays attention to a promising Dutch startup Ecovat, that offers a solution for seasonal storage of heat in the soil.

[] – Attention for Ecovat in Austrian magazine
[] – AEE – Institut für Nachhaltige Technologien (1988)
[deepresource] – District Heating with Seasonal Storage in Vojens Denmark
[deepresource] – Our Ecovat posts

Ecovat Haalbaarheidsstudie Thermische Opslag Panningen

Het initiatief

In Panningen werkt Ecovat sinds 2018 samen met Peel Energie aan de ontwikkeling van een Warmte | Koude-net. In 2021 hebben de gemeente Peel en Maas en de woningcorporatie Wonen Limburg zich aangesloten bij het initiatief. Het Warmte | Koude-net Panningen biedt een duurzame en betaalbare oplossing voor de lange termijn om huishoudens van het aardgas af te koppelen. Door gebruik te maken van duurzame energiebronnen zoals lokale restwarmte, wind en zon, is er maar weinig tot geen CO2 uitstoot.

Rendabel van het aardgas af

In 2020 is er een haalbaarheidsstudie uitgevoerd door Ecovat. In deze haalbaarheidsstudie zijn de technische en financiële haalbaarheid van een Warmte | Koude-net met een Ecovat seizoensbuffer onderzocht. Uit de studie volgt dat de gebouwde omgeving van Panningen bestaat uit 4.779 woningequivalenten (WEQ) waarvan 3.261 woningen en 1.518 WEQ utiliteit. Voor een groot deel hiervan is het technische en financieel haalbaar om met een projectrendement van 4,6% aan te sluiten op het Warmte | Koude-net, namelijk 3.576 WEQ (2.500 woningen en 1.076 WEQ utiliteit).

[] – Ecovat warmte- en koudesysteem voor Panningen (pdf, 51p)
[] – Nederland bij uitstek geschikt voor energieopslag en omzetten energie

PVT – the Hidden Solar Trump Card

An Amsterdam houseboat owner has installed PVT panels on the deck of his ship, which feeds a heat-pump.

Most people associate solar power with photo-voltaic solar panels, not in the least because of spectacular price decline, with panels of 100 x 160 cm and 300 Watt Wp, costing 100-150 euro.

That wasn’t always the case. The solar revolution started with thermal solar collectors, used for tap water heating, when astronomically priced panels were reserved mostly for space exploration. Increasingly, people begin to understand that both functions can very well be combined. Solar panels are black, meaning that they are energetically “black bodies”, meaning that they absorb almost all solar radiation, go to good old Max Planck for the physics details. That solar radiation can be used both for electricity and heat generation, with a total yield of 1400 Wp per 100 x 160 cm panel.

Modern, commercial solar panels have an efficiency of 20% or more, thermal collectors much higher. Enter “photovoltaic thermal hybrid solar collector” (PVT). PVT panels are more expensive than solar panels [*], but the realization that in the urban environment, space rather than money, is the real limiting factor, PVT could become big, now that the solar revolution is picking up serious momentum, especially in overcrowded and prosperous renewable energy laggard Holland, that enjoyed the ownership of a huge natural gas field, it could milk for decades until prices for renewable energy came down sufficiently to jump on that bandwagon, leaving the real innovation effort to the Danes and Germans, who (deservedly) now own the industries, good for them. (Never mind, we’ll make our renewable energy money from maritime installations and monopiles, North Sea electricity production we can export into the EU and perhaps a share in the future hydrogen trade).

We have collected a few examples of PVT-projects in the Netherlands, captured in video.

[*] – as a rule of thumb, solar collectors cost per m2 about twice as much as solar panels, so for PVT expect a price per m2, three times that of a solar panel.

[] – Black Body
[] – Photovoltaic thermal hybrid solar collector
[deepresource] – Our PVT articles
[] – PVT-producer and installer

PVT-panels applied in a new housing project in Utrecht, this is the easy, happy flow.

Adding solar panels/collectors to new buildings is easy, where solar panels can become the roof itself, eliminating the need for tiles and save cost. The real challenge is to integrate PVT-panels in buildings that weren’t designed for solar, like here in Delft.

In this project it is stressed that PVT-systems can eliminate the need for expensive intrusive underground and thus stationary heat exchangers and instead opt for solar radiation and heat extraction from flowing thin air.

Waalre, Brabant.

Hallelujah-video from a Dutch producer of PVT-systems, QPanel by HRSolar.

PV-panels have 300 Wp, PVT-panels 1400 Wp!

Woning van het Gas af met Warmtepomp en PVT-Panelen

District Heating with Seasonal Storage in Vojens Denmark

In Vojens, in the not too sunny Denmark, the largest storage of seasonal solar heat project in the world is operational since 2016. Denmark is unique in that it has many district heating systems in place, that can be fairly easily adapted to cooperate with large arrays of solar thermal collectors and seasonal storage of the resulting heat in large pits, filled with gravel and water.

Operator: Vojens Fjernvarme
Storage volume: 200,000 m3
Depth storage: 13 m
Circumference: 610 m
Solar collector area: 70,000 m2
Pump capacity: 50 m3/hour
Charging time: 5 months
Location: old gravel pit
Insulation: 60 cm clay and plastic sheet
Number of households: 2,000
Solar heat coverage connected households: 45%
Consequences heating bill: 10-15% less (for 45% no more fuel, just amortization)
CO2-emissions avoided: 6,000 Tonnes/year
Other energy sources: 3xgas engines, 10 MW electric boiler, absorption heat pump, gas boilers
Price pit storage in 2020: 30 €/m3 for storage volume > 100,000 m3
Price storage pit per household: 1,500 €
Installation overhead per household: 100 m3 storage volume and 35 m2 solar thermal collectors

The positive news is that if you can get the thermal solar generation and storage scheme financed, your heating bill actually decreases with 10-15%. This could set in motion an avalanche of projects all over Europe, certainly in countries with more solar radiation than Denmark, that is almost everybody.

In the context of the renewable energy transition, focus is on wind and pv-solar. This is not justified. For an average Dutch household of 2.2 persons, the yearly consumption of energy for heating is 34 GJ. For electricity that is merely 12 GJ. The difference is almost a factor of 3.

[Google Maps] – Vojens district heating

[] – Vojens district heating
[] – Seasonal pit heat storages – Guidelines for materials & construction
[] – South-Jutland stores the sun’s heat in the world’s largest pit heat storage
[] – Seasonal thermal energy storage

Read more…

Largest Solar Thermal Project in Ludwigsburg-Germany

20,000 m3 heat storage is being built in Ludwigsburg and is part of the largest thermal-solar project in Germany. Capacity: 9.6 MW thermal solar. Annual output 5,500 MWh from a collector field with a gross area of 14,800 m2. Main contractor: the Danish Arcon-Sunmark company. Completion date: May 2020.

[] – Solarwärme vom Römerhügel
[Google Maps] – Römerhügel, Ludwigsburg
[] – Contractor site
[] – Large-scale solar heat is cost-competitive in Germany

Thermal Solar to Electricity Conversion Efficiency 34% With Stirling Engine

CSP-Stirling is known to have the highest efficiency of all solar technologies (around 30%, compared to solar photovoltaic’s approximately 15%), and is predicted to be able to produce the cheapest energy among all renewable energy sources in high-scale production and hot areas, semi-deserts, etc.[citation needed] A dish Stirling system uses a large, reflective, parabolic dish (similar in shape to a satellite television dish). It focuses all the sunlight that strikes the dish up onto a single point above the dish, where a receiver captures the heat and transforms it into a useful form. Typically the dish is coupled with a Stirling engine in a Dish-Stirling System, but also sometimes a steam engine is used. These create rotational kinetic energy that can be converted to electricity using an electric generator.

In 2005 Southern California Edison announced an agreement to purchase solar powered Stirling engines from Stirling Energy Systems over a twenty-year period and in quantities (20,000 units) sufficient to generate 500 megawatts of electricity. In January 2010, Stirling Energy Systems and Tessera Solar commissioned the first demonstration 1.5-megawatt power plant (“Maricopa Solar”) using Stirling technology in Peoria, Arizona. At the beginning of 2011 Stirling Energy’s development arm, Tessera Solar, sold off its two large projects, the 709 MW Imperial project and the 850 MW Calico project to AES Solar and K.Road, respectively. In 2012 the Maricopa plant was bought and dismantled by United Sun Systems. United Sun Systems released a new generation system, based on a V-shaped Stirling engine and a peak production of 33 kW. The new CSP-Stirling technology brings down LCOE to USD 0.02 in utility scale.[citation needed]

According to its developer, Rispasso Energy, a Swedish firm, in 2015 its Dish Sterling system being tested in the Kalahari Desert in South Africa showed 34% efficiency.

Website comment: interesting! But one would tentatively guess that an array of solar panels will probably be cheaper in a long-term per kWh cost.

[] – Solar Thermal Energy, Dish Designs
[] – Company Site

Stirling Motor for Flying?

Robert McConaghy created the first flying stirling engine powered aircraft in August 1986. The Beta type engine weighed 360 grams, and produced only 20 Watts of power. The engine was attached to the front of a modified Super Malibu radio control glider with a gross takeoff weight of 1 kg. The best published test flight lasted 6 minutes and exhibited “barely enough power to make the occasional gentle turn and maintain altitude”

The main argument against using a Stirling engine in an aircraft was its weight. But with the rise of new strong and lightweight materials, conditions could change.

[] – Airbus (formerly EADS)
[] – Stirling Engine
[] – Stirling Engine for an Emission-free Aircraft (EADS, 2016)
[] – Stirling engine with flapping wing for an emission-free aircraft (EADS, 2011)
[] – Solar thermal aircraft (2004, Lawrence Livermore)
[] – Aircraft Hot Air Power Generator Innovative Stirling Engine

Stirling Engine & Solar Thermal Power

Simple solar thermal power with a Stirling engine. Storage comes included.

[] – EuroDish – Stirling System Description
[] – Company site
[] – Company site

Read more…

There is Still Potential in Thermal Solar

[] – Solarthermie: Effizienter durch neue Techniken

Solar Air Collectors

Early December, outside temperature 6C/43F. Two simple air collectors and ventilators. Max output temperature: 62C/143F

[] – Solar air collector project in northern Germany

Still waiting for the first solar air collector project where the black absorber back plate consists of a black solar panel. The collector should be constructed as such that the glass/acryl cover can be removed in the spring and put back again in the autumn to avoid too high solar panel temperatures during the summer. Special construction absorber with window screen.


Siebdruckplatten: Materialstärke (Seitenwände) 21 mm – 35 €/m²
Materialstärke 9 mm (Rückwand) – 20 €/m²
Acryllack, Dose mit 125 ml – 4,99 €
Aluschiene, 1 cm x 3 cm x 200 cm (2mm), 2 Stück –
Aluschiene, 3 cm x 3 cm x 200 cm (2mm), 1 Stück –
Aluschiene, H – Form
Schrauben V2A, 4 x 25
Schrauben V2A, 3,5 x 16
Schrauben V2A, 4,5 x 45
Fiberglasnetz, 1m x 3,40 m
Acrylglasscheibe (Gewächshaus) 70 x 160 cm
Computerlüfter 12 V, 120 mm, 115 m³/h

Acryl cover

The end result

Some data:

01.03.2013 – complete sunny day
Collector temperature: 39,5 °C

Hybrid Solar

panel-thermoSolar thermal-electric hybrid

volther-powertherm-180wConventional thermal solar collector

In densely packed cities in overcrowded north-western Europe, space is the real scarce commodity, more than money. The consequence is that if this scarce (roof) space is used for solar energy, preference is usually given to solar panels over thermal solar collectors. In fact, when we visited the 2014 Munich Intersolar exhibition, there were hardly any producers of solar thermal collectors present.

It is premature however to write-off thermal solar completely. If sun rays hit a solar panel, ca. 15% is converted into electricity and the rest is lost in heating up the panel, which degrades performance. The idea of hybrid solar is to use the same (scarce) surface for both electricity and heat:

A solar hybrid panel has two energy outlets: one for electricity and one for hot fluid, utilizing nearly all solar energy.


[] – Photovoltaic Thermal PVT
[] – Solartherm Hybrid PV
[] – Volther Hybrid PV-T Panels
[] – Volther PowerVolt PV-T Hybrid Collector

hybrid-solar[source] Robust two-edged sword

DIY Solar Collector For Domestic Heating

build a solar heater 01 cover jpg[source]
You typically are living in a home that has been built years ago, in a time when no energy problems existed. Your energy bills are rising all the time and you have a number of unused square meters on your roof or in your garden and you are thinking how to utilize them. No off-the-shelve solutions are available so you have to come up with something yourself, like all the people showin the videos below have done. No doubt your own collector is going to be different than all the ones presented here. Nevertheless, before you begin designing your own, it is good to pick up ideas and learn from mistakes others have made.

Read more…

Transpired Solar Collector

A conventional solar thermal collector in essence consists of a glass cover, a black absorption plate and an insulated back cover. If however there is large blind facade available, it may be considered to eliminate the expensive glass cover and compensate the loss of thermal efficiency by an enlarged collector area. These Unglazed Air Collectors or Transpired Solar Collectors are typically used to heat ambient air in commercial, industrial, agriculture and process applications. According to wikipedia:

It is typically the most cost-effective out of all the solar technologies, especially in commercial and industrial applications, and it addresses the largest usage of building energy in heating climates, which is space heating and industrial process heating.

[] – Solar air heat

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World’s Largest Thermal Solar Plant Online in Arizona

280 MW. World’s largest parabolic trough array with thermal storage. Constructed by Spanish group Abengoa. More spectacular thermal solar projects are underway in Arizona, putting this technology back on the map in competition with photovoltaics.


Passive Solar Space Heating

A relatively cheap way to reduce your fossil fuel bill is to apply passive solar heating. In general it comes down to a glass plate covering a black plate or wall. Sunlight is absorbed and heats the air between glass plate and black absorber. The warm air rises and is lead into the building at the top. Air to be heated is lead into this space from the bottom. No moving parts necessary.

[wikipedia] – Solar wall
[wikipedia] – Trombe wall

Read more…

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